Effects of nutrient supply on the Perumytilus purpuratus community in central Peru.

FIRSTATER F.N; HIDALGO F.J.; LOMOVASKY BETINA JUDITH; RAMOS E.; IRIBARNE OSCAR

Lima

Simposio; CENSOR Endterm Symposium; 2008

On Peruvian rocky shores the mussel Perumytilus purpuratus monopolize the primary substratum creating a structure that consists of the mussel matrix and an assemblage of associated organisms. We hypothesis that nutrient supply may modify Perumytilus community by either two mechanisms: (a) by enhancing primary production on the mussel shells surface, or (b) by modifying structural complexity within mussel beds mediated by the increasing primary production in water column, which in turn enhance Perumytilus shell growth. No effect of nutrient addition on Perumytilus assemblage was detected neither by analyses of functional groups, nor by analyses of the community structure. Addition of nutrient did not result in increased abundance of chlorophyll-a on the shells surface. To evaluate the effect of nutrients on Perumytilus growth by enhancing food availability, we used a mesocosm experiment. Shell growth rate of mussels in fertilized mesocosms was higher than those in non-fertilized ones. The importance of mussel size in community structure was revealed by a transplant experiment. Almost all faunal functional groups were more abundant at large mussels matrix compared to small ones. In conclusion, point-source nutrient addition, during the timescale of our experiment, did neither result in enhancement of primary production nor changes in the community structure of the Perumytilus bed. However, long-term fertilization of the water column had a positive effect on mussels shell growth, via higher food availability, which in turn may cause differences in the structure of Perumytilus faunal assemblage.