DOI: 10.5061/dryad.zpc866t9t
title: Positive interactions between corals and damselfish increase coral resistance to temperature stress

description: 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 (Fv/Fm) and developed larger
 endosymbiont populations. When exposed to thermal stress, corals with fish
 performed as well as 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. By 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.
description: To assess how fishes influenced coral physiology and thermal
 tolerance, we measured the dark-adapted quantum yield, symbiont density,
 and tissue protein content of coral fragments throughout a thermal stress
 experiment. Measurements were taken on Day 1 when the corals were brought
 to shore, prior to acclimation with damselfish, and on Day 14 after two
 weeks of acclimation with or without damselfish present. Temperatures were
 then increased in half of the tanks over 24 hours to 30.5°C, and
 subsequent measurements made on Days 17, 20, and 24, corresponding to 3,
 6, and 10 days of temperature stress, respectively. After completing our
 measurements on Day 24, we lowered the temperatures in the heated aquaria
 back to 27.5°C over 24 hours and collected final measurements on Day 34,
 after 10 days of recovery. At each sampling time point,
 we haphazardly selected one fragment from each tank for sampling. We used
 PAM fluorometry to measure the maximum dark-adapted quantum yield of PSII
 (F<sub>v</sub>/F<sub>m</sub>) after 30 minutes of
 dark acclimation. After taking fluorescence measurements, we removed the
 tissue from each fragment with a waterpik and centrifuged the resulting
 tissue slurry at 5,000xG for 5 minutes to separate the coral tissue and
 Symbiodineaceae. Symbiont pellets were resuspended in 1 ml filtered
 seawater while the coral tissue was rapidly frozen by submersing the
 sample tubes in -80°C acetone for 5 minutes, followed by storage at -80°C
 for protein analysis. Symbiont density of each fragment was calculated
 from eight replicate counts on a Neubauer hemocytometer and normalized to
 the fragment's skeletal surface area, as determined by wax dipping
 (Stimson and Kinzie, 1991). To determine protein content of coral tissue,
 we lyophilized the frozen coral tissue at -80°C to a constant weight.
 Next, the freeze-dried tissue was homogenized and diluted in 0.5 ml of PBS
 buffer, vortexed for 20 min, and immersed in a sonicating water bath for
 an additional 20 min. The solution was then filtered through a 0.2 μm
 filter and the resulting supernatant analyzed on a Millipore Direct Detect
 infrared spectrometer against a bovine serum albumin standard (EMD
 Millipore, Billerica MA, USA). Finally, we measured differences in coral
 calcification rates, as determined by changes in buoyant weight (Davies
 1989), for the fragments collected on the final day of thermal stress and
 after the 10-day recovery period. To determine how the
 yellowtail dascyllus impacted nutrient levels we measured ammonium
 (NH<sub>4</sub><sup>+</sup>), nitrate
 (NO<sub>3</sub><sup>-</sup>), and soluble reactive
 phosphorus (SRP) in every aquarium approximately weekly throughout the
 experiment.
description: # Positive interactions between corals and damselfish increase coral
 resistance to temperature stress
 [https://doi.org/10.5061/dryad.zpc866t9t](https://doi.org/10.5061/dryad.zpc866t9t) Supplemental data for “Positive Interactions Between Corals and Damselfish Increase Coral Resistance to Temperature Stress”. Data uploaded include coral physiological measurements with descriptors on first page of excel sheet and nutrient measurement data with descriptors on first page of excel sheet. Any questions regarding this data should be directed to ashantz@FSU.edu ##