Have you seen me? The Breede estuary shoreline is littered with the fragile shells of the Heart Urchin or sometimes known as a Sea Potato (Echinocardium cordatum). The color is grey or light brown. The spines are of variable length. The diameter is usually no more then 5 cm, but individuals as large as 9 cm have been reported.
They live buried, just below the surface, in sandy substrate and depend on sheltered areas as the shell is incredibly fragile. Echinocardium is usually found at depths of about 2 cm to 7 cm below the surface of the sand, and its presence is recognized mainly by the characteristic funnel-and-hole above it marking the top of its respiratory opening, through which it draws down seawater containing oxygen.
The explanation usually given is that they have been killed by severe storms which have disturbed the seabed, first burying the urchins deeply enough to suffocate them, and later exposing them again, either throwing the dead urchins or bare ‘tests’ (the thin white shells that reveal the heart shape) on to the shore, or leaving them lying on the seabed. Another explanation is algal blooms. However, we have had neither of these and the Heart Urchins appeared before the much-appreciated rain this week so we are a bit stumped – anyone with any suggestions?