Scale Matters: Understanding how small-scale interactions may determine the success of Marine Protected Areas

When creating management plans for commercially and recreationally fished species, it is important to account for the availability of habitat and resources necessary to maintain managed populations. Marine protected areas (MPAs) often include large spatial areas (up to thousands of square kilometers) and are designed to include essential habitats, i.e. habitats that have energetically dense prey resources or other key features necessary for the success of the target species. However, for many species success is dependent on habitat interactions at relatively small scales. By understanding the spatial scale of species-habitat interactions and focusing on the distribution of essential habitats across these scales, MPAs may be able to be smaller and yet remain effective in supporting target species. Utilizing technology such as drones and geographic information systems (GIS) mapping for habitat assessment and stable isotope analysis to determine resource utilization, we can better understand how small-scale habitat features affect the success of target species. Our monitoring of California Spiny Lobster (Panulirus interruptus) on Catalina Island, California, USA revealed lobster density was higher, individuals were larger, and there were more fecund females in non-MPA habitats adjoining the Blue Cavern State Marine Conservation Area. By incorporating habitat assessments with diet assessments, we found that small-scale resource availability, specifically the presence mussel beds, were a potential factor in the observed differences in lobster populations outside the MPA. Lobsters are energetically dependent on these mussel beds during their reproductive season and we found the MPA site does not have a sustained mussel beds, forcing lobsters to forage upon lower value prey. Understanding the spatial scale of species-habitat interactions may also help us to understand the resilience of MPAs to climate change. For example, with the climate changing and ocean heat waves, we have witnessed the loss of these beds over time and with small scale habitat assessments we can understand which beds or zones of beds are most susceptible to climate change. As we look to create new protected areas and evaluate current MPA designs, it is crucial to understand the critical small-scale interactions between species and their environment and consider the value of essential habitats and resource availability on a scale that matches these interactions.