Authorities in Cape Town predicted that the ecological damage from an oil spill caused by a tanker that sank Friday could get much worse. The slick reached the mainland Saturday, the day after the Panamanian-registered Treasure went down. The Robben Island nature reserve, home to about 14,000 endangered adult jackass penguins and 6,000 chicks, was hit badly. The South African Maritime Safety Authority estimated that 400 tons of oil were released. Earlier estimates had put the amount spilled at between 100 and 300 tons.