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.
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.
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.
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/.
Written By: Laura Tiu, Holden Harris, and Alexander Fogg
It’s early morning as Dreadknot Charters speeds out of Destin Harbor towards the offshore reefs in the Gulf of Mexico. Researchers Holden Harris (Graduate Research Fellow, University of Florida), Alex Fogg, (Marine Resource Coordinator, Okaloosa County), and the Dreadknot crew, Josh and Joe Livingston, ready their equipment on board. They’re working on a new method of capturing invasive lionfish: deepwater traps.
Non-containment lionfish traps being tested by the University of Florida offshore Destin, FL. Invasive lionfish are attracted to the lattice structure, then captured by netting when the trap is pulled from the sea floor. The trap may have the potential to control lionfish densities at depths not accessible by SCUBA divers. [ALEX FOGG/CONTRIBUTED PHOTO]
Red lionfish (Pterois volitas / P. miles) are a popular aquarium fish with striking red and white strips and graceful, butterfly-like fins. Native to the Indo-Pacific region, lionfish were introduced into the wild in the mid-1980s, likely from the release of pet lionfish into the coastal waters of SE Florida. In the early 2000s lionfish spread throughout the US eastern seaboard and into the Caribbean, before reaching the northern Gulf of Mexico in 2010. Today, lionfish densities in the northern Gulf are higher than anywhere else in their invaded range.
Invasive lionfish negatively affect native reef communities. They consume and compete with native reef fish, including economically important snappers and groupers. Their presence has shown to drive declines in native species and diversity. Lionfish possess 18 venomous spines that appear to deter native predators. The interaction of invasive lionfish with other reef stressors – including ocean acidification, overfishing, and pollution – is of concern to scientists.
Lionfish harvest by recreational and commercial divers is currently the best means of controlling their densities and minimizing their ecological impacts. Lionfish specific spearfishing tournaments have proven successful in removing large amounts in a relatively short amount of time. This year’s Lionfish Removal and Awareness Day removed almost 15,000 lionfish from the Northwest Florida waters in just two days. Lionfish is considered to be an excellent quality seafood, and they are now being targeted by a handful of commercial divers. Several Florida restaurants, seafood markets, and grocery stores chains are now regularly serving lionfish.
While diver removals can control localized lionfish densities, the problem is that lionfish also inhabit reefs much deeper than those that can be accessed by SCUBA divers. Surveys of deepwater reefs show lionfish have higher densities and larger body sizes than lionfish on shallower reefs. In the Gulf of Mexico, the highest densities of lionfish surveyed were between 150 – 300 feet. While SCUBA diving is typically limited to less than 130 feet, lionfish have been observed deeper than 1000 feet.
For the past several years, researchers have been working to develop a trap that may be able to harvest lionfish from deep water. Dr. Steve Gittings, Chief Scientist for the Office of National Marine Sanctuaries at the National Oceanic and Atmospheric Administration, has spearheaded the design for a “non-containment” lionfish trap. The design works to “bait” lionfish by offering a structure that attracts them. The trap remains open while deployed on the sea floor, allowing fish to move in and out of the trap footprint. When the trap is retrieved, a netting is pulled up around
the fish inside and they are brought to the surface.
Deep water lionfish traps being tested by the University of Florida offshore Destin, FL. [ALEX FOGG/CONTRIBUTED PHOTO]
The researchers are headed offshore to retrieve, redeploy, and collect data on the lionfish traps. Twelve non-containment traps are currently being tested offshore NW Florida. The research is supported by a grant from the Florida Fish and Wildlife Conservation Commission. The study will try to answer important questions for a new method of catching lionfish: where and how can the traps be most effective? How long should they be deployed? And, is there any bycatch (accidental catch of other species)?
Recent trials have proved successful in attracting lionfish to the trap with minimal bycatch. Continued research will hone the trap design and assess how deployment and retrieval methods may increase their effectiveness. If successful in testing, lionfish traps may become permitted for use by commercial and recreational fisherman. The traps could become a key tool in our quest to control this invasive species and may even generate income while protecting the deepwater environment.
Outreach and extension support for the UF’s lionfish trap research is provided by Florida Sea Grant. For more information contact Dr. Laura Tiu, Okaloosa and Walton Counties Sea Grant Extension Agent, at email@example.com / 850-689-5850 (Okaloosa) / 850-892-8172 (Walton).
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.
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.
Are you interested in learning about marine life, going fishing, or exploring the underwater world with a mask and snorkel? If so, this is the camp for you! This local education opportunity for budding marine scientists will be happening this summer at Camp Timpoochee in Niceville, FL. The camps enable participants to explore the marine and aquatic ecosystems of Northwest Florida; especially that of the Choctawhatchee Bay. Campers get to experience Florida’s marine environment through fishing, boating snorkeling, games, STEM (science, technology, engineering & math) activities and other outdoor adventures. University of Florida Sea Grant Marine Agents and State 4-H Staff partner to provide hands-on activities exploring and understanding the coastal environment.
Sampling the benthic community at Timpoochee.
Florida Sea Grant has a long history of supporting environmental education for youth and adults to help them become better stewards of the coastal zone. This is accomplished by providing awareness of how our actions affect the health of our watersheds, oceans and coasts and marine camp is a great opportunity for sharing that information. Many of the Sea Grant youth activities use curriculum developed by the national Sea Grant program and geared toward increasing student competency in math, science, chemistry and biology. The curriculum is fun and interesting!
Marine Camp is open to 4-H members and non 4-H members between the ages of 8-13 (Junior Camp) and, new this year, ages 14-17 (Senior Camp). There will be two Junior Camps in 2018. The July 23-27 camp is full, but there are still openings for the June 25-29 session. The cost for Junior Marine Camp is $275.00 for the week. A more intensive Senior Marine Camp has been scheduled for July 16-20. This camp will contain a community service component and costs $300 for the week.
If Marine Camp sounds interesting to someone you know, visit the Camp Timpoochee website at http://florida4h.org/camps_/specialty-camps/marine/ for the 2018 dates and registration instructions. A daily snack from the canteen and a summer camp T-shirt are included in the camp fees, along with three nutritious meals per day prepared on site by our certified food safety staff. All cabins are air-conditioned. So many surprises await at marine camp, come join the fun.
Seining the sea grass at Timpoochee.
Larval fish in the Timpoochee oyster reef.
In the last article, we discussed what phytoplankton are, what their needs were, and their importance to marine life throughout the Gulf and coastal estuaries. In this article, we will discuss the different types of phytoplankton found in our waters.
The spherical shape of the centric diatom.
Image: Florida International University
Marine scientists interested in the diversity and abundance of phytoplankton will typically sample using a plankton net. There are a variety of different shapes and sizes of these nets, but the basic design would be funnel shaped with a sample jar attached at the small end of the funnel. The plankton net would be towed behind the research vessel at varying depths for a set period of time. All plankton collected would be analyzed via a microscope. According to the text Identifying Marine Phytoplankton (1997) there are at least 14,000 species of phytoplankton and some suggest as many as 120,000. Most of these, 12,000-100,000, are diatoms, one of five classes of marine phytoplankton. The majority of the phytoplankton fall into one of two class, the diatoms and the dinoflagellates.
Diatoms are typically single celled algae encased in a clear silica shell called a frustule. The frustule can come in a variety of shapes, with or without spines, and many resemble snowflakes – their quite beautiful. They are found in the bay and Gulf in great numbers, as many as 40,000,000 cells / cup of seawater. They are the dominate phytoplankton in colder waters and are most abundant near upwellings. These are the “grasses of the sea” and the base of many marine food webs. When diatoms die, their silica shells sink to the seafloor forming layers of diatomaceous earth, which is used in filters for aquariums and oxygen mask in hospitals.
Dinoflagellates differ from diatoms in that they produce two flagella, small hair-like projections from the algae that are used for generating water currents and movement. Their shells are not silica but layers of membranes and are called thecas. Some membranes are empty and others contain different types of polysaccharides. Dinoflagellates are more abundant than diatoms in warmer waters. There are about 2000 species of them. One type, Noctiluca, are responsible for what locals call “phosphorus” or bioluminescence. These dinoflagellates produce a blue-ish light when disturbed. Many see this when walking the beach at night. Their footprints glow for a few seconds. At night, boaters can see this as their prop wash turns the dinoflagellates in the water column. The bioluminescence is more pronounced in the warm summer months and is believed to be defense against predation. The light is referred to as “cool” light in that the majority of the energy is used in producing light, not lost as heat as with typical incandescent bulbs – hence the birth of the LED light industry.
The dinoflagellate Karenia brevis.
Photo: Smithsonian Marine Station-Ft. Pierce FL
Several dinoflagellates produce toxins as a defense. Some generate what we call red tides. In the Gulf of Mexico, Karenia brevis is the species most responsible for red tide. Red tides typical form offshore and are blown into coastal areas via wind and currents. They are common off the coast of southwest Florida but occur occasionally in the panhandle. Many local red tides are actually formed in southwest Florida and pushed northward via currents. Red tides are known to kill marine mammals and fish, as well as closing areas for shellfish harvesting.
Like true plants, phytoplankton conduct photosynthesis. Between the diatoms and dinoflagellates, 50% of the planet’s oxygen is produced. These are truly important players in the ecology of both the open Gulf and local bays.
Annett, A.L., D.S. Carson, X. Crosta, A. Clarke, R.S. Ganeshram. 2010. Seasonal Progression of Diatom
Assemblages in Surface Waters of Ryder Bay, Antarctica. Polar Biology vol 33. Pp. 13-29.
Hasle, G.R., E.E. Syvertsen. 1997. Identifying Marine Phytoplankton. Academic Press Harcourt Brace and
Company. San Diego CA. edited by C.R. Tomas. Pp. 858.
Steidinger, K.A., K. Tangen. 1997. Identifying Marine Phytoplankton. Academic Press Harcourt Brace and
Company. San Diego CA. edited by C.R. Tomas. Pp. 858.
The St Andrew Bay pass jetty is more like a close family friend than a collection of granite boulders. The rocks protect the inlet ensuring the vital connections of commerce and recreation. One of the treasured spots along the jetty is known locally as the “kiddie pool”, which is accessible from St Andrew’s State Park. There are similar snorkeling opportunities throughout northwest Florida. Jetties provide an opportunity to explore hard substrate or rocky marine ecosystems. These rocks are home to a variety of colorful sub-tropical and migrating tropical fish.
Snorkelers and divers who visit are likely to see a variety fish like sergeant majors, blennies, surgeon and doctor fish, just to name a few. Photo by L Scott Jackson.
Exploring a jetty is more like a sea-safari adventure than an experience in a real swimming pool – it is a natural place full of potential challenges that first time visitors need to prepare to encounter.
Divers and snorkelers are required to carry dive flags when venturing beyond designated swimming areas. These flags notify boaters that people are in the water. Brightly colored snorkel vests are not only good safety gear but they help you rest in the water without standing on rocks which are covered in barnacles and sometimes spiny sea urchins.
According to the Florida Department of Health, most sea urchin species are not toxic but some Florida species like the Long Spined Sea Urchin have sharp spines can cause puncture injuries and have venom that can cause some stinging. Swim and step carefully when snorkeling as they usually are attached to rocks, both on the bottom and along jetty ledges. Photo by L Scott Jackson
Dive booties also help protect your feet. I found out the hard way! A couple of years ago my foot hit against a sea urchin puncturing my heel. The open back of my dive fin did not provide any protection resulting in a trip to the urgent care doctor. My daughter later teased it was an “urchin care” doctor! Sea urchin spines are brittle and difficult to remove, even for a doctor. Lesson Learned: “Prevention is the best medicine”.
After a couple of weeks of limping around and a course of antibiotics, I recovered ready to return one of my favorite watery places – a little wiser and more prepared. I now bring a small first aid kit, just in-case, to help take care of small scrapes, cuts, and other minor injuries.
Gloves are recommended to protect hands from barnacle cuts and scrapes. Shirts like a surfing rash guard or those made from soft material help keep your body temperature warm on long snorkel excursions. Along with sunscreen, shirts also protect against sunburn.
There’s opportunity to see marine life from the time you enter the water with depths for beginning snorkelers at just a few feet deep. Some SCUBA divers also use the jetty for their initial training. Most underwater explorers are instantly hooked, and return for many years to come. Photo by L Scott Jackson
Finally, know the swimming abilities of yourself and your guests, especially when venturing to deeper areas. It’s good to have a dive buddy even when snorkeling. Pair up and watch out for each other. Be aware that currents and seas can change dramatically during the day. Know and obey the flag system. Double Red Flag means no entry into the water. Purple flags indicate presence of dangerous marine life like jellyfish, rays, and rarely even sharks. Local lifeguards and other beach authorities can provide specific details and up to date safety information.
Follow these beach safety tips for helping your family enjoy the beach while protecting coastal wildlife.
An Equal Opportunity Institution. UF/IFAS Extension, University of Florida, Institute of Food and Agricultural Sciences, Nick T. Place, dean for UF/IFAS Extension. Single copies of UF/IFAS Extension publications (excluding 4-H and youth publications) are available free to Florida residents from county UF/IFAS Extension offices.