Lobsters are armored bottom-dwellers that can live for years, and much of what shapes their lives happens out of sight on the seafloor. The biggest recent story about them is not fishing but water temperature, which has redrawn where American lobsters thrive.1Gulf Of Maine Research Institute. New Study: Warming, Conservation, and Lobsters The same warming that brought one region a historic boom pushed a neighboring population into steep decline. Lobsters also turn out to be more socially complex, and more likely to feel something like pain, than their reputation suggests.
How Lobsters Grow by Shedding Their Shells
A lobster’s shell can’t stretch, so the animal grows by molting: it splits and sheds the old shell and swells into a new, soft one. The new shell takes time to harden, which leaves the lobster vulnerable for a while. Hormones trigger the process, and injecting one such hormone can make lobsters molt on demand.2PubMed. Molt induction in lobsters (Homarus americanus) by intramuscular injection of ecdysterone triacetate
Young lobsters molt many times a year, while adults do it far less often. Each molt is a risky window, because predators and rivals can injure a soft animal, so a lobster hides in shelter until the new shell firms up. That’s also why a shell on a beach may be a molt, not a dead lobster. Because lobsters shed their shells, scientists long struggled to tell a lobster’s age. But tiny teeth in the lobster’s stomach lay down about one growth band a year, much like tree rings.3Canadian Journal of Fisheries and Aquatic Sciences. Direct determination of age in shrimps, crabs, and lobsters In Caribbean spiny lobsters of known age, band counts landed within one year of true age 94% of the time.4Fisheries Research. Gastric mill ossicles record chronological age in the Caribbean spiny lobster (Panulirus argus) Size alone is a poor guide to age, since same-size lobsters can differ in age.5Fisheries Research. Gastric mill ossicles record chronological age in the Caribbean spiny lobster (Panulirus argus) That matters for fishing rules: managers set limits by how fast lobsters reach breeding age, and guessing age from size can misjudge the stock.
Lost legs grow back over several molts. A lobster can drop a trapped or injured leg at a built-in breaking point.6Proceedings of the Royal Society of Edinburgh. Regeneration of the Legs of Decapod Crustacea from the Preformed Breaking Plane A valve-like flap at that point seals the wound, and it stops bleeding better than clotting does.7Proceedings of the Royal Society of Edinburgh. Regeneration of the Legs of Decapod Crustacea from the Preformed Breaking Plane A folded new limb bud then grows inside the old shell and expands to several times its size at the next molt.8Proceedings of the Royal Society of Edinburgh. Regeneration of the Legs of Decapod Crustacea from the Preformed Breaking Plane Even then, the new leg’s muscles need several days after molting before they work fully.9Proceedings of the Royal Society of Edinburgh. Regeneration of the Legs of Decapod Crustacea from the Preformed Breaking Plane
How Lobsters Communicate and Choose Mates
Lobsters release chemical signals in their urine, squirted from near the head, to tell rivals who is in charge.10PubMed. Spiny lobsters use urine-borne olfactory signaling and physical aggressive behaviors to influence social status of conspecifics When two male American lobsters meet again after a fight, the loser backs off almost at once on smelling the winner’s urine.11Behaviour. Olfactory Recognition of Urine Signals in Dominance Fights Between Male Lobster, Homarus Americanus In European lobsters, blocking urine release kept second-day fights long and fierce.12Marine and Freshwater Behaviour and Physiology. Maintenance of dominance is mediated by urinary chemical signals in male European lobsters, Homarus gammarus
Spiny lobsters use scent too. Dominant Caribbean spiny lobsters release urine far more often during encounters than subordinates do.13PubMed. Spiny lobsters use urine-borne olfactory signaling and physical aggressive behaviors to influence social status of conspecifics When dominants couldn’t release urine, they started more physical attacks.14PubMed. Spiny lobsters use urine-borne olfactory signaling and physical aggressive behaviors to influence social status of conspecifics Urine alone made lone spiny lobsters avoid an area, both in tanks and in the wild.15PubMed. Spiny lobsters use urine-borne olfactory signaling and physical aggressive behaviors to influence social status of conspecifics
Courtship is led by females. Female American lobsters do the searching, and they choose the locally dominant male.16Canadian Journal of Fisheries and Aquatic Sciences. Review of Sexual Selection and Chemical Communication in the Lobster, <i>Homarus americanus</i> A day or several before molting, she moves into his shelter and stays 1 to 2 weeks.17Canadian Journal of Fisheries and Aquatic Sciences. Review of Sexual Selection and Chemical Communication in the Lobster, <i>Homarus americanus</i> Mating happens about 30 minutes after she molts, while her shell is soft.18Canadian Journal of Fisheries and Aquatic Sciences. Review of Sexual Selection and Chemical Communication in the Lobster, <i>Homarus americanus</i>
She is defenseless while soft, and staying with a dominant male protects her. He, in turn, gains a mate by holding the best shelter.
Egg strategies differ between lobster types. Clawed lobsters tend to carry fewer, larger eggs.19Bulletin of Marine Science. Egg production and life-history strategies in some clawed and spiny lobster populations Spiny lobsters often make many small eggs to offset heavy losses among their young.20Bulletin of Marine Science. Egg production and life-history strategies in some clawed and spiny lobster populations
Where Lobsters Live and What Makes Good Habitat
In the Gulf of Maine, where lobsters live depends most strongly on water temperature and depth.21Marine Ecology Progress Series. Estimating spatial distribution of American lobster Homarus americanus using habitat variables Males and females shift their locations differently through the seasons.22Marine Ecology Progress Series. Estimating spatial distribution of American lobster Homarus americanus using habitat variables Suitable habitat also depends on salinity and seafloor type.23Journal of Shellfish Research. Spatiotemporal Variability of Suitable Habitat for American Lobster (Homarus Americanus) in Long Island Sound Across the Northeast U.S. shelf, the amount of tiny drifting animal food also shapes good habitat.24Fisheries Oceanography. Dynamic changes in American lobster suitable habitat distribution on the Northeast U.S. Shelf linked to oceanographic conditions
The ideal home is a rocky bottom with crevices to hide in. Lobsters forage mostly at night and shelter by day, and many move to deeper water in winter and shallower in summer. Young lobsters need cobble shelter to survive.
Bottom temperature matters more than surface temperature because lobsters live on the seafloor. Bottom water can be much colder or warmer than the top. Good lobster habitat has grown in the Gulf of Maine and shrunk in southern New England.25Fisheries Oceanography. Dynamic changes in American lobster suitable habitat distribution on the Northeast U.S. Shelf linked to oceanographic conditions
How Warming Water Created a Boom and a Bust
Over about 30 years, the Gulf of Maine lobster population rose an estimated 515%.26Gulf Of Maine Research Institute. New Study: Warming, Conservation, and Lobsters The southern New England population fell an estimated 78% in the same period.27Gulf Of Maine Research Institute. New Study: Warming, Conservation, and Lobsters Warming shifted the best summer temperatures northeast.28Gulf Of Maine Research Institute. New Study: Warming, Conservation, and Lobsters
South of Cape Cod, warming pushes water past 20°C, above what lobsters tolerate well.29PubMed Central. The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine That heat has been tied to stress, more disease and mass die-offs.30PubMed Central. The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine The deaths cut breeding and the number of young settling on the bottom.31PubMed Central. The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine
In the Gulf of Maine, warming brought more seafloor into the temperature range young lobsters need to settle.32PubMed Central. The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine Lobster harvests rose about sixfold historically.33PubMed Central. The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine Within Maine, the biggest catches have shifted from the southwest coast to the middle and northeast coast.34Frontiers in Marine Science. Spatial dynamics of Maine lobster landings in a changing coastal system
Acidification is a second threat. In more acidic water, American lobster larvae grew shorter shells and took longer to reach each stage.35JNAFS. Ocean Acidification Decreases Growth and Development in American Lobster (Homarus americanus) Larvae European lobster larvae in acidic water ended up with lighter, less mineralized shells.36Biogeosciences. Effect of CO2-related acidification on aspects of the larval development of the European lobster, Homarus gammarus (L.)
Whether Maine’s boom lasts is an open question. The same warming that helped could push Maine past the 20°C limit too, as southern New England shows.
For lobster towns, the shift is already real. Fishing communities in the south lost much of their catch, while northeastern Maine harbors gained new income.
Shell Disease and Lobster Health
In shell disease, bacteria eat away the shell, leaving dark pitted patches. Warmer water and shell disease both changed the mix of bacteria living on lobster shells.37bioRxiv. Warmer water temperature and epizootic shell disease reduces diversity but increases cultivability of bacteria on the shells of American Lobster (Homarus americanus) Some bacteria common on healthy shells were missing or scarce on diseased ones.38bioRxiv. Warmer water temperature and epizootic shell disease reduces diversity but increases cultivability of bacteria on the shells of American Lobster (Homarus americanus) Yet possible disease-causing bacteria were found on all shells, sick or healthy.39bioRxiv. Warmer water temperature and epizootic shell disease reduces diversity but increases cultivability of bacteria on the shells of American Lobster (Homarus americanus)
The dark, eroded spots can spread, and badly affected lobsters may die during molting. The meat is generally still safe, but the lobster is hard to sell. Heat stresses lobsters and weakens their defenses, and shell disease spread most where water got hottest, which adds to the decline in the south.
Bacteria inside lobsters matter too. Gut bacteria help spiny lobsters digest food, make vitamins and fight infection.40Fishes. Gastrointestinal Microbiota of Spiny Lobster: A Review Viral infection can change those gut bacteria in young Caribbean spiny lobsters.41PubMed. Alterations in the gut-associated microbiota of juvenile Caribbean spiny lobsters Panulirus argus (Latreille, 1804) infected with PaV1
How Traps Are Designed to Protect Young Lobsters
Lobsters are measured by carapace length, the length of the main body shell behind the eyes. An escape vent is an opening in the trap that lets small lobsters crawl out. A single 45 by 152 mm vent made traps effectively release lobsters under an 81 mm legal size.42Marine Fisheries Review. The Effects of Different Escape Vents on the Selectivity of Lobster Traps But in Mexican spiny lobster traps, undersized lobsters still made up 83 to 92% of the catch even with vents.43Ciencias Marinas. Escape vents in traps for the fishery of the California spiny lobster, Panulirus interruptus, in Baja California Sur, Mexico Vent design has to fit the species and place to work well. Letting small lobsters go matters because they need to survive to breed at least once, and releasing them in the trap avoids handling injuries.
Other rules work alongside vents. Many areas protect egg-carrying females, and some protect very large breeders with a maximum size. Trap limits and licenses cap fishing effort.
Lobster Gear and Endangered Whales
Right whales are dying from ship strikes and entanglement in trap ropes.44ICES Journal of Marine Science. How we can all stop killing whales: a proposal to avoid whale entanglement in fishing gear Fishing rope has become much stronger, making entanglements more often deadly.45ICES Journal of Marine Science. How we can all stop killing whales: a proposal to avoid whale entanglement in fishing gear The proposed fix is to remove vertical ropes from the water entirely.46ICES Journal of Marine Science. How we can all stop killing whales: a proposal to avoid whale entanglement in fishing gear Traps would be marked electronically and raised only when the boat arrives.47ICES Journal of Marine Science. How we can all stop killing whales: a proposal to avoid whale entanglement in fishing gear
A traditional trap line runs from the seafloor to a surface buoy. Ropeless traps instead release a buoy or line on an acoustic signal, and fishers find their traps on a digital map rather than by buoy.
Fishers are wary. New gear is costly to buy and learn, and without buoys, boats may set traps over each other’s. Closures to protect whales can be costlier still.
Why Lobsters Matter to Kelp Forests
California spiny lobsters are key predators of sea urchins, which eat kelp.48californiampas.org. Lobster Biology, Habitat, and Conservation Insights Without predators, urchins multiply and strip kelp forests bare.49californiampas.org. Lobster Biology, Habitat, and Conservation Insights Heavy lobster fishing likely contributed to destructive urchin grazing from the 1950s on.50Journal of Experimental Marine Biology and Ecology. Spiny lobsters and sea urchins: Analysis of a predator-prey interaction After disease wiped out sunflower sea stars, lobsters and sheephead fish still kept urchins low inside protected areas.51PubMed Central. Trophic redundancy and predator size class structure drive differences in kelp forest ecosystem dynamics Kelp shelters fish and other sea life, while urchin barrens are bare rock with little life.
Big lobsters matter most because large ones can crack larger urchins. Fishing removes the biggest ones first.
Do Lobsters Feel Pain
Crustaceans meet several signs of possible pain: suitable nerves, learning to avoid harm, and protective behaviors such as guarding an injury.52Applied Animal Behaviour Science. Pain and stress in crustaceans? Norway lobsters tail-flipped when given electric shocks.53PubMed Central. Effects of analgesia on the response to a noxious stimulus in Norway lobsters (Nephrops norvegicus) Aspirin and the numbing drug lidocaine reduced that reaction.54PubMed Central. Effects of analgesia on the response to a noxious stimulus in Norway lobsters (Nephrops norvegicus) That suggests the shock felt like a negative experience, not just a reflex.55PubMed Central. Effects of analgesia on the response to a noxious stimulus in Norway lobsters (Nephrops norvegicus) Shocked crustaceans also showed stress chemistry beyond what their movement explained.56PubMed Central. A History of Pain Studies and Changing Attitudes to the Welfare of Crustaceans Even being handled stressed Norway lobsters.57PubMed Central. Effects of analgesia on the response to a noxious stimulus in Norway lobsters (Nephrops norvegicus)
Their stress systems work similarly to those of vertebrates, so they may suffer in similar ways.58Applied Animal Behaviour Science. Pain and stress in crustaceans? How lobsters are handled and killed in the food industry may therefore pose welfare problems.59Applied Animal Behaviour Science. Pain and stress in crustaceans?
Some countries, such as Switzerland and the UK, now recognize crustacean welfare. Stunning or quick splitting before cooking is promoted as more humane, and keeping lobsters cool and handling them gently reduces stress.
Scientists still debate it. Pain-like behavior doesn’t prove a conscious feeling, and lobster brains are built very differently from ours. Still, many researchers see the response to painkillers as one of the stronger signs.
From Prison Food to Luxury and Farming
In early America, lobster was so plentiful it was considered poor people’s food and even fertilizer.60Business Insider. The Remarkable Story Of How Lobster Went From Being Used As Fertilizer To A Beloved Delicacy In the mid-1800s, canned lobster and train travel spread demand inland and to coastal tourists.61Business Insider. The Remarkable Story Of How Lobster Went From Being Used As Fertilizer To A Beloved Delicacy Prices climbed from the 1880s, and by World War II lobster was a delicacy.62Business Insider. The Remarkable Story Of How Lobster Went From Being Used As Fertilizer To A Beloved Delicacy
Farming has been held back by cannibalism, which forces each lobster into its own cage.63Elsevier / Aquacultural Engineering. Commercial land-based farming of European lobster (Homarus gammarus L.) in recirculating aquaculture system (RAS) using a single cage approach It also needs heated water, good feed and costly equipment.64Elsevier / Aquacultural Engineering. Commercial land-based farming of European lobster (Homarus gammarus L.) in recirculating aquaculture system (RAS) using a single cage approach Still, a Norwegian farm now raises European lobsters to plate size on land, using robots and cameras to watch each animal.65Elsevier / Aquacultural Engineering. Commercial land-based farming of European lobster (Homarus gammarus L.) in recirculating aquaculture system (RAS) using a single cage approach Hatcheries also raise young lobsters to restock the wild.