Trawling for Plankton
In Mozambique we started a new marine research project. We are studying the ocean’s largest fishes by researching one of the ocean’s smallest components – plankton. Plankton is the name given to any organisms that are moving with the water column. Most of these are small but the plankton also includes larger organisms such as jellyfishes. They can be phytoplankton – the plants of the ocean, which photosynthesize, or zooplankton – the animals that eat the phytoplankton. In turn, zooplankton is eaten by larger organisms such as whale sharks and manta rays. See how it all comes together?
From this study we hope to help elucidate the diversity of plankton in the coastal water off of Tofo, Mozambique, and compare differences in the plankton in other locations. The aim of this research is to see common plankton contents where large planktivores are feeding, which will help us predict planktivore sightings and conserve their feeding areas. Furthermore, this research will help us understand their movements across the ocean, specifically whether they are migrating to obtain different food or nutrients.
Dr Rowena White, a plankton specialist, will be spending the next few years looking at the plankton from areas around the Indian Ocean where whale sharks and manta rays are known to feed. Rowena has several collaborators from across the Indian Ocean; All Out Africa is her collaborator in Mozambique.
In order to compare the samples gathered across the different areas it is very important that we strictly adhere to the same protocol for sample collection and storage. Rowena’s plankton sample collection protocol involves trawling for plankton at five meters for 10 minutes using a special net and collection mechanism. The exact rate of water flow is measured using a flow meter. The sample is collected at the same point once a week on the ocean safari. The plankton are then washed carefully into a sample container and stored for further processing once we reach land.
A second plankton trawl at the surface will be conducted once per month on the ocean safari to look at the diversity of species across the water column. Over time we will learn if there are variations in the plankton composition of the water column when whale sharks or mantas are feeding as opposed to when they are absent or not feeding.
Once back to shore, the sample is further processed by washing it carefully through a fine 60-micron mesh. Then the sample is washed into a storage jar and stored in buffered formalin to preserve the contents, labeled fully and kept in a cool dark place. It is important to thoroughly wash the nets and equipment and store it for the next collection trip.
All Out Africa thanks Peri Peri Divers for their keen interest in marine biology and for facilitating this research on their boats. If you or someone you know would fancy studying how marine food chains connect different organisms, join us in Tofo via our Whale Shark Conservation programme!