Plasticity of marine sponge habitat preferences with regard to light and water motion: The example of Batzella inops (Topsent, 1891) in submerged caves

This study examined the effects of environmental conditions on the distribution of marine sponges. We measured the abundance of the sponge Batzella inops (Topsent, 1891) in two contrasting habitats: inside submerged caves and on the surfaces of submerged boulders. We hypothesised that caves are a preferred habitat for B. inops over the boulder surfaces, and tested this by descriptive (quadrate sampling) and manipulative (reciprocal transplantation) experiments. In addition, we tested B. inops in situ for the presence of photosynthetic activity. We found that B. inops is more abundant inside the caves (mean ± s.e.m., 1.2 ± 0.6 individuals m^-2) than on the outside boulder surfaces (0.15 ± 0.19 individuals m^-2). We also detected photosynthetic activity in B. inops in both habitats. The results of transplantation experiments suggested that the sponge prefers the transfer from inside to outside the cave rather than vice versa. Therefore, we conclude that although B. inops is more abundant in sheltered habitats, such as submerged caves, adult individuals of this sponge can survive transfer to exposed conditions. Altogether, our findings point to the plasticity of B. inops habitat preferences and may aid further research into conservation or mariculture of this and possibly other sponge species.