The First Cut Is the Deepest: Trawl Effects on a Deep-Sea Sponge Ground Are Pronounced Four Years on

Katelin M Morrison,Heidi Kristina Meyer,Hans Tore Rapp,Christopher Kim Pham,Emyr Martyn Roberts,Ana Colaço

doi:10.3389/fmars.2020.605281

Katelin M Morrison, Heidi Kristina Meyer + Show 4 more

Open Access

https://doi.org/10.3389/fmars.2020.605281

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Abstract

Few studies have described the effects of physical disturbance and post-recovery of deep-sea benthic communities. Here, we explore the status of deep-sea sponge ground communities four years after being impacted by an experimental bottom trawl. The diversity and abundance of epibenthic megafauna of two distinct benthic communities in disturbed versus control areas were surveyed using a remotely operated vehicle on the Schulz Bank, Arctic Ocean. Four years after disturbance, megafaunal densities of the shallow (∼600 m depth) and deep (∼1,400 m depth) sites were significantly lower on the disturbed patches compared to the control areas. Multivariate analyses revealed a distinct separation between disturbed and control communities for both sites, with trawling causing 29–58% of the variation. Many epibenthic morphotypes were significantly impacted by the trawl, including ascidians, Geodia parva, Hexactinellida spp., Craniella infrequens, Lissodendoryx complicata, Haliclonia sp. Stylocordyla borealis, Gersemia rubiformis and Actiniaria sp. However, we found some smaller morphospecies to be equally abundant with control transects, including Polymastia thielei, Geodia hentscheli, and Stelletta rhaphidiophora, reflecting lower trawl impact for these morphotypes. Overall, our results suggest that these are fragile ecosystems that require much more time than four years to recover from physical disturbance typical of trawling activities.

Highlights

Under favorable environmental conditions, dense aggregations of large sponges form diverse structural habitats known as sponge grounds (Hogg et al, 2010)
This is the first study looking at recovery of Arctic sponge grounds following physical disturbance
Our results provide useful insight on how the diversity and megafaunal composition of sponge-dominated communities can be affected by anthropogenic activities like trawling

Summary

Introduction

Dense aggregations of large sponges form diverse structural habitats known as sponge grounds (Hogg et al, 2010). Sponge grounds are found globally at varying depths and physiographic features, like seamounts, oceanic ridges, continental slopes, and canyons (Howell et al, 2016; Maldonado et al, 2017; Roberts et al, 2018). It is poorly understood what drives the formation of these habitats, but it is known that their distribution relies on moderate water flow to supply nutrients and gases while inhibiting sedimentation (Vogel, 1974). Many animals are associated with sponge grounds; fishes and invertebrates use them as an indirect food source (Kunzmann, 1996), shelter from predators (Kunzmann, 1996; Cook et al, 2008), spawning, and nursery grounds (Freese and Wing, 2003; Amsler et al, 2009)

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