The Terrestrial Macroinvertebrates of the Sub-Antarctic Iles Kerguelen and Ile de la Possession. Maurice Hulle

the first part, we present the general characteristics of the Îles Kerguelen and Île de la Possession: their geography, their climate and their main landscapes, which constitute the environment and the habitats of terrestrial invertebrates. We also dedicate a paragraph to the first scientific discoveries that marked the knowledge of the natural history of these islands, then briefly mention the current scientific themes concerning invertebrates, as well as the measures of protection that have been put in place since the creation of a natural reserve in 2006.

      In the second part, we present all species of macroinvertebrates. For each one, we evoke its status: endemic for the species found only on one of the two archipelagos, native for those present on other islands of the South Indian Ocean Province or other sub-Antarctic provinces, introduced for naturalized alien species and finally transient for species observed regularly but who are not reproducing on the islands. We also give information on known distribution, identification and elements of ecology. For the Archipel Crozet, we only present the fauna of Île de la Possession because the other islands have not been sufficiently explored to have such a thorough knowledge of the species.

1

      General Presentation

      1.1. Physical environment

      1.1.1. Location and size

      The sub-Antarctic Îles Kerguelen and Îles Crozet belong to the South Indian Ocean Province, as do the Heard and McDonald Islands, and the Prince Edward Islands (Marion Island and Prince Edward Island) (Figure 1.1). Only Heard Island and McDonald Island are located in the very cold Antarctic waters. The others are located above the Polar Front, separating the very cold Antarctic waters from the sub-Antarctic cold waters.

      The Îles Kerguelen are located at 49°21’S, 70°13’E (Port-aux-Français) and Île de la Possession at 46°24’S, 51°46’E (Base Alfred-Faure). They are respectively 3,250 km and 2,800 km from Île de la Réunion, 3,800 km and 2,400 km from South Africa and 1,900 km and 2,100 km from the Antarctic Continent. The Îles Kerguelen and Heard Island are located on the same continental shelf and are only 423 km apart. The Îles Crozet and the Prince Edward Islands are a second, more western subgroup.

      The Îles Kerguelen are 130 km long and 120 km wide. Their total area is 7,215 km² including 6,675 km² for the main island which is called Grande Terre (Figure 1.2). The Îles Crozet are composed of an eastern group of islands (Île de l’Est and Île de la Possession) and a western group about 110 km away (Îlots des Apôtres, Île aux Cochons and Île des Pingouins) (Figure 1.3). Île de la Possession, the only inhabited island, is much smaller than Grande Terre, at only 150 km².

      1.1.2. Topography

      The morphology of the Îles Kerguelen is mainly related to their magmatic origin and glacial erosion. Their geological history is long. The most ancient parts emerged about 35–40 million years ago and the last magmatic events date back to about 30,000 years ago. Mount Ross rises to the South at 1,830 m a.s.l. Part of the western and central regions is covered by an ice cap, the Cook cap, which rises to 1,000 m a.s.l. and covers about 550 km². The North (Péninsule Loranchet) and the South-West (Péninsule Rallier du Baty) are mountainous and rise to 1,260 m a.s.l. To the east, Péninsule Courbet constitutes a vast area of glacial erosion which is at a low altitude and is dotted with numerous lakes (Giret et al. 2003a) (Figure 1.4).

      Figure 1.1. South Indian Ocean sub-Antarctic islands

      Île de la Possession was formed between 8 million years ago and about 10,000 years ago for the most recent episodes (Delépine 1973; Giret et al. 2003b). The island culminates at 934 m a.s.l. at Pic du Mascarin. Large alluvial valleys (Vallée de la Hébé and Vallée des Branloires) open onto the north-east coast (Figure 1.5).

      Figure 1.2. The Îles Kerguelen

      Figure 1.3. The Îles Crozet

      Figure 1.4. Topography of the Îles Kerguelen

      Figure 1.5. Topography of Île de la Possession (Crozet)

A large part of the two islands, Kerguelen and Possession, is mountainous with an altitude of over 200 m a.s.l. Areas below 100 m in altitude represent 32% and 22% respectively on the Îles Kerguelen and Île de la Possession, and areas below 200 m represent 50% and 40%, respectively (Figures 1.4 and 1.5).

      1.1.3. Climate

      As with all remote sub-Antarctic islands, both the Îles Kerguelen and Île de la Possession have an oceanic cold climate, strongly influenced by the South Indian Ocean. They are located at the same latitude as France and therefore have an equivalent photoperiodic regime, with long days in summer and short days in winter. The mean air temperature for 1951–2013 at sea level was 4.8°C at Îles Kerguelen and 5.5°C at Île de la Possession (Figure 1.6). Seasonal variations are low, between 2°C and 8°C at Îles Kerguelen and 3°C and 8°C at Île de la Possession. Summer temperatures may temporarily reach or exceed 15°C. At the Îles Kerguelen, average temperatures increased by 1.9°C between 1964 and 1981 and then stabilized to around 5.2°C. Concomitantly, the number of freezing days has decreased from 130 days per year in the 1960s to 100 days per year now. At Île de la Possession, the number of freezing days is less than 60 per year.

      Air temperature decreases by approximately 1°C per 100 m increase in altitude (Pointe Suzanne and Port-Jeanne d’Arc, Kerguelen; M. Hullé unpublished data). This steep decay means that the thermal thresholds of development of many insects may be reached rapidly with altitude. The mean temperature is below 3°C from 200 m a.s.l., and insect life is consequently mainly concentrated on low-lying coastal areas (Figures 1.4 and 1.5).

      The average rainfall of Île de la Possession is high with 2,390 mm per year (Figure 1.6). On the Îles Kerguelen, there is a rainfall gradient from west to east. The west coast receives about 2,000 mm per year, and Port-aux-Français, located to the east, receives about 700 mm per year. At Port-aux-Français, rainfall oscillates between years of drought, for example, 1965 with 350 mm, and wet years, for example, 1987 with 1,150 mm.

      Winds are predominantly from the northwest, west and southwest. The average wind speed is 35 km/h on the Îles Kerguelen and 38 km/h on Île de la Possession. Strong winds are frequent. They are mostly from the northwest (Figure 1.7). The strongest gusts can exceed 200 km/h. They reach an average speed of 131 km/h on the Îles Kerguelen and 141 km/h on Île de la Possession. The number of days with winds above 100 km/h is 68 per year on the Îles Kerguelen.

      Figure 1.6. Climate at Port-aux-Français (Îles Kerguelen) (left) and Base Alfred-Faure (Île de la Possession) (right):