Macquarie Island is an Australian subantarctic island and a unique case of seafloor that has risen above sea level (Selkirk et al., 1990). As part of the Macquarie Ridge, the island is formed of oceanic crust from tectonic emergence and has never been attached to any other landmass (Varne et al., 1969; Selkirk et al., 1990). This rare formation draws researchers to study the remote aspects of the island, its distinctive geology and the evolution of its biodiversity.
Macquarie Island's climate is strongly influenced by the Southern Ocean. Conditions are cool, moist and windy, with a mean maximum daily temperature ranging from 8.8° C in January to 4.9° C in July (ONERC, 2009). The temperature is largely determined by atmospheric pressures above the Southern Ocean, which can cause warm northeasterly or cold southerly air flow over the island (Adamson et al., 1988). The island is mainly exposed to westerly surface winds and often endures cyclones and gale force winds (Selkirk et al., 1990; Eriksson et al., 2013). Wind, cloud cover, precipitation and relative humidity vary little throughout the year (Selkirk et al., 1990). Annual mean precipitation reaches 920 mm per year and is well distributed throughout the year, with about 312 days of rain and 80 days of snowfall per year (Selkirk et al., 1990; ONERC, 2009). The island is typically covered by clouds and only receives an average of 2.2 hours of sunshine per day (ONERC, 2009).
Marine, glacial, and erosional processes have all aided in the development of Macquarie Island (Duncan & Varne, 1988). Today, the island consists of an undulating plateau 300 metres above sea level and dotted with several lakes and streams (Lugg et al., 1978; Selkirk et al., 1990). The plateau has a steep slope to reach the low-lying coastal fringe of cobbled and sandy beaches interspersed with basalt rocks (Selkirk et al., 1990; Scott, 1994; Eriksson et al., 2013). These rocks were formed by crustal accretions during the seafloor spreading and have properties that correspond with those of ocean-floor basalts (Duncan & Varne, 1988; Selkirk et al., 1990). Macquarie Island is essentially formed of fault-bounded blocks derived from different crustal levels (Varne & Rubenbach, 1972). Due to its location on an oceanic ridge, the island is subject to frequent and severe earthquakes and consequently, erosion is very active (Selkirk et al., 1990).
Macquarie Island is a subantarctic convergence site and a biological hub for plankton, birds and fish. The plants and animals that inhabit this island are fascinating for their origins via long-distance dispersal and for their survival and productivity in a remote and harsh environment (Selkirk et al., 1990).
i. Land Biodiversity
Plant biodiversity is limited by geographical isolation, low temperature, and low light levels. However, despite these limitations, the plants on the island use the available light efficiently and productivity is high (Selkirk et al., 1990). There are 41 species of vascular plants, 150 moss species, 150 lichen species, 260 fungi species and more than 120 freshwater algal species present on Macquarie Island (Selkirk et al., 1990; ONERC, 2009). Plant communities present on the plateau and in coastal areas are all low lying; tall tree species are absent as they cannot survive the harsh environment (ONERC, 2009). Snowfall on the island is minimal and does not stay on the ground for long, so vegetation is able to occupy a substantial surface area (Selkirk et al., 1990; Tweedie & Bergstorm, 2000).
ii. Sea Biodiversity
Macquarie Island is an important sanctuary for birds, as more than 3.5 million sea birds nest and reproduce on the island every year (ONERC, 2009; PWS, 2013). In the subantarctic, penguins account for the majority of total bird biomass with four different species occurring on Macquarie Island: the King penguin (Aptenoclytes patagonicus), Gentoo penguin (Pygoscelis papua), Eastern Rockhopper penguin (Eudyptes chrysocome filholi), and the Royal penguin (Eudyptes schlegeli) (Croxall & Prince, 1980; ONERC, 2009). Eastern Rockhopper penguins sometimes join or mingle with the Royal penguin colonies, and there has been controversy over whether the Royal penguins are an endemic species or a subspecies of the Eastern Rockhopper penguins (Selkirk et al., 1990; ONERC 2009). Furthermore, there have been recent declines in the penguin colonies, especially the Eastern Rockhopper, which may be attributed to climate change (Selkirk et al., 1990; ONERC, 2009).
There are four species of Albatrosses that nest on the island, with the most abundant being the light-mantled sooty albatross (Phoebetria palpebrata) calculated at 2,000 couples (ONERC, 2009). Other seabirds include Antarctic terns, Macquarie shag, Northern and Southern Giant petrels, skuas, gulls and ducks (Selkirk et al., 1990; ONERC, 2009). The only mammal indigenous to Macquarie Island is the seal. The southern elephant seal (Mirounga leonina) has the largest population on the island, as 80,000 elephants seals arrive annually to breed and moult (Goldsworthy et al., 2009; PWS, 2013). The re-colonisation of fur seals slowly began in the 1940s with three species now present; the Antarctic (Arctocephalus gazelle), the subantarctic (A. tropical) and the New Zealand (A. forsteri) fur seal (Goldsworthy et al., 2009).
iii. Introduced Species
Many species were introduced in the 19th century, including cats, rabbits, rodents, a wingless bird endemic to New Zealand (the weka) and possibly three plant species (Selkirk et al., 1990; ONERC, 2009). While sealers accidentally left some of these behind, the wekas and rabbits were deliberately introduced for a food supplement (Selkirk et al., 1990) for human inhabitants. The Tasmania Parks and Wildlife Service successfully eliminated the cat and weka populations by 2000; however rodents and rabbits are still a major problem (ONERC, 2009; PWS, 2013). A myxomatosis virus was deliberately introduced into the rabbit population to eradicate them, but they developed a resistance and reached a population of more than 100,000 individuals (ONERC, 2009). The introduced species are a threat because they damage local plant species and upset the ecological balance on the island (Selkirk et al., 1990). An eradication program is currently underway.
Macquarie Island is located at 54°37 South and 158°52 East (ONERC, 2009). It is situated halfway between Australia and Antarctica; north of the Antarctic Polar Front and approximately 1500 km southeast of Tasmania (Slip & Burton, 1990; ONERC, 2009). The island is elongated in a north-south orientation, stretching 34 km along the Macquarie Ridge and varying in width from 250 metres to a maximum of 5 km (Selkirk et al., 1990; Slip & Burton, 1990; Flynn & Williams, 2012). The subantarctic Front and the Antarctic Polar Front collide perpendicularly to Macquarie Ridge, causing Macquarie Island to be a location of upwelling and elevated chlorophyll levels and consequently, a biological hub for feeding animals (Flynn & Williams, 2012).
Figure 1: Map of Macquarie Island including research stations, walking tracks and topography (PWS, 2013).
Macquarie Island was officially discovered on the 11 July 1810 by British captain Frederik Hasselborough on-board the HMS Perseverance and named in honor of the New South Wales governor, Lachlan Macquarie (ONERC, 2009). The discovery immediately brought sealers to the island, where they brutally hunted local fur seals into extinction in just ten years (Shaughnessy & Fletcher, 1987; ONERC, 2009). When the pelt industry was no longer profitable, the sealers turned to hunting elephant seals to make oil from their blubber, and then eventually to penguins (ONERC, 2009). The ruthless slaughter and exploitation for pelts and oil continued until 1920 (Selkirk et al., 1990; ONERC, 2009). Around this same time, a territorial dispute broke out between the Tasmania colony and the New Zealand colony until Tasmania was awarded sovereignty (ONERC, 2009). Macquarie Island still remains politically a part of Tasmania and is still part of the Huon Township (Selkirk et al., 1990).
Research Establishment & Tourism
In 1911, Sir Douglas Mawson established the first Macquarie Island scientific base and worked over the next 20 years to declare the island as a wildlife sanctuary (ONERC, 2009). In 1977, the island formally became a UNESCO World Heritage Site and listed as a Commonwealth Marine Reserve in the Southern Ocean (ONERC, 2009; Flynn & Williams, 2012). Today, the Tasmanian government’s Parks and Wildlife Service manages the island as a nature reserve and manages the World Heritage values on behalf of the Australian government (PWS, 2013). An ANARE - define - station now covers Mawson’s old base and six field huts are scattered around the island, connected by a system of footpaths (Selkirk et al., 1990). Research takes place under strict Tasmania State Legislature policies, with modern marine research focusing on distribution and abundance of various species, trophodynamic interactions, debris accumulation, rare geological features, as well as many other projects (Selkirk et al., 1990; Flynn & Williams, 2012; Eriksson et al., 2013). Macquarie Island has also recently become a popular tourism destination for voyages heading to Antarctica. Visitors must apply for a permit to visit the island, with limitations on the number of visitors per season as well as the number of visitors ashore at any time (AAD, 2013).
Tourists on Macquarie Island, Image © Greg H/Australian Antarctic Division
Inter-annual temperatures at Macquarie Island have increased by 0.3°C over the 50-year period from 1948 to 1998 (Tweedie & Bergstorm, 2000). This information was combined with evidence from Mawson’s expedition to conclude that there has been a 0.6° increase from 1912 to 1998 (Tweedie & Bergstorm, 2000). In addition, Tweedie and Bergstorm (2000) also predict an additional 0.2° increase in temperature by 2030. Higher levels of precipitation have also been recorded and may be periodically concentrated (Selkirk et al., 1990; ONERC, 2009). These are some of the only climate projections available for this area and are therefore subject to bias, yet it still remains clear that global warming is negatively affecting Macquarie Island (Davies & Melbourne, 1999; ONERC, 2009).
There has been an increased human presence in the subantarctic due to research, fisheries and especially tourism. More vessels venture south every year to Macquarie Island and bring with them an increased probability for damage, pollution and oil spills (Ruoppolo et al., 2013). To prevent any problems associated with human impacts, there is a demand for logistical support and strict agreements between vessels on how to deal with any unwanted circumstances (Ruoppolo et al., 2013)
The future of Macquarie Island will be affected the most by climate change and invasive species. Temperature increases and environmental change could force species to migrate from the island to colder regions, while those species whose distribution is normally high-latitude may suffer endangerment (Kiefer, 2002). Changes in precipitation levels will have significant consequences, especially changes in the uniform distribution of precipitation (ONERC, 2009). For example, heavy concentrated rainfall is not very common on the island, but if it does start to occur it could potentially increase erosion of slopes and flooding of seabird’s nests (ONERC, 2009).
Climate change may also increase the threat of introduced species by promoting their expansion and reproduction, increasing their pressure on the environment (Davies & Melbourne, 1999; ONERC, 2009). Rabbits have already degraded many plant communities via grazing and have had indirect consequences on nesting sites for birds by upheaving soil layers and causing erosion (ONERC, 2009; PWS, 2013). Landslides are already very common due to the landscape and soil nature, and rabbits increase landslides even more by decimating the plant cover (ONERC, 2009). In addition, following the eradication of cats, rabbits and rodents were able to increase populations and colonize new spaces, while reducing the availability of nesting sites for birds (ONERC, 2009). This shows how eradication can be very complex as it is hard to determine interdependencies and indirect effects that may be caused (Raymond et al., 2011). Research has been conducted in order to help establish proper management practices for eradication of these species and promote a healthy future and habitat for Macquarie Island. In 2007, the PWS began a seven-year eradication program to attempt to restore the island’s natural balance (AAD, 2013). Their efforts have appeared successful and just five rabbits are estimated to remain on the island (AAD, 2013). Eradication efforts will continue until the invasive species have been completely removed.
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