Symbiont acquisition in Caribbean coral recruits

5-month-old Orbicella faveolata recruits from Eleuthera in the Bahamas. The polyp in the foreground is growing quickly and recently laid down new tissue and skeleton - so new, it hasn’t acquired symbionts yet! That’s why it is clear/white, while the rest of the polyp is brown.

5-month-old Orbicella faveolata recruits from Eleuthera in the Bahamas. The polyp in the foreground is growing quickly and recently laid down new tissue and skeleton - so new, it hasn’t acquired symbionts yet! That’s why it is clear/white, while the rest of the polyp is brown.

A magnified photograph of a month-old Orbicella faveolata recruit, which had just started to acquire symbionts.

A magnified photograph of a month-old Orbicella faveolata recruit, which had just started to acquire symbionts.

One-month-old Orbicella faveolata polyps fluorescing under violet light. The red fluorescence in their bodies and tentacles comes from Symbiodinium cells.

One-month-old Orbicella faveolata polyps fluorescing under violet light. The red fluorescence in their bodies and tentacles comes from Symbiodinium cells.

The early life stages of corals are crucial.

Since coral spawning and settlement in the Caribbean coincides with the warmest ocean temperatures of the year, and because corals in their early life stages are particularly vulnerable to environmental stress and high mortality, it is important to understand how coral juveniles might become more thermally resilient from the start. 

Most Caribbean corals take up new algal symbionts (family Symbiodiniaceae) through horizontal transmission from the environment upon larval settlement to the reef. Warming ocean temperatures may favor initial uptake of the thermally tolerant symbiont Durusdinium (Abrego et al. 2012), although this process is not well understood in Caribbean coral recruits. Moreover, nearby adult corals may influence symbiont availability by continuously discharging symbionts into the environment (Hoegh-Guldberg & Smith 1989), where they may persist in the sediment and water column (Cunning et al. 2015) and increase the rate of symbiont acquisition by newly settled recruits (Nitschke et al. 2015). Therefore, as symbionts like Durusdinium become more prevalent on reefs due to increasingly frequent thermal stress and mass bleaching events, they may accelerate the positive feedbacks of thermally tolerant symbionts at the ecosystem level. Such dynamics have significant implications for reef performance and responses to environmental change.

Since beginning my Ph.D. in August 2017, I have been evaluating metacommunity feedbacks in coral symbiosis ecology by studying whether differences in the local availability of different types of Symbiodiniaceae influence the composition of symbiont communities populating juvenile corals. Focusing on key reef-building species including Orbicella faveolata (mountainous star coral) and Diploria labyrinthiformis (grooved brain coral) collected from various sites across the Caribbean, I am conducting larval settlement and symbiont uptake experiments in the presence of adult corals with different symbiont assemblages in order to quantify the degree to which the existing symbiont metacommunity on a reef influences the establishment of symbiosis in coral recruits. My goal is to elucidate potential intergenerational feedbacks that may drive the future trajectory of coral symbiosis ecology in the Caribbean.

I am working with partners including SECORE International, the Perry Institute for Marine Science, The Nature Conservancy, Shedd Aquarium, and NOAA's Southeast Fisheries Science Center to collect and rear coral juveniles.

6-month-old O. faveolata colony, which started as one polyp and is now budding off to form new ones.

6-month-old O. faveolata colony, which started as one polyp and is now budding off to form new ones.

6-month-old O. faveolata colony, which started as one polyp and is now budding off to form new ones.

6-month-old O. faveolata colony, which started as one polyp and is now budding off to form new ones.

2-month-old Diploria labyrinthiformis recruits.

2-month-old Diploria labyrinthiformis recruits.

The same 2-month-old Diploria labyrinthiformis recruits as pictured above, fluorescing under violet light. The red fluorescence comes from Symbiodinium cells in the coral tissues.

The same 2-month-old Diploria labyrinthiformis recruits as pictured above, fluorescing under violet light. The red fluorescence comes from Symbiodinium cells in the coral tissues.

Experimental setup with 12 aquaria. Half were kept at ambient temperature and Half were kept at elevated temperature. At each temperature, half the aquaria held an adult coral colony with <95% Durusdinium, and the other half held an adult colony <95% Cladocopium. This created triplicates for 4 different treatments. Ceramic plugs with recruits were evenly distributed amongst aquaria.

Experimental setup with 12 aquaria. Half were kept at ambient temperature and Half were kept at elevated temperature. At each temperature, half the aquaria held an adult coral colony with <95% Durusdinium, and the other half held an adult colony <95% Cladocopium. This created triplicates for 4 different treatments. Ceramic plugs with recruits were evenly distributed amongst aquaria.

Newly settled, aposymbiotic Orbicella faveolata recruits on a ceramic plug.

Newly settled, aposymbiotic Orbicella faveolata recruits on a ceramic plug.

Orbicella faveolata recruits fluorescing recruits under violet light.

Orbicella faveolata recruits fluorescing recruits under violet light.

A single O. faveolata recruit (&gt;1 mm in diameter) is sampled with a razor blade to be stored in 1% SDS for later DNA extraction.

A single O. faveolata recruit (>1 mm in diameter) is sampled with a razor blade to be stored in 1% SDS for later DNA extraction.