I attended a meeting recently where one of the participants stated – “We have been looking at a lot of water quality parameters within our bay in recent years, and plan to look at more, but has anyone been looking at temperature?”
What he was referring to was that the focus of most monitoring projects has been nutrients, dissolved oxygen, etc. But most agencies and universities who have been conducting long term monitoring in our bays are collecting temperature data as well. His question was not whether they have or not but has anyone looked at this long-term temperature data to see trends.
I know from some of the citizen science monitoring I have been involved with that temperature is collected but (anecdotally) does not vary much. It is like pH, we collect it, it is there, but does change drastically (anecdotally) over time. However, it has been a very hot year. This “heat dome” that has been sitting over the Midwest and southeast this summer has set records all across the region. Someone monitoring water temperature in East Bay recently reported surface water temperature at 96°F (36°C). Many have stated that swimming in our waters at the moment feels like swimming in bath water. It’s not just warm in your yard, it is warm in the bay. And this brings up the question of thermal tolerance of estuarine species.
All creatures have a temperature tolerance range. They resemble a bell curve where you have the thermal minimum at one end, the thermal maximum at the other, and the “preferred” temperatures near the top of the bell curve (see image below). Many creatures have a large tolerance for temperature shifts (their bell curves extend over a larger temperature range). You find such creatures in the temperate latitudes where temperature differences between summer and winter are larger. Others have a lower tolerance, such as those who are restricted to polar or tropical latitudes. Within an estuary you can find creatures with varying thermal tolerances. Some have a larger tolerance than others. Ectothermic (cold-blooded) creatures often have a wider range of temperatures they can survive at than endothermic (warm-blooded) ones. Homotherms (creatures who maintain their body temperature near a fixed point – such as humans 98.6°F/37°C) expend a lot of energy to do this. When environmental temperatures rise and fall, they have to expend more to maintain it at their fixed temperatures.
Image provide by Research Gate.
It is also true that most creatures prefer to exist near their thermal maximum. In other words, the bell curve is sort of skewed towards the warmer end of their range. But what is their thermal maximum? What happens when they reach it? How hot can they go?
Local waters are warmer this year.
Photo: Rick O’Connor
The studies I reviewed suggested that the thermal maximum is dependent on other environmental factors such as salinity and dissolved oxygen. In most cases, the higher the salinity, the higher the thermal maximum was. I looked at studies for the eastern oyster (Crassostrea virgincia), the brown shrimp (Farfantepenaeus aztectus), the blue crab (Callinectes sapidus), the Spot Croaker (Leiostomus xanthurus), and the pinfish (Lagodon rhomboides). The oyster, shrimp, and blue crab support important commercial fishery. The spot croaker is a dominant fish species in the upper estuary where the pinfish is a dominant species in the lower sections. These studies all suggested that again, depending on salinity, dissolved oxygen, pressure, and rate of temperature increase, the thermal maximum could happen as low as 30°C (86°F) and as high as 40°C (104°F), with many having a thermal maximum between 35-40°C.
At these temperatures proteins begin to denature and biological systems begin to shut down. Most of the studies determined the endpoint at “loss of equilibrium” and not actually death. Our estuaries can certainly reach these temperatures in the summer. Again, one recent reading in East Bay (within the Pensacola Bay system) was 96°F (36°C).
So, what do these creatures do when such temperatures are reached?
The most obvious response is to move, find cooler water. These are often found in deeper portions of the bay below the thermocline (a point in the water column where water temperatures significantly change – usually decreasing with depth). However, many sections of our estuaries are shallow and deep water cannot be found. In these cases, they may move great distances to seek deeper water areas, or even move to the Gulf of Mexico. In some cases – like with oysters – they cannot move, and large die-offs can occur. Other responses include lower metabolic rates and decline in reproduction.
We know that throughout history, there have been warmer summers than others and heat waves have happened. In each case, depending on other environmental factors, estuarine creatures have adapted, and some members have survived, to keep their populations going.
We know that large scale die-offs have occurred in the past and the tougher species have continued on.
We also know that the planet is warming, and it would be interesting to look at how the water temperatures have changed over the last few decades. Are they increasing? Are they reaching the thermal maximums of the creatures within our bay? How will these creatures respond to this?
You might say this is a strange title – “meet the barnacle” – because everyone knows what a barnacle is… or do they?
As a marine science instructor, I gave my students what is called a lab practical. This is a test where you move around the room and answer questions about different creatures preserved in jars. Almost every time that got to the barnacle they were stumped. I mean they knew it was a barnacle but what kind of animal is it? What phylum is it in?
Going through a thought process they would more often than not choose that it was a mollusk. This makes perfect sense because of the calcium carbonate shell it produces. As a matter of fact, science thought it was a mollusk until 1830 when the larval stage was discovered, and they knew they were dealing with something different. It is not a mollusk. So… what IS it? Let’s meet the barnacle…
Barnacles along the seashore is a common site for many.
Photo: NOAA
The barnacle is actually an arthropod. Yep… the same group as crabs and shrimp, insects and spiders. Weird right…
But that is because the creature down within that calcium carbonate shell is more like a tiny shrimp than an oyster. It is in the class Cirripedia within the subphylum Crustacea. It is the only animal in this class and the only sessile (non-motile) crustacean.
Barnacles are exclusively marine. This has been helpful when conducting surveys for terrapins or assessing locations for living shorelines – if you see barnacles growing on rocks, shells, or pilings, it is salty enough. There are over 900 species described and they live independently from each other attached to seawalls, rocks, pilings, boats, even turtle shells. Louis Agassiz described the barnacle as “nothing more than a little shrimplike creature, standing on its head in a limestone house kicking food into its mouth.”
This image from a textbook shows the internal structure of a barnacle. Notice the shrimplike animal on its back with extendable appendages (cirri) for feeding.
Image: Robert Barnes Invertebrate Zoology.
The planktonic barnacle larva settles to the bottom and attaches to a hard substrate using a cement produced from a gland near the base of their first set of antenna (crustaceans, unlike insects and spiders, have two sets of antenna). It is usually head down/tail up and begins to secrete limestone plates forming the well known “shell” of the animal. Some barnacles produce a long stalk near the head end (called the peduncle) which holds the adhesive gland and it is the peduncle that attaches to the hard substrate, not the head directly. The goose neck barnacle is an example of this. We find them most often in the wrack along the Gulf side of our beaches attached to driftwood or marine debris.
Lucky was found in the Gulf of Mexico. He had been there long enough for these goose neck barnacles to attach and grow.
Photo: Bob Blais
The “shell” of the barnacle is a series of calcium carbonate plates they secrete. These plates overlap and are connected by either a membrane or interlocking “teeth”. The body lies 90° from the point of attachment on its back.
There are six pairs of “legs” which are very long and are extended out of the “doors” of the shell and make a sweeping motion to collect planktonic food in the water column. They are most abundant in the intertidal areas were there are rocks, seawalls, or pilings.
Most species are hermaphroditic (possessing both sperm and egg) but cross fertilization is generally the rule. Barnacles signal whether they are acting males or females via pheromones and fertilization occurs internally, the gametes are not discharged into the water column as in some mollusks and corals. The developing eggs brood internally as well. Our local barnacle (Balanus) breeds in the fall and the larva (nauplius) are released into the water column in the spring by the tens of thousands. The larva goes through a series of metamorphic changes until it settles on a hard substrate and becomes the adult we know. They usually settle in dense groups in order to enhance internal fertilization for the next generation. Those who survive the early stages of life will live between two and six years.
So, there you go… this is what a barnacle is… a shrimplike crustacean who is attached to the bottom by its head, secretes a fortress of calcium carbonate plates around itself, and feeds on plankton with its long extending legs. A pretty cool creature.
Reference
Barnes, R.D. 1980. Invertebrate Zoology. Saunders College Publishing. Philadelphia PA. pp. 1089.
I recently wrote an article introducing some to a panhandle turtle that is not as well-known as most – the map turtles. This week I am going to write about another lesser-known species – the chicken turtle.
Some may say “is there a turtle REALLY called the chicken turtle?” and “if so, why is it called that?”.
The long neck and oval shell of the Florida Chicken Turtle.
This one is missing a rear leg, probably attacked by a raccoon.
Photo: Molly O’Connor
The answer is yes… there is a turtle called a chicken turtle (Deirochelys reticularia). It is a member of the family Emydidae, which is the family where you find the different pond, river, and lake turtles, as well as the terrapins and box turtles. The name chicken may refer to the unusually long neck this turtle has, but more than likely it comes from an early description of the species in the 1800s that stated it “taste better than the cooters – more like chicken.”
The reason some are not aware of this animal is because of their habitat selection, behavior, and low population densities. Though they are aquatic turtles, they are very selective of which waterbodies they inhabit and may spend months out of the water in upland forested areas.
Chicken turtles seem to prefer quiet shallow waterways where the water is clear, or at least tannic, they dislike turbid/muddy systems. They avoid rivers, creeks, streams, and many lakes. Most of the waterways they inhabit are ephemeral, meaning they dry up during part of the year. During these dry times they, again, seek upland habitats and have been found as far as a 150 meters (510 feet) from any water source. The females appear to avoid their landward movements during the peak of summer. However, males are opposite – moving upland during summer and not as common during the winter months. These overland treks by the females seem to be associated with nesting activity. Where the upland movement of males seem to focus on finding new waterways after the ones they were in have become dry.
Their distribution extends across the southern coastal plains. From Virigina, throughout the deep south, west to Texas, and north to Arkansas. They are found throughout the state of Florida. There are three recognized subspecies –
The Eastern Chicken Turtle (Deirochelys reticularia reticularia)– is found from southern Virginia, coastal Carolinas, southern Georgia, Alabama, Mississippi, and the Florida panhandle. In addition to the long neck, the carapace is sort of “domed” shaped. Terms like “helmet” and “pear” shaped have been used as well. The coloration is dark gray to olive green with a distinct yellow line pattern that resembles a cast net covering the carapace. The plastron is solid yellow to a yellow-orange color. The underside of the bridge (portion of the shell connecting the carapace to the plastron) usually has two dark blotches. This subspecies often has dark spots along with the dark bars on the underside of the bridge.
The Florida Chicken Turtle (D. r. chrysea) – is found in the Florida peninsula. The dark markings on the underside of the bridge are absent in this subspecies.
The Western Chick Turtle (D. r. miaria) – is found west of the Mississippi River in Louisiana, Texas, and Arkansas. Its plastron is not solid yellow, but rather has dark markings within the seams of the plastron scutes.
Chicken turtles are of average size, with carapace lengths near nine inches, and (as with many turtles) females are larger than males. The young and males feed on the larva of such things as dragonflies and damselflies, as well as other aquatic bugs. Crayfish seem to be a particular favorite, especially with the larger females.
Mating occurs underwater. Nesting begins in summer and continues through fall and winter. Two to 19 eggs are deposited but the average is around 10/clutch, and she will lay more than one clutch each year.
Threats to their populations include being hit by cars while crossing highways. Their overland treks enhance this problem. Other threats include predation by raccoons and alligator snapping turtles, the pet trade, and it was once a food item – “taste like chicken”. With low densities of chicken turtles, this may be the result of overharvesting years ago. Potential threats include habitat loss and invasive species are very likely.
Statewide turtle surveys suggest that chicken turtles are found but their abundance/density is low compared to other species. It is exciting for folks exploring both our ephemeral wetlands and upland areas to find it. Hopefully, one day, you will encounter one as well.
Florida has a great variety of turtles. Actually, the species richness here is higher than any other state – though Alabama may argue. Many are familiar to us. If we have not seen them, we have at least heard of them. But that may not be the case with map turtles.
Map turtles are in the same family as many of the common ponds turtles but are in the genus Graptemys. The patterns on their shells and skin are beautiful and they have raised scutes along the midline of their shells giving them a “sawback” or “dinosaur” look. They are associated with alluvial rivers due to their diet of shellfish, which cannot be found in the low pH waters of tannic rivers. To our west, in Alabama and Mississippi, there are several species of them. And as you move up into the Mississippi valley and into the Midwest, there are even more. But here in Florida there are only two. Let’s meet them.
The Barbour’s Map Turtle (Graptemys barbouri) is associated with the Apalachicola River system. First discovered in the Chipola River, it has now been found in the Chattahoochee, Flint, and Apalachicola River systems, as well as the Choctawhatchee and Pea Rivers. It may have been introduced to the Ochlockonee and Wacissa.
Barbour’s Map Turtle.
Photo: Rome Etheridge
Female map turtles are much larger than the males, and the female Barbour’s Map is the largest of all map turtles – with a carapace length of 33cm (13 in.). She has a very broad head (8cm, 3in. wide) to crush the shells of her favorite prey – snails. The males only reach 13cm (5in.) carapace length and their heads are much narrower. Barbour’s Maps prefer flowing rivers with limestone outcrops. These outcrops support the snails they like to eat. That said, they have been found in high numbers within the silty channels of these rivers.
Females take many years to mature, possibly as long as 14. Males mature in 3-4 years. Breeding begins in the spring and nesting begins in late April but will continue into August. Like most turtles, they seek out sandy beaches where they will lay multiple clutches of 7-10 eggs over the span of the nesting season.
Fallen trees (snags) are important basking areas and map turtles use them frequently. During the cooler months, and low water periods along the river, they will hide in deep pockets within the limestone rock. Their home range along the rivers are between 250 and 1500 meters (74 and 441 feet), with males having a larger range. Other than nesting, activity on land is not common.
Their populations seem to be stable, though they are protected by FWC and possession without a permit is illegal. Harvest does still happen, and the activity known as “plinking” (shooting them off their basking logs) occurs as well. Nest depredation, and the killing of adults, by raccoons is common. Crows are another threat.
The Escambia Map Turtle (Graptemys ernsti) is associated with the Escambia River. With the Florida section of this river only being 54 miles long, it has the most restricted range of any turtle in the state. That said, along these stretches of river, it is one of the more abundant turtles. Paddling a lower section of the Escambia I counted an average of 11 individuals per basking log. It has been found in the Yellow and Shoal Rivers as well. But due to the lower pH and lack of mollusks, they are not found in the nearby Blackwater and Perdido Rivers.
The Escambia Map Turtle is only found in the Escambia, Yellow, and Shoal Rivers.
Photo: Molly O’Connor
Like all map turtles, it has beautiful markings on the shell and head. Like all map turtles, it has the characteristic “sawback” appearance down the middle of the carapace. Like all map turtles, the females are much larger than the males. However, the female of this species is not as large as the female Barbour’s Map – with a carapace length of 28cm (11in.).
The males of this species feed on a variety of insects but the females stay with the characteristic molluscan diet. The introduced Asiatic clam (Corbicula fluminea) is a particular favorite. Breeding occurs in the spring and nesting area are sandbars found along the river’s edge. These turtles are having problems with ATVs using such nesting areas, the removal of snag basking trees, and plinking. There are also concerns with the building of dams along the Alabama portion of the river. They are protected by FWC, and you cannot possess them without a permit.
With only two species of map turtles in the entire state, and both only found in the panhandle, these are unique species to the rich variety of turtles found here.
As I write this, we are in the middle of our 2023 Scallop Search, an event we do each year to assess whether the scallops in Pensacola Bay are trying to make a comeback on their own. Each year I am amazed at how popular this little mollusk is. On the day I am writing, I will be working with a marine science class from the University of Southern Mississippi driving over from Ocean Springs. This past weekend I worked with two families who trailered their boat from Enterprise Alabama to participate. Those on the eastern end of the panhandle are well aware of the popularity of this creature. Folks from all over the southeast travel there to go scalloping. Many of the locals in my area, when I am training them how to do a scallop search, tell me that they head east and go scalloping every year. Some even have condos for that week and it is a large part of their annual vacation plans. And many of the locals here would love to see them return to Pensacola Bay.
This is a creature that draws a lot of attention. But most know very little about it. They know it has small eyes and can swim – actually… I have recently found that not everyone knows they can swim. We know they like grassbeds and they can be harvested in the summer. They may have done this long enough to know the prime spots within the grassbeds to search for them – their “sweet spots”. But not much more.
So… let’s meet the bay scallop.
Volunteers conducting the great scallop search.
Photo: Molly O’Connor
Its scientific name is Argopecten irradians. It is a mollusk in the class Bivalvia and the family Pectinidae. There are numerous species, and the group is found all over the world. The greatest variety of them are from the Indo-Pacific region, and in each case, they are a popular seafood. Most can swim, though erratically – they are not Michael Phelps – and they use this ability to avoid predators such as starfish, which they can see with the set of simple eyes.
There are five subspecies of A. irradians. A. irradians irradians, known as the bay scallop, or Atlantic Bay scallop (and from here is just “the scallop”) is our local variety. It is found from Cape Cod to the Gulf of Mexico. They begin life as a microscopic egg produced during the mass spawning of the hermaphroditic parents (hermaphroditic meaning each parent can produce sperm and egg). The timing of the release of gametes is triggered by warming water and usually occurs in the late summer/early fall. This early egg stage sinks to the bottom where it remains for a few weeks before hatching.
The hatched larva remain microscopic, are transparent, resemble the parents, and are called spat. The spat become part of the plankton in local estuaries but eventually return to the grass in what is called “spatfall” where they attached to the seagrasses using byssal threads. They continue to grow, eventually release from the grass, and become the scallops we all know and love. Many species of scallops can live over 20 years, but our local one only lives for one.
As most know, adult scallops have two shells (bivalves) connected at the hinge on the dorsal side of the animal. Though they do add weight to the shell, a disadvantage for a swimmer, the “ribs” provide a sturdier shell. The two shells are connected by a single, large adductor muscle, which is used to open and close the valves during swimming. It is this adductor muscle we eat when consuming scallops.
Like all bivalves, scallops are filter feeders but unlike most bivalves they lack siphons to draw water in and out of the digestive tract. Rather they lie with their valves slightly gaped and allow water to pass over them. Plankton is collected by a mucous layer and then moved to the gut by cilia (small hair-like structures) where it is digested.
Bay Scallop.
Photo: FWC
Like all bivalves, scallops lack a brain as we know it but rather function using a series of ganglia (groups of nerve cells) connected to a nerve ring. These ganglia can control movement of the muscle, gills, eyes, and are connected to a statocyst, which tells the scallop how it is oriented in the water column.
There are numerous eyes aligned along the edge of each valve that can detect movement and shadows. It is believed that they use their eyes to detect potential predators and possibly initiate the swimming behavior they are famous for.
Living only one year, and reaching maximum size in late summer during spawning, scallop harvesting is regulated to that time of year in Florida. Once common from Pensacola to Miami, they are now only found in large numbers in the Big Bend region. Due to the loss of scallops in other areas, many visit the Big Bend each year to go scalloping, putting heavy harvest pressure on those stocks. There have been efforts to try and enhance the existing populations as well as restore historic ones. Here in Pensacola Bay, Florida Sea Grant works with volunteers to monitor the water quality and seagrasses, as well as assess how the few existing scallops are doing.
For more information on panhandle scallops, contact your local Sea Grant Agent at the county extension office.
