Bathyal and abyssal demersal bait-attending fauna of the Eastern Mediterranean Sea

Thomas D Linley,Alan J Jamieson,Jessica Craig,Imants G Priede

doi:10.1007/s00227-018-3413-0

Abstract

Baited cameras were deployed over a depth range of 532–5111 m in the Ionian Sea to characterise the large mobile fauna. The planned installation of a neutrino telescope also offers the potential for biological observatories. The current study was intended to aid observatory placement. At increasing depths, sediment was observed to become more uniform and animal burrows and tracks reduced. A total of 10 species of deep-sea fishes were identified from images; four elasmobranchs, which were not recorded deeper than 1841 m, and six teleosts. At depths > 3000 m, including Calypso Deep, the deepest point in the Mediterranean, only one fish species was observed; the Mediterranean grenadier, Coryphaenoides mediterraneus (3400–5111 m), extending this species’ maximum recorded depth to 5111 m. Four species of decapod crustacea could be identified from images. The dressed deep-sea shrimp, Acanthephyra eximia (1346–5111 m) was the only invertebrate recorded at abyssal depths, including the deepest point. A faunal change was detected at ~ 1000 m depth. Incorporating other studies from the Eastern Mediterranean identified additional faunal boundaries at ~ 1500 m and ~ 2500 m. The time from landing the observation equipment to the arrival of the first fish increased exponentially with depth at a slower rate to that observed in the Atlantic Ocean. The estimated density of bait-attending deep-sea fish was, therefore, significantly impoverished compared to the Atlantic Ocean at equivalent depth. Barriers to colonisation, low resource input, and high temperature at depth relative to the Atlantic Ocean are probable causes of the impoverished fauna.

Highlights

The Eastern Mediterranean Sea extends down to over 4000 m depth in a series of fore-arc basins sometimes known collectively as the Hellenic Trench (Fig. 1) associated withResponsible Editor: G.H
Sea trawl surveys (D’Onghia et al 2004; Mytilineou et al 2005) with the exception of the Longnose skate Dipturus oxyrinchus, which is recorded from the Western Mediterranean (Griffiths et al 2011), the Aegean Sea (Yigin and Ismen 2010) and the Gulf of Sirte
D’Onghia et al (2012) found that that Conger conger, Helicolenus dactylopterus and Polyprion americanus generally occur in higher abundance in cold-water coral areas than on open slopes of the Northern Ionian Sea at 450–650 m depth

Summary

Introduction

The Eastern Mediterranean Sea extends down to over 4000 m depth in a series of fore-arc basins sometimes known collectively as the Hellenic Trench (Fig. 1) associated withResponsible Editor: G.H. The Hellenic Arc subduction zone, where the African plate descends beneath the European tectonic plates (Royden and Papanikolaou 2011). These deep basins constitute the largest area of warm abyssal ocean (depth > 3000 m) on the planet, where the deep-sea temperature is 13–14 °C (Roether et al 1996), compared with typical temperatures of 2–4 °C in the major oceans (Thistle 2014). This is considered similar to conditions that prevailed globally 100 million years ago during the Cretaceous, before deep-sea cooling was established (Priede 2017)

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