The Ecology of Lough Ine

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Abstract
The Western Trough of Lough Ine [Scotland, United Kingdom] forms a trench between 40-50 m in depth. It communicates with the inflow area and rapids only via the main body of the south basin, which has a maximum depth of about 25 m. Thermal stratification of Lough Ine became established from the end of March and broke down in the middle of Nov. There is a steep thermocline in summer, extending from -20 to -30 m and centered at about -23 to -25 m. It is inferred that the level of the thermocline is determined by the topography. There is a severe depletion of the dissolved O2 of the hypolimnion during the period of stratification, with levels of less than 5% saturation in late summer. The mud surface turns black. Some stagnation can also occur in winter. The flora and fauna of the mud bottom of the Western Trough was investigated by grab sampling and by diving, and the major bottom facies of the whole lough was mapped by divers. A characteristic mud-burrow zone occupies the bottom at -17 to -25 m, with Nephrops norvegicus, Calocaris macandreae, Turritella cummunis, Amphiura chiajei and associated species. From -25 m downwards there is a spionid zone characterized by a carpet of upwardly projecting tubes of Pseudopolydora pulchra with an associated fauna. The tubes were inhabited by living P. pulchra and reached densities averaging about 8000/m2 in July. By mid-Aug. no living animals except the burrowing lamellibranch Corbula gibba were taken in grab samples from depths exceeding 30 m. Examination by the divers showed that from -28 m downward the tubes had collapsed and were disintegrating. No living animals were found in grab samples from -30 m downwards in Sept. Groups of crabs were suspended at various depths in the Western Trough for 2 days in survival tests. There was good survival at all depths in July, but in late Aug. almost all from below the thermocline were dead when retrieved. O2 deficiency (possibly with some accumulation of H2S) regularly destroys the benthic fauna in late summer.