Mar Biol DOI 10.1007/s00227-007-0717-x 123 RESEARCH ARTICLE Substratum preferences in planula larvae of two species of scleractinian corals, Goniastrea retiformis and Stylaraea punctata Yimnang Golbuu · Robert H. Richmond Received: 10 July 2006 / Accepted: 23 April 2007  Springer-Verlag 2007 Abstract To test whether coral planulae recruit randomly to diVerent coral reef habitats or have speciWc substratum preferences, the settling behavior of planulae from two shallow water coral species from Pago Bay, Guam (13°25.02N, 144°47.30E) were examined in the laboratory in June and July of 1995. Goniastrea retiformis is generally restricted to the shallow reef front (<10 m depth) in areas dominated by crustose coralline algae (CCA), while Stylaraea punctata is abundant on inner reef Xats were CCA coverage is low and sand and carbonate rubble covered by bioWlms is com- mon. When presented with four substrata (1) carbonate rock scrubbed free of bioWlm and dried as a control, (2) the CCA Hydrolithon reinboldii, (3) the CCA Peyssonelia sp., and (4) naturally conditioned carbonate rubble covered by a bioWlm, G. retiformis larvae showed a signiWcant preference for H. reinboldii, and S. punctata larvae for the carbonate bioWlm treatment. The preference shown by S. punctata larvae for bioWlmed surfaces did not diminish with increasing larval age up to 11 days. These results suggest that the larvae of both species are capable of habitat selection, and that the preferred substrata among those tested bears a relation- ship to the habitats in which adult colonies were found. Introduction Many sessile, benthic marine invertebrates have planktonic larvae that diVer morphologically and physiologically from the juvenile and adult forms, and constitute the dispersal stage in the organisms’ life history. The period during which these larvae can successfully settle and metamor- phose into the juvenile form is called the competency period, and is aVected by both intrinsic and extrinsic factors including nutritional mode, resource availability, tempera- ture and the presence of speciWc chemical cues (Richmond 1987). Successful reproduction is only the Wrst step in the process of population replenishment, maintenance and growth. Larvae must recruit, that is, settle and metamor- phose, in order to become part of the population. Settlement is a physical process, during which larvae leave the water column and come into contact with the substratum, and is often reversible, with larvae contacting unsuitable substrata returning to the water column. Metamorphosis is a physio- logical process, during which morphological, physiological and metabolic changes occur, and with few exceptions, is non-reversible (Richmond 1985). Once larvae settle and come into contact with the substratum, chemicals associ- ated with the substratum, conspeciWcs or preferred prey may be responsible for metamorphic induction (Morse 1990; Pawlik and HadWeld 1990; HadWeld and Paul 2001). Studies of larval recruitment in corals can help determine the extent to which distribution patterns are shaped by post- metamorphic events, with settlement and metamorphosis occurring randomly in available space, rather than pre- metamorphic events, such as the organisms’ responses to Communicated by J. P. Grassle. Electronic supplementary material The online version of this article (doi:10.1007/s00227-007-0717-x) contains supplementary material, which is available to authorized users. Y. Golbuu (&) Palau International Coral Reef Center, P.O. Box 7086, Koror, PW 96940, Palau e-mail: ygolbuu@picrc.org R. H. Richmond Kewalo Marine Laboratory, University of Hawaii at Manoa, 41 Ahui Street, Honolulu, HI 96813, USA