Community–environment interactions explain octopus-catshark spatial overlap

Abstract

The octopus Eledone cirrhosa and the catshark Scyliorhinus canicula present the same feeding habits and distributional preferences in the Mediterranean Sea. We explore patterns of spatial overlap between these species to address coexistence and infer possible competition from spatial patterns in the western Mediterranean Sea. A spatially explicit modelling approach revealed that spatial overlap mainly responded to the distribution of shared resources, where coexistence is allowed by different ecological processes. Catshark (k-strategy) was highly abundant and widely distributed. However, the fluctuating population dynamics of octopus (r-strategy) explained the variations in spatial patterns of overlap. Spatial structuring across the study area was observed both in population distributions and in species interactions (coexistence or exclusion). Areas with high resources in terms of specific prey items (Catalan Sea) or alternative supplies, such as niche opportunities and ecosystem functions defined by community diversity (Balearic Islands), favoured species coexistence. Sea surface temperature showed opposite effects on overlap in northern and southern regions of the study area, which were not related to differences in species sensitivity. We suggest a surface trophic link, where different phytoplankton communities at each region might have opposite responses to temperature. This triggers contrasting mechanisms of food transfer to deeper benthic communities that subsequently facilitates species overlap. Characterizing how benthic and pelagic seascape properties shape species interactions across space and time is pivotal to properly address community spatial dynamics and move towards ecosystem-based management for sustainable fisheries and conservation planning