Baseline study assessing the composition of deep-sea Porifera communities among seamount ecosystems in the Galapagos Marine Reserve (GMR), Ecuador

The deep-sea is the largest marine biome, and yet the least explored one. Among deep ecosystems, seamounts are productive and rich habitats whose hard substrates are suitable for engineer species such as deep-sea sponges to settle. Deep-sea sponges are a major component of the seamount benthic fauna, whose presence and aggregations can enhance biodiversity; however, sponges are threatened by destructive activities such as bottom-trawling. Recognized as good indicators for ecosystem health, deep-sea sponges have recently become a priority for conservation strategies. The Galapagos Marine Reserve (GMR) harbors ~350 seamounts of ecological and commercial importance for the local community, notably for fishery and tourism. Nonetheless, little is known about Galapagos seamount biodiversity and ecosystem functioning. The GMR is UNESCO world patrimony site and a marine protected area, nonetheless, artisanal fishery is allowed in more than 60% of the reserve. Since 2014, the Galapagos Seamounts Project explored 27 seamounts of the GMR, as the first baseline study of seamount ecosystems in the Galapagos. The project was created to improve current understandings of seamount benthic diversity to contribute to the maintenance and development of conservation and sustainable management measures of seamount resources in the GMR. For the present study, three seamounts of the northern part of the GMR were explored using ROV video transects. Biological samples were collected as well. Taxonomic diversity was assessed by morphological and genetic identification of 14 sponge vouchers. Species richness was investigated with respect to site, depth and substrate type, and the influence of these factors on sponge assemblages and distribution was also studied. High proportions of potentially new species were found for both Demospongiae (89%) and Hexactinellida (75%), including two potentially new genera of Phellodermidea and Farreidae. Taxonomical findings could be further investigated, for instance for biochemical compounds that could interest th pharmaceutical industry, while genetics could help to assess patterns of connectivity and possible endemism in the region. Morphospecies richness was higher on hard substrate for all sites and generally at shallow depths (> 900m), whereas relatively low richness was observed at greater depths (> 1500m). Distribution of morphospecies assemblages seemed to be mainly influenced by depth. Variations in temperature and oxygen appeared as important variables among depth ranges. The first ever characterization of sponge diversity patterns provide baseline information for the identification of seamounts of interest for sponge diversity and morphospecies richness. Thus, Galapagos seamounts appeared to be diverse and unique ecosystems that need to be protected and studied deeper.