Nutrient subsidies delivered by seabirds to mangrove islands

ArticleinMarine Ecology Progress Series 525 · April 2015with 339 Reads 
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Abstract
In nutrient-poor landscapes, external nutrient subsidies are important for sustaining local production. Seabirds can transport marine nutrients in the form of guano to terrestrial and coastal ecosystems where they can relieve nutrient limitation. We assessed whether seabirds provide nutrient subsidies to mangrove islands that are strongly limited by phosphorus (P) in the Yucatan Peninsula. Our hypotheses were: (1) seabirds transport nutrients to mangrove islands, (2) mangroves use marine-derived nutrients and (3) nutrient inputs are higher during the nesting season. We chose 6 mangrove islands within a coastal lagoon: 2 with no birds, 2 with temporary birds and 2 with permanent bird colonies. On each, we measured forest structure and soil characteristics (P, pH, salinity and organic matter) for 3 seasons (dry, wet and trade wind season). We collected leaves (green and senescent) to determine P content and resorption efficiency as a measurement of nutrient limitation. Green leaves were also sampled for δ13C and δ15N to determine nutrient origin. Results show that islands with permanent bird colonies have the highest soil nutrients, which are used by the mangrove trees and relieve some of their nutrient limitation. Nutrient inputs were homogenously distributed through the sediment column, although a decrease in P and an increase in the N:P ratio in the first 20 cm suggests bacterial consumption. Bird nutrient inputs are seasonal, with highest inputs during the nesting season. This study shows an example in which marine-derived nutrients could be important for production of coastal mangrove islands.

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  • ... p = 0.031), with lowest values in the layer below 50 cm, although the difference was small (\2 %). Mangrove values were obtained from Wooller et al. (2003a, b), Fry andCormier (2011), Lovelock et al. (2011) and Adame et al. (2015a, b) Peat swamps and marsh had large depth-related variations with d 13 C value differences of up to 6 % (Fig. 5). In the peat swamp soil, d 13 C values increased with time, while in the marsh soil the d 13 C values decreased; d 15 N was variable. ...
    Article
    Wetlands can store large quantities of carbon (C) and are considered key sites for C sequestration. However, the C sequestration potential of wetlands is spatially and temporally variable, and depends on processes associated with C production, preservation and export. In this study, we assess the soil C sources and processes responsible for C sequestration of riverine wetlands (mangroves, peat swamp forest and marsh) of La Encrucijada Biosphere Reserve (LEBR, Mexican south Pacific coast). We analysed soil C and nitrogen (N) concentrations and isotopes (δ13C and δ15N) from cores dated from the last century. We compared a range of mangrove forests in different geomorphological settings (upriver and downriver) and across a gradient from fringe to interior forests. Sources and processes related to C storage differ greatly among riverine wetlands of the Reserve. In the peat swamp forest and marsh, the soil C experienced large changes in the past century, probably due to soil decomposition, changes in plant community composition, and/or changes in C sources. In the mangroves, the dominant process for C accumulation was the burial of in situ production. The C buried in mangroves has changed little in the past 100 years, suggesting that production has been fairly constant and/or that decomposition rates in the soil are slow. Mangrove forests of LEBR, regardless of geomorphological setting, can preserve very uniform soil N and C for a century or more, consistent with efficient C storage.
  • ... Besides, station 21 is around Isla Pájaros where a diversity of birds have their nests. Higher SRP values can be associated with the abundance of birds' feces (Adame et al., 2015). Yalahau's SRSi values were overall good during fronts and good to fair in rains. ...
    Article
    Holbox Island faces issues related to the availability of freshwater and living space given the increasing coastal migration and tourism development in the region. We report the water quality of 12 tidal inlets (which are geomorphological features of barrier islands), which neighbor hotels. Because no previous studies of tidal inlets exist on Holbox, we used reference published values of water quality and unpublished water values collected at 43 sampling sites throughout the Yalahau Lagoon. Analyses of water quality variables and the trophic index (TRIX) were measured. Inlets sites salinity values ranged from 11 to 36 psu. Average values for nitrates (0.83 μmol l⁻¹), and nitrites (0.14 μmol l⁻¹), at inlets, had lower values in the fronts season. Soluble reactive phosphate (48.8μmol l⁻¹), and silicate (78.6 μmol l⁻¹) were higher at inlets during rains and chlorophyll-α (29.7 mg/m³) was more top at inlets during fronts. TRIX values for inlets ranged between 2 and 6, indicating low water quality in most inlets associated with hotel sites. Seasonal changes in soluble reactive phosphate and chlorophyll-α at inlets suggests these could be receiving sewage water discharges from human activities. Besides inlet's higher water residence time and slower water interchange rate can favor the accumulation of pollutants. Results demonstrate that water quality issues exist on Holbox and need management actions to prevent the decay of coastal ecosystem services. These are necessary for positive feedback between local communities’ wellbeing and successful tourism development in the region.
  • ... Mangroves provide critical foraging and nesting habitat for a variety of waterbirds, yet the role of birds as nutrient vectors in mangrove ecosystems has received little attention in the scientific literature (Buelow and Sheaves 2015;Reef et al. 2010). Only two studies to date have measured the effects of avian nutrient enrichment in mangroves, neither of which report nutrient inputs (Adame et al. 2015;Onuf et al. 1977). In this study we examined the effects of nutrient enrichment by colonial waterbirds in two mangrove sites in the Gulf of Fonseca, Honduras. ...
    Article
    Full-text available
    Mangroves provide numerous ecosystem services, including biodiversity values such as nesting sites for piscivorous waterbirds. High concentrations of waterbirds at nest sites are hypothesized to affect ecosystem dynamics, yet few studies have examined their effects as a nutrient source in mangroves. We examined the effects of nutrient enrichment by colonial waterbirds at a mangrove rookery in the Gulf of Fonseca, Honduras. We compared nutrient inputs via bird guano deposition and macronutrient levels in the vegetation and soils between a small island that hosted large numbers of roosting waterbirds and an adjacent island with little evidence of waterbird activity. Nest density at the rookery was 1721 ± 469 nests ha−1. Rookery birds deposited 7.2 ± 3.4 g m−2 day−1 guano dry weight, delivering an estimated 1.12 Mg ha−1 nitrogen and 0.16 Mg ha−1 phosphorus to the island over a 120 day breeding season. This large nutrient influx contributed to substantially higher concentrations of biologically important nutrients in the rookery soils (seven times more plant available phosphorus, eight times more nitrate, and two times more ammonium). Rookery mangrove leaves contained significantly higher concentrations of nitrogen and phosphorus compared to the control site. These results suggest that colonial waterbirds significantly influence nutrient dynamics of mangroves at local scales. Further research is needed to understand the effects of avian derived nutrients on mangrove growth rates, nutrient export to adjacent waters, invertebrate communities, and mangrove associated fisheries.
  • ... En los trabajos de la PY, algunos del GM y uno del PS, incluyen datos de nutrimentos en sedimentos, pero no son suf icientes para hacer relaciones y extraer patrones. Lo que sí parece ser una constante, es que los manglares de la PY están limitados por fósforo (Adame et al., 2013;Adame et al., 2015b). ...
    Article
    La cobertura de los manglares de México los coloca en cuarto lugar a nivel mundial. Se reconocen sus múltiples servicios ecosistémicos, pero también altas tasas de deforestación. Evaluaciones en otras partes del mundo destacan el papel de los manglares en el ciclo del carbono, principalmente como almacenes de carbono orgánico (Corg) en los sedimentos y exportadores de Corg disuelto y particulado. Para estimar la contribución de los manglares, a escala local, regional y de país, en estrategias como la Reducción de Emisiones por Deforestación y Degradación (REDD+), es indispensable determinar los almacenes de Corg como línea base de emisiones. En este estudio se realizó una búsqueda bibliográfica sobre almacenes y flujos de carbono en manglares de México mediante diferentes fuentes de información. De más de 200 estudios, solo 48 contenían datos o información para hacer una revisión del estado que guarda el conocimiento de almacenes y flujos de Corg en los manglares de México. Regionalmente, la zona del Pacífico Central tiene menos información y la Península de Yucatán donde más datos existen. Los mayores almacenes de Corg total se localizan en el Golfo de México y en los manglares de tipo ribereño (>1200 Mg C ha-1). Existe menos información sobre flujos de Corg, dominando los relacionados con la caída de hojarasca. En la zona del Pacífico Sur y en el manglar ribereño se observaron los valores más altos. La extensión y variabilidad de condiciones ambientales en los manglares de México son una oportunidad para desarrollar múltiples temas de investigación, como la caracterización de paisajes y mapas locales de coberturas relacionados con variables del agua (hidroperíodo), del suelo (topografía) y procesos microbiológicos. La extensión y distribución de los manglares ofrecen la oportunidad para formar grupos de investigadores a escala regional y abordar de forma consensada estudios bajo una estrategia metodológica interoperable.
  • ... En los trabajos de la PY, algunos del GM y uno del PS, incluyen datos de nutrimentos en sedimentos, pero no son suf icientes para hacer relaciones y extraer patrones. Lo que sí parece ser una constante, es que los manglares de la PY están limitados por fósforo (Adame et al., 2013;Adame et al., 2015b). ...
    Article
    Full-text available
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  • ... Glucose was applied at a rate of 130 g m À2 , NH 4 SO 4 was applied at 39 g m À2 , urea at 32 g m À2 , and gallic acid and NaH 2 PO 4 were made to saturation at 25 C and hence applied at approximately 13 g m À2 . In an ecological sense, relatively pristine mangrove ecosystems have been observed to receive high nutrient loadings to soils from seabird and/or bat guano or mammal droppings (Adame et al., 2015;Reef et al., 2014). At least occasional inputs of high nutrients from perching birds in particular are likely at our sites on the Exmouth Gulf. ...
  • ... birds fishing in oceans but defecating guano ashore or bears hunting salmon in rivers and pulling their carcasses into forests [50,[53][54][55]). ...
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    The meta-ecosystem framework demonstrates the significance of among-ecosystem spatial flows for ecosystem dynamics and has fostered a rich body of theory. The high level of abstraction of the models, however, impedes applications to empirical systems. We argue that further understanding of spatial dynamics in natural systems strongly depends on dense exchanges between field and theory. From empiricists, more and specific quantifications of spatial flows are needed, defined by the major categories of organismal movement (dispersal, foraging, life-cycle, and migration). In parallel, the theoretical framework must account for the distinct spatial scales at which these naturally common spatial flows occur. Integrating all levels of spatial connections among landscape elements will upgrade and unify landscape and meta-ecosystem ecology into a single framework for spatial ecology.
  • ... In many cases seabirds are important transport agents (Hobara et al., 2005;Nie et al., 2012;Szpak et al., 2012;Hawke and Condron, 2014). Apart from wetland (e.g., Litaor et al., 2016), this process is most likely to occur on marine islands (Erskine et al., 1998;Adame et al., 2015). Mulder et al. (2011) detailed seabird island ecosystems, compared relevant ecological studies such as the impact of seabird colonies on biogeochemical processes, and further assessed and reviewed island management. ...
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    The nitrogen (N) utilization strategy of plants has become a topic of interest within the field of phytoecology. However, few studies have considered N cycling on coral island ecosystems from the perspective of their evolution. The aim of this study was to test the impacts of biological transport by seabirds, on the sources and uses of N by plants, and pathways of N cycling in soil-plant ecosystems on coral islands. A series of eight coral islands were investigated, five of which were affected to a varying extent by seabirds. The total phosphorus (TP) concentration from avian sources and the δ15N values of total nitrogen (TN) and inorganic nitrogen (IN: NH4+-N, and NO3--N), δ18O of NO3--O, in soils were determined, as well as proxies in plant leaves of two dominant plant species, including TN, the carbon/nitrogen ratio (C/N), and δ13C and δ15N values. The results show that, with an increase of TP, the TN and IN content, and δ15N values in soils all increased. Plant C/N and δ15N values decreased and increased, respectively, as the soil N content increased. When the TN content of the soil was low, the δ15N value in plant leaves was similar to that in soil NO3-, but was much lower than that in soil NH4+. When the soil TN content was high, the δ15N values were similar. Both plants and soil were probably N-limited prior to seabird colonization, with the N source on the barren coral islands originating primarily from atmospheric deposition. With seabird guano input and subsequent pedogenesis, the source of N switched to guano. Under these conditions, most of the N utilized by plants originated from NH4+, while nitrate is dominant for non-seabirds islands. Seabird activities have played a key role in the N dynamics of soil-plant ecosystems at coral islands.
  • ... In nutrient-poor habitats such as island mangroves, external nutrient subsidies are important for sustaining local production. Seabirds can transport nutri-ents in the form of guano and nesting materials from mainland mangrove ecosystems to island mangrove ecosystems and thereby reduce nutrient limitation (Adame et al., 2015). Furthermore, high concentrations of colonial water birds can increase concentrations of nitrogen and phosphorus of mangroves at local scales (McFadden, Kauffman, and Bhomia, 2016). ...
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    Full-text available
    Chen, Q.; Lin, G.; Ma, K., and Chen, P., 0000. Determining the unsuitability of exotic cordgrass (Spartina alterniflora) for avifauna in a mangrove wetland ecosystem. Journal of Coastal Research, 00(0), 000-000. Coconut Creek (Florida), ISSN 0749-0208. Avifauna are essential for maintaining the structure and functioning of mangrove ecosystems, which are particularly sensitive to habitat transformation. Although exotic cordgrass, Spartina alterniflora, is an increasing threat to mangrove ecosystems (including the associated unvegetated shoals) of China, its effects on the avifauna in such ecosystems are poorly understood. In Zhanjiang, China, the avifaunal Shannon-Weiner diversity, Simpson's diversity, Margalef's species richness, Pielou's evenness and density indices were compared in (1) an Avicennia marina monoculture vs. an S. alterniflora-invaded A. marina stand (a mixture of A. marina and S. alterniflora) and (2) an unvegetated shoal vs. an S. alterniflora-invaded shoal that had rapidly become an S. alterniflora monoculture. All avifaunal community parameters except for the Simpson index were significantly lower in the S. alterniflora þ A. marina mixture than in the A. marina monoculture, and in the S. alterniflora monoculture than in the unvegetated shoal. These results indicate that the presence of S. alterniflora reduces the suitability of the Zhanjiang mangrove ecosystem for avifauna. Among the four habitats, the Shannon-Weiner diversity index, species richness, and density of the avifaunal community were highest in the unvegetated shoal. Further analysis indicated that the differences in the avifaunal community between invaded and noninvaded sites were associated with vegetation characteristics (mainly plant height and density) and macrobenthic faunal metrics (mainly species richness and density). The reduced avifaunal diversity and abundance associated with S. alterniflora invasion probably resulted from the decline in food resources or from the increased difficulty in foraging and roosting. The findings indicate that the conservation of birds in mangrove ecosystems may depend on controlling or eradicating exotic S. alterniflora, maintaining tidal mudflats, and diversifying the habitats in mangrove wetlands.
  • ... Another key factor for which they are considered a priority is the particular life-history traits of these groups (e.g. deferred sexual maturity, longevity, and low productivity) as well as their key ecological role as apex consumers and/or nutrient transporters (Adame, Fry, Gamboa, & Herrera-Silveira, 2015;Baum & Worm, 2009;Heithaus, Frid, Wirsing, & Worm, 2008;Jackson et al., 2001). The impact caused by human activities such as fishing on these predators can alter the structure of the food chain and affect the equilibrium between species (Arcos, Louzao, & Oro, 2008;Baum & Worm, 2009;Furness, 2003;Heithaus et al., 2008). ...
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    • Commercial fishing has been identified as one of the main threats affecting the survival of most seabird species. Although seabird mortality in Argentine longline and demersal trawl fisheries has already been characterized and quantified, the interactions with pelagic trawl fisheries targeting anchovy (Engraulis anchoita Hubbs & Marini, 1935) remains unknown. • The goal of this study was to characterize seabird assemblages attending pelagic trawl vessels and to analyse their interactions (i.e. contact of the birds with the vessel and/or fishing gear and by‐catch). Data were obtained by on‐board observers during three consecutive fishery runs, 2011–2013. • From a total of 333 observations, seabird abundance averaged 157.3 ± 229.7 birds per haul (totalling 23 species). Procellariiform followed by Charadriiform birds were the more frequent and abundant groups. The black‐browed albatross (Thalassarche melanophris (Temminck, 1828)), shearwaters (Ardenna spp. and Puffinus spp.), white‐chinned petrel (Procellaria aequinoctialis Linnaeus, 1758), and the kelp gull (Larus dominicanus Lichtenstein, 1823) were the most frequent and abundant attending species. • The seabird abundance increased when the swell and the number of neighbouring vessels decreased. • Seabird interactions with the vessel and/or fishing gear occurred in approximately 70% of the observations, with most of these representing interactions with the net (92%). The estimated contact rate was 16.7 birds h⁻¹ per haul. A total of 121 birds were by‐caught and the average mortality rate was 0.55 birds h⁻¹ per haul. Shearwaters and Magellanic penguins (Spheniscus magellanicus (Forster, 1781)) were the main by‐caught species (101 and 12 individuals, respectively). Lower levels of mortality were recorded in black‐browed albatrosses and white‐chinned petrels. • The interactions increased in the presence of fishing discards and during haulback operations. • This study is relevant to the implementation of the Argentine National Plan of Action – Seabirds, as well as for the continuing certification process in the anchovy fishery.
  • ... For all vegetation tissue types, δ 13 C and δ 15 N values, total organic carbon and nitrogen contents were analyzed. However, we only used two replicate samples of each vegetation tissue from each sampling location due to cost limitations, and assumed that elemental properties and stable isotope signatures of each tissue were not different across vegetation species (Adame et al., 2015;Werth et al., 2015). ...
    Article
    Full-text available
    Mangrove organic carbon is primarily stored in soils, which contain more than two-thirds of total mangrove ecosystem carbon stocks. Despite increasing recognition of the critical role of mangrove ecosystems for climate change mitigation, there is limited understanding of soil organic carbon sequestration mechanisms in undisturbed low-latitude mangroves, specifically on organic carbon burial rates and sources. This study assessed soil organic carbon burial rates, sources and stocks across an undisturbed coastal mudflat and mangrove hy-drogeomorphological catena (fringe mangrove and interior mangrove) in Bintuni Bay, West Papua Province, Indonesia. 210 Pb radionuclide sediment dating, and mixing model of natural stable isotope signatures (δ 13 C and δ 15 N) and C/N ratio were used to estimate organic carbon burial rates and to quantify proportions of al-lochthonous (i.e., upland terrestrial forest) and autochthonous (i.e., on-site mangrove forest) organic carbon in the top 50 cm of the soil. Burial rates were in the range of 0.21-1.19 Mg C ha −1 yr −1. Compared to the fringe mangroves, organic carbon burial rates in interior mangroves were almost twice as high. Primary productivity of C 3 upland forest vegetation and mangroves induced soil organic carbon burial in interior mangroves and this was consistent with the formation of the largest organic carbon stocks (179 ± 82 Mg C ha −1). By contrast, organic carbon stored in the fringe mangrove (68 ± 11 Mg C ha −1) and mudflat (62 ± 10 Mg C ha −1) soils mainly originated from upland forests (allochthonous origin). These findings clearly indicate that carbon sequestered and cycling in mangrove and terrestrial forest ecosystems are closely linked, and at least a part of carbon losses (e.g., erosion) from terrestrial forests is buried in mangrove ecosystems.
  • ... However, there was no relationship between leaf δC 13 values and the probability of TIP colony presence. This contrasts other studies that have found leaf δC 13 enrichment in areas near bird colonies, likely due to higher leaf nitrogen levels and plant growth rates (Wainright et al., 1998;Cordell et al., 1999;Adame et al., 2015). It is possible that variation in leaf δC 13 enrichment could be related to differential light availability for individual plants that were sampled in the present study (Buchmann et al., 1997), something worth controlling for in future studies. ...
  • ... As one of the methods for analyzing the contribution of MDN, stable isotope analysis (SIA) is increasingly being used to examine connectivity in coastal aquatic-terrestrial ecosystems, such as the input of MDN from the open ocean to coastal and river ecosystems (Wyatt et al., 2010a(Wyatt et al., , 2010b(Wyatt et al., , 2012Havik et al., 2014;Adame et al., 2015). Isotopic methods as an intrinsic geospatial tracer may thus provide a means to quantify cross-ecosystem transfer of nutrients from the ocean to watersheds. ...
    Article
    Total nitrogen (TN), consisting of total particulate nitrogen (TPN) and total dissolved nitrogen (TDN) pools, may be transported to the ocean not only via river channels but also from across the entire river basin via groundwater and migratory animals. Since marine derived nitrogen (MDN) is hypothesized to largely be transported in particulate form, it is necessary to investigate the contribution of particulate MDN in ground surface soils to the total MDN at the river ecosystem scale. In this study, we investigated TN export from an entire river basin to the ocean, and also estimated the contribution of pink (Oncorhynchus gorbuscha) and chum salmon (O. keta) to total oceanic nitrogen input across a river basin. The maximum potential contribution of MDN entering the river basin from the ocean as salmon was 23.8% relative to the total amount of TN exported from the river basin. The contribution of MDN from the ocean to particulate nitrogen in river basin soils was estimated to be 22.9% with standard deviation (SD) of 3.6% using stable isotope analysis (SIA) of nitrogen (δ¹⁵N).
  • ... Water column DIP is low, limit- ing coastal productivity. Therefore, lagoons respond rapidly to even small DIP additions ( Adame et al., 2015). ...
    Chapter
    The southern Gulf of Mexico is characterized by coastal ecosystems with high freshwater input, extensive wetlands and coastal lagoons, productive fisheries, and human settlements whose economy is largely based on the rich natural resources of the area. The Grijalva-Usumacinta River and delta region has high riverine input and extensive wetlands. The CENTLA Biosphere Reserve was established to protect this important region. The management plan is based on the identification of natural environmental units that are grouped into two nucleus zones with high levels of protection and a number of buffer zones designed to allow some economic activities. Laguna de Terminos, the largest lagoon-mangrove system in Mesoamerica, has a long history of scientific study. The system has a high habitat diversity. Primary producers have peak production at different times of the year leading to overall sustained high productivity throughout the year. There is a high diversity migratory nekton community that uses the lagoon habitats at times when they are most productive ensuring overall high secondary production that supports a multistock fishery. The area has been designated as a natural protected area to ensure sustainable management. The coastal zone of the Yucatan Peninsula is fed by the extensive ground water system that supports a unique system of karstic freshwater lakes, brackish lagoons, estuarine coastal lagoons, and reef lagoons with extensive mangrove swamps and submerged aquatic vegetation. The main source of inorganic nutrients is ground water and in some parts of the coast elevated levels have the potential to cause eutrophication and harmful algal blooms. Along the northern and eastern coasts of the Yucatan, rapid development has led to extensive habitat degradation and water quality problems. Ecosystem-based management could lead to improved environmental quality and restoration. Some global climate models suggest that this region will experience strong decreases in precipitation and this may become the most serious problem for this region. Mexico has established 17 natural protected areas in the southern Gulf of Mexico and Yucatan to enhance sustainable management in the region. In this chapter we review the structure and functioning of this regional coastal system, describe human impacts, review sustainable management of the area, and discuss the potential impacts of climate change.
  • ... Similarly, there are examples of subsidies that provide a particular limiting nutrient to systems that might otherwise support high rates of primary and secondary productivity. Phosphorus is limiting in certain mangrove and coastal nearshore systems, but cross-system subsidies provide this nutrient with follow-on ecosystem impacts (mangroves: Adame et al. 2015; nearshore coastal environments: Deegan 1993). Lacking, however, are studies looking at the extent and impact of cross-ecosystem trophic subsidies to systems that are known for their high internal productivity. ...
    Article
    Full-text available
    The movement of trophic resources between and among ecosystems, referred to as cross‐ecosystem subsidies, is a common phenomenon. In the marine environment, both adjacent and distant ecosystems are connected by oceanographic forces that transport nutrients, organisms, and other materials. Kelp forest ecosystems are one example of an open marine system that both exports and receives trophic subsidies. Though rocky reefs are rich in kelp‐based energy produced internally, kelp forest organisms also rely on phytoplankton, and the influx of holoplankton and meroplankton from adjacent open ocean habitats. In this paper, we seek to clarify the identity of holoplanktonic and meroplanktonic subsidies, quantify their energetic and nutrient contributions to the kelp forest, and further explore the impacts of these subsidies for individual consumers and for kelp forest communities. We reviewed six individual subsidy organisms that are commonly advected to kelp forests on the West coast of North America, and show that these organisms from the pelagic ocean represent important resource pulses for kelp forest consumers. In addition, we summarize the characteristics of subsidies, consumers, and recipient ecosystems that provide insight into the dynamics of subsidy influx and impacts to recipient systems. Finally, we provide suggestions as scientists move forward with efforts to quantify the impacts of cross‐ecosystem subsidies. Trophic subsidies are a major force shaping both marine and terrestrial communities and ecosystems. Quantitative information about these subsidies and their impacts on food webs will not only improve our understanding of these ecosystems, but also improve food web models, and predictions of ecosystem response to change.
  • ... www.nature.com/scientificreports/ subsidies have increased production of mangroves 72 and seagrass 73 and the current study shows that ornithogenic nutrients result in a nutrient-replete environment that can enhance coral production. The composition of seabird guano contains essential nutrients (nitrogen, phosphorus), including trace elements 58 and iron 74 , in sufficient amounts that biochemical functions remain stable 37 . ...
    Article
    Full-text available
    Nutrient subsidies across ecotone boundaries can enhance productivity in the recipient ecosystem, especially if the nutrients are transferred from a nutrient rich to an oligotrophic ecosystem. This study demonstrates that seabird nutrients from islands are assimilated by endosymbionts in corals on fringing reefs and enhance growth of a dominant reef-building species, Acropora formosa. Nitrogen stable isotope ratios (δ15N) of zooxanthellae were enriched in corals near seabird colonies and decreased linearly with distance from land, suggesting that ornithogenic nutrients were assimilated in corals. In a one-year reciprocal transplant experiment, A. formosa fragments grew up to four times faster near the seabird site than conspecifics grown without the influence of seabird nutrients. The corals influenced by elevated ornithogenic nutrients were located within a marine protected area with abundant herbivorous fish populations, which kept nuisance macroalgae to negligible levels despite high nutrient concentrations. In this pristine setting, seabird nutrients provide a beneficial nutrient subsidy that increases growth of the ecologically important branching corals. The findings highlight the importance of catchment–to–reef management, not only for ameliorating negative impacts from land but also to maintain beneficial nutrient subsidies, in this case seabird guano.
  • ... There is an extensive body of research demonstrating that animals across taxa transport nutrients within and among ecosystems (e.g. Polis, Anderson & Holt, 1997;Helfield & Naiman, 2001;Bauer & Hoye, 2014;Adame et al., 2015). This literature shows that animals can redistribute large masses of nutrients in the environment by (i) consuming and transporting biomass (e.g. the deposition of waste products by migrating grazers such as wildebeest (Connochaetes taurinus; Holdo et al., 2007)) and (ii) serving as the supply of biomass themselves (e.g. via predator consumption or decomposition of wildebeest carcasses; Subalusky et al., 2017). ...
    Article
    Animal movements are important drivers of nutrient redistribution that can affect primary productivity and biodiversity across various spatial scales. Recent work indicates that incorporating these movements into ecosystem models can enhance our ability to predict the spatio-temporal distribution of nutrients. However, the role of animal behaviour in animal-mediated nutrient transport (i.e. active subsidies) remains under-explored. Here we review the current literature on active subsidies to show how the behaviour of active subsidy agents makes them both ecologically important and qualitatively distinct from abiotic processes (i.e. passive subsidies). We first propose that animal movement patterns can create similar ecological effects (i.e. press and pulse disturbances) in recipient ecosystems, which can be equal in magnitude to or greater than those of passive subsidies. We then highlight three key behavioural features distinguishing active subsidies. First, organisms can transport nutrients counter-directionally to abiotic forces and potential energy gradients (e.g. upstream). Second, unlike passive subsidies, organisms respond to the patterns of nutrients that they generate. Third, animal agents interact with each other. The latter two features can form positive-or negative-feedback loops, creating patterns in space or time that can reinforce nutrient hotspots in places of mass aggregations and/or create lasting impacts within ecosystems. Because human-driven changes can affect both the space-use of active subsidy species and their composition at both population (i.e. individual variation) and community levels (i.e. species interactions), predicting patterns in nutrient flows under future modified environmental conditions depends on understanding the behavioural mechanisms that underlie active subsidies and variation among agents' contributions. We conclude by advocating for the integration of animal behaviour, animal movement data, and individual variation into future conservation efforts in order to provide more accurate and realistic assessments of changing ecosystem function.
  • ... These mobile predators translocate organic material and nu trients through their foraging migrations and return to roosting/ resting sites (Schmitz et al. 2010, Valencia-Aguilar et al. 2013, Buelow & Sheaves 2015, Moss 2017. The faeces of birds and caiman at roosting/ resting sites subsidise the nutrient load in what are often nutrient-limited mangroves (Fittkau 1970, Adame et al. 2015, Alongi 2018. Such nutrient subsidies can be strong enough to fun damen tally alter ecosystem functioning (Fittkau 1970, Powell et al. 1991, Maron et al. 2006, Graham et al. 2018), yet we have little understanding of these processes in mangrove-lined estuaries. ...
    Article
    Seascape connectivity is crucial for healthy, resilient ecosystems and fisheries. Yet, our understanding of connectivity in turbid mangrove-lined estuaries - some of the world’s most productive ecosystems - is limited to macrotidal systems, and rarely incorporates highly mobile top predators. We analysed δ13C and δ15N isotope values of seven primary producers, 24 invertebrate taxa, 13 fishes, four birds and one reptile to reveal trophic interactions within and between a mangrove and adjacent mudflat in a microtidal system of the Gulf of Paria, Orinoco River estuary. Primary producers, invertebrates and fishes collected within the mangrove were significantly depleted in 13C and 15N compared to those collected on the mudflat. Stable isotope mixing models showed that mangrove-derived carbon was predominantly assimilated by invertebrates (78±5%) and fishes (88±11%) sampled in the mangrove. In contrast, invertebrates and fishes sampled in the mudflat derived less than 21% of their carbon from mangrove sources. Instead, microphytobenthos and phytoplankton underpinned the mudflat food web. Scarlet ibis (Eudocimus ruber) and night heron (Nyctanassa violacea) were also highly associated with mangrove carbon sources. However, osprey (Pandion haliaetus), snowy egret (Egretta thula), and caiman (Caiman crocodilus) obtained carbon from both mangrove and mudflat sources, effectively integrating the food webs. The present study demonstrates simultaneous aspects of food web segregation and connectivity, as well as the importance of surveying the entire food web across a range of tidal systems when investigating seascape connectivity.
  • ... For example, a group of metals and metalloids in sediments have been identified as seabird-related elements Shoji et al., 2018;Sun et al., 2000). P in soil or sediments is a marker for seabird influence (Adame et al., 2015;. For ornithogenic sediments on the Xisha Islands, P is also one of the most typical bio-elements. ...
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    Seabirds are typical bio‐vectors, delivering both nutrients and metals across ecosystem boundaries. However, seabird transfer of Ag and Co has not been well documented. Using an ornithogenic sediment core collected from the remote Zhaoshu Island, South China Sea, we investigated potential impacts of seabirds on Ag and Co transportation. These two elements exhibited peak abundance in a guano layer in the sediment profile. Via statistical analyses, Ag, Co and previously identified avian bio‐elements (Cn, Zn, Cd, P, As, Se) had a common source, i.e. guano. Guano input was also partly responsible for the distribution of Y, Ce, La, Sc and U in the bulk sediments. The concentration‐versus‐depth profiles of Mn, Mo, Bi, Rb and W were possibly associated with organic matter.
  • Article
    Nitrogen (N) enrichment can have large effects on mangroves’ capacity to provide critical ecosystem services by affecting fundamental functions such as N cycling and primary productivity. However, our understanding of excess N input effects on N cycling in mangroves remains quite limited. To advance our understanding of how N enrichment via water or air pollution affects mangroves, we evaluated whether increasing N inputs would decrease biological N fixation (BNF), but intensify N dynamics and N losses to the atmosphere in these systems. We measured N concentrations in sediment and vegetation, rates of BNF in sediment and litter, and net sediment ammonification and nitrification rates. We also evaluated long-term integrated N dynamics and N losses to the atmosphere using the natural abundance of N stable isotopes (δ15N) in the sediment–plant system and in estuarine water. We performed these analyses at non-N-enriched and N-enriched (that is, polluted) fringe and basin mangroves in southeastern Brazil. The δ15N in the sediment–plant system was higher at N-enriched than non-N-enriched fringe sites, indicating increased N losses to the atmosphere from N-enriched sites. However, N concentrations in sediment and vegetation were similar or lower at N-enriched relative to non-N-enriched sites. BNF and net ammonification and nitrification rates were also similar between N-enriched and non-N-enriched sites. Excess N inputs intensified N losses to the atmosphere from mangroves, but N pools, BNF, and net ammonification and nitrification rates were not affected by N enrichment, likely because excess N was quickly lost from the system by direct denitrification and volatilization. This is a post-peer-review, pre-copyedit version of an article published in Ecosystems. The final authenticated version is available online at http://dx.doi.org/10.1007%2Fs10021-018-0327-0. Use the following link to get access to the full-text view-only version https://rdcu.be/bfRMO
  • Article
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    Background Mangrove forests provide many ecosystem services, including the provision of habitat that supports avian biodiversity. However, hurricanes can knock down trees, alter hydrologic connectivity, and affect avian habitat. In 1995, Hurricanes Opal and Roxanne destroyed approximately 1,700 ha of mangrove forest in Laguna de Términos, Mexico. Since then, hydrological restoration has been implemented to protect the mangrove forest and its biodiversity. Methods Since avian communities are often considered biological indicators of ecosystem quality, avian diversity and species relative abundance were evaluated as indicators of mangrove restoration success by comparing undisturbed mangrove patches with those affected by the hurricanes. Using bird surveys, similarity analyses, and generalized linear models, we evaluated the effects of water quality variables and forest structure on the relative abundance and diversity of the avian community in disturbed, restored, and undisturbed mangrove patches. Results Higher bird species richness and relative abundances were found in disturbed and restored sites compared to the undisturbed site. After restoration, values of frequency of flooding, water temperature, tree density, and the number of tree species were more similar to that of the undisturbed site than to the values of the disturbed one. Such variables influenced the relative abundance of bird guilds in the different habitat conditions. Furthermore, some insectivorous bird species, such as the Yellow Warbler and Tropical Kingbird, were found to be similarly abundant in both undisturbed and restored sites, but absent or very low in occurrence at the disturbed site. Conclusions Collectively, our results strongly suggest that hydrologic restoration helps to enhance niche availability for different bird guilds, including water and canopy bird species. Our work can help inform management strategies that benefit avian communities in mangrove forests and wetland systems.
  • Article
    There is convincing evidence that large land mammals were formerly responsible for substantial transfers of nutrients across the freshwater and land system. Many of them were made extinct, probably by human hunting, around 10 000 to 14 000 BP, and the populations of the survivors were severely reduced as the Holocene progressed. Evidence is examined that such transfers were equally important among the oceans, coastal waters and inland systems as a result of the activities of anadromous fishes, marine reptiles, seabirds and marine mammals. Numbers of all of these have also been greatly reduced as a result of human activities, though largely in the past few hundred years. Their past and present status and potentialities for nutrient recycling and transfers are assessed. Large marine animals have potentially substantial top-down effects in structuring marine communities, though there is good evidence only for sea turtles and inshore habitats. There are many potential pathways for nutrient transfer, reflected in large accumulations on land of guano from seabirds. Great whales, because of their size and movement range, also offer large potentialities for transfer of nutrients across the oceans and from deep water towards the surface. However, from the very limited evidence available, it appears that the absolute global effects of these are likely to have been and to be minor. Transfers on land benefited from large nutrient supplies available in soils, from high productivity arising from light availability, from a dense and diverse mammal community and from a much smaller ratio of freshwater volume to land area. The huge volume of ocean water, its much greater mixing by wind and currents, and lower overall productivity preclude against globally significant changes in nutrient concentrations as a result of the movements of large animals, despite sometimes dramatic local effects of seabirds nesting on land and anadromous fish moving from the ocean to their freshwater spawning grounds. The intense scientific interest in these models, and the supportive vocabulary created to describe these processes, may have led to an overemphasis of their global significance.
  • Chapter
    Seabird islands house large colonies of seabirds that feed at sea but return to land to breed. Seabirds deposit large amounts of nutrients of marine origin onto islands; many species also disturb soil and vegetation during the building and maintenance of nests. Nutrient subsidies and physical disturbance by seabirds alter island soils and vegetation and modify plant and animal communities. Introduction of non-native predators has resulted in population decreases or local extinction of many seabird species. Recent efforts at eradication of introduced seabird predators have been successful, but re-establishment of seabirds and seabird island communities will likely take additional active restoration. Many other factors impact seabird populations such as overfishing, seabirds caught as by-catch, increases in sea surface temperature, sea level rise, and various sorts of marine pollution, including plastics consumed by seabirds. These factors directly and indirectly affect the ecology of seabird islands.
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    Colonial nesting and roosting birds can degrade their habitat by soil salinization, eutrophication, and acidification associated with excessive deposition of avian excreta. We studied the impact of a protected wading bird colony on soil microbial communities from cork oak woodlands in Doñana National Park (SW Spain). Over one year we analyzed soil properties (pH, salinity, soluble N and P forms, extractable organic carbon - EOC -), microbial activity (basal respiration, community-level physiological profile, extracellular enzyme activities) and community structure (fungal, bacterial and archaeal terminal restriction fragments -TRFs-) along a gradient of bird nesting intensity. Bird nesting largely impacted soil chemical environment, with increases from 25 to 500 μS cm⁻¹ in soil salinity, from 6 to 725 mg kg⁻¹ in soil P, from 5 to 22 mg kg⁻¹ in N-NH4, and from 5.4 to 245 mg kg⁻¹ in N-NO3 between the extremes of the nesting intensity gradient in the wet season. Most of these chemical changes were enhanced in the dry season. We observed positive linear or log-linear relationships between the bird nesting footprint on soils (indicated by an integrated soil chemistry index) and microbial biomass, basal respiration and most of the studied enzyme activities. This was likely due to the concurrent increases in EOC along the avian intensity gradient, which counteracted the negative impacts of salinity. Soil P and EOC were the main drivers for fungal, bacterial and archaeal TRFs diversity. Bacterial TRFs richness and diversity index decreased along the avian intensity gradient in the dry season, while archaeal TRFs diversity increased in those soils highly salinized by excess of avian excreta deposition. Our study clearly shows that this oversized bird colony has profound effects on soil chemistry and biological activity, and highlights the need for a re-evaluation of management strategies in this protected area, towards a greater consideration of soil processes in conservation priorities.
  • Chapter
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    INTRODUCCIÓN A lo largo de casi un tercio de los 10 000 km de longitud que conforman la banda litoral de México se contabilizan aproximadamente 164 cuerpos de agua costeros (De la Lanza-Espino et al., 2013). Abonando a la generalidad, más que a las particularidades morfológicas y geológicas que estos cuerpos de agua costeros pudieran albergar, se denomina lagunas costeras a las bahías someras, sondas, bocas, esteros, estuarios y caletas (Figura 1). En el interior de las lagunas costeras coexisten productores primarios como fitoplancton, microfitobentos y pastos marinos, favoreciendo una alta productividad durante todo el ciclo anual, aún en el marco de un ambiente fluctuante como el que caracteriza a estos sistemas, el cual selecciona bajo una alternancia programática, al mayor contribuyente de entre esta variedad de productores primarios (Medina-Gómez y Herrera-Silveira, 2006). Particularmente, una alta biodiversidad del componente de vegetación acuática sumergida (VAS) brinda no sólo áreas críticas para numerosas especies, sino también insumos de materia y energía que abastecen procesos de transformación biogeoquímica que ocurren tanto en la columna de agua, como en la biota y los sedimentos. A pesar de la gama de ecosistemas que se agrupan en la categoría de lagunas costeras, un rasgo esencial en todos ellos es la presencia de diversos sistemas circundantes, tanto hacia el continente (manglares y marismas) como oceánicos (mar de plataforma), así como el transporte activo de materiales a través de las fronteras que estos sistemas comparten y de las múltiples interfaces internas (aire-columna de agua, sedimento-columna de agua, agua dulce-salobre-marina) que resultan de la contigüidad con dicho mosaico de ecosistemas. Esta conexión está determinada por la geomorfología de cada ecosistema, la cual concierne a la intermitencia o permanencia de apertura de la boca lagunar y otras fronteras que guarda con ecosistemas vecinos, desempeñando un papel importante al materializar el acoplamiento con aquellos. También, los patrones de circulación del agua dentro de dichos ecosistemas controlan la tasa y magnitud del intercambio de materiales con los distintos ambientes costeros, definiendo al contexto climatológico y la hidrodinámica como reguladores preponderantes del grado de interacción a lo largo de este continuo ecológico. La interacción entre los diferentes ecosistemas, llamada conectividad, es evidente en las lagunas costeras, las cuales constituyen fundamentalmente un escenario ambiental que recibe el suministro de distintos aportes, entre ellos carbono inorgánico disuelto y carbono orgánico particulado (CID y COP, respectivamente). Se calcula en 1.0 Pg C año-1 el incremento de los flujos de carbono hacia aguas epicontinentales debido a alteraciones de origen humano desde la era industrial, principalmente asociadas a actividades de explotación del suelo (Reigner et al., 2013). Se considera que las lagunas costeras desempeñan un papel crucial en el denominado Carbono Azul, a consecuencia de su alta capacidad para secuestrar este insumo de carbono (C), ya sea en material vivo o como
  • Article
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    Hurricanes are recurring high-energy disturbances in coastal regions that change community structure and function of mangrove wetlands. However, most of the studies assessing hurricane impacts on mangroves have focused on negative effects without considering the positive influence of hurricane-induced sediment deposition and associated nutrient fertilization on mangrove productivity and resilience. Here, we quantified how Hurricane Irma influenced soil nutrient pools, vertical accretion, and plant phosphorus (P) uptake after its passage across the Florida Coastal Everglades in September 2017. Vertical accretion from Irma’s deposits was 6.7 to 14.4 times greater than the long-term (100 y) annual accretion rate (0.27 ± 0.04 cm y ⁻¹ ). Storm deposits extended up to 10-km inland from the Gulf of Mexico. Total P (TP) inputs were highest at the mouth of estuaries, with P concentration double that of underlying surface (top 10 cm) soils (0.19 ± 0.02 mg cm ⁻³ ). This P deposition contributed 49 to 98% to the soil nutrient pool. As a result, all mangrove species showed a significant increase in litter foliar TP and soil porewater inorganic P concentrations in early 2018, 3 mo after Irma’s impact, thus underscoring the interspecies differences in nutrient uptake. Mean TP loading rates were five times greater in southwestern (94 ± 13 kg ha ⁻¹ d ⁻¹ ) mangrove-dominated estuaries compared to the southeastern region, highlighting the positive role of hurricanes as a natural fertilization mechanism influencing forest productivity. P-rich, mineral sediments deposited by hurricanes create legacies that facilitate rapid forest recovery, stimulation of peat soil development, and resilience to sea-level rise.
  • Increasing awareness of avian ecological function Development of allometric relations for three mangrove species in South Florida for use in the Greater Everglades ecosystem restoration Utilization of nitrogen derived from seabird guano by terrestrial and marine plants at St
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  • The habitat function of mangroves for terrestrial and marine fauna: a review Interactions of nutrients, plant growth and herbivory in a mangrove ecosystem A manual of chemical and biological methods for seawater analysis
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  • Article
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    Mangrove islands in Belize are characterized by a unique switching from nitrogen (N) to phosphorus (P) limitation to tree growth from shoreline to interior. Fertilization has previously shown that Rhizophora mangle (red mangrove) fringe trees (5-6 m tall) growing along the shoreline are N limited; dwarf trees (less than or equal to 1.5 m tall) in the forest interior are P limited; and transition trees (2-4 m tall) are co-limited by both N and P. Growth patterns paralleled a landward decrease in soil flushing by tides and an increase in bioavailable N, but P availability remained consistently low across the gradient. Stable isotopic composition was measured in R. mangle leaves to aid in explaining this nutrient switching pattern and growth variation. Along control transects, leaf delta(15)N decreased from +0.10parts per thousand (fringe) to -5.38parts per thousand (dwarf). The delta(15)N of N-fertilized trees also varied spatially, but the values were consistently more negative (by similar to3parts per thousand) compared to control trees. Spatial variation in 815 N values disappeared when the trees were fertilized with P and values averaged +0.12parts per thousand, similar to that in control fringe trees. Neither variation in source inputs nor microbial fractionation could fully account for the observed patterns in delta(15)N. The results instead suggest that the lower delta(15)N values in transition and dwarf control trees were due to plant fractionation as a consequence of slower growth and lower N demand. P fertilization increased N demand and decreased fractionation. Although leaf delta(13)C was unaffected by fertilization, values increased from fringe (-28.6parts per thousand) to transition (-27.9parts per thousand) to dwarf (-26.4parts per thousand) zones, indicating spatial variation in environmental stresses affecting stomatal conductance or carboxylation. The results thus suggest an interaction of external supply, internal demand, and plant ability to acquire nutrients under different hydro-edaphic conditions that vary across this tree-height gradient. The findings not only aid in understanding mangrove discrimination of nitrogen and carbon isotopes, but also have implications for identifying nutrient loading and other stress conditions in coastal systems dominated by mangroves.
  • Chapter
    Although most basic principles and techniques for studying mineral nutrition were developed in agriculture, they can, with some modification, be used for studying the mineral nutrition of wild plants. In this chapter we describe procedures that have proven useful in ecology and forestry and discuss the advantages, disadvantages and potential sources of error involved with each method.
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    Root production influences a range of belowground processes, such as soil accretion, carbon sequestration and nutrient acquisition. Here, we measured biomass and root production of mangroves surrounding a karstic oligotrophic lagoon that spans a nutrient and salinity gradient. We also measured forest structure and soil physicochemical conditions (salinity, bulk density, carbon, nitrogen (N) and phosphorus (P)) in order to determine factors associated with root production. We tested the following hypotheses: 1) root biomass and production increase at low soil P and N in order to maximize resource utilization, and 2) root biomass and production increase with high interstitial salinity. Root biomass (947–3,040 g m−2) and production (0.46–1.85 g m−2 day−1) increased where soil P and interstitial salinity were relatively high. Thus, we rejected the first hypothesis and confirmed the second. The larger root fraction (5–20 mm) was the major contributor to root biomass and production. Our findings suggest that root production and thus capacity for belowground carbon storage in karstic regions, where P is often limiting, is greater where interstitial salinity and P are higher. This contrasts with past assessments indicating that P-deficiency stimulates root growth, suggesting wide variation in belowground responses in mangroves.
  • Article
    Bacterial productivity ((3)H-thymidine incorporation into DNA) and intertidal microbenthic communities were examined within five mangrove estuaries along the tropical northeastern coast of Australia. Bacteria in mangrove surface sediments (0-2 cm depth) were enumerated by epifluorescence microscopy and were more abundant (mean and range: 1.1(0.02-3.6)×10(11) cells·g DW(-1)) and productive (mean: 1.6 gC·m(-2)· d(-1)) compared to bacterial populations in most other benthic environments. Specific growth rates (¯x=1.1) ranged from 0.2-5.5 d(-1), with highest rates of growth in austral spring and summer. Highest bacterial numbers occurred in winter (June-August) in estuaries along the Cape York peninsula north of Hinchinbrook Island and were significantly different among intertidal zones and estuaries. Protozoa (10(5)-10(6)·m(-2), pheopigments (0.0-24.1μg·gDW(-1)) and bacterial productivity (0.2-5.1 gC·m(-2)·d(-1)) exhibited significant seasonality with maximum densities and production in austral spring and summer. Algal biomass (chlorophylla) was low (mean: 1.6μg·gDW(-1)) compared to other intertidal sediments because of low light intensity under the dense forest canopy, especially in the mid-intertidal zone. Partial correlation analysis and a study of possible tidal effects suggest that microbial biomass and bacterial growth in tropical intertidal sediments are regulated primarily by physicochemical factors and by tidal flushing and exposure. High microbial biomass and very high rates of bacterial productivity coupled with low densities of meiofaunal and macroinfaunal consumers observed in earlier studies suggest that microbes may be a sink for carbon in intertidal sediments of tropical mangrove estuaries.
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    Poor water quality affects the biogeochemistry functions and the biological community structure of coastal ecosystems. In this study we investigated the effect of water quality on: (a) The exchange of dissolved organic carbon (DOC) between floodwater and mangrove forests, (b) the abundance of sediment bacteria, (c) the microbial community composition, and (d) the microbial catabolic activity. We selected six mangrove forests that were flooded by creeks with differing water qualities to test for thresholds of nutrient concentrations associated with changes in DOC dynamics and the microbial community. Our results show that in sites flooded by water high in soluble reactive phosphorus (SRP) (>20 μg l−1) and NH4+ (>30 μg l−1) the DOC concentrations in the floodwater were higher than in ebb water, suggesting DOC import by the mangroves. In contrast, in sites flooded by water low in SRP (<20 μg l−1) and NH4+ (<30 μg l−1), DOC concentrations in the floodwater were lower than in the ebb water, suggesting DOC export by the mangroves. Bacterial abundance was higher in sediments with low bulk density, high organic carbon and when flooded by water with low N:P (1–2), but the microbial composition and total catabolic activity assessed using Biolog Ecoplates™ did not differ among sites. The relationship between water quality, microbial communities and DOC exchange suggests that, at least during some periods of the year, poor water quality increases bacterial abundance and modifies DOC exchange of mangrove forests with floodwater and thus, their role in supporting near-shore productivity.
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    Tropical cyclones can be devastating to ecosystems, but they can also result in pulses of fresh water and sediments delivered in floodwaters to the coastal zone. In the arid zone the pulses provided by cyclones may be particularly important for the maintenance of productivity. We examined the impacts of Cyclone Pancho on growth and nutrient limitations to growth in mangroves on the arid coast of Western Australia. We found that growth of trees was enhanced after the cyclone, more than doubling their rates of stem extension. Fertilisation studies showed that before the cyclone tree growth was nutrient limited. After the cyclone fertilisation treatments had no significant effect on growth, indicating nutrients had been delivered during the storm. Additionally, before the cyclone the efficiency of resorption of phosphorus and nitrogen from senescent leaves was higher than after the cyclone, suggesting that nutrient availability was enhanced. Analysis of stable isotopes of leaf tissue indicated that the cyclone was associated with small changes in water use efficiency, consistent with decreased soil salinity associated with the cyclone. There was, however, significant reductions in δ15N indicating enhanced N supply potentially from a new source. We conclude that in the arid zone, floodwater associated with cyclones is important for the delivery of nutrient subsidies that stimulate mangrove growth and that predicted future reductions in the frequency of cyclones will have negative impacts on the productivity of these ecosystems.
  • Article
    The mechanisms governing dispersion processes in the northern Yucatan coast are investigated using a barotropic numerical model of coastal circulation, which includes wind-generated and large scale currents (i.e. Yucatan Current). This work provides the foundations for studying the dispersion of harmful algal blooms (HABs) in the area. Modelling experiments include effects of climatic wind (from long term monthly mean NCEP reanalysis), short term wind events (from in situ point measurements), and Yucatan Current (YC) characteristics. Its magnitude was approximated from published reports, and its trajectory from geostrophic current fields derived from altimeter data. These provided a range of real and climatic conditions to study the routes in which phytoplankton blooms may travel. The 2-D model results show that a synthetic and conservative bloom seeded in the Cabo Catoche (CC) region (where it usually grows), moves along the coast to the west up to San Felipe (SF), where it can either move offshore, or carry on travelling westwards. The transport to the west up to SF is greatly influenced by the trajectory, intensity and proximity of the YC jet to the peninsula, which enhances the westward circulation in the Yucatan Shelf. Numerical experiments show that patch dispersion is consistently to the west even under the influence of northerly winds. When the YC flows westward towards the Campeche Bank, momentum transfer caused by the YC jet dominates the dispersion processes over wind stress. On the other hand, when it flows closer to Cuba, the local processes (i.e. wind and bathymetry) become dominant. Coastal orientation and the Coriolis force may be responsible for driving the patch offshore at SF if external forcing decreases.
  • Article
    Mangrove islands in Belize are characterized by a unique switching from nitrogen (N) to phosphorus (P) limitation to tree growth from shoreline to interior. Fertil-ization has previously shown that Rhizophora mangle (red mangrove) fringe trees (5–6 m tall) growing along the shoreline are N limited; dwarf trees (1.5 m tall) in the forest interior are P limited; and transition trees (2–4 m tall) are co-limited by both N and P. Growth patterns paralleled a landward decrease in soil flushing by tides and an increase in bioavailable N, but P availability remained consistently low across the gradient. Stable isotopic composition was measured in R. mangle leaves to aid in explaining this nutrient switching pattern and growth variation. Along control transects, leaf 15 N decreased from 0.10‰ (fringe) to 5.38‰ (dwarf). The 15 N of N-fertilized trees also varied spatially, but the values were consistently more negative (by 3‰) compared to control trees. Spatial variation in 15 N values disappeared when the trees were fertilized with P, and values averaged 0.12‰, similar to that in control fringe trees. Neither variation in source inputs nor microbial fractionation could fully account for the observed patterns in 15 N. The results instead suggest that the lower 15 N values in transition and dwarf control trees were due to plant fractionation as a consequence of slower growth and lower N demand. P fertilization increased N demand and decreased fractionation. Although leaf 13 C was unaffected by fertilization, values increased from fringe (28.6‰) to transition (27.9‰) to dwarf (26.4‰) zones, indicating spatial variation in environmental stresses affecting stomatal conductance or carboxylation. The results thus suggest an interaction of external supply, internal demand, and plant ability to acquire nutrients under different hydro-edaphic con-ditions that vary across this tree-height gradient. The findings not only aid in understanding mangrove discrimination of nitrogen and carbon isotopes, but also have implications for identifying nutrient loading and other stress conditions in coastal systems dominated by mangroves.
  • Article
    Dense, conspicuous colonies of seabirds and pinnipeds breed on ocean islands throughout the world. Such colonies have been shown to have local impacts on prey populations, but whether or not they affect nutrient cycling has been debated. We determined the natural abundance levels of the stable isotopes (C and N) of primary producers, seabirds and other consumers at and near St. Paul Island, Pribilof Islands, Bering Sea, in summer 1993. Marine primary producers (phytoplankton, as particulate organic matter, and kelp) collected near seabird colonies were ca. 6.5‰ enriched in both 15N and 13C relative to those collected further from shore. Terrestrial plants collected near the seabird colonies were enriched in 15N (δ15N ca. 22‰) compared with conspecifics collected away from the colonies (δ15N ca. 11‰). The trend towards higher δ15N values in marine and terrestrial plants near bird colonies is consistent with their uptake of ornithogenic N. This 15N-enrichment of plants using ornithogenic N can be attributed to a combination of two processes: trophic enrichment, and volatilization of ammonia produced during degradation of terrestrially deposited guano. Seabird breeding colonies at St. Paul Island appear to be significant sources of recycled nitrogen for terrestrial plants in the vicinity of colonies and for phytoplankton in the nearshore zone.
  • Article
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    studied temporal variation in abundance of Nearctic-Neotropical mi- grants, particularly the Northern Waterthrush (Seiurus noveboracensis), Prothonotary War- bler (Protonoturia citrea), and American Redstart (Setophaga ruticillu) in two black man- grove sites of central Panama from September 1993 through May 1995. The two sites, on the Caribbean and the Pacific coasts, differ importantly in annual rainfall, tide amplitude, and seasonal invertebrate abundance. Most migrant species varied temporally in abundance with the opposite pattern at each site, suggesting mid-winter movements correlated with abundance of food resources. Because of their wide geographic distribution and their par- ticular response to hydrographic factors, mangroves are likely to have a temporally com- plementary role in sustaining migrant populations throughout the Neotropics. However, vari- ations in migrant numbers reported in other Neotropical habitats could also reflect large- scale movements by migrants. Occurrence of mid-winter (facultative) migration has been documented mostly for the Palearctic-African migratory system, and needs to be investigated in the Nearctic-Neotropical realm for proper conservation of migratory species. Received
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    Tropical storms can shape the structure and productivity of mangrove forests. In this study, we compared current litterfall with historical tropical storm disturbance in the karstic Yucatan Peninsula (YP). We also explored the relationship between litterfall and the fresh/seawater mixture of floodwater. Our hypotheses were that litterfall peaks at moderate perturbations and in sites where seawater dominates the floodwater mixture, and thus, where soil total phosphorus (TP) is relatively high. Litterfall was sampled for 2 yr, from eight mangrove forests around the YP. At each site, forest structure, interstitial salinity, TP, nitrogen, carbon, pH, and bulk density were measured. Our results show that mangrove forest from northeast YP are historically impacted by stronger and more frequent tropical storms compared with those in northwest and southeast YP, where tropical storm intensity is moderate and mild, respectively. Litterfall was higher in northwest YP (≥3 g/m2 d) compared with northeast and southeast (≤ 2 g/m2 d), mimicking a subsidy-stress gradient where highest productivity is reached at moderate perturbations. Neither salinity nor forest structure alone satisfactorily explained litterfall variability. Soil TP followed a similar geographical pattern as the disturbance gradient: highest concentrations in the northwest YP (≥0.05%) and lowest in the northeast and southeast (≤ 0.03%). Thus, it is likely that TP, and not tropical storm disturbance, is the main driver of litterfall in mangrove forests of the YP. Alterations in TP availability (e.g., sea level rise and aquifer contamination) have the potential to modify mangrove productivity in the region.
  • Article
    To help define nitrogen (N) sources and patterns of N processing in mangrove ecosystems, mangrove leaf nitrogen contents and δ15N values were assayed in three marshes along the south Florida coast. In each marsh, leaf samples were collected from dwarf mangroves at interior locations and taller mangroves at the ocean fringe. Leaf %N and δ15N values did not differ consistently between dwarf and tall mangroves, even though there were large variations in δ15N (18‰ range, −5 to +13‰) and %N (1·2% range, 0·9–2·1%). Highest %N and δ15N values occurred along the western margin of Biscayne Bay where canals draining agricultural lands deliver high-nitrate waters to fringing mangrove marshes. High mangrove δ15N values may be good biomonitors of anthropogenic N loading to south Florida estuaries. Lower values likely reflect less anthropogenic N entering the mangrove marshes, as well as differences in plant physiology that occur along the fringe-dwarf gradient.
  • Article
    We report 87Sr/86Sr and ion concentrations of sulfate, chloride, and strontium in the groundwater of the northern and central Yucatan Peninsula, Mexico. Correlation between these data indicates that ejecta from the 65.95 m.y. old Chicxulub impact crater have an important effect on hydrogeology, geomorphology, and soil development of the region. Ejecta are present at relatively shallow subsurface depths in north-central Yucatan and at the surface along the Rio Hondo escarpment in southeast Quintana Roo, where they are referred to as the Albion Formation. Anhydrite/gypsum (and by inference celestite) are common in impact ejecta clasts and in beds and cements of overlying Paleocene and Lower Eocene rocks cored around the margin of the crater. The sulfate-rich minerals that are found in rocks immediately overlying the impact ejecta blanket, may either be partially mobilized from the ejecta layer itself or may have been deposited after the K/T impact event in an extensive pre-Oligocene shallow sea. These deposits form a distinctive sedimentary package that can be easily traced by the Eocene–Cretaceous 87Sr/86Sr signal. A distinct Sr isotopic signature and high SO4/Cl ratios are observed in groundwater of northwestern and north-central Yucatan that interacts with these rocks. Moreover, the distribution of the gypsum-rich stratigraphic unit provides a solution-enhanced subsurface drainage pathway for a broad region characterized by dissolution features (poljes) extending from Chetumal, Quintana Roo to Campeche, Campeche. The presence of gypsum quarries in the area is also consistent with a sulfate-rich stratigraphic “package” that includes ejecta.
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    Coastal wetlands can have exceptionally large carbon (C) stocks and their protection and restoration would constitute an effective mitigation strategy to climate change. Inclusion of coastal ecosystems in mitigation strategies requires quantification of carbon stocks in order to calculate emissions or sequestration through time. In this study, we quantified the ecosystem C stocks of coastal wetlands of the Sian Ka'an Biosphere Reserve (SKBR) in the Yucatan Peninsula, Mexico. We stratified the SKBR into different vegetation types (tall, medium and dwarf mangroves, and marshes), and examined relationships of environmental variables with C stocks. At nine sites within SKBR, we quantified ecosystem C stocks through measurement of above and belowground biomass, downed wood, and soil C. Additionally, we measured nitrogen (N) and phosphorus (P) from the soil and interstitial salinity. Tall mangroves had the highest C stocks (987±338 Mg ha) followed by medium mangroves (623±41 Mg ha), dwarf mangroves (381±52 Mg ha) and marshes (177±73 Mg ha). At all sites, soil C comprised the majority of the ecosystem C stocks (78-99%). Highest C stocks were measured in soils that were relatively low in salinity, high in P and low in N∶P, suggesting that P limits C sequestration and accumulation potential. In this karstic area, coastal wetlands, especially mangroves, are important C stocks. At the landscape scale, the coastal wetlands of Sian Ka'an covering ≈172,176 ha may store 43.2 to 58.0 million Mg of C.
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    1.Metrosideros polymorpha (O’hia), the dominant tree species in Hawaiian forest ecosystems, grows from sea level to treeline (2500 m). Consistent changes in its morphology and anatomy occur along this altitudinal/temperature gradient. Patterns of variation in photosynthetic gas exchange, leaf nitrogen content, nitrogen-use efficiency, δ¹³C, and morphological and anatomical characteristics were determined across the elevational gradient. In addition, on-line carbon isotope discrimination studies of high and low elevation M. polymorpha were performed.
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    Una zona importante de distribución de manglares en Yucatán está asociada al sistema lagunar de la Reserva de la Biosfera Ría Celestún, localizada al noroeste de la Península. Los principales impactos hacia este ecosistema son la interrupción de flujos de agua, el crecimiento urbano no controlado, el cambio en el uso del suelo y la deforestación. El suelo de la región es cárstico y altamente permeable; al no existir ríos, la única fuente de agua son la precipitación pluvial (760 mm año-1) y las descargas de agua subterránea las cuales tienen su mayor influencia en la parte interna de la laguna, reflejándose en un gradiente de menor a mayor salinidad hacia la boca de la laguna que la conecta con el Golfo de México. Debido a este gradiente se observaron diferentes grados de estructura, dominancia de especies y productividad, registrándose las mayores estructuras y valores de caída de hojarasca de 4,09 g m2 día-1 en la parte interna y de 2,59 g m2 día-1 en la zona de la boca. Temporalmente la productividad de la laguna está relacionada con la variabilidad climática de la región (nortes, secas y lluvias). Los diferentes patrones de estructura y producción de hojarasca fueron determinados por características del suelo como la salinidad y del clima. Por lo tanto las estrategias de manejo deben considerar estos aspectos, así como la variabilidad espacial y temporal de la hidrología, ya que modificaciones, incluso pequeñas, de este aspecto producirían impactos negativos de mayor escala, sugiriendo la vulnerabilidad de este ecosistema a los cambios hidrológicos y ambientales climáticos.
  • Article
    The ramifying effects of top predators on food webs traditionally have been studied within the framework of trophic cascades. Trophic cascades are compelling because they embody powerful indirect effects of predators on primary production. Although less studied, indirect effects of predators may occur via routes that are not exclusively trophic. We quantified how the introduction of foxes onto the Aleutian Islands transformed plant communities by reducing abundant seabird populations, thereby disrupting nutrient sub-sidies vectored by seabirds from sea to land. We compared soil and plant fertility, plant biomass and community composition, and stable isotopes of nitrogen in soil, plants, and other organisms on nine fox-infested and nine historically fox-free islands across the Aleu-tians. Additionally, we experimentally augmented nutrients on a fox-infested island to test whether differences in plant productivity and composition between fox-infested and fox-free islands could have arisen from differences in nutrient inputs between island types. Islands with historical fox infestations had soils low in phosphorus and nitrogen and plants low in tissue nitrogen. Soils, plants, slugs, flies, spiders, and bird droppings on these islands had low 15 N values indicating that these organisms obtained nitrogen from internally derived sources. In contrast, soils, plants, and higher trophic level organisms on fox-free islands had elevated 15 N signatures indicating that they utilized nutrients derived from the marine environment. Furthermore, soil phosphorus (but not nitrogen) and plant tissue ni-trogen were higher on fox-free than fox-infested islands. Nutrient subsidized fox-free islands supported lush, high biomass plant communities dominated by graminoids. Fox-infested islands were less graminoid dominated and had higher cover and biomass of low-lying forbs and dwarf shrubs. While 15 N profiles of soils and plants and graminoid biomass varied with island size and distance from shore, after accounting for these effects differences between fox-infested and fox-free islands still existed. Fertilization over four years caused a 24-fold increase in graminoid biomass and a shift toward a more graminoid dominated plant community typical of fox-free islands. These results indicate that apex predators can influence plant productivity and composition through complex interaction web pathways involving both top-down forcing and bottom-up nutrient exchanges across systems.
  • Article
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    Aim: 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 man-groves of the Caribbean Region to better understand biological controls on habitat stability. Location: Mangrove-dominated islands on the Caribbean coasts of Belize, Honduras and Panama were selected as study sites. Methods: 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. Results: 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. Main conclusions: 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.
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    1 A gap dynamic model ( FORMAN) was developed as a first synthesis of available data for three Caribbean mangrove species into an individual-based model that simulates the long-term dynamics of mangrove forest development. 2 Field observations at three sites along the Shark River estuary were compared with simulation results, assuming development following Hurricane Donna in 1960. Total basal area simulated for each site was within ±10% of that observed, although species-specific basal area predictions were less accurate. 3 A decrease in nutrient availability from marine to mesohaline sites modelled the reduced basal area of Avicennia germinans and Laguncularia racemosa. However, at the lower nutrient site a 83% reduction in maximum sapling recruitment of both A. germinans and L. racemosa was required to fit field results. Increased basal area of A. germinans and L. racemosa limited the development of Rhizophora mangle at higher nutrient downstream sites, apparently due to competition for light resources. Both observed and simulated results indicated that R. mangle had higher frequencies in the smaller size classes at all three sites, compared to a bell-shaped size-class distribution of L. racemosa, particularly at the higher nutrient sites. 4 Succession was projected for the next 500 years at a site in the lower estuary. Long-term forest dynamics were sensitive to species-specific maximum sapling recruitment rates. In the absence of large-scale disturbance, initial dominance by L. racemosa was predicted to be replaced eventually by A. germinans, even when maximum sapling recruitment rate of A. germinans was set at half of L. racemosa and R. mangle. 5 Response curves for each species along gradients of soil nutrient resource and salinity illustrated their relative competitive balance over time (up to 300 years). Laguncularia racemosa dominated in fertile soils with low salinity at early stages of recovery, but its abundance decreased over time while A. germinans increased. The dominance of R. mangle was limited to regions with low nutrient availability and low salinity. Avicennia germinans dominated at higher salinities, where the effect of nutrient availability was overwhelmed by the tolerance of individual species to salt stress.
  • Article
    This study described the nutrient dynamics in a tropical coastal lagoon that is affected by the infiltration of cold nutrient-rich groundwater. The spatial and time variation of physicochemical characteristics (e.g., temperature, salinity, oxygen) and nutrients (e.g., nitrate, ammonium, soluble reactive silicate, soluble reactive phosphorus) are depicted and show changes with respect to weather conditions. The lagoon shows a permanent salinity gradient from the inner zone (14–19). Nitrate and soluble reactive silicate (SRSi) are inversely correlated with salinity. Soluble phosphorus (SRP) shows highest levels in the inner zone during winter months (>9 M). Ammonium shows two high peaks, one in the rainy season (15 M) and the other during winter (11 M). The intensity and quality of rainfall influences the nitrate and SRSi inputs, while biological activity influences the SRP and ammonium levels.
  • Article
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    Carbon and nitrogen stable isotopic data from the primary producers in mangrove ecosystems are needed to investigate trophic links and biogeochemical cycling. Compared with other mangrove species (e.g. Rhizophora mangle) very few measurements have been conducted on the white mangrove, Laguncularia racemosa. The carbon and nitrogen stable isotopic and elemental compositions of L. racemosa were analyzed and compared from Florida and Belize. 13C values of L. racemosa from Florida (mean = –26.4) were slightly higher than those from Twin Cays, Belize (mean = -27.4), which may be due to higher salinity in some parts of the Florida site. There was no difference between the 15N values from L. racemosa from these two sites (Florida mean = 0.6; Belize mean = 0.3), which are indicative of nitrogen derived from nitrogen fixation in a planktonic marine system. However, higher 15N values from L. racemosa at Man of War Cay in Belize (11.4 and 12.3), which is fertilized by roosting marine birds (14.0), illustrate that L. racemosa can sensitively reflect alternative nitrogen sources. Although the isotopic data could not distinguish between Avicennia germinans, R. mangle and L. racemosa in Belize the L. racemosa had considerably higher C/N ratios (46.5 – 116.1) compared with the Florida samples (42.2 – 76.0) or the other mangrove species. Unlike some previous findings from R. mangle, substrate characteristics (e.g. salinity, NH4 +, and H2S) were not related to the isotopic or elemental composition of L. racemosa. 13C, 15N and C/N were analyzed for ecosystem components from L. racemosa habitats at Twin Cays, including other plants (e.g. R. mangle, A. germinans and seagrass), detritus, microbial mats and sediments. Results from mass-balance calculations show that mangrove detritus composes very little of the sediment, which is principally composed of microbial biomass (80 – 90%). Detritus at some sites is also influenced by sources other than that from L. racemosa, including seagrass leaves.
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    Mathematical relations that use easily measured variables to predict difficult-to-measure variables are important to resource managers. In this paper we develop allometric relations to predict total aboveground biomass and individual components of biomass (e.g., leaves, stems, branches) for three species of mangroves for Everglades National Park, Florida, USA. The Greater Everglades Ecosystem is currently the subject of a 7.8-billion-dollar restoration program sponsored by federal, state, and local agencies. Biomass and production of mangroves are being used as a measure of restoration success. A technique for rapid determination of biomass over large areas is required. We felled 32 mangrove trees and separated each plant into leaves, stems, branches, and for Rhizophora mangle L., prop roots. Wet weights were measured in the field and subsamples returned to the laboratory for determination of wet-to-dry weight conversion factors. The diameter at breast height (DBH) and stem height were also measured. Allometric equations were developed for each species for total biomass and components of biomass. We compared our equations with those from the same, or similar, species from elsewhere in the world. Our equations explained ≥93% of the variance in total dry weight using DBH. DBH is a better predictor of dry weight than is stem height and DBH is much easier to measure. Furthermore, our results indicate that there are biogeographic differences in allometric relations between regions. For a given DBH, stems of all three species have less mass in Florida than stems from elsewhere in the world.
  • Article
    Colonies/roosts of piscivorous birds in Florida Bay, a subtropical estuary, concentrate nutrients by feeding away from their colonies/roosts and returning with food for young and to defaecate. Seagrass beds surrounding the colony islands were markedly different from those around similar islands that did not contain colonies. Seagrass standing crop was enhanced up to 200 m from bird colony islands compared with islands without colonies. The species of seagrass were also different at colonies, where Halodule wrightii and Ruppia maritima predominated in zones close to the colony islands. Around islands without colonies, only Thalassia testudinum was present.Experimental bird perches placed to stimulate concentrated bird presence produced changes in adjacent seagrass meadows that were similar to differences between islands with colonies and those without. Over 5 years, seagrass standing crop increased around the experimental perches, and species dominance shifted from T. testudinum to H. wrightii. No similar changes occurred at control locations. These experimental results indicate that the bird concentrations are responsible for the observed differences in seagrass communities surrounding islands that contain colonies.These enriched areas are significant to the seagrass ecosystem because many seagrasses in Florida Bay appear to be nutrient-limited. Demersal fish and invertebrate density and species richness have been shown to be a function of the seagrass standing crop and species composition, so the changes in seagrasses stimulated by localized bird concentrations have the capacity to alter the entire community structure.
  • Article
    This work is the beginning of a coastal water quality monitoring program to establish the baseline for the implementation of an integrated coastal management of the Yucatán Peninsula tropical ecosystem. Coastal water quality is affected by the increasing economic development. This area has no rivers because of its karst geomorphology, and the coastal freshwater comes from springs or seeps. Coastal water quality was studied in four towns from January to December 2000. Statistically significant differences among water quality variables and processes are discussed. Along with groundwater discharge, domestic and shrimp farming sewage are the main sources of nutrients, predominantly of nitrogen and silica. Salinity dilution is used to estimate the groundwater fraction that influences each area in northwestern Yucatán.
  • Article
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    This paper reports problems associated to the use of the Point-Centred Quarter Method (PCQM), as well as their possible solutions. Problematic settings in the application of the PCQM are amongst others due to the presence of multiple-stemmed trees (MST), to ambiguous settings for measuring the sampling point to nearest tree distance or the tree diameter, both of which may result in erroneous estimation of silvimetric variables and parameters. The analysis is based on a database of effective individual tree records including distances, diameters, and heights measured in the field in a Sri Lankan mangrove forest between 1997 and 2002, and randomly compiles a series of records that were used as PCQM sampling points. Various structural forest parameters were calculated, with particular emphasis on density and basal area.
  • Article
    This study quantifies the how of energy and biomass from a productive marine system to a relatively unproductive terrestrial system. Biomass from marine food webs (here, the Gulf of California) enters the terrestrial webs of islands and coastal areas through two conduits: (1) shore drift of algal wrack and carrion and (2) colonies of seabirds. Both conduits support dense assemblages of consumers: arthropods are 85-560 times more abundant in the supralittoral than inland and 2.2 times more abundant on islands with seabird colonies than those without. Marine input (MI), not terrestrial primary productivity (TP) by land plants, provides most energy and biomass for terrestrial communities on 16 of 19 study islands. The ratio of perimeter to area (PIA) significantly predicts arthropod abundance on islands and is the major determinant of the relative importance of allochthonous how; we expect PIA ratio to be important wherever transport of nutrients, detritus, and organisms among habitats occurs. Similar transport phenomena generally take place, often with significant impact, on coastal habitats and islands worldwide. Such input subsidizes a diverse array of terrestrial consumers; in many cases, subsidized consumers reach extraordinarily high densities and thus can depress their in situ resources. In general, we propose that such flow is often a key feature of the energetics, structure, and dynamics of populations, food webs, and communities whenever any two habitats, differing in productivity, are juxtaposed.
  • Article
    Coral cays form part of the Australian Great Barrier Reef. Coral cays with high densities of seabirds are areas of extreme nitrogen (N) enrichment with deposition rates of up to 1000 kg N ha(-1) y(-1). The ways in which N sources are utilised by coral cay plants, N is distributed within the cay, and whether or not seabird-derived N moves from cay to surrounding marine environments were investigated. We used N metabolite analysis, N-15 labelling and N-15 natural abundance (delta(15)N) techniques. Deposited guano-derived uric acid is hydrolysed to ammonium (NH4+) and gaseous ammonia (NH3). Ammonium undergoes nitrification, and nitrate (NO3-) and NH4+ were the main forms of soluble N in the soil. Plants from seabird rookeries have a high capacity to take up and assimilate NH4+, are able to metabolise uric acid, but have low rates of NO3- uptake and assimilation. We concluded that NH4+ is the principal source of N for plants growing at seabird rookeries, and that the presence of NH4+ in soil and gaseous NH3 in the atmosphere inhibits assimilation of NO3-, although NO3- is taken up and stored. Seabird guano, Pisonia forest soil and vegetation were similarly enriched in N-15 suggesting that the isotopic enrichment of guano (delta(15)N 9.9parts per thousand) carries through the forest ecosystem. Soil and plants from woodland and beach environments had lower delta(15)N (average 6.5parts per thousand) indicating a lower contribution of bird-derived N to the N nutrition of plants at these sites. The aquifer under the cay receives seabird-derived N leached from the cay and has high concentrations of N-15-enriched NO3- (delta(15)N 7.9parts per thousand). Macroalgae from reefs with and without seabirds had similar delta(15)N values of 2.0-3.9parts per thousand suggesting that reef macroalgae do not utilise N-15-enriched seabird-derived N as a main source of N. At a site beyond the Heron Reef Crest, macroalgae had elevated delta(15)N of 5.2parts per thousand, possibly indicating that there are locations where macroalgae access isotopically enriched aquifer-derived N. Nitrogen relations of Heron Island vegetation are compared with other reef islands and a conceptual model is presented.
  • Article
    Mangroves are defined by the presence of trees that mainly occur in the intertidal zone, between land and sea, in the (sub) tropics. The intertidal zone is characterised by highly variable environmental factors, such as temperature, sedimentation and tidal currents. The aerial roots of mangroves partly stabilise this environment and provide a substratum on which many species of plants and animals live. Above the water, the mangrove trees and canopy provide important habitat for a wide range of species. These include birds, insects, mammals and reptiles. Below the water, the mangrove roots are overgrown by epibionts such as tunicates, sponges, algae, and bivalves. The soft substratum in the mangroves forms habitat for various infaunal and epifaunal species, while the space between roots provides shelter and food for motile fauna such as prawns, crabs and fishes. Mangrove litter is transformed into detritus, which partly supports the mangrove food web. Plankton, epiphytic algae and microphytobenthos also form an important basis for the mangrove food web. Due to the high abundance of food and shelter, and low predation pressure, mangroves form an ideal habitat for a variety of animal species, during part or all of their life cycles. As such, mangroves may function as nursery habitats for (commercially important) crab, prawn and fish species, and support offshore fish populations and fisheries. Evidence for linkages between mangroves and offshore habitats by animal migrations is still scarce, but highly needed for management and conservation purposes. Here, we firstly reviewed the habitat function of mangroves by common taxa of terrestrial and marine animals. Secondly, we reviewed the literature with regard to the degree of interlinkage between mangroves and adjacent habitats, a research area which has received increasing attention in the last decade. Finally, we reviewed current insights into the degree to which mangrove litter fuels the mangrove food web, since this has been the subject of longstanding debate. Yes Yes
  • Article
    We focus on the implications of movement, landscape variables, and spatial heterogeneity for food web dynamics. Movements of nutrients, detritus, prey, and consumers among habitats are ubiquitous in diverse biomes and can strongly influence population, consumer-resource, food web, and community dynamics. Nutrient and detrital subsidies usually increase primary and secondary productivity, both directly and indirectly. Prey subsidies, by movement of either prey or predators, usually enhance predator abundance beyond what local resources can support. Top-down effects occur when spatially subsidized consumers affect local resources by suppressing key resources and occasionally by initiating trophic cascades. Effects on community dynamics vary with the relative amount of input, the trophic roles of the mobile and recipient entities, and the local food web structure. Landscape variables such as the perimeter/area ratio of the focal habitat, permeability of habitat boundaries, and relative productivity of trophically connected habitats affect the degree and importance of spatial subsidization.
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