Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

John W. Fleeger

Abstract

The objective of this dissertation was to investigate the small-scale spatial and abundance patterns of meiofauna and their relationship with sediment microtopography and hydrodynamics. Meiofauna are known to be aggregated at small spatial scales. A study was first undertaken to determine, how patchiness differed over seasons and habitats. Significant small-scale aggregations were remarkably consistent across different seasons and habitats for all abundant copepods of an intertidal mudflat. Spatial autocorrelation analysis showed that the abundance of copepods was autocorrelated at short distances (cm scale) on all sample collecting dates, indicating a consistent spatial pattern. Small-scale variation contributed heavily to the components of variance among the three different spatial scales studied. Direct comparisons between sediment microtopography (depressions), using image analysis of photographs, and the distribution of meiofauna, as determined by coring of the area photographed, were undertaken. Copepods were twice as abundant in depressions compared to non-depression areas. Microtopographic features were very dynamic with longevities were $<$24 hr, implying that aggregations of copepods were also dynamic with a similar longevity. Increased meiofaunal abundances in depressions could be due to active selection associated with meiofaunal behavior or, alternatively, passive settlement driven by hydrodynamic forces. A flume colonization study indicated that active selection of epibenthic copepods for preferred sediment played a major role in copepod settlement at a low flow, but at a high velocity, passive process (hydrodynamic effects) overwhelmed active selection. In a field study, colonization of epibenthic copepods into depressions was rapid compared to non-depressions and was determined by depression aspect-ratio, suggesting passive settlement into depressions. However, meiobenthic burrowers such as nematodes displayed a radically different pattern. The density of nematodes in depressions depended mainly on depression circumference:area ratio as well as the distance between the depression and ambient sediment. A model is proposed for the two different responses. Settlement of epibenthic copepods into the depressions is mainly through a water-column transport; burrowers colonized mainly through an bed-load transport which may involve both passive and active processes.

Pages

132

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