Prince Edward Archipelago Research Articles

Observations of the island mass effect in the Prince Edward archipelago

The distribution of diatoms around the sub-Antarctic Prince Edward Island archipelago, as affected by the island mass effect is examined. Collections were made by continuous flow filtration of surface waters interrupted arbitrarily to give individual integrated samples. These were analyzed and the number of each species per cubic meter determined. Chlorophyll a was measured spectrophotometrically. Potential Primary Productivity was measured by the carbon-14 method. The major inorganic nutrients were analyzed by on-board use of an autoanalyzer. In May 1987 a massive bloom of Chaetoceros radicans was encountered in the island waters. The distribution was found to be closely correlated with high Chl a and potential primary productivity values. Of the major inorganic nutrients analyzed silicate was found to be inversely correlated with phytoplankton standing stock. Nitrate and phosphate showed a complex patchiness which was, however, obviously correlated directly with the phytoplankton bloom. The nitrate/phosphate ratio is shown to be variable with time and this may be attributed to the high phosphate content of the island leachate or differential phosphate depletion at time of bloom. A situation is described where, in 1983, the temperate diatom C. radicans and the Antarctic silicoflagellate Dictyocha speculum occurred in bloom stage in adjacent, separate communities. This suggests that separate watermasses of different origin were present at the time.

Quantitative differences between the insect faunas of sub-antarctic Marion and Prince Edward islands: A result of human intervention?

The two islands in the sub-Antarctic Prince Edward archipelago are only 22 km apart and are similar in age, geology, physiognomy and climate, yet their insect faunas show both qualitative and quantitative differences. During three visits in 1983 and 1984, the insect fauna of Prince Edward Island was sampled to compare with that of a survey carried out over one year on Marion Island. Two species of weevil (Curculionidae), previously known only from Marion, were recorded on Prince Edward for the first time. The biomass of two major groups of invertebrate decomposers (Lepidoptera and Curculionidae larvae) was significantly higher in heavily manured plant communities on Prince Edward than on Marion. Possible reasons for these quantitative differences are discussed. Although differences in species assemblage play a role, it is concluded that the effects of human influence on Marion Island may be paramount.