HR: 16:30h
AN: H44A-05    [Abstracts]
TI: Isotopic Perspectives on the Foundation of Estuarine-Dependent Fish Biomass: Macrophytes Versus Microphytes
AU: * Hollander, D J
EM: davidh@marine.usf.edu
AF: College of Marine Science, University of South Florida 140 7th Ave. S., St. Petersburg, FL 33701 United States
AU: Malkin, E
EM: emalkin@marine.usf.edu
AF: College of Marine Science, University of South Florida 140 7th Ave. S., St. Petersburg, FL 33701 United States
AU: Murasko, S
EM: murasko@marine.usf.edu
AF: College of Marine Science, University of South Florida 140 7th Ave. S., St. Petersburg, FL 33701 United States
AU: Peebles, E
EM: epeebles@marine.usf.edu
AF: College of Marine Science, University of South Florida 140 7th Ave. S., St. Petersburg, FL 33701 United States
AB: Considerable trophic heterogeneity exists among the tidal rivers on Florida's west coast. Spring-fed estuaries tend to be oligotrophic, and urbanized surface-fed estuaries may be hypereutrophic. We compared wet- and dry-season primary producer sources of fish biomass among four rivers with differing trophic states. Dry-season 15-N distributions for vascular plants, microalgae and estuarine fish reflected river trophic status. Within rivers, 15-N values in vascular plants were regulated by extent of immersion in river water. All subaerial plants had 13-C values indicative of a common atmospheric CO2 source, whereas subaqueous microalgae had 13-C values that changed seasonally. In all rivers except the spring-fed Weeki Wachee, recycling of nitrogen within the sediments (i.e., denitrification) appeared to provide some of the nutrients used by benthic microalgae (BMA) during the dry season; the BMA were N-enriched relative to phytoplankton (POM) from the same waters. Most consumers appeared to be dependent on BMA during the dry season. Among Myakka and Peace River consumers, there was a pronounced shift from dry-season dependence on BMA to dependence on POM during the wet season. This contrasted with the oligotrophic Weeki Wachee River, where consumers remained dependent on BMA during both seasons. In the hypereutrophic Alafia River, only a partial shift to POM occurred, suggesting that the wet-season POM in the Alafia was less available to consumers. During the wet season, the chlorophyll maximum in the Alafia River shifts downstream to dredged locations that are prone to benthic hypoxia. We suggest that wet-season benthic hypoxia interferes with the transfer of sedimented POM biomass to higher trophic levels via surface-deposit-feeding macroinvertebrates.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2005 Joint Assembly