The mesophotic ecosystem of archipelago Espíritu Santo as a refuge from climate change

Abstract

Background. Coastal environments such as the intertidal zone and rocky and coral reefs are exposed to natural disturbances such as tides, storms, hurricanes, and cyclones and human activities such as fishing, tourism, and pollution. The deep reef refuge hypothesis posits that organisms that can inhabit greater depths would be less vulnerable to anthropogenic impacts, greenhouse warming of the sea surface, and ocean acidi-fication caused by the increased partial pressure of CO2. Consequently, deep rocky or coral reefs can function as “insurance” against the effects of climate change. Objective. To analyse biotic and abiotic variables of the mesophotic ecosystem of Archipelago Espíritu Santo to assess it as a refuge against climate change-related disturbances. Methods. Bathymetry, profiles of temperature, salinity, and dissolved oxygen; determination of the euphotic zone, sampling in shallow and deep waters collecting water for analysis of carbonate system, video transects with remotely operated vehicles for the identification of benthic species and estimation of their abundance including those of commercial importance or conservation. Calculation of ecological indices and the reef-functional index. Results. Deepest recorded point was 78m, shallowest mesophotic zone was 11m. Temperature does not show a stratification either in April or in October 2021, but the salinity registers a peak near 30 m depth, and the dissolved oxygen decreases at 20 m. W Aragonite is below 3.0; there is spatial variation in the structural indices of the benthic community, and the reef-functional index is between 0.16 and 0.65. Conclusions. There are sharp spatial variations within the same locality, limiting the assertion that mesophotic ecosystems can serve as a refuge from climate change.