The California spiny lobster (Panulirus interruptus) is a species of spiny lobster found in the eastern Pacific Ocean from Monterey Bay, California, to the Gulf of Tehuantepec, Mexico. It typically grows to a length of and is a reddish-brown color with stripes along its legs, and has a pair of enlarged antennae but no claws. The interrupted grooves across the tail are characteristic for the species.
Females can carry up to 680,000 eggs, which hatch after 10 weeks into flat phyllosoma larvae. These larvae feed on plankton before their metamorphosis into the juvenile state. Adults are nocturnal and migratory, living among rocks at depths of up to , and feeding on sea urchins, clams, mussels and worms. The spiny lobster is eaten by various fish, octopuses and sea otters, but can defend itself with a loud noise produced by its antennae. The California spiny lobster is the subject of both commercial and recreational fishery in both Mexico and the United States, with sport fishermen using hoop nets and commercial fishermen using lobster traps. It is also considered a keystone species because of their control of urchin species which would otherwise damage kelp forests.
Morphology
Appearance In common with all spiny lobsters, the California spiny lobster has two large, spiny antennae, but no large claws on its legs. The California spiny lobster is one of the largest spiny lobster species, and grows up to long, but does not usually exceed . Males can weigh up to ., with the record being a 16 lbs., 1 oz. male caught off Catalina island in 1968. The upper side of the animal is brownish red, without the paler bands or spots seen in some other spiny lobsters. The legs are a similar color, but with one or more lighter streaks running along their length. California spiny lobsters in particular have very brightly colored eye-spots.
Sexual differences Males and females of all ages can be distinguished by the position of the two round genital openings or gonopores. In females, they are at the bases of the third pair of pereiopods, while in males they are at the base of the fifth (last) pereiopods, furthest from the head and the closest to the abdomen. Mature females have a small claw on the fifth pereiopod, and enlarged pleopods.
Distribution The California spiny lobster is found in parts of the Gulf of California, and along the Pacific coast of the length of the Baja California peninsula, extending as far north as San Luis Obispo Bay, California. There are occasional records from Monterey Bay, but the water there is too cold for the California spiny lobster to breed, and it is thought that any adult found in Central California arrived as a larva during El Niño years.
California spiny lobsters live on rocky substrates, at depths of up to . Although adults can be found in shallow water, including tide pools, they are more frequent in deeper waters. Juveniles generally inhabit rocky habitats at a depth of with dense plant cover, especially the surf grass Phyllospadix torreyi.
Ecology and behavior
Feeding behavior California spiny lobsters are nocturnal, hiding in crevices during the day, with only the tips of their long antennae showing as a means of avoiding predators. In these crevices, they can either be found alone or with 2 to 15 lobsters. The lobsters that are in the crevices tend to retreat further back into the burrow and brace their bodies against the rocky walls instead of chaotically or synchronously swimming out and away from predators. Towards dawn, the spiny lobsters form aggregations, which they maintain until dusk. At night, they emerge and feed on sea urchins, clams, mussels and worms. This activity is important in limiting sea urchin populations, and, subsequently, maintaining healthy seabed communities. Spiny lobsters show a gregarious approach to feeding because they are able to recruit other members of their species to feeding sites. They can recruit by using chemical and olfactory cues and social behavior. However, this is not always a positive trait as fishermen can take advantage of this and use other lobsters to attract more to their traps.
Predators Natural predators of the California spiny lobster include bony fish such as the California sheephead, giant sea bass and cabezone, sharks such as the horn shark and leopard shark, octopuses and sea otters. In response to an approaching predator, spiny lobsters, including the California spiny lobster, can produce a loud noise using the stick-slip phenomenon, akin to a bowed instrument. The bases of the antennae act as a plectrum (similar to a pick), which is rubbed over a file on the edge of the antennular plate. If a predator is very close, spiny lobsters will flex their muscular tail in order to escape the predator, backwards.
California Spiny lobsters are also able to detect predators using chemical cues. The ability for these lobsters to chemically detect conspecifics and guide lobsters to suitable shelters is called the guide effect. They have a small home range which is strongly influenced by habitat.Hovel, Kevin, et al. “Baseline Characterization of California Spiny Lobster (Panulirus Interruptus) in South Coast Marine Protected Areas.” 2015. It is estimated that their home range is maximum 0.57 km2 while in many New Zealand species the spiny lobsters would travel a linear distance between 3.1-5km. California spiny lobster exhibit homing behavior which is common in many other species. This homing behavior allows the lobsters to be able to locate prey, avoid predators, and return to their shelters. Also, females have been proven to travel farther distances compared to the males and this usually increases when they are brooding and when the larvae is about to be released. California spiny lobsters lack fine-tuned locomotor control while swimming meaning that they exhibit short bursts of speed to try to escape a predator but are unable to control their movements while swimming fast, prioritizing speed over accuracy. They rely heavily on walking and crawling instead of swimming fast. Another defense mechanism that these lobsters utilize is when a group of them gather in a circle and create a spiny pincushion which repels the predator instead of the group attacking the predator. They orientate their bodies in such a way that points their spiny backs towards the predators so they are too dangerous to attack. This defense mechanism is used due to the aforementioned lack of ability of the lobsters to swim away effectively. Their most well-known defense mechanism is the rasping sound that they make when attacked by a predator. The spiny lobster uses this rasp as a startle or aposematic signal. This rasp can also be coupled with the flashing of their spines to deter predators from attacking them and to let them go free.
There is an annual migration, in which spiny lobsters enter shallower water in spring and summer, and head out to deeper water in fall and winter, reaching depths as great as , perhaps to avoid the effects of winter storms.
The California Spiny Lobster plays a key role in structuring communities in kelp forests. However, the increase in fishing has decreased both the population size and the body size of the lobster. This has changed the trends in predation of the lobster because the lobster’s predators need to eat more lobster because of their smaller sizes. Also their larger body size is one of the ways that California spiny lobsters deter predators so with decreasing numbers they are less likely to deter the predators causing a decline in numbers.
Acoustic signaling California spiny lobsters use acoustic signaling as a defense mechanism because they lack large pinchers on their claws. To produce this rasp sound, they have a sound-producing apparatus at the base of their spiny antennae evolved approximately 125 million years ago.
To produce this sound the lobsters rub a soft-tissue extension at the base of each antenna over a smooth file under each eye. The sound is created using stick-slip friction between the antenna and the surface under the eye. Because they use non-rigid surfaces to produce these stick-slip sounds the lobsters can continue to generate these sounds during their molt cycle which provides acoustic defenses when their exoskeletons are softened. Even though their physical defenses are weakened during their molt cycle they can still defend themselves using acoustic defenses.
The antenna is used for both mechanical and acoustic weaponry because they can use their spiny, sharp antennae as a shield or a sword to ward off the predator and they use their antennas to make the screeching, rasping sound that startles the predator. Once physically contacted by the predator the California spiny lobster makes the rasp sound. This rasp functions both as a vibratory escape mechanism and as an acoustic startle mechanism. Not only does the rasp sound startle the predator but the vibrations that are caused from this rasp sound cause the predator to loosen its grip on the lobsters, allowing for the lobster to escape. The vibrations can also orient the predator toward the antennae, which can cause the predator to attack the antenna. If the predator attacks the antennae then the lobster can make an escape and leave their antennae behind. They can grow back their antenna after subsequent molts. The acoustic structures don’t differ between males and females.
Life cycle
Female California spiny lobsters reach sexual maturity at a length of , which is typically at an age of 5–9 years; males are sexually mature after 3–6 years. Because all the hard parts are lost at each molt, the life span of mature spiny lobsters is uncertain; they are thought to live for 50 years or more.
Spiny lobsters do not have the gonopods (first pleopods modified for reproduction) that occur in clawed lobsters and crabs, and females do not have a deep pocket on the sternum in which to store sperm. Instead, a spermatophore is transferred directly from one of the male's gonopores to the sternum of the female. The male gonopore is, however, adorned with a "penile process", which is straight and serrated, with a small "hairbrush". The sternum of mature females has three "windows" on the last three segments, which uniquely among Panulirus species, span both halves of the sternum. These windows are softer than the rest of the exoskeleton, and are thought to help the male locate the correct location to place the tar-like spermatophore.
After mating, the fertilized eggs are carried on the female's pleopods until they hatch, with between 120,000 and 680,000 carried by a single female. The eggs begin coral red, but darken as they develop to a deep maroon. When she is carrying the eggs, the female is said to be "berried". The eggs are ready to hatch after 10 weeks, and spawning takes place from May to August, The larvae that hatch (called phyllosoma larvae) do not resemble the adults. Instead, they are flat, transparent animals around long, but as thin as a sheet of paper. The larvae feed on plankton, and grow through ten molts into ten further larval stages, the last of which is around long. California spiny lobsters have complex and extended pelagic larval phases. During this phase the lobsters pass through 11 distinct developmental stages. The majority of these phases occur while the lobsters are tens to hundreds of kilometers off the shore in oceanic waters. While they are in the larvae phase offshore, the spiny lobster larvae cycle through the oceans for 6-9 months before they settle. Because they cycle through the ocean for so long it is very unlikely that co-denning lobsters are kin.