The short-term impacts of a cyclone on seagrass communities in Southwest Madagascar

Abstract

Cyclones are large-scale disturbances with highly destructive potential in coastal ecosystems. On February 22, 2013, a powerful tropical cyclone made landfall on the southwest coast of Madagascar, a region which is infrequently hit by such extreme weather events coming from the Mozambique Channel. Seagrass ecosystems, which provide valuable ecosystems services to local communities, are especially vulnerable because they thrive in shallow waters. The impact of Cyclone Haruna on seagrass diversity, height and coverage and associated fish diversity, abundance and biomass was assessed in 3 sites near Andavadoaka (22°07'S, 43°23'E) before and after the event using fish underwater visual census, video-transects, and seagrass quadrats. The cyclone caused a significant loss in seagrass cover at all 3 sites. Thalassia hemprichii and Syringodium isoetifolium were the most affected species. Andavadoaka beach, the most exposed site, which was also subject to human use and was most fragmented, suffered the largest negative effects of the cyclone. Cyclone Haruna was not found to significantly affect fish assemblages, which are highly mobile organisms able to use a diversity of niches and adjacent habitats after seagrass fragmentation. Extensive sampling and longer time-scale studies would be needed to fully evaluate the cyclone impact on communities of seagrass and fish, and track potential recovery in seagrass coverage. The intensity and destructive potential of cyclones is expected to increase with global warming, which is of concern for developing countries that encompass most of the world's seagrass beds. This study provided a unique and key opportunity to monitor immediate impacts of an extreme disturbance in a region where cyclones rarely hit coastal ecosystems and where local populations remain highly dependent on seagrass meadows.

Spatial Patterns of Coral Community Structure in the Toliara Region of Southwest Madagascar and Implications for Conservation and Management

“…Tropical storms and cyclones generally hit Madagascar from November to May, and are common in the northern and eastern part of the island (94 tropical cyclones recorded from 1948 to 2010) [36]. The southwest region is less affected as the passage or formation of cyclones in the Mozambique channel is relatively rare [37,38]. Malagasy coral reefs have suffered from bleaching events caused by abnormal increases in SST, with major events in 1998 and 2015-2016.…”

Earth observation for ecosystem accounting: spatially explicit national seagrass extent and carbon stock in Kenya, Tanzania, Mozambique and Madagascar

“…These highly valued seagrass ecosystem services are yet facing numerous challenges. More frequent and intense tropical storms, rising thermal stresses and sea level, coastal eutrophication and development, overfishing and seaweed farming are all impacting seagrass health and the livelihoods of their dependent coastal societies (Amone‐Mabuto et al., 2017; Côté‐Laurin et al., 2017; Cullen‐Unsworth et al., 2014; Eklöf et al., 2008; United Nations Environment Programme, 2020a, SMART Seas, 2021). These threats are coupled with uneven levels of protection: only Madagascar recognizes the climate change mitigation and adaptation benefits of seagrasses, while Tanzania only recognizes their adaptation potential (Herr & Landis, 2016).…”

Hydrodynamics across seagrass meadows and its impacts on Indonesian coastal ecosystems: A review

“…The eroded sediment mostly buried the canopies, and the loss due to 1 day storm was estimated to be equal to that of −160 years of anthropogenic influences (Oprandi et al, 2020). Similar extreme events resulting in massive losses have been documented in other areas across the globe, such as the United States (e.g., Carlson et al, 2010) or Africa (e.g., Côté-Laurin et al, 2017). Interestingly, while shorelines and seagrass meadows may suffer significant physical damage after high wave events, which is a consequence of the flexible shoot structures, many reports show seagrass meadows could recover quickly.…”