A Subtidal Spree at Sodwana Bay

By Drs. Kerry Sink, Toufiek Samaai , Olivier de Clerck and Yves Samyn

In November 2003, twelve marine scientists spent a week at the Triton dive camp in Sodwana Bay, northern KwaZulu-Natal. Peter Timm, the camp owner, wave technician (skipper!) and the discoverer of the Sodwana Bay coelacanths facilitated a total of 170 man dives on the reef and rubble habitats of the Greater St Lucia Wetland Park. The group comprised a team of phycologists from UCT, MCM and the University of Ghent in Belgium, an echinoderm expert (Free University of Brussels), a sponge systematist (University of KwaZulu-Natal), two researchers working with isotopes (Rhodes University), team members of the Ezemvelo KwaZulu-Natal Wildlife (EKZNW) Reef Project and a marine ecologist from the African Coelacanth Ecosystem Program (ACEP). Armed with several cameras, collecting bags and more enthusiasm than air, we set up makeshift labs and got down to investigating some new habitats and documenting the seaweeds, echinoderms and sponges we collected there.

 

The collaboration between the various teams was initiated by EKZNW. A joint Belgian-UCT project was initiated in 1998 with the aim of studying diversity and biogeographical patterns of marine macroalgae and echinoderms (Bolton et al. 2001, 2004). This project worked closely with marine scientists from EKZNW and has played a critical role in identifying algal and echinoderm specimens as part of the coastwise reef project led by Cloverley Lawrence. During the 2002 Coelacanth expedition, EKZNW divers and members of the coelacanth discovery team conducted SCUBA transects inshore of the submarine canyons to determine habitat types and characteristic communities between 15 and 50m (Sink and Timm 2000). This was the first time many of these sites had been dived and a startling diversity of habitats and species were uncovered. Faced with a bewildering array of unidentified taxa, researchers approached experts in the different taxonomic groups to build on studies documenting subtidal biodiversity in the Park.

 

One of the surprising discoveries of 2002 was the presence of algal-dominated communities on mixed substrata and rubble habitats, particularly in deeper water. The find that caused the most excitement was the

some of us, reluctant to give up on the red blades, conducted a final deep dive inshore of Jesser canyon. We returned with some small red blades and handed them over to the phycologists with trepidation. They were not the Halymenia but something else – another new red alga, probably Sebdenia, that is common on the deep unconsolidated sediments.

Among the most exciting algal discoveries of the deep water habitats was a small green alga which after examination in the laboratory proved to be Pseudocodium floridanum, a species originally described from Florida and since then only reported from Papua New Guinea. Such highly disjunct distributions are puzzling. Most likely, however, are they the result of dramatic undersampling of most deep water reef habitats in tropical regions. Although there is no proof for this hypothesis, it is remarkable that in the last decade more and more algae, that was previously restricted to remote well-studied tropical area’s (e.g. Hawaii, Australia), are now reported from deep water habitats in South Africa as well. Gelatinous red algae are a very good example. Before the start of the Belgian-UCT project, only a single gooey red had been reported for KwaZulu-Natal. This trip resulted in the discovery of at least six new species records, several of which are unreported for the entire Indian Ocean.

 

Despite the failure to find the elusive red blades, this quest led to some exciting echinoderm finds. These included Holothuria (Microthele) fuscopunctata, a huge aspidochirotid species whose most southern western Indian Ocean distribution was Nosy Be, Madagascar and a large (approx. 60 cm long) orange sea cucumber that probably belongs to the monotypic holothurian subgenus Stichothuria Cherbonnier, 1980. An exciting discovery indeed as this subgenus was, until now, considered endemic to New Caledonia (the sole species being Holothuria (Stichothuria) coronopertusa Cherbonnier, 1980. Further investigation of the ossicle (microscopic calcareous skeletal elements of echinderms) assemblage of the different body tissues will bring certainty towards its formal identification. In total some 150 specimens of echinoderms were collected. As their identification is largely dependent on skeletal morphology, they can only be reliably identified in a well-equipped lab and by consulting all the available literature. This takes time.

 

During our week at Sodwana, 110 sponge specimens representing at least 80 taxa were collected and "Sponge Bob" was busy until the early hours of the morning taking photos, making spicule preparations and educating his colleagues on the art of sponge taxonomy. His experience on this trip was one of discovery and excitement, as every crevice, overhang, rubble patch and coral bed he sampled, made him realize how little we know of the east coast fauna in terms of sponges. The sponge diversity at Sodwana Bay is astonishing in terms of the sheer abundance and taxonomic diversity. The sponge assemblages come in a multitude of shapes, sizes and colours: barrels, vases, cups, tubes, blobs, some with big pores that look like Swiss cheeses and others with smaller pores that for expansive flat sheets. Ecologists demanding instant identifications were quieted with " It’s a species of Spirastrella / Theonella / Spheciospongia / Axinella / Stelletta, Aplysilla / Clathria or Suberetis" and with excitement "Sponge Bob" would also say, "We found a new one!". On one of our dives, we spotted a Hawksbills turtle feeding on an encrusting sponge, and only after competing fiercely with the turtle, we managed to obtain a tiny section of the sponge, which turned out to be a specimen of Hymeniacidon sublittoralis. As with echinoderms, sponge identification is largely dependent on skeletal and spicular morphology (but a bit more difficult!) and one needs to be a "Sherlock Holmes" to piece together the clues to solve the species identification. This takes time and explains why our favourite sponge taxonomist has been confined to his lab since November. It has become‘Sponge Bob’s’ life mission to get more respect for the sponges of the world, and especially South Africa, for there is still so much that we don’t know about them, but what we see never fails to stimulate the imagination and wonder at their extreme beauty and diversity.

 

Aside from the exciting science, sundowners at Lake Sibaya and Ngoboseleni pan as well as plenty of time around the Triton campfire, afforded an important opportunity for us to share ideas. Interdisciplinary biodiversity studies as the present one have interesting intrinsic and extrinsic aspects. Intrinsically describing biodiversity is the first step towards actual understanding of the diversity of life. Such comprehension depends on getting the biological classification right, whereafter reliable biotic checklists can be drawn. These in turn facilitate biogeographic analyses that shed light on the processes that shape(d) biodiversity. Extrinsically, an understanding of biodiversity is essential for management and conservation.

Reference:

Bolton J.J., Coppejans E., Anderson R.J., De Clerck O., Samyn Y., Leliaert F. & Thandar A.S. 2001. Biodiversity of seaweeds and echinoderms in the western Indian Ocean. Meeting Report. South African Journal of Science 97: 453.

BOLTON J.J., LELIAERT F., DE CLERCK O., ENGLEDOW H.E., ANDERSON R.J. & COPPEJANS E. 2004. Where is the western limit of the tropical Indian Ocean macroalgal flora?: An analysis of shallow-water seaweed distribution patterns on the east coast of South Africa. Marine Biology 144: 51-59.

SINK K.J. & TIMM P.G. 2002. Report on shore-based sampling of invertebrate communities adjacent to the submarine canyons of the Greater St Lucia Wetland Park. Unpublished Report, South African Institute of Aquatic Biodiversity.