Elevated temperature decreases stony coral tissue loss disease transmission, with little effect of nutrients

Abstract

Stony coral tissue loss disease (SCTLD) is the deadliest scleractinian coral disease reported, causing significant coral loss in the Western Atlantic reefs. Environmental conditions are known to influence disease dynamics, but determining the specific conditions that exacerbate SCTLD remains challenging. We developed a robotic multi-stressor system to study the effects of temperature and ammonium on SCTLD transmission. For a month, coral fragments were preconditioned to two temperatures (28 °C and 31 °C) and nutrient treatments (with and without ammonium dosing), and subsequently exposed to SCTLD. Environmental treatments only caused modest effects in the corals (based on calcification, photochemical efficiency, and symbiotic algal communities). However, SCTLD incidence was strongly reduced at higher temperature (17% at 31 °C compared to 70% at 28 °C), contrasting with other coral diseases that typically worsen with increased heat. Disease management approaches may involve concentrating SCTLD treatment efforts during warmer periods when reduced incidence might enhance treatment efficacy.

Keywords: Orbicella faveolata; Coral disease; Disease transmission; High temperature; Multiple stressors; Nutrients.

Fig. 1

Panoramic view of the STAR system. The picture shows the two robot arms dosing the experimental corals with artificial seawater (previously exposed to healthy or diseased coral colonies) and ammonium.

Fig. 2

Physiological response of O. faveolata to the environmental treatments (mean ± 95% CI) before disease exposure. (A) Photochemical efficiency of the algal symbionts (F_v/F_m). (B) Calcification rates (mg g⁻¹ d⁻¹). The colors represent the combined temperature and nutrient treatments. The letters represent post hoc Tukey HSD groups. Linear model outputs are shown in Tables S1 and S3 and Tukey HSD tests in Tables S2 and S4.

Fig. 3

Symbiodiniaceae algal communities after 14 days of exposure to the environmental treatments. (A) Total Symbiodiniaceae to host cell ratio (mean S/H ± 95% CI). Algal abundance was higher for corals in HN compared to LN, but colony had the biggest effect (Table S5). (B) Percentage of Durusdinium (± 95% CI). The colors represent the combined temperature and nutrient treatments. The shapes represent the different coral colonies. Letters in panel B represent post hoc Tukey HSD groups (Table S7).

Fig. 4

Probability of O. faveolata remaining healthy (with no lesions) after exposure to SCTLD. (A) Mean (± 95% CI) probabilities by temperature treatments (nutrients and colonies pooled by temperature). The number of fragments exposed to SCTLD represents the number of corals that remained healthy on a given day and were available to become diseased. (B) Probabilities parsed by coral colony, nutrients, and disease treatments.

Fig. 5

Diagram of the experimental setup showing the water flow between the tanks and the experimental combinations: Top—artificial seawater flow into the healthy and disease donor tanks, followed by flow into the dosing boxes attached to the robot arms. Bottom—All the possible combinations of treatments and beaker content in a given tank. The diagram represents all possible treatments, but not the replication. For replication see Table 1. Detailed STAR system parts are shown in Figure S1. Treatment and coral colony position in the tanks were randomized but are shown here in order for easier visualization.

Fig. 6

Experimental timeline and environmental conditions. (A) Temperature in the experimental tanks holding the beakers (mean ± se). The black dots and horizontal line denote the days when experimental data was collected. (B) Ammonium (NH₄) concentration in the experimental beakers (mean ± se). The colors represent the environmental treatment assigned to the beakers as a combination of nutrient and temperature treatments. The vertical lines and black arrows demarcate the days when dosing with nutrients, control seawater and disease-exposed seawater were initiated.