Assessment of some controls in experimental transplants of intertidal gastropods

Abstract

Some factors associated with transplant experiments using a small high-shore gastropod, Littorina unifasciata Gray have been investigated. These included: (1) the effects of marking the test animals and the associated disturbance; (2) the pattern of dispersion of the test animals at the start of the experimental period; (3) the past history of the test animals, moving animals into a new patch of the same habitat or zone as opposed to a different habitat or zone; and (4) differing densities of conspecifics in the experimental areas. In addition, spatial and temporal variability in the results were examined. Disturbance, translocation into a new area and density of conspecifics had little effect on the subsequent movement of the test animals, and animals from different areas at the same level on the shore behaved similarly when moved between areas. The area in which the experiment was done, rather than the characteristics of the sample of snails used in the experiment, determined the pattern of movement. The pattern of dispersion of the test animals at the start had a significant effect on subsequent movement, because animals which were placed in clumps tended to move in the same direction. Of more importance, however, the data showed considerable spatial and temporal variability, in both the directions and distances displaced by the animals. It is extremely important to investigate the variability in the results obtained in such experiments, before detailed transplant experiments are done. In the case of L. unifasciata replicate experiments in a number of areas, on a number of occasions, and for differing periods are clearly needed before conclusions can be drawn about patterns of movement, and their importance in the establishment and maintenance of this snail's patterns of distribution and abundance.