Browsing Marine Science and Limnology by Title
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Wasting disease and environmental variables drive sea star assemblages in the northern Gulf of AlaskaSea stars are ecologically important in rocky intertidal habitats. The recent (starting 2013) sea star die-off attributed to sea star wasting disease throughout the eastern Pacific, presumably triggered by unusually warm waters in recent years, has caused an increased interest in spatial and temporal patterns of sea star assemblages and the environmental drivers that structure these assemblages. This study assessed the role of seven potential static environmental variables (distance to freshwater, tidewater glacial presence, wave exposure, fetch, beach slope, substrate composition, and tidal range) influencing northern Gulf of Alaska sea star assemblages before and after regional sea star declines. For this, intertidal surveys were conducted annually from 2005 to 2018 at five sites in each of four regions that were between 100 and 420 km apart. In the years leading up to the regional mortality events, assemblages were different among regions and were structured mainly by tidewater glacier presence, wave fetch, and tidal range. The assemblages after wasting disease were different from those before the event, and there was a partial change in the environmental variables that correlated with sea star structure. In these recent years, the environmental variables most highly correlated with sea star assemblages were slope, wave fetch, and tidal range, all of which relate to desiccation, attachment, and wave action. This indicates that the change in sea star density and structure by wasting disease left an assemblage that is responding to different environmental variables. Understanding the delicate interplay of some of the environmental variables that influence sea star assemblages could expand knowledge of the habitat preferences and tolerance ranges of important and relatively unstudied species within the northern Gulf of Alaska.
Zooplankton abundance, community structure, and oceanography northeast of Kodiak Island, AlaskaZooplankton community dynamics and correlations with physical characteristics of the water were studied in the northwestern Gulf of Alaska. Zooplankton were collected systematically northeast of Kodiak Island, Alaska in March, May, August and November of 2002 to 2004. Species composition, total abundance and spatial community structure were correlated to physical variables. Small copepods (numerically>50%) dominated the zooplankton composition and were most abundant in August. Average biomass was 48.7 g WW m⁻² in May and 52.0 g WW m⁻² in August in Kodiak region. Interannual zooplankton abundance variations were large, with May 2003 having a dramatically higher abundance (2x10⁴ individual m⁻³ higher) than 2002 and 2004, probably due to the higher temperature (1° C higher) and lower salinity in May 2003. Small to moderate correlations (r<0.7) were found between temporal zooplankton abundance and selected physical variables. Spatial patterns in zooplankton composition among stations were more discernable in May than in August, likely due to water column stability in the spring and more dynamic influences in the summer, but revealed no consistent spatial patterns. The zooplankton community patterns in this region thus appear to arise due to complex oceanographic and bathymetric interactions, and suggest high variability can occur in the availability of prey for higher trophic levels.
Zooplankton ecology of Norton Sound, AlaskaThe zooplankton distribution in Norton Sound was monitored for the Outer Continental Shelf Environmental Assessment Program. Salinity, temperature, and predation were investigated as factors controlling species composition and community structure. Sampling was concentrated along the eastern coast of Norton Sound during July and August, 1976. The copepod Acartia clausi and the cladocerans Evadne sp. and Podon sp. were numerically dominant in the samples. These species are able to tolerate the widely ranging salinities and temperatures of the coastal waters. The A. clausi population abundance was correlated with water temperature, while cladoceran and larval mollusc populations were correlated with salinity. No differences in species composition were discerned between stations along the shallow coast; however, the seaward community contained a greater diversity of organisms supporting a larger planktonic carnivore biomass. Zooplankton was a numerically dominant item in the diets of many fish species, although the epibenthic mysid community was volumetrically most important.