GROWTH AND REGENERATION RATES IN THINLY ENCRUSTING DEMOSPONGIAE FROM TEMPERATE WATERS

Thinly encrusting species of subtidal sponge grow at slow but measurable rates over natural surfaces by lateral spreading. Of the eleven species studied here, Aplysilla rosea had the highest undisturbed rate of growth and Microciona sp. the lowest with an overall negative change in size. Using the mean growth rate it can be estimated that the largest sponge patches observed in the field may be over seventy years old. Growth rates of individual patches were varied but this variation was not synchronous within a species nor did it show any regular temporal pattern. Similarly, no relation between the normal thickness of the species, the wet weight, or true organic content of the species with undisturbed rates of growth could be found. However, the mean patch size of the species was correlated with the undisturbed growth rates. If the tissues of the sponges were damaged, rapid regeneration was initiated at rates many times greater than the undisturbed growth rate of the species. It was also found that even very small sponge patches could recover after almost all living tissue was scraped from the rock.