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!
by Chris Verlinde | May 1, 2020
Black Skimmers foraging for fish. Photo Credit: Jan Trzepacz, Pelican Lane Arts.
Black Skimmers and Least Terns, state listed species of seabirds, have returned along the coastal areas of the northern Gulf of Mexico! These colorful, dynamic birds are fun to watch, which can be done without disturbing the them.
Shorebirds foraging. Photo Credit: Jan Trzepacz, Pelican Lane Arts.
Black Skimmer with a fish. Photo Credit: Jan Trzepacz, Pelican Lane Arts.
What is the difference between a seabird and shorebird?
Among other behaviors, their foraging habits are the easiest way to distinguish between the two. The seabirds depend on the open water to forage on fish and small invertebrates. The shorebirds are the camouflaged birds that can found along the shore, using their specialized beaks to poke in the sandy areas to forage for invertebrates.
Both seabirds and shorebirds nest on our local beaches, spoil islands, and artificial habitats such as gravel rooftops. Many of these birds are listed as endangered or threatened species by state and federal agencies.
Juvenile Black Skimmer learning to forage. Photo Credit: Jan Trzepacz, Pelican Lane Arts.
Adult black skimmers are easily identified by their long, black and orange bills, black upper body and white underside. They are most active in the early morning and evening while feeding. You can watch them swoop and skim along the water at many locations along the Gulf Coast. Watch for their tell-tale skimming as they skim the surface of the water with their beaks open, foraging for small fish and invertebrates. The lower mandible (beak) is longer than the upper mandible, this adaptation allows these birds to be efficient at catching their prey.
Least Tern “dive bombing” a Black Skimmer that is too close to the Least Tern nest. Photo Credit: Jan Trzepacz, Pelican Lane Arts.
Adult breeding least terns are much smaller birds with a white underside and a grey-upper body. Their bill is yellow, they have a white forehead and a black stripe across their eyes. Just above the tail feathers, there are two dark primary feathers that appear to look like a black tip at the back end of the bird. Terns feed by diving down to the water to grab their prey. They also use this “dive-bombing” technique to ward off predators, pets and humans from their nests, eggs and chicks.
Least Tern with chicks. Photo Credit: Jan Trzepacz, Pelican Lane Arts.
Both Black Skimmers and Least Terns nest in colonies, which means they nest with many other birds. Black skimmers and Least Terns nest in sandy areas along the beach. They create a “scrape” in the sand. The birds lay their eggs in the shallow depression, the eggs blend into the beach sand and are very hard to see by humans and predators. In order to avoid disturbing the birds when they are sitting on their nests, known nesting areas are temporarily roped off by Audubon and/or Florida Fish and Wildlife Conservation Commission (FWC) representatives. This is done to protect the birds while they are nesting, caring for the babies and as the babies begin to learn to fly and forage for themselves.
Threats to these beautiful acrobats include loss of habitat, which means less space for the birds to rest, nest and forage. Disturbances from human caused activities such as:
- walking through nesting grounds
- allowing pets to run off-leash in nesting areas
- feral cats and other predators
- litter
- driving on the beach
- fireworks and other loud noises
Audubon and FWC rope-off nesting areas to protect the birds, their eggs and chicks. These nesting areas have signage asking visitors to stay out of nesting zones, so the chicks have a better chance of surviving. When a bird is disturbed off their nest, there is increased vulnerability to predators, heat and the parents may not return to the nest.
Black Skimmer feeding a chick. Photo Credit: Jan Trzepacz, Pelican Lane Arts.
To observe these birds, stay a safe distance away, zoom in with a telescope, phone, camera or binoculars, you may see a fluffy little chick! Let’s all work to give the birds some space.
Special thanks to Jan Trzepacz of Pelican Lane Arts for the use of these beautiful photos.
To learn about the Audubon Shorebird program on Navarre Beach, FL check out the Relax on Navarre Beach Facebook webinar presentation by Caroline Stahala, Audubon Western Florida Panhandle Shorebird Program Coordinator:
In some areas these birds nest close to the road. These areas have temporarily reduced speed limits, please drive the speed limit to avoid hitting a chick. If you are interested in receiving a “chick magnet” for your car, 
to show you support bird conservation, please send an email to: chrismv@ufl.edu, Please put “chick magnet” in the subject line. Please allow 2 weeks to receive your magnet in the mail. Limited quantities available.
by Rick O'Connor | Feb 13, 2020
An eastern cottonmouth basking near a creek in a swampy area of Florida.
Photo: Tommy Carter
When you think of reptiles you typically think of tropical rainforest or the desert. However, there is at least one member of the three orders of reptiles that do live in the sea. Saltwater crocodiles are found in the Indo-Pacific region as are about 50 species of sea snakes. There is one marine lizard, the marine iguana of the Galapagos Islands, and then the marine (or sea) turtles. These are found worldwide and are the only true marine reptiles found in the Gulf of Mexico.
Sea turtles are very charismatic animals and beloved by many. Five of the seven species are found in the Gulf. These include the Loggerhead, which is the most common, the Green, the Hawksbill, the Leatherback, and the rarest of all – the Kemp’s Ridley.
Many in our area are very familiar with the nesting behavior of these long-ranged animals. They do have strong site fidelity and navigate across the Gulf, or from more afar, to their nesting beaches – many here in the Pensacola Beach area. The males and females court and mate just offshore in early spring. The females then approach the beach after dark to lay about 100 eggs in a deep hole. She then returns the to the Gulf never to see her offspring. Many females will lay more than one clutch in a season.
The largest of the sea turtles, the leatherback.
Photo: Dr. Andrew Colman
The eggs incubate for 60-70 days and their temperature determines whether they will be male or female, warmer eggs become females. The hatchlings hatch beneath the sand and begin to dig out. If they detect problems, such as warm sand (we believe meaning daylight hours) or vibrations (we believe meaning predators) they will remain suspended until those potential threats are no more. The “run” (all hatchlings at once) usually occurs under the cover of darkness to avoid predators. The hatchlings scramble towards the Gulf finding their way by light reflecting off the water. Ghost crabs, fox, raccoon, and other predators take almost 90% of them, and the 10% who do reach the Gulf still have predatory birds and fish to deal with. Those who make it past this gauntlet head for the Sargassum weed offshore to begin their lives.
These are large animals, some reaching 1000 pounds, but most are in the 300-400 pound range, and long lived, some reaching 100 years. It takes many years to become sexually mature and typically long-lived / low reproductive animals are targets for population issues when disasters or threats arise. Many creatures eat the small hatchings, but there are few predators on the large reproducing adults. However, in recent years humans have played a role in the decline of the adult population and all five species are now listed as either threatened or endangered and are protected in the U.S. There are a couple of local ordinances developed to adhere to federal law requiring protection. One is the turtle friendly lighting ordinance, which is enforced during nesting season (May 1 – Oct 31), and the Leave No Trace ordinance requiring all chairs, tents, etc. to be removed from the beach during the evening hours. There are other things that locals can do to help protect these animals such as: fill in holes dug on the beach during the day, discard trash and plastic in proper receptacles, avoid snagging with fishing line and (if so) properly remove, and watch when boating offshore to avoid collisions.
If we include the barrier islands there are more coastal reptiles beyond the sea turtles. There are freshwater ponds which can harbor a variety of freshwater turtles. I have personally seen cooters, sliders, and even a snapping turtle on Pensacola Beach. Many coastal islands harbor the terrestrial gopher tortoise and wooded areas could harbor the box turtles. In the salt marsh you may find the only brackish water turtle in the U.S., the diamondback terrapin. These turtles do nest on our beaches and are unique to see. Freshwater turtle reproductive cycles are very similar to sea turtles, albeit most nest during daylight hours.
An American Alligator basking on shore.
Photo: Molly O’Connor
The American alligator can also be found in freshwater ponds, and even swimming in saltwater. They can reach lengths of 12 feet, though there are records of 15 footers. These animals actually do not like encounters with humans and will do their best to avoid us. Problems begin when they are fed and loose that fear. I have witnessed locals in Louisiana feeding alligators, but it is a felony in Florida. Males will “bello” in the spring to attract females and ward off competing males. Females will lay eggs in a nest made of vegetation near the shoreline and guard these, and the hatchlings, during and after birth. They can be dangerous at this time and people should avoid getting near.
We have several native species of lizards that call the islands home. The six-lined race runners and the green anole to name two. However, non-native and invasive lizards are on the increase. It is believed there are actually more non-native and invasive lizards in Florida than native ones. The Argentina Tegu and the Cuban Anole are both problems and the Brown Anole is now established in Gulf Breeze, East Hill, and Perdido Key – probably other locations as well. Growing up I routinely find the horned lizard in our area. I was not aware then they were non-native, but by the 1970s you could only find them on our barrier islands, and today sightings are rare.
An eastern cottonmouth crossing a beach.
Photo: Molly O’Connor
Then there are the snakes.
Like all reptiles, snakes like dry xeric environments like barrier islands. We have 46 species in the state of Florida, and many can be found near the coast. Though we have no sea snakes in the Gulf, all of our coastal snakes are excellent swimmers and have been seen swimming to the barrier islands. Of most concern to residents are the venomous ones. There are six venomous snakes in our area and four of them can be found on barrier islands. These include the Eastern Diamondback Rattlesnake, the Pygmy Rattlesnake, the Eastern Coral Snake, and the Eastern Cottonmouth. There has been a recent surge in cottonmouth encounters on islands and this could be due to more people with more development causing more encounters, or there may be an increase in their populations. Cottonmouths are more common in wet areas and usually want to be near freshwater. Current surveys are trying to determine how frequently encounters do occur.
Not everyone agrees, but I think reptiles are fascinating animals and a unique part of the Gulf biosphere. We hope others will appreciate them more and learn to live with and enjoy them.
by Rick O'Connor | Jan 14, 2020
Standing on one of our local beaches, the Gulf of Mexico appears to be a wide expanse of emerald green and cobalt blue waters. We can see the ripples of offshore waves, birds soaring over, and occasionally dolphins breaking the surface. But few of us know, or think, about the environment beneath the waves where 99% of the Gulf lies. We might dream about catching some of the large fish, or taking a cruise, but not about the geology of the bottom, what the water is doing beneath the waves, or what other creatures might live there.
The Gulf of Mexico as seen from Pensacola Beach.
Photo: Molly O’Connor
Scanning the horizon from the beach, you are gazing at 600,000 square miles of open water. It is about 950 miles from the panhandle to Mexico. Traveling at 10 knots, it would take you about 3 days to cross at its widest point. The Gulf is almost an enclosed body of water. The bottom is somewhat “bowl” shaped with the deepest portion slightly west of center at a location known as the Sigsbee Deep. The island of Cuba serves as the “median” between where the ocean enters and exits the Gulf. Cycling water from the Atlantic crosses from Africa, through the Caribbean, and enters the between Cuba and the Yucatan. The seafloor here sinks and spills into the Sigsbee Deep. The pass between Cuba and Yucatan is about 6500 feet deep and the bottom of the Sigsbee Deep is about 12,000. If you are looking due south from the Florida Panhandle, you would be looking at this pass.
If your gaze shifted slightly to the right – maybe “1:00” – you would be looking at the Yucatan. The Yucatan itself forms a peninsula and a portion of it is below sea level extending further into the Gulf. This submerged portion of the Yucatan is what oceanographers refer to as a continental shelf. On the “leeward” side of the Yucatan Peninsula lies an area of the Gulf known as the Bay of Campeche. There is a shallow section of this “bay” known as the Campeche Banks which supports amazing fisheries and some mineral extraction. Off the Yucatan shelf there is a current of water that rises from the ocean floor called an upwelling. These upwellings are usually cold water, high in oxygen, and high in nutrients – producing an area of high biological productivity and good fishing.
Continuing to circle the Sigsbee Deep and looking about “2:00”, northwest of the Bay of Campeche, you enter the western Gulf which extends from Vera Cruz Mexico to the Rio Grande River in Texas. The shelf is much closer to shore here and the marine environment is still tropical. There is a steep continental slope that drops into the Sigsbee Deep. Water from the incoming ocean currents usually do not reach these shores, rather they loop back north and east forming the Loop Current. The shelf extends a little seaward where the Rio Grande discharges, leaving a large amount of sediment. In recent years, due to human activities further north, water volume discharge here has decreased.
In the direction of about “2:30”, is the Northwestern Gulf. It begins about the Rio Grande and extends to the Mississippi Delta. Here the continental shelf once again extends far out to sea. One of the larger natural coral reefs in the Gulf system is located here; the Flower Gardens. This reef is about 130 miles off the coast of Texas. The cap is at 55 feet and drops to a depth of 160 feet. Because of the travel distance, and diving depth, few visit this place. Fishing does occur here but is regulated. This shelf is famous for billfishing, shrimping, and fossil fuel extraction. The Mississippi River, 15th largest in the world and the largest in the Gulf, discharges over 590,000 ft3 of water per second. The sediments of this river create the massive marshes and bayous of the Louisiana-Mississippi delta region, which has been referred to as the “birds’ foot” extending into the Gulf. This river also brings a lot of solid and liquid waste from a large portion of the United States and is home to one of the most interesting human cultures in the United States. There is much to discuss and learn about from this portion of the Gulf over this series of articles.
The basin of the Gulf of Mexico showing surface currents.
Image: NOAA
At this point we have almost completely encircled the Sigsbee Deep and move into the eastern Gulf. Things do change here. From the Mississippi delta to Apalachee Bay west of Apalachicola is what is known as the Northeastern Gulf – also known as the northern Gulf – locally called the Gulf coast. This is home to the Florida panhandle and some of the whitest beaches you find anywhere. Offshore the shelf makes a “dip” close to the beach near Pensacola forming a canyon known as the Desoto Canyon. The bottom is a mix of hardbottom and quartz sand. Near the canyon is good fishing and this area, along with the Bay of Campeche, is historically known for its snapper populations. It lies a little north of the Loop Current but is exposed to back eddies from it. Today there is an artificial reef program here and some natural gas platforms off Alabama.
Looking between “9:00-10:00” you are looking at the west coast of Florida and the Florida shelf. Here the shelf extends for almost 200 miles offshore. Off the Big Bend the water is shallow for miles supporting large meadows of seagrass and a completely different kind of biology. The rock is more limestone and the water clearer. In southwest Florida the grassflats support a popular fisheries area and a coral system known as the Florida Middle Grounds. At the edge of the shelf is a steep drop off called the Florida Escarpment, which forms the eastern side of the “bowl”. Another ocean upwelling occurs here.
Looking at “11:00” you are looking towards the Florida Keys. Between the Keys and Cuba is the exit point of the Loop Current called the Florida Straits. It is not as deep as here as it is between Cuba and the Yucatan; only reaching a depth of 2600 feet. This is mostly coral limestone and the base of one of the largest coral reef tracks in the western Atlantic. The coral and sponge reefs, along with the coastal mangroves, forms one of the more biological productive and diverse regions in our area. It supports commercial fishing and tourism.
We did not really talk about the bottom of the “bowl”. Here you find remnants of tectonic activity. Volcanos are not found but you do find cold and hot water vent communities, which look like chimneys pumping tremendous amounts of thermal water from deep in the Earths crust. These vent communities support a neat group of animals that we are just now learning about. Brine lakes have also been discovered. These are depressions in the seafloor where VERY salty water settles. These “lakes” have water much denser than the surrounding seawater and can even create their own waves. Many of them lie as deep as 3300 feet and can be 10 feet deep themselves. There is one known as the “Jacuzzi of Despair”. They are so salty they cannot support much life.
In the next addition to this series we will begin to look at the some of the interesting plant and animals that call the Gulf home.
Embrace the Gulf.
by Rick O'Connor | Jan 10, 2020
It’s an amazing place really – the Gulf of Mexico. Covering over 598,000 square miles this almost a complete circle of water and home to some interesting geological features, amazing marine organisms, some of busiest ports in the United States, offshore mineral extraction, great vacation locations, and amazing local culture.
View from the Navarre Beach pier Photo credit: Lydia Weaver
As you stand along Pensacola Beach and look south, you see a wide expanse of water that seems to go on forever. However, in oceanographic terms, the Gulf is not that large of a body of water. Though it is close to 600,000 square miles in size, the Atlantic Ocean is 41,000,000 and the Pacific is 64,000,000 square miles. In addition to area, the mean depth of the Atlantic is a little over 12,000 feet and the Pacific is 14,000 feet. In comparison, the deepest point of the Gulf is 14,000 feet and the mean depth is only 5,000. The shape of the bottom is like a ceramic bowl that was not centered well when fired. The deepest point, the Sigsbee Deep, is about 550 miles southwest (about “2:00” if you are looking from the beach). The shape appears like a hole made by a golf ball that landed in a sand trap. As a matter of fact, there are scientists who believe this is exactly what happened – a large asteroid or comet made have hit the Earth near the Gulf forming a large series of tsunamis and created the Gulf as we know it today.
Either way the “pond” (as some oceanographers refer to it) is an amazing place. The bottom is littered with hot vents, brine lakes, and deep-sea canyons. Large areas of the continental shelf support coral reef formation and a great variety of marine life. Some of the busiest ports in the United States are located along its shores, and it supplies 14% of the wild domestic harvested seafood. Everyone is aware of the mineral resources supplied on the western shelf of the Gulf and the tremendous tourism all states and nations that bordering enjoy.
The emerald waters of the Gulf of Mexico along the panhandle.
This year the Gulf of Mexico Alliance will be celebrating “Embracing the Gulf” with a variety of activities and programs across the northern Gulf region. We will be dedicating this column to articles about the Gulf of Mexico all year and discussing some of the topics mentioned above in more detail. We hope you enjoy your time here and get a chance to explore the Gulf’s seafood, fishing, diving, marine life, ship cruises, unique cultures, and awesome sunsets. Embrace the Gulf!
