Oculina arbuscula

Oculina arbuscula is a branching temperate coral found along the east coast of the United States from Florida to North Carolina.[1] It has a facultative symbiosis with microalgae of the family Symbiodiniaceae. Unlike tropical corals, O. arbuscula can survive without its algal endosymbionts by switching to a predominantly heterotrophic feeding strategy. Symbiotic colonies are typically found in shallower waters due to light availability, whereas aposymbiotic (without symbionts) or mixed colonies are found as deep as 200m.[2] The ability of O. arbuscula to exist in different symbiotic states makes it a good model system for studying the cnidarian-dinoflagellate symbiosis.

Symbiotic Oculina arbuscula colony collected from Radio Island, NC, US
Oculina arbuscula fragments with mixed symbiotic states. Collected from Radio Island, NC, USA

Oculina arbuscula
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Class: Hexacorallia
Order: Scleractinia
Family: Oculinidae
Genus: Oculina
Species:
O. arbuscula
Binomial name
Oculina arbuscula
Agassiz, 1880

Morphology

O. arbuscula forms colonies up to 0.5 meters in diameter with relatively short stubby branches.[2] Symbiotic colonies, depending on symbiont density, range from light to dark brown in color, whereas aposymbiotic colonies are white. Oftentimes colonies with mixed symbiotic states will be seen, with some branches or parts of branches appearing brown and others white.[2]

Feeding strategy

In low light environments, O. arbuscula relies on filter feeding particles from the seawater as its primary trophic strategy, likely because maintaining algal symbionts is not energetically favorable in those environments. Symbiotic colonies will also filter feed; however, their primary source of nutrition is from photosynthates derived from their endosymbionts. O. arbuscula is generally a very hardy coral and can survive even when deprived of food and light for six weeks.[2]

Reproduction

Like most corals, O. arbuscula can reproduce both sexually and asexually by fragmentation.[3] The reproductive biology of O. arbuscula has not been studied in detail, but it is suspected that this species is a gonochoric broadcast spawner due to its similarities to another species in the same genus, Oculina varicosa. Additionally, the presence of larval recruitment throughout the year indicates that O. arbuscula is reproductively active year-round, unlike tropical corals that typically have one annual reproductive event.[4]

Symbiosis

The microbial community of O. arbuscula has not yet been characterized. However, it is known that the predominant and nearly exclusive algal symbiont species present in the tissue is Breviolum psygmophylum.[1] Like tropical corals, this symbiosis is threatened by environmental stressors such as temperature and nutrients.[5][6]

References
  1. Rivera, H. E.; Davies, S. W. (2021-10-27). "Symbiosis maintenance in the facultative coral, Oculina arbuscula, relies on nitrogen cycling, cell cycle modulation, and immunity". Scientific Reports. 11 (1): 21226. doi:10.1038/s41598-021-00697-6. ISSN 2045-2322. PMID 34707162.
  2. Mw, Miller (1995-06-15). "Growth of a temperate coral: effects of temperature, light, depth, and heterotrophy". Marine Ecology Progress Series. 122: 217–225. doi:10.3354/meps122217. ISSN 0171-8630.
  3. Wagner, Lauren (2006). "Population Genetic Structure of the Temperate Scleractinian Coral, Oculina Arbuscula, in Coastal Georgia".
  4. Gleason, Daniel F.; Harbin, Leslie R.; Divine, Lauren M.; Matterson, Kenan O. (2018-09-01). "The role of larval supply and competition in controlling recruitment of the temperate coral Oculina arbuscula". Journal of Experimental Marine Biology and Ecology. 506: 107–114. doi:10.1016/j.jembe.2018.06.006. ISSN 0022-0981. S2CID 91025819.
  5. Aichelman, Hannah E.; Townsend, Joseph E.; Courtney, Travis A.; Baumann, Justin H.; Davies, Sarah W.; Castillo, Karl D. (September 2016). "Heterotrophy mitigates the response of the temperate coral Oculina arbuscula to temperature stress". Ecology and Evolution. 6 (18): 6758–6769. doi:10.1002/ece3.2399. ISSN 2045-7758. PMC 5058543. PMID 27777745.
  6. Ries, J. B.; Cohen, A. L.; McCorkle, D. C. (2010-09-01). "A nonlinear calcification response to CO2-induced ocean acidification by the coral Oculina arbuscula". Coral Reefs. 29 (3): 661–674. doi:10.1007/s00338-010-0632-3. ISSN 1432-0975. S2CID 8693805.
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