Date of Award

12-2001

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Andrew Thomas

Second Committee Member

David W. Townsend

Third Committee Member

Neal R. Pettigrew

Abstract

An examination is made of the qualitative and quantitative relationships between satellite derived sea-surface temperature (SST) and chlorophyll patterns and the distribution of Alexandrium, the toxic dinoflagellate species responsible for HABs in the GOM. Daily images coincident with five ECOHAB survey cruises in 1998 and 2000 are composited over each cruise period to create mean patterns for each sample period. Contours of surface Alexandrium cell concentrations are superimposed on the images as well as images showing the strength and location of SST frontal zones to examine qualitative relationships. Results indicate that high concentrations of Alexandrium are located primarily in the eastern Maine coastal current (EMCC) and that frontal zones in this region generally act as boundaries to their surface distributions. Linear regressions are used to explore quantitative relationships between location-specific satellite data extracted from the composites and in situ parameters important to the ecology of Alexandrium . The most consistent results of these analyses were a linear relationship between satellite SST and Alexandrium that was used in a simple model to extrapolatelinterpolate the distribution of Alexandrium based on satellite data. The regression results also suggest a seasonally shifting optimal temperature range for maximum Alexandrium concentrations. No qualitative or quahtitative relationships between the SeaWiFS chlorophyll data and Alexandrium distributions in the GOM were found. Relationships between satellite-measured SST patterns and toxicity in the western GOM were examined during a paralytic shellfish poisoning (PSP) closure in western GOM in May 2000 to test the hypothesis that toxicity events in the western GOM require a transport mechanism for Alexandrium cells in the EMCC to get into the western GOM and inshore. Thermal patterns evident in the satellite SST data at the time of the May 2000 closure were consistent with enhanced connectivity and advection from the EMCC to western GOM. Ten years (1990-1999) of retrospective toxicity data from five sites along the coast of Maine and coincident AVHRR SST data are used to test the temporal stability of the observed May 2000 relationship between toxicity events in the western GOM and satellite-measured SST patterns. Results show that the occurrence of strong thermal gradients between eastern and western GOM, indicative of reduced alongshore connectivity, plays a key role in the occurrence and timing of toxicity event in the western GOM. The results of this work indicate the utility of satellite derived SST data in defining hydrographic patterns associated with elevated Alexandrium cell concentrations and in the detection and monitoring of oceanographic features that are conducive of toxicity events along the coast of western Maine. Future work making use of the optical and biological information in SeaWiFS data, wind data and other SST products will likely improve the utility of satellite data in understanding the ecology of Alexandrium in the GOM demonstrated here.

Download

Included in

Oceanography Commons

Share