Low-Temperature Tolerance of Age-0 Atlantic Croakers: Recruitment Implications for U.S. Mid-Atlantic Estuaries

Abstract

Age‐0 Atlantic croakers Micropogonias undulatus overwinter in Mid‐Atlantic Bight (MAB) estuaries, where interannual variability in year‐class strength is pronounced. Previous researchers have hypothesized that this variability is the result of cold‐induced winter mortality of age‐0 Atlantic croakers within estuarine nurseries. We tested this hypothesis by means of laboratory experiments designed to (1) estimate the effects of winter severity and duration on the probability of survival of age‐0 fish, (2) determine the relationship between body size and cold tolerance, and (3) examine the effects of temperature decline rate and salinity on susceptibility to low‐temperature mortality. Age‐0 Atlantic croakers (15–65 mm standard length, SL) were collected from Delaware Bay during October, acclimated to 8°C in the laboratory, and then cooled (1.0°C/d) to treatment levels of 1, 3, 5, or 7°C that were designed to simulate varying levels of winter severity in MAB estuaries. Survival ranged from 0% at 1°C to 99.3% at 7°C, increasing dramatically between 3°C (1.3%) and 5°C (86.8%). Cold tolerance was size dependent, with smaller individuals surviving significantly longer than larger ones. The rate of temperature decline (1.0°C/d versus 0.2°C/d) did not affect survival at lower winter temperatures. Atlantic croakers remained intolerant of temperatures of 3°C or less even when these temperatures were approached gradually. Cold tolerance increased with increasing salinity, implying that the risk of overwinter mortality varies spatially along an estuarine salinity gradient. The mean survival duration at 3°C increased from 5.9 d at 2‰ to 14.7 d at 10‰ and to 17.1 d at 26‰. Our findings provide empirical support for the hypothesis that cold‐induced overwinter mortality regulates the year‐class strength and recruitment success of Atlantic croakers in the Mid‐Atlantic Bight.

Thermal tolerance and potential distribution of invasive lionfish (Pterois volitans/miles complex) on the east coast of the United States

“…Similar results were observed with Atlantic croaker, where a 5-fold increase in rate of decline (-0.2 to -1.0°C d -1 ) did not affect survival at low temperatures (Lankford & Targett 2001). Rate of temperature decline also had no effect on low temperature tolerance of American shad Alosa sapidissima (-0.5 to -1.9°C d -1…”

“…Chronic lethal methodology was used to determine the temperature tolerance of lionfish, with death as the endpoint (Becker & Genoway 1979, Shafland & Pestrak 1982, Fields et al 1987, Prentice 1989, Zale & Gregory 1989, Lankford & Targett 2001. This methodology allows simulation of natural temperature conditions, as well as the assessment of key points such as feeding cessation and behavioral characteristics that may be overlooked using other methods (Doudoroff 1942, Schwartz 1963, 1964, Elliott 1981, Prentice 1989, Baker & Heidinger 1996, Lankford & Targett 2001, Hurst & Conover 2002.…”

“…This methodology allows simulation of natural temperature conditions, as well as the assessment of key points such as feeding cessation and behavioral characteristics that may be overlooked using other methods (Doudoroff 1942, Schwartz 1963, 1964, Elliott 1981, Prentice 1989, Baker & Heidinger 1996, Lankford & Targett 2001, Hurst & Conover 2002. Sudden (acute) changes of temperature, such as those experienced in low thermal plunge conditions, are not commonly found in nature (Doudoroff 1942), whereas the chronic lethal minimum gives an indication of the survival requirements of fishes in natural habitats (Bennett et al 1997).…”

“…Observations and temperatures were recorded for each fish when feeding cessation, loss of equilibrium and death occurred. Death was defined as the cessation of fin, body and opercular movement and a total lack of organismic response (Becker & Genoway 1979, Lankford & Targett 2001. Expt 2.…”

“…Laboratory temperature-tolerance studies have been used to examine temperaturelimited distributions of both invasive and non-invasive species: red-bellied piranha Pygocentrus nattereri in the United States (Bennett et al 1997), southern flounder Paralichthys lethostigma in Texas estuaries (Prentice 1989), Atlantic croaker Micropogonias undulatus in mid-Atlantic estuaries (Lankford & Targett 2001), and 14 introduced freshwater fishes in Florida (Shafland & Pestrak 1982). Temperature data for the southeast continental shelf were combined with experimentally determined low temperature tolerances to create a map of potential lionfish habitat in introduced waters.…”