Islands' work – spawning season 2018
Photos: left) collecting coral spawn on Curaçao; middle) coral egg and sperm bundles accumulate in sampling vial on top of collection net, Curaçao; right) coral embryos are ready to be added to new pool―newly designed floating coral larvae rearing pools―by 'proud parents'; all Paul Selvaggio.
Nature is not always predictable, as we know, but this year's spawning pattern made it a special challenge to accomplish our spawning work― which may have been similarly experienced by others in the field as well. . Every few years, there is a so-called “split spawn” year. To synchronize their spawning, the corals follow the annual sea water temperature to choose the month while the lunar cycle determines the night they will spawn during that month. When there are two full moons occurring in the relevant temperature range, there could be a split spawn, where some colonies spawn during earlier moon, while the others wait for the later one.
“We had predicted, along with most other experts in the region, that because the full moon was timed so late in the month, that the Acroporas would spawn on the ‘front end’ of August, after July's full moon that is, rather than the ‘back end'”, explains Dr. Margaret Miller, SECORE's Research Director. “This was based on quite a few past observations from distant locations. So we planned our main Acropora expeditions―especially Curaçao and Bahamas―for the early part of August. In fact, virtually no Acropora spawning was observed throughout most of the Caribbean during this week. More of it spawned the following month, but tremendous asynchrony was observed among reef sites within a location. For example in Curacao, our team documented spawning at one site two nights before the full moon, and at another site 10 nights after the full moon.” A similar unclear pattern was observed by our teams that monitored elkhorn corals in Mexico. To do more reliable predictions for such split spawning years in the future remains a challenge: what has caused this patchy spawning pattern is not really resolved yet.
This patchy spawning pattern happened for other coral genera as well and for corals in the wild it may have been difficult to mate under these conditions. “One of our two spawning dives in Eleuthera, Bahamas, we observed only two colonies of the brain coral Pseudodiploria strigosa spawning”, says Miller. “It is unlikely that this small number of parents spawning would have had successful fertilization after the gametes had traveled to the ocean surface 10 meter up and were diluted. By collecting the bundles and keeping them concentrated, we were able to obtain almost 100 percent fertilization and about 400,000 larvae.” The larvae are settled on special substrates to be able to grow into young corals.
“The substrates with larvae settled on them are called Seeding Units and can be subsequently outplanted to the reef with comparatively little effort”, explains Miller. “And we have been testing the new design for our floating coral rearing pools.” The idea of the pools is to rear coral larvae independent from land-based facilities and in quantities that enable larger scale restoration efforts. The first test-runs were undertaken during the restoration workshops in Mexico 2015. Now, with input from engineers and specialists, a new generation of coral kindergartens are on the home stretch.
Photos: left) setting up a coral kindergarten; middle) fertilization work needs absolute focusing; right) different types of coral settlement tiles; all at Bahamas and by Paul Selvaggio.
Two of our main operating sites are based on Islands: at CARMABI Research Station on Curacao and at Cape Eleuthera Institute, on Eleuthera, Bahamas. Most of our main restoration research is done on Curaçao, where we have a well established structure, regular spawning workshops, and a pilot and demonstration site for outplanted corals. By contrast, our joint efforts with the Perry Institute for Marine Science on Eleuthera happens on relatively virgin territory: “This year’s work in The Bahamas focused on coral spawning in new sites off Abaco and Eleuthera Islands and testing new technology for larval culture and settlement”, explains Dr. Craig Dahlgren, Director of the Perry Institute of Marine Science. “This is part of our overall goal to reverse the decline of Bahamian coral reefs by reducing threats, building reef resilience, promoting Diadema antillarum recovery, and restoring corals using larval propagation as well as asexual techniques.”
Photos: left) preconditioned coral settlement tiles displaying various shapes...; middle) ...to test for settlement preferences by coral larvae, also in the presence of grazers like diadema sea urchins; right) ...and on a micro-habitate scale; all at Curaçao, first two by Paul Selvaggio; last photo by Sina Löschke.
Insights from the field
The Bahamas being a relatively new working site, all of the background knowledge is starting from ground zero. Some of this background relates to operational constraints, and, we have devised good plans to overcome these in future operations.
There is also local ecological knowledge that we need to build. For instance, there are few observations on spawning times for most species in this area. Still, you need to start somewhere! “While corals in The Bahamas were not observed to spawn in August during our window for field work, we were able to successfully test the new floating larval rearing pool design in a remote area and have some suggestions for improvement”, says Dahlgren. “In September, although the weather made it a real challenge to undertake the required night dives, our team was able to collect spawn of Orbicella annularis, Orbicella faveolata, and Pseudodiploria strigosa on two nights. As a result, we were able to successfully raise larvae for P. strigosa and the two Orbicella species and study hybridization between Orbicella species.”
About 275,000 larvae were cultured and distributed between one of the new pool designs and an ‘old model’ pool transferred from last year’s Bahamas work in Nassau. The new pool design proved to function very well, while the old design showed flaws by leaking considerable amounts of larvae during tide changes.
In addition to the pools, coral larvae were raised in three large aquaculture tanks at the Cape Eleuthera Institute. Larvae of O. annularis and P. strigosa were stocked at a density of ~ 100,000 per tank. Despite lacking temperature control in the tanks, the larvae did very well and settled successfully on about 200 conditioned substrates per tank. By contrast, unconditioned concrete substrates yielded essentially zero settlers, confirming the need for suitable biofilm to make any new home attractive for coral larvae in search of the right place to become a young coral.
About 1500 of settled substrates, from both pool designs and tanks, are already outplanted to two demonstration sites with a density of up to 8 substrates per m². All in all, a successful spawning season with all partners working alongside and a promising outlook for next year―and hopefully many young corals have grown into little colonies by then!
Photo: adding coral larvae to floating rearing pool – SECORE's coral kindergarten; Bahamas, Paul Selvaggio
On Curaçao, our team has collected spawn of the brain coral Diploria labyrinthiformis, the elkhorn coral Acropora palmata (thanks to the tireless night diving), and the staghorn coral A. cervicornis and has cultured about 235,000 resulting coral larvae. They have just collected spawn of the brain corals Colphophillia natans and Orbicella faveolata during our restoration workshop on-site; and there is still more spawning to come...
During the whole spawning season, Dr. Valerie Chamberland and Kelly Latijnhouwers, SECORE'S Research Scientist and Restoration Technician on Curacao, respectively, have set-up experiments on coral larvae settlement choice, including the different new substrate prototypes and microhabitat preferences. Team Curaçao has also been conducting an experiment investigating the influence of Diadema sea urchins' grazing on coral settlement and early life-stage survival. These urchins, by acting like ‘lawnmowers of the reef’, may be a key to maintaining the habitat quality of the reef substrate that will enable larval recruits to thrive. Propagation and restoration of these urchins have also been under consideration as additional restoration measures to integrate with coral outplanting.
Several hundred Seeding Units, each harboring dozens of settlers, have been outplanted so far and there are more to come before the end of this year. We are eagerly anticipating the first survivorship surveys to occur in November in both locations to see if our new prototype substrates have succeeded in providing the settlers a good home.
Stay tuned for our next spawning update from the Riviera Maya, the Caribbean coast of Mexico, where the team under the lead of Dr. Anastazia Banaszak had an especially busy and successful spawning season as well! Let take a look behind the scenes there...