METABOLIC RESPONSES OF SPOT, LEIOSTOMUS XANTHURUS, AND 



ATLANTIC CROAKER, MICROPOGONIAS UNDULATUS, LARVAE 



TO COLD TEMPERATURES ENCOUNTERED FOLLOWING 



RECRUITMENT TO ESTUARIES 



Donald E. Hoss, Linda Coston-Clements, David S. Peters, 

 AND Patricia A. Tester^ 



ABSTRACT 



The larvae of marine fishes that spawn during fall-winter in coastal North Carolina waters experience 

 a decrease in temperature as they enter estuarine nursery areas. To determine the effect of changes 

 in temperature on larval metabolism, the oxygen consumption of spot, Leiostomus xanthurus, and Atlantic 

 croaker, Micropogonias undulatus, was measured and their QO2 and Q^g values were determined. Atlan- 

 tic croaker respiration decreased with temperature at rates that would be expected if no compensation 

 or stress were involved. Spot showed unexpectedly high respiration rates at low temperature. The in- 

 creased respiration is apparently due to stress. Based on laboratory feeding and growth data, we con- 

 cluded that spot are subject to an energy deficit at <10°C. We infer the timing of larval immigration 

 corresponds with environmental temperatures reaching tolerable levels. Atlantic croaker larvae immigrate 

 earlier in the winter and are exposed to cold water for longer periods than spot larvae. Our conclusion 

 is that stress and energy loss experienced by early immigrating spot larvae may result in increased 

 mortality. 



The larvae of fishes that spawn during fall and 

 winter in offshore North Carolina waters experience 

 a decrease in both temperature and salinity as they 

 enter estuarine nursery areas (Fig. 1). The spot, 

 Leiostomus xanthurus, and Atlantic croaker, Micro- 

 pogonias undulatus, two sympatric species of Sciae- 

 nidae, are representative of winter spawning species 

 off the North Carolina coast. 



Previously, we have examined the effects of in- 

 creased temperature on the oxygen and food con- 

 sumption of the postlarval stages of these two 

 species (Hoss et al. 1971, 1974; Peters and Kjelson 

 1975). In this paper we continue our research on the 

 early life history of these species and evaluate how 

 decreasing water temperature, encountered follow- 

 ing recruitment into estuarine waters, might affect 

 oxygen consumption, food consumption, and ulti- 

 mately survival. 



Crawshaw et al. (1981) stated that young fish 

 typically select warm shallow water because 1) it 

 permits more rapid growth owing to higher metab- 

 olism, given an adequate food supply, and 2) the 

 predation by larger fish is less in shallow water. For 

 some fish this explanation is plausible, but this does 

 not apply to the larvae of many winter-spawning 



'Southeast Fisheries Center Beaufort Laboratory, National 

 Marine Fisheries Service, NOAA, Beaufort, NC 28516. 



marine fishes which begin life in relatively warm 

 coastal waters and then enter colder estuarine 

 waters. For these species we expect that metabolism 

 and growth of the estuarine immigrants should be 

 reduced (Brett 1956). The specific objective of this 

 paper is to describe how decreasing temperature 

 affects the metabolism of larval fish as they are 

 moved from warm to cold water by a combination 

 of passive and active transport mechanisms that are 

 not, as yet, completely understood. Oxygen con- 

 sumption is a common method of estimating meta- 

 bolic activity, which frequently changes in response 

 to environmental conditions (O'Hara 1968). In this 

 study we measured routine oxygen consumption 

 which is the amount used by fish whose only move- 

 ments are spontaneous. 



STUDY AREA AND METHODS 



Spot and Atlantic croaker spawn off the North 

 Carolina coast inshore of the Gulf Stream over the 

 continental shelf (Hildebrand and Cable 1930; 

 Dawson 1958; Powles and Stender 1978). Here, spot 

 spawn from October to February, but principally 

 from December to January while Atlantic croaker 

 spawn from September to May but principally be- 

 tween October and December (Lewis and Judy 

 1983). After between 30 and 60 days in coastal 



Manuscript accepted May 1988. 



FISHERY BULLETIN: VOL. 86. NO. 3, 1988. 



483 



