Date of Award

Spring 1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Committee Director

John R. McConaugha

Committee Member

Larry P. Atkinson

Committee Member

Robert K. Cowen

Committee Member

John J. Govom

Abstract

Most marine fish have retained pelagic larval stages that are spawned away from juvenile habitats. Physical and biological processes on a number of scales may affect larval survival. Mesoscale features like estuarine or riverine plumes and fronts are thought to affect larval survival by transporting larvae to juvenile habitats or by retaining larvae in favorable developmental habitats. It is likely that these features are major contributors in the regulation of shelf-spawned estuarine-dependent taxa.

This study examined how physical oceanographic features affected the spatial distribution of ichthyoplankton across the Chesapeake Bay Plume. Larval surveys were conducted across the shelf and within the baymouth during August 1988, July and August 1992, and from July through September, 1994. Samples were collected at varying horizontal and vertical scales to understand the variability in larval distribution across the plume.

The Chesapeake Bay outflow plume and its front affected the spatial distribution of larvae and ichthyoplankton assemblages at all spatial and temporal scales sampled. The plume front delineated the seaward extent of bay-spawned taxa as exemplified by Anchoa spp. Multi-specific larval peaks occurred inshore and offshore of the plume front, but aggregation within the plume front itself was nor observed. These multi-specific peaks consisted of pre-flexion and flexion larvae. and result from tidal oscillations of the front as it moves across the inner-shelf. This mechanism may retain larvae near shore, where the estuarine circulation can transport larvae into the bay.

Coastal upwelling associated with southerly winds transported plume and bay-spawned larvae to the shelf rapidly (days). Sub-surface water was transported to the coast during these upwelling events. Shelf-spawned larvae within this subsurface water were transported to the coast.

Larvae of the plume and shelf ichthyoplankton assemblages exhibited different vertical and ontogenetic distributions, across the inner-shelf. Etropus microstomus, a shelf-spawned and shelf-dependent taxa, exhibited differences in diel vertical distributions, and this may retain these larvae in shelf waters. Symphurus spp., a bay-spawned taxa exhibited an ontogenetic migration from the Chesapeake Bay plume to shelf waters, where its settles as a juvenile.

The results show that the Chesapeake Bay Plume outflow affects the spatial distribution of larval fish. The effect varies within members of an assemblage and between ontogenetic stages of some taxa. These findings support the hypothesis that estuarine plumes and mesoscale physical features may control larval survival by affecting spatial distribution.

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DOI

10.25777/egrb-aq28

ISBN

9780591481372

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