Environmental Engineering Reference
In-Depth Information
Hall & Harding 1997, Roberts 1997, Watling & Norse
1998, Collie
et al.
2000, Kaiser
et al.
2000), although
perhaps not so pervasive as when rocky substrates are
simply knocked off in the search for an economically
valuable shellfish resource (Fanelli
et al.
1994). We
therefore concur with Hall (1994, p. 194), who in his
review of physical disturbance and marine benthic
communities states that 'there is increasing recogni-
tion of the role man plays in physically disturbing
marine sediment environments, the most obvious and
widespread being commercial fishing'.
oysters in western Europe suffer little predation from
birds and crabs. Pacific oysters may soon compete for
space and food with the native biota.
13.3.3 Water-borne influences: pollution
and eutrophication
Chemical water pollution comes in many different
forms, some of which are known to affect the inhab-
itants of intertidal flats. A well-known case of the
near-disappearance of a sensitive fish-eating bird in
the Dutch Wadden Sea is the poisoning of Sandwich
terns (
Sterna sandvicensis
), with a drop from 20,000
to fewer than 2000 pairs in the early 1960s. Once this
was traced back to releases in the Rhine of the insec-
ticides telodrin and dieldrin (Koeman
et al.
1967),
the releases were stopped and there has been a par-
tial recovery of the Sandwich terns in the ensuing
decades (van de Kam
et al.
2004).
A toxic chemical that continues to damage coastal
environments worldwide is the antifouling chemical
tributyltin (Page
et al.
1996). Even at very low con-
centrations, tributyltin disrupts the gonadal develop-
ment of marine invertebrates such as the littorinid snail
Littorina littorea
(Bauer
et al.
1995) and the whelk
B. undatum
(Mensink
et al.
1996). The International
Maritime Organisation passed a resolution prohibiting
the use of tributyltin in 2003, but this resolution still
awaits full implementation until 2008. Meanwhile, new
chemicals continue to be developed at breathtaking
speed. Some old ones, and an unknown fraction
of the new ones, continue to be a concern in many
estuaries around the world. The incredible variety of
chemical products means that only a small selection of
chemical substances - those that are established to be
poisonous - can be monitored in water samples and
in bird eggs (Bakker & de Jonge 1998, Becker
et al.
1998).
Eutrophication, the increase in the amount of
organic material entering an ecosystem, is a very dif-
ferent type of pollution (Nixon 1995). Depending on
your viewpoint, eutrophication may be considered a
good thing or a bad thing for intertidal flat eco-
systems. Eutrophication can originate from a single
point of discharge, or can come with the tidal streams
as increased input of the nutrients nitrate and phos-
phate. If the production of pelagic and benthic algae
13.3.2 Invasions
Invasions of exotic species are now considered a
major problem in coastal marine communities, espe-
cially the intertidal areas (Carlton 1999, Grosholz
2002). An assessment for the North Sea coasts
showed the presence of a minimum of 80 exotic
invaders introduced by transoceanic shipping and
aquaculture, especially in the 1970s (Reise
et al.
1999). Most introduced invertebrates were brought
in by ships and came from the western side of the
Atlantic, whereas the Pacific supplied exotic oysters
that brought with them invading algae. Some inva-
sions, such as that of
M. arenaria
, thought to have
been brought in from the north-west North American
coast by Vikings, are ancient and may actually rep-
resent recolonizations after a Pleistocene extinction
(Strasser 1999). Others, such as the successful inva-
sion of the Wadden Sea by the American razor clam
(
Ensis americanus
) in the late 1970s, are much more
recent (Essink 1986, Armonies & Reise 1999).
Although there is as yet little evidence of direct com-
petition between these intertidal benthic invaders and
the resident species, the recent establishment of the
Pacific oyster (
Crassostrea gigas
) could start an era of
serious ecological problems. Between 1964 and 1977
small Pacific oysters from British Columbia, Canada,
were deliberately released in north-western Europe
(Drinkwaard 1999). By 2000, Pacific oysters had
become firmly established and reproductively success-
ful at many sites around the North Sea. In the Dutch
Delta and the international Wadden Sea they are
now forming extensive oyster beds covering many
hectares, sometimes overgrowing or displacing native
mussel beds. Unlike the native bivalve species, Pacific
