Evaluating the Effect of Symbiodiniaceae on the Survival, Acquisition, and Growth of Newly Settled Corals of Three Caribbean Species

As coral reef restoration increases the focus on ex situ coral spawning, larval rearing, and grow-out, it is important to understand the role of the endosymbionts Symbiodiniaceae on newly settled corals grow-out. Corals provide Symbiodiniaceae a sheltered microhabitat, rich in carbon dioxide and nutrients, while the Symbiodiniaceae provide the coral energy in the form of photosynthesized sugars and essential amino acids. Restoration efforts can be enhanced by provisioning newly settled corals with cultured symbionts that improve the host health. This study assesses the effect of four commonly cultured Symbiodiniaceae (Symbiodinium, Breviolum, Durusdinium, and Fugacium) on the differential survival and growth of newly settled corals of three Caribbean species (Orbicella faveolata, Pseudodiploria strigosa, andColpophyllia natans). Symbiodiniaceae were introduced via horizontal transmission at a concentration of 10⁴ – 10⁵ Symbiodiniaceae cells per mL of artificial seawater during the log phase of their growth curve, three days per week for the first two weeks. Corals were examined under a microscope and photographed weekly during the first month, and monthly thereafter for an additional five months. Survival was censused using coral maps. Photographs were used to determine the degree of pigmentation via a color gradient chart, and to measure coral surface area using the image analysis program cellSens; changes in these measurements over time were used to determine acquisition of Symbiodiniaeceae and growth rates, respectively. These findings will improve the use of Symbiodiniaceae species to seed newly settled corals and successfully rear them ex situ without the need for cohabitation with adult corals, and potentially increase the success of coral grow-out ex situ.