Friday, November 12, 2010

Zooplankton, miniature aliens

During the seamounts cruise, specialized nets were regularly deployed to capture zooplankton; tiny creatures that drift in the open ocean and feed predominantly on even smaller plant-like organisms called phytoplankton. Zooplankton comprise several groups of small pelagic animals such as krill, jellyfish and fish larvae and because they are incredibly abundant, form an integral part of the marine ecosystem. Notably, they are the primary food source for a variety of fish and sea mammals including the largest animal on earth; the blue whale. The objectives of the plankton netting survey were primarily to determine species diversity and to estimate abundance around seamounts. Workshop participants Riaan Cedras and Gildas Todinanahary calculate the volume of zooplankton biomass per unit of water trawled over the seamounts (the collection net was fitted with a water-flow meter). Then they extract random samples from each lot (there are too many creatures to count, never mind identify!) and stare through their high-powered microscopes for hours on end to identify the tiny creatures.

Picture 1: Gildas (left) and Riaan hold up examples of zooplankton captured over seamounts using ‘bongo nets’.

Picture 2: Examples of larger zooplankton species: A = Krill, B = Benthic Polychaete, C = Chaetognath, D = Pelagic Polychaete, E = Larvae of a fish and a squid, F = Amphipod (The movie “Aliens” was inspired by a similar species to this one!)

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