finding suggests that spawning in a species is strongly influenced by local 

 conditions. Thus, behaviors that in one location may reduce egg mortality 

 might increase egg mortality if repeated precisely at another site. 



In summary, reproductive efforts in a species often can be shown to diminish 

 predation on spawned eggs and enhance the chance of their dispersal. But, many 

 species show variable spawning behavior. It is therefore uncertain that all 

 reproductive behaviors are selected to reduce egg predation and/or assure 

 dispersal . 



DISPERSAL -- THE PELAGIC PHASE 



Hypotheses to Explain the Pelagic Larval Phase 



Why should almost all coral reef fishes cast their eggs and/or larvae 

 offshore? Three primary hypotheses have been suggested: (1) the antipredator 

 hypothesis, (2) the food hypothesis, and (3) the dispersal hypothesis (see 

 Johannes, 1978, for review). Johannes, who favors the antipredation hypothesis, 

 argues that if the eggs and larvae were left on the reef unprotected, they 

 would be subject to an excessive mortality by reef predators (see also Smith, 

 1978). Although it is certain that predation on eggs and larvae is very high 

 by reef plankti vorous fishes (Hobson and Chess, 1978) and by sessile filter 

 feeders (Johannes, 1978), it is not clear how much predation is reduced when 

 eggs and larvae are offshore (Barlow, 1981). Egg mortality offshore can approach 

 30% per day (Jones and Hall, 1974; Ware, 1975). Considering the relative merit 

 of these factors and others led Barlow (1981) to postulate that the reduction 

 in predation achieved from a pelagic phase was of less significance to survival 

 than the advantages that are derived from dispersal (over both short and long 

 distances). Barlow sees dispersal as a means to ensure survival of a species 

 by reducing inbreeding (Bengtsson, 1978), and, particularly, as an adaptation 

 to the instability of reef communities (Connell, 1978; Sale, 1978a_). He argues 

 that the longer an egg or larvae travels, the less its chance of survival 

 (Thorson, 1946; Gadgil, 1971). For long-range dispersal to succeed, reef fishes 

 must produce numerous offspring, which they do, and larvae must be adapted for 

 a lengthened pelagic life, which in many species is true (e.g., in surgeonfishes, 

 butterf lyfishes, wrasses, and in eels; Barlow, 1981). The possibility exists, 

 nevertheless, that cohorts from a single spawning may remain together as eggs 

 and larvae in the plankton, and thus maintain genetic relatedness among recruits 

 (see Shapiro, 1983). This interesting possibility, which would increase inbreeding 

 success, remains to be documented. 



The food hypothesis is dismissed by both Johannes (1978) and Barlow (1981) 

 because in general planktonic food is less available offshore than inshore; 

 thus, the advantage of offshore disperal must find another explanation, such as 

 a reduction in predation or enhanced dispersal. 



Although Johannes and Barlow are aware that both recolonization and long- 

 range dispersal occur, their respective arguments favor different views of the 

 role of dispersal in larval recruitment from the plankton. Barlow (1981) views 

 the long-range transport of larvae to other localities than the parent reef 

 (island, etc.) as the essential selective force that has operated. In contrast, 



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