Exploring the Biodiversity of Understudied Benthic Taxa at Mesophotic and Deeper Depths: Examples From the Order Zoantharia (Anthozoa: Hexacorallia)

James Davis Reimer,Dhugal John Lindsay,Maria E A Santos,Takuo Higashiji,Yehuda Benayahu,Hiroki Kise,Richard L Pyle,Brian W Bowen,Masanori Nonaka,Joshua M Copus

doi:10.3389/fmars.2019.00305

Abstract

Research on so-called ‘minor taxa’ at mesophotic depths has lagged behind that of more commonly researched groups such as fish or hard corals. Exemplar taxa include species of the order Zoantharia, benthic colonial anemones that are cosmopolitan in distribution but understudied in many ecoregion and ecosystems. In this study, we examine the results of rare mesophotic to deep sea surveys (one rebreather, one remotely operated submersible (ROV) + nets, two ROV surveys) from Japan and Israel. We examined the collected images and video data to provide a first estimate of Zoantharia diversity at mesophotic depths. Zoantharians were observed in all surveys, indicating their ubiquitous presence in mesophotic and deeper ecosystems. Additionally, specimens (n=12) acquired via these surveys were phylogenetically analyzed with three DNA markers. Phylogenetic results showed the presence of undescribed species based on the uniqueness of acquired DNA sequences, including one specimen belonging to the family Abyssoanthidae, previously only reported from depths below 2000 m. Other specimens belong to groups that inhabit shallower and deeper depths (Antipathozoanthus, Epizoanthus and Parazoanthidae). These results depart from surveys of mesophotic coral ecosystem fishes and crustaceans, which indicate affiliations almost exclusively with shallow genera and families. We hypothesize that mesophotic depths are an ecotone for zoantharian diversity, with links to both deeper and shallower ecosystem diversity. Future surveys in mesophotic depths should incorporate phylogenetic methods to better catalogue so-called ‘minor taxa’ (not only including Zoantharia) and enhance the scientific foundation for conserving the biodiversity of these threatened ecosystems.

Highlights

Marine biodiversity has always been less well understood than that of terrestrial ecosystems
Analyses of the PICASSO video surveys showed the presence of zoantharians on the stalks of numerous glass sponges at the summit of the Sagami Knoll in Sagami Bay at 473 m, and these were identified as Epizoanthus cf. stellaris based on their epizoic association on the stalks of these sponges (Beaulieu, 2001)
An image of a zoantharian on a eunicid worm from 111 m was acquired from a site off Ishigaki Island, Okinawa (24◦15.69’N 124◦4.24’E), and was identified as E. cf. illoricatus based on its epizoic association with eunicid worms (Kise and Reimer, 2016)

Summary

Introduction

Marine biodiversity has always been less well understood than that of terrestrial ecosystems. Technological advances in both smaller, remotely operated submersibles (ROVs) (Fricke and Knauer, 1986; Stewart and Auster, 1989; Love et al, 1994; Lindsay et al, 2012), and in rebreather diving equipment (Stone, 1990; Pyle, 1999, 2000), have allowed exploration of these mesophotic ecosystems to expand greatly in scale and frequency Research in these ecosystems have yielded important new discoveries about marine biodiversity (Erdmann et al, 1998; Pyle, 2000; Kane et al, 2014; Rowley, 2014; Kosaki et al, 2017). As seen from both shallow-water and deep-sea work, studies on understudied, or so-called “minor taxa”, have lagged

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