Krill on the MAR

Krill (Euphausiacea) are typical and abundant members of macrozooplankton, but their abundance and distribution remain poorly known even in the Atlantic Ocean. Bsc-student Tom Bech Letessier has analysed krill-samples from the 2004 "G.O Sars"-expedition!
Tom Letessier

Student of the month
Tom Bech Letessier

Describing the abundance and distribution of krill associated with the MAR

Fourth year Bsc Hon Marine Biology University of Aberdeen

On 27 January 2006, Letessier successfully defended his thesis

Figur 1: An example of Thysanopoda cornuta, and giant deep sea species

Krill (Euphausiacea) are typical and abundant members of macrozooplankton but their abundance and distribution remain poorly known even in the Atlantic Ocean. Krill are similar in shape and size to shrimps, but are different in that they have exposed gills, below their carapace. In many marine ecosystems krill function as direct connections between the primary producers (phytoplankton) and the higher trophic groups, like fish, whales and birds. Krill is in many waters a major source of food for pelagic fishes, including some that are commercially exploited commercial. It is important to determine which species are present on the  MAR and how abundant they are.

Figur 2: An example of Meganyctiphanes norvegica, a typical euphausiid in the North Atlantic 
Krill-samples were collected on the 2004 "G.O Sars"-expedition using a macrozooplankton trawl equipped with five cod-ends. This gear enabled us to collect samples from different depths and to describe the vertical distribution of the individual species. 17 sites were sampled, each situated close to the MAR.

The samples were identified over the summer 2005 at the Institute of Marine Research, in Flødevigen, Norway, looking at the shape of their eyes and rostrum. Each individual was weighed and measured, in order to describe the overall characteristics of the population.

An interesting finding

Figur 3: Population size frequency distribution of Thysanopoda cornuta. X-axis represent carapace length in mm. Y-axis represent frequency.

Eleven species were identified, some typical, like Meganyctiphanes norvegica and Thysanopoda acutifrons, and some rare, like Thysanopoda egregia and T cornuta. Statistical analyses indicated that species clustered in to three types of habitats, all in relation to the temperature of the water. Analyses of diversity also showed that the diversity increased with decreasing latitude, or probably rather as water becomes warmer moving southwards. 

Some of the results suggest that the species composition is different on either side of the MAR, an interesting finding in relation to major questions addressed by MAR-ECO!