Floating Life

Dr. Barbara Niehoff is studying the key species of marine plankton communities to find out what strategies they use to be able to respond to changes in food supply or temperature. Her results contribute to assessing how climate change influences marine ecosystems. Even as a young girl, Barbara Niehoff was an active nature conservationist, for example, protecting the resting and breeding grounds of birds. The transition to marine biology occurred gradually during her studies. "The animals living in the Wattenmeer mudflats, off Sylt, where I wrote my Diplom thesis, genuinely fascinated me," she remembers. Today, Barbara Niehoff is an expert for the ecology of plankton organisms in the polar seas, the North Atlantic and the North Sea. Around six years ago, the biologist returned from the famous Woods Hole Oceanographic Institution on the US East Coast to take up her research at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven. As a Young Investigators Group Leader she built up her own team, which focuses on understanding the trophic interactions among plankton organisms. At the same time, she gained her postdoctoral  habilitation (venia legendi) at the University of Bremen, where she now gives lectures regularly. Plankton (Greek for "wandering or drifting") is the generic term for all organisms that are unable to swim against the water currents and so just let themselves be carried along. Plankton includes metre-long jellyfish as well as tiny algae and bacteria, plus the larvae of many fish or urchin species. Copepods, which are found in all the world's oceans, are one of the most important animal plankton (zooplankton) groups. Copepods are just as numerous in the sea as are insects on land, and play a major role in the ecosystem. They are a vital food source for many organisms, including commercially important fish species and even whales. The copepods themselves mostly feed on the single-cell algae (phytoplankton) that float in the upper, sun-drenched water layers, where they bind carbon dioxide from the atmosphere by means of photosynthesis. Some of this CO2 then sinks down into the deep with the copepods' faecal pellets. The question of "who eats who?" is thus even connected to what drives the oceans' "carbon pump" and crucial for our understanding of ecosystem functioning.

A major part of the scientific work is performed on board the research vessels. Using large nets, Niehoff and her staff collect the zooplankton specimens and already start studying them on board, counting the eggs and measuring the sacs, in which some species store fat as an energy reserve for overwintering. Especially in Polar regions, this means working long hours in the cold - often on deck of a lurching ship. Further analyses are then conducted in the lab on "terra firma", to determine, for examples, the animal's nitrogen and carbon content, fatty acid composition, and metabolic activities. Niehoff is then able to reconstruct what the animals have been feeding on and compare this with their reproduction success. "Temora longicornis", a copepod species which is very common in the North Sea, generally eats everything - even its own eggs if need be, for example when only few algae can be found in the water."

Species such as T. longicornis, which respond highly flexibly to feeding conditions, act as a buffer in the oceanic food web. In future, they might become even more important, because climate change is also beginning to have an effect in the North Sea. Increasingly, thermophile species are migrating to this habitat and are competing for food, which could in turn change the predator-prey structure in the ecosystem. "We know only very little about this," says Niehoff. This is an extremely relevant research field for the future.