Friday, 31 October 2008

Small is beautiful (well ... sometimes)

While to date, much of the cruise blog has dealt with all things BIG, lets not forget about the small creatures of the ocean. Because of their small size, it is easy to forget about the zooplankton. Yet, in the oceans, it is these small animals that convert photosynthetic biomass into the animal biomass that ultimately feeds and sustains all of the larger predators. Without the zooplankton, most of the larger fish, whales and sea-birds could not survive!

Below are shown some of the strange and alien-looking creatures that are being picked up in our samples. (left: amphipod releasing egg; right: copepod; bottom left: ctenophore; bottom center: pelagic polycheate; bottom right: salp).

At the moment, zooplankton samples are being collected both by multi-nets (which can sample at different depths) and by Bongo (which collects larger amounts of zooplankton, but from the whole water column). Samples are being used to determine community composition, the geographical and depth distribution of different species as well as for stable isotope studies that investigate the importance of different zooplankton taxa as a food source for fish and squid.

In addition to being an important food source, zooplankton also harbor the juvenile stages of many commercially and ecologically important fish species. These are called the ichthyoplankton. During the life-cycle of most fish, it is the early juvenile stages that are most at risk from their environment. Due to their small size, the ichthyoplankton are at the mercy of the currents and individual larvae cannot protect themselves against predators. This is why the majority of fish die when they are very young (often >99%). It is frequently the success or failure of this planktonic life-stage that determines the potential success of adult fish stocks.

(left: fish larvae; center: fish larva; right: cephalopod larva)

text and images by: Sven Kaehler

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