Oratosquilla oratoria, commonly known as the Japanese mantis shrimp, is a species of mantis shrimp found in the western Pacific. It is known as shako in Japan, where it is widely harvested and eaten as sushi. This species is an important commercial fishing target and widely consumed in many countries along the coast of the Northwest Pacific Ocean.
It is a secondary consumer in its natural habitats, preying upon small creatures and being eaten by large fish and Cephalopods. Like other members of its order it has a powerful spear, which it uses to hunt invertebrates and small fish. It grows to a length of , and lives at depths of .
It lives in burrows on the muddy seafloor and conducts most of its activities inside those burrows, including spawning and feeding, for predator protection. This species has great temperature tolerance. Through altering its metabolic pathways it can regulate temperature sensitivity, allowing it to occupy a wide range of habitats. This species has been observed outside of its native range. It is now considered an invasive species in both New Zealand and Australia. Similar environmental conditions of the habitats, including muddy estuaries, have promoted the establishment of new invasive populations.
Similar to other Stomatopods, mantis shrimp possess highly specialized sensory systems to facilitate hunting and mating. Its complex compound eyes allow it to detect a broad spectrum of wavelengths, even ultraviolet and polarized light. The sensitivity of its visual system, however, makes this species potentially vulnerable to artificial polarized light pollution. It also relies on sensitive antennules with a chemoreceptor to detect chemical cues dissolved in the water.
Its normal population distribution is influenced by density, since cannibalism is possible when other food sources are scarce. During the mating season of late spring and early summer, males and females perform intricate social behavior. Then, females lay and nurse their eggs in the burrows until the larvae hatch. Being pelagic instead of benthic, the larval stage of this species adopts a reflective camouflage called eyeshine as crypsis. Habitat
Environmental conditions
Geographic ranges Japanese mantis shrimp typically reside in a wide variety of habitats including the shore, coral reefs, and level substrates. It is native to the Northwestern Pacific in the oceans near Korea, Japan, Taiwan, China, and Vietnam. This species can be found in temperate, sub-tropical, and tropical regions, with water temperature ranging from −1°C in northern Japan during winter to >30°C in the South China Sea during summer.
Temperature tolerance Cold temperature can alter the physiological processes of this species at the cellular level, including metabolism, immune response, and reproduction. Low temperature slows down lipid metabolism shifting its metabolic mode from lipid oxidation to a carbohydrate-based metabolic pathway in order to maintain ATP production and support the survival of cells in a low-temperature environment. Cold temperature also imposes pressure on the immune system and induces expression changes of related genes. By enhancing antioxidant capacity, maintaining protein stability, and promoting immunity, the individual's tolerance to cold stress is further strengthened. In addition, cold temperatures can disrupt reproductive behaviors by reducing the expression of genes related to sex hormones and vision.
Adaptations to darkness The Japanese mantis shrimp can adapt to the dark environment. It reduces the metabolism rate by downregulating several key genes controlling the gluconeogenesis pathways and other metabolic activities. This means it will conserve its energy and redirect energy toward growth and development. Genes that promote cell proliferation and differentiation show upregulation. Individuals that stay in a darker environment can increase tissue composition and may grow faster. Adaptations of sensory systems are also involved, especially for vision. Genes related to eye development and perception are all significantly affected, along with evidence of retinal adaptation.
Invasion In recent years, the Japanese mantis shrimp has been artificially introduced to oceanic waters near Australia and New Zealand where it has become an invasive species.Ahyong, Shane T. The Marine Fauna of New Zealand: Mantis Shrimps (Crustacea:Stomatopoda). National Institute of Water and Atmospheric Research (NIWA), 2012. As an invasive species in New Zealand, the Japanese mantis shrimp was first observed in the Kaipara Harbour in 2009, and further observations have confirmed its distribution expansion to both the east and west coasts of the North Island. Japanese mantis shrimp prefer seafloors with muddy sediments, which is consistent with the local environments of those invaded estuaries. Macrofaunal species diversity in those sites is low, but the Japanese mantis shrimp may still act as an active bioturbator through burrowing, predation of small fish and invertebrates, and prey of large fish. Anthropogenic sediment input into the harbor may provide more available habitats for Japanese mantis shrimp, and its temperature tolerance range is wider than the actual measured water temperatures around New Zealand.
Burrowing The Japanese mantis shrimp typically resides on the muddy seafloor composed of silt and clay at a depth of less than 40 meters. It occupies long, U-shaped burrows in soft sediments, which it excavates with its maxillipeds. Similar to other species in the genus Oratosquilla, the Japanese mantis shrimp starts the construction of a burrow by removing sediments using its maxilliped, positioning sediments below its abdomen, and dispersing them backward with its pleopods. When the hole is 3-4 centimeters deep, the Japanese mantis shrimp dives in for further digging, where it makes a 90° turn to build a horizontal tube. This causes the burrow to have a distinctive elongated part in the vertical direction below the entrance. When the construction is finished, the Japanese mantis shrimp uses a cap made of sediments and self-produced secretion, with a nearly invisible hole in the center, to cover both entrances.
It stays tucked away within these burrows in the daylight hours for refuge. and rarely emerges except at night. Most of the day, it stays at the entrance, with only its eyes and antennules protruding out. The horizontal section has a diameter greater than the Japanese mantis shrimp itself, and its length is proportional to the size of the dweller.
Most daily activities are conducted here for convenience and safety. These burrows are used to spawn and lay eggs in. The inner wall of the burrow is smooth, and the remains of prey are often scattered on the flat floor. A constricted area is found at the center of the horizontal tube that divides it into two segments. Since two individuals are not observed to share the same burrow, an extra chamber may serve as an additional refuge against predators. If the burrow is not of compatible size, egg laying is inhibited. As a result, if the burrow becomes too small, the Japanese mantis shrimp will expand it, or create a more suitably sized one.
Hunting and diet
Prey capture The Japanese mantis shrimp is regarded as a secondary consumer, feeding mainly on primary consumers. It is a predator that actively hunts and kills its prey. When it gets close to prey and recognizes it as the target for attack, it suddenly and rapidly launches the attack. At night it emerges from its burrow to hunt prey which it then brings back to their burrow in order to feed. It is considered to be a type in between spearer types, which use their claws to pierce soft bodied prey, and smasher types, which use a club to smash hard bodied prey. Such raptorial appendages allow it to capture a wide range of prey.
Food preference It feeds on an assortment of organisms varying with habitat including crustaceans, mollusks, small rays, small fishes, worms and algae. Some researchers believe that the occasional presence of algae found in their stomach contents might have been ingested during the process of hunting. Similar to other Oratosquilla species, the Japanese mantis shrimp has shorter raptorial appendages and smaller eyes compared to other mantis shrimp species that are more specialized for hunting fish. In experimental tanks, the Oratosquilla species were observed to be less successful hunting for fish, and even if they catch fish, their appendages have difficulty fixing the prey for feeding. Gobiid fish were found in the stomach contents of wild Japanese mantis shrimp, indicating the mantis shrimp's ability to capture and consume fish. However, its hunting success often depends on whether its prey can respond and whether the prey can escape in time. Fish and shrimp are very mobile, followed by brachiopods and crabs, while mollusks are the least mobile and are thus more likely to be eaten by the mantis shrimps. Besides catching, fish have bony spines, and other crustaceans have a hard shell, which make them hard for the mantis shrimp to break using its mandibles. Although mollusks also have shells, large Japanese mantis shrimps were observed in the aquaria smashing the thick shell of Bivalvia and consuming the soft tissue inside. When encountering thin-shelled Bivalvia, it will break them up with its mandibles and consume the meat with fragments of shells. Juveniles and small individuals cannot break those hard shells as efficiently as large adults. Fish and Polychaeta also appear more frequently in large individuals' stomachs. Despite this potential preference, the exact prey choice is habitat- and environment-dependent.
Dietary switch and cannibalism Before spawning, large females switch their diets to be more mollusk-based and reduce hunting for crustaceans. Nevertheless, the feeding intensity remains the same during the reproductive period. Instead of relying on active energy intake from ingestion for gametogenesis, female Japanese mantis shrimps are considered to be conservative, where much of the energy for gametogenesis comes from relocation of energy from muscles and hepatopancreas to gonads. During the period of sexual maturation, the amount of lipids and protein in muscles and hepatopancreas decreases, consistent with the highest value of lipids and protein content in gonads.
They have also been observed to cannibalize smaller members of their species in times of food scarcity. Though cannibalism plays an important part in the life of Japanese mantis shrimp, it requires less energy to capture and feed on other smaller prey rather than conducting cannibalism, since other mantis shrimps not only have a harder exoskeleton but also possess defensive weapons (predatory appendages), which makes them hard to subdue.
Reproduction and life cycle
Maturation and mating behavior Reproduction for Japanese mantis shrimp occurs between mature inter-molt pairs. Female Japanese mantis shrimp achieve reproductive maturity by late spring to early summer lasting until fall while males have year round reproductive maturity. There are several behavioral components in its courtship. One mating behavior that it demonstrates is attenuation between male and female where they face each other and mutually stroke antennas for several seconds. They have also been found to engage in pair walking, where mates walk closely together side by side, and engage in brushing where the male brushes the female with its appendages.
Egg spawning