Benthic megafaunal biodiversity of the Charlie-Gibbs fracture zone: spatial variation, potential drivers, and conservation status

Abstract

The Charlie-Gibbs Fracture Zone (CGFZ) is a prominent geological feature offsetting the Mid-Atlantic Ridge (MAR), consisting of two parallel fractures, creating a highly variable seafloor bathymetry. It has been defined as the most important latitudinal biodiversity transitional zone on the MAR. Despite this recognition, the faunal communities living on the fracture zone have not been extensively described. A remotely operated vehicle (ROV) was utilised during the TOSCA (Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone) survey. The survey included five ROV video transects at depths between 560 and 2900 m. The objectives of the study were to use this video footage to quantify benthic megafaunal density and biodiversity patterns on the CGFZ and their environmental drivers. Species accumulation curves and generalised additive modelling show that depth and the presence of hard substrates play an important role in explaining species richness and abundance at the CGFZ. Coral taxa showed highest abundance between depths of 1500 and 2000 m, while sponge taxa were more abundant between 1750 and 2250 m. A dense sponge aggregation was identified on a ridge feature at 2250 m depth. The high biodiversity and presence of dense sponge aggregations and coral gardens found in this study highlight the need for detailed surveys to help support decisions made by governing bodies on the protection status of the CGFZ.

Unveiling Ophiuroid Diversity Across North Atlantic Habitats: an integrative perspective

“…Comparing the appearance, the deep sea oor area of the Azores has a similar character to the abyssal plains, ne sediment, and limited hard substrate available. However, this sampled area is in the broader region around the MAR, which is characterized by faults, fracture zones and abyssal plains covered with volcanic rocks [73]. Fracture zones show high species diversity was observed on the steep slopes and rocks [74].…”

3d Mapping of Benthic Habitat Using Xgboost and Structure From Motion Photogrammetry

“…Underwater video surveys have recently gained significant interest for benthic habitat identification and classification (Keogh et al, 2022;Mohamed et al, 2022;Ternon et al, 2022). Videos are usually recorded using high-definition (HD) cameras mounted on remotely operated vehicles (ROVs) (Robert et al, 2017;Keogh et al, 2022).…”

“…Underwater video surveys have recently gained significant interest for benthic habitat identification and classification (Keogh et al, 2022;Mohamed et al, 2022;Ternon et al, 2022). Videos are usually recorded using high-definition (HD) cameras mounted on remotely operated vehicles (ROVs) (Robert et al, 2017;Keogh et al, 2022). These videos, in turn, are converted into 2D images to generate 3D point clouds using SfM photogrammetry (Casella et al, 2017;Price et al, 2021;Ventura et al, 2022).…”

“…These maps represent habitat types, and can be used to monitor changes over time, and inform management decisions. Traditionally, benthic habitat mapping has employed multibeam echosounder data acquisition (Brown et al, 2011;Trzcinska et al, 2020) and underwater imagery collection and annotation (Keogh et al, 2022;Mohamed et al, 2022).…”