The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat-fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat-fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land-sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/10-1510.1

The value of estuarine and coastal ecosystem services

Marine ecosystems are centrally important to the biology of the planet, yet a comprehensive understanding of how anthropogenic climate change is affecting them has been poorly developed. Recent studies indicate that rapidly rising greenhouse gas concentrations are driving ocean systems toward conditions not seen for millions of years, with an associated risk of fundamental and irreversible ecological transformation. The impacts of anthropogenic climate change so far include decreased ocean productivity, altered food web dynamics, reduced abundance of habitat-forming species, shifting species distributions, and a greater incidence of disease. Although there is considerable uncertainty about the spatial and temporal details, climate change is clearly and fundamentally altering ocean ecosystems. Further change will continue to create enormous challenges and costs for societies worldwide, particularly those in developing countries.

http://science.sciencemag.org/content/sci/328/5985/1523.full.pdf

The impact of climate change on the world's marine ecosystems.

Food’s environmental impacts are created by millions of diverse producers. To identify solutions that are effective under this heterogeneity, we consolidated data covering five environmental indicators; 38,700 farms; and 1600 processors, packaging types, and retailers. Impact can vary 50-fold among producers of the same product, creating substantial mitigation opportunities. However, mitigation is complicated by trade-offs, multiple ways for producers to achieve low impacts, and interactions throughout the supply chain. Producers have limits on how far they can reduce impacts. Most strikingly, impacts of the lowest-impact animal products typically exceed those of vegetable substitutes, providing new evidence for the importance of dietary change. Cumulatively, our findings support an approach where producers monitor their own impacts, flexibly meet environmental targets by choosing from multiple practices, and communicate their impacts to consumers.

/pdf/reducing-food-s-environmental-impacts-through-producers-and-2xmi5ihk3n.pdf

Reducing food’s environmental impacts through producers and consumers

Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering carbon dioxide (CO(2)). The carbon (C) sequestered in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes, has been termed blue carbon. Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long-term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of the C sequestration value of vegetated coastal ecosystems provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosystems. Here, we identify key areas of uncertainty and specific actions needed to address them.

https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1890/110004

A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2

Aim Our scientific understanding of the extent and distribution of mangrove forests of the world is inadequate. The available global mangrove databases, compiled using disparate geospatial data sources and national statistics, need to be improved.Here,we mapped the status and distributions of global mangroves using recently available Global Land Survey (GLS) data and the Landsat archive. Methods We interpreted approximately 1000 Landsat scenes using hybrid supervised and unsupervised digital image classification techniques. Each image was normalized for variation in solar angle and earth‐sun distance by converting the digital number values to the top-of-the-atmosphere reflectance. Ground truth data and existing maps and databases were used to select training samples and also for iterative labelling. Results were validated using existing GIS data and the published literature to map ‘true mangroves’. Results The total area of mangroves in the year 2000 was 137,760 km 2 in 118 countries and territories in the tropical and subtropical regions of the world. Approximately 75% of world’s mangroves are found in just 15 countries, and only 6.9% are protected under the existing protected areas network (IUCN I-IV). Our study confirms earlier findings that the biogeographic distribution of mangroves is generallyconfinedtothetropicalandsubtropicalregionsandthelargestpercentage of mangroves is found between 5° N and 5° S latitude. Main conclusions We report that the remaining area of mangrove forest in the world is less than previously thought. Our estimate is 12.3% smaller than the most recent estimate by the Food and Agriculture Organization (FAO) of the United Nations.We present the most comprehensive, globally consistent and highest resolution (30 m) global mangrove database ever created.We developed and used better mapping techniques and data sources and mapped mangroves with better spatial and thematic details than previous studies.

http://faculty.jsd.claremont.edu/dmcfarlane/bio176mcfarlane/pdf%20papers/world%20mangrove%20distribution.pdf

Status and distribution of mangrove forests of the world using earth observation satellite data

In order to determine the efficiency of in situ carbon recycling in tropical mangrove sediments, and the contribution of porewater dissolved organic carbon (DOC) to surface-sediment bacterial production, concentrations and fluxes of DOC were measured and compared with simultaneous estimates of bacterial densities, productivity and specific growth rates, in a mangrove forest in Queensland, Australia. The range of interstitial DOC concentrations (4 to 50mgC 1 ' ) was similar to that reported for temperate marine sediments although seasonal variations were much less apparent. Soluble tannins constituted 2 to 51 % of the interstitial DOC pools, which varied significantly with tidal elevation (high > mid > low intertidal) and showed significant variation with sediment depth (to 1 m) only in the mid intertidal. Bacterial densities and activity in surface sediments (to 1 cm) were high (annual range in productivity: 0.9 to 4.1 gC m-* d ' ) , consistent with previous estimates at this site. Surface (1 cm depth) sediment DOC concentrations varied with elevation in the intertidal zone (10 sites from low to high intertidal), and showed no correspondence with seasonal or spatial variations in bacterial parameters, except for a significant correlation (r= 0.71, n = 10) between DOC and bacterial growth rate, in austral autumn, for samples throughout the tidal range. Despite the high concentration gradient of DOC between porewaters and overlying tidal waters, significant efflux of DOC was rarely detected unless sediments were poisoned, to 1 cm depth, with mercury, which resulted in significant and generally high rates of efflux. Efflux rates varied widely with tidal elevation and season (range: 0 to 2 . 4 gC m-' d\" ' ) These DOC flux rates provide, on average, 35 % (range: 0 to 100 O h ) of bacterial productivity requirements at the sediment-water interface. This study suggests that the mangrove sediments function as an efficient sink for DOC and that its export from the system is minor.

https://www.int-res.com/articles/meps/51/m051p243.pdf

Dissolved organic carbon-bacteria interactions at sediment-water interface in a tropical mangrove system

A review of the tropical soft-bottom literature reveals that several general concepts in benthic ecology, formulated mainly from temperate work, are either in need of modification or are not readily applicable to tropical benthic ecosystems. Several concepts emerge from the present tropical literature suggesting that in comparison with temperate communities: (1) species diversity and faunal densities are not necessarily greater in the tropics, (2) environmental stress (excluding anthropogenic input) is generally more severe, (3) infaunal communities are composed of proportionately more small opportunistic species (4) predation by demersal fishes and crustaceans is more intense, (5) microbes may be a carbon sink in some shallow-water habitats, notably mangroves, (6) production is generally high, but breeding and reproduction are frequently nor continuous and,(7) the distribution and abundances of tropical benthos, like most other communities, reflect temporal and spatial mosaics of major regulatory factors (competition, predation, food supply, environmental disturbances).Several tropical marine ecosystems such as mangroves and coral reefs are unique, and other environments such as continental shelves possess several common features which distinguish them to some degree from their temperate counterparts. To confirm, reject or modify these emerging concepts, several aspects of tropical benthic ecosystems require further study, including effects of wet season activity, physiological tolerances, nutrient recycling, secondary production, benthic-pelagic coupling and pollution. Such information and emerging conceptualizations are necessary to permit proper and informed conservation and management of these unique ecosystems.

https://revista-ciencia-tecnologia.ucr.ac.cr/index.php/rbt/article/download/23625/23825

Ecology of tropical soft-bottom benthos - a review with emphasis on emerging concepts

Field and model studies were carried out of the flushing and processing of shrimp pond effluent in a mangrove-fringed tidal creek, Port Douglas, Australia. Tidal flushing results in the concentration of dissolved and particulate nutrients decreasing with distance downstream. Flushing is slow in this 6 km long mangrove creek, with a residence time varying between four days at spring tides and 10–15 days at neap tides. Since spring and neap tides alternate at seven days intervals, the system is never at equilibrium. As a result, occasional along-channel sampling of sediment and nutrients provide little information on the fate of the effluent. A quantitative estimate of the physical and biological processes of nutrients and suspended sediments in the creek was made possible by comparing their discharge from the farm with the net, tidal-averaged discharge in the creek at a point 1·3 km downstream. Significant changes in discharges of nutrients occurred in the creek; chl a and TDN increasing in the creek, and DON, PC, TDN, TDP and suspended sediments being removed from the creek. The results were very sensitive to the natural, small-scale variability in the creek, and this variability may be under-sampled by triplicate samples. High concentrations of plankton downstream of the discharge interact with suspended particulate matter (mud, detritus from mangroves and pond effluent) and generate muddy marine snow. Muddy marine snow is not present in non-impacted creeks. Several processes may limit eutrophication. These are tidal flushing, secondly, selective settling of low nutrient particles, thirdly, dilution with original creek mud, and finally, bacteria mineralizing nutrients on the muddy marine snow.

Modelling and visualizing the fate of shrimp pond effluent in a mangrove-fringed tidal creek

Mangrove forests store and sequester large area-specific quantities of blue carbon (Corg). Except for tundra and peatlands, mangroves store more Corg per unit area than any other ecosystem. Mean mangrove Corg stock is 738.9 Mg Corg ha−1 and mean global stock is 6.17 Pg Corg, which equates to only 0.4–7% of terrestrial ecosystem Corg stocks but 17% of total tropical marine Corg stocks. Per unit area, mangroves sequester 179.6 g Corg m−2a−1 and globally about 15 Tg Corg a−1. Mangroves sequester only 4% (range 1.3–8%) of Corg sequestered by terrestrial ecosystems, indicating that mangroves are a minor contributor to global C storage and sequestration. CO2 emissions from mangrove losses equate to 0.036 Pg CO2-equivalents a−1 based on rates of C sequestration but 0.088 Pg CO2-equivalents a−1 based on complete destruction for conversion to aquaculture and agriculture. Mangrove CO2 emissions account for only 0.2% of total global CO2 emissions but 18% of CO2 emissions from the tropical coastal ocean. Despite significant data limitations, the role of mangrove ecosystems in climate change mitigation is small at the global scale but more significant in the tropical coastal ocean and effective at the national and regional scale, especially in areas with high rates of deforestation and destruction.

Global Significance of Mangrove Blue Carbon in Climate Change Mitigation

The effect of tidal outwelling of mangrove detritus on sediment nutrient chemistry, nutrient regeneration and oxygen fluxes in a coastal area of the central Great Barrier Reef lagoon was examined. Organic carbon and total nitrogen concentrations ranged from 0·2 to 3·9% and 0·01 to 0·18% by sediment dry weight (DW), respectively, and were highest at stations receiving the greatest quantities of mangrove litter. Total phosphorus concentrations ranged from 0·013 to 0·048% by DW, but did not relate to outwelling. C:N:P. ratios ranged from 29:6:1 at the site receiving the least amount of detritus to a high of 397:17:1 at the station receiving the most litter. The effect of outwelling on dissolved inorganic nutrients in porewaters was less clear, with concentrations closely related to sediment type and obscured by contributions from continental runoff. Ammonium (range: 10–310 μM) and silicate (range: 10–315 μM) were in greatest concentration at most sites followed by phosphate (range: 1–12 μM) and nitrite and nitrate (0·07–6·0 μM). Directly measured fluxes of dissolved inorganic nutrients across the sediment-water interface were either undetectable or small [ΣN = −560 to +3503; PO43 = undetectable to +157; Si(OH)4 = undetectable to +6449 μmol m−2 day−1] and not related to outwelling. Addition of mangrove litter to ☐core samples incubated for 10 days in the laboratory did not affect rates of dissolved inorganic nutrient release. Oxygen consumption rates ranged from 8·7 to 60·2 mmol O2 m−2 day−1 and were highest at most sites closest to mangrove forests, in agreement with previous measurements of bacterial productivity. Rates of net community primary production were either undetectable or low (as were chlorophyll α and phaeopigments) ranging from 12 to 77 mg C m−2 day−1. It appears that much of the deposited mangrove litter is highly refractory, but the amount of sedimented material appears to be great enough to significantly enrich bulk concentrations of particulate carbon and nitrogen, and rates of oxygen consumption. Benthic nutrient regeneration contributes only a small proportion to the daily nitrogen (6%) and phosphorus (9%) demand of coastal phytoplankton, implying supplementation from continental runoff and/or high rates of pelagic recycling.

Daniel M. Alongi

Papers

Dissolved organic carbon-bacteria interactions at sediment-water interface in a tropical mangrove system

Ecology of tropical soft-bottom benthos - a review with emphasis on emerging concepts

Modelling and visualizing the fate of shrimp pond effluent in a mangrove-fringed tidal creek

Global Significance of Mangrove Blue Carbon in Climate Change Mitigation

Effect of mangrove detrital outwelling on nutrient regeneration and oxygen fluxes in coastal sediments of the central Great Barrier Reef lagoon