The cyclones Domoina and Imboa struck the St Lucia area in January/February 1984. Research in progress at the time made it possible to assess some of the effects of these cyclones on the mangrove communities of the St Lucia Estuary. Assessment has been based on aerial and ground observations, litter studies in an Avicennia marina (Forssk.) Vierh. and a Bruguiera gymnorrhiza (L.) Lam. stand, mortality counts in the above B. gymnorrhiza stand and biomass determinations of algae epiphytic on A. marina pneumatophores. The heavy rainfall which accompanied the cyclones, and the subsequent flooding of the rivers, caused lake levels to rise and the floodwaters inflicted damage on mangrove stands. Destruction of the A. marina stand in which litter collections were being made, terminated this study. However, continued recordings were possible in the B. gymnorrhiza stand which enabled an assessment of the effects of the cyclones on the production of leaf and stem litter and reproductive material to be made. Die-back of branches and trees resulted in a significant increase in leaf litter for up to 8 months following the cyclones. Propagules and flowering material were lost in the floodwaters, the loss of the latter material causing minimal propagule production in the fruiting season after the cyclones. Total counts of trees and saplings 1 m and over revealed that B. gymnorrhiza suffered the greatest mortality with 67.1% living and 32.9% dead, whereas A. marina had 83.8% living and 16.2% dead. However, of all woody plants in this stand B. gymnorrhiza comprised 92% and A. marina 5.5%. Low biomass values of epiphytic algae were recorded as a result of the floodwaters, but recovery was rapid and very high yields were recorded the following warm season. The species composition of this algal community was not altered by the events. The immediate effects of the cyclones comprised damage to the standing crop by the direct impact of the floodwaters and also a loss of plant litter. Long-term effects included a reduction in propagative material and stress, resulting in leaf loss and death, mainly of B. gymnorrhiza.