Resistance to nutrient enrichment varies among components in the Cymodocea nodosa community

Abstract

The response of the seagrass community to perturbations, such as nutrient enrichment, is far from being uniform, since different components of the community may have different degrees of resistance to disturbance. An in situ manipulative experiment was conducted to test the effects of nutrient enrichment on the resistance of the Cymodocea nodosa community (i.e. seagrasses, epiphytes and benthic fauna) over two consecutive summers. We recorded distinct responses in the studied components (i.e. autotrophs versus heterotrophs) of the C. nodosa community to nutrient enrichment. The biomass of the autotrophic component (e.g. C. nodosa and its epiphytes) remained unaltered during the first summer, showing initial resistance to nutrient enrichment, but seagrass biomass increased during the second summer. The lower shoot density recorded for C. nodosa during the second year may explain this result because the resulting sparse canopy could have led to less self-shading, thus boosting growth. Thus, resistance to nutrient enrichment in autotrophs was shown to be a density-dependent phenomenon in this community, revealing the importance of seagrass health in resistance to nutrient enrichment. In contrast, nutrient enrichment significantly increased benthic fauna diversity over the entire study period. Therefore, different components of the C. nodosa community showed different degrees of resistance to nutrient enrichment, with annual variation playing a role in the resistance of the autotrophic component of the community and the fauna community showing less resistance to nutrient enrichment through an increase in fauna diversity and abundance over both years.