Effects of point-source nutrient addition and mussel removal on epibiotic assemblages in Perumytilus purpuratus beds

nvaldivia [ at ] awi-bremerhaven.de


The objective of this study was to evaluate the effects of point-source nutrient addition and mussel removal on species diversityof the epibenthic assemblage of the purple mussel Perumytilus purpuratus. It was hypothesised that mussels cushion the effects ofdisturbance on the associated organisms and thereby favour species diversity in patches with added nutrients. In order to test thishypothesis, a two-factorial field experiment was conducted at an exposed rocky shore of northern-central Chile in which nutrientaddition and mussel removal were manipulated with two levels. Experimental units consisted of 100-cm2 mussel plots that weresampled after two months of experimental manipulations. Local nutrient addition was done with coated slow-release fertilisers.Mussel removal treatments consisted in three destructive events applied throughout the experimental phase, and each eventconsisted in the removal of 20% of the mussel biomass from each plot. While point-source nutrient addition had only minor effectson diversity, mussel removal had significant and negative effects on faunal species richness and the abundance of suspensionfeedersand sessile organisms. The abundance of predators/scavengers significantly decreased with mussel removal in the presenceof nutrient addition. Grazers and mobile organisms were very abundant in the mussel assemblage but their abundance remainedunaffected by treatments. Finally, species richness and total abundance of algae were also not affected by the treatments. Althoughthe duration of our experiment was relatively short, we suggest that the effects of local nutrient addition are of minor importance atthe study site in comparison to the effects of mussel removal. Based on our results and previous studies conducted in soft-bottomsystems, we suggest that physical and biological stress acting on exposed hard-bottom communities overshadows the potentialeffects of local nutrient addition.

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DOI 10.1016/j.seares.2006.06.003

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Valdivia, N. and Thiel, M. (2006): Effects of point-source nutrient addition and mussel removal on epibiotic assemblages in Perumytilus purpuratus beds , Journal of sea research, 56 , pp. 271-283 . doi: 10.1016/j.seares.2006.06.003

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