Further observations on the ecology of Chthamalus depressus (Poli)

Abstract

An account is given of the forms of Chthamalus depressus (Poli). An extreme hypobiotic form common in caves is described; it is shown that all forms may be found in very restricted localities (even on a single boulder) according to different micro-habitats. Some biometrical data on the species and regressions of the several variables are given; they indicate that thickness tends to increase with exposure. The effect of exposure on growth-form is considered and compared with similar data on the laying down of the shell in molluscs. Thickening of the shell is believed to be due to withdrawal of the mantle tissue under wave action. The effect of light on the penetration of algae is discussed; animals growing in darkness have no endolithic algae. Erosion is considered to be due to mechanical forces acting on shells much weakened by endolithic algae. The changes on transplantation to Scotland have been observed, and measurements of the growth rate made; growth is slow, but somewhat greater under conditions of total immersion. The reproductive and moulting cycles, fertility, and general behaviour have been determined and the results compared with similar data on C. stellatus (Poli). The results are discussed in relation to the ecology of C. depressus and, in particular, relative to possible competition with C. stellatus.