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Familiar ground - and exploring new grounds

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Brisingid sea star perched on a small rock clump covered in sponges, stylasterine corals and other epifauna observed along a transect in the Benthic Trawl Experiment area

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Close-up image showing three common species observed in the Benthic Trawl Experiment area - starfish Crossaster penicillatus, bristleworm and the large benthic isopod Munnopsurus mimus that we were able to identify thanks to a specimen being collected in Driaan Pretorius’ make-shift collection net attached to the SkiMonkey camera frame

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Invertebrate biodiversity observed at stations on Childs Bank, at this location, largely dominated by brittle stars, seen here extending their arms into the water column

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First visual confirmation of living cold-water coral species (probably Lophelia pertusa) on Childs Bank, seen here with two brittle stars and ascidians

By Lara Atkinson (SAEON), Charles von der Meden (SAEON), Colin Attwood (UCT) and Kerry Sink (SANBI)

There was some sense of familiarity as researchers once again gathered onboard the Department of Agriculture, Forestry and Fisheries’ (DAFF) research vessel, Ellen Khuzwayo, on 26 January 2015.

The second year of the benthic trawl experiment survey was about to depart and while the team were fairly confident and familiar with what lay ahead from the previous year’s experience, there was still a sense of excitement, and some nervousness, as to what this year’s survey would yield.

Associate Professor Colin Attwood (University of Cape Town) was once again our fearless cruise leader, joined by Dr Charles von der Meden (SAEON), Ms Karen Tunley (UCT), Mr Driaan Pretorius (Viking Fishing) and the DAFF technician, Mr Herman Engel, all of whom were part of the first survey in 2014 and leapt at the opportunity to participate again in 2015. New to the team this year was Dr Kerry Sink (Marine Programme Manager, SANBI) and Mr Jean van der Merwe (Sea Harvest), strengthening the diversity of experience on the team.

The objective of this long-term monitoring research is to assess for changes in the benthic fauna (infauna, epifauna and fish) in lanes that were closed to trawl fishing activity on 1 March 2014. This research is a collaboration among the South African Deepsea Trawl Industry (SADSTIA), DAFF and researchers from SAEON, UCT and SANBI in response to a condition of the Marine Stewardship Council certification for South Africa’s hake fishery.

High quality imagery for analysis

The SkiMonkey III benthic camera system was once again used to obtain imagery (still photos and video) of the seabed in each of five lanes in the experimental area (west of Childs Bank on the West Coast of South Africa), with alternate lanes being closed to trawl fishing, spanning depths from 370 m to 510 m. Three stations were surveyed in each lane with up to 170 photos and 10 minutes of video being captured at each station.

SAEON’s new benthic grab was used to collect triplicate samples of sediment and infauna at each station. Improvements in the configuration of the SkiMonkey III camera system, and Charles’ growing expertise on operation of this system, ensured that high quality imagery was obtained for further analysis.

Species observed

Epifaunal invertebrate species commonly encountered in the experimental area include starfish, Crossaster penicillatus, burrowing anemones, Cerianthid spp., bristleworms, isopods, burrowing urchins, Brissopsis lyrifera capensis and Spatangus capensis and anemone hermit crabs, Sympagurus dimorphus and Parapagurus bouvieri.

Some rocky clumps were observed in the trawl lanes that clearly support considerably different epifaunal species like brisingid sea stars, sponges and stylasterine corals (see picture). Fish species observed in the area include hake, Merluccius spp., kingklip, Genypterus capensis, rattails, jacopever, Helicolenus dactylopterus and spiny eels, Notocanthus sexpinnis.

The trend observed in sediment particle size was increasingly fine sediment with depth, however, laboratory sorting of samples will provide data for detailed analysis. Processing of imagery and infaunal samples are underway.

Whilst the video footage was very exciting to watch from the tiny operations room, Driaan Pretorius from Viking Fishing felt that bringing some specimens on deck would make it “more real”. Driaan and Jean van der Merwe cleverly rigged up a small mesh funnel and attached it to the frame of the SkiMonkey camera and when the camera returned on deck, there was much excitement to discover that the mesh funnel was full of small bentho-pelagic invertebrates … and one small fish!

Thanks to Driaan’s fishing skills, we have now been able to accurately identify a species of deepwater isopod, commonly occurring in the footage and previously called a “sea cockroach”, as being Munnopsurus mimus (see picture).

Venturing into new territory

Another exciting new component to the 2015 cruise was the inclusion of surveying the adjacent Childs Bank feature. Whilst the occurrence and location of this underwater feature is well known, marine researchers had never before had the opportunity to explore its biodiversity. The Childs Bank feature is probably best described as being similar to an underwater Table Mountain feature (different geological composition though), however, we have never been able to see what marine life lives there, unlike the well studied, famous flora and fauna of Table Mountain.

Dr Kerry Sink spent two sleepless nights onboard the Ellen Khuzwayo closely watching the echo-sounder picture on the bridge as the vessel steamed back and forth over Childs Bank. This echo-sounder overview provided Kerry a good idea as to where was best to put the camera down to get the first visuals of this feature.

The camera was used to sample four stations covering the south-west portion of the bank. The towed SkiMonkey configuration was used on the flat top of the feature, while a modified floating camera configuration (referred to as the ‘FloatMonkey’) allowed surveying of the rocky habitats of the upper and lower slopes.

This footage revealed that the top of the bank varies between 185 and 195 m in depth, is remarkably flat, similar to that of Table Mountain, with few rocks and common invertebrates such as heart urchins and brittle stars dominating the biota. The south-west slope of the bank revealed a terraced profile (Fig. 1) with three or four sills, each associated with a steep drop measuring between 30 and 80 m.

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Figure 1. Echogram of the south-western part of Childs Bank showing the terraced slope. The horizontal extent is 2.5 nautical miles

Epifaunal species associated with the slopes of Childs Bank include the pancake starfish Anseropoda grandis, bushy gorgonians (white and yellow), feather stars, sponges, brittle stars and the first live record of cold-water corals (probably Lophelia pertusa) seen in South African waters. Fish species observed along these transects include jacopever, long-snout bellows fish, hake and rattails.

Broken rock and coral were abundant in the footage, indicating evidence of trawl damage in the area and a broken trawl warp was recovered when it hooked onto the ski of the SkiMonkey camera! These surveys on Childs Bank have already been used to refine and support delineation of the boundaries for the Childs Bank Marine Protected Area that is being proposed through the Operation Phakisa Initiative.

The team returned to Cape Town harbour on 3 February 2015, having again completed a highly successful Benthic Trawl Experiment survey. Processing of imagery and samples are underway and the next survey is already being planned for early 2016.

Watch a short video of some of the highlights of the 2015 Benthic Trawl Experiment survey.

 

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