are better adapted to survive under fluctuating 

 food conditions. 



Survival observed in these experiments can be 

 compared with that reported previously (Houde in 

 press), when survival was related to prey den- 

 sities that were held constant from day 2 to day 16. 

 Predicted survivals at constant prey densities of 

 25-50/1 and 500/1 were 0.72-3.86% and 29.31%, 

 respectively, for bay anchovy larvae; and 5.94- 

 16.61% and 70.45% for sea bream larvae. Ob- 

 served survivals at 0-h and 13-h patch exposures 

 (Tables 1, 2), which correspond to the 25-50/1 and 

 500/1 constant prey concentrations, were only 

 slightly lower than those reported in the constant 

 prey level experiments (Houde in press). The 

 small differences probably were caused by the 

 siphoning and water exchange procedures which 

 did subject larvae to some stress. The similarity of 

 results in the two reports indicates that the patch 

 simulation procedure was effective in demonstrat- 

 ing the impact of patches on larval survival. 



Growth results were inconclusive. Significant 

 differences in mean lengths were observed among 

 patch exposure times for both species (Tables 1,2). 

 In sea bream there was no clear relationship be- 

 tween mean lengths and patch exposure times, 

 but, unexpectedly, bay anchovy mean lengths 

 were smallest at the longest patch exposure times. 

 Presumably only the hardiest larvae survived 

 when patches were presented for only a short time, 

 and these larvae also may have had a relatively 

 great potential for growth. At the long exposures 

 to patch densities, survival was better, but no im- 

 provement in growth was noted, possibly because 

 some larvae with relatively poor growth potential 

 survived, or because of density-dependent effects 

 on growth that have been previously observed 

 (Houde 1975, 1977). Another compensating factor 

 was that patches were only presented on day 2 to 

 day 6 of the experiments, the prey concentrations 

 in all experiments being held constant at 25-50/1 

 from day 7 to day 10. 



Only one possible patch regime was used in 

 these experiments. It is possible that other patch 

 densities or exposure schedules might alter re- 

 sults or conclusions. An infinite number of possi- 

 ble patch conditions could be simulated but future 

 experiments should be delayed until the temporal 

 and spatial scales of patchiness of organisms con- 

 sumed by marine fish larvae are better known. 

 Conditions that were simulated in these experi- 

 ments do not discount the possible ability of larvae 

 in the sea to maintain themselves within prey 



486 



patches that retain their integrity for days or 

 weeks. Hunter and Thomas (1974) demonstrated 

 that northern anchovy larvae could maintain 

 themselves within small patches of Gymnodinium 

 splendens in laboratory tanks. Lasker (1975) 

 found that feeding northern anchovy larvae were 

 relatively more abundant in the chlorophyll 

 maximum layer of the Los Angeles Bight, where 

 G. splendens was abundant, than in surface wa- 

 ters, and he suggested that larvae might be able to 

 maintain themselves in this rich source of food. 

 Bay anchovy larvae in our experiments derived 

 small benefits from the patch regime that we pro- 

 vided, but there may be stable patch conditions in 

 the sea which could greatly increase their poten- 

 tial for survival. 



Acknowledgments 



This study was supported by the National 

 Science Foundation, Biological Oceanography 

 Program, Grant OCE 74-18141. John Hunter re- 

 viewed and criticized an early draft of the manu- 

 script. Scott Siddall and A. Keith Taniguchi as- 

 sisted with the experiments. 



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