Palaemon elegans | What’s that marine bug?!

Gone snorkeling in Europe and saw a shrimp? If you were in the shallows, there’s a good chance you just met Palaemon elegans! Better known as the rockpool shrimp, or sometimes as grass prawn, this is one of the most ubiquitous invertebrates in the northeastern Atlantic, the Mediterranean and beyond.

If you spotted a rockpool shrimp and would like to know more, keep reading as we dive into its natural habitat, diet, habits and more.

Palaemon elegans appearance

The rockpool shrimp is a typical prawn in terms of appearance, so much so that it’s easy to confuse it with many of its cousins from the genus Palaemon, particularly Palaemon serratus. It grows to a maximum size of around 6 cm/2.4″ (with the females being larger than the males) and is mostly translucent.

Depending on the habitat, Palaemon elegans will usually sport a dark brown to black pattern of stripes and dashes, with white dots on the body and blue and yellow bands on the legs.

Name (common, scientific)Rockpool shrimp, Palaemon elegans
FamilyPalaemonidae
SpreadEuropean and North African waters
HabitatShallows and rock pools

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Palaemon elegans habitat

This prawn is ubiquitous in its natural range, which consists of the northeastern Atlantic as well as the Mediterranean Sea and Black Sea. As with many other species, also been much ado about it popping up in places where it doesn’t actually belong. According to the Invasive Species Compendium, it was introduced in the Caspian and Aral Seas back in the 1950s. It has also been spreading spectacularly quickly in the southern Baltic Sea, particularly on the Polish coast, and to the north up to Finland.

It’s not uncommon for Atlantic species to migrate further east (see the bearded fireworm in the Mediterranean, for example), but most don’t make it in areas like the Baltic Sea due to the higher salinity levels. The rockpool shrimp, though, doesn’t care much about the specific salt levels: it’s highly adaptable. This is one of the main reasons it has been able to spread so effectively. It has even been found on the east coast of the USA!

Palaemon elegans is a littoral species, meaning it inhabits shallow coastal zones as well as tide pools. It’s usually found in rocky zones, where it spends its time picking around for algae, biofilm and other edible morsels. For example, I took the photos featured in this article in Gran Canaria’s natural swimming pools, which are full of them. They like protected spots with some shade and cover from predators.

Palaemon elegans facts

Diet

Like most other shrimp, Palaemon elegans is an omnivore, and not a particularly picky one either. Whether it’s detritus, small organisms or algae, these guys will happily consume nearly everything.

One study found that individuals in the Baltic Sea ate around 60% animal matter and 40% algae, but those percentages may well vary based on what’s available at a particular location.

Reproduction

Palaemon elegans reproduces from spring to summer. Like other Palaemonid shrimp, it gives birth to larvae (also known as zoeae) rather than fully developed young. After mating, the female transfers hundreds of fertilized eggs from her ovaries to her belly, regularly fanning them with her back legs (also called pleopods) to keep them oxygenized. These eggs hatch into the zoeae, which do resemble shrimp but are so tiny they’re considered planktonic.

As the zoeae grow, they go through several different larval stages, each beginning with a molt of the exoskeleton. Eventually, they metamorphose into their adult form, although they will continue to grow and molt for around a year. The species’ total lifespan, according to one 2009 study, is 15 months for males and 21 months for females.

Use in research

A good bit of research has been done on Palaemon elegans. In particular, there are quite a few studies that look at the uptake and regulation of heavy metals like zinc, copper and cadmium by this shrimp species.

The interest in this topic is due to the fact that Palaemonid shrimp are actually able to somewhat regulate the levels of some of these metals in their body. This, in turn, is of interest because oceans across the world are increasingly contaminated with various heavy metals, which threatens many aquatic species.


If you have any more questions about Palaemon elegans or if you want to share something about your own encounters with this common rockpool shrimp, don’t hesitate to leave a comment below!

Sources

https://www.cabi.org/isc/datasheet/70617

Bilgin, S., Ozen, O., & SAmSuN, O. (2009). Sexual seasonal growth variation and reproduction biology of the rock pool prawn, Palaemon elegans (Decapoda: Palaemonidae) in the southern Black Sea. Scientia Marina73(2), 239-247.

Janas, U., Zarzycki, T., & Kozik, P. (2004). Palaemon elegans-a new component of the Gulf of Gdańsk macrofauna. Oceanologia46(1).

Jażdżewski, K., Konopacka, A., & Grabowski, M. (2005). Native and alien malacostracan Crustacea along the Polish Baltic Sea coast in the twentieth century. Oceanological and Hydrobiological Studies34(1), 175-193.

Lesutienė, J., Gasiūnaitė, Z. R., Strikaitytė, R., & Žilienė, R. (2014). Trophic position and basal energy sources of the invasive prawn Palaemon elegans in the exposed littoral of the SE Baltic Sea. Aquatic Invasions9(1).

White, S. L., & Rainbow, P. S. (1982). Regulation and accumulation of copper, zinc and cadmium by the shrimp Palaemon elegans. Marine Ecology Progress Series8(1), 95-101.