Morphological monitoring of subtidal sponge assemblages

The management of the marine environment requires effective temporal monitoring of communities and assemblages to detect any change above the level of natural variability. Even though sponges are usually abundant in subtidal hard substratum environments and have the ability to significantly influence other community members, they have often been excluded from monitoring programmes because they are taxonomically difficult and often hard to quantify compared to other marine groups. We consider the use of a morphological method to examine photoquadrat data collected at 3 hard substratum sites over a 10 yr period at Skomer Marine Nature Reserve, south-west Wales. Differences in the morphological assemblages and abundance were apparent between years, but the sponge assemblages showed rapid recovery (within 1 yr) to their original assemblage composition and abundance following declines. The changes were attributed to natural biological variation or a short-term impact, rather than any response to prolonged environmental change and there was no correlation between any of the changes in assemblages observed and the environmental variables measured. A comparison of morphological and species data enabled the same sponge assemblages to be identified at different sites, validating the method. This morphological approach to monitoring represents a cost-effective and realistic way of monitoring certain sponge assemblages.