Deep-sea Spider Crabs: Behold! The Crimson Hue
August 20, 2004
Western Washington University
Found in water 900-3000 m deep, the deep-sea spider crab, Macroregonia macrochira, is most abundant around a depth of 3,000 m. The wide ranges of depths at which these crabs can live makes them unique, and they may have several physiological adaptations that make them well suited for the extreme conditions at depth, including inflated brachial chambers, elongated legs, and bright red color.
We take several measurements and samples from each crab we collect. We measure carapace (shell) length and width, and claw height. (Claw height serves as an indicator of maturity and tells us whether the crab is a juvenile or adult.) We dissect the crabs to look at gonad size and color to determine reproductive potential. During the dissection, we will also take a gill sample for DNA analysis.
Blood samples also give us additional insight into growth and reproduction by enabling us to measure hormone levels and to study growth potential. Crabs must molt, or cast off their old shell, in order to grow. Ecdysteroids are hormones that control the molting process and the regeneration of lost limbs. These hormones also play a role in reproduction; and blood levels of these hormones are high during egg development and decrease after egg extrusion. Thus, we can predict when a crab will molt and assess where it is in its reproductive cycle by studying its hormone levels.
We will be using an enzyme-linked immunosorbent assay (ELISA) to determine hormone levels from the blood samples we collect. I expect the deep-sea spider crab to have lower hormone levels compared to other species of Majidea (spider) crabs that are found at shallower depths because of the lower availability of food in the deep sea. The reason for this is crabs are unable to produce sterols, which are key building blocks for the production of ecdysteriod hormones, so cholesterol (a type of sterol) is an important factor in crabs diets. Reduced food availability means lower cholesterol in-take, which in turn manifests as a lower concentration of ecdysteroid hormones in the blood.
Armed with this understanding, we will be able to learn a lot about deep-sea spider crabs from the blood samples we have collected on this cruise. Our findings may even help us understand more about the two commercially important species of spider crabs, the tanner and snow crabs.
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