Relationships between water motion and size-specific survivorship and growth of the demosponge Amphimedon compressa

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 (> 20 cm) and the highest (94.5%) for small sponges (< 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.