''Oculina varicosa'', or the ivory bush coral, is a

scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyp (zoology), polyps and have a cylindrical body crowned by an oral di ...

n deep-water

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

primarily found at depths of 70-100m, and ranges from

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and

Cape Hatteras Cape Hatteras is a cape located at a pronounced bend in Hatteras Island, one of the barrier islands of North Carolina. Long stretches of beach, sand dunes, marshes, and maritime forests create a unique environment where wind and waves shape ...

to the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

and the

Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...

. ''Oculina varicosa'' flourishes at the Oculina Bank off the east coast of

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

, where coral thickets house a variety of marine organisms. The U.S.

National Marine Fisheries Service The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the stew ...

considers ''

Oculina ''Oculina'' is a genus of colonial stony coral in the family Oculinidae. These corals are mostly found in the Caribbean Sea, the Gulf of Mexico and Bermuda Species of concern are those species about which the U.S. Government's

National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

(NOAA), National Marine Fisheries Service, has some concerns regarding status and threats, but for which insufficient information is available to indicate a need to list the species under the U.S. Endangered Species Act (ESA). While ''Oculina'' is considered a more robust genus in comparison to tropical corals, rising

ocean temperature The ocean temperature varies by depth, geographical location and season. Both the temperature and salinity of ocean water differs. Warm surface water is generally saltier than the cooler deep or polar waters; in polar regions, the upper layers of ...

s continue to threaten coral health across the planet.

Species description

''Oculina varicosa'' grows in arborescent branches, typically about 1 to 2 meters tall. polyps wrap around the coral branches and extend when feeding to provide ''Oculina'' with essential nutrients from various forms of

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

and

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

. ''O. varicosa'' has widely spaced, distinct

corallite A corallite is the skeletal cup, formed by an individual stony coral polyp, in which the polyp sits and into which it can retract. The cup is composed of aragonite, a crystalline form of calcium carbonate, and is secreted by the polyp. Corallit ...

s, approximately 3 millimeters in diameter. While ''O. varicosa'' most often exists as an aposymbiotic coral (without

symbiont Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

s), it can also exist with

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

which helps provide another food source. Symbiotic ''Oculina'' colonies with

zooxanthellae Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''Sy ...

generally come in various shades of brown, while azooxanthellate corals tend to have a lighter, whiter appearance. Corals usually receive their brilliant color from their symbionts, so aposymbiotic colonies tend to lack bright colors.

Ecology

Coral growth usually relies on both food and sunlight, but because ''O. varicosa'' exists primarily as a deep-water coral, it typically lacks zooxanthellae. Only shallow water forms of ''O. varicosa'' contain zooxanthellae because they have more access to sunlight. Zooxanthellae, or coral symbionts, serve in a mutualistic relationship as a source of energy for coral colonies, while also receiving shelter between coral polyps. Zooxanthellae

photosynthesize Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

and transfer sugars to the coral polyp, but azooxanthellate, or aposymbiotic, coral colonies rely on obtaining energy through

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

y. Coral polyps snatch planktonic matter out of the water column in order to produce energy for growth. Surprisingly, corals have mouths and stomachs to digest the food they catch with their tentacles. Coral

y is more nutrient dependent, while photosynthesizing symbiotic corals are more dependent on sunlight. Although ''O. varicosa'' is not considered a reef-building coral, it still serves an important role in creating larval habitat for native fish and

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s. ''Oculina'' provides a base for hard-bottom communities in supporting valuable fisheries species and a variety of other economically important organisms.

Habitat

While ''O. varicosa'' does exist in both shallow waters (6 meters) and deep water, at depths of greater than 100 meters, it almost exclusively thrives on the Oculina Bank off the coast of Florida. ''Oculina'' coral reefs off Florida have been identified as

essential fish habitat Essential Fish Habitat (EFH) was defined by the U.S. Congress in the 1996 amendments to the Magnuson-Stevens Fishery Conservation and Management Act, or Magnuson-Stevens Act, as "those waters and substrate necessary to fish for spawning, breeding, ...

for federally managed species. The

Experimental Oculina Research Reserve The Experimental Oculina Research Reserve preserves the Oculina Banks, a reef of ivory bush coral (''Oculina varicosa'') off the coast of Fort Pierce, Florida. ''Oculina varicosa'' is a U.S. National Marine Fisheries Service species of concern. Sp ...

preserves the Oculina Banks, a reef of ''Oculina varicosa'' existing between 70 and 100 meters depth, and spanning 130 nautical miles, approximately 15 miles off the coast of Daytona Beach. Because symbionts only coexist with ''Oculina'' in shallow water conditions, this excludes aposymbiotic colonies on the Oculina Bank. At this location, ''O. varicosa'' branches grow into massive thickets and can reach up to 2 meters in height. Tree-like colonies on the Oculina Bank create an ideal place for a diverse population of fish and invertebrates to thrive. More than 70 species of fish and over 380 invertebrates call the Oculina Bank their home. A variety of

Grouper Groupers are fish of any of a number of genera in the subfamily Epinephelinae of the family Serranidae, in the order Perciformes. Not all serranids are called "groupers"; the family also includes the sea basses. The common name "grouper" is u ...

species are known to spend much of their juvenile stages hiding in the branches of ''Oculina''; namely,

Gag A gag is usually an item or device designed to prevent speech, often as a restraint device to stop the subject from calling for help and keep its wearer silent. This is usually done by blocking the mouth, partially or completely, or attempting ...

, Scamp, Speckled Hind, Yellowedge and

snowy grouper The snowy grouper (''Hyporthodus niveatus'') is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is part of the family Serranidae, which also includes the anthias and sea basses. It is found in the western A ...

. Discovered in 1975, the Bank became a protected area by 1984 as the Oculina Bank Habitat Area of Particular Concern. The known and documented threat in the Oculina Banks area is damage from mechanical

fishing Fishing is the activity of trying to catch fish. Fish are often caught as wildlife from the natural environment, but may also be caught from stocked bodies of water such as ponds, canals, park wetlands and reservoirs. Fishing techniques inclu ...

gear, including dredges, bottom long lines, trawl nets and

anchor An anchor is a device, normally made of metal , used to secure a vessel to the bed of a body of water to prevent the craft from drifting due to wind or current. The word derives from Latin ''ancora'', which itself comes from the Greek ἄγ ...

s despite supposed habitat-based protections. Anchoring vessels and bottom-trending fishing gear became prohibited within the protected area, in an effort to maintain the ''Oculina'' thickets and the habitat as a whole. Temperature ranges from 7 to 27 degrees Celsius on the Oculina Bank. Such seasonal extremes effectively accustom ''Oculina varicosa'' to wide temperature shifts. This temperature resilience indicates that ''O. varicosa'' may be more apt to survive despite rising global ocean temperatures. Temperate corals, such as ''

Oculina arbuscula ''Oculina arbuscula'' is a branching temperate coral found along the east coast of the United States from Florida to North Carolina. It has a facultative symbiosis with microalgae of the family Symbiodiniaceae. Unlike tropical corals, ''O. arbuscu ...

'' and ''

Astrangia poculata ''Astrangia poculata'', the northern star coral or northern cup coral, is a species of non-reefbuilding stony coral in the family Rhizangiidae. It is native to shallow water in the western Atlantic Ocean and the Caribbean Sea. It is also found o ...

'', show relatively high tolerance to ocean warming because of these large seasonal shifts. During upwelling events at the Oculina Bank, temperatures can settle around 7 degrees Celsius for days at a time.

Research

Because the genus ''Oculina'' is considered one of the more resilient corals on the spectrum, it functions as a useful experimental subject, especially in the context of global climate change. Both cold and heat stress treatments on temperate corals serve as an important stepping stone in effectively dissecting coral health in response to rising ocean temperatures. Researching the effects of temperature stress on ''O. varicosa'' furthers understanding of how both this species and the hard bottom communities it helps form, will change under warmer oceans.

References

External links

* {{Taxonbar, from=Q3332468 Oculinidae Animals described in 1821