REEF FISHES AT SEA: OCEAN CURRENTS AND THE ADVECTION OF LARVAE 



Phillip S. Lobel and Allan R. Robinson 



Center for Earth and Planetary Physics 



Harvard University, Cambridge, MA. 02138 



ABSTRACT 



This paper presents an overview of an interdisciplinary 

 study of the kinematics and dynamics of reef fish larvae in 

 offshore currents, especially mesoscale quasigeostrophic eddies. 

 We develop herein the conceptual framework and background infor- 

 mation for our on-going studies, the preliminary results of which 

 will be presented at the 1983 ASZ meetings. The focus of this 

 research has been to define the appropriate scales in ocean cir- 

 culation relative to the developmental biology and reproductive 

 ecology of coastal marine fishes whose larvae are planktonic. 



INTRODUCTION 



Interest in the topic of larval dispersal by ocean currents 

 has been longstanding and its broad implications to ecology, evo- 

 lution and fisheries are well known. Yet, the factors that ulti- 

 mately limit the distribution of oceanic planktonic organisms 

 have not been clearly specified (Wiebe 1976) . The constraints 

 upon the transport of planktonic larvae along coasts and across 

 oceans are few. Only the direction and velocity of the prevail- 

 ing currents, the timing of reproduction, and the length of the 

 planktonic stage place limits upon where, when and how far 

 species are transported (Scheltema 1972, 1977). One critical 

 variable in the survival of certain shore-dwelling species may be 

 the phase and quantity of larvae of one species relative to the 

 phasing and quantity of another in contest for spaces sporadi- 

 cally open to occupancy (Sale 1977, 1978). 



Determining the fate of fish larvae as plankton in open 

 ocean currents is not just interesting with regard to the life 

 cycle of fishes. It is also crucial to the resolution of key 

 ecological hypotheses concerning species distributions and diver- 

 sity in reef and shore communities (Helfman 1978, McFarland 

 1982) . Furthermore, resolution of these important questions 

 leads directly into a discussion about the evolutionary stra- 

 tegies of island species, one notable feature of which is the 

 origin and maintenance of endemic species. Other aspects of this 

 work are basic to applied fisheries and the development of effec- 

 tive fisheries management plans, since a majority of food, game 

 and aquarium fishes possess planktonic larvae and/or may seek 

 larval fishes as food (e.g., Huntsman e_t al. 1982). 



The following discussion highlights the key questions and 

 outlines significant results and references pertaining to the 

 study of planktonic larvae of coastal marine fishes. 



An overall approach for the study of physical oceanic 

 processes affecting ichthyoplankton distributions ideally would 

 include: 1) mapping current patterns and confirming the appropri- 

 ate scales of variability, 2) strategic sampling of plankton in 



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