How Does Water Column Structure Influence Copepod Populations in Coastal Marine Systems?
Abstract:The influence of water column structure on zooplankton in coastal marine ecosystems was experimentally examined using enclosures (5 m deep; 13⋅m3 volume) containing both water column and benthos. The test involved a comparison of well-mixed versus stratified water columns. In the stratified system a salinity difference between surface and bottom waters and chilling of the lower layer maintained a very stable pycnocline at 2.5-m depth. Total turbulent energy input into each system was the same and temperature in the upper mixed layer of the stratified system matched that in the well-mixed system. The manipulation resulted in dramatic changes in the zooplankton community: copepods became much more abundant in the stratified system, steadily increasing their numbers despite a relatively low biomass of phytoplankton. Increases were seen for all species but dominance switched from Acartia tonsa in the well-mixed system to Oithona colcarva in the stratified. The interesting question is to determine what factors favored copepods in the stratified water column. Phytoplankton, while less abundant in the stratified system, may have been either more nutritious or more available than in :the well-mixed system. The pycnocline also acted to isolate the water column from any predators in the benthos, possibly reducing mortality rates in the stratified system.
Document Type: Research Article
Publication date: July 1, 1993
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