Complex Crustaceans: The Lobsters

spiny lobster

When I was a kid, starting every year somewhere around the beginning of April, I knew exactly how many days were left in the school year before the start of summer vacation. Like every other kid in my world, by Thanksgiving I was always keenly aware of how many days there were until Christmas. When it came to sports, I always knew how many days until the season opened and until my team’s next game. All of my friends knew these numbers because it was the way we measured time.

Unfortunately, as adults too often we mark time by noting how many more days are left until April 15 and tax time, and until the first of the month when bills are due. But there are exceptions to the strict use of this adult calendar. Take my lobster-diving buddies as examples. Friends of mine that live in Australia, North Carolina, Florida, Texas and Southern California mark time by the opening of lobster season, or “bug” season as they know the time of year when lobsters are legal fare. For these divers, the rituals of lobster season are not to be messed with.

Underwater photographers, videographers and other divers might not mark the passing of time by the opening and close of lobster season as our lobster diving pals are sometimes inclined to do, but if you hang around the diving community for very long, you will surely run into divers whose calendars revolve around bug season. So whether you are a beginning diver, a person who enjoys an occasional culinary treat or an all-out lobster maniac, the odds are that you will find a dive into the natural history of lobsters a fascinating dive indeed.

More Than a Main Course

Invertebrates, lobsters are described in the phylum Arthropoda. With more than 1 million living species, this group contains the most living species of any phylum. The phylum name is derived from the Greek arthros, “joint,” and podos, “foot,” and the phylum name seems most apropos as soon as you see your first lobster taking a stroll around a reef, as the possession of jointed appendages is a characteristic of all arthropods. Although terrestrial insects make up the majority of arthropods, many members of this phylum are marine creatures. Arthropods have well-developed physiological systems, a distinct head and well-developed central nervous system as well as keen senses of vision, smell and touch. The bodies of arthropods display bilateral symmetry, meaning that the two sides of the body are mirror images of each other.

Some of the better-known marine arthropods are further described in the class Crustacea. In addition to lobsters this class includes shrimps, crabs, barnacles, amphipods, copepods and isopods. Crustaceans are further characterized by their segmented bodies that are protected by hardened shells, two pairs of antennae, gills used for respiration, and a body that has seven or more pairs of sometimes very different appendages that are used for locomotion, feeding and sex.

Even given all of this scientific input, it doesn’t take long for a well-traveled or well-read diver to begin to realize that the creatures we call lobsters take on a variety of forms. Some, like the Maine lobster (Homarus americanus) have big, powerful-looking claws that are used for defense, capturing prey and food gathering, while the many species referred to as spiny lobsters lack claws altogether. Slipper lobsters look like the terrestrial insects known as “rolly pollies” (pill bugs), and still other species are called squat lobsters. These diminutive lobsters are armed with large claws compared with their relatively small body size. Some people refer to clawed species as “true lobster,” and to other species as spiny, slipper and squat lobsters, but this nomenclature can lead to misunderstanding and confusion.

The Maine lobster is also known as the American lobster, Massachusetts lobster, Canadian lobster and North Atlantic lobster. This species occurs in shallow reef communities down to depths of more than 2,275 feet (689 m) along the east coast of North America from Newfoundland to North Carolina. According to the Massachusetts Lobstermen’s Association, the largest specimen ever taken weighed 37.4 pounds (17 kg) and was just over 2 feet (60 cm) long, although some claim to know of a 45-pound (20-kg) animal.

Unlike the Maine lobster, spiny lobsters lack large, pinching claws, although the females possess a small pincer on the last pair of walking legs. Oddly enough, many people refer to spiny lobsters as crayfish because of the lack of a large, pinching claw, even though the freshwater crustaceans known as crayfish possess claws. Go figure.

Known to inhabit the cracks and crevices of rocky reefs from Point Arguello, California, well into the Pacific waters off Mexico’s Baja peninsula, the California spiny lobster (Panulirus interruptus) is believed to live up to 100 years. At least seven years are required to reach sexual maturity. The spiny lobster (Panulirus argus) is one of the more conspicuous creatures encountered on night dives along the southeastern coast of the United States as well as in the Bahamas and many portions of the Caribbean. The Spanish slipper lobster (also known as the ridged slipped lobster and slipper lobster) is also frequently encountered on night dives made in Caribbean reef communities.

Lobsters are often portrayed as being bright red in drawings and cartoons, but in the wild lobsters occur in a wide variety of colors including red, blue, tan, greenish-brown, gray, orange and calico. All of these possibilities make the phrase “red as a lobster” a bit misleading. However, most lobsters do turn red when they are steamed or boiled in hot water.

Shell Game

The hard shell of lobsters is laced with calcium carbonate that adds strength and rigidity to the shell. In addition to providing protection, the shield also promotes an animal’s dexterity via the strategic attachment of muscles to various hard plates in the body and shell.

While living inside of a hard shell offers some advantages, it also poses some logistical problems. For example, growth is both difficult and potentially dangerous. For a lobster to increase its size, it must “molt,” or shed its shell. A soft-bodied, unarmored lobster is extremely vulnerable to predators during the early stages of molting before the new and larger outer shell begins to harden.

Molting is governed by hormones secreted from glands in the eyestalks. Before molting, lobsters undergo a period of heavy feeding and fat storage. Shortly afterward, they begin to form the foundation of a new shell under the old shell. Hormonal changes cause the old shell to begin to split and fracture, and the lobster will soon shed its old shell. In some instances, lobsters will consume part of the old shell to help restore the calcium that is required to harden the new shell, and in other instances they discard and ignore their old shell.

During the vulnerable stages of molting, lobsters seek the safety of hiding places where the new shell can harden. In some species, the only time a female can be mated is when she is molting. While the shell is soft, important hormonal processes enter into play, preventing the loss of vital body fluids and allowing time for body tissues to swell. Soon the new shell hardens over the bloated body. Not long afterward another hormonal change occurs and excess fluids are expelled from the body and the animal shrinks within the new shell. There is now ample room for growth before another molting is required.

Larval lobsters often molt 25 times or more before settling out of the water column. Once they have settled into reef communities, the frequency of molting lessens, but young lobsters still molt several times annually, and the frequency continues to slow with the aging process.

Mating and Reproduction

In lobsters, the sexes are separate. Mature females provide parental care for their offspring by carrying, guarding and oxygenating eggs that are attached to her small abdominal legs called swimmerets until the eggs hatch. Females with eggs attached are said to be carrying “berries,” and most divers refuse to take a female with berries even during lobster season because doing so can be so detrimental to future generations of both lobsters and lobster divers.

In the Maine lobster, when the female is ready to molt she approaches a male’s den, and having chosen her desired mate wafts a sex “perfume” called a pheromone in his direction. She usually seeks out the largest available male and stands outside his den, releasing her scent in a stream of urine from openings just below her antennae. If he responds favorably, he will emerge from his den with his claws raised aggressively. After getting to know each other, the female raises her claws and places them on his head to let him know she is ready to mate. Then the pair enters the male’s den, and a few hours to several days later, the female molts. At this point the male could mate with her or eat her, but he invariably does the noble thing and the pair mates.

During spawning, males deposit a string of sperm packets on the abdomen of females. When a female opts to lay her eggs, an event that commonly occurs several months after mating, the female digs a hole in the packets to fertilize her eggs. She continues to carry the eggs in grapelike clusters on her swimmerets for several months until they hatch.

Upon hatching, larval spiny lobsters are planktonic and they drift for as long as eight months in ocean currents, often covering hundreds of miles. Feathery hairs on their legs help larval lobsters swim near the surface for the first few months after hatching before the survivors eventually attempt to settle to the sea floor where they spend the rest of their lives, sometimes venturing into areas where we can enjoy, photograph and hunt them.

Reflexes and Regeneration

As members of reef communities, lobsters are hunted by seals, sea lions, fishes, octopods and, of course, humans. In many instances when in danger, lobsters and some other crustaceans can drop, or discard, a limb in a life-saving maneuver known as “reflex amputation.” This action is designed to allow a lobster to escape from a potential predator. Lobsters are equipped with the remarkable ability to regenerate some lost body parts including claws, walking legs and antennae. In turn, lobsters prey upon a wide variety of prey items including snails, mussels, crabs, worms, sea urchins, sand dollars, shellfish, algae and detritus.

Shark Snack?

It was well after midnight, but we were working late into the night as we followed and filmed a pack of whitetip reef sharks that were hunting along the rocky reefs at Costa Rica’s Coco Island. Each shark would swim a few yards and then poke its head into a hole looking for a sleeping fish or some other trapped prey. If one shark appeared to get excited, as if it had cornered a potential meal, the rest of the pack of a dozen or so sharks immediately closed in to try to take advantage of the situation.

There was no question that the sharks were hunting when they came across a solitary spiny lobster that was walking out in the open across the sandy bottom. As the first shark approached the lobster, the crustacean alternately raised its antennae high into the water column and then back over its own body. The spike-covered antennae whipped around in rapierlike fashion, but I thought that one lobster vs. a group of hunting sharks was the mismatch of the century. I was certain that the lobster was a late night snack for the sharks, and the only question was which shark would get how much lobster.

I was wrong. The lobster whipped its antennae around, beating, poking and slashing at the sharks, and each time a shark got struck the hunter gave ground. The sharks were persistent and continuously tried to get at the lobster, but the lobster managed to fend off the sharks for several minutes until the lobster reached the safety of the reef where the harried animal quickly found cover and disappeared.

Crustacean Caravan

The “march of the Caribbean spiny lobster” is a widespread phenomenon, occurring on both the Great and Little Bahama banks. A lobster march begins when a mass of young adult lobsters gathers on the banks. Hundreds of lobsters that have been gathering beneath ledges and overhangs begin to line up and march as fast as 5.2 yards (4.7 m) a minute across the shallow bank, into deeper water. In clear water, chains of lobsters marching in single file can be observed in water as shallow as 15 feet (4.5 m). In this supposedly defensive position, with each lobster’s vulnerable soft parts protected by the lobster behind, they become relatively bold and fearless, and have been known to march right over an observing diver.

Researchers believe the march is triggered by the combination of hormonal changes and environmental changes such as the arrival of storms, sudden changes in water temperature and abundance or lack of food.

Story and photos by Marty Snyderman