MarClim - Marine biodiversity and climate change

The most complete data sets are for the barnacles including Semibalanus balanoides

There is little doubt that the Earth's climate is getting warmer. Analysis of global air temperatures from 1856 to present showed the 1990s to be the warmest decade and 1997 and 1998 as the warmest years (Jones et al., 1999). Ocean temperatures have increased in parallel with those of the atmosphere. Long term records from the English Channel show that from the early 1980s the sea temperature increased slightly until 1990. During the following decade there was an increase of almost 1ºC. This increase was far greater than any change in the previous 100 years.

Not surprisingly, governments and trans-national bodies are becoming increasingly concerned about the implications of global climate change but to date little attention has been focused on the possible effects on marine biodiversity and the goods and services that biodiversity provides.

New project

In UK, a broad group of funding bodies has supported an initiative to assess and predict the influence of climatic change on intertidal rocky shore biota. The project, Marine Biodiversity and Climate Change (MarClim) is currently bringing together and analysing historical and recent data to establish the extent to which the fauna of rocky seashores has already changed as a response to climate. It will go on to use models developed by the UK Climate Impacts Programme models to predict future changes in shore biodiversity. Such predictions are needed for the conservation, management and protection of the marine environment in Britain and Ireland. The broad range of interested parties combined with the policy-driven nature of the project outputs has led to MarClim becoming a national forum for marine scientists, marine conservationists and climatic change experts in both Britain and Ireland.

The rocky shore fauna of the British Isles is particularly well documented; as long ago as the 1950s, workers in Britain began to map the distribution of the dominant intertidal rock species (Southward & Crisp, 1956; Crisp & Southward, 1958). They showed that the fauna of the British Isles is composed of a mixture of cool-water boreal- and warm water Lusitanian species and includes a number of common species that are either at, or close to, their northern or southern geographic limits of distribution.

Ultimately, broad-scale patterns of distribution are set by temperature. Lewis (1976) proposed that species close to their northern distributional limits in UK were prevented from spreading further by the severity of winter conditions; species approaching their southern limit of distribution were limited by summer conditions. If the climate of the British Isles becomes warmer it can be broadly predicted that existing patterns of species distribution will move northwards. The question that MarClim must answer is how far and how fast patterns of distribution will shift.

Changes in species distribution as a response to climate change are unlikely to be a simple northward projection of the current pattern; much will depend on the biological properties of individual species such as the timing of spawning, the length of the spawning period and the length of larval life. Biological characteristics will interact with coastal topography and inshore hydrography to determine the way in which species will extend their range. Predictions can only be made for species for which we have a good knowledge of their reproductive and recruitment biology which can be coupled to reliable predictions of the movement of inshore water.

Good rocky-shore record

The biota of the British Isles is one of the most thoroughly researched in the world but there are surprisingly few species for which we have a sufficient depth of knowledge to make valid predictions of their response to climate warming. The rocky shore is one of the only habitats where such predictions are a realistic proposition. Rocky habitats have been popular areas for ecological study for many years and so there are a good number of long-term data containing a vast store of information on the distribution and temporal variability their biota. The most complete data sets are for the barnacles Semibalanus balanoides, Chthamalus montagui, and Chthamalus stellatus, the limpets Patella vulgata and Patella depressa and the trochid gastropods Gibbula umbilicalis and Osilinus lineatus. The main rocky shore data sets vary greatly in spatial and temporal extent but over large parts of the British Isles there is moderate to good coverage for the period between the 1950s and 1980s. Unfortunately, there is little information available for the 1990s, the period of greatest change in sea temperatures.

One of the key priorities of the MarClim project is to bring together and analyse as many as possible of the long term data series to determine the responses of individual species during a period of fluctuating climate.

In view of the lack of data from the 1990s, the first year of the MarClim project has been focussed on returning to as many as possible of the long-term study sites in the British Isles to assess the extent of the changes that occurred during the period of greatest temperature change. It is fortunate that among the MarClim team are some of the scientists who made observations in the 1950s and '60s (A.J.Southward) and 1970s and '80s (S.J.Hawkins and M.A.Kendall). Their presence ensures that contemporary studies take place in exactly the same locations and use the same methodology; as a result historical and modern data are directly comparable.

Clear signs of change

At the end of its first year the MarClim team has visited approximately 240 sites from the Isles of Scilly to the north coast of Scotland. Fully replicated quantitative data have been collected on the species for which we hold the most complete datasets and abundance-scale (SACFOR) information has been recorded for a further 58 species that have distribution patterns suggesting they are climate sensitive. Initial results are highly encouraging and show that some of the projects target species have expanded their geographical range by 30-50km since the 1980s. The same animals have increased in abundance by 2-3 times at sites close to their range edges. Further resurvey data will be collected and analysed during 2003. The outputs of analysis will be incorporated into mathematical models coupled to UKCIP predictions of climate change under a range of scenarios to enable predictions to be made of changes in patterns of species distribution on the rocky shore.

Analysis of the MarClim data sets will also highlight the most appropriate species to be monitored as sentinels of future marine climate change. The project is charged with setting up an extensive monitoring network to be sustained after MarClim finishes in 2005. It is envisaged that this will involve following changes in selected species at a series of carefully chosen site around the coastline of the British Isles. Long term changes in the biota of rocky shores have been show in the past to match changes in other marine ecosystems that are far more difficult to sample. The outputs from MarClim have the potential to underpin future marine monitoring strategies.