Conservation benefits of marine reserves depend on knowledge integration of genotypic and phenotypic diversity

Conserving intraspecific trait variation is vital for maintaining the viability of species. It ensures a species to adapt to warming and increasingly stochastic environments, and to recover following extreme events. Here we investigate the selective effects of spatial management on intraspecific genetic and phenotypic variation of two sympatric but genetically distinct Atlantic cod ecotypes in a Norwegian fjord. We found that phenotypic differences between sympatric cod genotypes were mainly driven by morphological and metabolic traits. Offshore cod had higher metabolic maintenance costs at cool temperatures but lower aerobic capacity at warm acclimation than coastal ecotypes, indicative of thermal constraint of aerobic physiological processes beyond metabolic maintenance. Offshore cod also had larger and thicker peduncles and better body condition. We found that protection benefits from the no-take zone (NTZ) of the Tvedestrand marine protected area were independent of individual space-use size, but instead resulted from ecotype-specific differences in habitat occupation. Results specifically show that the current delimitations of the NTZ do not cover habitats occupied by the coastal and highly resident cod ecotype which shows greater metabolic thermal tolerance but is considered to already be in a depleted state. Our study exemplifies why protecting intraspecific diversity is directly relevant for management implementations aimed at reducing the impact of further selection pressures such as ongoing environmental change. Careful investigation of intraspecific diversity and integration of such knowledge to fisheries management and design of protected areas may prevent unwanted additional selective pressures and contribute to offer broad protection to genotypes and phenotypes.