Tide pools of Carrigathorna and Barloge Creek

Abstract

An ecological account is given of tide pools on the remote promontory of Carrigathorna, formed of Devonian slates on edge, on the open Atlantic coast, and on a sheltered but otherwise similar slate reef nearby. Both sites are at the entrance to Lough Ine, County Cork, Republic of Ireland. In addition to its immediate ecological concern, this study is intended to provide a basis for comparison in the future, in case of climatic or other environmental change. The pools have been charted, and their levels and dimensions are specified. They range from 0.3 to 5 m in depth, and the largest holds over 100 m3. The highest studied are only replenished by wave-wash, and the lowest are never completely disconnected from the sea. As is generally recognized, various environmental conditions are subject to wider fluctuations in tide pools than in the sea. Examples are shown of diurnal and tidal changes in temperature and pH, and some readings of oxygen content and salinity are given. The deeper pools remain cool below even when their upper waters are warmed, and this is probably important in permitting the survival of Laminaria forest within them. Temperatures of over 25 °C were attained in high-level pools, and pools with much of the green alga Enteromorpha reached pH 10. Salinity ranged up to 40 ‰ in the highest pools, and oxygen tensions to nearly twice the saturation level. Five ecological facies characterized the tide pools of the open coast, from high level downwards: Enteromorpha scrub, smooth encrusting coralline alga scoured by limpets, Corallina scrub (extending into Laminaria forest as undergrowth), Laminaria forest, and Dictyota scrub (with other non-calcareous algae). Enteromorpha covered the bottoms of tide pools just above the highest tides, where the number of species present was small but in some cases the number of individuals very large. The extension of Enteromorpha to lower pools is largely prevented by limpets, themselves probably limited upwards by extreme conditions of temperature, pH, salinity etc. The extension of limpets in any numbers to lower pools is probably limited by the tough calcareous alga Corallina officinalis . Laminaria forest takes over in mid-tidal pools where the water is deep enough, and Corallina gives way at depth to Dictyota and other algae, possibly in relation to reduced illumination. The small Laminaria-eating limpet Patina pellucida reaches higher numbers in the shelter of tide pools than in the sublittoral Laminaria forest of the nearby open coast. The fauna associated with Corallina has been studied by means of 0.20 m x 0.15 m quadrats taken from many of the pools. Quantities of epiphytic coralline algae, spirorbid tube-worms, and epizoic Bryozoa have been assessed from 10 g aliquots of Corallina , and numbers of other species have been determined from the complete quadrat collections. Many progressive changes from high-tidal to low-tidal pools are described. One aberrant pool at Carrigathorna drains by slow leakage over the period of neap tides, and is occupied by a blanket of a blue-green alga ( Lyngbya confervoides ) populated by larvae of Halocladius fucicola (Diptera, Chironomidae). It is to be expected that L. confervoides (like other blue-green algae) can survive considerable desiccation. A pool on the more sheltered reef (‘Urchin Reef’) in the mouth of Barloge Creek contains much of the brown alga Cystoseira nodicaulis , which together with Corallina accommodates extremely large numbers of individuals of many invertebrate species. This sheltered pool, replenished on every tide, acts as a rich marine aquarium. Crevices in the bottom hold over 100 of the sea urchin Paracentrotus lividus , of which only a few specimens are found on the open coast. The hard slate probably does not allow this urchin to burrow, so that it probably cannot resist storms on the open coast. A large population exists in Lough Ine in shallow places where the water warms up in summer, and this population possibly provides larvae for settlement. The occurrence is recorded of 111 species of algae and of 198 species of algae and of 198 species of animals in the tide pools.