Our research this season involved a closer look at plankton. We have on occasion witnessed some heightened activity in our research area, and last season we made some daily surface plankton trawls to see if at least one of these might coincide with one of these suspected feeding events. In 2009 we witnessed during this heightened activity some barrel rolling and flared gills, suggesting feeding was happening. Sadly in 2010 when we began our trawls, no such event took place. So this year we opted for a broader look at the plankton issue, with once weekly trawls but at various depths and stations to get a better picture of what was happening on that day.

As luck would have it, during one of our weekly trawls, we witnessed another state of heightened activity in the area. Many mantas were seen breaching, with a breach every half hour or so throughout the day, and a lot of mantas swimming at a more rapid pace than normal with many many individuals at the surface. Our plankton trawls were carried out with great trepidation, with us concerned a manta would swim headlong into the nets. One this day, our samples showed a dense concentration of copepod (above) and we are looking at what species this might be. The amount of copepod in the water and the buzzing state of the mantas suggest this is at least one confirmed food source for them in the area.

The next micro life we note on our mantas is an abundance on some individuals of another type of copepod, this time an ectoparasite of the genus caligus ( image below). Some mantas seem completely clear of them, whereas other hold literal infestations. This could be for a variety of reasons, one of which could be that individual mantas do not spend a lot of time together in the same locations, and that sites such as Isla de la Plata are important aggregation zones visited for brief time periods. Could giant mantas be spending a lot of time leading a solitary existence? Pure speculation of course, but such issues if proven would further raise the importance of protection of such aggregation sites, and also help our understanding of mantas when they are between such places.

There is much speculation about what would happen to our oceans if we were to remove one or other key element. Some studies have indicated that this would be disastrous and change our oceans forever for the worse. One thing is for sure: a seemingly passive entity like the giant manta exists not by its own intent, but is part of a complex web of life, and we cannot say for sure what will happen if one part of that web is lost.