The ecology of a tidal pool at St. Andrews, Fife

Abstract

Literature dealing with rook pools is scanty, and as a rule they have been studied either very generally or over a rather short period of time. During the course of the present work a single pool, 3.7 x 1.5 m., just below high water neap tide level on the St. Andrews shore, has been studied in detail from June 1950 to March 1954, in an endeavour to correlate changes in flora and fauna with variations in environmental conditions. The location and topography, periods of exposure, illumination, temperature, hydrogen ion concentration and salinity have been measured to a greater or lesser extent, and observations made or estimations formed of the probable importance of desiccation, wave action, dissolved oxygen concentration, inorganic substances other than chlorides in solution, organic matter present, and biotic factors. It has been shown that conditions vary very considerably from one part of the pool to another at any one time, and in particular parts at different times of the day or seasons of the year, and that various factors are so closely linked in their effects that they cannot usefully be considered independently. An ecological classification of the pool vegetation has been evolved which emphasises the parallel between the range of conditions (and hence of types of algal growth) within the pool and on the shore in general. The high incidence of epiphytism is considered in some detail, and its importance and effects in the case of both host and epiphyte assessed. Healthy plants seem less liable to epiphytic settlement than unhealthy specimens; species which are generally epiphytic do not as a rule thrive in other situations, and vice versa; the principal danger to the actual life of the host plant seems to lie in the greater liability to removal, due to increased resistance to wave force. Comparison of the life cycles within the pool of the various algal species has shown the prevalence of vegetative reproduction, including regeneration, from perennial basal parts, amongst the community-forming plants of the pool. The flora (80 species identified, including 24 unpublished St .Andrews records) and the fauna (98 identified, including 35 unpublished) are listed, with notes on times of occurrence, frequency, habit, size, reproduction end other noteworthy features, and additional notes are provided amplifying these details for species of particular nomenclatural, taxonomic or ecological interests. The relations between plants and animals are considered in further detail, with reference to quantitative samples of the flora and fauna taken from time to time. Faunal populations are shown to vary amongst different types of vegetation, and in some oases to be closely dependent on the presence of particular algal species. The vital importance of atmospheric conditions during the prolonged exposure of the pool at times of poor neap tides is illustrated and discussed. High water neap tide level is considered to be highly critical for the flora and fauna of rook pools. The seasonal cycle of vegetation and the faunal population of the pool are shown to have varied somewhat from year to year, and an attempt is made to correlate these changes with the correspondingly exceptional meteorological conditions. Species frequent in neighbouring pools but rare or absent in the case of this particular pool are instanced and discussed. Temperature fluctuations are considered to be probably the most important limiting factor for the majority of the algae concerned. The generally stunted nature of the vegetation and frequently reduced cell size are attributed primarily to the shallowness of the pool, exposure to violent wave action, (and adverse conditions during the normal growing season. Browsing animals constitute a serious menace to spores, sporelings and minute plants, but are probably rarely lethal where the larger plants are concerned. The dynamic nature of the relationships of the population to its environment is stressed. Three main trends of change are shown to exist in the pool: the complex succession from bare rock to semi-permanent covering by a dense algal community, the catastrophic effects of neap tide conditions, especially during spring and early summer, and the more or less regular seasonal succession of vegetative changes. Particular stress is placed on the importance of long-term observations in assessing the distribution of population within this type of habitat.