Potential feedback between coral presence and farmerfish collective behavior promotes coral recovery

Abstract

Stable between‐group differences in collective behavior have been documented in a variety of social taxa. Here we evaluate the effects of such variation, often termed collective or colony‐level personality, on coral recovery in a tropical marine farmerfish system. Groups of the farmerfish Stegastes nigricans cultivate and defend gardens of palatable algae on coral reefs in the Indo‐Pacific. These gardens can promote the recruitment, growth, and survival of corals by providing a refuge from coral predation. Here we experimentally evaluate whether the collective response of farmerfish colonies is correlated across intruder feeding guilds – herbivores, corallivores and egg‐eating predators. Further, we evaluate if overall colony responsiveness or situation‐specific responsiveness (i.e. towards herbivores, corallivores, or egg‐eaters in particular) best predicts the growth of outplanted corals. Finally, we experimentally manipulated communities within S. nigricans gardens, adding either macroalgae or large colonies of coral, to assess if farmerfish behavior changes in response to the communities they occupy. Between‐group differences in collective responsiveness were repeatable across intruder guilds. Despite this consistency, responsiveness towards corallivores (porcupinefish and ornate butterflyfish) was a better predictor of outplanted coral growth than responsiveness towards herbivores or egg‐eaters. Adding large corals to farmerfish gardens increased farmerfish attacks towards intruders, pointing to possible positive feedback loops between their aggression towards intruders and the presence of corals whose growth they facilitate. These data provide evidence that among‐group behavioral variation could strongly influence the ecological properties of whole communities.

Effects of corallivory and coral colony density on coral growth and survival

“…2). Repeated observations of our experimental corals revealed the pattern of tissue and skeletal loss for the exposed nubbins was precisely that known to be caused by excavating corallivores: bites that remove a portion of the distal end, gradually reducing the length of a nubbin over time (Johnson et al 2011;Kamath et al 2019;Fig S3). With respect to growth, corals exposed to corallivores showed no measurable signs of skeletal growth after 30 days (Fig.…”

“…Branching Acropora corals commonly grow on the tops of these Porites reefs and vary naturally in density (Johnson et al 2011;Lenihan et al 2011). Our study focused on A. pulchra due to this known variation in density, as well as its high growth rate and sensitivity to predation pressure (Kamath et al 2019).…”

Herbivorous damselfishes expand their territories after causing white scars on Porites corals

“…Increased territorial damselfishes expand the area of turf algae inside their territories on disturbed reefs, which prevents corals from recovering 18 , 19 . Conversely, these territories can actually provide a suitable substrate for coral recruitment and growth, especially for corals susceptible to corallivory, because these territories are defended against grazers and even corallivores by the damselfishes 28 , 29 , 36 , 40 . In fact, the number of coral recruits has been reported to be higher inside territories of S. nigricans than outside them on shallow backreefs at Moorea, French Polynesia 37 .…”

“…The defensive behaviour of S. nigricans involves weeding and chasing away grazing fishes and invertebrates 15,26,27 . S. nigricans also chases away corallivorous fishes and maintains coral colonies inside its territories [28][29][30] . Extensive farmers defend large territories and mixed algal turfs comprising palatable filamentous algae and unpalatable algae 15,25 .…”

Predictors of colony extinction vary by habitat type in social spiders

“…Identifying spatial (between environments) and temporal (between seasons and across years; as in Bengston 2018) variation in selection on collective phenotypes helps us to understand the context-dependent evolution of these traits (Wray et al 2011, Scharf et al 2012, Jandt et al 2014, Jolles et al 2018, Kamath et al 2018b. In a prior study, Pruitt et al (2018) demonstrated the existence of site-specific selection on colony aggression in S. dumicola.…”