Date of Award

2020

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Gardiner, Jayne

Area of Concentration

Marine Biology

Abstract

Red tide is a toxic algal bloom caused by the dinoflagellate Karenia brevis that occurs frequently off the west coast of Florida in the Gulf of Mexico. Red tide events can result in massive fish kills; however, only a few studies have been done on the recovery of estuarine ecosystems after a massive red tide event. In the summer of 2018, a massive red tide bloom struck Sarasota Bay, resulting in a dramatic shift in fish abundance and community structure. Incidentally, another nearby embayment, Terra Ceia Bay, did not experience any red tide conditions that year. We continued to monitor elasmobranch and teleost abundances in Sarasota Bay and Terra Ceia Bay by conducting monthly gillnet surveys from April 2019 to October 2020. Using previously collected data from 2017 and 2018, we compared the relative abundances of sharks, batoids, and teleosts between Sarasota Bay and Terra Ceia Bay before, during, and after the 2018 red tide event. We found that there was a decrease in shark, batoid, and teleost abundances in Sarasota Bay during the 2018 red tide. The following year, the abundance of sharks and teleost increased, but the relative abundance of batoids remained very low. The abundance of batoids and sharks increased significantly during the 2018 red tide event; however, the abundance of sharks and batoids in Terra Ceia Bay after red tide was similar to the abundance of sharks and batoids in Terra Ceia Bay before red tide. The increase in elasmobranch abundance in Terra Ceia Bay during red tide may suggest that these organisms migrate to avoid the toxic bloom. Individual species were affected differently by red tide. Bonnetheads and ladyfish abundances in Sarasota Bay decreased during red tide; but after red tide the abundance of these two species was similar to the abundance prior to red tide. Permit and crevalle jack abundances in both Sarasota Bay and Terra Ceia Bay decreased during red tide and remained relatively low after red tide. Hardhead catfish abundances did not appear to be affected by red tide. More species specific analysis of the effects of red tide on fish would be important to better understanding the broader ecological effects of red tide.

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