Porcupine Marine Natural History Society Newsletter

Abstract

In the UK, the sunset cup coral Leptopsammia pruvoti is a species of particular marine natural heritage importance: it is nationally rare and has its own Biodiversity Action Plan (BAP). As a Mediterranean-Atlantic species, L. pruvoti is at the northern extreme of its range at Lundy. In south-west Britain, it is also found in the Isles of Scilly, off Plymouth Sound, in Lyme Bay and at Portland Bill. Of concern, however, is that there seems to be very little new recruitment to the present populations in south-west Britain and the number of individuals is declining. A population of L. pruvoti re-photographed at Lundy on an annual basis between 1983 and 1990 was found to have lost 8% of its individual corals, and between 1984 and 1996 part of this same population had declined by 22%. A number of possible factors affecting this decline are considered. L. pruvoti is thought to be slow-growing and long-lived. Recruitment (i.e. the successful production and settlement of larvae) is likely to be slow for a population at the limit of its distribution, with failure probably due to the water temperature being unsuitable for promoting gamete production and/or the synchrony of gamete release. Fertilised eggs have been found to survive for up to six weeks in aquaria, though planula larvae are likely to settle close to the adults within 24 hours. Besides the difficulties of recruitment, a number of organisms have been identified as possibly being responsible for the decline in the adult population. In particular, it is thought that certain boring organisms are capable of weakening the attachment of the adult skeleton to the substratum, increasing the likelihood of it becoming detached from the rock surface. Introduction The sunset cup coral Leptopsammia pruvoti is a Mediterranean-Atlantic species of particular marine natural heritage importance in the UK: it is nationally rare and since 1999, it has had its own Biodiversity Action Plan (UK Biodiversity Group, 1999). However, in spite of this ‘important’ status, there has yet to be any significant improvement in the measures required to ensure its continued presence in British waters. It remains unprotected under any UK or European legislation. Description and habitat Leptopsammia pruvoti is a scleractinian stony coral, typically found growing as single individuals or as ‘pseudocolonies’ (i.e. where a number of individuals are attached at their bases). Although the calcareous skeleton (or corallum) of the coral is described as being external, it is typically hidden from view by the bright yellow soft tissue of the polyp. The corallum is porous and grows as an inverse cone in shape, circular in young individuals though becoming more oval with age. Its distal end (from where the polyp’s tentacles extend) reaches 17 mm in width, and it grows to 60 mm in height (Manuel, 1988). This is noticeably taller than the more common Devonshire cup coral Caryophyllia smithii, which has a maximum height of just 15 mm (Manuel, 1988). L. pruvoti is found on shaded, bedrock habitats, such as on the underside of overhangs, in gullies or in caves, on open coast locations preferably in the lee P O R C U P I N E 2 0 0 4