Rock pool gobies change their body pattern in response to background features

Some species actively change color and pattern for camouflage on a range of background types. Such dynamic cam- ouflage may be particularly advantageous for species inhabiting heterogeneous habitats, such as intertidal zones, where individuals are exposed to both terrestrial and marine predators depending on tides and wave action. Most studies of dynamic pattern camouflage have focused on relatively few species, and rarely species inhabiting the intertidal zone. We used image analysis and predator (avian) vision modelling to determine if rock gobies (Gobius paganellus) change their body pattern in response to their background, and to explore how background marking size influence pattern change. Rock gobies rapidly (within 1 min) changed their pattern when placed on checkerboards with different sized squares, and on backgrounds resembling natural substrates. On backgrounds resembling natu- ral substrates, those with a small grain size, such as sand, elicited a larger degree of pattern change than those with a larger grain size. However, despite this, the majority of fish showed little or no improvement in background match- ing over time. Instead, the markings elicited are characteristic of disruptive coloration and may function primarily through breaking up the body outline rather than via improved match to the background pattern itself.