Coastal marine and estuarine ecosystems are highly productive and serve a nursery function for important fisheries species. They also suffer some of the highest rates of degradation from human ...impacts of any ecosystems. Identifying and valuing nursery habitats is a critical part of their conservation, but current assessment practices typically take a static approach by considering habitats as individual and homogeneous entities. Here, we review current definitions of nursery habitat and propose a novel approach for assigning nursery areas for mobile fauna that incorporates critical ecological habitat linkages. We introduce the term ‘seascape nurseries’, which conceptualizes a nursery as a spatially explicit seascape consisting of multiple mosaics of habitat patches that are functionally connected. Hotspots of animal abundances/productivity identify the core area of a habitat mosaic, which is spatially constrained by the home ranges of its occupants. Migration pathways connecting such hotspots at larger spatial and temporal scales, through ontogenetic habitat shifts or inshore–offshore migrations, should be identified and incorporated. The proposed approach provides a realistic step forward in the identification and management of critical coastal areas, especially in situations where large habitat units or entire water bodies cannot be protected as a whole due to socio‐economic, practical or other considerations.
Coastal ecosystems, such as estuaries, salt marshes, mangroves and seagrass meadows, comprise some of the world’s most productive and ecologically significant ecosystems. Currently, the predominant ...factor considered in valuing coastal wetlands as fish habitats is the contribution they make to offshore, adult fish stocks via ontogenetic migrations. However, the true value of coastal nurseries for fish is much more extensive, involving several additional, fundamentally important ecosystem processes. Overlooking these broader aspects when identifying and valuing habitats risks suboptimal conservation outcomes, especially given the intense competing human pressures on coastlines and the likelihood that protection will have to be focussed on specific locations rather than across broad sweeps of individual habitat types. We describe 10 key components of nursery habitat value grouped into three types: (1) connectivity and population dynamics (includes connectivity, ontogenetic migration and seascape migration), (2) ecological and ecophysiological factors (includes ecotone effects, ecophysiological factors, food/predation trade-offs and food webs) and (3) resource dynamics (includes resource availability, ontogenetic diet shifts and allochthonous inputs). By accounting for ecosystem complexities and spatial and temporal variation, these additional components offer a more comprehensive account of habitat value. We explicitly identify research needs and methods to support a broader assessment of nursery habitat value. We also explain how, by better synthesising results from existing research, some of the seemingly complex aspects of this broader view can be addressed efficiently.
Fragmentation is a major driver of ecosystem degradation, reducing the capacity of habitats to provide many important ecosystem services. Mangrove ecosystem services, such as erosion prevention, ...shoreline protection and mitigation of climate change (through carbon sequestration), depend on the size and arrangement of forest patches, but we know little about broad-scale patterns of mangrove forest fragmentation. Here we conduct a multi-scale analysis using global estimates of mangrove density and regional drivers of mangrove deforestation to map relationships between habitat loss and fragmentation. Mangrove fragmentation was ubiquitous; however, there are geographic disparities between mangrove loss and fragmentation; some regions, like Cambodia and the southern Caribbean, had relatively little loss, but their forests have been extensively fragmented. In Southeast Asia, a global hotspot of mangrove loss, the conversion of forests to aquaculture and rice plantations were the biggest drivers of loss (>50%) and fragmentation. Surprisingly, conversion of forests to oil palm plantations, responsible for >15% of all deforestation in Southeast Asia, was only weakly correlated with mangrove fragmentation. Thus, the management of different deforestation drivers may increase or decrease fragmentation. Our findings suggest that large scale monitoring of mangrove forests should also consider fragmentation. This work highlights that regional priorities for conservation based on forest loss rates can overlook fragmentation and associated loss of ecosystem functionality.
Habitat loss is accelerating a global extinction crisis. Conservation requires understanding links between species and habitats. Emerging research is revealing important associations between ...vegetated coastal wetlands and marine megafauna, such as cetaceans, sea turtles, and sharks. But these links have not been reviewed and the importance of these globally declining habitats is undervalued. Here, we identify associations for 102 marine megafauna species that utilize these habitats, increasing the number of species with associations based on current International Union for the Conservation of Nature (IUCN) species assessments by 59% to 174, accounting for over 13% of all marine megafauna. We conclude that coastal wetlands require greater protection to support marine megafauna, and present a simple, effective framework to improve the inclusion of habitat associations within species assessments.
Marine megafauna and vegetated coastal wetland habitats (seagrasses, saltmarshes, and mangroves) are under intense threat and declining globally.Emerging research and novel methodologies have unveiled important, previously unknown habitat associations between marine megafauna and these habitats.Unless we can conceptualize and critically examine these habitat associations, management and conservation can be undermined.Identifying threatened species that are dependent on threatened habitats is essential for informing on actions to prevent population declines.
As human impacts increase in coastal regions, there is concern that critical habitats that provide the foundation of entire ecosystems are in decline. Seagrass meadows face growing threats such as ...poor water quality and coastal development. To determine the status of seagrass meadows over time, we reconstructed time series of meadow area from 175 studies that surveyed 547 sites around the world. We found an overall trajectory of decline in all seven bioregions with a global net loss of 5602 km2 (19.1% of surveyed meadow area) occurring since 1880. Declines have typically been non‐linear, with rapid and historical losses observed in several bioregions. The greatest net losses of area occurred in four bioregions (Tropical Atlantic, Temperate North Atlantic East, Temperate Southern Oceans and Tropical Indo‐Pacific), with declining trends being the slowest and most consistent in the latter two bioregions. In some bioregions, trends have recently stabilised or reversed. Losses, however, still outweigh gains. Despite consistent global declines, meadows show high variability in trajectories, within and across bioregions, highlighting the importance of local context. Studies identified 12 different drivers of meadow area change, with coastal development and water quality as the most commonly cited. Overall, however, attributions were primarily descriptive and only 10% of studies used inferential attributions. Although ours is the most comprehensive dataset to date, it still represents only one‐tenth of known global seagrass extent, with conspicuous historical and geographic biases in sampling. It therefore remains unclear whether the bioregional patterns of change documented here reflect changes in the world's unmonitored seagrass meadows. The variability in seagrass meadow trajectories, and the attribution of change to numerous drivers, suggest we urgently need to improve understanding of the causes of seagrass meadow loss if we are to improve local‐scale management.
We reconstructed time series of seagrass meadow area at 547 sites and found declining trends in all seven bioregions with a total loss of 5602 km2 (19.1% of surveyed meadow area) since 1880. Declines were usually non‐linear, often with rapid losses, but, in some bioregions trends have recently stabilised or reversed. Meanwhile, in individual meadows, trends were highly variable. Poor water quality and coastal development were commonly cited reasons for change; however, these attributions were primarily descriptive. This suggests that we urgently need to improve understanding of the causes of seagrass meadow loss if we are to improve local‐scale management.
This study aims to determine the drivers of root decomposition and its role in carbon (C) budgets in mangroves and saltmarsh. We review the patterns of root decomposition, and its contribution to C ...budgets, in mangroves and saltmarsh: the impact of climatic (temperature and precipitation), geographic (latitude), temporal (decay period) and biotic (ecosystem type) drivers using multiple regression models. Best-fit models explain 50% and 48% of the variance in mangrove and saltmarsh root decay rates, respectively. A combination of biotic, climatic, geographic and temporal drivers influences root decay rates. Rainfall and latitude have the strongest influence on root decomposition rates in saltmarsh. For mangroves, forest type is the most important; decomposition is faster in riverine mangroves than other types. Mangrove species Avicennia marina and saltmarsh species Spartina maritima and Phragmites australis have the highest root decomposition rates. Root decomposition rates of mangroves were slightly higher in the Indo-west Pacific region (average 0.16%day−1) than in the Atlantic-east Pacific region (0.13%day−1). Mangrove root decomposition rates also show a negative exponential relationship with porewater salinity. In mangroves, global root decomposition rates are 0.15%day−1 based on the median value of rates in individual studies (and 0.14%day−1 after adjusting for area of mangroves at different latitudes). In saltmarsh, global root decomposition rates average 0.12%day−1 (no adjustment for area with latitude necessary). Our global estimate of the amount of root decomposing is 10TgCyr−1 in mangroves (8TgCyr−1 adjusted for area by latitude) and 31TgCyr−1 in saltmarsh. Local root C burial rates reported herein are 51–54gCm−2yr−1 for mangroves (58–61TgCyr−1 adjusted for area by latitude) and 191gCm−2yr−1 for saltmarsh. These values account for 24.1–29.1% (mangroves) and 77.9% (saltmarsh) of the reported sediment C accumulation rates in these habitats. Globally, dead root C production is the significant source of stored sediment C in mangroves and saltmarsh.
Mangroves have among the highest carbon densities of any tropical forest. These ‘blue carbon’ ecosystems can store large amounts of carbon for long periods, and their protection reduces greenhouse ...gas emissions and supports climate change mitigation. Incorporating mangroves into Nationally Determined Contributions to the Paris Agreement and their valuation on carbon markets requires predicting how the management of different land-uses can prevent future greenhouse gas emissions and increase CO2 sequestration. We integrated comprehensive global datasets for carbon stocks, mangrove distribution, deforestation rates, and land-use change drivers into a predictive model of mangrove carbon emissions. We project emissions and foregone soil carbon sequestration potential under ‘business as usual’ rates of mangrove loss. Emissions from mangrove loss could reach 2391 Tg CO2 eq by the end of the century, or 3392 Tg CO2 eq when considering foregone soil carbon sequestration. The highest emissions were predicted in southeast and south Asia (West Coral Triangle, Sunda Shelf, and the Bay of Bengal) due to conversion to aquaculture or agriculture, followed by the Caribbean (Tropical Northwest Atlantic) due to clearing and erosion, and the Andaman coast (West Myanmar) and north Brazil due to erosion. Together, these six regions accounted for 90% of the total potential CO2 eq future emissions. Mangrove loss has been slowing, and global emissions could be more than halved if reduced loss rates remain in the future. Notably, the location of global emission hotspots was consistent with every dataset used to calculate deforestation rates or with alternative assumptions about carbon storage and emissions. Our results indicate the regions in need of policy actions to address emissions arising from mangrove loss and the drivers that could be managed to prevent them.
With the growth of smartphone usage the number of social media posts has significantly increased and represents potentially valuable information for management, including of natural resources and the ...environment. Already, evidence of using ‘human sensor’ in crises management suggests that collective knowledge could be used to complement traditional monitoring. This research uses Twitter data posted from the Great Barrier Reef region, Australia, to assess whether the extent and type of data could be used to Great Barrier Reef organisations as part of their monitoring program. The analysis reveals that large amounts of tweets, covering the geographic area of interest, are available and that the pool of information providers is greatly enhanced by the large number of tourists to this region. A keyword and sentiment analysis demonstrates the usefulness of the Twitter data, but also highlights that the actual number of Reef-related tweets is comparatively small and lacks specificity. Suggestions for further steps towards the development of an integrative data platform that incorporates social media are provided.
•The geographic spread of Twitter posts makes them useful for environmental research.•A critical mass of tweets is obtained in regions that are frequented by tourists.•A small proportion of tweets refer to marine environmental conditions.•Sentiment analysis is useful to monitor human perceptions of key marine targets.•More environmental research using collective knowledge is warranted.
To promote the sequestration of blue carbon, resource managers rely on best-management practices that have historically included protecting and restoring vegetated coastal habitats (seagrasses, tidal ...marshes, and mangroves), but are now beginning to incorporate catchment-level approaches. Drawing upon knowledge from a broad range of environmental variables that influence blue carbon sequestration, including warming, carbon dioxide levels, water depth, nutrients, runoff, bioturbation, physical disturbances, and tidal exchange, we discuss three potential management strategies that hold promise for optimizing coastal blue carbon sequestration: (1) reducing anthropogenic nutrient inputs, (2) reinstating top-down control of bioturbator populations, and (3) restoring hydrology. By means of case studies, we explore how these three strategies can minimize blue carbon losses and maximize gains. A key research priority is to more accurately quantify the impacts of these strategies on atmospheric greenhouse-gas emissions in different settings at landscape scales.
Summary
Stable isotopes of carbon and nitrogen are mainstay tracers in diverse fields of ecology, particularly in studies of food webs.
Investigators are generally interested in tracing dietary C and ...N, and hence routinely remove non‐dietary, inorganic C contained in calcified structures (e.g. shells, bones) by chemical dissolution of the carbonates. Acid treatment can, however, isotopically fractionate samples if part of the organic matter is lost or chemically modified, resulting in potentially altered δ13C and δ15N values.
Here, we synthesize the effects of acid treatments on stable isotope analysis reported in the literature, showing that: (i) the method can change both δ13C and δ15N values; (ii) shifts in δ13C are generally, but not always, consistent with expectations of more depleted carbon ratios after the removal of the isotopically heavier inorganic carbonates; (iii) nitrogen ratios either decrease or increase in 15N content; and (iv) the majority (74–79% of comparisons) of reported changes to δ13C and δ15N values attributable to acid treatment are <1 ‰, but larger acid effects can occur.
Acidification is needed if mechanical removal of calcified structures is unfeasible in carbonate‐rich sample matrices containing low organic C and N, but should otherwise be very carefully considered before its use as a routine pre‐treatment step of biological samples in isotope ratio mass spectrometry.
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