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Macrobenthic communities associated with deep wood falls lying in submarine canyons

Final Report Summary - DEEPFALL (Macrobenthic communities associated with deep wood falls lying in submarine canyons)

The deep sea – the portion of the oceans below the 200 m depth – is the largest ecosystem on the planet and covers about 60% of the Earth’s surface. Nevertheless it remains largely unknown. Indeed we know more about the moon’s surface than the ocean seafloor. The life in the deep-sea mostly depends on the rain and fall of particles and matter that comes from shallower waters and are consumed by deep-sea organisms.
Recent research shows that human activities affect the seafloor in deep-sea environments even far from land, where anthropogenic materials accumulate together with natural matter. This phenomenon affects also submarine canyons, which are high priority conservation areas and biodiversity hotspots. They may trap falling materials (e.g. litter, terrestrial debris, and wood) from wide areas. Deep-sea canyons are also likely increasingly subjected to physical disturbance as a result of higher frequency and intensity of climate-driven episodic events. The accumulation of marine litter needs urgent attention by policy makers, managers and society: several studies showed that waste, pollutants, woods, and litter (e.g. plastics) threaten the deep sea and heavily affect the living stocks. Obtaining knowledge on processes like organic matter cycling, energy transfer up through food chain and ecosystem connectivity is fundamental and far to be complete to understand deep-sea ecosystems’ functioning and services.
By studying sunken wood samples collected between 400 and 3000 m depth, in the Pacific and the Atlantic Ocean, the DeepFall Project aimed at contributing to study the mechanisms of wood degradation in various deep-sea habitats, trying to answer what is the fate of the terrestrial debris and wood that accumulate on the ocean floor.
Sunken wood attracts a variety of deep-sea species, including chemo-synthetic bacteria and opportunistic and specialized invertebrates. Among them, several mollusc species of the family Xylophagaide, wood-boring bivalves that may digest cellulose, attract other invertebrates to newly generated trophic resources and highly contribut to the development of the deep-sea trophic web.
The main objectives of the DeepFall project have been:
1) To investigate the macrobenthic community in sunken wood lying on deep-sea canyons;
2) To study the diversity, biology, and reproduction of Xylophaga spp. (as primary wood degraders in deep-sea ecosystems) by means of morphological, histological, and molecular analysis;
3) To study the phylogeny and phylogeography of Xylophagaidae using nuclear and mitochondrial markers;
4) To study the population genetics and connectivity among different depths and canyons.
The obtained results provide new insights on the deep-sea woodborers’ diversity, dispersal, and connectivity among submarine canyons, being the first application of both morphological and molecular techniques to study these organisms. There has been a fundamental contribution to the identification of woodborer species by combining classical morphology with novel molecular analyses and a new method has been implemented to study their population genetics. Furthermore, the newly generated data on of deep-sea populations’ connectivity, either along depth and/or among canyons, will be essential for the sustainable management of deep-sea resources
and may contribute to the development of conservation-based policies, as well as to the design of marine protected areas.