As we continue our series on marine life in the Gulf of Mexico, we also continue our articles on marine worms. Worms are not the most charismatic creatures in the Gulf, but they are very common and play a large role on how life functions in this environment. Roundworms are VERY common. There are at least three phyla of them but here we will focus on one – the nematodes.
A common nematode.
Photo: University of Florida
Most nematodes are microscopic, a large one would be about 2 inches, and some beach samples have found as many as 2 million worms in 10 ft2 of sand. So, what do we know about them? What role, or function, do they play in the ecology of the Gulf of Mexico?
Well first, they are long and round – cylinder shaped. There is a head end, but it is hard to tell which end is the head. Round is considered a step up from being flat in that it can allow for an internal body cavity. An internal body cavity can allow for the development of internal body organs. Internal body organs can move large amounts of nutrients, blood, oxygen, and hormones around the body allowing the animal to become larger. Some argue that a larger body can have advantages over smaller ones. Some say the opposite, but either way – a large body has been successful for some creatures and an internal body cavity is needed for this.
That said, the nematodes do not have a complete internal body cavity. So, they do not have a complete assortment of internal organs. Being round reduces your efficiency in absorbing enough needed nutrients, oxygen, etc. through your skin alone and this MAY be a reason they are small. They are very small.
There are free living and parasitic forms in this group. There are at least 10,000 species of them, and they can be found not only in the marine environment, but also in freshwater and in the soil found on land. They have played a role in the success of agriculture, infesting both crops and livestock. Nematodes can be a big concern for farmers and gardeners.
The free-living forms are known to be carnivorous, feeding on smaller microscopic creatures. They have toothed lips, and some have a sharp stylet to grab or stab their prey. Some stylets are hollow and can “suck” their prey in. Moving through the environment, they can consume algae, fungi, and diatoms. Some are deposit feeders and others are decomposers. On our farms and in our gardens, they are known to enter plants via the roots and can be found in the fruit.
The life cycle of the human hookworm.
The parasitic version of nematodes has been a problem for some species. In humans we have the hookworms and pinworms. Dogs have their heart worms. An interesting twist on the parasitic nematode way of life, compared to flatworms like tapeworms, is their lack of a secondary (or intermediate host). The entire life cycle can take place in the same animal.
Females are larger than males and fertilizations is internal. Males are usually “hooked” at the tail end and hold on to the females during mating. About 50 eggs will be produced and released into the digestive tract, where they exit the animal in the feces and find new hosts either by the feces being consumed or drifting in the water column.
There multiple forms of parasitism in nematodes.
– Some are ectoparasites (outside of the body) on plants.
– Some are endoparasites in plants – some forming galls on the leaves.
– Some infest animals but only as juveniles.
– Some live-in plants as juveniles and animals as adults.
– Some live-in animals as juveniles and plants as adults.
It would be fair to say that many forms of marine creatures have nematodes living either within them, or on them. Some can be problematic and cause disease; some diseases can be quite serious. Others play an important role in “cleaning” the ocean, filtering the sand of organic debris. Many have heard of nematodes but know little about them. Either good or bad, they do play roles in the ecology of the Gulf of Mexico.
Sea pork comes in a wide variety of shapes and sizes. Photo credit: Carrie Stevenson, UF IFAS Extension
Recently I was walking the beach, enjoying a sunset and looking around at the shells and other oddities in the wrack line where waves deposit their floating treasures. Something bright green and oblong caught my eye. It was emerald in color, smooth yet fuzzy at the same time, and firm to the touch. At first, I thought it was a sea bean–a collective term for the many species of seeds and fruits that float to our shores from tropical locations in the Caribbean or Central/South America. The bright green definitely seemed like something botanical in nature. However, the vast majority of sea beans have a woody, protective shell similar to our more familiar pecans or acorns.
I remembered a family member asking about finding a mystery chunk of pink mass she found on the beach a few years ago. It resembled a pork chop more than anything else.
A different variety of sea pork that really lives up to its name. Photo credit: Stephanie Stevenson, Duval County Master Gardener
Looking closer and consulting a couple of resources, I realized we had both (most likely!) happened upon one of the oddest and often-questioned finds on our beaches: sea pork. Ranging in color from beige and pale pink to red or green, sea pork is a tunicate (or sea squirt), a member of the Phylum Chordata, home to all the vertebrate and semi-vertebrate animals. While they look and feel more like a cross between invertebrate slugs or sponges, the tunicates are more advanced organisms, possessing a primitive backbone in their larval “tadpole” form. Despite their blob-like appearance, they are more closely related to vertebrate animals than they are to corals or sponges.
The unusual life cycle of the tunicate. Photo credit: University of Washington, used with permission with Florida Master Naturalist program
During their short (just hours-long) larval stage, the tunicate larvae uses its nerve cord (supported by a notochord similar to a vertebrate spine) to communicate with a cerebral vesicle, which works like a brain. Similar to fish, this primitive brain uses an otolith to orient itself in the water, and an eyespot to detect light. These brain-like tools are utilized to locate an appropriate location to settle permanently. Using a sticky substance, the tunicate will attach its head directly to a hard surface (rocks, boats, docks, etc.) and go through a metamorphosis of sorts. The tunicate reabsorbs its tail and starts forming the shape and structure it needs for adulthood.
As an adult, the organism has a barrel shape covered by a tough tunic-like skin (hence “tunicate”). Adult bodies have two siphons, one to bring water in, another to shoot it out (giving them their other nickname, the sea squirt). The water passes through an atrium with organs that allow it to filter feed, trapping plankton and oxygen. The tunicates will spend most of their lives attached to a surface, pumping water in and out as filter feeders. They may be solitary or live in colonies, and vary widely in color and shape, lending variety to those chunks of sea pork found washing up.
I am still awaiting positive identification from an expert on my green find to confirm that it is, indeed, a tunicate and not an unfamiliar plant. Consulting with Extension colleagues, for now we are pretty confidently going with green sea pork. If you have seen one of these before or something resembling sea pork, let us know! It is fascinating to see the variety and unusual shapes and colors.
Crawfish boils are popular in the springtime. Crawfish are generally harvested from aquaculture operations. Photo credit: Libbie Johnson, UF IFAS Extension
“You get a line, I’ll get a pole, we’ll go down to the crawdad hole, honey, baby, mine“…there are lots of great zydeco songs singing the praises of crawfish (aka crayfish, crawdads, mudbugs). They are in season now, and while crawfish festivals all around the southeast are canceled due to concerns over COVID-19, they are still available and make for great eating. Most of us would recognize a cooked one alongside a feast of corn and potatoes, but would you know an actual crawfish hole if you came up on it?
Last fall, our office welcomed about 500 kids (over several days) to the 4-H camp in Barrineau Park for a field trip. I showed every single one of them a small muddy mound with an opening in the top, and asked if anyone could tell me what it was. Not a single kid knew! Now, I make sure I point crawfish mounds out to anyone I happen to be walking with, as they are fascinating little structures. Also referred to as crawfish chimneys due to their upright, open construction, they are built by a crawfish in a muddy area, often near a creek or other water source.
Crawfish mounds are constructed using small pellets of mud, and the opening connects down to a burrow. Photo credit: Carrie Stevenson, UF IFAS Extension
The industrious invertebrate uses its legs and mouth to create pellets of mud as it digs its burrow. It places mud up above the ground, using the mud balls like small bricks. Bricking up the entrance to its burrow (as opposed to placing discarded mud elsewhere) also protects a crawfish from exposure to predators on open soil. The crawfish chimneys can be 6 inches tall (or more!) and connect down to a burrow that may reach 3 feet deep, some straight down and others with side tunnels extending different directions.
Since the crawfish lives in wetland areas, it is theorized that these chimneys extending above the soil allow for better oxygen flow in the burrow. During a drought, crawfish will plug the opening of their mounds with mud, to keep water in the burrow from evaporating.
Crawfish in the wild are rarely harvested, although some folks do fish for them like the song referenced earlier. For the vast majority of crawfish harvested in commercial production, two species are the most popular–the white river crawfish (Procambarus zonangulus) and red swamp crawfish (Procambarus clarkii). They are typically farmed in coordination with rice, as both commodities thrive in flooded conditions. Most aquaculture operations are associated with Louisiana, but at least five other southern U.S. states farm crawfish. To learn more about this industry, check out LSU AgCenter’s informative video.
White-topped pitcher plants in bloom at Tarkiln State Preserve. Photo credit: Carrie Stevenson, UF IFAS Extension
If you live in northwest Florida or southeast Alabama and have never laid eyes on our wild native carnivorous plants, it is about time! April and early May are the best time to see them in bloom. We have six species of pitcher plants (Sarracenia), the most common being the white-topped (Sarracenia leucophylla). However, they come in multiple colors, from yellow and red to a deep purple, and in different sizes.
Pitcher plants and their pinwheel-shaped flowers at Splinter Hill Bog. Photo credit: Carrie Stevenson, UF IFAS Extension
One thing they have in common, though—they eat meat. Carnivorous plants all over the world have evolved in places that left them few other options for survival. These plants are typically found in extremely wet, acidic, mucky soils with very low nutrient levels. Normally, plants uptake nutrients like nitrogen and phosphorus from the soil around them. Not being available in these particular environments, carnivorous plants (or more specifically, insectivorous) developed a way to extract nutrients from insects.
Small parrot pitcher plants lie on the ground instead of standing upright at Blackwater State Forest. Photo credit: Carrie Stevenson, UF IFAS Extension
So how does it work? Pitcher plants have a modified leaf, which instead of lying out flat like most plants, is rolled up into a tube, or “pitcher” shape. The inside of the pitcher has a sweet sap, and the walls of the tube are lined with tiny, downward-pointing hairs. Separate from the leaf, the plant has an elaborate flower structure, which attracts insects for pollination. While nearby, these insects are also attracted to the colorful leaf and the sweet sap in its pitcher. The insect will land on the lip of the leaf, then crawl down.
Those sticky, downward facing hairs are a trap, preventing insects from leaving the pitcher. Enzymes—a cocktail of proteins naturally found in many other plants but used creatively here—in the sap break down the bug bodies and convert them to nutrients for the plant. In fact, if you slice a cross-section into a pitcher wall or break open a dried one, you will see countless dried exoskeletons at the bottom of the tube. Several other enterprising species have taken advantage of the pitcher plant’s creative structure. More than once, I have seen tiny spiders spin webs across the mouth of the tube, or small lizards and frogs at the bottom, waiting patiently for prey.
Some of the best places to see pitcher plants in the area—they also bloom in October—are Tarkiln Bayou State Preserve, Weeks Bay National Estuarine Research Reserve, Splinter Hill Bog Preserve, and Blackwater State Forest.
Okay, this is a gamble.
I began this series to celebrate the year of the Gulf of Mexico – “Embracing the Gulf 2020”. The idea was to write about the habitats, creatures, economic impacts, and issues surrounding the “pond” that we live on. I did a few introductory articles and then jumped right into the animals. We began with the fun ones – fish, sea turtles, whales – and now we are in the more unfamiliar – invertebrates like sponges and jellyfish.
But worms? Really? Who wants to read about worms?
A classic flatworm is this lung fluke.
Photo: Kansas State University.
Well, there are a lot of them, and they are everywhere. You will find in many sediment samples that worms dominate. They also play an important role in the marine community. They are great scavengers, cleaning the environment, and an important source of food in the food chains of the more familiar animals. But they are gross and creepy. When we find worms, we think the environment is gross and creepy – and sometimes it is, remember they CLEAN THE ENVIRONMENT. But worse is that many are parasites. Yes… many of them are, and that is certainly gross and creepy. Flukes, tapeworms, hookworms, leeches, who wants to learn amore about those? Well, honestly, parasitism is an interesting way to find food and the story on how they do this is pretty interesting… and gross… and creepy. Let’s get started.
According to Robert Barnes’ 1980 book Invertebrate Zoology, there are at least 11 phyla of worms – it is a big group. We are not going to go over all of them, rather I will focus on what I call the “big three”: flatworms, roundworms, and segmented worms. We will begin with the most primitive, the flatworms.
As the name implies, these worms are flat. They are so because they are the last of what we call the “acoelomate” animals. Acoelomates are animals that lack an internal body cavity and, thus, have no true body organs – there is no where for them to go. So, they absorb what they need, and excrete, through special cells in their skin. To be efficient at this, they are flat – this increases the surface area in contact with the environment. There are three classes of flatworms – one free swimming, and two that are parasitic.
This colorful worm is a marine turbellarian.
Photo: University of Alberta
The free-swimming ones are called turbellarians. Most are very small, look like leaves, very colorful, and undulate as they swim near the bottom. They have “eye-like” cells called photophores that allow them to see light – they can then choose whether to move towards the dark or not. They have nerve cells but no true brain, and one only one opening to the digestive tract – that being the mouth, so they must eat and go to the bathroom through the same opening. Weirder yet, the mouth is usually in the middle of the body, not at the head end. Some are carnivorous feeding on small invertebrates, others prefer algae, others are scavengers (CLEANING THE OCEAN). They can reproduce by regenerating their bodies but most use sexually reproduction. They are hermaphrodites – being both male and female. They can fertilize themselves but more often seek out another worm. Fertilization is internal and they lay very few eggs.
The human liver fluke. One of the trematode flatworms that are parasitic.
Photo: University of Pennsylvania
The second group are called trematodes and they are the parasites we know as “flukes”. We have heard of liver flukes in livestock and humans, but there are marine versions as well. They have adhesive organs located at the near the mouth that help hold on, and a type of skin that protects them from their hosts’ defensive enzymes. They feed on cells, mucous, and sometimes blood – yep… gross and creepy. Some are attached outside of their hosts body (ectoparasites) others are attached to internal organs (endoparasites). The ectoparasites breath using oxygen (aerobic), endoparasites are anaerobic. Like their turbellarian cousins, they are hermaphroditic and use internal fertilization to produce eggs. They differ though in that they produce 10,000 – 100,000 eggs! Their primary host (the one they spend their adult life feeding on) is always a vertebrate, fish being the most common. However, their life cycle requires the hatching larva find an intermediate host where they go through their developmental growth before returning to a primary host. These intermediate host are usually invertebrates, like snails. The eggs are released with the fish feces – a swimming larva is released – enters a snail – begins part of the developmental growth – consumed by an arthropod (like a crab) – completes development – and the crab is consumed by the fish – wah-la. The adults are usually found in the gills/lungs, liver, or blood of the vertebrate hosts. Gross and creepy.
The famous tapeworm.
Photo: University of Omaha.
Better yet are the tapeworms. We have all heard of these. They are also all parasites, but all are endoparasites. Weirder, they do not have a digestive tract. Gross and creepy. Their heads are very tiny compared to their bodies and have either four sets of suckers, or hooks, to hold onto the digestive tract of their hosts (usually vertebrates). The head is actually round but the body is very flat and divided into squares called proglottids. Each proglottid gets larger as you move towards the tail and each possesses all of the reproductive material needed to produce new worms – they too are hermaphrodites. They also have a type of skin that protects them from the enzymes of their hosts. They also require an intermediate host to complete their life cycle so the proglottids will exit the hosts body via feces and complete the cycle similar to the trematodes.
I began this with a comment on how worms benefit the overall marine environment of the Gulf. It is hard to see that in these flatworms. They are either just another consumer out there, or nasty parasites others in the community must deal with. Well… we look at the roundworms next time and see what they have to offer.
Barnes, R. 1980. Invertebrate Zoology. Saunders College Press. Philadelphia, PA. pp. 1089.
If you like summer fireworks events, there is a great show ongoing during our warm summer months that you shouldn’t miss. Find an unlit dock along our coastal environs and take the time to pause, get down on your knees, and gaze into the starry… water. Our night skies are quite impressive in their own right, but our night waters will also put on an amazing show of glowing critters and flashing lights if you take the time to notice. Thousands of different marine organisms have the ability to produce light and the purposes served by this trait are many. Some animals use this tactic as camouflage and others to stand out for one reason or another. Being seen by others can assist with predation (luring), defense (startling or warning), or even reproduction (attracting a mate).
Thousands of marine creatures create their own light, including many jelllyfish
Bioluminescence is the most accurate term for light emitted by living organisms; although sometimes you will hear it referred to as fluorescence or phosphorescence. Fluorescence however, is the term describing something that absorbs light energy from an external source and then almost immediately re-emits it. When the external source goes away, so does the fluorescence; i.e. it doesn’t keep going in the dark. Phosphorescence describes when something absorbs light energy from an external source and then slowly re-emits it over a longer timeframe, i.e. glowing stickers. In contrast to these other terms, bioluminescence results from a chemical reaction within the body of an organism. The trigger mechanisms can be quite varied in nature and some are even directly controlled by linkages with an animal’s brain and nervous system. Other times the light is triggered simply by a physical disturbance. This is the most common phenomenon observed by people as the water seems to sparkle from a boat’s wake at night or waves breaking in the surf. One of my earliest memories of this was as a teenager in the Keys while wading along the shore at night. Each splash would trigger a shower of sparks.
So, what is taking place to create this chemical reaction that gives off light? Well, scientists have learned a lot about it but still don’t have all of the answers regarding the incredible variety of ingredients and processes involved in the bioluminescent realm. In general, a molecule called luciferin is involved and when exposed to oxygen, it gives off light. An enzyme named luciferase acts as a catalyst to help speed up the reaction. There are apparently many types of luciferins utilized by different animals; and I’m guessing, many variations on the actual luciferases involved too.
During summertime the warm waters of the Gulf and our coastal estuaries are rich with planktonic life. If you look close at a dock post beneath the water you will see continual, tiny flashes being triggered as water moves around the stationary post. When you walk down the dock (very carefully, without a flashlight), you can also see streaks of light from startled fish swimming away. This light is emitted by single-celled dinoflagellates that are triggered by a disturbance near them. One fascinating account I’ve read, told the story of Jim Lovell (Apollo 13 astronaut), who used bioluminescence to find his way safely home. When the navigation equipment failed at night in the navy plane he was flying, he was able to turn off his cockpit lights and see the glowing wake from his carrier and follow it. I’m sure he was forever grateful to the tiny marine creatures that made this possible! If you can get to a coastal dock near you this summer, be sure to turn out the lights, and look down in the water for a spectacular, miniature fireworks show. No earplugs required.