JR161: Food webs in the Antarctic



Cruise Diary

Monday 27 November
Scotia Sea: Lat 55.32.34S, Long 44.46.56 W

Day 34 of the cruise JR161 aboard the British Antarctic Research Ship RSS James Clark Ross

Tom writes:

We are well into the science program now: every day, all levels of the food web are sampled and characterised with a view to understanding food-web dynamics in the Scotia Sea so that key species can be conserved and environmental changes can be mitigated. Sampling the various aspects of the food web require different sampling strategies and equipment.

Concentrations of nutrients determine the abundance and growth rate of phytoplankton, the primary producers that support the rest of the food chain. Nutrients need to be sampled well away from potential contamination caused by the ship. The tow-fish, which is a torpedo-shaped pumping system, allows clean surface waters to be collected.

Vertical profiles of nutrients and phytoplankton concentrations are collected using the CTD system.  As well as recording the physical nature of the water column, (temperature, salinity and density), samples of water from specific depths can be collected using 10-litre bottles.  Phytoplankton abundance and health is also recorded in vertical profiles using the FRRF, which is a system that records fluorescence emitted by photosynthetic pigments.

Consumers in the food chain are collected using net sampling systems. These are towed behind the ship at specific depth, as in the case of the LHPR, or vertically sample the water column, for example, the Bongo net system (so named as it looks a bit like a bongo drum). These nets sample zooplankton such as salps, which are filter feeders, jellyfish, myctohid fish, and of course krill by the bucket load.

Higher predators such as fish, birds, seals and whales are observed by BAS scientist Ewan Wakefield, ably assisted by the ship doctor. He makes daily observations of species abundance and behaviour (such as foraging and resting activities). Ewan’s observations help to understand the population size of many of Antarctica’s most famous inhabitants such as albatross.


More soon - please visit us again in a few days' time for the next installment....

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