Boom and bust in starfish populations in a semi-enclosed Irish sea lough

Abstract

A 25-year study (1994–2019) of starfish in Lough Hyne, Europe’s first statutory marine reserve, in SW Ireland documents a highly fluctuating but overall proliferation of spiny starfish ( Marthasterias glacialis ), a virtual disappearance of the common starfish ( Asterias rubens ), and low-level fluctuations of cushion stars ( Asterina spp.). Although explosive recruitment booms and subsequent declines of M. glacialis in shallow water have been previously noted in the past two decades, the positive correlation of the cushion star population to that of the spiny starfish and the general decline of A. rubens have, to date, not been documented. A strong recruitment of Asterina phylactica was noted throughout much of the south basin in 2019 and a moderate recruitment of Asterina gibbosa occurred in 2017 and 2019. The 7-armed ‘super-predator’ ( Luidia ciliaris ) and the southern Bloody Henry ( Henricia oculata ) were seen episodically (at extremely low densities) on shallow subtidal shores. Subtidal surveys in 2019 indicated a paucity of all starfish species relative to the early 1980s. The ecological implications of ‘boom-and-bust’ starfish populations with consequent changes in predation in subtidal habitats could be far-reaching (e.g., appearance/disappearance of a ‘super-predator’ and the extreme fluctuations of a generalist feeder, the spiny starfish) but are currently under-studied and should be included in monitoring programmes in the reserve.

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