Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Many ecosystems are facing environmental change and anthropogenic pressures that may affect communities in terms of both structure and/or function. Disturbances and stresses are commonly co-occurring in nature, however the interaction between them are generally considered as being additive without knowing the true in situ effects. The response of a Zostera marina bed community (1 m2 plots) facing two stresses (sediment enrichment through slow nutrient diffusers; light reduction through shading) and one disturbance (80 % eelgrass density reduction) was studied in the summer of 2015. The major and interactive effects were estimated based on diversity indices and community structure of the associated species, as well as the density and relative eelgrass growth. Density reduction increased the values (per g of Zostera) of the diversity indices and affected community structure over the course of the entire experiment (10 weeks). Sediment enrichment temporarily decreased diversity while shading increased diversity although these effects disappeared after five weeks. Antagonistic effects were observed when two disturbances/stresses were applied to community richness and evenness. Additive and antagonistic effects were observed for eelgrass growth (shading and density reduction) and for plant density (shading and enrichment). The inclusion of multiple disturbances and stresses in field experiments in order to assess their potential interactive effects will help disentangle the mechanisms structuring communities following disturbances.