Volume 55

Oceanographic Features and Zooplankton Community Structure in Mayagüez Bay, Puerto Rico


Authors
Alfaro, M.; García, J.R.
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Date: 2004


Pages: 1004


Event: Proceedings of the Fifty Fifth Annual Gulf and Caribbean Fisheries Institute


City: Xel Ha


Country: Mexico

Abstract

This study was part of a multidisciplinary research effort aimed to establish a characterization of the oceanographic features and the zooplankton community structure that could serve to evaluate the response of marine communities to a water quality restoration initiative. Monthly samplings consisted of conductivity, temperature and depth (CID) and chlorophyll-afluorescence profiles. Grab samples for nutrients determination (N03/N02 organic N, NH4+ and P04-3) and Secchi transparency. Zooplankton was collected by oblique tows using a 1m5 Tucker Trawl System with three nets of O.202 mm mesh. Sampling program included twelve cruises from February, 1997 through January, 1998 at six stations. Density profiles at Ocean station showed permanent stratification with well developed pycnoclines associated with increasing salinity and declines of water temperature with depth. Inshore stationshad well-mixed water columns, vertical stratification associated to freshwater lenses at the surface during large rainfall events. Maximum water column chlorophyll-a concentrations were consistently higher at Atuneras and AAA stations. Chlorophyll-a concentration was positively correlated with streamflow at Manchas and Rodríguez, but varied independently from streamflow at the other stations. Organic nitrogen (Org-N) was the nutrient in highest concentration; followed by ammonium-ion (NH4+) and nitrate (N03-N). Concentrations of orthophosphate (PO4-3BP) were only detected during April in Añasco. These data suggests that phosphate may be regulating plankton production at stations with good light penetration. Secchi transparency penetrated less than 50% of the water column at Atuneras and AAA stations.\Total zooplankton abundance varied between 8288B2,135 ind/m3 during the dry season and between 1,365-3,040 ind/m3 during the rainy season. Zooplankton abundance was higher at inshore station (1,905-2,588 ind/m3) compared to Ocean station (1,097 ind/m3). Meroplankton represented less than 5% of total zooplankton abundance. Principal component analysis indicated that meroplankton abundance at Ocean station explained 85% of the variation of meroplankton taxonomic groups. Higher abundances of fish larvae from the families Clupeifonnes, Pomacentridae, Haemulidae and Holocentridae accounted for the separation of inshore station. Clupeiformes were more abundant during heavy rainfall events and during night-time collectios.

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