Relationships between water motion and size-specific survivorship and growth of the demosponge Amphimedon compressa Alex E. Mercado-Molina ⁎, Paul M. Yoshioka Department of Marine Sciences, University of Puerto Rico-Mayagüez, P.O. Box 9013, Mayagüez, PR 00681, USA abstract article info Article history: Received 8 September 2008 Received in revised form 5 April 2009 Accepted 9 May 2009 Keywords: Amphimedon compressa Size-specific growth Size-specific survivorship Sponge Tropical Storm Water motion We examined the relationships between water motion and the distribution, abundance, and sizes (heights) of Amphimedon compressa, an abundant sponge in reefs of La Parguera, Puerto Rico. Amphimedon populations were surveyed at different depths (3, 5, 8 and 12 m) in 3 inner-shelf and 3 mid-shelf reefs, which are protected and fully exposed to wave action respectively. More detailed studies on sponge survival and growth were performed at Las Pelotas (LP), a low wave energy site, and Media Luna West (MLW), a fully exposed reef. The effects of Tropical Storm Dean on sponge survivorship were also evaluated at these reefs. With the exception of an inner-shelf site, Amphimedon was absent in the 3 m depth zone in all reefs. Otherwise, no consistent depth-related patterns in abundances were detected among reefs. Sponges' heights generally increased with depth with the tallest sponges occurring in the 12 m zone. Survivorships at LP before Dean were not size-specific with semiannual rates averaging 86.3%. Survivorships at MLW before Dean were size-specific with the lowest semiannual rates (69.4%) for large sponges (N 20 cm) and the highest (94.5%) for small sponges (b 10 cm). Tropical Storm Dean reduced survivorships to 41% and 30% at LP and MLW, respectively. At both sites, small and large sponges suffered significantly more losses compared to the mid-size sponges. Sponge growth rates were significantly higher at LP (4.5 cm yr -1 ) compared to MLW (1.5 cm yr -1 ). Growth rates were not size dependent at MLW while larger sponges grew faster at LP. The results of this study suggest that water motion may be an important factor controlling and structuring populations of A. compressa. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Sponges are one of the most important and diverse components of the benthic fauna of coral reefs. Thus, understanding the processes that influence the ecology and distribution of sponges may provide valuable insights into the structure and organization of coral reef communities. Like many other marine sessile organisms, the distribu- tion and life history traits (e.g. growth and survivorship) of sponges are influenced by physical factors such as water movement (Vogel, 1974; Bell and Barnes, 2000b), light (Wilkinson and Vacelet, 1979) and sedimentation (Könnecker, 1973). Among these, water motion has been recognized as one of the most important in shaping the population structure of marine sponges (Vogel,1974; Bell and Barnes, 2000b) by influencing their growth and survivorship. For instance, high water flow seems to facilitate the growth of sponges (Watson, 1976; Hiscock, 1983) by increasing the food supply per unit time (Vogel, 1974) and by removing metabolic waste (Bell, 2002). In contrast, growth rates of sponges inhabiting habitats of high ambient flow rates could be reduced due to greater metabolic investment in skeletal and basal structures (Palumbi, 1986). The effect of water motion on the survival of sponges is also variable. Wilkinson and Vacelet (1979) reported that survival was greatly reduced for sponges which grew in low water flow relative to high flow areas. However, strong water movement due to high wave energy related to storms can increase sponge mortality rates by fragmentation and partial mortality (Wulff, 1995). These results suggest that the relationship between water motion and the growth and survivorship of sponges cannot be generalized; hence, that its role on the population size structure and dynamics of sponges should be assessed by detailed studies at the species-specific level. This study focused on Amphimedon compressa, one of the most common shallow-water demosponge inhabiting Caribbean coral reefs (Wulff, 1991). A. compressa normally grows as a single erect branch, although, repent forms and sponges with multiple branches (as a result of fusion between conspecific individuals) can be found (Wulff, 1985; pers. obs). Color varies from brilliant red to purple. Its surface is smooth with a compressible consistency, and oscules are distributed uniformly throughout the body. Preliminary observations indicate that A. compressa sizes (heights) tend to be larger in inner-shelf reefs and that maximum Journal of Experimental Marine Biology and Ecology 375 (2009) 51–56 ⁎ Corresponding author. Sociedad Ambiente Marino HC-01 Box 5700, Barranquitas, PR 00794, USA. Tel.: +1 787 519 5942. E-mail address: amolinapr@gmail.com (A.E. Mercado-Molina). 0022-0981/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2009.05.003 Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe