Not every threat faced by young South African fur seals is as obvious as a shark or hyena. As NATURE's GOLDEN SEALS OF THE SKELETON COAST shows, the red or brown clouds that sometimes appear along the coastline like oil slicks can also pack a deadly punch.

These "red tides" are actually masses of algae: microscopic, single-celled plants that live in the sea. While most species of algae are not harmful, and are indeed necessary to sustain life in the sea, a few produce potent neurological poisons. These chemicals can become concentrated in algae-eating fish and crustaceans, then poison and paralyze the birds and seals that feed on them. Red tides can also use up the oxygen in seawater, suffocating sea life. That happens when the algae die and decompose on the bottom.

While the exact causes of red tides vary -- they can be sparked by changes in water temperature or nutrients, and some scientists believe that human pollution is making them worse -- their effects can be dramatic. As GOLDEN SEALS shows, one red tide off South Africa caused millions of spiny lobsters to flee the sea and pile up on beaches. Birds and seals -- and people -- feasted on the disoriented crustaceans, which cost up to $15 a pound at restaurants. Hundreds of police were called in to head off the near riots that had accompanied an earlier red tide.

"If they allow the people to pick up the kreef (lobsters), there will be chaos again," Sonya Strydom of the Elands Bay hotel predicted to local reporters. At the earlier mass beaching, she noted, "People came from all over [to collect the delicacies]. They drove their vehicles over people's lawns, over the dunes; they stole dustbins so they could put the crayfish in them." All in all, she said, the red tide "was terrible" for everyone involved.