Ecosystem services provided by Modiolus modiolus biogenic reefs

Abstract

Ecological field studies were carried out in situ on Modiolus modiolus biogenic reefs throughout the UK to quantify the functional importance of these habitats and the associated ecosystem services that they provide to society. Using a combination of techniques, including Underwater Visual Censuses (UVCs), video transects and pot fishing, the key species associated with M. modious reefs were found to be Buccinum undatum and Aequipecten opercularis. B. undatum catches were three times higher on the M. modiolus reefs compared to adjacent habitats and the UVCs showed that A. opercularis were five times more abundant on M. modiolus reef sites. By providing a habitat for these commercially important shellfish, M. modiolus reefs act as an Essential Fish Habitat and support sustainable livelihoods. M. modiolus are ecosystem engineers and can occur as dense aggregations, which form raised, three dimensional reef structures on the seabed. A new method was developed to measure M. modiolus biodeposition rates in situ and this provides the first evidence of the scale at which M. modiolus are able to enhance sedimentation and contribute to the downward flux of material to the seabed. M. modiolus biogenic reefs are recognised as biodiversity hotspots and protected in Marine Protected Areas. However, under controlled conditions when subject to seawater temperatures above those experienced in the wild, byssus thread production is compromised whilst biodeposition rates are modified also. M. modiolus reefs at the southern limit of their known distribution will continue to exist in the short term but with predicted increased seawater temperature, M. modiolus may not be able to function to their full ability. These habitats are vulnerable to physical impact from mobile fishing gear and the results presented here suggest that reef recovery through byssus attachment and clump formation would be limited, especially in southern populations. Management of protected reefs should take this into account and ensure that ecosystem resilience is maximised through well enforced management measures.