A Photographic Method for Recording the Underwater Distribution of Marine Benthic Organisms

Abstract

In recent years the development of SCUBA? diving has provided a new tool for the marine biologist (Parker 1966). Prior to the introduction of SCUBA, marine studies involved sampling by grab or trawl, occasionally by helmet diving (Kitching, Macan & Gilson 1934), or by observation with surface controlled cameras, including television (Barnes 1963). Diving techniques are proving particularly useful in areas inaccessible to surface probing, such as under rock overhangs and in sub-littoral caves and canyons. Although many studies using SCUBA have been carried out in northern waters (e.g. Forster 1955; Kain 1960, 1962), the main developments have occurred in warmer seas, including the Mediterranean (e.g. Molinier & Picard 1952; Molinier 1960; Peres 1967). One important problem facing workers employing diving methods is the establishment of suitable quantitative sampling procedures. Conventional techniques of the land ecologist, including quadrat analysis, are frequently employed and semi-quantitative methods such as modifications of the plant sociological techniques of the ZurichMontpellier school (Braun-Blanquet & Pavillard 1925) have provided useful information about the Mediterranean marine benthos (Molinier & Picard 1952; Molinier 1960). One further difficulty encountered in underwater studies is the short duration of work possible with the diving equipment available. However, technical developments under way at present should help to reduce this problem, such as the introduction of liquid-air breathing equipment (Tzimoulis 1967) and the construction of underwater laboratories and vehicles (Rechnitzer 1965; Valery 1967). Although it will be some time before these developments are available to the average marine ecologist, they will permit work in excess of 300 m and underwater projects lasting weeks or even months. The investigation described was part of a study of techniques aimed at making the maximum use of time spent in surveys underwater, and its basis was a rapid but precise photographic recording underwater, leaving the time-consuming problem of measurement and calculation to the laboratory. The techniques described were employed to survey the physical features of small areas of the sea-bed for the preparation of maps and profiles; to plot the distribution and cover of particular species; and to follow the movement of selected species of mollusc and echinoderm, during a biological survey of the marine benthos in the eastern Canary Islands. Although underwater photography has proved extremely valuable in qualitative investigations, it has seldom been used in quantitative work. Photogrammetry has been employed by cartographers for many years, particularly in map construction from aerial survey data, but normally it requires complex, bulky equipment and can be attempted