User:Reneynz/Pavona varians

Introduction
Pavona varians, also known by its common name corrugated coral, is a species from the genus Pavona. Pavona varians is a type of hermatypic coral commonly distributed across tropic environments.

Distribution and Ecological Role
Distribution of the coral include the equatorial Indian and Pacific Ocean, and notably, not found in the Atlantic ocean. Pavona varians have also been found to be distributed as North as the sea of Japan, in the Red Sea, and islands off the Pacific coast of Columbia and Costa Rica. Pavona varians are typically found an average of 45 feet below water on vertical surfaces in turbid, nutrient rich, water. Specifically, Pavona varians are found between crevices of the reef crest habitats and back reef habitats, including lagoons. Low-energy environments rarely harbor P. varians, but they can be found under weak-to-strong current systems.

Pavona varians typically grow small plate-like colonies no larger than 25 centimeters on rocky surfaces, preferably in calm waters. Researchers have noted the coral's ability to rapidly colonize environments where other species of coral have either died or struggled to colonize. Notably, Pavona varians has been able to colonize areas where once large colonies of Goniopora and Porites once were distributed.

Competition and Predation
Typical P. varians compete with sponges, bryozoans, coralline algae, and Gonoipora and porites coral. The sea stars, Acanthaster planci and Acanthaster meleagris, are well known predators of  P. varians extending from the Coco Islands off Myanmar ro Costa Rica. Typically, competition over space and resources, and predation from sea stars limit the population of this coral.

Feeding
Like many hermatypic coral, P. varians appear to have a mutual relationship with zooxanthellae, providing shelter in return of important nutrients like oxygen.

Symbiosis
Current, limited, evidence of symbiosis between Endeis sp. species and Pavona varians colonies exist around Magoodhoo Island. This species of sea spiders were mainly found on and between the corallines of P. varians. There is no clear relationship between Pavona varians and Endeis sp. on this reef, although it is likely that sea spiders inhabiting these corals as well as other coral cryptobenthic associates are commensals seeking shelter.

Morphology
The Pavona varians are an encrusting species of coral that vary in color and tend to have red polyps, a green coenosteum, as well as blue mouths. Pavona varians is often mistaken for its relative, Pavona sp.a, but differs in structure due to their unique ridges that sometimes take on a cup-like form.

Reproduction and Growth
Pavona varians colonies are hermaphroditic broadcast spawning coral that has both male and female reproductive organs and releases gametes into the water column during spawning events. P. varians colonies spawn eggs or sperm at least once a month, with eggs varying in color from white to beige and are positively buoyant. Reproductive activity appears to be active throughout the year, but is most active in dry seasons, with an average of anywhere from 5 to 10 spawn cycles a year. The eggs vary in size from 100 to 105 micrometers, making it one of the smallest eggs in the Pavona family. Average egg production for each cycle varies depending on environmental quality, but estimates range from as low as 400 to as high as 22,300 eggs.

The colonies have distinct lobed morphology with deep valleys which separate polyp covered ridges. Polyps release their gametes into water during spawning events, where they fertilize to form free-swimming planula larvae onto a suitable substrate to form new colonies.

A mature gamete is shed into a coelenteron and spawned through the mouth. A planula larva develops from a zygote. Prior to larval settlement, tentacles, septa, and pharynx undergo early morphogenesis.

The average P. varians grows about 3.5 mm per year on hard surfaces. Compared to other coral species, this species of coral is less dominant than others.

Climate Change
During the 1982- 1983 El Nino Event, coral reef population decreased as a result of bleaching from Myanmar extending to Costa Rica. Many members of the Pavona family, and other coral families, faced population crashes, but after the event, populations slowly recovered. Due to the low recovery rate of many corals, coral populations took a while to rebound from the event.

However, Pavona varians have been shown to be resistant to high levels of environmental stress, and as a result, have not taken major decreases in population from climate change. Additionally, they are opportunistic, and have demonstrated capabilities of taking over areas where dead coral, like Porites, have once dominated. In particular, P. varians off the Coco Islands near Myanmar have taken over reefs at a fast rate.

P. varians survive between 28℃ and 30.5℃, but cannot tolerate waters higher than 31.5℃, making them more likely to survive warmer waters than many coral. This coral has shown to be more resistant to bleaching as a result, avoiding major bleaching events that impacted coral population in 1982 and 1998, leading to it being categorized as “Least Concern” by the International Union for Conservation of Nature’s Red List. However, Pavona varians are not invincible and have seen population decreases in major warming events, like most recently in 2001.