Historical changes on rocky shores in the Western Cape, as revealed by repeat photography

Master Thesis


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University of Cape Town

Photography has always had a record-keeping purpose, whether to document famous people, or other news-worthy events, such as wars (Webb et al . 2010). Prior to photography becoming a practical tool, researchers in biology relied on drawings and precise descriptions to pass on what they observed during field work (George 1980). In truth, there are very few fields in science which have not made use of photography in some form (George 1980). Taxonomy has been a benefactor, since colour images taken in the field can be used to record distinctive characteristics of organisms that may later lose their pigmentation during preservation (George 1980). Of more relevance to this paper are the many uses of photography in marine ecology which George (1980) suggests are “...to aid site and habitat description, to record the relationship of plants and animals to the environment and to one another, to measure population numbers and the size of individual organisms, and to record the changes in community structure that take place with time.” This list does not take into account the advantages of video to document behavioural studies. As the old adage explains, “a picture is worth a thousand words” and photographs taken at the shore are often far more valuable than lengthy written descriptions used to “set the scene” (George 1980). As with all methods of sampling, however, there is a trade-off between the advantages and disadvantages involved. The disadvantages are similar to those shared with most disciplines interested in sea-shore studies. For example, time is a limiting constraint, as most photographs need to be taken at low tide and indeed the most effective photographic sampling is carried out during spring low tides , when the greatest area of intertidal habitat is exposed. Capturing images during these brief windows often complicates large-scale spatial studies, especially with limited resources (Murray et al . 2006). Furthermore, issues may arise with the detail that can occur due to the resolution of the photograph, as well as identifying taxa of a similar appearance, and problems with analysis may arise where the organisms are in high concentrations and/or stratified (Murray et al . 2006). There are, however, many advantages to the correctly applied photographic method: the greatest perhaps being that the images may be stored and used for further analysis at a later date. These stored images can also be kept on record and used to analyse changes that may have occurred over time. Photographs also have another advantage, in that they are more easily interpreted by people without scientific backgrounds that may not easily understand graphs or complicated figures (Murray et al . 2006). Further examples of the application of photographic techniques in marine biology include photographic surveys and photographic tagging, which has for many years been used in identifying whales, dolphins or seals (McConkey 1999). Photography has also proved useful as a tool for conducting population counts, such as on the West Coast, where seal populations are photographed from the air to determine breeding success (Griffiths et al . 2004). Aerial photography has also been used in conjunction with infra-red photographic techniques to determine the extent of kelp populations along the South African coast (Bolton and Anderson 1990)... This chapter uses repeat photography to illustrate changes that have occurred on rocky shores in the Western Cape over the past hundred years. Changes are documented under four categories; changes in range, climate change, intertidal invasion and direct anthropogenic effects. Images were sourced from books, members of the public and subject specialists and were selected based on their suitability. The sites of the images were identified and repeat photographs captured. The images depict the slow but progressive easterly spread of the kelp Ecklonia maxima and the range contraction of the warmer-water mussel Perna perna. Evidence suggests that a changing climate is the major driver of both of these changes. No change in zonation due to changing sea levels was observed. However, the range contraction of P. perna is complicated by the introduction of an alien mussel, Mytilus galloprovincialis. Repeat photography shows the changes that M. galloprovincialis has caused on the intertidal community in Saldanha Bay. Another invasive organism, Balanus glandula, is shown to have greatly altered the community structure of the Blouberg intertidal zone. Also of interest is the degree of building development that has taken place along the shore. Repeat photography proved a useful tool for documenting changes that are separated by large amounts of time, and is recommended as a useful technique for the surveillance and monitoring of rocky shores.

Includes bibliographical references.