Our shared sea

Mechanisms of ecosystem change in the Western Channel

Climate change, artificial habitats and biological invasions

This section of the Marinexus programme addresses two major environmental concerns, climate change and biological invasions, which both require the broad geographical perspective provided by cross-Channel collaboration and which potentially interact. Two habitats are targeted, one natural and one man-made: rocky shores and harbours/marinas. In both, non-native species are prevalent, and rapid changes in the geographical distributions of many species are occurring.

The western English Channel is a zone of changeover between northern (Boreal), and southern (Lusitanian) marine species. However, the geographic ranges of species are changing in response to climate change. The laboratories in Roscoff and Plymouth have both studied distributions and geographical ranges of species for several decades, and are combining under Marinexus to adopt a common detailed approach, the MarClim protocol, to provide a fully integrated picture of changes in our shared geographical region. This focuses on intertidal species of invertebrates and macroalgae. One early finding from monitoring on the shore is that the cold winter in England in 2009/2010 resulted in heavy settlement of the cold-water native barnacle Semibalanus balanoides. This species has been rapidly declining in SW England throughout the 2000s and its southern range limit has retracted to the Bay of Biscay region in France. The strong recruitment in spring 2010 may have restored populations nearing localised extinction. The recruits appeared to have survived in high densities at local sites revisited during summer 2010.

Harbours and marinas are thought to be key habitats for the establishment and spread of introduced species. These man-made habitats were thus selected for a series of experiments and surveys in the Marinexus programme. Sites were selected in NW Brittany and SW England for monitoring the prevalence of invasive species. Two approaches were adopted: 1) monitoring using settlement panels, which are scored after one year , and 2) “Rapid Assessment Survey” visits to the same sites near the beginning and end of the project to document changes in distribution. The work has already detected extensions to the previously known distributions of some species, and an additional non-native species of sea squirt, originating from the Southern Hemisphere, has been identified. The population genetics of introduced species will also be studied to investigate their pattern of geographical spread and possible genetic diversification through time, and the role of accidental dispersal by human activities.

DNA-based techniques are being developed for the identification of the larvae of marine invertebrates potentially carried in the ballast water of commercial ships.

Two non-native species, the NW Pacific alga Sargassum muticum (Wireweed) and the Pacific Oyster (Crassostrea japonica, another native of the NW Pacific) are the subject of monitoring studies on natural shores to characterise their seasonal patterns of growth and reproduction. As part of these studies, ‘robo-oysters’, oyster shells fitted internally with a temperature loggers, are being fixed on the shore amongst live oysters to monitor the range of body temperatures experienced by oysters at different times of the year. Wireweed is being experimentally manipulated to investigate the effect this alien has on photosynthesis and respiration by the community of seaweeds on the shore.

The effects of another aspect of global change, reduction in ocean pH as a result of increasing atmospheric levels of carbon dioxide, is being investigated in the North American Slipper Limpet (Crepidula fornicata), which forms dense populations along the Channel coast, impacting oyster fisheries. Comparative studies of the seasonal reproductive cycle of this species on both sides of the Channel are also getting underway.

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