The Importance of Horizontal Swimming Behavior in the Patch Dynamics and Transport of Larval Crabs: Do Biochemical Cues Have an Effect?EPA Grant Number: MA916357
Title: The Importance of Horizontal Swimming Behavior in the Patch Dynamics and Transport of Larval Crabs: Do Biochemical Cues Have an Effect?
Investigators: Houser, Letise T.
Institution: University of Delaware
EPA Project Officer: Zambrana, Jose
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $95,292
RFA: GRO Fellowships for Graduate Environmental Study (2004) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Science , Academic Fellowships , Ecological Indicators/Assessment/Restoration
The objective of this research project is to combine the results of laboratory and field components to provide insight in answering the following broad research questions:
(1) Do crab larvae alter their swimming behavior in response to the biological and physical structure in their environment and regulate their position, at a small spatial scale, in the dominant flow regime?
(2) Does this ability help form and maintain their aggregative patches?
(3) Does this affect their displacement and later settlement in juvenile habitat?
(4) Does the magnitude of this settlement ultimately affect the size and location of adult populations?
Crab larvae are among the strongest swimmers in the zooplankton and can sustain directional swimming at speeds on the order of millimeters per second to a few centimeters per second. Therefore, they might be able to influence their horizontal distribution, at least on a small spatial scale (millimeters to meters), by overcoming the effects of turbulent diffusion. This ability might be a key component in helping form and maintain their patches across time and space.
Crab larvae have been found in discrete patches in the water column, even in areas where aggregative physical structures (e.g., fronts and pycnoclines) are rare or absent. One possible explanation is that larval crabs might alter their swimming behavior in response to biochemical cues in the water. Experiments are under way to test this idea. In these experiments fiddler crab (Uca pugnax) and blue crab (Callinectes sapidus) megalopae are observed in a laminar-flow flume after putative cues have been introduced into the flow field. Swimming behavior of the megalopae is digitally videorecorded under far-red light, and the resulting images are analyzed to determine changes in horizontal orientation, displacement, and swimming speed of megalopae.
In addition, a field study was conducted during the summer of 2003 that included physical and biological sampling with combined objectives that primarily address the maintenance or dissipation of a patch. This study was designed to test the idea that maintenance of patches is dependent on swarming (i.e., schooling) behavior of the larvae. As part of that investigation, tagged patches of larvae with satellite-tracked drifters. This allowed me to follow the patches for several days and to observe their spatial dynamics (i.e., any changes in density of larvae within the patches or in the size and shape of the patches). Analysis of results currently is underway and includes calculation of rates of turbulent diffusion in the study area and a determination of whether diffusion alone is sufficient to explain the observed spatial dynamics of the patches. If the patch dynamics cannot be explained completely by the physical data, then the behavioral component might be the missing factor. Thus, the mechanisms involved in offsetting the physical dispersion of those patches may lie in the results of the laboratory experiments described above.