Elemental composition of meso-zooplankton around the Crozet Islands (Southern Ocean) and their role in iron biogeochemistry
|Author(s)||Nedelec Florence, Fielding Sophie, Anderson Thomas R., Statham Peter J.|
|Meeting||Challenger Society Conference 2006, 11-15 September, Oban|
|Abstract||Zooplankton take up trace metals either from the surrounding aquatic medium or from their food. Accumulated trace metal concentrations therefore vary with the bio-availability of the metal in seawater and in the diet, and with the physiology of the organisms (Rainbow, 2002).
The Antarctic copepods Rhincalanus gigas, and Calanus sp. are herbivorous, and the amount of Fe assimilated by these grazers is affected by the iron status of their prey. In incubation experiments the Fe:C ratio of copepods was lower than their prey. This may be due to copepods having a lower iron demand than phytoplankton, or to iron not being efficiently assimilated (Schmidt et al., 1999). If iron is not assimilated efficiently and given that respiratory systems may require more iron than photosynthetic systems, copepods may potentially suffer from iron deficiency in iron-poor waters. A threshold Fe:C ratio corresponding to the estimated enzymatic requirement for iron may therefore be used to defin the iron status of copepods. If the Fe:C ratio is higher than the threshold value, then copepods may play a significant role in the recycling or export (in faecal pellets) of iron in the upper ocean. This work investigates the role that mesozooplankton play in the iron biogeochemical cycle within the ocean.
Zooplankton samples were collected during the CROZet EXperiment (CROZEX, 2004-2005) in- and outside the bloom observed around the Crozet archipelago (Southern Ocean), which is thought to be controlled by iron inputs. Iron, copper, and manganese concentrations in copepods and euphausiids were compared to reported values from different oceanic provinces. Values were then compared to the estimated enzymatic requirement or metals by crustaceans to determine their potential iron status, and the copepods body Fe:C ratio was discussed.