Large-scale dieback of mangroves in Australia

Abstract

This study records and documents the most severe and notable instance ever reported of sudden and widespread dieback of mangrove vegetation. Between late 2015 and early 2016, extensive areas of mangrove tidal wetland vegetation died back along 1000km of the shoreline of Australia’s remote Gulf of Carpentaria. The cause is not fully explained, but the timing was coincident with an extreme weather event; notably one of high temperatures and low precipitation lacking storm winds. The dieback was severe and widespread, affecting more than 7400ha or 6% of mangrove vegetation in the affected area from Roper River estuary in the Northern Territory, east to Karumba in Queensland. At the time, there was an unusually lengthy period of severe drought conditions, unprecedented high temperatures and a temporary drop in sea level. Although consequential moisture stress appears to have contributed to the cause, this occurrence was further coincidental with heat-stressed coral bleaching. This article describes the effect and diagnostic features of this severe dieback event in the Gulf, and considers potential causal factors.

The state of the world’s mangroves in the 21st century under climate change

“…In addition to sea-level rise, climate change is expected to result in increased frequency and intensity of rainfall and associated flooding that can discharge massive amounts of sediment into nearshore environments, which then provide favorable new substrate for rapid seaward expansion of mangroves, as has been observed in Northern Australia along the Gulf of Carpentaria (Ashbridge et al, 2016). However, this expansion of mangrove area may be short-lived if it is followed by a large-scale drought, as has more recently occurred along the Gulf of Carpentaria (Duke et al, 2017). The rapid mangrove expansion and growth documented by Ashbridge et al (2016) following the sedimentation event may have made the mangroves along that coast more sensitive to the drought conditions that followed (Lovelock et al, 2009).…”

“…Alongi (2015) predicted that the impact of climate change would be felt most acutely by mangroves along arid coasts as salinities increase, freshwater supplies decrease, and critical temperature thresholds are reached. This prediction was recently borne out by large diebacks of mangroves along Australia's Gulf of Carpentaria (Duke et al, 2017) and the coast of Western Australia (Lovelock et al, 2017b) in response to a prolonged drought. Mangroves are also expected to decline along riverine systems as a result of reduced sediment supplies, increased salinities, and higher sea levels (Alongi, 2015), as have already been observed in many mangrove systems (e.g., Lovelock et al, 2015;Woodroffe et al, 2016;Meeder et al, 2017).…”

“…This is due in large part to anthropogenic impacts on mangroves, including conversion to aquaculture and agriculture, urbanization, and pollution (UNEP, 2014). As a transitional intertidal ecosystem, mangrove forests are also considered to be particularly vulnerable to climate change stressors, such as sea-level rise (Lovelock et al, 2015) and drought (Duke et al, 2017), where changing environmental conditions push mangroves beyond speciesspecific thresholds of tolerance (Ball, 1988). Mangrove loss may not always be attributable to a single driver like agriculture; instead, many natural and anthropogenic stressors often interact additively or synergistically, leading to rapid and large-scale dieoffs in some locales, exemplified by recent (2016) events in Australia (Duke et al, 2017;Lovelock et al, 2017a).…”

Wetlands In a Changing Climate: Science, Policy and Management

“…However, such invasions significantly change habitat structure and we know little about impacts on biotic interactions, potential lags for co-evolved species to shift, or challenges to mosquito control management (Dale et al 2013). While SLR is expected to enable mangroves to migrate inland where other obstacles do not occur, the example of mangrove dieback in northern Australia (Duke et al 2017) shows that the impact of climate is more complex, with changes in the regional climate patterns resulting in lower rainfall and tidal depression during the hot part of the year being suggested as the cause of the dieback.…”

Simple Modeling to Inform Harvest Strategy Policy for a Data‐Moderate Crab Fishery

“…The catch in the WGOCMCF in 2016 was exceptionally poor, coinciding with prolonged drought conditions, significant mangrove dieback, and extreme ocean‐warming events (Duke et al. ; Benthuysen et al. ).…”