Date of Award

Winter 2012

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

James E Byers

Abstract

This study examined the influence of localized disturbances on the heterogeneity of ecological communities at multiple temporal and spatial scales. Foraging disturbances by the epibenthic predator, Atlantic Horseshoe Crab Limulus polyphemus, on the intertidal mudflats of Great Bay estuary, New Hampshire, USA were used as the study system.

This study overcame methodological hurdles in the study of small localized disturbance over extensive areas of soft-sediments. Using a novel, low-cost technique to monitor Limulus foraging disturbances, Great Bay's tidal flats were found to be critical feeding habitats from late spring till fall. Foraging Limulus disturbed the benthos of Great Bay at high frequencies and intensities -- disturbing 67-70% of the survey area more than once every four weeks over the intertidal foraging season. It was also found that Limulus disturbance within a single site exhibited a clustered spatial pattern over a spatial scale of 3 weeks and also over the entire intertidal foraging season.

Infauna densities in individual Limulus feeding pits were significantly lower than in undisturbed sediment, and recovered to resemble the structure of undisturbed communities within 28 days. The role of Limulus disturbance on infaunal community structure was confirmed by long-term exclusion experiments in 2009 and 2010. Removal of Limulus disturbance resulted in significant increase in predatory polychaetes in both years, although there were no significant trends observed in abundance of total infauna or deposit feeding polychaetes and oligochaetes. On the other hand, bivalve, Macoma balthica, abundance and biomass were significantly higher within exclusions. On the scale of the estuary, Limulus disturbance was found to contribute between 24% to 91% of the variability of total infaunal abundance, and had similarly negative effects on the abundance of predatory and deposit feeding polychaetes across the estuary. However, Limulus disturbance patterns did not explain the variability of Macoma abundance and biomass across the estuary. Observational and experimental results revealed that Limulus is a critical factor structuring infaunal communities in Great Bay. However, the infaunal taxa that is most affected by Limulus foraging disturbance varies from the localized scale of individual disturbances to the landscape scale of the estuary.

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