Invertebrate effects on sediment biogeochemistry and microphytobenthos following estuarine macroalgal blooms

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Title: Invertebrate effects on sediment biogeochemistry and microphytobenthos following estuarine macroalgal blooms
Author: Premo, Katherine
Abstract: Eutrophication has led to the proliferation of devastating macroalgal blooms in shallow coastal estuaries. Processes at the sediment surface in shallow marine environments can ultimately affect nutrient cycling and the progress of eutrophication. Through bioturbation and grazing of microphytobenthos (MPB) infaunal invertebrates significantly alter redox dependent chemical and microbially-mediated transformations of nutrients and their subsequent release to or uptake from the overlying water column. This study used a series of experiments to investigate the effects of invertebrates on sediment biogeochemistry and nutrient cycling at early and late stages of eutrophication. Unique aspects of this study were the inclusions of multiple species, trophic levels and the use of technology to better understand the effects of invertebrates on processes. A non-destructive method of remotely sensing the MPB community through the use of reflectance spectra of the sediment surface was developed. Indices, derivatives and continuum removal band depths were valid for non-destructively quantifying MPB biomass at different time points in an ecological microcosm experiment. In another experiment, we evaluated the effects of two species of invertebrates, Ilyanassa obsoleta and Mercenaria mercenaria, alone and in combination, on the removal of detritus, oxygen consumption and nutrient release following the collapse of a large algal bloom. The effect I. obsoleta had on detritus removal was context specific, due to changes in food preferences in different sediment types. M. mercenaria’s effect on sediment oxygen concentrations was substantially lower in the presence of I. obsoleta suggesting the importance of inter-specific interactions. In a third experiment we found that non-lethal predation by mud-crabs substantially affects invertebrates‟ behavior by reducing their activity. I. obsoleta grazed less, resulting in greater MPB biomass and decreased sediment ammonium release. Likewise, higher porewater ammonium concentrations when M. mercenaria was in the presence of a predator indicate lower bioturbation within the sediments. Based on these studies, we conclude that environmental conditions and assemblage diversity ultimately affect the behavior of the organisms, which has potentially important consequences on the progress of eutrophication.
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Date: 2011-07-18

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