GEOMORPHOLOGICAL SUBMARINE FEATURES IN THE MENORCA CHANNEL (WESTERN MEDITERRANEAN)

Based on geophysical (multibeam echosounder and very high resolution parametric profiles) and sedimentological (Shipek dredge) data acquired during the INTEMARESCANAL0419 expedition, different geomorphologic features have been identified. The study area is located in the continental shelf of the Menorca Channel between 37 and 116 m water depth (mwd). Shallower zones are dominated by lense shaped bedforms, up to 1 m high. They are characterized by very low backscatter values. Also small circular -or slightly elongated- mounds are very frequent morphologies occurring up to 100 mwd. Their sizes range from 1 to 5 m high and 20 to 80 m of diameter with high backscatter values. The most prominent morphological features at intermediate depths are a set of channels that dig in the shelf from 60 to 90 mwd. They show vertical walls and extend up to several km. In the parametric profiles, paleochannels filled by a sedimentary layer approximately 30 ms (two-way time) thick can be observed. The deepest zones are characterized by an erosive surface covered by a thin layer of no consolidated sediments. A visual analysis of the samples shows that sediments are characterized by coarse sand and gravel mainly composed of biogenic particles (carbonated fragmented bioclasts). Higher values of backscatter correspond to samples with a variable abundance of rhodoliths whereas lower values correspond to sands. The variety of morphological features can be mainly related to erosive and depositional Quaternary processes in the continental. Benthic communities strongly influence sediment composition, which was found to be characterized by a high carbonate content

Trawling footprint and diversity of benthic communities in the Menorca Channel (western Mediterranean).

It is well known that bottom trawling affects the abiotic (seafloor morphology, sediment resuspension, water turbidity) and biotic components (biodiversity, biomass and production) of habitats. However, comparative studies on the effect of trawling on epibenthic communities of sedimentary bottoms are scarce. One of the objectives of LIFE IP INTEMARES project is to assess the impact of bottom trawling on vulnerable benthic habitats of the circalittoral bottoms of the Menorca Channel (western Mediterranean), designated Site of Community Importance (SCI) within the Natura 2000 network. The present study compares the benthic communities of four areas subjected to different bottom trawl fishing intensity levels (null, intermediate and high). The assignment of fishing effort levels was based on the fishing effort distribution in the area calculated from Vessel Monitoring System (VMS) data. The biological samples were collected from 46 beam trawl stations sampled during a scientific survey on April 2019. In order to detect differences related to the different levels of fishing intensity, we calculated four “traditional” diversity indices (i.e. species richness, Margalef’s richness, Pielou’s evenness and Shannon’s diversity), and the recently developed N90 diversity index, which has shown to be useful in the detection of the response of demersal and benthic communities to fishing pressure. Our results show the highest values of all the analyzed indices in the nonimpacted area, suggesting a negative effect of bottom trawling on the benthic communities present in Menorca Channel. However, no clear pattern was observed between different degrees of trawling intensity and diversity values, so other factors such as environmental conditions must be also considered to explain these results