it is known that coves are natural habbitats for mermaids, they're swarming with glowing fish and infested with algae.
The caves unique shapes of rock echo the mermaids singing further out making the trance stronger on the unknowing victim.
The shapes of the rocks also help mermaids to hide or camoufladge against predators considering mermaids do not have any form of offense.
Algae is known to stick on rocks or moist surfaces in coves. They contain a deadly poisen which mermaids
and fish are immune too. The chloryphyll contained in the algae shimmer a translucent blue making it easy
to lure animals into eating it, the poisin makes it's way down to the victims congestion system and slowly
but surely kills off the cells leaving the animal to turn purple and unresponsive.