The Sea of Kythera is known for its rich sea flora and the cleanliness of its waters. The sea floor is rocky and steep and waters run very deep. At a mere 40 to 50 nautical miles to the west of the island the sea depth reaches 3,000 to 4,000 m, and southwest of Cape Tainaron the sea is 4,500 m deep, the deepest point of the Mediterranean Sea. The strong currents, combined with strong and virtually permanent winds, are not conducive to the setting-up of fish farms. Species of fish found in the Sea of Kythera include the red mullet, the common sea bream, the common dentex, the Mediterranean grouper, the scorpion fish, the bogue, the picarel, the saddle bream, the sea bream, the bass, the whiting, the Spanish sea bream, the redfish, the moray eel, etc. Cephalopods living in Kytherean waters include the octopus, the cuttlefish and the squid. Among the shellfish we find the lobster, the crab and the crayfish. Among the mollusks the most famous is Bolinus brandaris, called “porphyra” in Greek. Known since the Antiquity, porphyra was the raw material for the crimson hue, which was used to dye the cloths of Byzantine emperors.
The Monachus monachus seal is a frequent visitor of the island of Kythera, where it finds shelter. Unfortunately, only a little over a dozen of these seals still live around the island. Dolphins can often be seen off the coast of Kythera as well as a species of whale. Dolphins prefer to swim in the waters between Cape Spathi (north of Kythera) and the small Dragonares islands (towards the east) where there is plenty of food. The loggerhead turtle can often be seen in the Sea of Kythera.