Ecosystem services provided by the Baltic Sea ... - Naturvårdsverket

SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak
Economic Marine Information
Excessive exploitation and bycatch
The pressures of fishing have given rise to a new category of species depletion:
commercial extinction. Fish populations are depleted to the point that it is no
longer economically feasible to fish. While not extinct, these species are certainly
no longer playing their traditional roles in their ecosystems. Fishing operations,
such as trawling and dragging destroy bottom habitats (with consequences discussed
above) and deplete species populations; repetition of such activities delays
or prevents recovery. In the Baltic and Skagerrak, over-fishing is considered one of
the greatest threats to ecosystems in general and to biodiversity in particular (16)
Excessive fishing has already reduced genetic diversity among Baltic cod (18) and
the farming of salmon is causing impoverishment of wild salmon stocks. In addition,
seals, harbour porpoises and birds are involuntarily caught in fishing gear.
Current estimates of the extent of bycatch are uncertain. The fact that the Baltic
population of harbour porpoises has been subject to dramatic decrease compared to
historical levels makes it particularly vulnerable.
Pollution
Hazardous substances can reduce genetic diversity within a population (57). The
effect may go unnoticed until environmental conditions are altered. Having been
selected to withstand hazardous substances, the intraspecific ability to respond
differently to other disturbances, like temperature increase and acidification, may
have been reduced or lost. This illustrates the problem with various threats acting
in synergy.
Alien species
Of the 168 alien species considered as threats to Swedish ecosystems, 20 are fishes.
Among them we find the round goby (Neogobius melanostomus), which has already
invaded the Polish coast, successfully outcompeting and even excluding
many native species (chapter S3). Globally, invasive alien species are considered
as the second leading cause of biodiversity loss after habitat alteration (58).
Climate change
With increased temperatures, the distribution and abundance of species will shift
according to their thermal tolerance and ability to adapt. Not only are physiological
responses to increased seawater temperatures expected, alterations in seawater pH
and salinity are also expected to have major consequences for marine life. For example,
the ability to navigate during migration in the red-listed eel, appears related
to salinity and temperature patterns (59). A milder climate would also reduce ice
conditions, which in the Baltic would specifically threaten the ringed seal (Phoca
hispida), an endemic species that is dependent on ice surfaces in order to reproduce.
Although chemical changes in the oceans are still poorly understood, it appears
that acidification may cause failure to produce calcareous structures by
shells, crustaceans, zooplanktons, coralline algae and corals, to mention some, as
well as reduce reproductive capacity among others. According to researchers, the
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