Abstract
Seagrass beds are an important component of coastal environments and serve as important nursery grounds for juvenile and commercially important fish species. Seagrass beds are often monospecific, composed of just one species of seagrass. However, macroalgal species such as Halimeda, Laurencia, and Dictyota (among others) can also be found in seagrass beds in quantities that vary depending on many factors including grazing pressures. This study focuses on the grazing dynamics of Lagodon rhomboides (commonly referred to as pinfish) between two different macrophytes (Thalassia testudinum and Halimeda incrassata) over a temperature gradient in a laboratory setting representative of a seagrass bed from the middle Florida Keys (Heine Grass Bed; HGB). HGB, where samples were collected for this study, is a long-term study site for Ciguatera Fish Poisoning (CFP) research as well. CFP is a form of food poisoning in humans who consume tropical reef fish that have accumulated high levels of ciguatoxins. Ciguatoxins are naturally produced lipid-soluble toxins produced by the benthic dinoflagellate, Gambierdiscus, which enter reef food webs through the consumption of these epiphytic cells by herbivorous fishes. Thalassia testudinum and Halimeda incrassata are known to harbor high quantities of toxic Gambierdiscus species within their associated epiphytic community in areas such as HGB. The overall objective of this study is to examine the grazing dynamics of pinfish on Thalassia testudinum and Halimeda incrassata under varying temperatures within a seagrass bed environment (HGB) in the middle Florida Keys. This study will also aid in determining how ciguatoxins are being introduced into the marine food web through grazing processes occurring within seagrass beds in the middle Florida Keys and assist modeling efforts for CFP outbreaks. Additionally, it will identify if specific temperatures influence the grazing behaviors of pinfish which will lend insight into how grazing pressures change seasonally and how they may change as the climate warms. This study found that pinfish did not consume one macrophyte agar (Thalassia testudinum or Halimeda incrassata) at a significantly higher amount than the other at ambient temperature. In addition, the results also suggest that pinfish are not significantly increasing their grazing intensity on Thalassia testudinum agar across a temperature gradient (22°C – 30°C). However, the grazing intensity of pinfish on Halimeda incrassata agar did significantly increase with increasing temperature but the strength of this linear correlation is fairly weak (R2 = 0.2154). Finally, pinfish ate a marginally significantly larger amount of the Halimeda incrassata agar cubes than the Thalassia testudinum agar cubes over the temperature gradient tested (22°C – 30°C; p = 0.052).