This thesis centres on mesoscale spatial patterns in species richness, as a measure of intertidal biodiversity. It is split down two lines of enquiry. The first correlated primary producer species richness with trophic functioning (SIA) within two biogeographical regions. Consumers were anticipated to either specialise or generalise their resource use depending on the richness of these resources or, alternatively, mesoscale environmental features were anticipated to dominate resource contributions. Across Northern Ireland, a gradient contrasting semi-enclosed water bodies with the operl coast was recorded, with isotopic variation reflecting physical (e.g. fetch, embayment) rather than biological (e.g. macroalgal diversity) factors. Along Northern Chile, isotopic variation alluded to a broad split in resource use between localities on the outer Mejillones Peninsula and those in bay situations. Mussel utilisation of kelp matter was supported where other POM constituents were scarce. Macroalgal community compositions tracked environmental patterns, suggesting predictability of consumer 81SN. Furthermore, taxonomic relatedness was hypothesised to source trophic equivalence. Despite large regional differences in abiotic conditions (although not biotic differences), hypothesis support was found in suspension feeding mussels, potentially allowing broad-scale comparison of isotopic baselines (Post, 2002). , Secondly, adaptable proxies for sampling effort were developed to enable use of collated datasets following Blight et al. (2009). Macroalgal and molluscan species richness across Northern Ireland were influenced by mesoscale wave fetch, tidal range, and sampling effort variables, but OLS regression was inadequate. The extent to which rare and common species contribute to UK-wide richness patterns for major intertidal taxonomic groups was investigated, finding that common species held stronger correlations than the full assemblage groups, whilst rarer species were variable. On-going work is planned to investigate the relationship of these patterns with abiotic and biotic habitat variables using a robust spatial regression model. Salient themes of the thesis were discussed in the final chapter.