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Geo-acoustic mapping of benthic habitat distribution

Final Report Summary - GEO-HABIT (Geo-acoustic mapping of benthic habitat distribution)

The EU FP7 Marie Curie Project GEO-HABIT (GEO-acoustic mapping of bentHic hABitat distrIbuTion) (individual action IEF 298274) was developed with the aim to highlight the evolution and present-day characteristics of carbonate deep-sea habitats and to apply statistical models for mapping the habitat distribution in poorly known areas. The project implied a holistic scientific approach, with marine geology, benthic ecology, oceanography and the application of geo-statistical analysis interacting as crucial components for the achievements of its objectives.
GEO-HABIT was specifically fitted to study Cold-Water Coral (CWC) communities, considered biodiversity hotspots in the deep sea, and to the investigate CWC Mounds, carbonate build-ups yielding valuable paleoclimatic and paleoenvironmental records. The project general objective was twofold, with strong implications for the management of present-day natural resources and for paleo-environmental characterization of deep-sea ecosystems. The main questions tackled during the project were:
1) which are the main physical governing factors ruling the development, maintenance and decline of specific CWC Mounds in the Mediterranean?
2) How can the occurrence of CWC communities and associated sensitive habitats be predicted at a fine scale over large areas?
The study areas of GEO-HABIT covered the Eastern Alboran Sea (Western Mediterranean), where the research on CWC Mounds was focussed, and the Cap de Creus shelf and slope system (Northwestern Mediterranean), where predictive habitat distribution models were applied.

In 2012 the GEO-HABIT Marie Curie researcher (Dr. Claudio Lo Iacono) lead and partially funded the MELCOR Cruise, dedicated to acquire a high resolution geophysical dataset over the newly discovered CWC Mound fields of the Alboran Sea. Two mound areas were unveiled and their physical and large-scale biotic environment comprehensively characterized (seafloor morphology and sedimentology, water column, megafauna): the West Melilla Mounds, 9 km west of Cape Tres Forcas (Moroccan Margin) and the Cabliers Mound, 80 km northeast Cape Tres Forcas. Up to 103 mounds, organized in two main lobe-shaped clusters, were identified in the West Melilla Mound field, within a depth range of 299–590 m, displaying a high density of 5 mounds/km2. According to the seismic records crossing the CWC mound field and the acquired ROV video data, most of these mounds appear partly draped by a transparent fine sediment layer. Seismic data suggest the two clusters are different in age, with the older likely developed since the middle Pleistocene. The second newly mapped mound area, the Cabliers Mound, consists of a 15 km long NNE-SSW oriented linear to sinuous mound/ridge system, from 60 to 105 m tall and with the summit from 295 to 620 m deep. ROV videos recorded along the summit of the Cabliers Mound show an extremely thriving CWC reef, with large colonies of Lophelia pertusa, Madrepora oculata, cup sponges, gorgonians and anthipatarians. These observations are also confirmed by the collected infauna and epifauna samples, revealing an uncommonly increased biodiversity for this region. This is the only CWC reef so far discovered in the Mediterranean, with such a rich CWC community, which truly makes it a unique location for the understanding of CWC growth and environmental requirements.
The new mound fields were eventually re-visited and sampled through 4 gravity cores, from 5 to 11 m long, during the EU FP7 Eurofleets GATEWAYS MD194 Cruise in 2012. High density of CWC framework and strong variability of CWC species, demonstrated by novel high-resolution CT scans, suggest that the Cabliers Mound corresponds to a peculiar feature compared to the other mounds of this region. The data acquired in the frame of the GEO-HABIT Project represent a step forward in understanding the evolution of the Alboran Giant CWC Mounds, and gives new insights their bio-geographic distribution at a regional scale. A short documentary on the MELCOR Cruise has been produced as a product for the Marie Curie outreach activity, with the aim of describing the main scientific sea-going tasks dedicated to map the habitats of CWC mounds. The integration between the data acquired during the MELCOR and GATEWAYS Cruises will represent the base for forthcoming studies on CWC Mounds, having a strong impact on the understanding of the biogeographic and paleoceanographic evolution of CWC in the Mediterranean Sea and in highlighting the role of living CWC reefs in maintaining a high biodiversity in the Alboran Sea and in the whole central-western Mediterranean.

The development of spatial analysis and predictive modelling as tools for natural resources management was the second aim of the GEO-HABIT Project. Predictive habitat mapping has shown in the last years great promise to improve the understanding of the spatial distribution of benthic habitats and to highlight species-environment relationships. However, although the resulting maps surely represent an important step forward in process-based ecosystem management, their predictive efficiency is not always tested by independent groundtruthing data. The aim of the GEO-HABIT Project was to apply and critically test different spatial models to statistically predict the distribution of three Cold-Water Coral (CWC) species (Madrepora oculata, Lophelia pertusa and Dendrophyllia cornigera) in the Cap de Creus Canyon (NW Mediterranean). Despite the expected differences between the three adopted non-linear models (MaxEnt, GAM, Random Forest) a common ecological pattern in the coral distribution was evident in all the outputs. As a final step, a probabilistic predictive ensemble was produced, merging the outcomes of the three models considered, providing a more robust prediction for the three species. Single models may not always be the most appropriate and definitive option, particularly when a limited number of observations is available. We suggest that a more reliable prediction could be obtained by merging models into spatial ensembles, able to reduce differences and associated uncertainties, showing hence a strong potential as an objective approach in the planning and management of natural resources.

The final results of the GEO-HABIT Project represent in their totality valuable and relevant insights in the evolution of deep-sea carbonate CWC Mounds since the Late Quaternary to the present-day, and provide a new and reliable methodology to produce predictive habitat maps for natural resource management in submarine canyons. The obtained results could potentially form the basis for a significant paleoclimatic and paleoceanographic study of the Mediterranean Sea. Moreover, the development and application of ensemble models to statistically predict the distribution of sensitive deep-sea benthic communities can have a direct impact in creating efficient and cost-saving science-based mapping methodologies useful for stakeholders in the management of natural resources.