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Abstract

abstract

The shores of the volcanic islands Marion and Prince Edward are rocky and consist mainly of steep cliffs and beaches composed of boulders the sizes of which vary from a few centimetres to several metres in diameter. All the shores are exposed, those with a westerly aspect being severely so. Tidal range is 71 cm at springs, 21 cm at neaps. Swell heights on the east coast vary between 0 and 4 m. Salinity and temperature are typical of the area. Gales, high humidity, abundant precipitation and relatively little fluctuation of temperature characterize the climate. Basic zonation on plane sloping rocky faces consists of a black lichen (Verrucaria) zone in the supra-littoral, a Porphyra zone in the mid and upper littoral, a kelp zone of Durvillea antarctica in the lower littoral, and a lower red zone of delicate rhodophytes in the upper sub-littoral. Five transacts on different types of shore showed up departures from the basic pattern as a result of increased shelter, increased shade and decreased stability of substrata. The shallow sub-littoral is characterized by abundant corallines and other rhodophytes as well as phaeophytes of the genera Desmarestia and Durvillea. In parts large aggregations of the patellid Nacella delesserti were found. Pools are infrequent and biota in them vary with salinity. A wide variety of invertebrates are associated with the kelps Macrocystis and Durvillea. Trophic levels consist of primary producers and primary, secondary and tertiary consumers. Zonation conforms with the pattern noted on other sub-Antarctic islands except Tristan da Cunha. lt is not possible to adapt the universal scheme of zonation of Stephenson & Stephenson (1949) effectively to the pattern on Marion and Prince Edward. The biogeographical affinities lie within the sub-Antarctic and to a lesser degree within the Antarctic. The young age of the islands and relatively recent glacial and volcanic activity may account for paucity of species and low endemicity.