Date of Award

5-2012

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Sara M. Lindsay

Second Committee Member

Peter A. Jumars

Third Committee Member

Lawrence Mayer

Abstract

Marine infaunas influence sediment chemistry, nutrient cycling, and microbial communities as they burrow, feed, defecate, and irrigate their tubes and burrows. Non-lethal tissue loss to predators or other disturbances has been frequently observed in macrofaunal communities and previous research has reported significant effects of one-time injury on animal activity. Supply of nutrients can also influence infaunal activity. In laboratory studies, we examined effects of injury and nutrient enrichment on bioturbation rates of a common deposit-feeding polychaete, Clymenella torquata. Individual worms were held in PVC cores in a recirculating seawater system. Defecation and sediment mixing by worms were monitored in all experiments. Specific growth rates, tissue regeneration rates and surface-evident behaviors were monitored in some experiments. Worms held in control sediment or low homogeneously enriched sediment were injured once or twice in two 21 d experiments. Worms held in control sediment or sediment with high surface enrichment were observed in a 7 d experiment following repeated injury. Injury treatments were posterior segment ablation and intact control; nutrient supply treatments were diatom-enriched sediments and unenriched sediment controls. Injury and nutrient supply treatments were crossed in all experiments. Bioturbation by C. torquata significantly decreased following a repeated posterior injury, but only modest (non-significant) effects of homogeneous microalgal enrichment were observed. Repeated injury correlated with greater reductions in the proportion of worms defecating and the amount of fecal mass, with effects of repeated injury evident over a longer time frame. Specific growth rate decreased following repeated injury relative to controls. Regeneration rates did not vary based on injury type or homogenous sediment enrichment. Vertical profiles of microbead tracers, representing a cumulative record of surface subduction over the week following injury, showed little difference between worms with single or repeated injury and controls. Population sediment reworking estimates calculated from per-worm measurements indicate that significantly less sediment (50%) would be translocated by a population containing one-half of individuals with a repeated injury, relative to a population of only intact worms. The same hypothetical population of injured worms translocates even less sediment (39%), in the presence of low-level sediment enrichment. A follow-up study confirmed that sediment bioturbation decreases with repeated injury in C. torquata. In this case, microalgal enrichment at the sediment surface, simulating post-bloom conditions in subtidal locations, correlated with an increase in bioturbation. Repeated injury resulted in significant decreases in total recorded surface activities and defecation. Intact worms in enriched sediment showed more total recorded activities and more probable hoeing than those in other treatments. Overall, injured worms transported significantly less surface sediment attributed to surface subduction than intact worms. Vertical profiles indicated that worms in enriched sediment produced the greatest subsurface tracer maxima, with the highest peaks produced by intact worms. These findings help explain how infaunal activities are modified by injury and sediment nutrition, and can be used to improve future models of bioturbation. Improved models will help to elucidate complex benthic community dynamics by linking these factors to marine sedimentary community ecology.

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