Temperature-mediated variation in early life history traits and recruitment success of the coral reef fish Thalassoma bifasciatum in the Florida Keys

Abstract

Thirteen cohorts of the Caribbean reef fish Thalassoma bifasciatum were collected over 4 yr (2000 to 2003) in the upper Florida Keys, USA. Juvenile fish were censused and collected from replicate reefs shortly after settlement. The otoliths were examined to obtain early life history information such as timing of spawning, larval growth, pelagic larval duration, size-at-age, timing of set- tlement, and juvenile age and growth. Mean water tem- perature over the reef during the larval period explained 78% of the variation in larval growth among cohorts. Faster-growing warm-water fish had shorter pelagic lar- val durations (PLD), and larval growth explained 85% of the variation in PLD. Relative (otolith) size-at-settlement was a function of larval growth as well as PLD: settling larvae were largest at intermediate water temperatures. Early juvenile growth was also directly related to water temperature, which enabled smaller warm-water settlers to grow rapidly and eventually exceed juvenile size-at- age of the cooler-water cohorts. Cohorts encountering intermediate water temperatures remained the largest throughout early juvenile life on the reef. The relative size of recruitment events could not be explained by any larval or juvenile trait, nor by water temperature. Recruitment was generally low for cool-water cohorts but quite vari- able among warm-water cohorts. This may be due to in- creased difficulty in sustaining high growth rates in warm water (i.e. beyond a threshold temperature of 28.5°C) or the interference of mesoscale advection processes. When 4 cohorts that settled during the passage of mesoscale eddies were omitted from the analysis, 61% of the varia- tion in recruitment magnitude could be explained by water temperature alone. The dynamic oceanographic setting of the Florida Keys may obscure the relationship between seasonal water temperature, early life history traits, and magnitude of recruitment events.