Hope for Threatened Pillar Corals

by Kim Weisenborn

Pillar Corals Successfully Fertilized in Curaçao Laboratory

Close-up image of pillar coral, Dendrogyra cylindrus. Image source: http://www.dcnanature.org/pillar-coral/

Close-up image of pillar coral, Dendrogyra cylindrus. Image source: http://www.dcnanature.org/pillar-coral/

Coral reef ecologist, Kristen Marhaver and her team at the Curaçao-based CARMABI Foundation have found a way to successfully fertilize threatened Caribbean pillar coral, Dendrogyra cylindrus. The team spent three years and five lunar cycles observing the spawning behavior of pillar corals in Curaçao, which only spawn a few specific nights out of the year. They collected gametes from the spawning individuals on three occasions to take back to their laboratory in an effort to rear the larvae and primary polyp settlers, which is no easy feat [a,b].

“It’s often really hard work to get each step figured out, but eventually scientists are able to get the whole process to work,” says Marhaver about getting conditions just right for in vitro fertilization [a].

While other species of coral have been successfully grown in laboratories, this is the first time that pillar corals have been spawned in vitro. Caribbean reefs have been surveyed for over 30 years, and never have sexually-produced larvae pillar coral recruits been observed. Marhaver and her team were some of the first ecologist to observe the spawning behavior of these species. Many coral species are hermaphrodites, broadcasting both male and female gametes into the water column. Pillar corals are gonochoric, meaning they are either female producing all-female gametes, or are male producing all-male gametes. Because of this, synchrony in spawning within a colony is especially important for successful fertilization–hence spawning on a predicted lunar cycle [a].

Marhaver and her team found that after successful fertilization, rapid embryonic development occurs. This is contrary to the developmental growth of juvenile pillar corals into adults, which can take more than 10 years to reach full maturity (pillar corals mean annual growth is a mere 8mm!) [b,d].

Marhaver’s report, “Reproductive natural history and successful juvenile propagation of the threatened Caribbean Pillar Coral Dendrogyra cylindrus” describes in detail the successful propagation of embryos into free-swimming larvae, the larval settlement, and the survival of primary polyp settlers in the laboratory over the period of seven months. Colony-level data collected in Curaçao over the past three years has allowed the researchers to make better predictions of spawning times relative to the lunar year. Their research has also confirmed that males begin spawning before female pillar corals and that split-spawning occurs across months of time [b]–all important findings for better understanding the life histories of wild pillar coral.

Hope for Conservation

Corals face a wide array of threats that, when combined on top of each other, greatly hinder a reef’s chances for recovery. Threats, like overfishing, climate change, ocean acidification, sedimentation, coral harvesting, physical damage from human recreation, bleaching and disease all add up. They drastically decrease a coral’s ability to sustain resilience, especially for the slow growing pillar coral. For an ecosystem that supports 25% of the oceans marine life, threats like these place the livelihood of over 400 million people in jeopardy [c].

Information on pillar coral life history previous to this three year study was severely lacking. With the successful in vitro spawning, researchers can focus more attention on what ideal combination of conditions will create the best environment for conserving these corals. It may be too early to tell if lab-spawned pillar corals will grow successfully in the wild, but the hope is that these and future lab-spawned corals can be transplanted back into areas of the Caribbean to promote more resilient colonies [a]. Though juvenile survivorship in the wild can be low, there have been instances of juvenile corals thriving in areas where adult corals are suffering. This gives hope to the idea that areas can recover from injury [b].

Marhaver says that “a precautionary approach for conservation is warranted, given this species’ peculiar life history traits and still unresolved population structure,” but that the “natural history and husbandry contributions presented here should facilitate accelerated research and conservation of this threatened coral [b].”

Reef fish swimming around a colony of pillar coral.

Reef fish swimming around a colony of pillar coral. Image source: http://www.divingplaya.com/

Sources

a. Gammon, Katherine. “Baby Corals Grown in the Lab Could Save Threatened Ocean Reefs.” Takepart. 16 Mar 2015.

b. Marhaver, Kristen L., Vermeij, Mark J.A., and Medina, Mónica M. “Reproductive natural history and successful juvenile propagation of the threatened Caribbean Pillar Coral Dendrogyra cylindrus.” BMC Ecology: 15:9, 2015.

c. Woody, Todd. “Climate Change Is Killing Coral Reefs, and That Could Cost the Economy $1 Trillion a Year.” Takepart. 9 Oct 2014.

d. “A Species Action Plan for the Pillar Coral Dendrogyra cylindrus.” Florida Fish and Wildlife Conservation Commission. 1 November 2013.