Effects of ocean acidification on sponge communities

The effects of ocean acidification on lower invertebrates such as sponges may be pronounced because of their low capacity for acid–base regulation. However, so far, most studies have focused on calcifiers. We present the first study of the effects of ocean acidification on the P orifera. Sponge species composition and cover along pH gradients at CO 2 vents off I schia ( T yrrhenian S ea, I taly) was measured at sites with normal p H (8.1–8.2), lowered p H (mean 7.8–7.9, min 7.4–7.5) and extremely low p H (6.6). There was a strong correlation between p H and both sponge cover and species composition. C rambe crambe was the only species present in any abundance in the areas with mean p H 6.6, seven species were present at mean p H 7.8–7.9 and four species ( P horbas tenacior , P etrosia ficiformis , C hondrilla nucula and H emimycale columella ) were restricted to sites with normal p H . Sponge percentage cover decreased significantly from normal to acidified sites. No significant effect of increasing CO 2 levels and decreasing p H was found on spicule form in C rambe crambe . This study indicates that increasing CO 2 concentrations will likely affect sponge community composition as some demosponge species appear to be more vulnerable than others. Further research into the mechanisms by which acidification affects sponges would be useful in predicting likely effects on sessile marine communities.