Sexual recruitment of the corals Favia fragum and Agaricia humilis in a 30-m(3) exhibit aquarium: species-specific limitations and implications on reproductive ecology.
We studied the recruitment of the Caribbean reef building corals Favia fragum (F. fragum) and Agaricia humilis(A. humilis) in captivity. Thirty colonies of each species collected in Curaçao, Netherlands Antilles, reproduced sexually during a temporary stay in a 30-m(3) closed system from November 2001-January 2002. Twelve months later, the F1 generation of F. fragum started reproducing and formed an F2 generation. No reproduction of the F1 recruits of A. humilis was observed. Two years after the introduction of the field colonies, sexual recruits of both species were assessed using two different methods: recruits were estimated using quadrats (quadrat sampling method) and the total number of recruits was counted by creating a map of the artificial rock work divided in distinct areas (area census method). Recruitment rates of F. fragum were highest for the F2 generation on horizontal surfaces (area census method: 137.9+/-191.7 recruits m(-2); quadrat sampling method: 272.0+/-254.8 recruits m(-2); mean+/-SD) and were overall lowest for the F1 generation on overhanging areas of the tank (area census method: 3.8+/-4.0 recruits m(-2); quadrat sampling method: 4.0+/-6.1 recruits m(-2); mean+/-SD recruits m(-2)). The populations of both species showed similar patterns independent of the applied assessment method with highest densities on horizontal surfaces followed by vertical surfaces and lowest densities on overhanging surfaces; however, both methods showed conflicting results when the influence of the surface orientation on the population densities was statistically analyzed. The maximum density of A. humilis (1.4+/-2.7 recruits m(-2) on horizontal surfaces) was much lower than the maximum density of the F1 generation of F. fragum (24.7+/-18.3 recruits m(-2)). Colony sizes of recruits within each population (F. fragum F1: 3.12+/-0.98 cm, F2: 0.83+/-0.41 cm; A. humilis F1: 3.79+/-1.35 cm; maximum diameter+/-SD) did not differ between different orientations (horizontal vs. vertical vs. overhanging). Calculated growth rates in the aquarium reflected those observed for F. fragum in the field, whereas A. humilis showed slower growth in the aquarium than in the field. Factors such as competition, sedimentation, and predation, that generally reduce in situ recruitment may be excluded in captivity resulting in far higher recruitment rates. This study confirms that aquarium exhibits can serve as a comparative model to study the ecology of corals under semi-controlled conditions. Zoo Biol 0:1-17, 2007. (c) 2007 Wiley-Liss, Inc.
Rotterdam Zoo, Rotterdam, The Netherlands.
Dirk
D
Petersen
Michaël
M
Laterveer
Gerard
G
Visser