Biomass spectra in Narragansett Bay from phytoplankton to fish

Brooke A Longval, University of Rhode Island

Abstract

Biomass spectra were constructed for the biotic community of Narragansett Bay in size classes ranging from phytoplankton to fish to determine the usefulness of biomass spectra in determining spatial and temporal trends in community structure and pattern. ^ Yearly, regional and seasonal biomass spectra for fish and macro-invertebrates were constructed with data from two long-term trawl surveys from 1990-2005. Spectral slopes agreed with the predicted value of -1 for all regions and years except 1991. This consistency indicated minimal impact of fishing, climate or anthropogenic effects on the community's size structure; spectral slope was not a good indicator of change in this community. Spectral intercept was strongly correlated with total biomass. Regionally, spectra indicated that the Lower bay was more productive for large benthic fish and the Mid bay was important habitat for pelagic fish and crabs. After 2002 the Upper bay fish community appeared to shift to a new regime, with increased large fish biomass. ^ Seasonal biomass spectra showed strong differences and also showed intra-annual trends indicating within-season shifts. Winter fish biomass steadily declined and was composed mainly of skates rather winter flounder. Summer fish size was five times smaller than winter fish size. Spring, summer and fall biomass increased after 2002. Migratory and warm-water fish appeared to be increasing their biomass and the amount of time spent in the bay. ^ Whole-system biomass spectra (phytoplanIcton, zooplankton, benthic infauna, ctenophores, crabs and fish) were constructed for one station in Mid Narragansett Bay for a warm winter year (2002) and a cold winter year (2004). Yearly spectral slopes were indistinguishable from -1 despite twofold variation in individual trophic group biomass. Modeling of the variation in group biomass showed that large (up to 4x) changes were required to produce slopes significantly different from -1. Cooler winter temperatures in 2004 were linked to higher phytoplankton biomass, but lower biomass of ctenophores and benthic infauna. The warmer winter in 2002 produced opposite results; the increased temperatures may have allowed faster growth of ctenophores and benthic fauna. The biomass-size relationship produced a reasonable estimate of bacterial biomass but overestimated seabird biomass by two orders of magnitude. ^

Subject Area

Biology, Oceanography

Recommended Citation

Brooke A Longval, "Biomass spectra in Narragansett Bay from phytoplankton to fish" (2009). Dissertations and Master's Theses (Campus Access). Paper AAI3401124.
http://digitalcommons.uri.edu/dissertations/AAI3401124

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