The natural history of the Antarctic limpet Patinigera polaris (Hombron and Jacquinot)

approved: I Professor Patinigera polaris is tie only large invertebrate commonly found in the littoral zone of Arthur Harbor, Anvers Island, Antarctica. From January 1970 through March 1971 the general ecology and physiological ecology of this large patellid limpet was studied. Patinigera polaris is found in the littoral zone at Palmer Station throughout the year during both high and low tides. The largest live limpet collected was slightly over 58 mm in length. The largest limpet shell found in the Arthur Harbor vicinity was 61 mm in length. Its population density is lower during the austral winter than during the austra]. summer. Patinigera polaris responds to the tide by moving with it up and down the littoral zone. By moving into crevices and cracks in the granitic littoral zone, P. polaris may be protected from thermal stress and the crushing effects of sea-borne ice. Littoral and upper-sublittoral limpets in exposed situations have thicker, more robust shells than do sublittoral limpets. The morphological variations in the shell of P. polaris may be due to the selective pressures of ice. The development of the thick shells appears to be in response to the environment in which the animal occurs rather than a strictly inherited trait. Redacted for Privacy Respiration rates I or ni era polaris are high. For the median size class (21-35 mm) an oxygen consumption rate of 22.2 l O/hr/g was determined. Patinigera polaris is a non-selective herbivore. Major predators of P. polaris include the Dominican Gull Larus dominicanus, and the Sheath Bill, Chionis alba, the asteroids Diplasterias brucel, Odontaster validus, and Perkuaster sp. , and to a less extent, the fish Notothenia coriiceps, the echinoid Sterechinus neumayeri, and the pycnogcnids Colossendeis robusta, C. megalonyx and Pentanymphon sp. Larus dominicanus appears to take the greatest numbers of limpets of all the identified predators. Patinigera polaris exhibits a positive phototactic response which is augmented by very low water pressure gradients or currents. The chemical oceanographic conditions of both littoral rock poois and surface water of Arthur Harbor showed very marked seasonal variation in dissolved oxygen, pH, temperature, and salinity. These variations are related to intense seasonal primary production, ices and fresh water run off The tides in Arthur Harbor are of the mixed, dominant semidiurnal type. The mean tide level is +0.73 m above mean lower low water, The maximum range observed during 1970 was 1.89 m. The minimum range of 0.02 m. The principal tidal harmonic constants were determined for Arthur Harbor. During the austral winter, shore ice forms protective barriers between the fauna and flora of littoral rock pools and the low air temperatures and crushing forces of sea and swell transported ice. Littoral rock pools which occur below this ice foot are often linked to the subtidal by ice-free corridors. These corridors allow fresh sea water to circulate in the pools on the return of the tide. Estimates of growth rates and absolute growth were made by marking and releasing over 600 limpets from different depths. After almost a year, 31% were recaptured and remeasured. Up to a length of approximately 25 mm, growth rates are relatively high (2-5 mm per year) and approximately linear. For larger individuals the rate of growth declines sharply up to a length of about 38 mm. Individuals above 38 mm exhibited changes in length which were generally less than the accuracy of the vernier calipers. It is suggested that Patinigera polaris can live to be in excess of 60 years old, Linpets 60 mm in length may be older than 100 years. Reproductive maturity occurs at an age of four years and there is no upper age or size limit on fecundity. The parental stock of Patinigera polaris is probably the southern South American limpet Nacella mytilina which has been found in deposits of the Eocene Age. The break-up of Gondawanaland in the vicinity of South America and Antarctica during the Late CretaceousEarly Tertiary, and consequent interruption of gene flow led to the separation of the N. j4jna population along the Scotia Ridge region. Selection for species tolerant to the Antarctic environment probably contributed to the evolution of Patinigera polaris. The most striking aspect, not only of the life history of Patinigera polaris, but also of its ecology and physiology, is that this limpet is not greatly different from limpet species inhabiting warmer climates. Patinigera polaris differs from those species in two major aspects: its extremely slow growth rate and its extended iongevity. The range of this species' tolerance to a variety of thermal and osmotic stresses is similar to that of other limpet species throughout the world. The life history features of P. polaris suggest that it is a K-strategist associated with density dependent population regulation. The Natural History of the Antarctic Limpet Patinigera polaris (Hombron and Jacquinot)