The study of intertidal mollusc polymorphism using spectroradiometry and visual modelling

Cruickshanks, Katie Lawson (2006) The study of intertidal mollusc polymorphism using spectroradiometry and visual modelling. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Here I present data concerning the discriminability of different morphs of intertidal littorinid species against natural backgrounds in the visual systems of potential predators. Two distinct habitats were studied, firstly the relatively simple high shore splash zone where Littorina saxatilis lives and secondly the complex algal canopy inhabited by L. obtusata and L. fabalis. By collecting reflectance spectra in the field and modelling it into the visual systems of predators I have shown that the extent of background matching in a particular Littorina saxatilis population is dependent on the shore geology and that greater background heterogeneity may provide more opportunities for crypsis. In populations of exposed and sheltered ecotypes of L. saxatilis chromatic differences between littorinids and backgrounds were observed which indicated that the populations subjected to predation by birds with high visual acuity are more cryptic than those preyed upon by crabs. On a smaller scale, background heterogeneity differences between lichen covered rock and bare rock were quantified. The extent to which different morphs of L. saxatilis matched these two background types was quantified in the visual systems of crabs and birds. I revealed that the more uniform background provided more opportunities for L. saxatilis cryptic which contradicts the patterns observed between shores dependent on geology. The algal habitat was studied in terms of visual heterogeneity of two different algal species and the extent to which different morphs of L. obtusata and L. fabalis matched the backgrounds and certain structural parts of the algae. In agreement with the lichen-bare rock system, the more uniform algal background (Fucus serratus) provided more opportunities for crypsis than the more visually heterogeneous algal species (F. vesiculosus).