Currents are a decisive physical force in our oceans and act as transport systems for nutrients, plankton and also larger animals. Madeira’s waters are subject to a great deal of current movement; from the upwelling currents in the deep, bringing nutrients to the surface up to the surface currents transporting both prey and predator. The latter is frequently represented in the presence of Portuguese Man O’ Wars (Physalis physalis) at this time of the year, colonial cnidarians of the high seas that arrive in large numbers together with their predators. Predators of these Siphonophores include the pretty Bubble-rafting snail (Janthina janthina) and the lovely Loggerhead turtle (Caretta caretta).
Equally beautiful visitors, the Short-beaked common dolphins (Delphinus delphis), arrive to prey on the schooling fish feeding on plankton at the surface. Many cetaceans tend to transition between the shallower and deeper layers of our water column to pursue prey. The common dolphins belong to this who prefer surface prey. The Blainville’s beaked whales (Mesoplodon densirostris), a species we saw during the afternoon tour, spend most of their time in the deep, mainly to forage on deep-sea cephalopods, similar to the deep-sea squid we discovered at the surface this morning. Bottlenose dolphins (Tursiops truncatus), also dive to hunt squid and some species of dolphins even target squid as prey during pregnancy, to increase water intake.
So apart from bringing us nutrients and plankton, currents also bring all the wonderful creatures that depend on the input on this important physical force.
By Paula Thake
Sightings of the day
09:30 Bottlenose dolphins, Loggerhead turtle
13:30 Blainville’s beaked whales, Short-beaked common dolphins, Loggerhead turtle