Cues for Epifauna Bailout

Abstract

Mobile epifauna are known to ‘bailout’ rapidly from host seaweed after detachment of their host but the cue(s) that elicit this behaviour have not been studied. This thesis documents the extent of bailout behaviour of epifauna on common seaweed species with respect to epifaunal taxon and body size and investigates the cue(s) that the epifauna use to detect the detacment of their host. Bailout behaviour was studied across common and abundant macroalgal species Carpophyllum plumosum, Carpophyllum maschalocarpum, Cystophora retroflexa, Ecklonia radiata (Class Phaeophyceae) and Melanthalia abscissa (Class Rhodophyta) in northeastern New Zealand. Epifauna of all size classes examined (>1 mm, 500-1000 μm and 200-500 μm) rapidly abandoned all the host species within 15 s of detachment and the response peaked by 1 min. Mean bailout increased with increasing epifaunal body size. Bailout varied across epifauna taxa on all hosts, with some more reluctant to abandon the host, but not for majority of the taxa across all seaweed species. This indicates that bailout is primarily influenced by changes in the physical environment and not the host attributes. However, significant number of individuals remained associated with the host at 5 minutes post-detachment, and could potentially be transported with floating hosts across great distances. Pressure and light, the two most obvious physical factors changing after detachment, were investigated as potential cue(s) for bailout, using epifauna on Carpophyllum plumosum as a model system. Field experiments using a Plexiglas chamber in which pressure could be increased or decreased on the seafloor, or held constant while the seaweed was brought to the surface, showed that pressure was the primary cue influencing bailout. On manipulating the magnitude and rate of pressure epifauna bailed out only on reduction of pressure (simulating floating to surface) and not with an increase (simulating sinking), the bailout increasing with increase in the magnitude of pressure. Bailout was not influenced much by the rate of change of pressure. Experiments investigating the effect of changes in intensity of light and comparing bailout during daytime and night concluded that changes in light intensity or absence of light as a cue does not affect bailout.