OVERVIEW: THE DYNAMICS OF RECRUITMENT IN CORAL REEF ORGANISMS 



William N. McFarland 



Section of Ecology and Systematics 



Division of Biological Sciences 



Cornell University 



Ithaca, New York 14853 



In her introduction to volume 1 of these proceedings, Marjorie Reaka 

 states, "The second set of papers addresses the issue about which we probably 

 know the least in coral reef ecology: what factors control recruitment?" One 

 must conclude from the three contributed papers in volume 1 of these proceedings 

 (Lobel and Robinson, 1983; Shapiro, 1983; Victor, 1983) and the papers in the 

 present volume (Brothers and Thresher, 1985; Lobel and Neudecker, 1985; McFarland 

 and Ogden, 1985) that data on reproduction, larval development, and recruitment 

 are sparse. This is astonishing when we consider that almost all coral reef 

 fishes, and a great majority of tropical invertebrates too, cast their eggs and 

 larvae into the plankton where they must survive and grow before they can settle 

 again to the reef as juveniles. 



The discussion held on December 27, 1983, at the ASZ meeting in Philadelphia, 

 dwelled on two aspects of recruitment, what we actually know and what we need 

 to know to better understand the dynamics of reef recruitment. About 20 par- 

 ticipants were involved in the discussion. Here I will summarize the more 

 important trends of the discussion. 



Given the ubiquity of a planktonic larval phase in so many coral reef 

 organisms, why is so little known about recruitment? The answer is multiple. 

 The eggs and larvae of most reef organisms are small, translucent, and difficult 

 to identify to species. They are extremely hard to maintain and study in 

 captivity because they are fragile and nutritional requirements often are 

 either unknown or difficult to adequately provide. In addition, only over the 

 last decade have newer techniques (e.g., otolith aging, increased use of SCUBA 

 and saturation diving for observations, improved methods for measuring currents, 

 etc.) become accessible to reef biologists. The paper by McFarland and Ogden 

 (this proceeding) addresses what is known about why so many fishes cast their 

 eggs and larvae into the plankton. They conclude that there is yet no definitive 

 answer; that the function of a pelagic larval phase for one reef organism may 

 not apply to another species; that in most species multiple functions prevail; 

 and that avoiding predation and dispersal appear to be the most important 

 factors that favor long-lived planktonic larvae. In addition, the times of 

 spawning in most reef species are poorly known. In recent years, however, 

 considerable effort has been placed on in situ observations of where and when 

 reef fish spawn. Lobel and Neudecker's paper (this volume) describes spawning 

 in a hamlet ( Hypoplectrus guttavarius ) and also reviews important papers on 

 reproduction in other species of fishes. Although many reef species spawn at 

 specific spawning sites and during a rush toward the surface, the time of 

 spawning is variable, often occurring in the late afternoon and dusk (Lobel and 

 Neudecker, 1985). However, spawning also often occurs during midday or midafter- 

 noon (Colin, 1982; Robertson, 1983). It was the general conclusion in the 



