Molecular evidence for the intermediate disturbance hypothesis in an acidified marine system

Abstract

The Intermediate Disturbance Hypothesis (IDH), postulated by Connell (1978), suggests that ecosystems exhibit higher species diversity when disturbances occur at intermediate scales. In this study, the applicability of the IDH at the intraspecific scales (organismal) was investigated using molecular data. As an experimental perturbation framework, a naturally acidified system located in La Palma Island, Canary Island (Spain) with a sharp fluctuating pH gradient was sampled. Molecular data were obtained from sequences of a fragment of the mitochondrial Cytochrome C Oxidase subunit I gene in two sea urchin species (Arbacia lixula and Paracentrotus lividus) to explore genetic diversity at the organism level. These data were compared with previous metabarcoding results of taxonomic benthic diversity at the community level. Both sea urchin species showed the highest levels of haplotype and nucleotide diversity at the intermediate pH fluctuation zone, mirroring metabarcoding data that revealed the highest levels of taxonomic diversity at the same zone. The results support the validity of the IDH in marine ecosystems affected by strong pH fluctuations and across different levels of biological organization (from organisms to communities).