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Moray Eels: Participating in the Food Chain
Introduction
The ocean is filled with fascinating creatures of all shapes, sizes, colors, and unique characteristics. One of the most awe-inspiringÑor fear producingÑforms of life is the eel. When I first began collecting information for my research I planned to simply discuss the topic of Òthe eelÓ. However, upon finding myself assailed with a wealth of knowledge on eels I realized that I would need to focus my attention on simply one type of eelÑthe moray eel or ÒmorayÓ. Further research into the moray eel again led me to concentrate on these aspects of the moray eelÑtheir role in the food chain (what they are predators to and what they are prey to), and also some of their unique feeding characteristics.
Eels
To bring into perspective the life form that I will be discussing, I will first discuss the key characteristics and qualities of the overall eel population. According to Merriam-Webster Dictionary Online, eels are classified as ÒAny of various long, snakelike, scaleless marine or freshwater fishes of the order Anguilliformes or Apodes that lack pelvic fins and characteristically migrate from fresh water to salt water to spawn.Ó The difference between Anguilliformes and Apodes is that Anguilliformes are called Òtrue eelsÓ as opposed to similar-type fish (Apodes) such as spiny eels and electric eels. While the two main classifications of eels are ÒmarineÓ versus ÒfreshwaterÓ, there are actually many different classifications of eels. Precisely, there are four suborders, nineteen families, one hundred and ten genera, and six hundred species of eels (FishBase). As many as there are species of eels there are nearly as many different sizes of eels. Eels can range in length anywhere from five centimeters to over twelve feet long! As suggested by the two main categories of eels, eels can live in both ocean and fresh water. While there are many lengths of eels, there is one characteristic of eels that make them fall into the Anguilliform order, which is that their dorsal and anal fins are fused with their tail fin to give them their ribbon-like shape. Now, with a basic concept of what an eel is and what makes them unique to other fish, I will highlight what makes moray eels different from all other types of eels.
Moray Eels
The pictures and video clips of the fluorescent yellow-green eel (the giant moray eel) jutting its head out of a crevice, jaws open wide, make moray eels one of the most well-known types of eels. However beyond these pictures and representations of moray eels as snake-like, slimy monsters, morays are very interesting creatures. Merriam-Webster Dictionary defines moray eels as ÒAny of numerous often brightly colored eels that have sharp teeth capable of inflicting a severe bite, that occur in warm seasÉÓ This covers over 100 of the 600 species of eels as recorded by Atlantis Marine WorldÑall of which fall under the family of Muraenidea. According to Mysterra Magazine, there is no ÒtypicalÓ size for moray eels and their length can vary almost as much as the variance in length of all eels (twenty-five centimeters to over twelve feet long). Atlantis Marine World narrows the range of habitats for moray eels from that of the broader order of all eels; morays live entirely in warm waters and most often in subtropical reefs below the sea surface.
Moray Eels As Predators
Before explaining the habits and characteristics of moray feeding, it is important to understand just what moray eels actually eat. Moray eels are predators to a large range of animals. Surprisingly, Adam Summers in his article ÒJaws TwoÓ from Natural History says that moray eels can eat rather large-sized prey for having fairly slender bodies. Depending on the age, size, and type of moray, their diets can range from shrimp and small fish (MorayEel.info) to crabs, wrasses, and squid say Kellyn Betts and Tony Rath in their article ÒStalking the ReefÕs Night Stalkers.Ó
Moray Eel Feeding Characteristics
Now that we know what role moray eels play on the predatory side of the food chain, I will discuss some of the factors that play into how moray eels participate in the food chain. Three main feeding characteristics of moray eels are their concealment, their having pharyngeal jaws, and their cooperative hunting.
Concealment
According to Rita Mehta and Peter Wainwright in their article ÒRaptorial Jaws in the Throat Help Moray Swallow Large PreyÓ, the living arrangements of moray eels are assisted by their body structure. These eelsÕ elongated body, lack of pelvic fins, and cross-sectional area all allow for them to fit into small, confined areas (Mehta 79). This is important because one factor in the feeding habits of moray eels is related to how they remain well-concealed to hide from their potential prey. This concealing is also aided by the fact that moray eels are nocturnal predators as told by Betts and Rath. According to Betts and Rath, only on some occasions are morays ÒluredÓ out of their daytime slumber which occurs between coral formations and other rocks and crevices.
Pharyngeal Jaws
One of the most extraordinary characteristics of the moray eel relates to how it feeds.
Mehta and Wainwright say that most bony fish such as eels rely on suctioning methods to capture and contain their prey. Moray eels, however, do not have this suctioning ability. In the article ÒWild ThingsÓ found in Smithsonian, it is suggested that this is because they cannot expand due to their confined living spaces. Because of this they rely on a different type of mechanism to capture and hold their food. Hannah Schardt from the National Wildlife Magazine explains that moray eels have not one, but two jaws: an oral jaw and a pharyngeal jaw. The oral jaw is the outer jaw that most other animals have. It is similar to the jaws that humans have. The pharyngeal jaw is a very unique trait of moray eels. The pharyngeal jaw is behind the oral jaw in the throat of the eel. It allows the moray eel to deliver what Mehta calls a Òdouble biteÓ to its prey. Mehta explains in another article, ÒBite, Bite, Gulp: ThatÕs a MorayÓ, that this is through unexpectedly thrusting forward, grasping, retracting, and gripping its prey.
The teeth contained in the pharyngeal jaw are also unique in that they are made for tearing flesh, rather than chewing flesh. One particularly interesting finding of Rita Mehta as cited in ÒEcomorphology of the Moray Bite: Relationship between Dietary Extremes and Morphological DiversityÓ, is that morays do not all have the same pharyngeal jaw. Instead, depending on different speciesÕ diets, morphological variation is presentÑdifferent morays have different types of teeth in their pharyngeal jaws.
Cooperative Hunting
Perhaps the most surprising feeding characteristic of moray eels is what is referred to as Òcooperative hunting.Ó Cooperative hunting is a phenomena that has just recently been discovered after much time spent watching and analyzing the relationship between moray eels and another type of fishÑthe grouper. In ÒAn Amazing First: Two Species Cooperate to HuntÓ, Charles Q. Choi says that the behavioral ecologist who noticed this relationship upon first watching a grouper Òshake its headÓ in front of a moray eel, thought the two types of fish were about to fight. Yet they then swam off together. In fact, in ÒFishy CooperationÓ by Frans B.M. de Waal, he described this occurrence as the pair swimming off together like Ògood friends on a stroll.Ó Upon further observation it became apparent that the grouper and moray eel were cooperatively hunting, and when prey swam into a crevice or part of the coral that the grouper could not go into, the moray eel would. Through this type of ÒsignalingÓ as it is called in the article ÒHead of the PackÓ in Psychology Today, the grouper makes it so that prey cannot run and the moray makes it so that the prey cannot hide. The grouper and moray eel would then take turns ÒsharingÓ their spoils (de Waal 2175). This is especially remarkable because outside human-to-human relationships, such cooperative hunting has never been found (Chou).
Moray Eels as Prey
Upon understanding what moray eels eat and how they do it, there is one last piece of the puzzle relating to their role in the food chain. This is how moray eels are prey. Moray eels are not eaten by many sea creatures because of the high levels of toxicity in their skin. An example of a large fish that does eat moray eels is the barracuda. More often, morays (and other eels) are consumed by humans. Toxicity of moray eel skin is strong enough to kill humans, but upon cooking these toxins, they are eliminated, making them edible. In the article ÒYou Gotta Remember, Eels Are WeirdÓ by Bruce Watson, some of the different regions and cultures that include moray eels in their diet are referenced. Moray eels are a large, yet expensive part of Japanese dietÑespecially Cantonese and Shanghai cuisine. Koreans also eat moray eels and in fact eating these creatures in this culture is supposed to build stamina in men. Finally, some countries of European decent such as England and even the U.S. also eat morays. Jellied eel and deep-fried elvers (baby eels) are favorite ways of eating eels in these countries.
Conclusion
Moray eels are especially important for our purposes not only because we may come in contact with them on our exploration of the ocean, but also because of the role they play in coral reefs. According to Glenn Almany in ÒDifferential Effects of Habitat Complexity, Predators
and Competitors on Abundance of Juvenile and Adult Coral Reef FishesÓ, habitat complexity on coral reefs are effected by two ÒresidentÓ predators. One of these is the moray eel. This habitat complexity refers to the multitude of organismsÑboth plants and animalsÑthat reside in or around coral reefs. More specifically, the presence or absence of moray eels around coral reefs has a direct correlation on the abundance or absence of juvenile and adult fish around coral reefs. This fish population has a great effect on these coral reefsÑcoral reefs that are very important to us and the delicate balance of our ecosystem. Thus moray eels, though at first glance may seem to be just Òsea monstersÓ, truly play a unique role in the natural world.
Works Cited ÒMoray Eel.Ó Merriam-Webster Dictionary Online. Accessed: 12 Apr 2009.
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Almany, Glenn R. ÒDifferential effects of Habitat Complexity, Predators and Competitors on Abundance of Juvenile and Adult Coral Reef Fishes.ÓOecologia; Sep2004, Vol. 141 Issue 1, p105-113.
ÒMoray Eel.Ó Atlantis Marine World. Accessed: 10 Apr 2009.
Betts, Kellyn; Rath, Tony. ÒStalking the ReefÕs Night Stalkers.Ó Sea Frontiers; May/Jun93, Vol. 39 Issue 3, p22-29.
Blumberg, Jess; Frail, T.A.; Gambino, Megan; Helmuth, Laura. ÒWild Things.Ó Smithsonian; Nov2007, Vol. 38 Issue 8, p14-14.
De Waal, Frans B.M. ÒFishy Cooperation.Ó PLoS Biology; Dec2006, Vol. 4 Issue 12, p2175.
ÒEel.Ó Merriam-Webster Dictionary Online. Accessed: 12 Apr 2009.
ÒEels.Ó FishBase.org. Accessed: 18 Apr 2009.
Hutson, Matthew. ÒHead of the Pack.Ó Psychology Today; July/Aug2007, Vol. 40 Issue 4, p15.
Mehta, Rita S. ÒEcomorphology of the Moray Bite: Relationship between Dietary Extremes and Morphological Diversity.Ó Physiological and Biochemical Zoology; Jan/Feb2009, Vol. 82 Issue 1, p90-103.
Mehta, Rita. ÒBite, Bite, Gulp: ThatÕs a Moray.Ó National Wildlife; Dec2007/Jan2008, Vol. 46 Issue 1, p10.
Mehta, Rita. ÒRaptorial Jaws in the Throat Help Moray Eels Swallow Large Prey.Ó Nature: Vol. 449, 9 Sep 2009, p. 79-83.
ÒMoray Eel Food.Ó MorayEel.Info. Accessed: 17 Apr 2009.
ÒMoray Eels.Ó Mysterra Magazine. Accessed: 12 Apr 2009.
Watson, Bruce. ÒYou Gotta Remember, Eels are Weird.Ó Smithsonian; Feb2000, Vol. 30 Issue 11, p124-132.
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