Shallow and mesophotic environments of the Pemba Channel


In this latest study published in Ocean & Coastal Management on 29th December 2020, Kennedy Osuka and co-authors from the SOLSTICE-WIO project and University of York utilised autonomous underwater vehicle (AUV) to describe the characteristics of water column, substratum and benthic communities occurring in the shallow (<30 m) and mesophotic (30–150 m) depths. The AUV was deployed at four sites in the Greater Pemba Channel in Tanzania and collected in-situ temperature, oxygen concentration, bathymetry, acoustic backscatter and photographic data. Generalised additive models (GAMs) were further applied to determine useful predictors of substratum and benthic community.

The bulk of the seafloor remains under-sampled, unstudied and unmapped. The mesophotic coral ecosystems (MCEs) of the Western Indian Ocean are particularly understudied. This is mainly due to the high vessel operation costs and the apparent lack of technology.

Key results

 – Presence of a complex seafloor with pockmarks, steep slopes, submarine walls, and large boulders.

 – Presence of MCE composed of corals, algae and fishes on the eastern margins of the Pemba Channel.

 – The key predictors of hard substrata and the coral reef communities were depth and seafloor slope.

 – The upper boundary of MCEs was present at 30–40 m.

 – The upper 100 m of water column had stable temperatures (25–26 ◦C) and oxygen concentrations (220–235 μmol/l).

Application

AUVs are rapidly becoming part of the standard toolbox for collecting information in the deep environments. They are capable of collecting high-resolution, multi-parameter data over wide range of depths and at lower costs compared to traditional research vessel. The published results highlight application of marine robots such as AUVs in filling the knowledge gap for areas not readily accessible by divers or with surface vessels, and their potential application for the initial survey and subsequent monitoring of Marine Protected Areas.

The article is open access and can be accessed through this link.