Showing papers by "David L. Strayer published in 1996"

Arrival, spread, and early dynamics of a zebra mussel (Dreissena polymorpha) population in the Hudson River estuary

Abstract: Les effectifs de la moule zebree (Dreissena polymorpha) dans l'estuaire de l'Hudson ont augmente et se sont propages rapidement depuis la decouverte des premiers individus en mai 1991. La population s'etablissait a 550 milliards de moules (4000 moules/m 2 , moyenne etablie pour la portion dulcicole de la riviere qui est soumise aux marees) a la fin de 1992. Elle formait alors plus de 70% de la biomasse zoobenthique et filtrait quotidiennement un volume equivalent a toute la colonne d'eau. Plus de 95% des moules vivaient fixees aux pierres de la zone subtidale. Par suite de l'explosion demographique enregistree en 1991-1992, le succes de la reproduction (nombre de jeunes de l'annee par adulte) a chute de quatre ordres de grandeur en 1993-1994. En outre, la taille des jeunes de l'annee a la fin de la saison de developpement de 1993-1994 atteignait seulement 20 a 30% de celle des jeunes de l'annee de 1991. L'incapacite des larves de resister a la forte competition pour la nourriture exercee par les adultes pourrait avoir ete la cause de ce phenomene. Les auteurs estiment que de telles populations limitees par la nourriture pourraient etre particulierement frequentes dans les rivieres et les estuaires, ou la quantite de nourriture par rapport a la surface des supports est faible.

Filtration of Hudson River water by the Zebra mussel (Dreissena polymorpha)

Abstract: Zebra mussels (Dreissena polymorpha) graze on phytoplankton, and decreased phytoplankton concentrations have been associated with zebra mussels in lakes. It is not known, however, how the zebra mussel will affect phytoplankton in turbid systems such as rivers and the freshwater portions of estuaries. To determine whether zebra mussels can effectively remove phytoplankton in these turbid systems, and to determine what components of the suspended material are removed and at what rates, we conducted a series of grazing and size-selection experiments using ambient Hudson River water and its natural phytoplankton community. Zebra mussels removed both phytoplankton and total suspended weight (TSW) at comparable rates (∼115 ml mussel−1 h−1). Variation in filtration rates were not correlated with TSW or chlorophylla (chla) concentration, and did not appear to depend on relative proportions of either component. Mussels removed particles with approximately equal efficiency in all particle size classes measured (0.4 μm to >40 μm). Zebra mussels appear to remove Hudson River phytoplankton effectively in the presence of suspended sediment and do so at rapid rates. Based on our measurements and unpublished estimates of the size of the population, zebra mussels filter a volume equivalent to the entire volume of the tidal freshwater portion of the Hudson River about every 2 d.

Exotic species in the Hudson River basin: A history of invasions and introductions

Abstract: We compiled information about the distribution of exotic organisms in the fresh waters of the Hudson River basin. At least 113 nonindigenous species of vertebrates, vascular plants, and large invertebrates have established populations in the basin. Too little was known about the past or present distributions of algae and most small invertebrates to identify exotic species in these groups. Most established exotic species in the Hudson River basin originated from Eurasia or the Mississippi-Great Lakes basins, and were associated with vectors such as unintentional, releases (especially escapes from cultivation), shipping activities (especially, solid ballast or ballast water), canals, or intentional releases. Rates of species invasions of fresh and oligohaline waters in the basin have been high (ca. one new species per year) since about 1840. For many well-studied groups, introduced species constitute 4% to nearly 60% of the species now in the basin. Although the ecological impacts of the invaders in the Hudson River basin have not been well studied, we believe that about 10% of the exotic species, have had major ecological impacts in the basin. Since, the rates, of entry and composition of exotic species in the Hudson basin are similar to those observed., previously for the Laurentian Great Lakes, invasions tended to occur earlier in the Hudson basin, probably reflecting the earlier history of human commerce. While most exotics have had negative impacts on local flora and fauna, some fish species have provided unique angling opportunities and important economic benefits.

A Range-Wide Assessment of Populations of Alasmidonta heterodon, an Endangered Freshwater Mussel (Bivalvia:Unionidae)

Abstract: The purpose of this study was to estimate the densities and sizes of the major remaining populations of Alasmidonta heterodon, a unionid mussel listed as endangered by the United States Fish and Wildlife Service. We studied 13 streams from New Hampshire to North Carolina. At 2-9 reaches on each stream, we assessed A. heterodon populations using both timed searches and quadrats, and measured the shell lengths of all living A. heterodon that we found. All populations of A. heterodon that we studied had 3 characteristics: 1) low density, with mean densities typically 2 ; thus, low or declining density per se may threaten populations of A. heterodon; 2) recent reproduction, as shown by the presence of young animals or gravid females; and 3) vulnerability to loss from small ranges, low population densities, linear ranges, or a combination of these 3 factors. Furthermore, several of the populations that we studied included 100s to 10s of 1000s of animals, so these populations probably were...