Invasive alien plants (IAPs) are a significant threat to the biodiversity and ecological functioning of the sub-Antarctic Prince Edward Islands (PEIs); however, weed biological control has not yet been implemented as a management tool. The PEIs have had 23 alien plants recorded, of which several are considered beyond eradication and therefore could benefit from the release of safe and effective biocontrol agents. We used the South African Biological Control Target Selection (BCTS) system to provide a ranked list of the target species in order of priority for further biocontrol research. The highest-scoring species, and therefore those that should be considered first to be targeted, were Sagina procumbens and Cerastium fontanum. No biocontrol agents for IAPs have been released in any climate with as consistent low temperatures as in the PEIs, so the climatic compatibility of agents will be essential prior to any decision to release. However, with very few native species present on the PEIs, the programmes would involve limited host specificity testing, which would improve the feasibility and speed with which new biocontrol agents could be developed. Biocontrol may offer an environmentally safe and sustainable method of reducing the negative impacts of these priority species and thus warrants further investigation.

In the 1980s, penguins dominated the prey remains of sub-Antarctic skuas Stercorarius antarcticus breeding on Marion Island, whereas on neighbouring Prince Edward Island burrowing petrels made up >95% of prey remains in nest middens. This difference resulted at least in part from the impact of introduced cats Felis catus on Marion Island’s burrowing petrel populations. Cats were introduced to Marion Island in 1949, and prior to their eradication in 1991, they killed an estimated 450 000 petrels each year, greatly reducing the densities of petrels breeding on the island. A repeat survey of skua prey remains showed that penguins still dominated the prey of breeding sub-Antarctic skuas on Marion Island in the summer of 2010–11, two decades after cats were eradicated from the island. The proportion of penguin remains decreased slightly compared to 1987–88, but this might be expected given the decreases in penguin numbers on Marion Island over this period. Regurgitated pellets confirmed the dominance of penguin prey on Marion Island. Taken together with the decrease in skua numbers on Marion Island over the last two decades, our results suggest that there has been little recovery in the population of at least summer-breeding burrowing petrels since cats were eradicated.

We describe the habitat use of 22 male southern elephant seals (Mirounga leonina) satellite tagged at Marion Island between 2004 and 2008. While a few areas of increased utilization appeared to be associated with areas of shallower bathymetry (such as sea-floor ridges and fracture zones), seals in our study did not target other areas of shallow bathymetry within close proximity to Marion Island. Rather, most elephant seals foraged pelagically over very deep water where much variation was evident in diel vertical migration strategies. These strategies resulted in generally deeper and longer dives than what has been reported for male elephant seals from other colonies. No significant differences were recorded for dive durations or dive depths between adults and sub-adults. However, younger animals displayed a positive relationship between dive durations and age, as well as between dive depths and age, while these relationships became negative for older animals. Mixed model outputs suggested that seals increased their aerobic fitness as migrations progressed, enabling them to undertake longer dives. We conclude that Marion Island male elephant seals exhibit much variability in dive strategy and are seemingly capable of exploiting a range of different prey types occurring in various depth layers.

Seven community complexes have been described across sub-Antarctic Marion Island, amongst these fellfield that comprise low plant cover dominated by Azorella selago Hook. f. Azorella is considered a keystone species since it forms nutrient rich environments for microarthropod communities and epiphytic plants. Two distinct growth forms typify Azorella, namely discrete cushions and continuous mats. Whether these continuous mats normally consist of a single large cushion individual, or whether several individual plants merge, interdigitating to form a continuous area, remains unclear. As such, it is important to obtain some measure of Azorella growth dynamics before embarking on phylogeographic studies. Previous genetic studies indicated that several microarthropod species are significantly substructured across Marion Island, but it remains unclear whether similar subdivisions characterize Azorella. We used chloroplast sequence data (trnH-psbA) and amplified fragment length polymorphism (AFLP) to investigate these questions. No sequence variation characterized the trnH-psbA region in Azorella across Marion Island. In contrast, the AFLP results indicated that an A. selago mat comprises multiple individuals. We argue that mats can be formed through at least two processes namely fragmentation, where parts of the cushion plant die off creating open areas for the establishment of different individuals and/or high density of interdigitating individuals merging to form the mat. Fragment data further indicated significant substructure for Azorella across Marion Island (FST = 0.101, P = 0.01) and we attribute this to past vicariance.

The consumption of food by the four species of breeding penguins at the Prince Edward Islands is assessed on an annual and seasonal basis. Total annual food consumption was estimated at 880 000 t, of which king penguins accounted for 74%, macaroni penguins 21%, rockhopper penguins 5% and gentoo penguins <1%. Pelagic fish, almost entirely myctophids, were the most important prey (70% of total prey biomass), followed by pelagic crustaceans (18%) and cephalopods (11%). Demersal fish and benthic crustaceans accounted for <1% of total consumption, being consumed only by gentoo penguins. Peak demands of between 2 and 3.3 × 106 kg d−1 occurred from October–December when three of the four species were breeding, including the two demi-populations of king penguins. Food demand decreased to 1.2 × 106 kg d−1 during winter when only king and gentoo penguins were present. Much of the prey are presumably captured within 300 km of the islands. Assuming an even distribution of foraging effort within their respective foraging ranges, rates of food transferred to penguins in November ranged from 4.1 × 10−3 g m−2 d−1 for macaroni penguins to 1.24 × 10−2 g m−2 d−1 for king penguins. In mid-July, transfer rates to king and gentoo penguins were 3.9 × 10−3 g m−2 d−1 and 6.7 × 10−3 g m−2 d−1, respectively. The importance of pelagic myctophid fish to penguin populations at the Prince Edward Islands is clear.

Five populations of habitat-specific, morphologically distinct Algophagus mites (Astigmata: Algophagidae) were found to occur on the sub-Antarctic Prince Edward islands. Although these mites did not differ among themselves with respect to idiosomal setal characteristics, which were also similar to those of known sub-Antarctic Algophagus taxa, morphometric analyses revealed leg and idiosomal size differences. In addition to morphometric differences, leg setal positions and porose axillary organ structure, indicated that the morphotypes were taxonomically discrete. The taxa were found to include the known A. antarcticus Hughes, 1955, A. laticollaris Fain, 1974 (new status), a sub-species of A. semicollaris Fain, 1974, and two new species, A. brachytarsus sp. nov. and A. macrolithus sp. nov. With the exception of A. semicollaris, the taxa are described or redescribed in this paper. Morphological features of the females in particular, and notably leg proportions, claw dimensions, and apodeme positions, corroborate discrete terrestrial (A. brachytarsus and A. macrolithus) and aquatic forms (A. antarcticus, A. laticollaris, and A. semicollaris), and vary in a manner suggesting a functional relationship to habitat occupation by the various taxa.