Publication Date

2009-06-24

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Fisheries (Marine)

Date of Defense

2009-04-14

First Committee Member

Su Sponaugle - Committee Chair

Second Committee Member

Robert K. Cowen - Committee Member

Third Committee Member

Michael C. Schmale - Committee Member

Fourth Committee Member

Joseph E. Serafy - Committee Member

Fifth Committee Member

Jonathan A. Hare - Outside Committee Member

Abstract

The supply of coral reef fish larvae from the open ocean to reefs is vital for the persistence of local fish populations. Whether larvae are dispersed over hundreds of km or only few km depends on biophysical interactions between larvae and their environment. Relationships between environmental variables, larval swimming behavior, and larval transport were examined for reef fish larvae in the Florida Straits. In a series of research cruises, the upper 100 m of the water column was sampled with plankton nets fishing at four different depths. Variability in the vertical distributions of most larvae was not consistently related to measured environmental variables. Relative densities of larvae were predictably related to sampling depth in five taxa. In seven taxa, more developed larvae were distributed significantly deeper than less developed larvae, revealing ontogenic vertical migrations. In three taxa, vertical distributions varied significantly between day and night, revealing diel migrations. Since the Florida Current was strongest near the surface, observed vertical distributions and migrations resulted in reduced larval transport relative to surface currents. To identify cues involved in regulating vertical distributions, behavioral experiments were conducted with larvae from four reef fish families. All four groups showed significant responses to pressure cues, swimming up in response to high pressure and down in response to low pressure. In two families there was a significant correlation between capture depth and experimental pressure preference, suggesting that larvae use similar behavior to regulate depth in situ. To study horizontal swimming behavior, late-stage larvae of one species were caught in light-traps and observed by SCUBA divers ~1 km offshore of the Florida Keys barrier reef. All larvae swam remarkably straight, but their swimming directions were distributed randomly. A simulation model was used to generate swimming trajectories of longer duration than could be observed directly. Observed and simulated trajectories indicated that horizontal swimming by larvae with or without an external reference frame was important at spatial scales of several km. Overall, some larvae exercised a strong influence on transport, either by vertical or horizontal swimming. Behaviors varied between species and families, highlighting the need for more species-specific data.

Keywords

Larval Transport; Swimming Behavior; Vertical Distribution; Population Connectivity; Orientation; Depth Regulation

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