Ricardo Calado on Calcinus Hermit Crabs
Hermit Crabs from the Genus Calcinus

Doctor Ricardo J G Calado is an assistant researcher at the CESAM Centre for Environmental and Marine Studies, which is part of the Department of Biology at the University of Aveiro, Campus Universitário de Santiago in Aveiro, Portugal. While that is impressive, we are even more impressed with his knowledge of hermit crabs fron the genus Calcinus. These are the small hermit crabs that we at Blue Zoo Aquatics highly recommend for detritus clean-up crews. They also happen to do a great job with some nuisance algae.

Dr. Calado was kind enough to sit down with Blue Zoo News recently to share some of his insight on this fantastic reef aquarium hermit crab.

BZN: Thanks so much for taking the time to chat with us about these little hermit crabs. To begin with, what can be said in general about the genus?

RC: It is a widely distributed genus of small and colorful hermit crabs—mainly occurring in the Indo-West Pacific, but with species also being recorded from the East Pacific, West Atlantic and East Atlantic—which is incredibly popular among marine aquarium keepers. The first species in this genus was described in 1836 by H. Milne Edwards from New Guinea and is a commonly available species in the aquarium trade known as Calcinus elegans or the electric blue hermit crab.

BZN: What ecological niche do species in this genus fulfill?

RC: These organisms are very common on intertidal and subtidal rocky shores, although species that inhabit deeper waters are also present in the genus. For example, Calcinus anani commonly occurs between 100 and 250 m of depth.

BZN: What is the taxonomical state of the genus at present? How many species have been reliably described?

RC: Currently, between 45 to 50 species are known. The attention currently paid to color pattern—a feature that can now be easily recorded after the advent of digital photography and that was commonly lost in preserved specimens in museums—has allowed researchers to discover and validate several new species. In fact, for the genus Calcinus, coloration is an extremely important diagnosing character.

BZN: In terms of your research, have you witnessed reproduction in the laboratory? If so, what conditions were optimal for reproduction?

RC: Yes I have. Just the average conditions which are also commonly displayed by reef tanks; they don’t require any particular feature. It is much more common to record copulation between a pair of hermit crabs than to witness the exact moment when newly hatched larvae start leaving the female shell. You must be really lucky to witness that!

BZN: You have said that there is "high maternal reproductive investment" in some species. What does this mean exactly?

RC: When a female hermit crab only produces a couple of eggs—some species may only produce two embryos per brood—these are commonly larger than average and display high energetic reserves that enable the larvae to hatch in a much more advanced stage of development than it normally happens for other species in the genus. This strategy of producing highly energetic oocytes—and in this way decrease the chances of their larvae being exposed to starvation periods due to food patchiness—always require a higher maternal reproductive investment, since the energy required to produce these oocytes will not be used elsewhere—e.g. in growth.

BZN: In your opinion, are species from the genus Calcinus good detritivores?

RC: Yes, and also a good choice to control the growth of certain nuisance algae that sometimes may take over reef tanks.

BZN: Are any species, in your opinion, better suited for aquaria?

RC: Those species commonly traded, such as Calcinus tibicen and C. Elegans, are highly suitable for reef tanks.

BZN: Finally, I have seen your paper titled "Marine ornamental species from European waters". Can you briefly tell our readers what our thesis in that paper is?

RC: Basically it is an alert for the potential that many species that occur in European waters present for the aquarium industry—including a Calcinus species, C. Tubularis—due to their stunning coloration and ability to stand reef tank temperatures (26-28ºC). The current lack of suitable legislation to regulate the collection and trade of these organisms may be a major problem in the near future, and an unmonitored collection of these organisms, which unfortunately is already taking place for some species of snails and decapod crustaceans, may result in an unsustainable practice that may enhance the pressure on European coastal ecosystems.

BZN: That is not unlike some of the problems we see with various sub-tropical snails on the West Coast of the America. Perhaps we’ll learn more on that issue from you in the future, but for now, thank you for taking the time to sit down and speak with us about hermit crabs from the genus Calcinus. We’re sure our readers will appreciate your perspective, and we would welcome you back at any time to chat more about hermit crabs, marine aquaria or anything else.

Published 15 July 2008. © Blue Zoo Aquatics