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Quality Status Report 2000
Chapter 5 - Biology
5.1 Introduction
5.2 General description of the biology of the OSPAR area
5.3 Impact of human activities
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5.1 Introduction
The organisms living in the OSPAR maritime area belong to a wide range
of taxonomic and ecological groups,
including viruses, bacteria, plankton, benthos, fish, squid, birds,
mammals and turtles. A general description of
these groups of organisms is given in Section 5.2, while the impact of
various human activities on the organisms is
presented in Section 5.3. This chapter forms a basis for the overall
assessment of the impacts of human activities
in Chapter 6.
The various groups of organisms are interlinked in more or less tightly
coupled food webs which together with
the abiotic environment, make up the marine ecosystems. In terms of
principles, the organisation of marine
ecosystems is similar in all OSPAR Regions. Microscopic phytoplankton
constitute the ‘grass’ of the sea and the
basis for production at higher tropic levels. Phytoplankton is grazed
by zooplankton, which again forms the food
for plankton-feeding fish (e.g. anchovies, herring, mackerel) and
whales. Benthic animals living in or on the seabed
feed on plankton and dead organic material sinking out from the upper
layer. Fish, squid, sea mammals and
seabirds feed on smaller fish or benthic animals. Kelp and other
macroalgae grow as plants in the lighted zone in
shallow waters. Microorganisms contribute to decomposition of organic
material and recycling of nutrients.
Many species of plants and animals have restricted distributions, and
the biogeographical regions give distinct characteristics in terms of biodiversity to various parts of the OSPAR
area.
Annex V to the OSPAR Convention, adopted in 1998, aims at protecting
species and habitats in the OSPAR
area. The Annex V strategy is to identify species and habitats for
which protection measures will be considered.
This work is ongoing and criteria for identifying species and habitats
have been developed, including criteria for
species and habitats under threat or subject to rapid decline.
5.2 General description of the biology of the OSPAR area
5.2.1 Microorganisms
Microorganisms, principally bacteria (but also yeasts,
fungi and viruses), are constituents of the plankton as well
as of the benthos. Planktonic bacterial production in the
open sea is related to primary production and the
abundance of bacteria increases following phytoplankton
blooms. One of the main functions of bacteria in marine
ecosystems is to remineralise organic matter (including
oil) to inorganic components. In doing so, benthic
bacteria show great metabolic diversity, utilising oxygen,
nitrate or sulphate as their reduction substrate. Their
respiratory activity creates a chemical gradient within the
sediment with oxygen-utilising forms closest to the
sediment/water interface and sulphate-utilising forms at
greater depths.
5.2.2 Phytoplankton
Phytoplankton biomass shows considerable spatial
variability in the OSPAR area (Figure
5.1). The seasonal cycle is typical of temperate latitudes with a spring increase,
summer decline and a second, generally less high,
autumn increase. The spring bloom is generated mainly
by diatoms which decline as concentrations of the winter
accumulated nutrients (e.g. silica and nitrate) are utilised
and as grazing pressure from zooplankton increases. In
ice covered waters in the Arctic the seasonal cycle has a
pronounced peak as the developing bloom moves north
with the retreating ice edge. South of 40° N, in the wider
Atlantic, the upper water column stays stratified
throughout the year so the biomass is lower and less
variable throughout the seasons.
The timing of the spring bloom is closely linked with
the developing water stratification, which allows phytoplankton
cells to remain in the higher light levels of the
upper water column. During summer months recycling of
nutrients occurs and other algal groups such as the
dinoflagellates dominate the phytoplankton. Diatoms may
return again in the late autumn as stratification breaks
down and nutrients are again mixed into surface waters.
There is marked interannual variability in the timing and
intensity of phytoplankton growth, and long-term trends
(both up and down) have been described for different
parts of the OSPAR area. These trends appear to be linked
to changes in coupled ocean-atmosphere circulation.
A wide diversity of different phytoplankton species is
found in the North Atlantic. Named species range from
~ 300 in the Arctic to ~ 1000 in Region IV, although many
species have not yet been described. Traditionally
diatoms were seen to be the most important group, it is
now recognised that many very small flagellates and other
algal classes may dominate at times. When temperatures
increase in the summer flagellates dominate; most toxic
species belong to this group (see Section 5.3.2 and
Table 5.5).
Total annual production of phytoplankton varies from
region to region. The lowest rates (c.45 g C/m2/yr) are
found in the Wider Atlantic south of 40º N, the highest
(> 400 g C/m2/yr) on the Galician shelf and in the
Cantabrian sea. In the North Sea the rate in the coastal
areas (c.
400 g C/m2/yr at a station 6 km off the Dutch
south-west coast) is nearly an order of magnitude higher
than in its central part. The rates also vary considerably
within each region.
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Figure 5.1 SeaWiFS satellite images of chlorophyll concentrations in the
North-east Atlantic. Source: CCMS.
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5.2.3 Zooplankton
The zooplankton of the epipelagic zone (0 – 200 m) is
dominated by species with a size spectrum ranging from
protozoans to crustacean euphausiids. In shelf seas,
larval stages of benthic organisms (e.g. echinoderms)
may be important in spring and summer. In the deep
ocean waters of the Wider Atlantic, the maximum number
of species occurs at around 1000 m depth. However, the
biomass at this depth is an order of magnitude lower than
that found in the epipelagic zone.
Zooplankton are the main source of food for pelagic fish and the early life stages of all fish. Variations in
zooplankton composition and in the timing and location of
occurrence can thus have important effects on fish recruitment
and growth.
The growth of zooplankton is governed by temperature
and food availability so that their seasonal cycle is
linked to that of the phytoplankton. For example, some
species such as Calanus
finmarchicus hibernate
during
winter in deep water timing their arrival in near surface
waters to exploit the phytoplankton spring bloom. The
herbivorous copepods of the genus Calanus play a key
role in ecosystems of the OSPAR area. They are the most
abundant form of zooplankton and may account for over
90% dry weight of the total zooplankton biomass in the
northern and eastern part of the area.
There are strong year to year variations in zooplankton
abundance. For example, C.
finmarchicus and
C. helgolandicus abundance
in the Irish Sea can vary by
an order of magnitude between years. The zooplankton
biomass and composition in the central and northern
Barents Sea have also shown several fold variations
between years, which in part appears to be caused by fish
predation. Elsewhere, as for phytoplankton, longer-term
changes for many species appear to be related to variability
in ocean-atmosphere circulation.
5.2.4 Benthos
The biota living near, on or in the seabed are collectively
called the benthos. A distinction is made between plants
(phytobenthos) and animals (zoobenthos). The phytobenthos may be composed of microalgae or macroalgae, the
latter being colonised by epiphytic plant and animal
species. The
zoobenthos either lives as infauna within the
sediments or as epifauna on the seabed.
Diversity and biomass of the benthos are dependent
on a number of factors including substrate (e.g. sediment,
rock), water depth, salinity and hydrodynamics.
Depending on the characterisation of habitats by such
factors, certain communities can be expected.
Phytobenthos
Since it is light dependent, the micro- and
macrophytobenthos is restricted to shallow waters. Whilst the
microphytobenthos may thrive on any substrate, thus for
example contributing to the stabilisation of loose
sediments, perennial red and brown macroalgae (e.g. Lithothamnion, Fucus)
require a hard substrate (e.g. rock,
stones) whilst green algae (e.g. Ulva)
may thrive on
mussel beds or even (solid) sediments. Higher plants
such as eelgrass (e.g. Zostera)
may be found on sandy
sediments.
The total number of macroalgal species decreases
from south to north within the Arctic and northern
temperate areas. The dominating macrophytes of these
areas are large, brown algae (Laminarians or ‘kelp’). The
main depth to which macroalgae grow is in general lower
at high latitudes than in temperate regions.
In the southern part of the OSPAR area the coastal
environment is highly heterogeneous in terms of habitats.
For this reason, the algal diversity is high. For example,
approximately 700 macroalgal species are found in the
Channel area. The sediments of intertidal flats are
colonised by hundreds of species of microscopic benthic
algae. Most of them are diatoms, whose populations are
also accompanied by blue-green algae and interstitial
flagellates. In addition to the microalgae populations
shallow areas are to some extent covered by beds of
higher plants such as Zostera and Ruppia species.
Besides providing habitat for epiphytic species,
macroalgae and eelgrass provide food for numerous
grazers and deposit feeders. As with excessive algal
blooms, mass development of macroalgae due to excess
nutrients may entail oxygen depletion in the bottom water
following microbial breakdown of the excess biomass.
Zoobenthos
The bathymetry of the OSPAR area ranges from shallow
continental shelf to abyssal plains (around 5000 m depth).
Deep-ocean benthos tends to be much smaller than its
shallow-water counterparts and it is generally accepted
that species diversity increases with depth in the continental
shelf regions to a maximum just seaward of the
continental rise, and then decreases with increasing
distance towards the abyssal plain (Levinton, 1995).
The Greenland–Scotland Ridge is a major biogeographical
boundary for benthos within the OSPAR area. This ridge
forms a barrier between warm- and cold-water species.
Large areas of coral banks of Lophelia occur in the
Atlantic Ocean near the continental shelf break off Ireland,
Scotland, the Faroe Islands, Norway, and off the south
coast of Iceland. High diversity of biota is associated with
these coral banks.
In shallow shelf areas such as the North Sea, benthic
and pelagic processes are often strongly coupled and
work in concert to make the region highly productive.
Highly productive benthic communities can be found in
tidal areas, for example in the Wadden Sea along the
south-eastern border of the North Sea, and in several
estuaries along the western European coast.
On the shores of northern and north-western Spain
and on the Portuguese shore hard substrata are
dominated by sessile and slow moving macrofauna in the
upper levels. Intertidal and subtidal soft bottoms on the
shores of northern and north-western Spain have a rich
infauna related mainly to grain size and organic matter
content. Along the Portuguese coast, intertidal sands
have a low faunal density, whereas fauna in the subtidal
soft substrata is more abundant due to the increase in
sediment organic matter.
Frontal regions, where different ocean currents meet,
normally have a high primary production resulting in
highly productive benthic communities. Such frontal
regions occur throughout the OSPAR area: in the
Denmark Strait, between Iceland and the Faroe Islands, in
the western part of the Barents Sea, in the Norwegian
Sea, in the North Sea, in the Kattegat/Skagerrak area and
the Irish shelf front, to the west of Ireland.
5.2.5 Fish and squid
Over a thousand species of fish have been recorded in
the OSPAR area. Of these, about 5% can be commercially
exploited and about 2% of species make up 95% of the
total fish biomass. The major commercially exploited fish
stocks in each part of the OSPAR area are given in
Table 5.1. The
larvae of many commercially important fish
species disperse into the open ocean from their spawning
grounds at the continental shelf and in estuarine areas.
Some fish species perform long annual migrations
between the feeding, spawning, and overwintering areas.
Variability in stock recruitment is related to both the size of
the parental stock and to a number of factors, including
environmental variability and predation, which affect egg
and larval survival.
Approximately 160 species of fish have been
recorded in the Barents Sea, with the total number of
species in Region I unlikely to exceed 200. Much of the
total fish biomass is concentrated in a few species,
which are exploited commercially. The number of fish
species is comparatively low in the shallow southern
North Sea and eastern Channel and increases towards
the Celtic Sea and Bay of Biscay. Overall, around 250
species have been found in Region II, with more species
occurring commonly than in Region I. In the Bay of
Biscay and Region III the number of species reaches
700, since many northern species reach their southern
limit of distribution and many southern species reach
their northern limit of distribution along the boundary for
cold temperate species in the vicinity of 47° N. Along the
Iberian coast in Region IV, the number of species
remains high, as more demersal species of southern or
Mediterranean distribution occur. The biodiversity of
Region V is less well quantified, particularly in deeper
waters, but fewer species are likely to occur than on the
continental shelf.
Many deep-water species have an extensive
geographical distribution owing to the small environmental
variations of their habitat. In the Wider Atlantic, top
predators such as sharks probably play an important role
in maintaining the structure and diversity of fish assemblages.
Large pelagic predators (tuna and marlin) are
highly migratory, ranging far beyond the boundaries of the
OSPAR region.
The biology of squid is poorly known despite being
very abundant especially in the Wider Atlantic. Only a few
species are exploited commercially but squid are of
considerable ecological importance as predators and as
the food of some whales, fish and seabirds.
5.2.6 Birds
Almost all parts of the OSPAR area support breeding and
migratory birds dependent on the sea. Proportionately, the
greatest numbers of breeding seabirds nest on the coasts
of Arctic waters and the North Sea. Total numbers of individuals
in these northern areas are several orders of
magnitude greater than those in the southern regions of
the OSPAR area (Figure
5.2). The total
numbers of
species, and two most common species in each Region
are shown
in Table
5.2. Only the great
skua (Catharacta skua) is endemic
to the OSPAR area, although some
species are near-endemic (e.g. Manx shearwater (Puffinus
puffinus)) or
have endemic sub-species (e.g. shag
(Phalacrocorax aristotelis)).
Surveys of distribution at sea
have not been carried out in all parts of the OSPAR area,
but in those that have been studied surveys show shelf
seas to hold substantially higher densities than oceanic
waters. Large intertidal flats, such as in estuaries and in
the Wadden Sea are particularly important for wading
birds. Some 6 – 12 million birds of more than 50 different
species may be present in the Wadden Sea at some times
of the year.
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Table 5.1 Landings and spawning stock biomass of the commercially
important fish species in the OSPAR area, and status of the stock
according to whether it is within ‘safe biological limits’. Source:
ICES (1999).
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Table 5.2 Number of species of seabirds breeding on coasts of the OSPAR
Regions, with approximate population sizes for the two most common species in each Region. Note that even for the most common
species, population sizes are not all well known. |
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Figure 5.2 Location of large seabird breeding colonies in the OSPAR area.
Source of data: Grimmett and Jones (1989). |
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5.2.7 Marine mammals and turtles
Cetaceans
Whales are divided into two groups: baleen whales
(primarily feeding on small fish and plankton) and toothed
whales (preying on fish, squid and marine mammals).
Over 30 species of cetaceans occur throughout the
OSPAR area, ranging in size from the small harbour
porpoise at < 2 m (Phocoena
phocoena) to the
giant blue
whale (Balaenoptera
musculus) at about
33 m
(Table 5.3).
Following the moratorium on commercial
whaling for most species, numbers of most species of
large whale are showing signs of recovery. There has
been an increase in recorded strandings of cetaceans in
the North Sea and the Celtic Sea over the past few
decades, but the reasons for this are not known.
Seals and bears
Some seal species live in coastal areas; others are
adapted to the sea ice and never come ashore. All seals
are carnivorous, feeding on fish, krill, pelagic amphipods
or benthic animals. The vast majority of the seal population
is found in Region I (Table
5.3). Individual
seals of all
species have occurred well away from their normal range
in the OSPAR area. Approximately 40% of the world’s
population of grey seals breed in the waters around
Europe. The number of pups has increased steadily (by a
factor of three or more) over the past 30 years.
Apart from the effects of commercial
sealing, the only
major change in the population of seals resulted from the
1988 phocine distemper virus outbreak. This fatal disease,
which took on epidemic proportions, had the greatest
impact on the eastern side of the North Sea where the
population of harbour seals in the Wadden Sea was
reduced from 10 000 to 4000 between 1988 and 1989.
Since then the population has recovered and in 1998
consisted of more than 14 000 individuals.
Polar bears have a circumpolar distribution and are
confined to ice covered areas of the Arctic (Table 5.3).
The distribution of bears between Eastern Greenland and Franz Josef Land
is largely determined by the extension of the pack ice.
Turtles
The range of most sea turtles is in tropical or subtropical
waters but some species undertake long migrations using
the warm current of the Gulf Stream. For this reason, a few
species visit the Bay of Biscay, the Iberian coast and the
wider Atlantic every year. The one species that is
frequently recorded in the OSPAR area is the loggerhead
turtle (Caretta
caretta).
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Table 5.3 Marine mammals of the OSPAR area. |
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5.3 Impact of human activities
Owing to large natural variability and limited knowledge of
cause-effect relationships, human influences on the
biology of the OSPAR area are difficult to establish in the
majority of cases. A direct link to human activities is clear
for some contaminants (e.g. TBT), the exploitation of
marine mammals, and for fishery effects on benthic invertebrates
and seabirds. The need for an improved
knowledge of anthropogenic effects on biota is
recognised and is being developed within OSPAR and
other bodies.
5.3.1 Impact of non-indigenous species
Non-indigenous species may arrive as a result of both
natural (e.g. water currents) and human-mediated
processes (e.g. ships’ ballast water, hull fouling and
commercial transport of fish and shellfish). To date, over
one hundred non-indigenous species representing a large
spectrum of taxonomic and ecological groups of
organisms (plankton, macroalgae and benthos) have
been recorded in the OSPAR area, mainly in the North
Sea, the Celtic Sea, the Bay of Biscay and along the
Iberian coast. A few non-indigenous species were deliberately
introduced to the area mainly for mariculture
purposes. The most significant ecological effects of these
introductions are competition (for food, space or light) or
predatory interactions with indigenous species, and
pathogenic or other harmful effects. A list of some of the
non-indigenous species that have had impacts in the
OSPAR area is shown in Table
5.4.
5.3.2 Harmful algae
The vast majority of algal phytoplankton are harmless and
form the basis for marine food webs. At times, however, they may occur in large concentrations and colour the
water red or brown. At these concentrations the algae
may be harmful to other marine life by reducing levels of
oxygen or clogging gills of fish. Some algal species are
toxic to marine life and to humans and some species may
through their breakdown cause large masses of foam to
develop on beaches that are aesthetically undesirable
and can affect tourism (see Table 5.5). Fish farmers
can
suffer serious financial losses if harmful algal blooms pass
through fish cages. In the period up to the early 1990s,
the occurrence of harmful algal blooms increased both in
space and time (Hallegraeff, 1995). Several mechanisms
related to human activities may have driven this trend:
- introduced species via e.g. ballast water, mariculture;
- coastal installations intensifying stratification e.g. Bay of
Vilaine;
- anthropogenic inputs and fluxes of nitrogen into areas
susceptible to eutrophication;
- unbalanced nutrient ratios, e.g. N : P and N :
Si;
- hydroelectric power plants – exceptional discharges; and
- increasing inputs of humic substances from rivers due
to acid rain.
Algal toxins can accumulate in the edible tissue of
bivalve molluscs (e.g. mussels) to levels that can be
dangerous to the human consumer. Many countries in the
OSPAR area have established biotoxin-monitoring
programmes that provide early warning of the composition
and numbers of toxic plankton species and levels of
toxins in bivalve tissue. Warning and closure notices can
be issued if permissible standards of toxins in shellfish are
exceeded. The principal toxins monitored in the OSPAR
area are those that cause Paralytic Shellfish Poisoning
(PSP), Diarrhetic Shellfish Poisoning (DSP) and Amnesic
Shellfish Poisoning (ASP). ICES provides decadal maps
which give information on the regional occurrence of
shellfish poisoning (ICES, 1999c and 2000).
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Table 5.4 Some of the non-indigenous species in the OSPAR area
including their mode of introduction and potential impact in each Region. |
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Table 5.5 Harmful algal bloom species in the OSPAR area. |
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5.3.3 Impact of microbiological pollution
Microbiological pollution may affect all marine biota,
including invertebrates, fish, and seals. In the OSPAR
area, the most important concerns are molluscs and
bathing water quality. Discharges of sewage (treated and
untreated) to the sea takes place throughout the coastal
regions of the OSPAR area. The bacteria and viruses
associated with sewage and other sources such as agricultural
run-off, mainly attached to fine particulate matter,
can affect bathing water quality and can accumulate in
filter feeding shellfish such as mussels. The EC Directives
for shellfish water quality (79/923/EEC) and shellfish
hygiene (91/492/EEC) lay down permissible limits for
levels of bacteria in water and shellfish respectively (the
latter also applies to Iceland, and both apply to Norway).
The country to which the relevant directive applies is
obliged to establish appropriate monitoring programmes
and to classify shellfish growing waters. Existing
standards for the microbiological quality of bathing water
(EC Directive on the quality of bathing water 76/160/EEC)
and shellfish, although important in the protection of
public health, may not protect all individuals against the
entire range of human pathogens to which they might be
exposed either through bathing or seafood consumption.
Bathing water quality
Since monitoring work began there has
been a marked improvement in quality of bathing water, owing to the use of
wastewater treatment plants. For example in the UK, the percentage of
bathing areas meeting the standards has increased from 66% in 1988 to 90%
in 1996. The vast majority of bathing waters in the OSPAR area now conform
to the standard under the EC Directive. Where standards are not met,
action is taken by the responsible authority within each country to
improve bacterial quality of the bathing water.
Shellfish hygiene directive
All molluscan shellfish harvesting areas are required by
EC Directive 91/492/EEC to be classified according to the
extent to which shellfish samples from each area are contaminated with
Escherichia
coli. The classification
of areas ranges from clean areas where molluscs can be sold for direct
human consumption, to those from which molluscs need to be treated before
consumption and those where molluscs are prohibited for human consumption.
In some OSPAR Regions, the contamination of shellfish with E.
coli has led to restrictions on marketing
shellfish and has increased processing costs, which have caused concern
within the shellfish industry. These concerns have focused attention on
water quality within shellfish harvesting areas and in some cases have
prompted water quality improvements through improved sewage treatment
systems.
5.3.4 Impact of fisheries on ecosystems
Commercial fishing has direct and indirect effects on the
marine ecosystem. These can be summarised as follows:
-
removal of target species;
- mortality of non-target species (fish and invertebrates),
birds and marine mammals, through their incidental
catch in fishing gear;
-
physical disturbance of the sea bottom through some
demersal fishing gear and therefore an adverse impact
on benthic habitats and communities;
-
shifts in community structure; and
-
indirect effects on the food web.
The fish stock biomass of the exploited species in the
main fishing areas has fluctuated considerably over the
past 50 years. Ten-year trends in the biomass of a number
of the spawning stocks in the OSPAR area are shown in
Figure 5.3. Two
main factors are responsible for these
fluctuations, namely commercial fishing pressure and the
recruitment of young fish to the spawning stock. In some
cases, intensive fishing combined with poor recruitment
depleted stocks to the point where they could no longer
support a commercially viable fishery. Examples of this
are a number of herring stocks such as the Norwegian
spring spawning and North Sea stocks that collapsed in
the 1960s and 1970s. As a result, bans on fishing were
imposed to allow the stock to recover. In 1999, ICES
reported that 40 of the 60 major stocks for which OSPAR
requested information were outside ‘safe biological limits’
(see definition in footnote to Table
5.1). The results
of this assessment are summarised in Table
5.1.
In regions where commercial stocks have been over-exploited,
fishing pressure is often switched to stocks in
other areas, including deep-sea populations. The slow
growth rates and low fecundity of many deep-sea fish
makes them especially vulnerable to overexploitation.
Evidence is beginning to emerge that deep-sea trawling
inflicts damage upon some of the deeper ecosystems.
These impacts may already be quite extensive and
recovery can be relatively slow.
Non-target catch can include juveniles of target
species and juveniles and adults of non-target species as
well as large benthos, mammals and seabirds. Juvenile
fish are sometimes unable to escape from trawl nets. This
occurs mainly where small mesh nets are used such as in
fisheries for shrimp and Nephrops,
and in mixed roundfish
and flatfish fisheries. High rates of capture of juvenile
whiting in the Irish Sea led in 1992 to the mandatory use
of square mesh panels in UK trawl nets. Ireland followed
in 1994. Other technical measures introduced to reduce
discarding include sorting panels or grids in fisheries for
shrimp and deep water Pandalus.
During the 1990s, about
half of the total catch in numbers of whiting and haddock
taken by trawlers off the west coast of Scotland were
discarded. In Nephrops fisheries in the
Irish Sea, just under half a tonne of whiting is discarded for every tonne
of Nephrops landed.
In certain flatfish fisheries in the
North Sea more than half of the weight of the fish caught
may be discarded. The discarded fish represent an
additional mortality to the stocks since they do not
normally survive to become adults. The discards also alter
the competitive relationships within the communities by
favouring the scavenging species.
Harbour porpoises, dolphins and seals are the most
common mammals entangled in fishing gear. Harbour
porpoises are particularly vulnerable to bottom-set
gillnets. Some dolphins are vulnerable to drift nets. A
Danish action plan for reducing incidental by-catches of
harbour porpoises includes measures such as the use of
acoustic alarms, modifications to fishing equipment and
regulation of certain types of fisheries. In order to assess
the significance of any by-catch, it is important to know
both the rate of annual by-catch, and the size of the
population from which that by-catch was taken. Biological
considerations indicate that by-catch rates above 1% of
abundance may not be sustainable, and rates above 2%
have an unacceptably high risk of unsustainability
(ASCOBANS 1997). There have been few studies in the
OSPAR area that have acquired the necessary data.
Estimates for the central North Sea (extrapolated from
Danish set-net fisheries) suggest that there was an
average annual by-catch of approximately 7000 harbour
porpoises over the period 1994 to 1998 (Vinther, 1999).
This estimate exceeds 2% of the relevant porpoise
population, which is considered non-sustainable. The
proportion of the harbour porpoise population by-caught
on the Celtic shelf may have exceeded 6% in the mid-1990s
(Tregenza et al.,
1997), but there has been some
reduction in fishing effort since the studies were carried
out. In the Bay of Biscay and along the Iberian coast,
during 1992 and 1993, observers on French Albacore drift
netters recorded a by-catch of 204 common dolphins
(Delphinus delphis)
and 573 striped dolphins during 1420
hauls. As a result of this and other observations, EU
Fisheries Ministers voted in June 1998 to introduce a ban
on drift net fishing for tuna. This will come into effect after
31 December 2001.
Increases in seabird populations over the past
decades have been attributed to a number of factors, for
example better protection, increases in small prey fish and
an increase in fish discards and offal from commercial
fishing boats. Periodically, some species have experienced a sharp fall in numbers. Some changes are directly
related to a decrease in fish prey for example the decline
in the common guillemot (Uria
aalge) and puffin
(Fratercula arctica)
populations in some parts of the Arctic
area following the decrease in stocks of capelin (Mallotus
villosus) and
herring respectively. In the North Sea, it is
estimated that seabirds annually consume approximately
50% of all discards (109 000 t) and offal (71 000 t).
Bottom fishing gear can cause death or severe
damage to benthos and physical disturbance to
sediments. The degree of the impact is related to towing
speed, gear size and weight, substrate type and local
hydrodynamic factors. It should be stressed, however,
that trawling is very patchy and that the impact of trawling
is less severe in areas naturally impacted by storms and
wave disturbance. The effects of gear type, in terms of
seabed disturbance and species affected, in the North and Celtic Seas are given in
Table 5.6. Otter trawl
boards
may penetrate into soft sediment seabeds by 6 – 20 cm.
The tickler chains from beam trawls plough sediments to
a depth of 4 – 8 cm. Deep-water benthic habitats tend to
be very susceptible to the impact of trawling, due to their
slow regeneration rate. A 1994 survey indicated that up to
25% of the Irish Sea seabed is disturbed by otter trawling.
The Irish otter trawl fleet alone trawls the Irish Sea
Nephrops grounds
up to five times per year. Data from the
Dutch beam trawl fleet, which represents approximately
80% of the total beam trawl effort in the North Sea,
indicate that about 171 000 km2 of the North Sea between
the Shetland Islands and the Hardangerfjord, and the
Strait of Dover (i.e. approximately 429 000 km2) is fished
by trawlers (Rijnsdorp et
al., 1997). Within
the fished area,
70% is trawled less than once a year and, in total, about
10% of the North Sea region specified above is fished
more than once per year. In the Dutch Wadden Sea,
fishing for cockles in years of low abundance of this
species has caused a food shortage for wader birds, for
example oystercatchers (Haematopus
ostralegus).
However, since 1993, strict regulations have prevented
this from occurring.
Disturbance of the seabed by fishing gear can also
change the species and size composition of benthos. For
example, in areas of the North Sea, where fishing disturbance has occurred over a long period of time, there has
been a shift in benthic diversity and composition from
larger more long-lived benthic species to smaller more
opportunistic species. In the Dutch Wadden Sea, there is
discussion about the effects of cockle fisheries on
possible changes in macrozoobenthos and sediment
composition. Research has been commissioned to
identify the precise nature of these effects. Recent investigations along the Norwegian coast show the damage
caused to the coral reefs by trawling to be quite extensive.
Legislation for the protection of reef areas in Norway has
been implemented.
|
 |
Figure 5.3 Ten-year trends in spawning stock
biomass for stocks in each of the four main OSPAR Regions together with
migratory stocks that extend into more than one Region. |
|
Table 5.6 Effects of different types of fishing gear in terms of seabed
disturbance, some of the species affected and estimated area trawled
in the OSPAR region. Source: Region II (5NSC, 1997); Region III (Kaiser
et al.,
1996).
|
|
5.3.5 Impact of mariculture
In the OSPAR region, mariculture activity consists of
salmon farming in large cages moored in sheltered waters
and intensive and extensive cultivation of bivalve
molluscs.
All types of mariculture are faced with the problem of
producing an excess of nutrients and deposition of
organic material in the vicinity of the mariculture facilities,
especially in areas with poor flushing characteristics. This
can result in increased organic content of sediments,
decreased faunal diversity and the prominence of opportunistic polychaetes.
Shellfish cultivation involves less intensive
manipulation
of the environment than finfish cultivation. Mussel
cultivation in the Wadden Sea involves the removal of
young specimens from natural mussel beds; this has
contributed to a decline in the area covered by wild
mussel beds over the last two decades. Where imported
bivalve molluscs are to be cultivated, there is always the
possibility of introducing pests and diseases to the area
that may affect indigenous species. In recognition of this
possibility, ICES issued a Code of Practice on the
Introductions and Transfer of Marine Organisms (ICES,
1994), to help minimise problems resulting from shellfish
and other introductions. To avoid the introduction of non-indigenous
species to Dutch coastal waters, a new policy
for the import of shellfish and crustaceans was developed
in 1996. Until 2003, specific restrictive regulations exist
regarding the introduction of indigenous species into the
Wadden Sea and eastern Scheldt area.
The effects of salmon farming are usually confined to
inshore waters. What is still not clear, owing to a lack of
data, is what effect escaped reared salmon will have on
the genetic structure of the wild salmon populations in the
OSPAR area.
Sea lice are copepod ectoparasites of fish that are
common to both wild and farmed fish. Infestation in most
marine salmon farms is initially from local wild salmon.
Heavy infection on farmed salmon may result in tissue
damage and heavy financial losses. Once caged fish
become heavily infected this can lead to them infecting the
nearby wild populations. There is also the potential for
other parasites and diseases to be transferred from
farmed to wild fish and vice versa. Improved husbandry
and farm management, combined with the use of chemical
treatments and vaccination, are being used to reduce
infections and the outbreak of diseases among farmed
stocks. In the UK, a recent joint Government–Industry
Working Group has identified a range of husbandry and
management measures to contribute to the control of
Infectious Salmon Anaemia (ISA).
Chemicals are used for different purposes in
mariculture,
for instance to prevent diseases (antibiotics), to get
rid of parasites (pesticides) and to prevent ‘growth’ on
cages/nets (antifoulants). There are general concerns over
the use of such chemicals but their impact is probably
limited to the immediate vicinity of the fish farm area.
5.3.6 Impact of eutrophication
Eutrophication, as defined by OSPAR, refers to the undesirable
effects resulting from anthropogenic enrichment by
nutrients as described in its Common Procedure for the
Identification of the Eutrophication Status of the Maritime
Area adopted in 1997. The impacts of eutrophication
include: increased phytoplankton and macroalgae
production and biomass; changes in species composition
(including the occurrence of harmful algae and short-lived
benthic algae in shallow waters as well as changes in the
animal communities); and increased oxygen consumption
in water and sediments, in some cases leading to detrimental
effects on benthic fauna. Eutrophication is
non-existent in the open shelf and deep areas of the
OSPAR region. However, within the coastal zone,
embayments and estuarine areas of some parts of the
maritime area, particularly the south-eastern part of
Region II, there is clear evidence of eutrophication. The
disturbance caused by increased nutrient loads in coastal
areas may also have an effect on marine ecosystems
outside the immediate area. The first step in the Common
Procedure is a Screening Procedure to identify the more
obvious non-problem areas. The results of the Screening
Procedure are illustrated in Figure
5.4. Classification
of
the eutrophication status of the remaining areas into
problem areas, potential problem areas or non-problem
areas will be made by applying the Comprehensive
Procedure, the second part of the Common Procedure
(see Figure 5.4).
However, several of these areas are
already being considered as problem areas by the coastal
states.
Some of the earlier eutrophication-linked events in the
North Sea have been documented in the 1993 North Sea
QSR (NSTF, 1993). These include increased production of
phytoplankton in the coastal areas of the eastern part of
the North Sea, the linking of inputs of nutrients to the
extended duration of blooms in the Wadden Sea and
changes in phytoplankton and zooplankton structure in
the German Bight. In the Celtic Seas, there are indications
that the Mersey Estuary / Liverpool Bay area and Belfast
Lough may be showing signs of eutrophication and, as a
result, reductions in nutrient inputs are probably required.
Concern has been expressed over the occurrence of
areas of anoxic sediment (‘black spots’) and accompanying mortality of benthos in the Wadden Sea in 1996,
which was the result of an exceptional coincidence of
meteorological and biological developments (de Jong
et al., 1999).
Temporarily increased concentrations of nutrients in
for example the Ria of Huelva (Spain) may be associated
with eutrophication. A further example is the Bay of
Vilaine, where oxygen depletion of bottom waters takes
place each summer following the phytoplankton blooms.
Depending on the level of spring rainfall and the extent of
nitrate input through key small rivers, a few hydrodynamically confined areas on the north coast of Brittany can
sometimes be affected by ‘green tides’, which deposit
thousands of tonnes of the macroalga Ulva
lactuca onto
the beaches. Under certain conditions, algal foams can
develop after spring blooms along the Belgian and Dutch
coasts.
|
 |
Figure 5.4 Parts of the OSPAR maritime area
to which the Comprehensive Procedure will be applied to determine their
status with regard to eutrophication. |
|
5.3.7 Impact of recreation and tourism
Pedestrian traffic and the use of motorised vehicles have
increased pressure on some coastal dune systems,
disturbing the natural vegetation and seabird habitats.
Coastal habitats are being reduced or disturbed through
the construction of recreational housing, caravan parks
and golf courses. On some recreational beaches close to
population centres the amounts of litter, particularly
plastics and drink containers, are a continuing cause for
concern. The growing popularity of yachting and boating
is increasing demand for new marinas as well as potential
for the introduction of non-indigenous species and
pollution from antifouling paints.
In the North Sea, bird-breeding areas on sandy
beaches have been almost completely lost because of
recreational activities. Little tern (Sterna
albifrons) and
Kentish plover (Charadrius
alexandrinus) are
most strongly
affected as their breeding success is reduced by human
activities. In contrast, cessation of hunting in parts of the
Wadden Sea has had a positive effect on the numbers of
Brent geese (Branta
bernicla), barnacle
geese
(B. leucopsis),
and curlews (Numenius
arquata). In
Bannow Bay in south-east Ireland, which is designated as
a Special Protection Area for birds, motorbike scrambling
has weakened the dune systems and shooting has
disturbed roosting birds. At other Irish sites, excessive
human activity has excluded seabirds from parts of their
natural habitat and denied them feeding opportunities.
This has led to the initiation of protection schemes,
especially along the east coast. Finally, disturbance of
small cetaceans occurs as a result of interaction with
high-speed boats (e.g. jet skis).
5.3.8 Impact of sand and gravel extraction
Sand and gravel extraction takes place in the inshore
areas of the North Sea, particularly the southern part, the
Celtic Sea and the French Atlantic coast. Not all of the
extracted material is retained on board the vessel. The
loss of material produces a temporary increase in turbidity
in the water column and benthic organisms outside the
dredged area may be impacted by settlement of both this
residue and any resuspended material arising from this
operation. In the short-term, the main impact on the
ecosystem is the disturbance and removal of benthic
organisms from the extraction site. There can be damage
to sites that act as spawning areas for fish that lay their
eggs directly on gravel, for example herring. In the longer-term,
the rate of recovery of a site depends on the
modifications made to the substrate and the potential of
the benthos to re-colonise the area. For example, studies
in the Wadden Sea showed that at extraction sites on
sheltered intertidal flats, recovery of sediment composition and benthic fauna took more than fifteen years,
whereas at sites with greater hydrodynamic activity,
recovery was much faster. Studies carried out off the east
coast of England, where extraction caused a reduction of
approximately 40% and 80% respectively in the number
and abundance of benthic species, revealed that a limited
re-colonisation had occurred within a year (Kenny and
Rees, 1994).
5.3.9 Impact of dredging and dumping of dredged materials
Most dredging serves navigational purposes in coastal
approaches to and inside seaports. In some cases, for
example near Rotterdam, dredged spoil from ports that is
contaminated above certain limits is being deposited in
specially built deposits. Slightly or non-contaminated
dredged spoil is disposed of at dumpsites in estuaries
and coastal waters. The effects of dredging activities are
threefold. Increases in suspended matter in the water
column can directly affect primary production and the
growth of filter-feeding organisms such as bivalve
molluscs. Enhanced sedimentation at dumpsites can lead
to burial of the resident benthos. Finally, contaminants can
be resuspended and remobilised from sediments and
taken up into the food chain. However, dredging in the
outer parts of estuaries may lead to larger-scale effects on
the sediment dynamics, benthic communities and
suspended matter regime.
5.3.10 Impact of coastal protection and land
reclamation
Coastal protection, land reclamation and development of
ports and harbours can affect coastal habitats. In many
cases, habitats and associated ecological processes
change permanently or even disappear. Examples of the
latter are natural transition zones between freshwater
habitats and coastal waters along the Dutch coast. At
present for much of the OSPAR coastline there is insufficient information on recent rates of habitat loss in relation
to habitat types and areas.
5.3.11 Impact of offshore activities and ship-generated
oil spills
All oil-related activity in European waters is done under
strict licence conditions, with the aim of minimising the
effects on marine ecosystems. It should be noted
however that this activity and the number of platforms
have increased since 1993. Impacts on the benthic
community are usually confined to a few kilometres
around the platforms. These impacts are largely caused
by the disposal of drill cuttings in the immediate vicinity of
the platform. There is a reduction in species diversity near
to the platform with polychaete worms dominating the
biomass. Biological changes are not usually detectable
beyond 3 km from platforms, but there are a few cases
where effects have been detected out to 5 km. Changes
in the regulatory regime governing the use of drilling fluids
are expected to contribute to reducing the impact on the
benthic communities. There is, however, uncertainty about
the possible environmental effects of removing cuttings
piles. Some alternatives to oil-based muds also possess
properties which could result in adverse impacts on
benthic communities.
There is uncertainty about the environmental effects of
discharges of produced water. In addition to oil, produced
water also contains a range of other natural organic
compounds including monocyclic aromatic hydrocarbons
(i.e. BTEX), 2- and 3-ring PAHs, phenols and organic
acids. This includes added production chemicals, and
may also include organic compounds not yet identified.
Increased levels of PAHs in caged mussels and passive
samplers have been found up to 10 km from produced
water discharge sites.
Accidental and illegal oil spills result in the oiling of
seabirds, shellfish, other organisms and the coastline,
with ecological and often economic consequences.
Measured in oiled seabirds, this type of contamination
remained at high levels throughout the years in some
parts of the North Sea, in others it declined for some time
whilst it has again increased in recent years. Even minor
accidents with ships can end in disaster as long as heavy
fuel oil or its residues are involved. When the ‘Pallas’
grounded in the Wadden Sea in 1998, it lost about 250 m3
of heavy fuel oil which killed about 16 000 birds overwintering in the area. The 10 000 – 15 000 t of heavy fuel oil
spilt when the ‘Erika’ broke apart off the French Atlantic
coast in December 1999, killed at least the 80 000 birds
collected on the beaches, with estimates running as high
as 200 000 – 300 000 birds killed. Slight contamination of
fish has been found in the vicinity of platforms. The overall
impact on fish stocks by low levels of hydrocarbons is
considered to be small, although long-term effects of
operational discharges of production water cannot be
ruled out. Future increases in shipping traffic may
increase the risk of pollution.
5.3.12 Impact of contaminants
The presence of high concentrations of metals and man-made
substances in marine seafood could pose a
problem for the human consumer, as has been demonstrated
for indigenous people in Greenland who have
been exposed to high levels of mercury and PCBs in
seafood. In view of this, most countries in the OSPAR area
have established monitoring programmes for contaminants in seafood to ensure that it is safe for consumption.
For example, due to high concentrations of different contaminants
in fish and shellfish there is advice against
human consumption of seafood from several fjords along
the Norwegian coast. Major wastewater discharges to
rivers or coastal areas are subject to environment impact
assessment and, as appropriate, the control requirements
of the EC Directives on urban wastewater treatment and
integrated pollution prevention and control.
The situation concerning impacts on marine life is
somewhat different. Only in some cases has the impact of
contaminants on populations or communities been
measured directly in the OSPAR area, although there is
much information about effects on individuals (referred to
as ‘biological effects’). BRCs and EACs were established
to be used as the best available assessment criteria for
contaminant levels and their effects, but the caution
expressed as to their limited usefulness must be
recognised. With respect to EACs it should be noted that
they refer primarily to acute toxicity. The derivation of
EACs does not include for example the bioavailability of a
contaminant under field conditions, the degree of bioaccumulation,
carcinogenicity, genotoxicity and hormone
balance disturbances (endocrine disruption). In addition,
the presence of other hazardous substances in the sea
may cause enhanced or combined adverse effects in
organisms or even on populations. Therefore, concentrations of a contaminant in the marine environment below
the EAC for that contaminant do not guarantee a safe
situation. On the other hand, it is not compelling that
biological effects occur where an EAC is exceeded. This
can only be established through biological investigations
in the field.
The biological effects studies run to date within the
OSPAR area have identified a number of places where
impacts have been observed at the cellular and individual
level. Biological effects essentially indicate the presence
of contaminants, which are taken up by organisms. Some
examples are given in the following paragraphs. An
important sub-lethal effect is endocrine disruption, the
impact of which may extend to the population level.
Tributyltin is one of the rare examples in the marine
environment where effects can be attributed to a single
substance. Exposure to TBT, originating for example from
antifouling paints, produces distinctive responses in a
number of organisms. These include shell thickening in
Pacific oysters and imposex/intersex (the imposition of
male characteristics in female gastropods). TBT is also
found in seabirds, marine mammals, fish and plankton.
Effects on hormone, reproductive, immune and certain
enzyme systems of fish are reported. An impact to
humans via the consumption of seafood might be
possible.
Surveys of imposex in British waters during 1997
indicate that biological effects are still evident at all but the
most remote coastal sites ten years after enforcement of
TBT restrictions. Some estuarine and coastal areas in
north-west Spain and northern Portugal have exhibited
significant levels of imposex in dogwhelks (Nucella
lapillus).
Although in the former case this has led to
female sterilisation, the dogwhelk population in north-west
Spain is not considered to be at risk of extinction.
Imposex has been documented in dogwhelks and
common whelks in harbours in Iceland, Norway and
Svalbard and in the North Sea region including the
Kattegat. Over a ten-year period of monitoring at twenty
sites on the Irish coast those with salmon farming
operations and small craft demonstrated a recovery from
TBT contamination; as indicated by a reduction in an
index of imposex (Relative Penis Size Index).
Imposex still occurs near shipping lanes all over the
world, and also in offshore areas, where it correlates
positively with shipping intensity and TBT levels in biota
and sediments. This is due to the present lack of regulations on the application of TBT to ships larger than 25 m.
The toxicological significance of the elevated
concentrations
of PCBs in marine organisms is unknown.
However, prior to death some of the otters with high PCB
body burdens have been reported to have behaved in a
manner suggestive of organochlorine poisoning. The
previously abundant Swedish otter population has for a
long time suffered from PCB pollution. Along the Swedish
Skagerrak coast concentrations of PCBs in fish are still
too high and no otters are currently found in the Swedish
coastal environment (Brunström et
al., 1998; Roos et
al.,
in press). PCBs can disturb reproductive, enzyme and
endocrine systems in marine mammals, for example in
harbour seals fed experimentally on fish from the Wadden
Sea. Such effects are found in certain populations outside
the OSPAR area, for example in Baltic grey seal and
ringed seal populations (Olsson et
al., 1992; Roos et
al.,
1998). High levels can affect the immune system of the
polar bear (Bernhoft et
al., in press) and
it is possible that
similar effects may be occurring in other marine vertebrates.
Various organic contaminants may induce higher
activity of the enzyme 7-ethoxyresorufin-O-deethylase
(EROD) in fish liver. The extent of this activity is used as an
indicator of the degree of exposure to a range of
compounds, including PCBs and PAHs. Elevated EROD
activity has been measured in the livers of flatfish. In UK
marine waters, the greatest activity was found in plaice in
the area of the Firth of Clyde sewage sludge disposal
ground at Garroch Head and near to industrial centres at
Hunterston and Irvine Bay.
There is clear evidence that a diverse range of natural
and man-made substances including PCBs, dioxins, TBT
and various other organometallic compounds, pesticides,
pharmaceuticals and industrial chemicals, have the
potential to impair reproduction in aquatic organisms
through interference with their endocrine (i.e. hormonal)
systems. Studies in freshwater environments have shown
that for some substances these endocrine-disrupting
effects can occur even at very low ambient concentrations,
considerably less than concentrations that are
either mutagenic or acutely toxic. To date, it remains
unclear which substances or combinations of substances
are responsible for the observed effects (e.g. feminisation
in male fish) but ethynylestradiol (a contraceptive agent),
PCBs and alkylphenols (derived from some industrial
detergents) have been positively implicated, as well as
natural hormones. Furthermore, it is important to note that
many different man-made and natural substances are
able to act additively at hormone receptors to produce
some of these effects. Although TBT-induced imposex in
gastropod molluscs is one of the few confirmed instances
of endocrine disruption in marine life at present, many
other endocrine-disrupting substances are known to be
present in effluents and river water discharged to the
OSPAR area. Furthermore, studies in the UK have shown
that a number of estuarine waters receiving effluents from
sewage treatment plants and industrial sources induce
oestrogenic effects (a form of endocrine disruption) in fish.
Effects observed in male flounder include production of
the yolk protein precursor vitellogenin and induction of
intersex, although, to date, no effects at the population
level have been demonstrated. Intersex, among other
effects, involves the appearance of egg cells in the testis,
and it is probable that it is associated with impairment of
reproductive output. It is important that effects like these
should receive further study, both to uncover the full range
of impacts in different species, and to decide whether
populations and communities are at long-term risk (as is
the case with TBT).
Potential for harm to North Sea organisms from metals
includes the effects of dissolved copper on lower trophic
levels such as phytoplankton, and the accumulation of
cadmium and mercury in top predators and lead in
shellfish. These effects are due in large part to the
tendency of these metals to bioaccumulate in organisms
through trophic interactions. However, these effects are
often local and occur most frequently in estuaries and in
the coastal zone. Although potential for biological effects
due to metals undoubtedly exists at some of the more
contaminated sites, particularly those subject to
continuing metal inputs, the regional QSRs provide no
recent reports of specific effects due to elevated metal
concentrations in sea water, sediments or biota.
Certain brominated flame retardants are known to
bioaccumulate and are suspected to have developmental
or behavioural effects on mammals.
Phthalates are known to persist under marine
conditions and to bioaccumulate at lower levels of the
food chain, in particular in sediment communities.
Nonylphenols degrade slowly, are known to
bioconcentrate
in salt-water fish and mussels and have been
reported to induce changes in the endocrine system in the
course of in vivo
tests. They are
also toxic to marine algae
but not at levels usually found in the marine environment.
Short-chained chlorinated paraffins are known to
persist in the environment and to bioaccumulate in marine
mammals (seals, beluga, and walrus). The levels recently
found in different Arctic regions were in the range of 200
to 800 µg/kg ww.
Copepods have been shown to be sensitive to a wide
variety of organic contaminants, such as insecticides,
organometals and oil. Field studies and mesocosm experiments
as well as model simulations have shown that
effects on zooplankton may cause increased phyto-plankton
densities due to reduction of grazing pressure.
Some decreases in numbers of seabirds have been
attributed to the effects of organochlorine compounds. In
the early 1980s concentrations of DDT in shags in one
area of Region III may have resulted in eggshell thinning.
More recent data suggest that this is unlikely to still be a
problem. In addition, bacterial poisoning associated with
feeding on municipal refuse sites in Region III has been
highlighted as a possible cause of a reduction in numbers
of birds.
Alkylphenols, alkyl-substituted
naphthalenes, alkyl-substituted fluorenes and dimethyl benzoquinone were
identified as possible causes of toxic effects in UK
estuaries. (Thomas et
al., 1999a,b). This
information has
been generated by Toxicity Identification Evaluation (TIE)
procedures using a variety of bioassays. It is noteworthy,
however, that no single contaminant was responsible for
observed biological effects in estuaries – effects generally
appear to result from the action of complex mixtures.
From mesocosm studies, there is evidence of a
correlation
between the occurrence of pre-stages of liver
tumours in North Sea flatfish and contaminants, particularly PAHs and possibly chlorinated hydrocarbons
(Vethaak et al.,
1996).
Adverse biological effects caused by mixtures of
unknown pollutants, tested using oyster embryo water
bioassays and whole sediment bioassays with amphipods
and annelids, including acute toxicity, have been
measured in some UK estuaries, for example the River
Tyne and River Tees (Jones and Franklin, 1998). The full
ecological significance of these observations is not
known, although invertebrate communities in some industrialised estuaries are known to be impoverished.
A further effect of mixtures of pollutants can be to
decrease ‘Scope for Growth’ in the mussel Mytilus
edulis.
This is a well established biological effects technique and
when combined with the measurement of chemical contaminants in the tissues of mussels provides a tool for
assessing spatial changes in environmental water quality.
Depression of Scope for Growth was demonstrated in the
North Sea UK east coast survey in the early 1990s (Widdows et al.,
1995). In 1996 and 1997 a further survey
was carried out at 37 locations in the Irish Sea, including
some sites on the east coast of Ireland. The results
indicated reduced Scope for Growth in the
Mersey/Liverpool Bay region and in Dublin Bay. High
Scope for Growth was recorded along the west coasts of Scotland and Wales. These results indicate that contaminants are interfering with the ability of shellfish to grow
normally in southern coastal areas of the North Sea, and
also in some coastal areas of the central Irish Sea.
5.3.13 Impact of radioactive disposals
Interest in the behaviour of radionuclides in the marine
environment has, until now, been driven by the objective
of protecting human health from ionising radiation through
the food chain. Whilst the system of human radiological
protection has been developed through the adoption of
internationally recognised guidelines and standards, there
are currently no internationally accepted radiological
criteria for the protection of marine flora and fauna. The
assumption has been that man is the most radiosensitive
organism and that if man is adequately protected, then
other living things are also likely to be sufficiently
protected. The International Commission on Radiological
Protection states that: ‘the standard of environmental
control needed to protect man to the degree currently
thought desirable will ensure that other species are not
put at risk. Occasionally, individual members of non-human
species might be harmed, but not to the extent of
endangering whole species or creating imbalance
between species’ (ICRP, 1991).
In 1994 OSPAR agreed that more emphasis should be
put on assessing biological and ecological effects in the
marine environment (including the vulnerability of marine
organisms and communities) arising from existing and
foreseen future discharges of radioactive substances
(PARCOM Decision 94/8). There is now a growing recognition
that protection of the environment merits attention in
its own right. The International Atomic Energy Agency
acknowledges that ‘there is a growing need to examine
methods to explicitly address the protection of the environment
from radiation. The concept of sustainable
development places environmental protection on an equal
footing with human protection, on the basis that it is
necessary first to protect the environment in order to
protect human populations.’ (IAEA, 1999). The OSPAR
Strategy with Regard to Radioactive Substances is
primarily concerned with reducing concentrations of
radionuclides in the marine environment, with dose to
man as a supporting consideration. The Strategy requires
the OSPAR Commission to undertake the development of
environmental quality criteria for protection of the marine
environment from adverse effects of radioactive
substances and to report on progress by 2003.
5.3.14 Impact of marine litter
Marine litter is derived from both land-based and marine
sources and its impact on marine life has been
observed. Most victims have been birds and the main
culprit has been plastics. The mechanism of damage
has either been by entanglement in plastic sheeting,
which can lead to the birds being drowned or by
ingesting small plastic objects, which can lead to
blockages in the stomach or intestines. Autopsies
carried out on dead mammals and turtles have also
revealed that death in some cases has been linked to
the ingestion of plastic waste. Studies have been
conducted over ten years (1988 to 1998) on leatherback
turtles (Dermochelys
coriacea) and
loggerhead turtles,
the two species occurring most frequently in Region IV.
Autopsies showed that respectively 58% and 11% of the
individuals had ingested plastic waste. Cetaceans can
also be significantly affected, and in the few observed
cases from several hundred autopsies, the species
affected seemed to be those that feed on cephalopods
and which might have mistaken plastic bags for their
prey. Floating litter also has the potential to act as a
vector for the spread of epiphytic organisms beyond
their normal ranges. |
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