Coastal Critters

The South Carolina coast hosts a treasure trove of biodiversity. The immense saltmarsh that lines our coast between the mainland and the barrier islands is a vital ecosystem and nursery ground for countless species. The saltmarsh supports life from all spectrums. Dolphins, crabs, turtles, mink, manatees, and numerous fish and bird species are just a few examples of some of the amazing creatures that thrive in this ecosystem. In the summer months ~39 species of sharks and rays use our saltmarshes, many of which use the estuaries and deep inlets to drop pups. With an exception for brackish areas where freshwater rivers reach the ocean, most of our saltmarshes are pure ocean water, coming in and out of inlets tidally twice a day. While the water in this ecosystem does not have high clarity, it is not due to pollution or dirty water. The saltmarsh is murky, not dirty, and this is due to detritus. Detritus is broken down organic material, and in the case of the saltmarsh it comes from the plant that dominates this ecosystem, Spartina grass (now referred to as Sporobolus). Detritus is vital for the survival of the many smaller creatures that this habitat supports. Larval crabs, shrimp, and many other minute organisms feed on the leftover nutrients from the decomposing marsh grass.

The apex predator of the saltmarsh is nothing shy of a fish-eating machine. The bottlenose dolphin can eat upwards of 30 lbs of fish a day. Unlike many other toothed whales that take bites out of fish, the bottlenose dolphin eats all of their fish whole. Until 2022, our inshore dolphins were described as Atlantic bottlenose dolphins. A ten-year study found that the inshore bottlenose dolphins vary from the offshore dolphins in size and flexibility. Inshore dolphins are more in-tune to flexibly moving around in shallow creeks, and therefore they do not get quite as long as their offshore counterparts. They also have fewer vertebrae and ribs. Coastal/nearshore dolphins are now referred to as Tamanend’s bottlenose dolphins (Tursiops erebennus), named after Chief Tamanend, a Native American chief of the Lenni-Lenape tribe in the Delaware Valley, where the holotype specimen was found.

As expected, the saltmarsh hosts far fewer reptilian species than freshwater but it still has several that call it home. The only reptile that lives full time in our marshes is the diamondback terrapin, a beautiful turtle with highly variable and intricate patterning. Terrapins primarily eat periwinkle snails, clams, and crabs. They were once considered a delicacy and overharvesting for food plummeted in the early 1900s their once thriving populations. Luckily, conservation work and protected areas are helping preserve healthy populations. When you think of conservation work in the reptile world, a lot of people’s minds go to the sea turtles, the reptile with the best PR team. Green sea turtles, loggerhead sea turtles, and Kemp’s ridley sea turtles all use our marshes as feeding grounds in the warmer months. Leatherbacks come up our coast but typically stay in the ocean, as they are a pelagic species, meaning they spend most of their time offshore. The last reptile, besides the occasional snake swimming from island to island, that temporarily lives in our marshes is the American alligator. Unlike crocodiles, alligators lack salt glands and therefore cannot survive long term in saltwater. Subsequently, they utilize the marsh as temporary feeding grounds, usually not too far from a freshwater source they can resort back to.

Much lower on the food chain comes a very diverse group of animals: Arthropods. Terrestrial examples include insects and spiders while marine examples are found in three main groups: sea spiders, horseshoe crabs, and crustaceans. The ancient living fossils known as horseshoe crabs are actually more closely related to scorpions than true crabs. Sea spiders, while not true spiders, certainly look the part despite lacking a large abdomen. They are commonly associated with hydroids, a type of cnidarian (the taxonomic clade that includes jellyfish), that grow on structure. Lastly, crustaceans are most aptly referred to as the insects of the sea. Examples of crustaceans include crabs, shrimp, lobsters, and even barnacles. Crabs are even further divided into true crabs, hermit crabs, and mole crabs. Defining a true crab falls to two main characteristics. True crabs sport modified tails folded flat underneath the body and a front pair of legs modified into pincers used for defense and feeding. The difference between hermit crabs and true crabs lies in the abdomen. Instead of the crab’s abdomen being tucked under its body, they salvage snail shells and curl their long, soft abdomen inside. Mole crabs, most commonly known as sand fleas, live in the sand in the surf. When the tide has them fully submerged, they sit under the sand with just their feathery antennae exposed, filtering in plankton and sand particles. They leave the task for separating the sand and food up to the internal organs.

One crab worth highlighting is the extremely well known Florida stone crab. They are some of the most sought after food crabs. In South Carolina it is legal to harvest the larger of the two claws (as long as it measures 2.75” from elbow to tip), meanwhile releasing the crab to live another day and regrow its claw. The process of molting to regenerate a claw takes around a year. After losing a limb, stone crabs always regenerate a new cutter claw. The preexisting cutter claw starts to change. It beefens up and grows molars, slowly morphing into a crushing claw. The large crushing claw of the stone crab packs around 15,000 pounds of crushing pressure while the cutting claw can cut with around 6,000 pounds of cutting pressure. Stone crabs eat whelks and clams and therefore use their claws to crush through the thick shells.

Another remarkable crab is the calico box crab, an uncommonly encountered crab that is stunning orange with intricate carapacial patterning. They are found in sandy creeks but can also live in water up to 150’ deep from the Chesapeake Bay to Mexico. Calico crabs possess broad flat claws they use to cover their face when buried under the sand. Box crabs are scavengers that eat decaying matter and detritus.

Sea snails (Univalves) are a diverse group of gastropods that thrive in our nearshore oceans and estuaries. Gastropod literally translates to “stomach-foot.” Many people only see the leftover remains of univalves in the form of their exoskeletons and do not realize much of the complexities of the living animal. People often refer to most of our sea snails as conchs. The fact of the matter is that there are no conchs in South Carolina. The most confusing example is the so-called horse conch, the largest of our native snails, reaching two feet in length, which is not actually a conch but a species of tulip snail.  Conchs live in areas with clear water where sunlight can reach the bottom to photosynthesize plants. Herbivorous snails require large seagrass beds that we lack. Our murky water is the ideal place for filter feeding clams which are the main prey items for whelks. Whelk snails use their large foot to pry bivalves open against the edge of their hard shell. One species of snail, the moon snail, has a different strategy to predate clams and other snails (even moon snails). They perch on top of an unfortunate victim and lick and spit for over the course of around a week. Eventually their radula, a sharp tongue covered with teeth, in addition to their saliva dissolves through the calcium shell, allowing the moon snail to suck the animal out, leaving behind an empty shell suited with a perfect hole.

Sea snails also have a shell-less counterpart, sea slugs. Sea slugs consist of nudibranchs and sea hares, both remarkable creatures. While much more well known and encountered on the west coast, the east coast also has a high diversity of slugs. Nudibranchs are incredibly variable – some species display vibrant orange and blue hues while others are completely white. One species even has vibrant blue and yellow rings. In their larval form, nudibranchs have a shell but it sheds off as they mature. Most nudibranchs are small, seldom reaching more than several inches in length. Sea hares, however, get quite large – some species reaching over two feet in length. They earn their name due to their rabbit-like appearance, with large ear-like wings they use to glide through the water. Sea hares, and most gastropods, are hermaphroditic, meaning they possess reproductive organs of both males and females, and can function as either sex. Unlike nudibranchs, they have an internal shell for protection. Similar to squids, sea hares produce a vibrant purple ink and do not hesitate to use it.

Clams, scallops, and oysters are all bivalves, meaning they have two shells. Bivalves are vital for a healthy saltwater ecosystem. Not only do they play a large role in the food chain, they also provide a filtration system. One single oyster can filter up to 50 gallons of water a day. Consequently, oysters are a keystone species of the saltmarsh. In addition to filtering water, they also provide valuable habitat for a large array of creatures. Many larval crabs and shrimp take shelter in the cracks and crevices that mounds of oysters provide.  One species of fish, the skilletfish, has a suction cup on its underside. They stick to oysters when the current is strong in order to not get swept away. Oyster pea crabs live within oysters, feeding on detritus and other food material as the oyster filters the water. They are most often encountered while consuming oysters, some even consider them good luck to eat. While some bivalves are sedentary, such as oysters and mussels, others move around. Some species, such as bay scallops, even swim. They pump their shells open and closed propelling themselves along.

The biodiversity of the coast is far more impressive than most people realize. There are several famous creatures that often enter our waterways without people ever knowing. Octopuses, sea horses, hammerhead sharks and spotted eagle rays are just a few examples. The diversity of fish that our coast supports is immense. Most people target a select few species of gamefish while fishing, but there are hundreds of other species that seldomly interest anglers. Next time you are lucky enough to explore the saltmarsh or beaches, I encourage you to take a closer look at some of the biodiversity. Even common seashells found while beachcombing often tell some amazing stories. Simply noticing the perfect hole perched on the clam tells you exactly how it met its demise.