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

FIRSTATER F. N.; HIDALGO F. J.; LOMOVASKY B. J.; RAMOS E.; IRIBARNE O. O.

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 hypothesize that nutrient supply may modify Perumytilus community by either two mechanisms: (a) by enhancing primary production on the mussel shells surface, or (b) indirectly by modifying structural complexity of mussel beds through the increment in Perumytilus shell growth mediated by the increased primary production in water column. 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, we used a mesocosm experiment. Shell growth 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 in matrixes of large mussels compared to matrixes of 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, probably by enhancing food availability, which in turn may cause differences in the structure of Perumytilus faunal assemblage.