Abandoned, lost and discarded fishing gear ‘ghost nets’ are increasing through time in Northern Australia

The remote Gulf of Carpentaria (GoC) represents 10% of Australia’s coastline. This large, shallow sea supports high value fishing activities and habitat for threatened species, and is a sink for abandoned, lost and discarded fishing gear (ALDFG) ‘ghost nets’, most originating from fishing activities outside of Australia’s Exclusive Economic Zone. With growing concerns about the plastic waste along the world’s coastlines, we retrospectively analyzed ghost net sighting information from four aerial surveys across 15 years, to investigate whether densities of ghost nets are changing through time or in space. We found an increase in ghost nets, despite more than a decade of illegal fishing countermeasure and clean-up efforts in the broader region. This demonstrates that the input of ALDFG into the system currently overwhelms the substantial net removal activities. We make recommendations for improving monitoring and consider the underlying drivers of nets being lost to improve ghost gear management on land and at sea

ENSO-driven extreme oscillations in mean sea level destabilise critical shoreline mangroves—An emerging threat

Recent ENSO-related, extreme low oscillations in mean sea level, referred to as ‘Taimasa’ in Samoa, have destabilised shoreline mangroves of tropical northern Australia, and possibly elsewhere. In 1982 and 2015, two catastrophic Taimasa each resulted in widespread mass dieback of ~76 km2 of shoreline mangroves along 2,000 km of Australia’s Gulf of Carpentaria. For the 2015 event, we determined that a temporary drop in sea level of ~0.4 metres for up to six months duration caused upper zone shoreline mangroves across the region to die from severe moisture deficit and desiccation. The two dramatic collapse events revealed a previously unrecognised vulnerability of semi-arid tidal wetland habitats to more extreme ENSO influences on sea level. In addition, we also observed a relationship between annual sea level oscillations and mangrove forest productivity where seasonal oscillations in mean sea level were co-incident with regular annual mangrove leaf growth during months of higher sea levels (March-May), and leaf shedding during lower sea levels (September-November). The combination of these periodic fluctuations in sea level defined a mangrove ‘Goldilocks’ zone of seasonal productivity during median-scale oscillations, bracketed by critical threshold events when sea levels became unusually low, or high. On the two occasions reported here when sea levels were extremely low, upper zone mangrove vegetation died en masse in synchrony across northern Australia. Such extreme pulse impacts combined with localised stressors profoundly threaten the longer-term survival of mangrove ecosystems and their benefits, like minimisation of shoreline erosion with rising sea levels. These new insights into such critical influences of climate and sea level on mangrove forests offer further affirmation of the urgency for implementing well-considered mitigation efforts for the protection of shoreline mangroves at risk, especially given predictions of future re-occurrences of extreme events affecting sea levels, combined with on-going pressure of rapidly rising sea levels

Winners and losers as mangrove, coral and seagrass ecosystems respond to sea-level rise in Solomon Islands

A 2007 earthquake in the western Solomon Islands resulted in a localised subsidence event in which sea level (relative to the previous coastal settings) rose approximately 30-70 cm, providing insight into impacts of future rapid changes to sea level on coastal ecosystems. Here, we show that increasing sea level by 30-70 cm can have contrasting impacts on mangrove, seagrass and coral reef ecosystems. Coral reef habitats were the clear winners with a steady lateral growth from 2006-2014, yielding a 157% increase in areal coverage over seven years. Mangrove ecosystems, on the other hand, suffered the largest impact through a rapid dieback of 35% (130 ha) of mangrove forest in the study area after subsidence. These forests, however, had partially recovered seven years after the earthquake albeit with a different community structure. The shallow seagrass ecosystems demonstrated the most dynamic response to relative shifts in sea level with both losses and gains in areal extent at small scales of 10-100 m. The results of this study emphasize the importance of considering the impacts of sea-level rise within a complex landscape in which winners and losers may vary over time and space

Public perceptions of mangrove forests matter for their conservation

Abstract not available

The Shoreline Video Assessment Method (S-VAM): using dynamic hyperlapse image acquisition to evaluate shoreline mangrove forest structure, values, degradation and threats

Climate change with human direct pressures represent significant threats to the resilience of shoreline habitats like mangroves. A rapid, whole-of-system assessment strategy is needed to evaluate such threats, better linking innovative remote sensing with essential on-ground evaluations. Using the Shoreline Video Assessment Method, we surveyed around 190 km of the mostly mangrove-fringed (78%) coastline of Kien Giang Province, Vietnam. The aim was to identify anthropogenic drivers of degradation, establishing baseline for specific rehabilitation and protection strategies. Fish traps occupy at least 87% of shoreline mangroves, around which there were abundant human activities – like fishing, crabbing, farming, plus collecting firewood and foliage. Such livelihoods were associated with remnant, fringing mangrove that were largely degraded and threatened by erosion retreat, herbivory, and excessive cutting. Our assessment quantified associated threats to shoreline stability, along with previous rehabilitation intervention measures. The method offers key opportunities for effective conservation and management of vulnerable shoreline habitats

More intense severe tropical cyclones in recent decades cause greater impacts on mangroves bordering Australia’s Great Barrier Reef

A number of published articles about the environmental impacts of climate change indicate that mangrove habitats are prone to greater damage from increasingly more intense tropical cyclones in recent decades. We reviewed such concerns by investigating the impacts of severe tropical cyclones (STCs) on shoreline mangroves bordering Australia’s Great Barrier Reef (GBR). Specifically, we considered the STCs having crossed the coastline during the last half century. There were 11 between 1987 and 2020. Available satellite data were used to quantify the extent and severity of damage to mangroves for each event, along with an appraisal of recovery. There were several significant findings. Firstly, we found that STC events had occurred widely across the GBR area from Torres Strait to the Tropic of Capricorn. Secondly, we observed notable increases in both the number and intensity of STCs. This was especially notable in the recent decade (2010-2019) with 7 in that decade, compared to the 0-2 per decade recorded earlier. This observation was significant because the damage to shoreline mangroves had increased markedly in unison with the increased intensity of recent STCs. We also observed some sites suffered repeated impacts from 2-3 STCs during the study period. These impacts were accumulative, further delaying and disrupting recovery. While natural recovery was shown to be efficient, the innate processes involved meant that it was linear taking set amounts of time. This situation presents natural resource managers with a well-known paradoxical dilemma of how to sustain natural ecosystems faced with unprecedented, ever-increasing external pressures? It seems the longer-term survival of mangrove ecosystems in the GBR area are becoming more dependent on adaptive management requiring threat minimisation whilst finding more effective ways to strengthen their resilience. In view of the rapidly changing environmental conditions, this study has demonstrated the considerable insights to be drawn from monitoring these valued coastal marine resources and one of the dominant driving processes

Processes and factors driving change in mangrove forests: an evaluation based on the mass dieback event in Australia’s Gulf of Carpentaria

A vast area of more than 80 km2 (6–10% of total) of mangrove forests bordering Australia’s Gulf of Carpentaria died en masse in late 2015 and early 2016. The dieback occurred over a number of months in synchrony across more than 1500 km of exposed Gulf shorelines. There are serious concerns about the implications of such an event given the important ecological and economic services provided by mangrove ecosystems, and the challenges to policy and management of such an abrupt loss of natural resources at both local and regional scales. In this chapter, we begin by structuring and quantifying the distinct and complex mix of processes involved in the natural establishment, growth, and development of mangrove stands in the context of enhanced environmental variability. Based on these findings, we develop a new evaluation framework to explain the severe response observed in late 2015 in mangroves of the Gulf of Carpentaria. We explore in detail the multiple drivers involved in the event and address the complex question of the role of climate change. These analyses and other observations about this unique event are brought together to assist the ongoing development and implementation of effective management policy, starting with monitoring programs at national and local scales. While this is a work in progress, these findings already provide unequivocal evidence that mangroves are vulnerable and acutely sensitive to extreme variations in sea level and climate change

Winners and losers as mangrove, coral and seagrass ecosystems respond to sea-level rise in Solomon Islands

A 2007 earthquake in the western Solomon Islands resulted in a localised subsidence event in which sea level (relative to the previous coastal settings) rose approximately 30-70 cm, providing insight into impacts of future rapid changes to sea level on coastal ecosystems. Here, we show that increasing sea level by 30-70 cm can have contrasting impacts on mangrove, seagrass and coral reef ecosystems. Coral reef habitats were the clear winners with a steady lateral growth from 2006-2014, yielding a 157% increase in areal coverage over seven years. Mangrove ecosystems, on the other hand, suffered the largest impact through a rapid dieback of 35% (130 ha) of mangrove forest in the study area after subsidence. These forests, however, had partially recovered seven years after the earthquake albeit with a different community structure. The shallow seagrass ecosystems demonstrated the most dynamic response to relative shifts in sea level with both losses and gains in areal extent at small scales of 10-100 m. The results of this study emphasize the importance of considering the impacts of sea-level rise within a complex landscape in which winners and losers may vary over time and space

Ices meets marine historical ecology: placing the history of fish and fisheries in current policy context

As a discipline, marine historical ecology (MHE) has contributed significantly to our understanding of the past state of the marine environment when levels of human impact were often very different from those today. What is less widely known is that insights from MHE have made headway into being applied within the context of present-day and long-term management and policy. This study draws attention to the applied value of MHE. We demonstrate that a broad knowledge base exists with potential for management application and advice, including the development of baselines and reference levels. Using a number of case studies from around the world, we showcase the value of historical ecology in understanding change and emphasize how it either has already informed management or has the potential to do so soon. We discuss these case studies in a context of the science-policy interface around six themes that are frequently targeted by current marine and maritime policies: climate change, biodiversity conservation, ecosystem structure, habitat integrity, food security, and human governance. We encourage science-policy bodies to actively engage with contributions from MHE, as well-informed policy decisions need to be framed within the context of historical reference points and past resource or ecosystem changes