The Habitats, Behaviors, and Importance of Groupers (Epinephelus/Mycteroperca) in Coral Reef Ecosystems

This topic submitted by Brian Commiskey at 6:09 AM on 6/10/06.

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The Habitats, Behaviors, and Importance of Groupers (Epinephelus/Mycteroperca) in Coral Reef Ecosystems

Groupers are any genera of fish in the subfamily Epinephelinae and the family Serranidae. The common name grouper is in fact a name that encompasses a vast amount of highly diverse sea creatures in the family Serranidae which also includes sea basses. However when the word grouper is used, it most often is meant to specify the organisms in one of two large genera: Epinephelus and Mycteroperca.
Fish that are in the genera Epinephelus and Mycteroperca are multicellular heterotrophs that over time were selected for the dominant trait of a notochord (backbone) which stiffened their bodies and allowed for better support. This enabled these organisms the ability to perform quicker and more rigorous locomotion than their predecessors giving them a significant advantage over those lacking this trait. Over time these ancestral notochord groupers made other evolutionary advancements such as jaws, changes in tail and fins providing greater maneuverability, “lighter and more flexible bones and scales, an internal muscular-tendonous system, neutral buoyancy via the swimbladder and improvements in mouth structure (3).” All of these acquired characteristics did their part in ensuring the survival of what we know today as the groupers.
Two common and prominent species of grouper are: the Nassau grouper and the Black grouper. The Nassau grouper, also known as Epinephelus striatus, is characterized by a large oblong body with large eyes and spiny fins. Its coloration is the most distinct with five dark vertical bars across its body, block dots around the eyes, and a forked pattern on the forehead. Nassau grouper can be found all across the western Atlantic Ocean, throughout the Caribbean Sea, and in scattered parts of the Gulf of Mexico. The Nassau grouper matures late from anywhere between four to seven years before being able to reproduce. Nassau groupers can grow up to four feet long, weigh over fifty pounds and live a maximum of sixteen years. As of right now all fishing of Nassau grouper is prohibited in the U.S., and it is a candidate for the U.S. Endangered Species List.
Black grouper, also known as Mycteroperca bonaci, is characterized by a large oblong body and a huge lower jaw. Its coloration is olive or gray with dark rectangular spots along its body, head and side. The Black grouper can be found of the coast of Bermuda, throughout the western Atlantic Ocean, the Caribbean Sea, and in the Gulf of Mexico. They can grow up to fifty-two inches long, weigh up to 179 pounds, and live over thirty years. The Black grouper is currently not threatened by extinction and is fished recreationally and commercially in the Gulf of Mexico.
Groupers can be found in every ocean on the planet. The specific habitat that groupers choose to live in, however, varies from species to species and depends on the age of the organism. Juvenile groupers are found closer to the shore and usually seek protection in seagrass beds or tidal pools until they reach maturity. Mature groupers, on the other hand, tend to reside on the bottom of tropical and subtropical waters and most species live on coral reefs. Groupers are rarely found in packs or schools, and tend to only group together when it is time to aggregate or reproduce. Mature groupers generally feed on a variety of fish such as parrotfish, wrasses, damselfishes and snappers. In addition mature groupers are also known to prey on octopus, crab, lobster, and crustaceans. Juvenile groupers on the other hand tend to eat plankton, crustaceans, microalgae and other small microorganisms.
Groupers are not long-distance or fast swimmers but rather choose to lie, wait, and ambush their prey with a quick flash of their powerful jaws. Many species of groupers have also been found following other fish such as moray eels “as they forage over the reef, in order to catch the small fishes and crustaceans that are frightened from their hiding places by the eels (2).” Most groupers don’t have teeth in their jaws to rip apart their prey, but instead are equipped with powerful mouths and gills that create a sucking system that pulls prey into their mouth from a long distance. In addition, they have teeth plates inside their pharynx to crush their prey and to prevent them from escaping after being swallowed.
Predators on the prowl for groupers are: barracuda, king mackerel, moray eels, the sandbar shark (Carcharhinus plumbeus) and the great hammerhead shark (Sphyrna mokarran). Groupers try to avoid their predators by using their coloration to their advantage and hiding. They can do this by changing their coloration quickly according to the environment and mood that they are in, by moving into an area that is inaccessible by their prey and by using their coloration as camouflage.
Parasites also pose a problem for many groupers. Groupers are subject to a wide variety of parasites that affect the nostrils, stomach and intestines. Some of these parasites include isopods, larval tapeworms, nematodes, trematodes, and cestodes. Groupers can try to clean themselves from these parasites by frequently visiting wrasse cleaning stations. At these cleaning stations the grouper will open its mouth in a non-threatening fashion and cleaning wrasse will enter its mouth to remove parasites and dead tissues from the grouper’s gills and body.
Reproduction in groupers is a very unique and interesting process and varies from species to species as well. They are known to be solitary creatures except during the spawning season. During spawning season groupers are well known for aggregating in very large numbers, some reported at 100,000 individuals, at specific areas during the winter full moon. They do this, much like corals do, in order to increase the probabilities of successful mating and to increase the chance of surviving. Males are known to be able to spawn many times during the breeding period; however females on the other hand can only spawn once a year. Recent studies have shown that some groupers tend to be protogynous hermaphrodite, meaning that the majority of juvenile groupers are female and transform to males as they grow larger.
Interestingly enough, after spawning as a female for one or more years a female grouper may be subject to a change of sex and will become a male, “At sexual transition, the oocytes degenerate, the spermatogonia proliferate, and the ovary is transformed into a functional testis (2).” This change of sex can also occur by larger female groupers if there is a drastic decline in the amount of large sexually mature male groupers. However one a female has been changed to a male they are unable to change back. This interesting adaptation that has taken place with groupers is one of the many ways that groupers have adapted overtime to ensure that they reproduce and survive.
Groupers to say the least are an essential part of the coral reef ecosystem. Their role as predators on the coral reefs keeps other animals in check from running rampant and the prevent overpopulation of certain organisms on the reef. However, the major importance of groupers as far as humans are concerned has historically been their economic value. Human beings are single-handedly overfishing and destroying many species of groupers by timing their catches to the grouper spawn season. This is a very effective way to catch fish, but it drastically damages the groupers numbers of sexually mature individuals. When a population’s sexually mature individuals are reduced it takes a dramatic toll on the traits of the next generation. Especially if the trait that is being lost is an advantageous one, this can kill entire populations.
On the other side of the issue there has been an increase in the decimation of sharks recently, which in many scientists’ opinions has given rise to a drastic increase in grouper populations. Since one of the groupers main preys is parrotfish, this increase in grouper populations has created fewer parrotfish in many areas which has lead to more algae overgrowing the coral reefs. This algae overgrowth leads to the eventual death of the coral reef, which will lead to the eventual extinction of the entire coral ecosystem in that niche.
Due to the dilemma of whether to limit or increase the population of groupers, a study was recently conducted by two American Museum of Natural History biologists. They took a certain sector of a reef in the Bahamas and set it off-limits to fishing for twenty years. Many scientists predicted that without the fishing of groupers, the parrotfish population would drastically plummet and therefore more algae would grow on the coral reef. However, contrary to common opinion the exact opposite happened. With the decrease in fishing scientists found that “a 20-year-old fishing ban within a marine park, in addition to resulting in an expected increase in groupers…has had positive effects on parrotfish, the primary grazers on Caribbean reefs (3).” This occurred because with the ban of fishing for such an extended period of time, parrotfish were allowed to grow to a substantially large size that the average grouper could not swallow. Since the parrotfish were allowed to reach a size where they could avoid being eaten by groupers; this lead to more and larger parrotfish, an increase in parrotfish grazing, and a decrease in algal growth on the coral reefs.
As the study pointed out, there is a distinct relationship between groupers, parrotfish, algae and coral reefs that must be in place to keep the survival of the coral reef ecosystem. If humans are ever going to consider saving our grouper population and coral reefs we must start considering conservation efforts on a drastic scale that focuses on the prevention of extinction of ecosystems rather than individual species genera. As has been shown by many scientists, the intricate relationships between species in ecosystems can not be ignored and is delicate at best. Hopefully in the future our leaders across the world will realize this and enact measures to prevent the destruction of these precious species and ecosystems.


(1) American Museum of Natural History Web Site. 79th Street @ Central Park West New York, New York 10024. http://www.amnh.org/home/?src=toolbar

Craig, Matthew T., and Daniel J. Pondella. 2001. Phylogenetic analysis of the new world groupers (Serranidae; Epinephelinae). A technical report submitted to the Florida Bureau of Marine Fisheries Management.

Craig, Matthew T., Daniel J. Pondella, II, and John C. Hafner, 1999. “Analysis of Age and Growth in two Eastern Pacific Groupers (Serranidae: Epinephelinae).” Bulletin of Marine Science Vol. 65(3):807-814.

Cowen, R K., C B. Paris, and A Srinivasan. "Scaling of Connectivity in Marine Populations." Science Volume 311 (January 27, 2006): 522-526.

Davidson, Gray Osha. The Enchanted Braid. John Wiley and Sons, Inc. 1998 Canada

(2) Heemstra, C. Phillip and Randall, E. James. FAO Species Catalogue Vol. 16. Groupers of the World (Family Serranidae, Subfamily Epinephelinae). An annotated and illustrated catalogue of the grouper, rockcod, hind, coral grouper, and lyretail species known to date.

(3) Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006.
The Animal Diversity Web (online). Accessed June 09, 2006 http://animaldiversity.org


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