THE EFFECTS OF RED TIDE (KARENIA BREVIS) ON UPPER TROPHIC LEVEL FISH COMMUNITIES IN SARASOTA BAY, FLORIDA

Alexa Baldino

Date of Award

2019

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Gardiner, Jayne

Area of Concentration

Natural Sciences

Abstract

Harmful algal blooms are naturally occurring, but with the increase in severity worldwide, few data exist that document their ecological impacts of upper trophic level organisms. Sarasota Bay is a 56-mile-long coastal lagoon system that sits on the south west coast of Florida, and was named an Estuary of National Significance in 1987. The toxic algal bloom Karenia brevis, commonly known as red tide, occurs here on a near annual basis. However, few data on the ecological impacts of red tide on upper trophic level fish communities exist. In this study, these effects were documented through monthly gillnet surveys occurring from April 2018 to February 2019. Fish abundance, diversity, species composition, salinity, temperature, and dissolved oxygen data were collected. There were significant decreases in teleost and elasmobranch abundances and overall diversity during and after red tide. There was a 100% decline of shark populations that directly corresponds to red tide. There was a dramatic shift in fish community structure during and after red tide. Two acoustically tagged blacktip sharks (Carcharhinus limbatus) were heard moving throughout Sarasota Bay before the red tide event, and have not been detected since, strongly supporting that red tide killed these animals. There were significant decreases in teleost and shark abundances compared to previous surveyed years, where 2018 was the only year to experience a major red tide event. It was concluded that red tide negatively impacts upper trophic fish community structure.

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