Long-term fluctuations in intertidal communities in an Irish sea-lough: Limpet-fucoid cycles

Long-term cyclical changes in rocky shore community structure were documented over two decades at sheltered shores in Lough Hyne Marine Reserve, County Cork, Ireland. Three peaks of abundance were recorded for the limpet, Patella vulgata (1990-5, 2002-6 and 2010-14) with oscillations that varied in amplitude and frequency among sites. The cover of the fucoid Fucus vesiculosus varied inversely with limpet abundance and showed the strongest negative correlation with a lag time of 0–2 years. The species complex Fucus spiralis/guiryi showed a weaker correlation with a lag time of 1–2 years. Two other fucoid species showed no such negative correlations despite their close proximity to limpets within the lough's compressed tidal range. There was no relationship between overall barnacle cover (dominated by Austrominius modestus ) and the limpet-fucoid cycles, suggesting that the shelter provided by A. modestus for algae to escape from limpet grazing pressure may not be necessary for these cycles to occur on wave-sheltered shores.