MusselMytilus edulis (Mytilacea) dynamics in relation to environmental gradients and intraspecific interactions

Implications of benthic ecological quality in structuring macrobenthos community in a tropical monsoon influenced port, New Mangalore, India

Soft bottom macrobenthos are highly diverse benthic invertebrates, and their diversity depends mainly on the health of the benthic habitat. The impact of anthopogenic stress and port related activites on macrobenthos diversity was studied in New Mangalore port, a tropical monsoon influenced environment. A shift in the macrobenthos abundance and diversity was observed with seasons, along with shift in the dominance of opportunistic species. The ecological quality status (EcoQS) indicated 'poor' to 'moderate' and also 'bad' status of benthic habitat, and this changed with the seasons and regions within the port. Higher diversity of macrobenthos at stations located in the high circulation area (HCA) compared to low circulation area (LCA) and oil and fertilizer wharf (OFW) indicated pivotal role of local hydrodynamics and activities within the port in structuring macrobenthos diversity. The occurrence of opportunistic species within the port demonstrated the role of anthropogenic stress in structuring macrobenthos community.

Linking individual and population patterns of rocky-shore mussels

Individual traits and population parameters can be used as proxies of processes taking place within a range of scales, thus improving the way we can evaluate species response to environmental variability. In intertidal rocky shores, patterns at the within-site scale, i.e., between centimeters to hundreds of meters, are important for understanding the population response into these highly variable environments. Here, we studied a rocky-shore mussel population at the within-site spatial scale (1) to test how intertidal height and orientation of the shore affect individual traits and population parameters, (2) to infer the link between individual and population level features, and (3) to explore the upscaling mechanisms driving population structure and processes. We analyzed the patterns of six population parameters: density, biomass, crowding, median individual size, recruitment and mortality rate, and four individual traits: growth rate, spawning phenology, size and condition index. Crowding was defined as the degree of overlapping of individuals within a given area, for which we created a "crowding index". Mussels were studied along the intertidal height gradient in two rocky shores with contrasted orientation at one site over a full year. Our results showed a significant effect of intertidal height and shore orientation on most of individual traits and population parameters studied. In contrast, biomass contained in a full covered surface did not vary in space nor in time. This pattern likely results from relatively constant crowding and a trade-off between median individuals' size and density. We hypothesize that growth, mortality and recruitment rates may all play roles in the stability of the crowding structure of mussel aggregations. Variation in spawning phenology between the two shores in the study site was also observed, suggesting different temporal dynamics of microclimate conditions. Interestingly, despite the different population size distribution between the two shores, our estimates indicate similar potential reproductive output. We hypothesize that the structure of the patches would tend to maintain or carry a maximum of biomass due to trade-offs between density and size while maintaining and maximizing the reproductive output. The patterns of spatial variability of individual traits and population parameters in our study site suggest that heterogeneous within-site conditions influence variation in individual performance and population processes. These results provide insights about the relationship between individual traits and how these relationships make patterns at the population level emerge. They provide baseline information necessary to improve models of metapopulation with spatially explicit processes.