Recent evidence indicates that climate change and intensification of the El Niño Southern Oscillation (ENSO) has increased variation in sea level. Although widespread impacts on intertidal ecosystems ...are anticipated to arise from the sea level seesaw associated with climate change, none have yet been demonstrated. Intertidal ecosystems, including mangrove forests are among those ecosystems that are highly vulnerable to sea level rise, but they may also be vulnerable to sea level variability and extreme low sea level events. During 16 years of monitoring of a mangrove forest in Mangrove Bay in north Western Australia, we documented two forest dieback events, the most recent one being coincident with the large-scale dieback of mangroves in the Gulf of Carpentaria in northern Australia. Diebacks in Mangrove Bay were coincident with periods of very low sea level, which were associated with increased soil salinization of 20-30% above pre-event levels, leading to canopy loss, reduced Normalized Difference Vegetation Index (NDVI) and reduced recruitment. Our study indicates that an intensification of ENSO will have negative effects on some mangrove forests in parts of the Indo-Pacific that will exacerbate other pressures.
Regional warming associated with climate change is linked with altered range and abundance of species and ecosystems worldwide. However, the ecological impacts of changes in the frequency of extreme ...events have not been as well documented, especially for coastal and marine environments. We used 28 y of satellite imagery to demonstrate that the area of mangrove forests has doubled at the northern end of their historic range on the east coast of Florida. This expansion is associated with a reduction in the frequency of “extreme” cold events (days colder than −4 °C), but uncorrelated with changes in mean annual temperature, mean annual precipitation, and land use. Our analyses provide evidence for a threshold response, with declining frequency of severe cold winter events allowing for poleward expansion of mangroves. Future warming may result in increases in mangrove cover beyond current latitudinal limits of mangrove forests, thereby altering the structure and function of these important coastal ecosystems.
Nutrient enrichment of the coastal zone places intense pressure on marine communities. Previous studies have shown that growth of intertidal mangrove forests is accelerated with enhanced nutrient ...availability. However, nutrient enrichment favours growth of shoots relative to roots, thus enhancing growth rates but increasing vulnerability to environmental stresses that adversely affect plant water relations. Two such stresses are high salinity and low humidity, both of which require greater investment in roots to meet the demands for water by the shoots. Here we present data from a global network of sites that documents enhanced mortality of mangroves with experimental nutrient enrichment at sites where high sediment salinity was coincident with low rainfall and low humidity. Thus the benefits of increased mangrove growth in response to coastal eutrophication is offset by the costs of decreased resilience due to mortality during drought, with mortality increasing with soil water salinity along climatic gradients.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Concerted mangrove research and rehabilitation efforts over the last several decades have prompted a better understanding of the important ecosystem attributes worthy of protection and a better ...conservation ethic toward mangrove wetlands globally. While mangroves continue to be degraded and lost in specific regions, conservation initiatives, rehabilitation efforts, natural regeneration, and climate range expansion have promoted gains in other areas, ultimately serving to curb the high mangrove habitat loss statistics from the doom and gloom of the 1980s. We highlight those trends in this article and introduce this special issue of
Hydrobiologia
dedicated to the important and recurring Mangrove and Macrobenthos Meeting. This collection of papers represents studies presented at the fourth such meeting (MMM4) held in St. Augustine, Florida, USA, on July 18–22, 2016. Our intent is to provide a balanced message about the global state of mangrove wetlands by describing recent reductions in net mangrove area losses and highlighting primary research studies presented at MMM4 through a collection of papers. These papers serve not only to highlight on-going global research advancements, but also provide an overview of the vast amount of data on mangrove ecosystem ecology, biology and rehabilitation that emphasizes the uniqueness of the mangrove community.
Salt marsh and mangrove have been recognized as being among the most valuable ecosystem types globally in terms of their supply of ecosystem services and support for human livelihoods. These coastal ...ecosystems are also susceptible to the impacts of climate change and rising sea levels, with evidence of global shifts in the distribution of mangroves, including encroachment into salt marshes. The encroachment of woody mangrove shrubs and trees into herbaceous salt marshes may represent a substantial change in ecosystem structure, although resulting impacts on ecosystem functions and service provisions are largely unknown. In this review, we assess changes in ecosystem services associated with mangrove encroachment. While there is quantitative evidence to suggest that mangrove encroachment may enhance carbon storage and the capacity of a wetland to increase surface elevation in response to sea‐level rise, for most services there has been no direct assessment of encroachment impact. On the basis of current understanding of ecosystem structure and function, we theorize that mangrove encroachment may increase nutrient storage and improve storm protection, but cause declines in habitat availability for fauna requiring open vegetation structure (such as migratory birds and foraging bats) as well as the recreational and cultural activities associated with this fauna (e.g., birdwatching and/or hunting). Changes to provisional services such as fisheries productivity and cultural services are likely to be site specific and dependent on the species involved. We discuss the need for explicit experimental testing of the effects of encroachment on ecosystem services in order to address key knowledge gaps, and present an overview of the options available to coastal resource managers during a time of environmental change.
Mangrove encroachment alters the ecosystem structure of coastal wetlands, with ramifications for ecosystem service delivery. The low vegetation structure of salt marsh provides roosting and feeding birds with a longer line of sight to any ambush predators, while insectivorous bats prefer to feed over open salt marsh or at the marsh–forest edge, avoiding the acoustic clutter of closed forest. The higher biomass and structural rigidity of mangrove may also increase storm wave attenuation.
The long-term stability of coastal ecosystems such as mangroves and salt marshes depends upon the maintenance of soil elevations within the intertidal habitat as sea level changes. We examined the ...rates and processes of peat formation by mangroves of the Caribbean Region to better understand biological controls on habitat stability. Mangrove-dominated islands on the Caribbean coasts of Belize, Honduras and Panama were selected as study sites. Biological processes controlling mangrove peat formation were manipulated (in Belize) by the addition of nutrients (nitrogen or phosphorus) to Rhizophora mangle (red mangrove), and the effects on the dynamics of soil elevation were determined over a 3-year period using rod surface elevation tables (RSET) and marker horizons. Peat composition and geological accretion rates were determined at all sites using radiocarbon-dated cores. The addition of nutrients to mangroves caused significant changes in rates of mangrove root accumulation, which influenced both the rate and direction of change in elevation. Areas with low root input lost elevation and those with high rates gained elevation. These findings were consistent with peat analyses at multiple Caribbean sites showing that deposits (up to 10 m in depth) were composed primarily of mangrove root matter. Comparison of radiocarbon-dated cores at the study sites with a sea-level curve for the western Atlantic indicated a tight coupling between peat building in Caribbean mangroves and sea-level rise over the Holocene. Mangroves common to the Caribbean region have adjusted to changing sea level mainly through subsurface accumulation of refractory mangrove roots. Without root and other organic inputs, submergence of these tidal forests is inevitable due to peat decomposition, physical compaction and eustatic sea-level rise. These findings have relevance for predicting the effects of sea-level rise and biophysical processes on tropical mangrove ecosystems.
The central‐marginal hypothesis (CMH) posits that range margins exhibit less genetic diversity and greater inter‐population genetic differentiation compared to range cores. CMH predictions are based ...on long‐held “abundant‐centre” assumptions of a decline in ecological conditions and abundances towards range margins. Although much empirical research has confirmed CMH, exceptions remain almost as common. We contend that mangroves provide a model system to test CMH that alleviates common confounding factors and may help clarify this lack of consensus. Here, we document changes in black mangrove (Avicennia germinans) population genetics with 12 nuclear microsatellite loci along three replicate coastlines in the United States (only two of three conform to underlying “abundant‐centre” assumptions). We then test an implicit prediction of CMH (reduced genetic diversity may constrain adaptation at range margins) by measuring functional traits of leaves associated with cold tolerance, the climatic factor that controls these mangrove distributional limits. CMH predictions were confirmed only along the coastlines that conform to “abundant‐centre” assumptions and, in contrast to theory, range margin A. germinans exhibited functional traits consistent with greater cold tolerance compared to range cores. These findings support previous accounts that CMH may not be a general rule across species and that reduced neutral genetic diversity at range margins may not be a constraint to shifts in functional trait variation along climatic gradients.
Aim
Climate change is leading to large‐scale shifts in species’ range limits. Mangroves, for example, are encroaching into saltmarshes at numerous tropical–temperate transition zones. However, ...mangrove expansion varies geographically, in large part because mangroves might not be fully occupying their fundamental niches across their range limits. Here we characterize and compare the fundamental versus realized thermal niches of two mangrove species found near their northern range limits on both coasts of North America.
Location
Atlantic and Pacific coasts of North America.
Taxa
Red mangrove (Rhizophora mangle), black mangrove (Avicennia germinans).
Methods
Red and black mangrove propagules were collected near range limits on the Atlantic and Pacific coasts and experimentally exposed to simulated overnight freezes ranging from −0.5 to −15°C, and grown in water temperatures ranging from 13 to 25°C. We then modelled range‐specific distributions based on threshold survival responses to cold treatments and compared these predictions to current distributions and climate envelopes.
Results
On the Atlantic coast, laboratory physiological thresholds closely matched realized distributions for both black and red mangroves. The Pacific black mangroves were less tolerant to freezes than the Atlantic populations, but laboratory determined thresholds essentially matched their realized distributions. In contrast, Pacific red mangroves were surprisingly freeze tolerant, and our laboratory threshold‐based model predicted suitable habitat far north of their current range limit. Our cold‐water tolerance experiments indicated that mangroves can tolerate chronically colder water temperatures than are currently experienced at either range limit.
Main conclusions
On its own, cold water temperature does not seem to be a limiting factor on either coast of North America. On the Atlantic coast, range limits for both mangrove species are set by extreme cold air temperatures and rapidly shifting in response to climate change. On the warmer but more arid Pacific coast, range limits for black mangroves only appear limited by cold air temperatures, but neither species seems to be undergoing climate change‐related migration. This supports the importance of other range‐restricting factors, such as aridity or dispersal limitation. Thus, distribution models need to incorporate species and range‐specific physiological data to predict the effects of climate change on population‐specific range limits.
Nutrition of mangroves Reef, Ruth; Feller, Ilka C; Lovelock, Catherine E
Tree physiology
30, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Mangrove forests dominate the world's tropical and subtropical coastlines. Similar to other plant communities, nutrient availability is one of the major factors influencing mangrove forest structure ...and productivity. Many mangrove soils have extremely low nutrient availability, although nutrient availability can vary greatly among and within mangrove forests. Nutrient-conserving processes in mangroves are well developed and include evergreeness, resorption of nutrients prior to leaf fall, the immobilization of nutrients in leaf litter during decomposition, high root/shoot ratios and the repeated use of old root channels. Both nitrogen-use efficiency and nutrient resorption efficiencies in mangroves are amongst the highest recorded for angiosperms. A complex range of interacting abiotic and biotic factors controls the availability of nutrients to mangrove trees, and mangroves are characteristically plastic in their ability to opportunistically utilize nutrients when these become available. Nitrogen and phosphorus have been implicated as the nutrients most likely to limit growth in mangroves. Ammonium is the primary form of nitrogen in mangrove soils, in part as a result of anoxic soil conditions, and tree growth is supported mainly by ammonium uptake. Nutrient enrichment is a major threat to marine ecosystems. Although mangroves have been proposed to protect the marine environment from land-derived nutrient pollution, nutrient enrichment can have negative consequences for mangrove forests and their capacity for retention of nutrients may be limited.
Climate change is driving the tropicalization of temperate ecosystems by shifting the range edges of numerous species poleward. Over the past few decades, mangroves have rapidly displaced salt ...marshes near multiple poleward mangrove range limits, including in northeast Florida. It is uncertain whether such mangrove expansions are due to anthropogenic climate change or natural climate variability. We combined historical accounts from books, personal journals, scientific articles, logbooks, photographs, and maps with climate data to show that the current ecotone between mangroves and salt marshes in northeast Florida has shifted between mangrove and salt marsh dominance at least 6 times between the late 1700s and 2017 due to decadal-scale fluctuations in the frequency and intensity of extreme cold events. Model projections of daily minimum temperature from 2000 through 2100 indicate an increase in annual minimum temperature by 0.5 °C/decade. Thus, although recent mangrove range expansion should indeed be placed into a broader historical context of an oscillating system, climate projections suggest that the recent trend may represent a more permanent regime shift due to the effects of climate change.
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