Intraspecific variation in the leaf traits and decomposition of estuarine primary producers across spatial gradients

Decomposition is a key process for carbon and nutrient cycles. Hence, understanding how biotic and abiotic factors interact to control decomposition is an important avenue of ecological research. This thesis investigated how climatic setting and nutrient enrichment directly and, via effects on leaf traits, indirectly influence the decomposition of two key estuarine primary producers, the seagrass Zostera muelleri and the mangrove Avicennia marina. It then considered how differences in decomposition processes among climatic settings influence the structure of benthic communities. Sampling within 16 estuaries spanning 7° of latitude, and varying in anthropogenic nutrient loading, revealed that the seagrass and mangrove displayed latitudinal variation in leaf traits, which in many instances differed between the two species. Nutrient statuses of estuaries were, by contrast, a poor predictor of leaf traits and the relationship between leaf traits and nutrient loading was highly temporally variable. Nevertheless, latitude and nutrient status of estuaries interacted to influence the decomposition rate of litter from a common source, perhaps due to spatial variation in decomposer communities. Further, at a common site, litter sources from high and low latitudes differed in decomposition rate, although relationships differed between the two species of macrophyte. Spatial variation in mineralization of detritus, resulting from differences in climate and unidentified factors, lead to spatially variable effects of organic enrichment on benthic communities. Overall, this study found that climatic setting and nutrient enrichment can act synergistically to influence decomposition processes via a combination of direct and indirect effects. Nevertheless, the relationship between decomposition processes and environmental factors differed markedly between the two co-occurring estuarine primary producers considered by this study. Hence, intraspecific variability in decomposition processes cannot be reliably predicted by broad-scale interspecific patterns.