STABILITY IN MEDITERRANEAN-ATLANTIC SESSILE EPIFAUNAL COMMUNITIES AT THE NORTHERN LIMITS OF THEIR RANGE

A marine monitoring programme was established by the UK Nature Conservancy Council in 1984 at the Lundy and Isles of Scilly proposed marine nature reserves in southwest England to help determine their management requirements. The aim was to provide information on important marine habitats, long-term changes in community structure and the life history (particularly longevity and growth rates) and ecology of species of high nature conservation interest. The benthic studies mainly concentrated on communities of Mediterranean-Atlantic species which are at or near the northern limits of their distribution in the study sites. Many of the species and communities studied are very stable, long-lived and slow recruiting. They are, therefore, also vulnerable to damage. Southern species of cup corals were found to grow slowly and reproduce very infrequently, with populations showing a general decline during the study period. Species of sponges and southern soft corals also typically displayed very slow growth. Periods of above or below average sea water temperature are considered to be particularly important factors affecting the persistence of Mediterranean-Atlantic species, with higher temperatures linked with recruitment events in scleractinians and unusually cold temperatures appearing to stop growth or even cause contraction in colony size or death in some species, such as certain sponges. The results illustrate the importance of abnormal climate years on species at the geographical limits of their distribution. The extreme stability of these communities of high nature conservation interest has implications for reserve management. Because of their poor capacity for recovery, long-lived and slowly recruiting Mediterranean-Atlantic species are considered to be particularly vulnerable to minor and infrequent damage, which might readily be overlooked in other communities, as well as to more major and widespread damaging events. Monitoring at Lundy and the Isles of Scilly will act as important control sites for monitoring work in the marine environment elsewhere around Britain.