SAEON participates in Comoros basin research cruise

Caren George, Intern, SAEON Egagasini Node

Charine Collins — a PhD student based at UCT and supervised by Dr Juliet Hermes of SAEON’s Egagasini Node — and Caren George, an intern at the Egagasini Node were part of a group of eight trainee/junior scientists who participated in an ASCLME research cruise in the Comoros basin.
Charine Collins — a PhD student based at UCT and supervised by Dr Juliet Hermes of SAEON’s Egagasini Node — and Caren George, an intern at the Egagasini Node were part of a group of eight trainee/junior scientists who participated in an ASCLME research cruise in the Comoros basin.

The ASCLME is a scientific programme with international collaboration that aims to understand the physical and biological dynamics of the Agulhas and Somali Currents located on the east coast of Africa. The programme includes sampling of this region through research cruises. The sampling is done aboard the RV Dr Fridtjof Nansen, which has been made available by Norway’s Institute of Marine Research. The joint FAO/ASCLME/SWIOPF cruise in the Comoros basin took place from 5October to 3 November 2009.

The aim of the cruise was to describe the physical, chemical and biological characteristics of the Comoros Gyre which has been observed through satellite tracking between 10 and 15 degrees south — between Madagascar and Mozambique. This was the first time that in-situ measurements were taken in this region.

Map of the track for the Comoros cruise

Sampling of the physical and chemical characteristics of the Comoros Gyre was completed by using a Conductivity, Temperature and Depth instrument (CTD). This instrument sampled the water column for information such as temperature, salinity and pressure/depth. Niskin bottles as well as a fluorometer and oxygen sensor were attached to the CTD frame. The Niskin bottles collected water that will be analysed for nutrient contents such as silicate, nitrate and phosphate.

Biological characteristics were also sampled using the water from the Niskin bottles, where a specific amount of water was filtered to determine the phytoplankton concentration, and samples were taken for phytoplankton identification.

FISH barcode of life

Bongo nets were used to sample the water column for zooplankton such as fish larvae and crustacean larvae. The fish larvae collected in the bongo nets were photographed and preserved in alcohol in order for their DNA to be analysed. Surface trawls were also conducted in order to sample the juvenile fish in the area. This formed part of the FISH barcode of life project that aims to identify the juvenile stages of fish through DNA analyses. This information is very important as it will be used in the study of fish reproduction and distribution.

Multinets were used to sample the zooplankton at different depths in the water column. These samples were preserved for later identification by specialists. Meso-pelagic and demersal trawls were conducted when conditions permitted. The fish species, coral and other marine organisms were identified, weighed, measured and preserved where appropriate to determine the biodiversity and assess the fauna species size and composition.

Acoustic surveys

Acoustic surveys were completed around the Comoros islands to determine the distribution and abundance of the small pelagic fish shoals. Whenever the eco-sounder showed a change in signal, a trawl would be conducted to sample the fish aggregation.

The cruise provided many learning opportunities for Charine and Caren. They worked 12-hour shifts (6 hours on and 6 hours off) for the duration of the cruise and received training in all the sampling methods. The ship has a well-stocked library and they were able to catch up on some of the relevant literature.

They were also exposed to many different cultures, which provided them with an opportunity to learn about different ways of living and broaden their communication skills. The trainees, who came from Madagascar, the Comoros, France and South Africa had different scientific backgrounds and ranged from marine biologists to physical oceanographers and marine engineers.

Charine will be using the physical characteristic data collected on this cruise in her PhD, which focuses on the dynamics of the Comoros Gyre and how it may impact on the coral reef biodiversity in the region.

Some preliminary results

The data collected during the cruise is currently being analysed. Preliminary results of the juvenile fish stages after 19 trawls indicated that species identified totalled 151, the highest density of juvenile fishes occurred along the Madagascan coast, with fewer around the Comoros and even less along the coast of Mozambique (Kaehler, S. Unpublished). These results need to be corroborated with a more comprehensive sampling regime in this area. The information will be useful for decision-making in fisheries management in the area.

The cruise was deemed a success by all parties concerned. The trainees learnt a lot and gained valuable exposure to in-situ sampling techniques. The data collected is invaluable in the understanding of the marine environment of the Comoros.