Response and Plasticity of a Cleaning Mutualism Following Short Term Reductions in Habitat Availability

Species interactions, facilitated by animal behaviour, drive global biodiversity, yet species interactions are being disrupted by environmental change across ecosystems. On coral reef ecosystems, cleaning mutualisms where a 'cleaner' species removes parasites from a 'client' species at dedicated cleaning 'stations' on live coral are directly impacted by ongoing declines in live coral due to environmental change. Using cleaning mutualisms as a model system, we hypothesised that reduced habitat availability will result in a decline in mutualism-associated behavioural expression. Through an in situ manipulation experiment on a Caribbean coral reef, we placed nets over obligate cleaner goby (Elacatinus lobeli) cleaning stations, reducing live coral and refuge access. We identified consistent declines in the quality (cleaning rate) and quantity (cleaning duration) of cleaning interactions, cleaner selectivity for specific clients and client signalling (posing) following habitat manipulations and an increase in cleaner responsiveness (flight initiation distance), whilst the abundance and diversity of the local reef fish community remained relatively unchanged. We also found evidence of behavioural plasticity, with mutualism-associated behaviours returning to pre-disturbance levels after the manipulation was removed. Whilst the functioning of marine cleaning mutualisms declines when habitat availability is reduced, plasticity in mutualism-associated behaviours can maintain cleaner-client interactions. Identifying thresholds of change beyond which such plasticity is no longer viable, resulting in a mutualism breakdown, is an important next step in preserving one of the world's most threatened ecosystems.