Positive interactions between corals and damselfish increase coral resistance to temperature stress

Abstract

By the century's end, many tropical seas will reach temperatures exceeding most coral species' thermal tolerance on an annual basis. The persistence of corals in these regions will, therefore, depend on their abilities to tolerate recurrent thermal stress.Although ecologists have long recognized that positive interspecific interactions can ameliorate environmental stress to expand the realized niche of plants and animals, coral bleaching studies have largely overlooked how interactions with community members outside of the coral holobiont shape the bleaching response. Here, we subjected a common coral, Pocillopora grandis, to 10 days of thermal stress in aquaria with and without the damselfish Dascyllus flavicaudus (yellowtail dascyllus), which commonly shelter within these corals, to examine how interactions with damselfish impacted coral thermal tolerance. Corals often benefit from nutrients excreted by animals they interact with and prior to thermal stress, corals grown with damselfish showed improved photophysiology (F v /F m ) and developed larger endosymbiont populations. When exposed to thermal stress, corals with fish performed as well as control corals maintained at ambient temperatures without fish. In contrast, corals exposed to thermal stress without fish experienced photophysiological impairment, a more than 50% decline in endosymbiont density, and a 36% decrease in tissue protein content. At the end of the experiment, thermal stress caused average calcification rates to decrease by over 80% when damselfish were absent but increase nearly 25% when damselfish were present. Our study indicates that damselfish-derived nutrients can increase coral thermal tolerance and are consistent with the Stress Gradient Hypothesis, which predicts that positive interactions become increasingly important for structuring communities as environmental stress increases. Because warming of just a few degrees can exceed corals' temperature tolerance to trigger bleaching and mortality, positive interactions could play a critical role in maintaining some coral species in warming regions until climate change is aggressively addressed.

Consumer feces impact coral health in guild-specific ways

“…Corals may acquire nutrients (Coma et al, 2001;Mills and Sebens, 2004;Allgeier et al, 2017;Shantz et al, 2023) and beneficial or harmful microbiota from fish feces (Muller Parker, 1984;Castro-Sanguino and Sańchez, 2012;Ezzat et al, 2019;Umeki et al, 2020;Ezzat et al, 2021;Grupstra et al, 2021;Velaśquez-Rodrıǵuez et al, 2021). As shown here (sterile feces treatments in Figure 1), particulate matter in fish feces may also sometimes smother coral polyps, resulting in mortality of the underlying coral tissue (Rogers, 1990;Krone et al, 2011).…”

Fish feces reveal diverse nutrient sources for coral reefs

“…Corals in particular, require an array of micro‐ and macronutrients (e.g., N, P, Mg, Mn, Fe, Cu, and Zn) to sustain their metabolism (Ferrier‐Pagès et al, 2018). For instance, nutrients produced by fishes can have positive effects on coral growth and were shown to increase coral thermal tolerance (Meyer et al, 1983; Shantz et al, 2023). In addition, Mg, Mn, and Fe are known to ensure proper photo‐physiological performance of coral symbiotic dinoflagellates, especially during periods of thermal stress (Ferrier‐Pagès et al, 2018).…”

“…However, reef fishes also support coral reefs via bottom‐up processes by supplying inorganic nutrients (nitrogen [N] and phosphorus [P]) to the reef ecosystem via excretion and egestion (Allgeier et al, 2017; Burkepile et al, 2013; Holbrook et al, 2008; Meyer et al, 1983). In fact, schooling fish that shelter within corals may stimulate coral growth by up to 21% through the provisioning of N and P (Meyer & Schultz., 1985), and these nutrients may enhance resistance to thermal stress in corals (Chase et al, 2018; Shantz et al, 2023).…”

Shifts in predator behaviour following climate induced disturbance on coral reefs

“…Community interactions (e.g. corallivore grazing) with corals during bleaching, for example, may have the ability to exacerbate bleaching intensity or severity (this study), or conversely may help bolster coral resilience [ 48 ]. Corallivores interact with corals ecologically, mainly through trophodynamics that can shift behaviourally in space and time [ 17 , 18 ].…”