The muddy waters of the uThukela shelf edge are worth protecting

By Ryan Palmer

“The uThukela muddy shelf edge” doesn’t sound very appealing, but this large area located north of Durban is one of 22 identified for protection under the Operation Phakisa marine protected area (MPA) network.  A number of different habitats are known to converge at the uThukela shelf edge, resulting in a unique and highly diverse seabed ecosystem.  The recent deployment of submersible camera has, for the first time, opened a window on this deep-sea world.

With increasing pressure for economic growth within the marine sector and subsequent demands on marine resources, it is essential that policy makers are provided with scientifically sound advice on which to base management decisions such as where to place marine protected areas and where they will be most beneficial, at the lowe4st cost to industry.

All the available information to date indicates that the uThukela muddy shelf edge should be protected, but nobody has actually been there to see what it looks like.  Spanning a depth range from the intertidal zone to approximately 1,400m off the uThukela River mouth, with one of the world’s strongest western boundary currents streaming through it, it is not the easiest place to access and very little of the system has ever been explored by visual means.

In order to get there one needs a suitable seagoing craft:  a remotely operated submersible vessel (ROV):  highly skilled personnel and a reasonably larger budget.

In May and June this year, the “Spatial Solutions” project undertook a first survey of the uThukela muddy shelf edge from the Angra Pequena, a Durban-based research vessel.  During the survey, a multi-disciplinary scientific team undertook bathy-metric surveys, ROV surveys, baited remote underwater video (BRUV) camera deployments, plankton sampling, and oceanographic measurements.  For the first time surveys went to a depth of over 200m.

The African Coelacanth Ecosystem Programme (ACEP) provides the necessary infrastructure and technical support for Spatial Solutions and additional funding and support is provided by the Wildlands Conservation Trust and the Grindrod Blue Fund which aims to build capacity in the marine sciences through the Ocean Stewards programme.

ACEP is a flagship project of the Department of Science and Technology managed by the South African Institute for Aquatic Biodiversity, a research facility of the National Research Foundation.  The Ocean Stewards Programme affords marine science students the opportunity to participate in the research cruises.

Diving into the unknown

After months of preparation and planning, excitement mounted as the ROV descended from the surface for the first 200m dive.

Researchers were not quite sure what to expect to see as the sunlight faded and the ROV entered the “twilight zone”.

At a little over 220m the bottom became visible and the ROV lande3d, stirring up a cloud of fine sediment:  uThukela mud!  As the “dust” cleared, where one may have expected to see a barren muddy landscape, there was an ecosystem teaming with biodiversity.

Burrows, castings, mounds and tracks cover the seafloor and fish and invertebrates go about their business as the ROV casts its light on them and, for the first time, allows researchers a glimpse into their world.

On this very first deep dive, a seabat and a coffin-fish - both new to science - rat trails, cusk eels, giant spider crabs, green eyes and snake eels, many of which were being discovered for the first time.  This demonstrates how little we know about what is going on down on the seabed.  The dive lasted for three hours, covered a distance of just over a kilometre and had all eyes on board glued to the screen.

Surprisingly varied world

As the team did more dives with the ROV it became apparent how patchy and variable these habitats can be.  The differences in sediment type from one site to the next, and even within the space of a single dive, was surprising.

A little further south, off Durban, a sandy bottom at similar depth is very different, covered in a vast field of sea urchins, pansy shells and foraminifera, while a little closer inshore, there is another muddy bottom, this time with interspersed sand dunes over it, each providing a different habitat and supporting a different community of fish and invertebrates.  Reef sites were also targeted, and the team was lucky enough to spot some of South Africa’s most threatened line-fish species, such as seventy-four, in relative abundance.

A wealth of visuals

A total of 45 ROV dives at carefully selected sites provide over 60 hours of footage and 12,000 still photos of the seabed.  Furthermore, over 60 hours of underwater footage taken with baited remote underwater video cameras will allow for in-depth analysis of the fish living on deep reef and soft bottom habitats in the region.  Tows with plankton-catching nets will result in an investigation of larval fish recruitment.

The dive lasted for three hours, covered a distance of just over a kilometre and had all eyes on board glued to the screen.

Maritime Review Africa | Ryan Palmer (ACEP technical and scientific management and the Programme's ROV pilot)