Competitive relationships between algae and corals on damaged coral reefs
Natural and anthropogenic catastrophes that occurred on coral reefs of the World Ocean at the end of the past century and at the beginning of this one and consequences of the catastrophes for ecosystems of the tropical shelf are described on the basis of literature data and our own investigations. During the last decades, coral abundance on coral reefs in the tropics and subtropics declined by 80% and in some regions corals disappeared completely. Biodiversity of coral reefs was significantly reduced. The main reason for the changes is elevated (by 1-2°С) temperature of surface sea water, compared to the average temperature during the hot season. The future fate of damaged coral reefs is discussed. Presumably, in unpolluted waters coral communities can recover after their damage and partial mortality, but in waters polluted due to human activity coral reefs degrade. The recovery rate of coral reefs depends on hydrological and hydrochemical conditions, the frequency of natural catastrophes, and competitive relationships between algae and corals on the damaged reef. Several aspects of the competitive relationships between algae and corals are considered in detail: the dynamics of overgrowth of the damaged and dead corals by algae of different species, mechanisms of competitive relationships, the influence of environmental conditions on competitive properties of corals and algae, and endogenous conditions of winning in the competitive struggle. The hypothesis of coral reef restoration via its temporary reformation into a plant reef is suggested. It is assumed that in the absence of natural catastrophes coral reefs damaged due to elevated temperatures can be restored to the original or changed state within several decades, but only in unpolluted waters.