The Decline of the Seaweed Fucus in the Baltic Sea:

The status of the brown seaweed Fucus vesiculosus reflects the dramatic alterations that are now occurring in the abundance and distribution of life in the Baltic Sea. The Fucus community provides shelter, spawning, and foraging for many economically important fish. Fucus is now, however, greatly diminished: in southwest Finland it nearly disappeared in the late 1970s; near Kiel, Germany, Fucus is now found no deeper than 2 m with a 95 percent decline of biomass since the 1950s; and in Sweden it is now limited to 3–4 m depth having once occurred to 6 m in the 1940s. Eutrophication from human activities appears to be the basis for these changes, although synergistic interactions with natural upwelling may have led to the disappearance of Fucus in Finland. Eutrophication led to increased phytoplankton and thus decreased light penetration, and also stimulated dense growths of epiphytic algae on the Fucus, greatly reducing fucoid growth rates and increasing their drag, making the plants more susceptible to storm removal. In different regions the kelp Laminaria saccharina, the mussel Mytilus edulis, and several species of filamentous algae are now replacing Fucus. The Baltic Sea may be an ideal system in which to assess the consequences of distinct species replacements on ecosystem function because of its well-known hydrographic history and relatively low species diversity.

   

Key References: Kangas et al., (1982); Larsson et al., (1985); Kautsky et al., (1986); Launiainen et al., (1989); Vogt and Schramm (1991).

The Functional Extinction of Oyster Reefs in Chesapeake Bay:

A combination of the anthropogenic effects that are now widely altering marine biodiversity is demonstrated by the virtual elimination of the once vast oyster reefs of the Chesapeake Bay. The native oyster Crassostrea virginica once supported an enormous fishery that began to show significant declines a century ago due to overfishing and associated activities (such as the nonreplacement of shell for larval oysters to settle upon). Pollution closed local beds. Dredging, siltation, and marinas physically destroyed oyster habitat. Beginning in the 1950s, two disease agents, "MSX" (caused by the protozoan Haplosporidium nelsoni) and "Dermo" (caused by the protozoan Perkinsus marinus) led to the final demise of many remaining populations. These epidemics may represent resurgences of native species, or these protozoans may have been introduced. A similar fate with the same causes had earlier befallen the oysters of adjacent Delaware Bay. It has been calculated that Atlantic oysters in the Chesapeake Bay were historically abundant enough to filter much of the Bay's water once a week. Today the remaining oysters would require an entire year to do so.

   

Key References: Maurer et al., (1971); Hargis and Haven (1988); Newell (1988).



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