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Mantis Shrimp

News Article Description

The Mantis shrimp is an armoured small crustacean that hides in the sand or rocky corals. It is carnivorous and can snatch prey in a fraction of a second. The Mantis shrimp name comes from its raptorial appendages that are similar to those of a praying mantis. They have an extremely powerful striking force which is used to smash prey such as other crustaceans.

Mantis shrimps first appeared 400 million years ago. Since, they have evolved to be efficient predators. There are 500 known species of Mantis shrimp. However, these organisms are very difficult to find thus, there are likely still unidentified species.

Mantis shrimp have compound eyes like other crustaceans but much more specialized. Two eye parts at the top and bottom are involved in distance vision while the middle eye is made of 6 rows of facets and is used for other abilities. Vision is used to get intimate and to signal non lethal intent.

Distribution

Found in areas with suitable burrowing conditions in the Mediterranean sea. In this area, the mantis shrimp are considered by-caught in Tunisian waters. High abundances in the Gulf of Tunis, Hammamet and Gabes. Maximum abundances were found in shallower waters of 50 meters or less. The highest by-product catch counts were found to be in summer and autumn.Another study looking at the population demography and spatial distribution of the mantis shrimp found that there was a high abundance of the mantis shrimp off the pacific coast of Costa Rica. They found that 56.8% of the population were meals and the other 43.2% making up the females. Shockingly, when surveyed, 87% of trawlers had reported catching mantis shrimp as by-caught.

The global species distribution for 'Odontodactylus sycllarus' (Peacock mantis shrimp)

Mantis shrimp have also been found in a wide range of habitats ranging from shoreline to coral reefs and along the whole Chinese coast. In Taiwan, there exists clear genetic differences between northern and southern groups of mantis shrimp. Due to tectonic movement, climatic fluctuations and ocean currents in previous geographical periods, the genetic variation of the mantis shrimp is restricted to its location.Mantis shrimp are also distributed in Atlantic waters, commonly caught by-catch between Angola and the Gulf of Cadiaz which is the most northern distribution area of the Atlantic. Typically found from 3-150 meters depth but has been recorded at depths down to 367 meters.The spottail mantis shrimp is located in the mediterranean sea as well as southern Europe and along West Africa. It is commercially exploited in the Mediterranean and seen in seafood markets in Italy and Spain. Commonly caught in the deltas of major rivers such as the Po, Ebro, Guadalquivir, Rhone and Nile. Caught typically by bottom trawls but also by dredges, trammel nets, gill nets, baited traps and pots.Common to benthic ecosystems in tropical and subtropical marine and brackish waters worldwide. However, there are a few species known to inhabit temperate seas. There are currently 485 species, 115 genera and 17 families of mantis shrimp currently described. Overall distribution in the Western Indian ocean is from Yemen, India, Pakistan, Madagascar, South Africa, to Thailand, Taiwan, Australia and Central Pacific waters. Mantis shrimp have evolved to possess both powerful striking force as well as impact- resistant armor. It is hypothesized that these adaptations are a result of telson sparring observed in these organisms. Telson morphology is diverse among more than 500 species of mantis shrimp indicating differences in genetic make up due to environmental factors forcing adaptations.Mantis shrimp were able to change their color vision over evolutionary time. In juvenile shrimp, color vision can be adjusted based on depth and light conditions.

Ecology

Mantis shrimp spend most of their time buried in sediment and U-shaped burrows. They are known to keep their living spaces clean regardless of the substrates they live in. Mantis shrimp are not considered to be endangered by the IUCN, but face a variety of threats. As we now know, mantis shrimp use their incredible speed and raptorial appendages to quickly and efficiently disable prey. Studies have shown that these swift appendages have potential to be exposed and vulnerable to the increasingly acidic ocean waters due to their compositions.

Exposure to climate change and isolation pressures

Calcified organisms are normally subjected to increased oxidative stresses and changes in their mineral composition as a result of ocean acidification. Such changes are predicted to have detrimental effects on the integrity of the mantis shrimp’s raptorial appendage. However, a manipulative study determined that mantis shrimp were able to withstand wide ranges of pH and temperature without negative impacts on the functionality or composition of their raptorial appendage.  Another study argued that parapatric speciation and reproductive isolation was a viable threat to mantis shrimp populations by investigating causes for reduced stock abundance in Tokyo Bay in 2006. The study stock abundance was positively correlated with larval abundance levels. It also highlighted the fragility of the mantis shrimp’s reproductive cycle and how small shifts in stock abundance can significantly decrease spawning stock as a result. With regards to detrimental human impacts on marine environments, it is reasonable to assume that human-environment interactions are going to increase in the coming decades as our population increases. Given this assumption, mantis shrimp may see an increase in the external influences that caused the Tokyo Bay stock abundance to abruptly decrease. As the study suggests, it may potentially lead to a cascade of sequential, negative impacts that affect critical stability in spawning stock abundance.

Anthropogenic pressures and cannibalism

Another surprising yet terrifying finding from Bohai bay (渤海湾) in China found that as a result of increased anthropogenic influence and food depletion, an astounding 69.08% of all mantis shrimp surveyed had cannibalistic tendencies. This could potentially result in decreased spawn abundance if breeding females are heavily predated on as the previous study outlined.

Morphological Adaptations

Power

Rounded and blunt appendages in a contracted position

Mantis Shrimp have developed the ability to break the hardened shells of marine invertebrates with their raptorial appendages. Previous studies indicated that Stomatopod appendages were previously thought to be limited to a maximum speed of 10m/s, but a study conducted in 2004 recorded dactyl heel’s reaching speeds of 23m/s. This unforgiving speed is created through the use of a ‘click mechanism’ specialized to store potential energy that can easily be transferred into kinetic energy over a short period of time.

Variability in raptorial appendages

Raptorial appendages seen in mantis shrimp generally show one of 3 characteristics. These appendages can be rounded and blunt, spear-like or undifferentiated. The spear-like appendages have developed an elbow joint greatly altering the spring mechanics from rounded and blunt appendage bearing mantis shrimp. Investigations into the comparative spring mechanics present across mantis shrimp species have found that overall, more potent spring mechanisms seen in mantis shrimp with rounded appendages resulted in faster, and more powerful hammering strikes when compared to spearing species.

Compound eyes

The mantis shrimp's complex, image forming eyes

The visual system of the mantis shrimp has the most photoreceptor classes in any living organism. The retina contain as many as 10 visual pigments - each in different photoreceptor classes.There are standard hexagonal ommatidia like other crustaceans, and six bands of specialized ommatidia. The eyes each have two hemispherical halves where there is overlap of the visual field which help them see and catch prey at precise distances.  The compound eyes are mounted on stalks where six muscle groups aid the eye to move freely along all axes. The free moving eyes are kept still most of the time so that there are no issues with relative motion. Mantis shrimps have rapid eye movements and object tracking abilities.