Coral bleaching response is unaltered following acclimatization to reefs with distinct environmental conditions

Abstract

Urgent action is needed to prevent the demise of coral reefs as the climate crisis leads to an increasingly warmer and more acidic ocean. Propagating climate change-resistant corals to restore degraded reefs is one promising strategy; however, empirical evidence is needed to determine whether stress resistance is affected by transplantation beyond a coral's native reef. Here, we assessed the performance of bleaching-resistant individuals of two coral species following reciprocal transplantation between reefs with distinct pH, salinity, dissolved oxygen, sedimentation, and flow dynamics to determine whether heat stress response is altered following coral exposure to novel physicochemical conditions in situ. Critically, transplantation had no influence on coral heat stress responses, indicating that this trait was relatively fixed. In contrast, growth was highly plastic, and native performance was not predictive of performance in the novel environment. Coral metabolic rates and overall fitness were higher at the reef with higher flow, salinity, sedimentation, and diel fluctuations of pH and dissolved oxygen, and did not differ between native and cross-transplanted corals, indicating acclimatization via plasticity within just 3 mo. Conversely, cross-transplants at the second reef had higher fitness than native corals, thus increasing the fitness potential of the recipient population. This experiment was conducted during a nonbleaching year, so the potential benefits to recipient population fitness are likely enhanced during bleaching years. In summary, this study demonstrates that outplanting bleaching-resistant corals is a promising tool for elevating the resistance of coral populations to ocean warming.

Keywords: adaptive management; climate change; coral bleaching; ocean warming; restoration.

Fig. 1.

(A) Map of the southern region of Kāneʻohe Bay on the island of Oʻahu (Inset) indicating locations of the Inner and Outer Lagoon reefs. Daily physicochemical dynamics of the seawater above the reef benthos at the Inner Lagoon (orange) versus Outer Lagoon (blue) reefs show the mean diel cycles of (B) seawater temperature, (C) salinity, (D) pH, and (E) DO. Diel cycles are shown as means ± 95% CI. Experimental setup at (F) the Outer Lagoon reef (image credit: The Ocean Agency) and (G) the Inner Lagoon reef.

Fig. 2.

Principal component analysis of coral performance following 3 (A–C) and 6 mo (D–F) of transplantation. Polygons outline the ordination groups, with Inner Lagoon in orange and Outer Lagoon in blue, whereas vectors in A and D indicate the loadings of the phenotypic variables to the PCs, with length of arrow signifying strength of loading. Plasticity, calculated as the distance in principal component space between each genet’s native phenotype (filled symbols) versus cross-transplanted phenotype (open symbols), are indicated by lines in B and E. The boxplots and data points for plasticity values of each species are shown in C and F.

Fig. 3.

Fitness score for (A) M. capitata and (B) P. compressa. Fitness score is a product of net growth and survival (G*S; solid lines) and for M. capitata was also calculated as the product of net growth, survival, and reproductive success (G*S*R; dashed lines). n = 10; error bars indicate SEM. Magnitude of local specialization for each genet of (C) M. capitata and (D) P. compressa. Local specialization values are defined as the difference in fitness score (G*S only) of a genet at its origin and destination reef, divided by the mean fitness score of all conspecifics at the destination reef. Positive values indicate local site specialization; negative values indicate destination reef favorable.

Fig. 4.

Coral performance following acute heat stress (high temperature; 32 °C) versus controls (ambient temperature; 27 to 28 °C). (A) Photosynthetic efficiency (dark-adapted yield; Fv/Fm), (B) gross photosynthesis rates, (C) LEDR rates, and (D) calcification rates. n = 8 to 10; error bars indicate SEM. Inset indicates statistically significant fixed effects (S, species; T, temperature; D, destination).