Overgrown with corals on the top close to the surface the St. Lazarus Bank has been specified sometimes as an atoll. But the reefs do not reach the surface and back-reef lagoons typical for atolls are lacking. The central, table-like platform of the seamount has a diameter of ca. 15 x 8 nm, ranging from six to about 60 m depth on the margins and falling down rapidly to more than 2000 m on all sides. This abrupt topography is being hit in the north by the powerful Mozambique current creating eddies and a circulation system (at about 1 m sec-1 speed) that may contribute to retain pelagic eggs and larvae on the platform. And indeed in each of the pelagic trawls performed in the area of this seamount a number of larvae or juveniles belonging to at least seven fish species were collected, among them also typical reef dwellers.
Even more exciting was to directly observe indications of ongoing reproductive behavior like pair formation and courtship displays in three species of coral reef fishes. Recordings (see video clips) made with the new campod shows a male and a female of the spotted sandperch, Parapercis punctulata (family Pinguipedidae, sandperches), sitting close together on a brain coral. The female differs from the male in having three black spots on the anterior belly. In the same area of the platform at about 30 m depth a pair of the sunburst butterflyfish, Chaetodon kleinii (Chaetodontidae, butterflyfishes), a reef-fish that feeds on coral polypes was observed. And, just a few meters apart, a courting pair of firegobies, Nemateleotris magnifica (Pteleotridae, dartfishes), were flicking their elongated first dorsal fins. It’s wedding time on top of the seamount. This bound is formed forever, as the firegoby is strictly monogamous like many butterflyfishes, too.
Large exemplars of predatory fish species were observed by campod or collected by various fishing methods including snappers (Lutjanidae, e.g., the red snapper Lutjanus bohar, collected both by trap and handline), jacks (Carangidae, e.g., bigeye trevally, Caranx sexfasciatus, collected by handline), or murray eels (Muraenidae; e.g., the laced murray), Gymnothorax favagineus (attains three m in length, males are often territorial and aggressive) observed with the campod.
Pelagic trawling during night resulted in collection of a considerable number of lanternfishes (Myctophidae) over the plateau and on its flanks down to 500 m depth (e.g., Myctophum spinosum) with several species being collected in this area for the second time after the 1978 cruise. The identification of these mesopelagic fishes is challenging, more than 25 species were collected by one deep trawl haul. After preliminary taxonomic studies on board this material shall be transferred to the fish collection of the South African Institute of Aquatic Biodiversity, Grahamstown, South Africa, for further examination. There is always a high chance that material from such unexplored and highly diverse areas like St. Lazarus bank proofs to be new for science.
By Bjørn Serigstad, Franz Uiblein and Bernerdino S. Malauena