Question

Green crabs (Carcinus maenas) are hyperosmotic regulators in brackish waters. When water salinity is lowered, a green crab responds by increasing its rate of urine production; its urine output, on average, rises from 4% to 30% of its body weight per day when the ambient salinity is reduced from 35 g/kg to 14 g/kg. Explain the value of this response. If one arranges to keep a green crab in full-strength seawater and bathe just its antennules with an alternative water source, urine production increases as the salinity of the water bathing the antennules is lowered. What can one conclude from this result?

Answer 1

Step-by-step explanation:

Green crabs have chemoreceptors located on an antenna.

These are long segmented appendages near the crab´s eyes that have both chemoreceptors and allow them to feel the surroundings.

Crabs also have antennules, like short appendages close to the antennas that allow them to sense their environment. A crab can "taste" using hairs on their mouthparts, pincers and even its feet.

So they can detect the salinity of the water by "taste" using the antennules. If these antennules are bathed with nonsalty water, the information the crab´s brain receives is to increase the salinity of its body by the system explained above, increasing its rate of urine production.

I hope it helps!