Significance of micro-and macrofauna from seeps along the Israeli coast (Palmahim Disturbance).

Cold seeps are important biodiversity hotspots, which support unique communities in the deep sea. The occurrence of living or fossil chemosymbiotic molluscs and low oxygen tolerant benthic foraminifera in the sediments, in association with other seepage related features (e.g. aragonite, authigenic carbonate crusts) are important indications of active or past fluid seepage.
The EU Eurofleets2 SEMSEEP Cruise on the R/V Aegaeo along the Israeli coasts (2016) provided sea floor data and sediments for this study.
Three deep-sea cores from representative environments from the Palmahim Disturbance, (coral-transition area, pockmark area and Gal-C channel area) spanning the last 5000 BP were investigated for pteropods, benthic foraminifera and molluscs and cross-analysed with ROV videos and surface samples.
The coral-transition core (AG16-20-BC1b) shows a sharp increase in low-oxygen benthic foraminifera (representing 100% of the faunal assemblage), no agglutinants, pyritized tubes and euhedral gypsum crystals in its bottom part. This evidence together with the low values of δ¹³C of C. oolina give indication that a short-lived advective fluid flux occurred approximatively at 3500 BP. Only few small individuals of the chemosymbiotic bivalve Isorropodon perplexum Sturany, 1896 have been observed above this interval, showing that the chemosynthetic environment was not conducive for the development of a full chemosymbiotic benthic community.
Similarly, evidences of methane emission have been observed in the pockmark core (AG16-23-BC2). Pteropods molds, composed by aragonite needles and High-Mg calcite crystals are present at the base of the core. Aragonite precipitates during advective emissions, when the Sulfate Methane Transition Zone (SMTZ) is located cm to dm below the seafloor, therefore the presence of pteropod molds recrystallized in aragonite is an important evidence that an advective emission occurred. However, these molds co-occur with authigenic carbonate crusts, shrimp claws, low-oxygen tolerant benthic foraminifera and a mature association of chemosymbiotic molluscs (including vesicomyids, lucinids, mytilids and thyasirids). Typically, these organisms are sustained by a moderate, diffusive, pervasive and persistent fluid flow. Therefore, we suggest that this environment was dynamic and supporting advective and diffusive emissions that were able to sustain recruitment and development of mature chemosymbiotic faunal assemblage. 

This research was funded by the Swiss National Science Foundation (SNSF) project Ref. 200021_175587, samples were collected during the EUROFLEETS2 SEMSEEP cruise that was funded by the European Union FP7 Programme under grant agreement n° 312762.