Changes in growth and timing of sex change in subtropical fishes as compensatory responses to a severe cold event in Florida

Objective We investigated observations that were hypothesized to be biological responses to a severe cold event in two subtropical fishes near their range limit in Florida. Following a cold event, an anomaly in otolith sections was observed in Gray Snapper Lutjanus griseus and conspicuously small females were observed during biological sampling of Common Snook Centropomus undecimalis, a protandric hermaphrodite. Methods To compare biological metrics before and after the cold event, increment analysis was conducted on otoliths of Gray Snapper that were collected from recreational and commercial fisheries as proxies for growth rates in different regions of Florida, whereas the proportion of females was assessed across size- and age-bins in Common Snook that were collected from several estuaries during fisheries-independent monitoring. Results A widespread anomaly that was found in the Gray Snapper otoliths was confirmed as indicative of a significant decrease in growth (46%) in the year following the cold event relative to that of a control group that was collected in a period before the cold event. However, growth rates increased (16–17% higher than fish in the control group) for several years after the event. After the cold event, Common Snook changed sex from male to female (younger and smaller females) earlier in an estuary at the northern end of its historic range where population declines of greater than 50% occurred. Conclusions After the cold event, increased growth following a period of arrested growth in Gray Snapper and early sex change in Common Snook were likely compensatory mechanisms that allowed for more rapid recovery at the organismic and population scales. Given that the frequency and severity of cold events control the distributions of many subtropical fishes, understanding their biological responses to these events can provide insight into how subtropical species can cope with periodic disturbances as their range continues to expand.