DIURNAL PERIODICITY OF SPAWNING ACTIVITY BY 

 THE HAMLET FISH, HYPOPLECTRUS GUTTAVARIUS (SERRANIDAE) 



Phillip S. Lobel 1 

 Center for Earth and Planetary Physics 

 Harvard University 

 Cambridge, Massachusetts 02138 



and 



Steve Neudecker 

 1301 Union Drive 

 Davis, California 95616 



ABSTRACT 



Many coral reef fishes spawn during the afternoon crepuscular period, a 

 time of increased predatory activity by piscivores. We document the diel 

 timing and spawning behavior of the hamlet fish, Hypoplectrus guttavarius , at 

 St. Croix, U.S. V.I. This fish spawns daily during dusk in the water column 

 above specific reef sites. 



The time of spawning relative to sunset was quantified at two sites at 

 different depths. Spawning commenced earlier at the deep reef site and 

 continued later at the shallow reef site. A field manipulation evaluated how 

 this species responded to disburbances during reproduction. When scuba divers 

 attempted to alter the fish's behavior by swimming vigorously toward mating 

 pairs, the hamlets did not abort spawning. The pair responded (1) by continuing 

 to spawn later into the night than those not disturbed and (2) by spawning 

 progressively nearer the substratum. 



INTRODUCTION 



Until the 1970s, the reproductive behavior of most tropical coastal 

 marine fishes eluded observation. This has changed recently with the discovery 

 that many species spawn during restricted times of ebb tide, off-reef current 

 flow, or crepuscular periods. A majority of coral reef fishes spawn eggs 

 that are bouyant and are advected by ocean currents. Having planktonic 

 propagules is thought to facilitate both rapid advection/dispersal in currents 

 and reduced predation by other reef fishes (Johannes, 1978; Lobel, 1978; 

 Barlow, 1981). In general, fishes seek out specific reef localities and/or 

 pinnacles over which they ascend and spawn. This behavior is particularly 

 interesting for fishes spawning shortly before and during dusk because 

 crepuscular periods are generally believed to be times of increased predator 

 activity and success (e.g., Hobson, 1968, 1972, 1974). Also, to witness 



1 Present affiliation: Woods Hole Oceanographic Institution, Woods Hole, 

 Massachusetts 02543. 



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