First visual imagery from six seabed areas off the coasts of South Africa

By Grant van der Heever and Dr Lara Atkinson, SAEON Egagasini Node Tweet

On 22 January a team of young scientists and technicians departed from Cape Town Harbour on board the Ellen Khuzwayo, a Department of Agriculture, Forestry and Fisheries (DAFF) research vessel.

The expedition aimed to obtain the first visual imagery from six seabed areas off the coast of South Africa, including two of the newly proposed marine protected areas (MPAs), Browns Bank and Robben Island, as well as a hardground site off Scarborough, a Southern Benguela muddy site and a heavily trawled Benguela Shelf area.

The imagery obtained would allow us to describe and characterise these habitat types and the biota living therein. The survey also enabled us to search for specific features which included coral mounds and muddy shelf areas, and to capture seabed imagery of a heavily trawled area for comparison to that observed in the Benthic Trawl Experiment lanes.

The scientists and technicians participating in the survey were from several institutions and included Dr Jock Currie (Chief Scientist) and Mari-Lise Franken from the South African National Biodiversity Institute (SANBI), Dr Anthony Bernard from the South African Institute for Aquatic Biodiversity (SAIAB), Fred Fourie from SeaTechnology Services, and Leila Nefdt and Grant van der Heever from SAEON.

Image 1: Localities of the sites surveyed over six successive days

Areas surveyed

Over a period of just six days the team managed to successfully survey 22 stations, across six habitat types, ranging between 90 and 700 metres depth (Image 1).

The first day commenced with “gear-trials” of the SAEON towed Ski-Monkey camera and the SAIAB Acoustic Release (AR) stereo Baited Remote Underwater Vehicle (BRUV) (Image 2) at a shallow (approximately 90 m), hard-ground site off Scarborough. Upon landing on the seabed, Ski-Monkey visuals displayed a seafloor covered in large boulders and overhangs!

As the camera operator, I was unsure whether to haul in the camera or continue the transect. A bad knock from a boulder could cause serious damage to the Ski-Monkey system. I swiftly decided to haul in cable and “fly” the camera over the boulders.

As we progressed along the transect, the screen (i.e. the seabed) lit up with a diverse array of colourful corals, sponges and starfish species (Image 3). Contrastingly, the hottentot seabream (Pachymetopon blochii) and the false jacopever (Sebastes capensis) were the only two fish species observed on the AR stereo BRUV system at this station.

On the second and third days the untrawled Browns Bank MPA and a feature previously detected on an echo-sound reading that appeared to be a large mound-like structure (thought to possibly be a coldwater coral reef), were surveyed. Here, we were delighted to find occasional patches of reef covered in soft corals, sea anemones and brittle stars, as well as numerous commercially important fish species, including Cape hake (Merluccius spp.), kingklip (Genypterus capensis), monk (Lophius vomerinus), jacopever (Helicolenus dactylopterus) and dory (Zeus spp.). The large mound-like structure we had hoped to see on the camera appeared to be a steep shelf drop off with interesting biota and geology, worthy of further exploration.

Image 2: Deployment of SAIAB’s acoustic release (AR) stereo baited remote underwater vehicle (BRUV)                                                        Image 3: Boulder at Scarborough hard-ground site covered in yellow encrusting sponge, soft corals, hydrozoans, bryozoans, brittle stars and the indistinct star, Cosmasterias felipes

Days four and five involved surveying the muddy and heavily trawled shelf areas. Interestingly, the deeper stations of the trawled shelf area hosted a high abundance of brittle stars and bristle worms, as well as three fish species (Cape hake, conger eel and rat-tail), which are commonly associated with commercial trawling.

The strong south-easterly wind on the final day of the survey forced us to seek shelter inshore and survey a shallow reef patch in the proposed Robben Island MPA. We were certainly not disappointed as we were met with a diverse array of invertebrate species, including a pancake star (Anseropoda grandis) (Image 5), seapens, sea urchins, starfish, sea spiders, sponges and dense aggregations of hermit crabs (Sympagurus dimorphus).

Image 4: The rich seabed diversity evident in the proposed Browns Bank MPA includes sea anemones, sponges, bryozoans, cup corals, hydrocorals, starfish and many more species  Image 5: The pancake star (Anseropoda grandis) was one of many invertebrate species observed in the proposed Robben Island MPA

Visuals from the AR Stereo BRUV captured only one fish species, resembling a gobie, as well as two inquisitive mantis shrimp (Pterygosquila capensis) and a red-spotted crab (Mursia cristiata).

Overall impressions 

The cruise was deemed a success and the information collected will assist in building our knowledge of the benthic diversity and distribution of South Africa's offshore habitat types. Information contained in the images will also contribute critical “baseline” information from within the newly proposed MPAs, enabling long-term monitoring into the future.