Mucus trails in the rocky intertidal: a highly active microenvironment

The significance of mucus trails derived from the herbivorous gastropods Patella caerulea, Monodonta turbinata and Tegula sp. in enhancing microbial activity in marine rocky intertidal and sublittoral zones was investigated by means of microcosm and field experiments. A pronounced increase of bacterial abundance concurrently with extracellular glucosidase activity (alpha-Dand betaD-glucosidase) was observed in mucus-enriched batch cultures within 2 d of incubation; maximum values of exoproteolytic activity (leucine-aminopeptidase) were reached ca 1 d later than the peaks in bacterial abundance and glucosidase activity. In all mucus-enriched treatments the levels of glucosidase activity were significantly correlated with bacterial abundance; a high correlation also existed between alpha-Dand beta-D-glucosidase activity in enriched treatments while exoproteolytic activity was less dependent on bacterial density in the later stage of decomposition; this decoupling might be caused by an enhanced aminopeptidase expression per cell. The activity of total glucosidase in the surrounding water closely followed the disappearance of total carbohydrates from mucous layers. Microalgal biomass on glass fiber filters coated with trail mucus was significantly higher (5.1 pg chl a (25 cm)-') after 1 wk of exposure in the field compared to mucus-free control filters (0.9 (rg chl a (25 cm)-'). It is hypothesized that mucus-derived polymers entering the DOM-pool are further hydrolyzed and taken up by the free-living bacterial community. The observed stimulation of microalgal growth supports the idea that the breakdown of mucous material by bacterial enzymes can provide a microenvironment ennched In regenerated inorganic nutrients. The estmated high area1 trail mucus production (81 g mucus dry wt m-2 yr-' for P. caerulea, 544 g mucus dry wt m-2 yr-' for M. turbinata) suggests that mucus is a significant source for microbial activity in some nearshore waters.