by Rick O'Connor | Oct 16, 2020
When most people think of reefs, they think of the coral reefs of the Florida Keys and Australia. But here in the northern Gulf the winters are too cold for many species of corals to survive. Some can, but most cannot and so we do not have the same type of reefs here.
That said, we do have reefs. We have both natural and artificial reefs. There are natural reefs off Destin and a large reef system off the coast of Texas – known as the “Flower Gardens”. Here the water temperatures on the bottom are warm enough to support some corals. The artificial reef program along the northern Gulf is one of the more extensive ones found anywhere. There is a science to designing an artificial reef – you do not just go out and dump whatever – because if not designed correctly, you will not get the fish assemblages and abundance you were hoping for. But if you do… they will come.
Reefs are known for their high diversity and abundance of all sorts of marine life – including fishes. There are numerous places to hide and plenty of food. Most of the fish living on the reef are shaped so they can easily slide in and out of the structure, have teeth that can crush shell – the parrotfish can actually crush and consume the coral itself, and some can be fiercely territorial. There are numerous tropical species that can be found on them and they support a large recreational diving industry. Let’s look at a few of these reef fish.
Moray eel.
Photo: NOAA
Moray Eels
These are fish of legend. There all sorts of stories of large morays, with needle shaped teeth, attacking divers. Some can get quite large – the green moray can reach 8-9 feet and weigh over 50 pounds. Though this species is more common in the tropics, it has been reported from some offshore reefs in the northern Gulf. There are three species that reside in our area: the purplemouth, the spotted, and the ocellated morays. The local ones are in the 2-3 foot range and have a feisty attitude – handle with care – better yet… don’t handle. They hide in crevices within the reef and explode on passing prey, snagging them with their sharp teeth. Many divers encounter them while searching these same crevices for spiny lobster. There are probing sticks you can use so that you do not have to stick your hand in there. There are rumors that since they have sharp teeth and tend to bite, they are venomous – this is not the case, but the bite can be painful.
The massive size of a goliath grouper. Photo: Bryan Fluech Florida Sea Grant
Groupers
This word is usually followed by the word “sandwich”. One of the more popular food fish, groupers are sought by anglers and spearfishermen alike. They are members of the serranid family (“sea basses”). This is one of the largest families of fishes in the Gulf – with 34 species listed. 15 of these are called “grouper” and there have been other members of this family sold as “grouper”.
So, what is – or is not – a “grouper”. One method used is anything in the genus Epinephelus would be a grouper. This would include 11 species, but would leave out the Comb, Gag, Scamp, Yellowfin, and Black groupers – which everyone considers “grouper”. Tough call eh?
These are large bodied fish with broad round fins – the stuff of slowness. That said, they can explode, just like morays, on their prey. Anglers who get a grouper hit know it, and divers who spear one know it. They range in size from six inches to six feet. The big boy of the group is the Goliath Grouper (six feet and 700 pounds). They love structure – so natural and artificial reefs make good homes for them. They also like the oil rigs of the western Gulf.
An interesting thing about many serranids is the fact they are hermaphroditic – male and female at the same time. Most grouper take it a step further – they begin life as females and become males over time.
The king of finfish… the red snapper
Photo: Florida Sea Grant
Snappers
The red snapper is king. Prized as a food fish all over the United States, and beyond, these fish have made commercial fishermen very happy. With an average length of 2.5 feet, some much larger individuals have been landed. This fishery put Pensacola on the map in the early 20th century. Sailing vessels called “Snapper Smacks” would head out to the offshore banks and natural reefs, return with a load, and sell both locally and markets in New York. There are large populations in Texas waters and down on the Campeche Banks off Mexico. “Snapper Season” is a big deal around here.
Though these are reef fish, snapper have a habit of feeding above, and away from, them. You probably knew there was more than one kind of snapper but may not know there are 10 species locally. Due to harvesting pressure, there are short seasons on the famous red snapper – so vermillion snapper has stepped in as a popular commercial fishery – and it is very good also. Some, like the gray snapper, are more common inshore around jetties and seawalls. Also known as the black snapper or mangrove snapper, this fish can reach about three feet in length and make a good meal as well.
The white grunt.
Photo: University of Florida
Grunts
Grunts look just like snapper, and probably sold as them somewhere. But they are a different family. They lack the canines and vomerine teeth the snappers have – other than that, they do look like snapper. Easy to tell apart right? Vomerine are tiny teeth found in the roof of the mouth, in snappers they are in the shape of an arrow. They get their name from a grunting sound they make when grinding their pharyngeal teeth together. A common inshore one is called the “pigfish” because of this. They do not get as large as snapper (most are about a foot long) and are not as popular as a food fish, but the 11 known species are quite common on the reefs, and the porkfish is one of the more beautiful fish you will see there.
Spadefish on a panhandle snorkel reef.
Photo: Navarre Beach Snorkel
Spadefish
This is one of the more common fish found around our reefs. Resembling an angelfish, they are often confused with them – but they are in a family all to themselves. What is the difference you ask? The dorsal fin of the spade fish is divided into two parts – one spiny, the other more fin-like. In the angelfish, there is only one continuous dorsal fin.
Spadefish like to school and are actually good to eat. It is also the logo/mascot of the nearby Dauphin Island Sea Lab.
Gray triggerfish.
Photo: NOAA
Triggerfish
“Danger Will Robinson!” This fish has a serious set of teeth and will come off the reef and bite through a quarter inch wetsuit to defend their eggs. Believe it – they are not messing around. Once considered a by-catch to snapper fishermen, they are now a prized food fish. They are often called “leatherjackets” due to their fused scales forming a leathery like skin that must be cut off – no scaling with this fish. They have the typical tall-flat body of a reef fish, squeezing through the rocks and structure to hide or hunt. We have five species listed in the Gulf of Mexico, but it is the Gray Triggerfish that is most often encountered.
Photo courtesy of Florida Sea Grant
Lionfish
You may, may not, have heard of this one – most have by now. It is an invader to our reefs. To be an invasive species you must #1 be non-native. The lionfish is. There are actually about 20 species of lionfish inhabiting either the Indo-Pacific or the Red Sea region.
#2 have been brought here by humans (either intentionally or unintentionally – but they did not make it on their own) – this is the case with the lionfish. It was brought here for the aquarium trade. There are actually two species brought here: The Red Lionfish (Pterois volitans) and the Devilfish (Pterois miles). Over 95% of what has been captured are the red lionfish – but it really does not matter, they look and act the same – so they are just called “lionfish”.
#3 they must be causing an environmental, and/or an economic problem. Lionfish are. They have a high reproductive rate – an average of 30,000 offspring every four days. There is science that during sometimes of the year it could be higher, also they breed year-round. Being an invasive species, there are few predators and so the developing young (encapsulated in a gelatinous sac) drift with the currents to settle on new reefs where they will eat just about anything they can get into their mouths. There have been no fewer than 70 species of small reef fish they have consumed – including the commercially valuable vermillion snapper and spiny lobster. There is now evidence they are eating other lionfish.
They quickly take over a reef area and some of the highest densities in the south Atlantic region have been reported off Pensacola. However, at a 2018 state summit, researchers indicated that the densities in our area have declined in waters less than 200 feet. This is most probably due to the harvesting efforts we have put on them. They are edible – actually, quite good, and there is a fishery for them. Derbies and ecotours have been out spearfishing for them since 2010. You may have heard they were poisonous and dangerous to eat. Actually, they are venomous, and the flesh is fine. The venom is found in the spines of the dorsal, pelvic, and anal fins. It is very painful, but there are no records of anyone dying from it. Work and research on management methods continue.
by Rick O'Connor | Sep 11, 2020
There is a lot of blue out there… a whole lot of blue. Miles of open water in the Gulf with nowhere to hide… except amongst yourselves. Their blue colored bodies, aerodynamically shaped like bullets with stiff angular fins, can zip along in this vast blue openness in large schools. Their myoglobin rich red muscle increases their swimming endurance – they can travel thousands of miles without tiring. Some species are what we call “ram-jetters”, fish that basically do not stop swimming – roaming the “big blue” looking for food and avoid being eaten, following the warm currents in search of their breeding grounds.
The open water is a place for specialists. Most of these fish have small, or no scales, to reduce frictional drag. They have a well-developed lateral line system so when a member of the school turns, the others sense it and turn in unison – just as the four planes in the US Navy Blue Angels delta do – perfect motion.
Many are built for speed. Sleek bodies with sharp angular fins and massive amounts of muscle / body mass, some species can reach speeds close to 70 mph – some can “fly”. There are fewer species who can live here, as opposed to the ocean floor, but those who do are amazing – and some of the most prized commercial and recreational fishing targets in the world. Let’s meet a few of them.
Flying fish do not actually “fly”, they are gliders using their long pectoral fins.
Photo: NOAA
Flying Fish
First, they do not actually fly – they glide. These tube-shaped speedy fish have elongated pectoral fins, reaching half the length of their bodies. The two lobes of their forked tail are not the same length – the lower lobe being longer. Using this like a rudder, they gain speed near the surface and, at some point, leap – extend the large pectoral fins, and glide above the water – sometimes up to 100 yards. As you might guess, this is to avoid the sleek speedy open water predators coming after them. You might also imagine that they, and their close cousins the half-beaks, are popular bait for the bill fishermen seeking those predators.
There are eight species of these amazing fish in the Gulf of Mexico ranging in size from 6-16 inches. Most are oceanic – never coming within 100 miles of the coast, but a few will, and can, be seen even near the pass into Pensacola Bay.
The cobia – also known as the ling, lemonfish, and sergeant fish, is a migratory species moving through our area in the spring.
Image: NOAA
Cobia
This is one of the migrating fish local anglers gear up for every year – the cobia run. When the water turns from 60° to 70°F in the spring – the cobia moves up the coastline heading from east to west. They have many different common names along the Gulf Coast. Ling, Cabio, Lemonfish, and Sergeant fish have all been used for this same animal. This is one reason biologists use scientific names – Rachycentron canadum in this case. That way we all know we are talking about the same fish. Whatever you call it, it is popular with the anglers and there is nothing like a fresh cobia sandwich – try one!
They can get quite large – 5 feet and up to 100 pounds – and resemble sharks in the water, sometimes confused with them. They seem to like drifting flotsam, where potential prey may hangout, and fishermen will toss their baits all around their schools trying to get them to take. At times, fishermen have confused sea turtles with cobia and have accidentally snagged them – only to release it, though it is a workout to do so, and they try to avoid it.
Cobia are in a family all their own. Their closest relatives are the remoras, or sharksuckers, which sometimes attach to them. They travel all over the Gulf and Atlantic Ocean.
Jacks have the sleek, fast design of the typical open water marine fish.
Photo: NOAA
Jacks
This is the largest open water family of fish I the northern Gulf – with 24 species. Not all jacks are open water, many are found on reefs and in estuaries. But these are aerodynamic shaped fish, with small scales and angular fins, and built for the open water environment. They vary in size, ranging from less than one foot, to over three. This group is identified by the two extended spines just in front of their anal fin. Several species – such as the amberjacks, pompano, and almaco jacks – are prized food fish. Others – like the jack crevalle and the blue runner (hardtail) – are just fun to catch, putting up great fights.
They are schooling fish and often associated with submerged wrecks and reefs, where prey can be found. The black and white pilot fish is called this because mariners would see them swimming in front of sharks – “piloting” them through the ocean. They are open water jacks but are more tropical and accounts in our area are rare.
The colors of the mahi-mahi are truly amazing.
Photo: National Wildlife Federation
Mahi–Mahi
This is the Hawaiian term for a fish called the dolphin (Coryphaena hippurus). You can probably guess why they prefer to call it by its Hawaiian name. It is a popular food fish, and to have “dolphin” on the menu – or to say “hey, we’re going dolphin fishing – want to come?” would raise eyebrows – and have.
The Mexicans call it “dorado”, and that term is used locally as well. Either name – it is an amazing fish. With the bull-shaped forehead of the males – they are sometimes referred to as the “bull-dolphin”. Their colors, and color changing, is amazing to see. Some biologists believe this may be some form of communication between members, don’t know, but the brilliant greens, blues, and yellows are amazing to see. They lose these colors shortly after death, so you must see it to believe it – or find one of the popular fish t-shirts.
Like jacks, dolphin like to hang around flotsam, or large schools of baitfish, looking for prey. As with many other open water predators, they will sometimes work in a team to scare, and scatter, individuals from the safety of their school. There are only two species in this family, and both are prized for their taste.
The Striped Mullet.
Image: LSU Extension
Mullet
This is not one you would typically call an “open water” fish. But in the nearshore Gulf and estuaries, they are more open water than bottom dwellers – though they do feed off the bottom. Sleek bodied, forked tail, angular fins, they have what it takes to be a fast swimmer. Though they do not “fly” as the flying fish do, they do leap out of the water. Many visitors hanging out around the Sound will hear a fish splash and immediately ask “what kind of fish was that?” Many locals will respond without looking up – “it was a mullet” – and they are probably right.
This brings up the age-old question… why do mullet jump? This was once asked of a marine biology professor. He paused… thought… and responded saying “for the same reasons manta rays jump”. That was it… another long pause. Finally, the students “took the bait” – “Okay, why do manta rays jump?”. The professor replied, “we don’t know”. So, there you go.
Another interesting thing about this fish is its wide tolerance of salinity. Mullet have been found in freshwater rivers and springs and the hypersaline lagoons of south Texas – they truly don’t care.
Locally they are popular food fish, and support a large commercial fishery in Florida, but in other parts of the Gulf not so much. It has to do with their environment and what they are feeding on. In muddier portions of the Gulf (or our bay for that matter) they have an oily taste and locals there call the “trash fish”. Even hearing that locals here eat them “grosses” them out. Local respond by giving it a more “high end” name – the Mulle (spoken with a French accent). This is actually the Cajun term for the fish. And let’s step it up a notch by adding that many locals eat mullet row – the eggs. Yea… getting hungry right? One of the popular cable food shows came here to try mullet roe. They said on a scale of 1 to 10, they give it a -4.
All that said, it is a local icon – with seafood stores selling “In Mullet We Trust” t-shirts, and the popular “Mullet Toss” event held every year on Perdido Key. It is a COOL fish.
This Spanish Mackerel has the distinct finlets of the mackerel family along the dorsal and ventral side of the body.
Image: NOAA
Mackerel
When you mention mackerel around here you usually think of one of two fish – the king mackerel (sometimes just referred to as “the king”) and the Spanish mackerel. But it is actually a large family of open water fish that includes the tuna, bonito, and the wahoo (of baseball fame).
They are some of the fastest fish in the sea, and several species are ram-jetters. Sleek bodies, sharp angular fins, they can be identified by the row of small finlets on the dorsal and ventral sides of their bodies near the rear. Full of red muscle, rich in myoglobin (which can hold more oxygen than hemoglobin alone), these are powerful swimming fish and very popular in the sushi trade. A bluefin tuna can be 14 feet long, 800 pounds, and bring a commercial fisherman tens of thousands of dollars. Because of this bluefin tuna are internationally protected and managed.
Another cool thing about these guys is that some species can control blood flow, and location, to help maintain a higher body temperature – “warm blooded” – allowing them to venture into colder waters of the world’s oceans. They are one of the big migratory fish we find. Following the large ocean currents, some species use this to play out their entire life cycle. Born in the warmer portions of the ocean gyres, they grow and feed in the cooler areas, returning in the warmer currents to breed.
There are 12 species in this family ranging in size from 1 to 15 feet. They have the characteristic “dark on top – light one bottom” coloration many animals have. This called countershading. It is believed to be used as a form of camouflage in the deep blue – with the darker blue-indigo on top (to blend in with the bottom if look from above) and the lighter silver-white on the bottom (to blend in with the sunlit surface if viewed from the below). This idea was used by the US Navy during World War II. If you visit our Naval Aviation Museum, you will see they painted the planes a darker blue on top and a lighter white on bottom. In hopes that the Japanese pilots would have a hard time spotting them over the Pacific Ocean. It is also believed to help with temperature control. The darker side will absorb heat, while the lighter side releases – avoiding over-heating. Amazing fish, aren’t they?
by Laura Tiu | Jul 3, 2020
Fishing is big business in Florida, contributing billions of dollars each year to the state’s economy. Fishing guides are an important part of the fishing industry. Guides provide locals and tourists alike with authentic Florida fishing experiences and memories that last a lifetime. Fishing guides are role models that can teach ethical angling through their onboard behaviors.
The Florida Friendly Fishing Guides Certification was developed by the University of Florida IFAS Extension, Florida Sea Grant, and the Florida Fish and Wildlife Conservation Commission with input from fishing guides. It is a voluntary certification program and involves no regulatory component. The target audience is flats guides, charter boat captains, and head-boat captains and crew. Recreational fishers are welcome to take the course, too.
What will I learn?
The Florida Sea Grant Florida Friendly Fishing Guide online course teaches best practices for catch and release fishing. Each lesson plan focuses on a different aspect of ethical angling. There are modules on seafood safety, federal and state fisheries management, onboard waste management, and how to teach your customers about the environment.
One environmental impact of fishing is what we call discard mortality. This is when a caught fish is released but does not survive. You will learn how to increase fish survival, how to identify barotrauma, and how to use descending and venting tools.
Starting July 15, 2020, a descending device will be required for head-boats, charter boats, commercial, and recreational vessels fishing for reef fish in federal waters of the Atlantic Ocean from North Carolina to Florida. The Florida Friendly Fishing Guide course will teach you how to identify barotrauma and select the right tool for sending fish back down to depth! Proper fish handling skills are important because up to 60% of caught fish are released.
The cost is $130 and the course takes about 4 hours to complete. Once you complete the course you receive a welcome package, public listing on the Florida Sea Grant website, and an optional social media promotion. For more information and registration go to https://www.flseagrant.org/florida-friendly-fishing-guide-certification/ or contact your local Florida Sea Grant agent, Laura Tiu, lgtiu@ufl.edu. Florida Friendly Fishing Guide Certification is a state-wide program for all saltwater fishing guides in Florida.
by Rick O'Connor | Jul 2, 2020
Cooters are one of the more commonly seen turtles when visiting a freshwater system. They are relatively large for a freshwater turtle (with a carapace about 13 inches long) and are often seen basking on logs, rocks, aerator pumps, you name it – and often in high numbers while doing so. They spook easy and usually leap into the water long before you reach them. But because of their beautiful smooth shells and large size, they can be seen from a distance – looking like wet rocks on a tree limb.
A “River Cooter” seen basking on a log in Blackwater River.
Photo: Molly O’Connor
They are in the genus Pseudemys (same as the Florida red-bellied turtles) and this genus is found throughout the southeastern United States. However, from there the breakdown of species becomes a bit challenging. There has been much debate how many species there really area, and how many are subspecies of those species. There are two distinct species for sure – the “River Cooter” (Pseudemys concinna) and the “Pond Cooter” (Pseudemys floridana). From here is gets a bit weird.
The “River Cooters” are just that – friends of rivers. They like those with a bit of a current, sand/gravel bottoms, basking spots, and grasses to eat. They have been found in estuaries, even with barnacles growing on them, so they have some tolerance for saltwater. River cooters can be distinguished from their “Pond Cooter” cousins in having a more aerodynamic shell (presumably for their habit of living in faster flowing rivers) with yellow-orange markings that form concentric rings on each scute (scale) of the carapace. Some of these seem to form a backwards “C”. Their plastron is yellow-orange but will have black markings along the margins of each scute.
This river cooter is basking on a log on the heads waters of the Choctawhatchee River in Alabama.
Photo: Molly O’Connor
The “Suwannee Cooter” is believed to be a subspecies (Pseudemys concinna suwanniensis) found in tannic rivers from the Ochlockonee just west of Tallahassee south to the Tampa Bay region. It has only been found in rivers that flow into the Gulf of Mexico. A couple of records have been found in rivers flowing towards the Atlantic, but it is believed these were relocated by humans.
The “Eastern River Cooter” is found from the Ochlockonee River west to Mobile Bay – possibly as far as Louisiana. There has been a suggestion that the one west of Mobile Bay is the “Mobile Cooter” (Pseudemys concinna mobilensis) but the naming of this group, again, has been a bit crazy.
As mentioned, “Pond Cooters” are fans of slow-moving waters with muddy bottoms. Unlike river cooters, pond cooters will travel over land other than to lay eggs. Many of their “pond” selections dry up and they must find new habitat. Like river cooters, pond cooters feed on vegetation so aquatic plants are must and they also like to bask in the sun on logs with many cooters basking at once.
A pond cooter in a canal within the Gulf Islands National Seashore.
Photo: Molly O’Connor
Physically they differ from river cooters in having a slightly domed shell near the head end. The yellow markings are not concentric, but rather are in straight lines and their plastrons are an immaculate beautiful yellow – with no markings on the margins. They do however have black circles on the bottom margins of their carapace. These are usually round with a small yellow spot in the center – resembling an “o”.
There is believed to be two subspecies of this group. Pseudemys floridana floridiana (the “Florida Cooter”) and Pseudemys floridana peninuslaris (the “Peninsula Cooter”). Told you it was all weird. The Florida cooter is found in the Florida panhandle and the Peninsula Cooter has been found all the way to the Florida Keys – though it does not seem to be common in the Everglades.
Add to the quagmire of species identification – there is hybridization between not only the types of pond and river cooters – but BETWEEN the pond and river cooters. So, if you live in the eastern panhandle where all of these seem to converge – just call them “cooters”!
They have an interesting nesting habit. When the females approach an open sunny sandy spot, she will dig a hole to lay about 20 eggs, but she will also dig two “satellite” nests on either side – and maybe place an egg or two in there. It is quite understood why they do this, but they do. They also may come to the beach up to five times in one year to lay eggs.
A pond cooter digging a nest on someone’s property.
Photo: Deb Mozert
Because of their high numbers and large size, this has been a favorite food item for humans for quite some time. Due to this, and the practice of shooting them off their basking spots, and alterations of river systems lower the habitat quality for the river cooters, their numbers have declined. The Suwannee Cooter in particular has been hard hit and is a species of concern. Due to this it no longer allowed to harvest them (or their eggs) from the wild. Because it is so hard to tell the Suwannee from other species/subspecies of cooters – ALL cooters are now protected by the Florida Fish and Wildlife Conservation Commission.
Another note – they do not eat fish. The young will eat worms and insects, but the adults are strictly herbivores. Many pond owners want to shoot them thinking they are eating the stocked fish by the landowner. They will not eat the fish – you are fine.
I think these are amazingly beautiful animals to see glimmering in the sunny on their basking logs as you explore our local rivers and wetlands. I hope you find them just as cool and appreciate them.
Resources:
Buhlman, K., T. Tuberville, W. Gibbons. 2008. Turtles of the Southeast. University of Georgia Press, Athens GA. 252 pp.
Florida Fish and Wildlife Conservation Commission. Freshwater Turtles https://myfwc.com/wildlifehabitats/wildlife/freshwater-turtles/.
Meylan, P.A. (Ed.). 2006. Biology and Conservation of Florida Turtles. Chelonian Research Monographs No.3, 376 pp.
by Rick O'Connor | Jun 26, 2020
This is a good name for this group. They are mollusk that have two shells. They tried “univalve” with the snails and slugs, but that never caught on – gastropods it is for them. The bivalves are an interesting, and successful, group. They have taken the shell for protection idea to the limit – they are COMPLETELY covered with shell. No predators… no way. But they do have predators – we will talk more on that.
An assortment of bivalves, mostly bay scallop.
Photo: Florida Department of Environmental Protection.
As you might expect, with the increase in shell there is a decrease in locomotion – as a matter of fact, many species do not move at all (they are sessile). But in a sense, they do not care. They are completely covered and protected. Again, we will talk more about how well that works.
The two shells (valves) are connected on the dorsal side of the animal and hinged together by a ligament. Their bodies are laterally compressed to fit into a shell that is aerodynamic for burrowing through soft muds and sands. Their “heads” are greatly reduced (even missing in some) but they do have a sensory system. Along the edge of the mantle chemoreceptive cells (smell and taste) can be found and many have small ocelli, which can detect light. The scallops take it a step further by having actually eyes – but they do live on the surface and they do move around – so they are needed.
The shells are hinged together at the umbo with “teeth like structures and the shells open and close using a pair of adductor muscles. Many shells found on the beach will have “scars” which are the point of contact for these muscles. They range is size from the small seed clams (2mm – 0.08”) to the giant clam of the Indo-Pacific (1m – 3.4 ft) and 2500 lbs.! Most Gulf bivalves are more modest in size.
Being slow burrowing benthic animals, sand and mud can become a problem when feeding and breathing. In response, many bivalves have developed modified gills to help remove this debris, and many actually remove organic particles using it as a source of food. Many others will fuse their mantle to the shell not allowing sediment to enter. But some still does and, if not removed, will be covered by a layer of nacreous material forming pearls. All bivalves can produce pearls. Only those with large amounts of nacreous material produce commercially valuable ones.
Coquina are a common burrowing clam found along our beaches.
Photo: Flickr
Another feature is the large foot, used for digging a burrowing in the more primitive forms. It is the foot we eat when we eat clams. They can turn their bodies towards the substrate, begin digging with their foot but also using their excurrent from breathing to form a sort of jet to help move and loosen the sand as they go – very similar to the way we set pilings for piers and bridges today.
These are the earliest forms of bivalves – the burrowers. Most are known as clams and most live where the sediment is soft. Located near their foot is a sense organ called a statocyst that lets them know their orientation in the environment. Most have their mantles fused to their shells so sand cannot enter the empty spaces in the body. To channel water to the gills, they have developed tubes called siphons which act as snorkels. Most burrow only a few inches, some burrow very deep and they are even more streamlined and elongated.
Some have evolved to burrow into harder material such as coral or wood. One of the more common ones is an animal called a shipworm. Called this by mariners because of the tunnels they dig throughout the hulls of wooden ships, they are not worms but a type of clam that have learned to burrow through the wood consuming the sawdust of their actions. They have very reduced shells and a very long foot.
This cluster of green mussels occupies space that could be occupied by bivavles like osyters.
Other bivalves secrete a fibrous thread from their foot that is used to grab, hold, and sometimes pull the animal along. These are called byssal threads. Many will secrete hundreds of these, allow them to “tan” or dry, reduce their foot, and now are attached by these threads. The most famous of this group are the mussels. Mussels are a popular seafood product and are grown commercial having them attach to ropes hanging in the water.
Another method of attachment is to literally cement your self to the bottom. Those bivalves who do this will usually lay on their side when they first settle out from their larval stage and attach using a fluid produced by the animal. This fluid eventually cements them to the bottom and the shell attached is usually longer than the other side, which is facing the environment. The most famous of these are the oysters. Oysters basically have lost both their “head” and the foot found in other bivalves. These sessile bivalves are very dependent on tides and currents to help clear waste and mud from their bodies.
Oysters are a VERY popular seafood product along the Gulf coast.
Photo: Rick O’Connor
Then there are the bivalves who actually live on the bottom – not attached – and are able to move, or even swim. Most of these have well developed tentacles and ocelli to detect danger in the environment and some, like the scallops, can actually “clap their shells together” to create a jet current and swim. This is usually done when they detect danger, such as a starfish, and they have been known to swim up to three feet. Some will use this jet as a means of digging a depression in the sand they can settle in. In this group, the adductor has been reduced from two (the number usually found in bivalves) to one, and the foot is completely gone.
As you might guess, reproduction is external in this group. Most have male and female members but some species (such as scallops and shipworms) are hermaphroditic. The gametes are released externally at the same time in an event called a mass spawning. To trigger when this should happen, the bivalves pay attention to water temperature, tides, and pheromones released by the opposite sex or by the release of the gametes themselves.
Scallop life cycle.
Image: University of Florida IFAS
The fertilized eggs quickly develop into a planktonic larva known as a veliger. This veliger is ciliated and can swim with the current to find a suitable settling spot. Some species have long lived veliger stages. Oysters are such and the dispersal of their veliger can travel as far as 800 miles! Once the larval stage ends, they settle as “spat” (baby shelled bivalves) on the substrate and begin their lives. Some species (such as scallop) only live for a year or two. Others can live up to 10 years.
As a group, bivalves are filter feeders, filtering organic particles and phytoplankton as small as 1 micron (1/1,000,000-m… VERY small). In doing this they do an excellent job of increasing water clarity which benefits many other creatures in the community. As a matter of fact, many could not survive without this “eco-service” and the loss of bivalves has triggered the loss of both habitat and species in the Gulf region. Restoration efforts (particularly with oysters) is as much for the enhancement of the environment and diversity as it is for the commercial value of the oyster.
Now… predators… yes, they have many. Though they have completely covered their bodies with shell, there are many animals that have learned to “get in there”. Starfish and octopus are famous for their abilities to open tightly closed shells. Rays, some fish, and some turtles and birds have modified teeth (or bills) to crush the shell or cut the adductor muscle. Sea otters have learned the trick to crush them with rocks and some local shorebirds will drop them on roads and cars trying to access them. And then there are humans. We steam them to open the shell and cut their adductor muscle to reach the sweet meat inside.
It is a fascinating group – and a commercial valuable one as well. Lots of bivalves are consumed in some form or fashion worldwide. Take some time at the beach to collect their shells as enjoy the great diversity and design within this group. EMBRACE THE GULF!
