Check out Arenal, a beautiful, active volcano in Costa Rica. Arenal is one of the most active volcanoes in the world.
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Bahamian Jaws
More than sharp teeth and jaws, sharks are a vital part of the oceanic ecosystem. Their placement and perfect adaptation to their world has allowed them to survive some 300 million years without change. Though humanized seas pose a significant threat to shark species, they continue to thrive in the Bahamas. ÒThe name Bahamas comes from the Spanish, Baja Mar, for "shallow seas." The archipelago rests atop a pair of limestone platforms, the Great and Little Bahama Banks, divided by channels that plunge as deep as 13,000 feet (4,000 meters). It's this combination of sheer drops and shallows, of rocky ledges and sandy shores, of coral reefs, grass flats, mangroves, and quiet lagoons that nurtures life of all sizes. Clean Atlantic waters and a warm current from the Gulf blend to create a seafood feast that draws sharks from near and farÓ (Holland 2007). Sadly, finning and habitat destruction have been costly to sharks around the world. ÒThe oceanic whitetip, one of the most abundant sharks just three decades ago, is critically endangered in parts of its range because of relentless demand for its finsÓ (Parsons 2006). Not only does the Bahamian reef support shark life, but sharks are critical to the reef ecosystem as well. As developers expand commercially around the islands, shark habitat will continue to be whisked away. If the sharks go, so will the bountiful ecosystem that feeds local people and attracts thousands of tourists, biologists, and conservationists.
Naturally there are a multitude of sharks that inhabit the waters surrounding the coral reef; but the reef shark, giant hammerhead, and nurse shark are the most common. ÒThe Caribbean reef shark (Carcharhinus perezi) is one of the most abundant sharks around the Bahamas and the Antilles. In the Atlantic, they are rarely found north of the Florida KeysÓ(Compagno, Dando, Fowler 2005). Characterized by a grey dorsal side, a white to yellowish ventral side, and a broad snout, they prefer shallow waters with a maximum depth around 30 meters. They are often found on the edges of coral reefs near drop offs and lie motionless on the ocean floor (Parsons 2006). Reef sharks feed on bony fish and large, marine invertebrates using their acute senses of smell, sight, touch, hearing, and electric vibration. This shark and others use small sensory pores under the skin called Ampullae of Lorenzini, and a lateral line canal system in the body to detect water vibration and catch prey (Carrier, Musick 2004). Reef sharks are considered passive for the most part but may be aggressive if provoked or cornered. Signs of an ensuing attack are an Òarched backÓ, and dorsal fins pointed downward. The shark may swim in erratic Òfigure eightsÓ if it feels threatened or snaps into attack mode.
Secondly, the great hammerhead sharks (Sphyrna mokarran) may be as long as 13-20 feet in length and are the largest of the nine identified hammerhead species. They are gray-brown to olive-green with off-white undersides, and they have heavily serrated, triangular teeth (Compagno, Dando, Fowler 2005). Their extra-tall, pointed dorsal fins are easily identifiable. ÒBy spreading their highly specialized sensory organs over their wide, mallet-shaped head, they can more thoroughly scan the ocean for small sharks, rays, squid and bony fishÓ (Carwardine, Watterson 2002). While most species of hammerhead arenÕt a threat to humans, giant hammerheads can be potentially dangerous, though few attacks have been recorded.
Lastly, nurse sharks (Ginglymostoma cirratum) are slow moving, bottom dwellers and are not a threat to humans. ÒHowever, they can be hugeÑup to 14 feet (4.3 meters)Ñand have very strong jaws filled with thousands of tiny, serrated teeth, and will bite defensively if stepped on or bothered by divers who assume theyÕre docileÓ (Dingerkus 1985). Their diet consists of shellfish and even coral, but they prefer to dine on fish, shrimp, and squid. Typically, they are gray-brown in color and have distinctive tail fins that can be up to one-fourth their total length (Carwardine, Watterson 2002).
Aside from the physical attributes and biological advantages of these three common tropical sharks, their role in the surrounding ecosystem has allowed them to withstand evolution and natural selection for over 300 million years. According to an article in National Geographic, the Bahamas has become a sanctuary for the sharks. Warm water from the gulf and clean water from the Atlantic blend into an ecosystem plentiful with fish and marine creatures for sharks to prey on (Holland 2007). In addition, the mangrove pools and inlets among the islands provide a safe haven for young sharks before they head out to deep, open water. Specifically, a lagoon in a strand of the Bahamas called Bimini is Òa birthing and feeding area where young lemon sharks can eat and grow without being eaten themselvesÓ(Holland 2007). Sharks commonly prey on their own younglings and the mangrove pools allow baby sharks to fully develop before having to fend for themselves in a hostile environment (Carrier, Musick 2004).
Unfortunately, commercial development and over fishing is continuing to reduce shark populations. The beautiful blue waters of the Bahamas and Caribbean attract fisherman and tourists, which leads to a direct decline in shark populations. According to a 2005 article, Òthe Integrative Ecology Group of Spain, and Enric Sala of University of Cal.-San Diego developed a model of a Caribbean marine ecosystem and details of its intricate predator-prey interactionsÓ(ÒResearch showsÓ 2005). The study, published in the April 12 edition of the Proceedings of the National Academy of Sciences, included an intricate network of more than 3,000 links between these species (ÒResearch showsÓ 2005). "It appears that ecosystems such as Caribbean coral reefs need sharks to ensure the stability of the entire system," said Sala, deputy director of the Center for Marine Biodiversity and Conservation (ÒResearch showsÓ 2005). In tropical waters, over fishing sharks causes a domino effect of changes in abundance that affects several fish species, ultimately contributing to the overall degradation of the reef ecosystem. For example, the absence of sharks in the reef allows carnivorous fish such as grouper to overpopulate and prey heavily on parrotfish and other important grazers. ÒThe decrease in parrotfish and other plant-eating animals has been party responsible for the shift of Caribbean reef from coral to algae dominatedÓ (ÒResearch showsÓ 2005). Therefore in a sense, reducing shark numbers hinders the coral reefsÕ resiliency against human development; and without the support of healthy coral reefs, shark populations will continue to drop -- a vicious cycle!
In conclusion, the reef shark, great hammerhead, and nurse shark are three of the most common shark species found in coral reef ecosystems near the Bahamas and Caribbean. Sharks and the reef act similarly to a system of checks and balances. Bahamian coral reefs are a haven for young and mature sharks, and sharks are vital to the health of the coral reef. At the peak of the food chain, sharks keep various fish populations in check, thus balancing and maintaining the aquatic ecosystem around them. Unfortunately, in various parts of the world, commercial development and game fishing is reducing shark numbers, directly leading to the destruction of coral reefs. Loss of these beautiful habitats will have a negative impact on the everyday lives of native people, as well as a countryÕs tourist appeal. Therefore, sharks should not be viewed as mindless predators, but rather evolutionary icons that balance ocean ecosystems and sustain the treasured coral reefs.
Works Cited
Carrier, J.C., & Musick, J.A. (2004). Biology of sharks and their relatives.Boca Raton, FL: CRC Press.
Carwardine, M., & Watterson, K. (2002). The shark watcher's handbook.Princeton, NJ: Princeton University Press.
Compagno, L., Dando, M., & Fowler, S. (2005). Sharks of the world. Princeton, NJ: Princeton University Press.
Dingerkus, Guido (1985). The shark watchers' guide. New York, NY: Julian Messner Inc. .
Holland, J.F. (2007, March). Blue waters of the bahamas -- an eden for sharks. National Geographic, Retrieved June 3, 2008, from http://ngm.nationalgeographic.com/ngm/0703/feature5/
Parsons, G.R. (2006). Sharks, skates, and rays of the gulf of mexico. University Press of Mississippi.
(2005, April, 11). Research shows overfishing of sharks key factor in coral reef decline. Biology News Net, Retrieved June 3, 2008, from http://www.biologynews.net/archives/2005/04/11/research_shows_overfishing_of_sharks_key_factor_in_coral_reef_decline.html
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