Long-term changes in distribution and abundance of rocky shore biota around South Africa, 1940-2007

PI: Prof Charles Griffiths, University of Cape Town

Researcher: Angela Mead, University of Cape Town

BACKGROUND: South Africa has a remarkably diverse marine environment, ranging from tropical coral reefs and mangrove forests in the North-east to cold-temperate kelp beds, seals and penguins along the west coast. Of particular note in the present context is that the coastline is almost linear, with very few significant bays or inlets, and presents a number of interesting physical and biological gradients. The most obvious of these is a marked gradient in water temperature from high (ca 24⁰C) in the east to low (ca 10⁰C) in the west, but this is also mirrored by gradients of declining nutrient concentration and primary productivity, from high in the west to low in the east. The shoreline thus forms an excellent natural laboratory to detect changes in distribution and abundance brought about by global climate change, since each degree change in water temperature should result in a significant westward extension of range. Indeed, several dramatic changes in distribution have recently been noted in commercially fished stocks – for example pilchard, traditionally fished entirely on the west coast, have now shifted their centre of gravity to the vicinity of Mossel Bay, on the south coast, where catches have leapt from just 2 000t to 121 000t in the past five years! Similar changes have been notes in the distributions of rock lobsters and seabirds.

South Africa is also fortunate to have had a long history of excellence in marine biological research. The University of Cape Town has been active in this field since 1903, when Prof John Gilchrist was appointed as first Professor of Zoology. Of particular interest in the current context is that the department was headed by Prof. T A Stephenson – an international authority on intertidal ecology - from 1930-1941 and subsequently by Prof John Day, who continued this tradition from 1946-1974. Stephenson and Day carried out extensive studies on the distribution and abundance of rocky shore biota over this period, resulting in a long series of publication, best summarized in the book ‘Life between tidemarks on rocky shores’ (Stephenson and Stephenson 1972).

We are fortunate to be in the position where we not only have access to these historic publications, but also to the original specimens collected (deposited in the South African Museum, Cape Town) as well as the original sample by sample field catalogues dating from that time.

AIMS OF THIS PROJECT: The principal aim would be to resample various of the sites surveyed by Stephenson and Day using the NaGISA protocol (intertidal zones only). These data can then form part of the NaGISA global coverage, but will also be used to investigate whether the distribution and abundance of species has changed since the 1930 - 1940’s, when most of the original surveys were done.

The original surveys sampled more than 20 localities around the coast and used these data to establish the now well-established biogeographic provinces around the South African coast. We will concentrate our survey efforts at the junctions of these provinces (ie in the Eastern Cape, where subtropical and warm-temperate provinces meet, and the S W Cape, where the warm and cool-temperate provinces meet), since these are the regions where range changes are most likely to be detected

This will form part of a larger PhD study in which we aim to examine various drivers of change in the composition and abundance of intertidal organisms. The drivers to be considered include not only range extensions brought bout by climate change, but also changes caused by the exploitation of intertidal resources and by the invasion of marine invasive aliens. By overlaying these threats in a GIS system we hope to identify the regions most under threat and the relative impacts of different drivers of change in each region.  These will be very different in the various areas, for example alien species are far more abundant on the west coast, whereas exploitation in much more intense along the heavily populated east coast.