A student of University of Amsterdam and a staff researcher of Naturalis Biodiversity Center and University of Groningen recently published the first detailed report of hard corals digesting salps in the Caribbean.  Three species of hard corals were spotted digesting salps in Curacao’s Director’s Bay in July 2021, providing exciting new insight into the coral reef predation.   

Salps, also known as sea grapes, are gelatinous, barrel-shaped tunicates. Multiple salp bodies can link together creating whole colonies, able to move through the water column by utilizing one of the most efficient jet population systems found in the animal kingdom.  Previously, fish were thought to be the main predators of salp, however new information is emerging on predation by corals as well.

Sea Grapes

To date, there is limited information on salpivorous corals. As salps are relatively large planktonic animals, it was assumed that predation by corals was limited to those with polyps with mouth’s larger than one centimeter, large enough to engulf an entire salp. However, observations from the Mediterranean have found polyps from smaller mouthed corals working together to digest larger catches, hinting that salp may be an important food source across a wide variety of coral species.

Observations on Curacao

In July 2021, a swarm of these salps were spotted in Curacao’s Director’s Bay.  Upon closer inspection, Lars J. V. ter Horst, student of University of Amsterdam also found captured salps amongst three different species of hard corals: yellow finger coral (Madracis auretenra), maze coral (Meandrina meandrites), and great star coral (Montastraea cavernosa).  He contacted Bert W. Hoeksema at Naturalis and the University of Groningen who previously published about salpivorous corals in Malaysia and Thailand. They then proceeded to publish a report together. This is important as this was the first record of yellow finger coral and maze coral as salp predators.  In addition, since salp swarms are frequent observed within the Caribbean, these findings hint that these swarms could potentially be a more common and widespread food source for corals than previously thought.

A salp caught by multiple polyps of the branched coral Madracis aurentenra (photo Lars J.V. ter Horst)

Implications

These findings provide exciting new insight into coral reef ecology and the importance of salp swarms as a food source. As coral reefs continue to face increasing pressures, a more holistic understanding of their dynamic ecosystems will be crucial for conservation management moving forward.

Find out more information by reading the full report on the Dutch Caribbean Biodiversity Database using the button below.

https://www.dcbd.nl/document/salpivory-colonial-reef-corals-cura%C3%A7ao...

Article published in BioNews 49

Abstract

Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2 , has attained international conservation status due to the rich diversity of species that reside on the bank. In order to assess the role of Saba Bank as a potential reservoir of diversity for the surrounding reefs, we examined the population genetic structure, abundance and health status of two prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongia muta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1- 5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) on Saba Bank and around Saba Island, and compared with published data across the wider Caribbean. Our data indicate that there is genetic connectivity between populations on Saba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean, ranging in distance from 100s–1000s km. The genetic diversity of Saba Bank populations of M. cavernosa (π = 0.055) and X. muta (π = 0.0010) was comparable to those in other regions in the western Atlantic. Densities and health status were determined along 11 transects of 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa (0.27 ind. m-2, 95% CI: 0.12–0.52) were average, while the densities of X. muta (0.09 ind. m-2, 95% CI: 0.02–0.32) were generally higher with respect to other Caribbean locations. No disease or bleaching was present in any of the specimens of the coral M. cavernosa, however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth (48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta (83.5%) showed signs of presumed bleaching. The combined results of apparent gene flow among populations on Saba Bank and surrounding reefs, the high abundance and unique genetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to replenish genetic diversity or as a storehouse of diversity that can be utilized if needed for restoration practices.