High flow correlates with increased skeletal growth in a reciprocal transplant experiment coral Pocillopora eydouxi

Smith, L; Wirshing, H; Baker, A; Birkeland, C

Reciprocal transplant experiments of the corals Pocillopora eydouxi and Porites lobata were carried out between two back reef pools to test effects of extrinsic versus intrinsic factors on skeletal growth rates. Pool 300 is relatively small and near the reef crest, resulting in greater environmental fluctuations than in Pool 400. Extrinsic factors include physical (temperature, irradiance, flow, etc.) and biological (competition, predation and disease) variables. Intrinsic factors include genetics of symbionts and host corals, as well as shape and size of coral colonies. During the experiment, data were collected on physical variables at the two transplant sites, and zooxanthella genotypes of transplant source colonies were tested at the beginning and end of the experiment. The experimental design controlled for effects of competition, predation, disease, transplant size, and transplant shape. For P. eydouxi, skeletal growth was affected by extrinsic but not intrinsic factors, resulting in higher growth in Pool 300 than Pool 400. There was no effect of extrinsic or intrinsic factors on skeletal growth of P. lobata. Pool 300 had more frequent and longer durations of seawater temperatures above the local summer mean (29.4 °C) than Pool 400, characteristics likely to decrease rather than increase skeletal growth. Pool 300 also had higher nutrient levels and flow velocities than Pool 400, characteristics that may increase skeletal growth. However, nutrient levels at both transplant sites were very low, and the difference between the sites not likely to have affected skeletal growth rates. In contrast, the higher flow velocities in Pool 300 than in Pool 400 were within the range of those likely to increase skeletal growth of P. eydouxi. The greater skeletal growth of P. eydouxi in Pool 300 occurred despite the presence of Clade D zooxanthellae in several source colonies in Pool 300, a clade known to result in greater heat resistance but slower skeletal growth in other reef-building corals.

High flow correlates with increased skeletal growth in a reciprocal transplant experiment coral Pocillopora eydouxi

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