Tawny Nurse Shark

A group of tawny nurse sharks (Nebris ferrungineus) circling each other at dusk. This behaviour may be related to reproduction, the female, top, looks heavily pregnant in this photo and the male, below, might be able to sense she is soon to give birth. Note in the background there is another group of sharks circling each other. Photo by Alexander Mustard, for more go to www.amustard.com

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Orectolobiformes
Family: Ginglymostomatidae
Genus: Nebrius
Species: Nebrius ferrugineus

I have this kids’ picture book that illustrates 1000 things you can find in the sea, and I use it on occasion to decide what I’m going to research next. I haven’t written about a shark in a while, so I decided to research the Tawny Nurse Shark, also called Nebrius ferrugineus. Though to her friends, she’s referred to as Madame X…

I wish I was kidding about the common name Madame X . Supposedly, the common name was coined in the 1930s by a shark fisherman that found a specimen in Australian waters; before then, it had not been recorded in those areas.

The tawny nurse shark is located in the Indian Ocean, and the in western and southwestern areas of the Pacific Ocean. This shark hangs out near or on the bottom in sheltered areas, including lagoons, channels, seagrass beds, caves on the outskirts of coral reefs, crevices in coral reefs, and right off beaches. They sleep together in secluded areas during the day and hunt for prey at night.

Around the mouth, tawny nurse sharks have barbels—whisker-like appendage—that help them sense prey. They eat small fish and benthic organisms (creatures that live on the seafloor), including crustaceans, sea urchins, and some cephalopods. When it finds potential food, the shark creates a suction to pull the prey out of hiding and into its mouth, where comb-like teeth help to break up hard shells.

This is a pretty docile shark. Divers consider it a favorite because the shark allows the divers to approach it, even touch it. However, when harassed, it will fight back and has been recorded to cause non-fatal bite injuries.

Please do not touch sea creatures unless you have the specific training to do so! You would lash out too if a stranger came up and started putting their hands all over you.

Tawny nurse sharks are considered vulnerable to extinction by the IUCN Red List, and their population numbers are declining. They have a limited home range, so their immediate environment is very important to them. Some populations are declining due to overfishing of the nearby reefs. Some sharks get caught up in gill nets and die as bycatch.

Bycatch refers to any creature that isn’t the target of the catch. So if fisherman are using nets to catch tuna, then anything that isn’t tuna that gets caught up in the net is considered bycatch. Typically, bycatch is thrown back into the ocean, whether it’s alive or dead, because most fishing boats have a bycatch limit.

Tawny nurse sharks are also considered game in some countries. Their “fighting spirit” and strength make them a popular shark to fish for, especially in competitive fishing. Some areas will eat the meat of the tawny nurse shark and ship the fins to Asian countries.

If we’re not careful, this is another species of shark that can disappear before we know it, especially since it has a low reproductive rate. A balance between the fishing industry’s needs and proper fishing regulations must be found in order to address this issue.

Sources and links:
Ocean the Definitive Visual Guide made by the American Museum of Natural History
https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/nebrius-ferrugineus/ ⇐lots of information
https://www.sharks.org/tawny-nurse-shark-nebrius-ferrugineus ⇐brief overview
https://www.fishbase.de/summary/Nebrius-ferrugineus.html
https://fishesofaustralia.net.au/home/species/1974#moreinfo ⇐talks about the Australian populations
https://www.iucnredlist.org/species/41835/10576661

Longnose Butterflyfish

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciforms
Family: Chaetodontidae
Genus: Forcipiger
Species: Forcipiger longirostris

Butterflyfish, like butterflies, come in all shapes, sizes and colors. Today, I’m going to introduce you to the longnose butterflyfish, or Forcipiger longirotris.

Longnose butterflyfish are distributed throughout the Indo-Pacific Ocean, including around the islands of Oahu and Maui of the Hawaiian island chain. These fish are found on the very edges of seaward reefs, or coral reefs that extend toward the sea.

When you look at the genus name Forcipiger, does anything pop-out at you? Forcip-iger

Forceps are pincer-like instruments made for grasping and holding objects, similar to tweezers. Forceps are typically used in medical and surgical situations.

Forcipiger refers to how the organism feeds, grasping and eating prey whole. The species name longirotris describes the fish’s long snout. F. longirotris feed on small crustaceans found in the rocky crevices of the reef, or they suck them right off of branching coral.

Most individuals of this species are bright yellow with a black head, and a long, thin, silvery-white snout. Rare individuals have been recorded as all black or brown instead of yellow, though this color change has never been recorded in an aquarium. All longnose butterflyfish have a clear caudal (tail) fin, but the rest of their fins are yellow. Near the base of its tail fin is a black spot called an eyespot.

A defense tactic, eyespots are spots on an organism that resemble eyes to confuse predators. Eyespots are typically located away from the head and anything vital. For fish, it’s to fool predators into thinking that the tail end of the fish is the head, especially since the eyes of F. longirotris are hidden in the black coloring of its head. For insects, these eyespots can look like the eyes of other organisms. Eyespots are a common defense found on fish, reptiles, and insects, and each group uses them differently.

Longnose butterfly fish have often been observed in pairs. These fish form monogamous pairs during the breeding season, though it’s unclear if the same two would pair up in the next breeding season. The female releases thousands of eggs into the water column to be carried elsewhere in the water current.

I’ve swum around reefs in the Pacific Ocean twice, once in Hawai’i and once off the Great Barrier Reef. Both times were snorkel only, so I didn’t explore too deep around the reefs, and I doubt I would have seen these fish. I hope to fix that someday because these guys look impressive with their long noses!
There is potential research for Forcipiger longirotris. One, there’s no clear explanation as to why some individuals change their color to all-black or brown and why it’s never done in an aquarium setting. Two, they are labeled as Least Concern by IUCN Red List, but their population numbers haven’t been evaluated since 2009, so there is potential research in re-evaluating their population numbers.

Sources and links:
https://fishesofaustralia.net.au/home/species/425#moreinfo
https://www.waikikiaquarium.org/experience/animal-guide/fishes/butterflyfishes/longnose-butterflyfish/
https://www.fishbase.se/summary/Forcipiger-longirostris.html
https://www.iucnredlist.org/species/165667/6085300

Lionfish

A lionfish (Pterois volitans) rises up from the reef to hunt silversides. Photo taken by Dr. Alex Mustard, you can find more at www.amustard.com

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygi
Order: Scorpaeniformes
Family: Scorpaenidae
Genus: Pterois
Species: Pterois volitans

When talking about invasive species, I mentioned the lionfish. Can they hurt you? Yes. Are they devastating Atlantic coral reefs? Yes. However, they are not evil fish, despite one of their other common names: the devil firefish.

Pterois volitans is a beautiful fish native to the tropical waters of the eastern Indian Ocean and the western Pacific Ocean. They can be found in depths of 7−180ft (2−55m) near seagrass beds, coral reefs, artificial reefs, and sunken ships. I’ve seen them hiding in crevasses or overhanging ledges on the reef.

When diving, lionfish can be fairly easy to identify. Along the head and body of the fish are alternating maroon and white strips, stretching from top to bottom. Long, unique, fan-like fins, with the same stipe pattern, help the lionfish corner its prey against a reef or hard surface. Along the top, are long striped spines that you want to avoid.

Lionfish are carnivorous fish that prey upon shrimp, crabs, and more than 50 species of fish. In their native habitats, they help to keep the reef healthy, and their populations are controlled by the few predators that eat lionfish, including a couple of species of moray eels and the bobbit worm.

In the Atlantic Ocean, however, they can eat all the available prey in a given reef if gone unchecked. With no natural predators in the Atlantic, and the fact that they produce a lot of eggs each year, their populations have boomed while the populations of herbivore and commercial fish have decreased.

Despite their invasion of the Atlantic, lionfish are quite important. Whether it’s in the Pacific, Indian, or Atlantic Ocean, Pterois volitans provides food and income to the coastal communities. Divers pay good money to see lionfish, and the fish is often the target of many spearfishing tournaments in the Atlantic. You can win hundreds of dollars, depending on where you sign up! Because they’re so distinctive, lionfish can be easy targets for divers.

P. volitans are also quite popular in home aquariums around the world. Their unique coloring and flamboyant fins make for a great conversation starter at a party! Just a reminder, though: if you’re getting rid of your aquarium fish, please don’t dump them in the ocean closest to you. Take them to your local aquarium and ask for help. You never want to dump a potential invasive species in your ocean.

Another common name for lionfish is tastyfish. When I was studying in Jamaica, our dive teams would always bring spear guns, and we would hunt lionfish while exploring or doing research. When we’d come back to the lab, we’d clean them and give them to the lab’s cafeteria. Let me tell you, those wonderful ladies made some amazingly spicy lionfish!

If we make it more popular to eat lionfish, then that will help solve the population issues in the Atlantic, and it will help take the pressure off some of our commercial fish. So, the next time you’re at your local fish market or restaurant, ask for lionfish and let the owners know you’re interested!

The coloration of a lionfish is a special adaptation called warning coloration, which indicates to potential predators that it’s unsafe to eat the lionfish. In this case, the warning is legitimate. In the spines along the top are glands that store venom. When the spines puncture the skin the glands release the venom into the wound. The venom can cause excruciating pain, sweating, paralysis, and respiratory distress; rarely has it been fatal to humans.

I had a couple of classmates get stung by lionfish. One kid got stung by a live one they didn’t see in the reef, which is why you never reach your hands into areas you can’t fully see. Another kid got stung when handling a dead lionfish. In both cases, they had to be rushed to the doctor, but even after being treated, the wounds remained quite painful for a while. So please be careful while diving around lionfish or when handling them!

Lionfish (Pterois volitans) fritters offered as an after dive snack. Photo taken by Dr. Alex Mustard, you can find more at http://www.amustard.com

Sources and links:
Ocean: The Definitive Visual Guide by the American Museum of Natural History
https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/pterois-volitans/
https://oceanservice.noaa.gov/facts/lionfish-facts.html
https://www.fisheries.noaa.gov/southeast/ecosystems/impacts-invasive-lionfish
https://www.britannica.com/animal/lionfish
https://blog.nationalgeographic.org/2013/07/19/top-5-myths-about-lionfish/
https://lionfishcentral.org/resources/lionfish-recipes/ ←lionfish recipes you can try at home!

Doctorfish

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Osteichthyes
Order: Perciformes
Family: Acanthuridae
Genus: Acanthurus
Species: Acanthurus chirurgus

Last time on Doctor Who, the Doctor was mortally wounded and forced to regenerate…again. This time, though, to everyone’s surprise and horror, the Doctor turned into a fish. And not just any fish, but the tropical surgeonfish known as the Doctorfish—bum bum buuuuuuuuuuuum!

For those of you who don’t know, I’m a giant nerd, and I laughed way too hard when I realized that I could combine Acanthurus chirurgus with Doctor Who. I have no shame—most of the time.

Anyways, the Doctorfish is a type of surgeon fish that inhabits coral reef areas and can be commonly found in Florida, Bahamas, and the Caribbean. They can also be found in the waters of the Gulf of Mexico, north to Massachusetts, south to Brazil, your neighbors’ exotic aquarium, and the tropical waters of West Africa.

Color is not always an easy way to identify these Doctorfish because they can range from bluish gray to dark brown, and they can pale or darken dramatically between individuals. The major way to identify them while diving is by looking at the body; all doctorfish have 10‒12 vertical bars between their head and their tail. They also have distinct markings around their eyes, almost like flashy eye make-up.

Acanthurus chirurgus are herbivores that feed on algae, and they even have special teeth that allow them to pick off the algae growing in the sand, in rocky areas, and even on coral. In fact, these guys are really important to reef health because they can consume the algae that grow on coral, which would otherwise smoother the coral and their best friends, the zooxanthellae.

The origin of their common name is pretty cool. A. chirurgus have spines on either side of their caudal peduncle, or the base of their tail, that were discovered to be really sharp like a scalpel that doctors use. When feeling defensive, surgeonfish will use those spines as weapons by slashing their tails side to side at their aggressors.

Typically, Doctorfish will keep their distance from divers and will try to stay away if approached. However, people handling these fish can get serious injuries which are often quite painful and can lead to serious infection, especially since there is a crazy amount of bacteria and viruses in a single drop of water! So please be careful when diving with or handling doctorfish!

They are a common fish species found in private aquariums, and while they are not considered to be at risk of becoming endangered, you should still be aware of how they are caught and sold before purchasing individuals for your aquarium.

The doctorfish was one of the fish species I had to learn to identify for my Coral Reef Ecology class in college. I’ve seen them a handful of times when diving around reefs, and I’ve even watched them eating the algae from the coral, which was pretty cool to witness. I’ve read that you can eat Doctorfish, but I won’t try that because of the slight chance of getting ciguatera poisoning—which I’ll save for another ramble!

Sources and cool links:
Reef Fish Identification: Florida Caribbean Bahamas 4th ed. By Paul Humann and Ned DeLoach
http://species-identification.org/species.php?species_group=caribbean_diving_guide&menuentry=soorten&id=209&tab=beschrijving
https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/acanthurus-chirurgus/
https://www.iucnredlist.org/species/177982/1510626
https://www.fishbase.de/summary/943

Giant/Boulder Brain Coral

A boulder brain coral (Colpophyllia natans) growing on a coral reef. Photo taken by D. Alex Mustard, more can be found at www.amustard.com

Domain: Eukarya
Kingdom: Animalia
Phylum: Cnidarian
Class: Anthozoa
Order: Scleractinia
Family: Mussidae
Genus: Colpophyllia
Species: C. natans

First let me state that I have a love/hate relationship with common names. Most people call the Colpophyllia natans the Boulder Brain Coral; however, there are some texts and articles that call it the Giant Brain Coral. Why is this frustrating and worth mentioning? I spent a good chunk of time trying to confirm that these guys are the same species with different common names—I really didn’t want to make a fool of myself!

C. natans are named Boulder Brain Coral because they typically form large rounded structures that look like, drum roll please, boulders. They can also form large rounded plate-like structures, encrusting over rocks and existing coral colonies.

Like other brain coral, C. natans look like someone gave a chisel to a child and told them to go wild on the coral, creating a random pattern of valleys and ridges on the surface. A thin groove runs along the very top of the ridges, though you usually can’t see it when diving because you’re too far away (and if you’re not, you should be).

A second line is found halfway down the ridge where the angle decreases and slopes to create the valleys. The valleys are usually long and wandering, almost path-like, but sometimes they’re closed up and look more like individual cells squished together. The coral polyps are found within the valleys; the long ones containing multiple individuals, while the closed ones hold one or two polyps.

The ridges and valleys are normally different colors from each other. Ridges are either brown or gray while the valleys can be green, tan, or whitish.

You can commonly find them on reef tops or seaward reef slopes in the tropical waters of the Gulf of Mexico and the Caribbean. They can grow to have a diameter of up to 16 feet and can live as long as 100 years! C. natans are extremely popular tourist attractions, especially in the Florida Keys. But divers aren’t the only things these guys attract; they also attract all kinds of fish, including some gobies that live permanently on the coral.

I’ve only ever seen these guys during day dives—which, trust me, is still really cool to find them because of their size and coloring. However, they’re even better to see on a night dive because that’s when the polyps let out their tentacles to fish for zooplankton. I’ve been told that the coral can look completely different at night, and I can’t wait to see it for myself in person!

Sources and cool links:
Coral Reef Identification: Florida, Caribbean, Bahamas 3rd Edition by Paul Humann and Ned DeLoach
Ocean The Definitive Visual Guide made by the American Museum of Natural History
http://species-identification.org/species.php?species_group=caribbean_diving_guide&menuentry=soorten&id=305&tab=beschrijving
http://www.coralsoftheworld.org/species_factsheets/species_factsheet_summary/colpophyllia-natans/
https://www.sealifebase.ca/summary/Colpophyllia-natans.html
http://www.wildernessclassroom.com/wilderness-library/giant-brain-coral/

Coral part 2

Photo taken by Dr. Alexander Mustard. You can find more of his amazing photos on his website www.amustard.com

Last time, I mentioned all the factors that determine a coral’s success in an area, and most of those factors relate to hard coral or reef building coral. Soft coral are a bit different from their constructive cousins; for instance, they don’t all rely on zooxanthellae, and so most of this information pertains to hard corals—but don’t worry, I’ll get to soft corals eventually!

For hard coral, the factors that affect their success in an area include water temperature, salinity, depth, water circulation, and clarity.

Most of these factors aren’t hard to explain because we can relate to them. For instance, we don’t like to be too warm or too cold. It’s the same with coral: they don’t like their water to be too warm or too cold, so their ideal range is between 85°F‒70°F. This is not a very strict range because there are reefs and species found outside these temperatures, but for the most part this is important for reef-building coral.

Hard corals also don’t like their water to be too fresh or too salty. They prefer their water to have a salinity level between 30 and 40 parts per thousand (ppt).

Next, we’ll talk about water circulation. This one is really important because coral can’t move elsewhere once the food is gone, they’re sedentary. They’re not like humans, who can get off the couch and grab food when they’re hungry. Coral pretty much have to be in an area that always has food—so it’s like if your cousin decided to live in the supermarket for the rest of their life. Coral feed on zooplankton, which for now let’s describe as plankton-size animals, and that means that the coral’s food isn’t regularly replenishing. Instead, coral rely on water circulation, either through water currents or wave actions, to stir up the water and bring nutrients and food to them. Without good circulation, coral can easily starve, even the hard coral that obtain most of their energy from zooxanthellae.

The final two factors determining coral survivability are especially important to hard coral because of their partnership with zooxanthellae, and these factors are related to sunlight: water clarity and depth. Water clarity is defined by how clear the water is. If the water is really cloudy and full of particles, then the zooxanthellae may not be able to receive enough light for photosynthesis. Depth has similar effects: sunlight can only penetrate so far into the ocean before the only visible light comes from bioluminescent creatures. If the coral is anchored too far from the surface, then the zooxanthellae may not get enough light and the pair can die.

There are coral that can survive outside of these factors; for instance, they have discovered coral in the deep ocean at depths of 6,000 m (20,000 ft)—that’s almost four miles below the ocean’s surface. Deep-sea coral are fascinating because they vary from their shallow-water relatives, but I’ll get to those later.

If the hard coral’s habitat changes beyond these set factors, then it can have devastating impacts on the organism. If the conditions don’t return to the normal, then the coral will expel their zooxanthellae in a process called Coral Bleaching. Some research has suggested that the coral can reacquire their zooxanthellae or even acquire new zooxanthellae. However, there are still a lot of unknowns in regards to Coral Bleaching and coral health, which is why continued research is so important!

If the coral die then the reef dies, and from there it’s a domino effect that will very quickly impacts us. Without the reefs the world fish populations will dramatically decrease. Less fish means less food for the animals that live in the ocean, and less fish for us as well. If we compete with creatures like dolphins and whales for food, then those populations of animals will dramatically decrease as well. All in all, coral reefs are the rainforests of the sea in terms of biodiversity, habitat, and oxygen production.

It’s not all desolate and hopeless. There is research being done through the field of aquaculture in trying to grow coral ourselves to help save the reefs, most of which are being done at aquariums and universities. Researchers are trying to figure out ways to preserve the reefs that we have now, and to protect them from further climate-change-inflicted damage.

However, a grim-looking future faces us if we can’t curb the effects of climate change on our oceans, and that’s why YOU are so important in this struggle too. Everything you can do, big or small, to saving energy and reducing plastic use to conservation research programs will help lessen the impact of climate change and preserve our reefs for future generations.

Yellowtail Damselfish

Adult male yellowtail damselfish, photo taken by Dr. Alex Mustard. Please check out his website www.amustard.com for more

Yellowtail Damselfish
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Family: Pomacentridae
Order: Perciformes
Genus: Microspathodon
Species: Chrysurus

I realized that I have yet to talk about fish, and because there are so many of them, I decided that it’s high time to start. I’m not sure why I wanted to kick it off with the Yellowtail Damselfish. I was going through a fish ID book I own, and it was the first one to catch my attention, maybe because I was already familiar with it. They are pretty neat looking fish and I want to share some interesting facts about them!

There are a lot of fish that are born looking completely different than their adult selves. Seriously, some fish can go through some intense changes before they settle into themselves as adults, but even then it might not be completely decided—I’m looking at you, clown fish! Yellowtail Damselfish are one of those species that look almost like a completely different fish at every stage of their life.

When they’re juveniles, they have these dark blue, almost black bodies that are littered in bright blue dots, with clear tail. Then in their intermediate stage, like high-school for humans, their dots shrink and their tail becomes a bright yellow. As adults, they lose the blue dots, but keep the dark color with the bright yellow tail.

Intermediate phase of the yellowtail damselfish, taken by Dr. Alex Mustard. Please visit his website, www.amustard.com for more!

Yellowtail Damsel can be found in the warm waters of Florida, the Bahamas, and the Caribbean. They live on the tops of coral reefs where they eat algae and the polyps of fire coral. The juveniles tend to stick close to the branches of the fire coral where they hide from predators and loud divers.

The Yellowtail Damselfish was one of the species I had to learn how to identify for a course I took in college. Its tail is a pretty clear giveaway for the species, at least from the list I had to identify. It was especially easy for me to recognize the juvenile stage. However, the individual I had to identify was completely yellow with flecks of blue, which is a temporary change they can accomplish. Anyways, I found the younger stages to be beautiful and a joy to spot on the reefs!

Sources:
Reef Fish Identification: Florida, Caribbean, Bahamas 2nd edition by Paul Humann and Ned Deloach
https://www.fishbase.se/summary/Microspathodon-chrysurus

Coral (part 1)

Photo taken by Dr. Alexander Mustard, find this image and many others on his website http://www.amustard.com/

When I first started reading about coral I never thought I’d want to study them. While they looked really cool and fascinating, they didn’t hold a candle to dolphins or sharks to my 8-year-old self. It wasn’t until I was older that I realized that there was more to them than appearances suggested.

Do you believe coral to be rocks, plants, or animals? Some of them appear to be very dull in color; this is especially true for some of the coral found in the Atlantic Ocean, which have various shades of brown or drab green. While some may look like rocks, I’m talking about you Boulder Coral, coral are most definitely not rocks because they feed and grow over time.

If they’re not rocks, then that makes them either plants or animals. Well, coral don’t really have legs, and we’ve never seen them move from point A to point B. In fact, they’re very much rooted to their spots and only move by swaying with the waves. So by this logic, they’re plants, right? They have no noticeable organs and they don’t have any independent movement. Until the early 1750s, they were classified as plants. It wasn’t until a French biologist, J.A. de Peysonell, determined that they were animals when he was completing a study of the Western Atlantic in 1753.

Coral are animals that belong to the Phylum Cnidaria, along with jellyfish and anemones. Like their cousins, coral have tentacles that they use to capture food. Coral also reproduce asexually, which allows them to expand and colonize an area.

All coral need is a good surface to attach to because once they land they can’t move locations, so real estate is very important to coral polyps. Good places for them are large rocks or other hard surfaces, like sunken ships, stone statues, or other man-made things, that won’t be easily moved during a storm or rough water action. If the coral’s substrate tips over or shifts, it can disrupt and hurt the coral, possibly leading to death.

They are very sensitive to their surroundings, requiring specific conditions for them to grow optimally. Those factors vary between the groups of coral, but if the conditions aren’t met then the coral may not grow. Worse yet, it can die.

Now, I can ramble on for hours about coral and everything about them that I find fascinating. However, I don’t want this to be like those long academic research papers that put insomniacs to sleep. So I’ll share the information with you in little bursts as I blog.

Source: Humann P, DeLoach N. 2013. Reef coral identification: Florida, Caribbean, Bahamas. 3rd ed. Jacksonville, Florida: New World Publications.

Elkhorn Coral

Image was taken by Dr. Alexander Mustard, who has given me permission to use his photos on this blog. You can look at his gallery here: http://www.amustard.com/

Domain: Eukaryota

Kingdom: Animalia

Phylum: Cnidaria

Class: Anthozoa

Subclass: Hexacorallia

Order: Scleractinia

Family: Acroporidae

Genius: Acropora

Species: palmata

So the first species I decided to tackle was a coral; gee, what a surprise. For those of you who don’t know, coral and their reefs are what held my interest in the ocean after my dolphin phase ended.

Acropora palmata, or the Elkhorn coral, is a species of branching coral that can be found in the Caribbean. This was one of the corals I had to learn to identify for an independent study and class my last semester of college, and one that I became very familiar with during an experiment I planned and executed. Elkhorn coral are also one of my favorite corals to find while swimming in their waters. Typically it appears brown to brownish-yellow in color and it has wide flattened branches that resemble…drum roll…elk or moose antlers. It looks very similar to one of its’ cousins in the same genius, Acropora cervicornis (Staghorn Coral), but its’ cousin has thin cylindrical branches that look like the rack of a buck.

In shallow, unprotected waters Elkhorn branches will grow to be rounder and stouter, like fat fingers, to help protect the coral against violent waves and storm surge by decreasing their surface area. Colonies found in more moderate depths, where wave action has less of an impact on the structure, have long, wide, and flattened branches like the leaves of palm trees.

Have you ever stuck your hand out the window in a moving vehicle? If not, you should try it next time, but please be careful—impacts from high-speed bugs hurt! When you stick your hand out the window with your fingers splayed out like a turkey, you feel less resistance from the wind because it has space to move around your fingers. When your fingers are close enough that they’re touching, you feel more resistance from the wind because now it has to move around your hand because there’s not enough space between your fingers.

The same happens with Elkhorn coral in high energy water, meaning lots of intense waves, they produce thick round branches to allow enough space for the water to flow through and reducing any potential damage to their structure. Outlining the Elkhorn branches are white terminal corallites, which are hard cups made of calcium carbonate secreted by the coral. A corallite is like the home of an individual polyp, it is a hard structure that houses the polyp and allows the individual a place to hide and retract itself when it’s not gathering food.

The Elkhorn coral was once abundant in the Florida Keys, but are now more scarce and scattered in the area. In the Bahamas and the Caribbean they are considered to be common, since they can be frequently found, but not at every dive site or reef. Divers saw a lot more of these coral before the 1990s, but since then they have suffered high mortality rates due to storms, bleaching, and most commonly by White-band Disease, a disease that I will discuss more later−just know that it is a disease that affects species of coral.

One of the cooler things that I learned about this coral is that you can determine the direction of the surge, or the typical movement of water, by the direction the branches grow. Elkhorn branches grow parallel to the direction the surge takes, much like some trees grow in the direction of the prevailing wind on land.

Elkhorn coral can be found between 1−35 feet of depth, and they prefer areas of constant water movement caused by incoming waves. They can grow rapidly under optimum conditions, growing up to five to six inches a year. Because of their rapid growth for reef builders, the family Acroporidae is commonly used in reef restoration and growth programs. They make for a good starting block for man-made or rehabilitated reefs.

If you see this coral while diving or snorkeling, please do not touch it, and try to keep your equipment from getting caught in it. While not extremely fragile, it can still break under pressure. So please be careful while you swim and enjoy the view from a far; reefs are very important not only to the ocean but to us as well!

Source: Humann P, DeLoach N. 2013. Reef coral identification: Florida, Caribbean, Bahamas. 3rd ed. Jacksonville, Florida: New World Publications.