Thresholds Database > Coral to brown algae, Caribbean Sea, South America

Background

By the late 1960's, high levels of fishing had significantly reduced fish biomass and by the late 1970's, the reefs were damaged, through the direct and indirect effects of fishing.

Alternate Regimes

1. Coral

2. Brown algae

Mechanism

Fishing first reduced the number of large predatory fish and when these populations were exhausted, herbivorous fish were caught. These herbivorous fish and the sea urchin Diadema both feed on algae, keeping it's density in check. The loss of the herbivorous fish provided a greater food source for Diadema, whose numbers increased. In 1981, a hurricane hit the area, killing or damaging most of the branching coral species, allowing for even more algal growth. The benthic algae were still controlled by Diadema until 1982/1983, when a species-specific pathogen killed 99% of the Diadema population in some areas. Brown algae then became very abundant, out-competing the remaining coral colonies and preventing coral larvae from settling.

Management Decisions in Each Regime