Research signed by researchers from the Oceanographic Institute of the University of São Paulo (IO-USP) shows that the most commonly used method for combating solar coral (Tubastraea spp.) can even help the animal reproduce if not done at the right times. The sun coral is native to the Pacific Ocean, was accidentally introduced to the Caribbean in the early 1940s, and is considered an invasive exotic species in Brazil, as it has been registered in the country since the late 1980s.
Published in the magazine Marine biologyThe work supported by Petrobras, the National Petroleum Agency (ANP) and FAPESP shows that despite the fact that the invasive coral emits planula-type larvae all year round, peaks in release occur mainly related to the rise in temperature and the cloudiness of the sea. water. Larval emission can occur over a short period of time in response to the stress of mechanical removal.
The researchers point out that the procedure should not be carried out during these periods because the larvae released in large numbers can spread through the environment. The manual removal method, which involves removing colonies with a sledgehammer and chisel during autonomous diving, is practiced in some conservation units, as mentioned in the National Plan for Prevention, Control and Monitoring of Coral-Sol (Tubastraea spp.) in Brazil.
“It is the strategy chosen by some Brazilian institutions because it does not use chemicals and focuses exclusively on sun coral. The recommendation is to try to remove intact colonies, as any remaining tissue has the capacity for regeneration,” he explains. Damian Mizrahiwho performed and was most of the work during his postdoctoral studies at IO-USP scholarship holder of FAPESP at the Center for Marine Biology (CEBIMar) at USP during the final stages of writing the article.
According to the researchers, colonies may release larvae in response to removal stress observed during the study. Therefore, they recommend that corals removed from the natural substrate be isolated in sealed containers immediately after mechanical removal.
A single colony can release more than 90 such larvae, increasing the chance of colonization of substrates such as rocks and even piers, ships and oil platforms.photo: Damián Mizrahi)
“The study showed that the sun coral emits larvae all year round, which is associated with a large variability of environmental conditions, but concentrates reproductive effort over short periods, with many planulae emitted simultaneously. Another ability of the organism is regeneration, where small fragments can give rise to new polyps. The combination of these two strategies increases the chance of spread,” says Rubens Lopesprofessor at IO-USP who coordinated the research.
Remove and isolate
Before taking measurements after removing the sun corals, the researchers collected 200 colonies and transferred them to two 500-liter tanks at the foot of the Oceanographic Institute in Ubatuba, about 25 kilometers away from the collection area, on Ilha dos Búzios, on the beautiful island Beautiful Island. . The tanks were equipped with two safety nets with a mesh size of 200 micrometers, which prevent the larvae emitted by the colonies from escaping from the culture system.
If the corals are maintained under conditions of temperature and sun exposure similar to those of colonies in nature, they could be used to monitor the species’ reproductive activity. The data obtained show that larval emission dynamics from solar coral cultures in the laboratory resemble those recorded in nature, suggesting that cultivation can help monitor reproductive activity.
Between December 2017 and February 2020, the researchers conducted ten mechanical coral removal and collection campaigns, approximately three months apart. Environmental data were used to evaluate oceanographic influences on coral larvae releases.
During the dives, each colony removed from the substrate was individually packed with seawater in a sealed plastic bag several seconds after removal. Once on the ship, they were deposited in individual containers, immersed in the local seawater.
Once in the laboratory, larvae emitted by each colony were counted within two hours of sampling. Over the next two days, the containers were further inspected, but they no longer contained larvae, indicating that the release of the larvae occurred due to the stress caused by the mechanical removal of the corals.
During the two years of this phase of the study, 977 colonies were collected. During most of the time the work was carried out, the number of larvae released remained low, confirming studies in other regions of the Brazilian coast – in the country, sun coral is distributed from Ceará to Santa Catarina, with an emphasis on the coast in the southeast. .
The exceptions were two campaigns, in December 2017 and October 2019, when clearances were higher than normal. “During these specific periods, maximum larval emissions were also observed in the tanks where laboratory cultures of sun coral breeding colonies were developed,” Lopes explains.
The researchers also noted that seawater temperatures between 24.5°C and 27°C promote larval release, while colder water limits fertility. The lunar cycles and colony size were not statistically significant to be used as parameters for increased or decreased larval release.
“Turbidity is an indication of the presence of organic matter in the water, i.e. food. At these times, the sun coral opens the polyps to eat and ultimately releases the larvae that were inside,” Mizrahi points out.
Monitoring
The researchers note, based on the results of this study, that maintaining sun coral cultures near invaded areas could support control and monitoring protocols, which should only be implemented during periods of reduced larval release.
In just a few campaigns, many larvae were released into the wild, without being accompanied by similar activity in the tanks at the Ubatuba base. According to the researchers, this may be further evidence that the stress caused by removal stimulated the release, reinforcing the need to follow environmental isolation protocol after removal.
“The method has been used in some conservation units in Brazil, but the dynamics of solar coral reproductive activity had not yet been carefully considered to plan these removals. We hope to conduct new studies to better understand the processes of release of solar coral larvae and the impact on their distribution in the marine environment,” said Lopes.
Recently, mechanical removal was halted by a marine sanctuary in the Gulf of Mexico. Managers of conservation units in the United States to argue effectiveness of the method was not observed, because the smallest fragment remaining on the substrate after removal gives rise to a new colony.
The article Release of sun coral larvae after mechanical removal: a two-year study on the southeastern Brazilian coast can be read by subscribers at: https://link.springer.com/article/10.1007/s00227-023-04296-z.
André Juliao | FAPESP Agency