This relaxing Minute features a colourful character, and its relationship with anemones, as well as certain coral species, and even some sea cucumbers: Harlequin Crab (Lissocarcinus laevis). In it, we see a Harlequin crab caught with its hand in the cookie jar, as it tries to get to some food before the anemone can eat it.
Take your minute to relax with Harlequin Crab (Lissocarcinus laevis)
As we look closely at this little scoundrel, we can see that the last hind legs are larger and flatter than the other ones. This is because they belong to the Portunidae family, also known as swimming crabs. With these flattened hind legs, these creatures are capable of swimming through the water column, when the need arises. However, like most swimming crabs, Lissocarcinus laevis prefers to keep its feet firmly on the seafloor, or on its host for that matter. But it’s nice to have options.
Smooth and colourful
This small, yet ornate species of swimming crab has a very smooth, reddish, light brown carapace with large white to yellow spots and markings which are often interconnected. So smooth in fact, that their genus name actually means „smooth crab“. Its claws are banded with white and brown/red bands. The females can be slightly larger than the males and can grow to a width of about 3,5cm, with a body that is wider than it is long.
As with most crustaceans, after the eggs are fertilised by the male, they’re carried under the body of the female, who will protect and oxygenate them, until it’s time to release them. Once they hatch, the larvae go through a pelagic phase of several weeks, before settling down and growing into their adult form.
In relation with Harlequin Crab (Lissocarcinus laevis)
They are guided to their host species, by the chemicals these host creatures release, to attract their symbionts. Interestingly enough, the chemicals produced by these host species might actually be meant to deter predators and parasites, but for Lissocarcinus laevis it’s a chemical trail, that leads to a compatible host, and hopefully the start of a long-lasting symbiotic relationship.
Chemical sensing is considered to be the most ancient and universal form of communication in the biosphere. All living organisms are able to detect chemical cues in their respective environments. These cues allow for different types of intra- and interspecific interactions between organisms. For example, mate recognition, prey/predator interactions, and symbiotic associations. The communication between symbionts and their hosts is needed to ensure appropriate host selection, as well as maintaining the symbiotic relationship through time, but is just one of the many chemical conversations that are taking place below the surface of the ocean.
Commensal relationship or mutually beneficial?
Although the symbiotic relationship of the Harlequin crab with its host is very common throughout the Indo-Pacific, the exact nature of the relationship between the hosts and symbiont is still somewhat unclear. Something which has made it very hard for scientists to classify their relationship on the symbiotic spectrum. It is currently listed as “commensal”, meaning one species gains benefits from the relationship while the other neither benefits nor is harmed.
Harlequin crabs are predators, that eat shrimps and other tiny planktonic organisms, as well as leftover food from their hosts. Scientists believe it might also be feeding on parasites from its hosts. If true, it might mean another shift on the symbiotic spectrum, but no studies have been done yet to prove this hypothesis.