Coral Reef Fish Spawning,
Aggregations, and Coastal Oceanography

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Coral reef fishes, including many groupers and wrasses, form aggregations for purposes of spawning. Such aggregations are predictable in time and place, once known they are easy to target and fishing pressure can remove a significant proportion of assembled fish. Scientific knowledge of spawning aggregations presently is limited and, given the level of worldwide pressure on aggregations through overfishing and habitat destruction, an understanding of the role and importance of aggregation in reproductive success of many reef fishes is sorely needed. The aim of this work is to allow thoughtful conservation and management of marine fishes, based on their biology and on the oceanography of coastal regions where they are spawned and spend their planktonic life. CRRF is closely involved with the Society for the Conservation of Reef Fish Aggregations (SCRFA), which aims to apply high quality scientific research to answer questions concerning the conservation of reef fish aggregations.

 
Humphead wrasse
The humphead wrasse, Cheilinus undulatus, is the largest wrasse (Labridae) in the world. It also is highly prized in the live-reef fish trade, with mature fish captured alive and shipped to places like Hong Kong for slaughter by the wealthy at huge prices (up to $200 a kilogram). As a result, the humphead wrasse is threatened throughout much of its range. Very little is known about the reproduction, early life-history, or population structure of this fish - information which is essential to develop conservation strategies and, perhaps, allow for mariculture of the species to relieve pressure on wild populations. Without basic scientific knowledge of the life histories of and geographic variation in such fishes, conservation efforts are being done in ignorance. CRRF is undertaking intensive field work on spawning aggregations of C. undulatus as well as investigating the geographic structure of genetic variation in this enigmatic species.

 

Herbivores
The presence of herbivorous reef fishes, typically members of the surgeonfishes (Acanthuridae; below left), parrotfishes (Scaridae; below center), and wrasses (Labridae; below right), is critical in maintaining the delicate balance between benthic algae, corals and other bottom-dwelling organisms on coral reefs. In areas, such as much of the Caribbean, where herbivores have been removed by fishing or disease, the dominance of benthic algae has changed formerly lush coral reefs into algal tangles nearly devoid of coral.

 

Groupers
See annotated stills from a spawning run by Nassau groupers.

 

Oceanography
The transport of land plants and animals among oceanic islands was a problem on which iconic scientists such as Darwin spent considerable time. Such issues, as they pertain to marine species, still pose considerable problems for biological oceanographers. Satellite imagery has contributed much to our knowledge of structure and currents in the oceans, but there is still no substitute for field studies that tie the flow of water to the movement of individuals. CRRF is studying current patterns at spawning sites around Palau to investigate dispersal and recruitment in coral reef fishes, information that is critical for designing marine protected areas and conserving endangered species.

 


Above- and below-water photographs of a "drogue" or "drifter".


Plankton net used to collect fish eggs.

 


Tracks of drogues during one tidal cycle (ebb-flood).

Drogues (left) deployed at coral reef fish spawning sites drift on local currents as do planktonic eggs spawned by the fish. Thus, by tracking the drogues (right), we track the fish eggs.

 

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