Abstract
Tropical cyclones are extreme random meteorological events that can have profound implications to coastal biodiversities. Given that the frequency, intensity and duration of these events are poised to increase due to the global climate change, understanding the ecological impacts of such erratic occurrences becomes imperative to devise better management strategies. The eventful passage of the tropical cyclone, Phyan, along the northwestern coast of India in November 2009, coupled with the availability of historical data presented a rare opportunity to elucidate the consequences on the polychaete assemblages of the Malvan Marine Sanctuary and their subsequent recovery. This was achieved by comparison of the pre- and post-Phyan seasonal data from four different sites in and around the Sanctuary. MDS analyses and polychaete community parameters suggested conspicuous cyclone related effects on the polychaete community characteristics in the three outer stations off Malvan, whereas the relatively protected bay station remained more or less unscathed. Impacts, attributable to the cyclone apart from seasonal variations, included changes in polychaete composition, reductions in total polychaete density, species diversity, evenness and functional groups. Dominance of the opportunistic polychaete, Paraprionospiopatiens was all pervasive just after Phyan, resulting in poor diversity and evenness values. In the outer stations, diverse feeding modes present prior to the cyclone were replaced by microphagous feeders post the disturbance. However, the study also observed complete recovery as substantiated by the improvement inpolychaete density, diversity indices and re-instatement of multiple feeding guilds in affected areas. This resilience of the coastal waters off Malvan is attributed to its marine protected status, implying that reduced human interference aided rapid revival of damaged ecosystems.
Highlights
Tropical cyclones can be destructive, often leading to extensive damage to coastal zones, communities and ecosystems especially in the Indian Ocean rim countries[1].Extremely powerful cyclonesare especially significant in shaping benthic communities, having the potential to cause severe damage to benthic fauna over large areas
Re-suspension, deposition or erosion of seafloor sediments associated with high wave action and currents [2] as well as sudden salinity fluctuations associated with high-intensity tropical cyclones can cause high mortality and redistribution of macrobenthos[3,4].Changes in sediment granulometry subsequent to cyclones and tsunamis have been shownto have modified thecommunity composition and structure of resident benthic organisms[5,6]
Malvan coast, which is open to the Arabian Sea and dominated by rocky outcrops with intermittent sandy beaches has been declared by the Government of India a Marine Sanctuaryin 1987 to protect the fragile ecology of this marine hotspot and to buffer it from the high fishing activity and rapid urbanization of the town
Summary
Tropical cyclones can be destructive, often leading to extensive damage to coastal zones, communities and ecosystems especially in the Indian Ocean rim countries[1].Extremely powerful cyclonesare especially significant in shaping benthic communities, having the potential to cause severe damage to benthic fauna over large areas. Re-suspension, deposition or erosion of seafloor sediments associated with high wave action and currents [2] as well as sudden salinity fluctuations associated with high-intensity tropical cyclones can cause high mortality and redistribution of macrobenthos[3,4].Changes in sediment granulometry subsequent to cyclones and tsunamis have been shownto have modified thecommunity composition and structure of resident benthic organisms[5,6]. Defaunation resulting from such episodic perturbations, often leads to recolonisation by different functional groups,thereby creating shifts in benthicstructure[3]. In such an assessment of post-incident ecological modifications, the pre-impact datasets have a vital role for reliable evaluation which have been missing in several studies available in the literature.The present study compares the benthic ecological modifications induced due to the tropical cyclone, Phyan, at Malvan on the northwest coast of India which was being routinely monitored by us prior to the cyclone, providing an excellent opportunity for the post-cyclone assessment
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