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Decapod crustaceans
A large and diverse group
30/11/2021
There are many species that we can find on the coast. One of the funniest are crabs: fast crustaceans that play hide and seek among rocks or sand. Also the lobsters with long antennae that act as sensors. Hermit crabs are good illusionists: inside their shell and still, it seems that the shell is empty. Prawns, lively dancers in the water. These and many other species are part of what we call ‘decapod crustaceans’ and everyone can contribute to their study through Observadores del Mar.
As species closely linked to gastronomy, we could expect that its life cycle and all its characteristics are well known. But there are species such as the lobster - the most emblematic species -, of which some aspects are still unknown, for example: his juvenile phase. Although the adult lobster was already known in Aristotle's time, it was not until 1995 that the juvenile lobster was discovered. Probably we weren’t looking for it in the right way, since the juvenile lobster is not found as deep as the adult lobster and can be seen at 15-20 meters deep. However, it is not easy to see; it hides between blocks of calcareous rock. To find it, we have to look between May and September (although the cycle is moving to June) and, very close to the bottom of the rock, we can try to glimpse its antennae and follow them until we see its small body identical in shape to that of the adult. We have to look at 'clean' rocks, without algae, since with their antennas - which are like sensors - they perceive their surroundings and the algae prevent them from doing so.
Like the lobster, there are other species with gastronomic value. One of them is the blue crab Callinectes sapidus, a species from the Atlantic and highly invasive in the Mediterranean. The blue crab is a predator that eats absolutely everything; it is omnivorous, scavenger and can even feed on its congeners. Its voracity is such that in the Ebro Delta it has wiped out all the crustaceans and molluscs in the area. Another invasive crab is Percnon gibbesi, a flat brown crustacean that reached the Balearic Sea at the end of the 20th century —the first dates were in the north of Mallorca, in Albufera, and in Menorca. It is an herbivorous species; it feeds mainly on algae. We can find it on flat rocks but hides very quickly. We still need to know its ecosystem impact; at the moment it is known that wherever this species is found, the abundance of algae decreases.
Speaking of non-native species, we could mention some curiosities at a global level. For example, in Japan we find the largest species in the world, called Macrocheira kaempfer. It is a giant crab, several meters in size taking into account its legs. Other species, on the other hand, can be very small and can be found by searching among the algae, but cannot be seen with the naked eye. If we want to look for nano crabs along the coasts of Mallorca, we can see them in Cystoseira —an alga shaped like a small fir tree and brown-garnet in color.
There are many species on the coast and maintaining biodiversity is vital for marine conservation. In this sense, , as in the case of Norway lobster - a species declared by FAO as overexploited - which has reappeared on the Catalan coast thanks to the existence of these protection zones. At Observadores del Mar and Fundación Marilles, and together with other organizations, we advocate promoting these areas and providing more resources to improve their management.
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Want to know more? Listen to our PODCAST episode nº06 "Crustáceos Decápodos".
This article was originaly posted at the Mallorca Daily Bulletin.
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Photo: Palinurus elephas by Juan Antonio Torres Balaguer. Source: Observadores del Mar.