by Rick O'Connor | Sep 2, 2018
Most kids who grew up on the Gulf Coast grew up catching blue crabs. These animals are common along our shorelines, relatively easy to catch, and adventurous because they may bite you. I caught my first one in 1965 and we proudly displayed the boiled shell over the kitchen bar for many years. This is also a popular seafood target with an estimated commercial landing value of $56,950 in the Pensacola Bay area in 2017.
Blue crabs are one of the few crabs with swimming appendages.
Photo: Molly O’Connor
But who is this crab that we enjoy so much? What do we know about it?
As you probably already know, it is one of an estimated 30,000 species of arthropods we call crustaceans. Crustaceans differ from insects and arachnids in that they have five pairs of legs and two sets of antenna. Insects typically have a head, thorax, and abdomen – however, in the crustaceans the head and thorax are fused into what is called a cephlathorax and covered with a section of the shell called the carapace. Like all arthropods, their body are completely covered in a chitinous shell that serves as their exoskeleton. This exoskeleton must be periodically shed (molting) so they can continue to grow. Crustaceans tend to molt about 10-11 times each year and typically in the summer months. To molt, crustaceans will remove some of the salts and minerals from the shell into their tissue, this weakens the shell enough to separate it. The crack is usually between the cephlathorax and abdomen. When they emerge, they are completely soft and about 30% larger than before – it is amazing to see this large crab emerge from the small shell it once lived in. Because of the softness of the body after molting, this is usually done under the cover of darkness for protection. The salts and minerals it removed during pre-molting are now used to harden the new shell – which can take a couple of days. It is at this stage we call them “soft shells”.
The crustaceans include many different kinds of arthropods – most notably are the crabs, shrimps, and lobsters. There are over 4500 species of crabs and they differ from shrimps and lobsters in the fact their abdomen flexes beneath their body – you do not see the “tail” you see in a lobster or shrimp – but its there. Crabs can also move very well laterally, which their cousins are not so good. Blue crabs differ from other crabs in that their last pair of legs are modified as paddles and the animal can swim. They can swim forwards, backwards, and laterally – and they are often seen swimming at the surface. There are other crabs who have these swimming paddles and they are all called protunid crabs.
Blue crabs perceive their world through their eyes, antenna, and sensory cells on their body. They are very good at burying in the sand – eyes and antenna exposed – and sensory cells all working – seeking prey and avoiding predators. Their eyes differ from ours in that they have numerous lenses, compared to our single one, and are called compound eyes. Each lens does not provide them with an image of you or me however. Rather each lenses provides them with a single pixel of light. It is much like the image you see on television when they are trying to block out a brand name, or someone’s face. The more pixels (lenses) you have, the clearer the image. Those this type of eye does not give as clear an image as ours; it is very good at detecting motion and has served the arthropods very well over the years.
For blue crabs, food can be just about anything. They are active hunters – usually using the ambush method of capture (buried in the sand), but are also known scavengers – eating any bits of food they can find. Those enjoy crabbing know this – you can put just about anything as bait in a crab trap and it works. They have numerous predators including fish, birds, mammals, and sea turtles.
Male and female blue crabs.
Photo:
Blue crabs can be found in a variety of salinities (euryhaline). Males are typically found in the lower salinities of the upper bay. Females join them during mating season – which is in late spring and summer. Males cradle the females beneath his legs for several days waiting for the right location and moment to breed. Fishermen refer to them as “doublers” during this time. The females will molt and the male will then deposit his sperm into a sac called a spermatophore – which he then deposits to the female. She will then migrate to the more saline lower portions of the lower bay, while he remains and seeks another female. This may be the only spermatophore she receives her entire life – which can be up to five years, though most do not live beyond three years. She will use sperm from this spermatophore over that time to fertilize eggs.
The eggs develop in a sponge mass that develops beneath her abdomen. This egg mass is orange when in early development and becomes a darker brown with age as the larvae consume the yolk. There can be between 750,000 and 2,000,000 developing eggs within this mass. The females are called gravid at this stage and it is illegal to harvest gravid crabs in Florida.
The eggs hatch in about two weeks and a small microscopic mosquito looking larvae emerges – at this stage, they are called zoea. The zoea drift into the Gulf of Mexico where they feed and molt. Eventually they return to the estuary and become a microscopic crab with a tail – this stage is called a megalops. The megalops will feed and molt. The tail will eventually flex beneath and the crab becomes sexually mature. The entire process from hatching to sexual maturity is about 12-18 months.
These are fascinating animals. They are very common and a large part of the coastal culture of the Florida panhandle. Kids will have great fun catching them with a hand net, letting them swim in their beach buckets, but be sure to let them go before you head home and watch those claws – they do know how to use them. It is a great animal.
The famous blue crab.
Photo: FWC
Recreational Blue Crab Harvest Regulations in Florida
No size limit
10 gallons whole / harvester / day
Harvesting gravid females is prohibited
Five crab traps / person – cannot be placed in navigation channels
Trap closed season in Florida panhandle – Jan 5-14 in odd years.
References
Barnes, R.D. 1980. Invertebrate Zoology. Saunders College Press. Philadelphia PA. pp. 1089.
Blue Crab. Callinectes sapidus. Chesapeake Bay Program. 2018. https://www.chesapeakebay.net/discover/field-guide/entry/blue_crab.
Florida Fish and Wildlife Conservation Commission. Commercial Landings in Florida. 2017-2018. http://myfwc.com/research/saltwater/fishstats/commercial-fisheries/landings-in-florida/.
Florida Fish and Wildlife Conservation Commission. Recreational Blue Crabbing. http://myfwc.com/fishing/saltwater/recreational/blue-crab/.
by Rick O'Connor | Aug 17, 2018
As a kid growing up here along the Gulf Coast, I had never heard of an osprey. Now, there is at least one mating pair on almost every body of water in the Pensacola Bay area. Where did this once unknown bird come from? How has it successfully colonized our coastal waterways?
Osprey nesting sites are commonly near water, and their food source.
The osprey, like many other fish eating birds, was a victim of the DDT story. This miracle pesticide was developed to battle insects attacking food crops but was found to be useful against mosquitos and many other unwanted pests. It was sprayed everywhere using planes, trucks, and tractors. With an extremely long half-life, wherever it landed it was going to be around for a while – it can still be found in the sediments of the Pensacola Bay System. It was one of those compounds that was difficult to excrete through an organisms excretory system – thus it accumulated within their tissues, and as organisms fed on other organisms, it was passed up the food chain – bioaccumulation. Birds of prey who fed on fish would accumulate DDT as well. It caused the shells of their eggs to become thinner – so nesting was not successful – and many of the aquatic birds of prey (pelicans and eagles alike) declined in number. DDT was banned in 1970s and many of these fish eating birds have made a remarkable recovery – a true success story.
So who is this fish eating bird of prey that can be found on dead trees and light posts all over the bay area?
Ospreys (Pandion haliaetus) are members of the family Accipitridae – the hawks and eagles.
They are predators with hooked bills and sharp talons to grab and dispose of prey. Ospreys can be identified by the hawk like silhouette hovering over a local waterway searching for fish – their primary food. They are usually in pairs and, at times, the young are hovering nearby. Their call is a high pitch chirping sound and if seen on a tree, or on their nest, they are brown on top and white beneath. These birds are common along both fresh and saltwater bodies of water.
Ospreys prefer waterways where fish are plentiful. For more successful hunting, they like waters that are relatively shallow and nesting locations that protect the young from mammalian predators. Many local osprey prefer large dead trees for their nests, and will often use manmade structures – such as power poles, navigation markers, and special platforms on poles placed there for the purpose of osprey nesting.
Osprey feed almost exclusively on fish. They are unique in the hawk world in that their talons can adjust so that the captured fish can be turned parallel to the osprey’s body – making it more aerodynamic when returning to the nest. Hunting osprey hover over the water searching and then dive, talons first into the water. They can only reach depths of about three feet so they typically hunt for surface schooling fish, or in shallow waters. Most of their captures are between 8-10 inches and include such fish as speckled trout, mullet, and catfish.
These birds are monogamous (mating pairs breed for life). During the breeding season, the male will collect sticks for the construction of their large nests. Bringing them back to the female, she will begin to arrange and construct the nest. The male provides seagrass and flotsam for the inner lining. There is a pre-courtship dance where the returning male flies over the nest with a fish. The pair produce between 3-4 eggs. Both parents will incubate the eggs but the female does the lions share. She will incubate while the male hunts. Returning with a fish for her, she will fly to a nearby branch to feed while he incubates the eggs – though they have seen the males incubate even without feeding the female. Evening incubation is always the female.
After hatching, the male will bring food to both the female and young. She does not leave the young at all for about 14 days. Afterwards, they will be left alone for periods of time, and are usually fledged by 50 days. Data shows that young fledglings rarely disperse more than 30 miles from the nest they hatched from – suggesting slow dispersal of this species. The mating pair will return to the same location for nesting every year for up to 30 years.
There are few predators of osprey due to their nesting habits. In some locations, where they nest on the ground, coyotes have been a problem. Locally, bald eagles are known to try to grab hatchlings and, occasionally, adults. There have been reports of crocodiles taking adults from the water in South Africa; this may be the case in South America as well, but no reports of American Alligators doing the same.
This is now a common bird along our shores and is a true conservation success story.
References
National Audubon Society Field Guide to North American Birds; Eastern Region. Ed. J. Bull, J. Farrand Jr. pp. 795.
Osprey. Neotropical Birds. Cornell Lab of Ornithology. https://neotropical.birds.cornell.edu/Species-Account/nb/species/osprey/overview.
by Rick O'Connor | Jul 6, 2018
The manatee may be one of the more iconic animals in the state of Florida. In Wyoming, we think of bison and bears. In Florida, we think of alligators and manatees. However, encountering this marine mammal in the Florida panhandle is a relatively rare occurrence… until recently.
Manatee swimming in Big Lagoon near Pensacola.
Photo: Marsha Stanton
For several years now, visitors to Wakulla Springs – in the eastern panhandle – have had the pleasure of viewing manatees on a regular basis. It is believed about 40 individuals frequent the river. Last year there were eight individuals that frequent the Perdido Key area, and a couple more were seen more than once near Gulf Breeze. This is not normal for us, but already this year one manatee has been spotted in the Big Lagoon area – so we may be seeing more as the summer goes on.
So what exactly is a manatee?
It is listed as a marine mammal, but frequents both fresh and saltwater habitats. Being mammals, they are warm blooded (endothermic). Maintaining your body temperature internally allows you to live in a variety of cold temperature habitats but water can really draw the heat quickly from anyone’s body. Marine mammals counter this problem by having a thick layer of fat within the skin – insulation called blubber. However, the manatees blubber layer is not very thick. So they are restricted to the tropical parts of the world and, in Florida, spend the winter near warm water springs. Many have learned the trick of hanging out near warm water discharges near power plants. In the warmer months, they venture out to find lush seagrass meadows in which to graze.
They are herbivores. Possessing flat-ridged molars for grinding plant material, they are more closely related to deer and cattle than the seal and walrus they look like. They lack canines and incisors, which deer and cattle use to cut the grass blades, but have large extending lips that grab and tear grasses with – very similar to the trunk of an elephant, which is their closest relative. Like many mammalian herbivores, they grow to a large size. Manatees can reach 15 feet in length and over 1000 pounds. They have two forearms that are paddle shaped and used for steering. The tail is a large circular disk called a fluke, which propels them through the water and is often seen breaking the surface. They are generally slow moving animals but can startle you when they decide to kick into “fourth gear” and burst across the river.
They are generally solitary animals, gathering in the wintertime around the warm springs. Males usually leave the females after breeding and do not form family units, or herds. Females are pregnant for 13 months and typically give birth to one calf, which stays with mom for two years. Like all mammals, the young feed on milk from mammary glands, but these glands are close to the armpits on the manatee. This makes it much easier for the calf to feed while both are swimming. This is not the case with dolphins and whales, where the mother must roll sideways to feed her young.
Manatees hanging out in Wakulla Springs.
Photo provided by Scott Jackson
There are three species of manatees in the world today. The Amazonian Manatee (Trichechus inunguis), the West African Manatee (Trichechus senegalensis) and the West Indie Manatee (Trichechus manatus). The Florida Manatee is a subspecies of the West Indian (Trichechus manatus latirostris). In the 1970’s it was estimated there were about 1000 West Indian manatees left in the word. Today, with the help of numerous nonprofits and state agencies, there is an estimated 6600 in Florida. Due to this increase, the manatee has moved from the federal endangered species list to threatened species. That said, human caused mortality still occurs and boaters should be aware of their presence. Since 2012, an average of 500 manatees die in Florida waters. Most of these are prenatal or undetermined, but about 20% are from boat strikes. Manatees tend stay out of the deeper channels, so boats leaving the ICW for a favorite beach or their dock should keep an eye out. Most of the time they are just below the surface and only their nostrils break for a breath of air. They usually breathe every 3-5 minutes when swimming but can remain below for up to 20 minutes when they are resting. Approaching a manatee is still illegal. Though their status has changed from endangered to threatened, they are still protected by state and federal law.
FWC suggest the following practices for boaters, and PWC, near manatees
- Abide by any speed limit signs – no wake zones
- Wear polarized sunglasses to aid in seeing through the water
- Stay in deeper water and channels as much as possible
- Stay out of seagrass beds – there is are numerous reasons why this is important, not just manatees
- If a manatee is seen, keep your boat/PWC at least 50 feet from the animal.
- Please do not discard your hooks and monofilament into the water – again, numerous reasons why this is a bad practice.
So Why are There More Encounters in the Florida Panhandle?
Good question…
Their original range included the entire northern Gulf coast. When their numbers declined in the 1960’s and 70’s there were fewer animals to venture this far north. Manatee sightings at that time did occur, but were very rare. Today, with increasing numbers, encounters are becoming more common. There is actually a Manatee Watch Program for the Mobile Bay area (https://manatee.disl.org/) and they have been seen as far west as Louisiana.
They are truly neat animals and to see one in our area is a real treat. Remember to view and photo, but do not approach. I hope that many of you will get to meet what maybe new summer neighbors.
Manatee swimming by a pier near Pensacola.
Photo: Marsha Stanton
References
2017 Manatee Mortality Data. Florida Fish and Wildlife Conservation Commission. http://myfwc.com/media/4132460/preliminary.pdf.
Florida Manatee Facts and Information. Florida Fish and Wildlife Conservation Commission. http://myfwc.com/education/wildlife/manatee/facts-and-information/.
Manatee Information for Boaters and PWC. Florida Fish and Wildlife Conservation Commission. http://myfwc.com/education/wildlife/manatee/for-boaters/.
Manatee Sighting Network. https://manatee.disl.org/.
West Indian Manatee. Wikipedia. https://en.wikipedia.org/wiki/West_Indian_manatee.
by Rick O'Connor | Jun 22, 2018
Just a decade ago, few people would have known what a gopher tortoise was and would have hard time finding one. But today, because of the protection they have been afforded by the state, they are becoming more common. This is certainly an animal you might see visiting one of our state parks.
This gopher tortoise was found in the dune fields on a barrier island – an area where they were once found.
Photo: DJ Zemenick
The gopher tortoise is one of only two true land dwelling turtles in our area and is in a family all to its own. They are miners, digging large burrows that can extend up to a depth of 7 feet and a length of 15 feet underground. However, tortoises are not very good at digging up towards the surface, so there is only the one entrance in and out of the burrow. The burrow of the tortoise can be distinguished from other burrowing animals, such as armadillos, in that the bottom line of the opening is flat – a straight line – and the top is domed or arched shaped; mammalian burrows are typically round – circular. Tortoise burrows also possess a layer of dirt tossed in a delta-shaped fan out away from the entrance (called an apron). Many times the soil is from deeper in the ground and has a different color than the soil at the surface. The general rule is one burrow equals one tortoise, though this is not always true. Some burrows are, at times, shared by more than one and some may not be occupied at all. Many field biologists will multiple the number of burrows by 0.6 to get an estimate of how many tortoises there are in the area.
The tortoise itself is rather large, shell lengths reaching 15 inches. They can be distinguished from the other land dwelling turtle, the box turtle, by having a more flattened dome to the shell and large elephant like legs. The forelimbs are more muscular than the hind and possess large claws for digging the burrow. They are much larger than box turtles and do not have hinged plastrons (the shell covering the chest area) and cannot close themselves up within the shell as box turtles can. Tortoises prefer dry sandy soils in areas where it is more open and there are plenty of young plants to eat; box turtles are fans of more dense brush and wooded areas.
Tortoises spend most of the day within their burrows – which remain in the 70°F range. Usually when it is cooler, early morning or late afternoon, or during a rain event – the tortoises will emerge and feed on young plants. You can see the paths they take from their burrows on foraging trips. They feed on different types of plants during different type times of the year to obtain the specific nutrients. There are few predators who can get through the tough shell, but they do have some and so do not remain out for very long. Most people find their burrows, and not the tortoise. You can tell if the burrow has an active tortoise within by the tracks and scrap marks at the entrance. Active burrows are “clean” and not overgrown with weeds and debris. Many times, you can see the face of the tortoise at the entrance, but once they detect you – they will retreat further down. Many times a photo shot within a burrow will reveal the face of a tortoise in the picture. There is a warning here though. Over 370 species of creatures use this burrow to get out of the weather along with the tortoise – one of them is the diamondback rattlesnake. So do not stick your hand or your face into the entrance seeking a tortoise.
Most of the creatures sharing the burrow are insects but there are others such as the gopher frog and the gopher mouse. One interesting member of the burrow family is the Eastern Indigo Snake. This is the largest native snake to North America, reaching a length of eight feet, and is a beautiful iridescent black color. It is often confused with the Southern Black Racer. However, the black racer is not as long, not as large around (girth), and possess a white lower jaw instead of the red-orange colored one of the indigo. The indigo is not dangerous at all, actually it feeds on venomous snakes and it is a good one to have around.
Federal and state laws protect the indigo, as with the gopher frog and mouse. All of these animals have declined in number over the past few decades. This is primarily due to loss of the needed gopher burrows, which have declined because the tortoises have declined, and this is due to habitat loss and harvesting. Again, tortoises like dry sandy soils for digging burrows. They prefer wooded areas that are more open and allow the sun to reach the forest floor where young grasses and flowers can grow. The longleaf pine forest is historically the place to find them but they are found in coastal areas where such open wooded areas exist. The lack of prescribe burning has been a problem for them. Florida is the number one state for lightning strikes. Historically, lightning strikes would occasionally start fires, which would burn the underbrush and allow grasses to grow. In recent years, humans have suppressed such fires, for obvious reasons, and the tortoise community has suffered because of it. Therefore, we now have prescribe fire programs on most public lands in the area. This has helped to increase the number of tortoises in the area and your chance of seeing one.
All of the members of the tortoise community are still protected by state, and – in the case of the indigo snake – federal law, so you must not disturb them if seen. Photos are great and you should feel lucky to have viewed one. Though they could be found anywhere where it is high, dry, and somewhat open – the state and national parks are good places to look.
Reference
Meylan, P.A. (Ed.). 2006. Biology and Conservation of Florida Turtles. Chelonian Research Monographs No. 3, 376 pp.
by Rick O'Connor | May 31, 2018
It is now late May and in recent weeks I, and several volunteers, have been surveying the area for terrapins, horseshoe crabs, and monitoring local seagrass beds. We see many creatures when we are out and about; one that has been quite common all over the bay has been the “stingray”.
The cownose ray is often mistaken for the manta ray. It lacks the palps (“horns”) found on the manta.
Photo: Florida Sea Grant
These are intimidating creatures… everyone knows how they can inflict a painful wound using the spine in their tail, but may are not aware that not all “stingrays” can actually use a spine to drive you off – actually, not all “rays” are “stingrays”.
So what is a ray?
First, they are fish – but differ from most fish in that they lack a bony skeleton. Rather it is cartilaginous, which makes them close cousins of the sharks.
So what is the difference between a shark and a ray?
You would immediately jump on the fact that rays are flat disked-shape fish, and that sharks are more tube-shaped and fish like. This is probably true in most cases, but not all. The characteristics that separate the two groups are
- The five gill slits of a shark are on the side of the head – they are on the ventral side (underside) of a ray
- The pectoral fin begins behind the gill slits in sharks, in front of for the ray group
Not all rays have the whip-like tail that possess a sharp spine; some in fact have a tube-shaped body with a well-developed caudal fin for a tail.
There are eight families and 19 species of rays found in the Gulf of Mexico. Some are not common, but others are very much so.
Sawfish are large tube-shaped rays with a well-developed caudal fin. They are easily recognized by their large rostrum possessing “teeth” giving them their common name. Walking the halls of Sacred Heart Hospital in Pensacola, you will see photos of fishermen posing next to monsters they have captured. Sawfish can reach lengths of 18 feet… truly intimidating. However, they are very slow and lethargic fish. They spend their lives in estuaries, rarely going deeper than 30 feet. They were easy targets for fishermen who displayed them as if they caught a true monster. Today they are difficult to find and are protected. There are still sightings in southwest Florida, and reports from our area, but I have never seen one here. I sure hope to one day. There are two species in the Gulf of Mexico.
Guitarfish are tube-shaped rays that are very elongated. They appear to be sharks, albeit their heads are pretty flat. They more common in the Gulf than the bay and, at times, will congregate near our reefs and fishing piers to breed. They are often confused with the electric rays called torpedo rays, but guitarfish lack the organs needed to deliver an electric shock. They have rounded teeth and prefer crustaceans and mollusk to fish. There is only one species in the Gulf.
Torpedo rays can deliver an electric shock – about 35 volts of one. Though there are stories of these shocking folks to death, I am not aware of any fatalities. Nonetheless, the shock can be serious and beach goers are warned to be cautious. I once mistook one buried in the sand for a shell. Let us just say the jolt got my attention and I may have had a few words for this fish before I returned to the beach. We have two species of torpedo rays in the Gulf of Mexico.
Skates look JUST like stingrays – but they lack the whip-like tail and the venomous spine that goes with it. They are very common in the inshore waters of the Florida Panhandle and though they lack the terrifying spine we are all concerned about, they do possess a series of small thorn-like spine on the back that can be painful to the bare foot of a swimmer. Skates are famous for producing the black egg case folks call the “mermaids’ purse”. These are often found dried up along the shore of both the Gulf and they bay and popular items to take home after a fun day at the beach. There are four species of skates found in the Gulf of Mexico.
Stingrays… this is the one… this is the one we are concerned about. Stingrays can be found on both sides of our barrier islands and like to hide beneath the sand to ambush their prey. More often than not, when we approach they detect this and leave. However, sometimes they will remain in the sand hoping not to be detected. The swimmer then steps on their backs forcing them to whip their long tail over and drive the serrated spine into your foot. This usually makes you move off them – among other things. The piercing is painful and spine (which is actually a modified tooth) possesses glands that contain a toxic substance. It really is no fun to be stung by these guys. Many people will do what is called the “stingray shuffle” as they move through the water. This is basically sliding your feet across the sand reducing your chance of stepping on one. They are no stranger to folks who visit St. Joe Bay. The spines being modified teeth can be easily replaced after lodging in your foot. Actually, it is not uncommon to find one with two or three spines in their tails ready to go. Stingrays do not produce “mermaids’ purses” but rather give live birth. There are five species in the Gulf of Mexico.
The Atlantic Stingray is one of the common members of the ray group who does possess a venomous spine.
Photo: Florida Museum of Natural History
Butterfly ray is a strange looking fish and easy to recognize. The wide pectoral fins and small tail gives it the appearance of a butterfly. Despite the small tail, it does possess a spine. However, the small tail makes it difficult for the butterfly ray to pierce you with it. There is only one species in the Gulf, the smooth butterfly ray.
Eagle rays are one of the few groups of rays that actually in the middle of the water column instead of sitting on the ocean floor. They can get quite large and often mistaken for manta rays. Eagle rays lack the palps (“horns”) that the manta ray possesses. Rather they have a blunt shaped head and feed on mollusk. They do have venomous spines but, as with the butterfly ray, their tails are too short to extend and use it the way stingrays do. There are two species. The eagle ray is brown and has spots all over its back. The cownose ray is very common and almost every time I see one, I hear “there go manta rays”… again, they are not mantas. They have a habit of swimming in the surf and literally body surfing. Surfers, beachcombers, and fishermen frequently see them.
Last but not least is the very large Manta ray. This large beast can reach 22 feet from wingtip to wing tip. Like eagle rays, they swim through the ocean rather than sit on the bottom. They have to large “horns” (called palps) that help funnel plankton into their mouths. These horns give them one of their common names – the devilfish. Mantas, like eagle and butterfly rays, do have whip-like tails and a venomous spine, but like the above, their tails are much shorter and so effective placement of the spine in your foot is difficult.
Many are concerned when they see rays – thinking that all can inflict a painful spine into your foot – but they are actually really neat animals, and many are very excited to see them.
References
Hoese, H.D., R.H. Moore. 1977. Fishes of the Gulf of Mexico; Texas, Louisiana, and Adjacent Waters. Texas A&M. College Station, TX. pp. 327.
Shipp, R. L. 2012. Guide to Fishes of the Gulf of Mexico. KME Seabooks. Mobile AL. pp. 250.
by Rick O'Connor | May 25, 2018
In recent weeks, volunteers and I have been surveying local estuaries counting terrapins, horseshoe crabs, and monitoring seagrass. One animal that has been very visible during these surveys is the relatively large snail known as the crown conch (Melongena corona). Its shell is often found with a striped hermit crab living within, but it is actually produced by a fleshy snail, who is a predator to those slow enough for it to catch.
The white spines along the whorl give this snail its common name – crown conch.
Photo: Rick O’Connor
The shell is familiar to most who venture to the estuary side of our beaches. Reaching around five inches in length, crown conch shells are spiral with a wide aperture (opening) and brown to purple to white in color. Each whorl ends with white spins giving it the appearance of a crown and – hence – it’s common name. They are typically seen cruising along the sediments near grassbeds, salt marshes and oyster reefs – their long black siphons extended drawing in seawater for oxygen, but also to detect scents that will lead them to food.
These snails breed from winter to early summer. Females, larger than males, will develop 15-500 eggs in capsules, which they attach to hard structures within the habitat; such as wood, seagrass blades, and shell material.
Crown conchs are subtropical species and have a low tolerance for cold water. They are common in the panhandle and may expand further north along the Atlantic coast if warming trends continue. They have a higher tolerance for changes in salinity and can tolerate salinity as low as 8 ppt. The salinities within Pensacola Bay can be as low as 10 ppt and Santa Rosa Sound / Big Lagoon are typically between 20-30 ppt. The developing young require higher salinities and thus breeding takes in the lower portions of our estuaries.
These are guys are snail predators – seeking prey slow enough for them to catch. Common targets include the bivalves such as oysters and clams, but they are known to seek out other snails – like whelks. Crown conchs are known to feed on dead organisms they encounter and may be cannibalistic. As with all creatures, they have their predators as well. The large thick shell protects them from most but other snails, such as whelks and murex, are known predators of the crown conch.
These conchs tend to stay closer to shallow water (less than 3 ft.) due the large number of predators at depth. They are common in seagrass meadows and salt marshes and – if in high numbers with few competitors – have been considered an indicator of poor water quality. There is no economic market for them but they are monitored due to the fact they affect the populations of commercially important oysters and clams.
The “snorkel” is called a siphon and is used by the snail to draw water into the mantle cavity. Here it can extract oxygen and detect the scent of prey.
Photo: Franklin County Extension
It is an interesting animal, a sort of “jaws” of the snail world, and a possible candidate for a citizen science water quality monitoring project. Enjoy exploring your coastal estuaries this summer and discover some of these interesting animals.
Reference
Masterson, J. 2008. Indian River Lagoon Species Inventory: Crown Conch Melongena corona. Smithsonian Marine Station at Ft. Pierce, Florida. http://www.sms.si.edu/irlspec/Melongena_corona.htm.
