Family Bythograeidae: Highly Specialized Crabs

By Rachael Ragen, SRC intern

The Family Bythograeidae are marine crabs that live near thermal vents. Most of them are colorless, but some may be yellow in color. The eggs and megalopa, which is a post-larva stage of the crab, tend to be orange or red. This coloration is likely due to carotenoids produced by hydrothermal vent bacteria, on which the crabs may be preying. Bythograeidae crabs are influenced by their environment including gametogenesis, which is part of the reproduction process for crabs. As different biological factors in their surroundings fluctuate, the size of oocyst and the rate of gametogenisis also changes. Their climate is therefore incredibly important to their survival.

Bythograeidae crab [Leignel, V., L. A. Hurtado, and M. Segonzac. “Ecology, adaptation, and acclimatisation mechanisms of Bythograeidae Williams, 1980, a unique endemic hydrothermal vent crabs family: current state of knowledge.” Marine and Freshwater Research, 2018, 69, 1-15.]

Hydrothermal vents present a very extreme habitat since they are located in deep sea environments and thermal vents release hot clouds full of chemicals. These crabs must withstand a high pressure climate of about 125 atm and a low temperature of about 2 to 25ºC. The environmental factors also tends to fluctuate frequently. In response to the fluctuations in their surroundings, these crabs are osmoconformers, meaning they can handle changes in salinity. Despite the importance of their environmental factors, there is not a distinct pattern in biogeography.

hydrothermal vent [http://www.photolib.noaa.gov/htmls/expl2218.htm]

As a result of their harsh living conditions, these crabs have developed many specialized behaviors. Since hydrothermal vents release a large amount of chemicals, these crabs must actively remove chemicals from their system. They are also able to handle higher metal concentrations due to episymbiotic bacteria, which has a symbiotic relationship with the crabs and lives on their shell, which aids in detoxification. Studies have shown that the crucial factor for these crabs is temperature and suffer once past their ideal range.

Works Cited:

Leignel, V., L. A. Hurtado, and M. Segonzac. “Ecology, adaptation, and acclimatisation mechanisms of Bythograeidae Williams, 1980, a unique endemic hydrothermal vent crabs family: current state of knowledge.” Marine and Freshwater Research, 2018, 69, 1-15.

 

Decorating behavior begins immediately after metamorphosis in the decorator crab Oregonia gracilis

By Nicolas Lubitz, SRC intern

Invertebrates, animals without a backbone, are the oldest form of animals that exist on our planet. The first fossils of invertebrates date back to 665 million years ago, and are sponges. Since then, they have diversified into a spectacular array of organisms, both marine and terrestrial. From insects, to squids and corals, to jellyfish, their forms and shapes seem to know no limits. Some studies suggest that invertebrates make up 97% of all animal life on the face of the earth. For example, coral reefs provide shelter and structures for other organisms, most invertebrates are prey for higher organisms, but many invertebrates are predators themselves, like squid. With no doubt those creatures are vital to our marine and terrestrial ecosystems, and understanding their biology helps us to ultimately understand how every part of an ecosystem revolves around another part.

Figure 1. Invertebrate diversity (http://www.deepseanews.com/2011/11/octopi-wall-street/)

Figure 1. Invertebrate diversity (http://www.deepseanews.com/2011/11/octopi-wall-street/)

Because of the fantastic diversity of tasks they perform conserving invertebrate diversity is important to ocean health. Steven R. Hein and Molly W. Jacobs from the University of Washington and Miami University, respectively, have shown that there is even more to consider when looking at marine invertebrates. In their recent paper they looked at the decorator crab Oregonia gracilis (figure 1). Decorator crabs are known to use debris and other organisms such as sponges and algae to cover their outer layer, most likely for camouflage and protection. Just like other invertebrates of the order crustacea (which includes crabs and lobsters) decorator crabs go through different stages in their lives from larvae, to an intermediate phase, the so called megalopa, to a juvenile phase to the final adult stage. Each phase is very different in appearance and behavior. Hein and Jacobs were interested in how those different life stages utilize different habitats and different forms of debris and organisms to decorate themselves and how.

The decorator crab, Oregonia gracilis (http://www.crabs.ru/russia/fam_oregoniidae_oregonia_gracilis.htm)

Figure 2. The decorator crab, Oregonia gracilis (http://www.crabs.ru/russia/fam_oregoniidae_oregonia_gracilis.htm)

In order to do so, they collected and bred different life stages of this particular decorator crab species and provided them with different decorating materials and habitats and compared the different stages for preferences. The results are clear: Although the early megalopa phases were found in mostly the same habitat as the juvenile phase, they did not decorate themselves at all. Juveniles, on the other side, utilized free floating organic debris to cover themselves which in turn is very different from adult individuals who use algae, sponges and other organisms. According to the researchers, the different body shapes of megalopae, juveniles, and adults requires all phases to adapt to different niches in order to survive.

When we look back to our idea of conservation we realize that when trying to come up with regulations and protective measurements for such organisms we should understand every single life stage of this particular organisms in order to ensure their conservation and protection. Hein and Jacobs indirectly demonstrated that laying out conservation measurements for just the adult phase appears to be insufficient since the whole life cycle has to be taken into consideration. Here we see that conservation is an integrative field and includes many components that we must look at for conserving our oceans.

Reference

Hein, S.R. & Jacobs, M.W. (2016) Decorating behavior begins immediately after metamorphosis in the decorator crab Oregonia gracilis. Marine Ecology Progress Series, 555, 141–150.