Functioning Of Coastal Ecosystems Research Articles

Seagrass contributes substantially to the sedimentary lignin pool in an estuarine seagrass meadow

Shallow coastal ecosystems are reservoirs of carbon derived from allochthonous organic matter and autochthonous organic matter produced by microalgae and macrophytes. Carbon stored in vegetated coastal ecosystems has attracted broad attention as an important component of carbon sinks. Characterizing the source of carbon in sediments is essential for quantifying the carbon-sequestration function of shallow coastal ecosystems. In this study, we investigated the origins of organic matter using organic biomarkers (lignin phenols, fatty acids, cutin acids, diacids, and ω-hydroxy acids) in surface sediments in a seagrass-dominated lagoon (Furen Lagoon, Japan). Biomarkers derived from allochthonous vascular plants, such as long-chain fatty acids, showed higher concentrations near river mouths. Furthermore, biomarker signals indicated that sedimentary organic carbon originated in large part from degraded allochthonous vascular plants including roots. A Bayesian mixing model using the ratios of syringyl phenols to vanillyl phenols and cinnamyl phenols to vanillyl phenols indicated that up to about 65% of lignin in the sediments was derived from seagrass. This result indicates a substantial contribution of seagrass to the sedimentary lignin pool in an estuarine seagrass meadow. However, the percent contribution of seagrass to the lignin pool varied, with higher values near a tidal inlet and relatively low values near river mouths. Vertical profiles of organic biomarkers varied with the differences in degradability of organic compounds. Specifically, long-chain fatty acids decreased with increasing depth more than the other compounds, suggesting that they degraded more easily. Conversely, we observed a tendency for lignin phenols to be selectively preserved in the vertical sediment profiles. Our results show that sediment organic biomarkers can provide diverse information such as the composition and origins of organic carbon, the contribution of seagrass derived lignin, and the varying degrees of decomposition. This approach should bring new insights to the estimation of carbon in future blue carbon studies.

Improved chromosome-level genome assembly and annotation of the seagrass, Zostera marina (eelgrass)

Background: Seagrasses (Alismatales) are the only fully marine angiosperms. Zostera marina (eelgrass) plays a crucial role in the functioning of coastal marine ecosystems and global carbon sequestration. It is the most widely studied seagrass and has become a marine model system for exploring adaptation under rapid climate change. The original draft genome (v.1.0) of the seagrass Z. marina (L.) was based on a combination of Illumina mate-pair libraries and fosmid-ends. A total of 25.55 Gb of Illumina and 0.14 Gb of Sanger sequence was obtained representing 47.7× genomic coverage. The assembly resulted in ~2000 unordered scaffolds (L50 of 486 Kb), a final genome assembly size of 203MB, 20,450 protein coding genes and 63% TE content. Here, we present an upgraded chromosome-scale genome assembly and compare v.1.0 and the new v.3.1, reconfirming previous results from Olsen et al. (2016), as well as pointing out new findings. Methods: The same high molecular weight DNA used in the original sequencing of the Finnish clone was used. A high-quality reference genome was assembled with the MECAT assembly pipeline combining PacBio long-read sequencing and Hi-C scaffolding. Results: In total, 75.97 Gb PacBio data was produced. The final assembly comprises six pseudo-chromosomes and 304 unanchored scaffolds with a total length of 260.5Mb and an N50 of 34.6 MB, showing high contiguity and few gaps (~0.5%). 21,483 protein-encoding genes are annotated in this assembly, of which 20,665 (96.2%) obtained at least one functional assignment based on similarity to known proteins. Conclusions: As an important marine angiosperm, the improved Z. marina genome assembly will further assist evolutionary, ecological, and comparative genomics at the chromosome level. The new genome assembly will further our understanding into the structural and physiological adaptations from land to marine life.

Sediment Characterization and Monsoonal Impact on Beach Morphology at the Three Beaches along the Karachi Coast, Pakistan

Sediment characteristics plays important role in the determination and functioning of coastal ecosystems. The present study is an attempt to evaluate the variability in sediment characteristics of the three beaches: Clifton, Sandspit and Buleji, at the Karachi coast. The samples were collected during pre-monsoon and south-west monsoon seasons to evaluate the seasonal differences. The sediments of the three sites showed variations in moisture content, organic matter and grain size. The highest mean moisture (27.17%) and organic contents (3.5 %) were recorded from the sediments of Clifton. The maximum fraction of sediments (> 80 %) consist of fine to very fine sand at all studied sites. The sediments of Clifton were high in very fine sand fraction and low in coarse sand fraction as compared to Sandspit and Buleji. The sediments of all the three studied sites are moderately sorted, negatively coarse-skewed and showed leptokurtic distribution. The studied beaches of Clifton, Sandspit and Buleji shows dissimilarity in sediment characteristics as indicated through Cluster and PCA analysis. The monsoonal influence on sediment characteristics was also observed at all the three studied beaches. The strong wave action during SW monsoon season results in the deposition of the coarser sediments at the high tide level thus increasing the steepness of the beaches.

Modelling spatial and temporal patterns in bioturbator effects on sediment resuspension: A biophysical metabolic approach

Tidal flats are biogeomorphic landscapes, shaped by physical forces and interaction with benthic biota. We used a metabolic approach to assess the overarching effect of bioturbators on tidal landscapes. The benthic bivalve common cockle (Cerastoderma edule) was used as model organism. The effect of C. edule on sediment resuspension was approximated as a function of the overall population metabolic rate per unit of area. We combined i) laboratory observations on how C. edule affect sediment resuspension along gradients of bioturbation activity, sediment cohesiveness and hydrodynamic force with ii) spatial data on the natural distribution of intertidal C. edule populations. This allowed us to build an integrated model of the C. edule effect on sediment resuspension along the tidal gradient. Owing to the temperature dependence of metabolic rate, the model also accounted for seasonal variation in bioturbators activity.Laboratory experiments indicated that sediment resuspension is positively related to the metabolic rate of the C. edule population especially in cohesive sediments. Based on this observation, we predicted a clear spatial and seasonal pattern in the relative importance of C. edule contribution to sediment resuspension along a tidal transect. At lower elevations, our model indicates that hydrodynamics overrules biotic effects; at higher elevations, inter-tidal hydrodynamics should be too low to suspend bioturbated sediments. The influence of C. edule on sediment resuspension is expected to be maximal at the intermediate elevation of a mudflat, owing to the combination of moderate hydrodynamic stress and high bioturbator activity. Also, bio-mediated sediment resuspension is predicted to be particularly high in the warm season.Research into metabolic dependency of bio-mediated sediment resuspension may help to place phenomenological observations in the broader framework of metabolic theories in ecology and to formulate general expectations on the coastal ecosystem functioning.

Ecohydrology: A management tool for aquatic ecosystem and SDGs implementation

The availability and quality of water resources are not only to support human health and well-being, but also are providing the functioning of essential ecosystems, including rivers, wetlands, lakes and coastal ecosystems. The contamination of the aquatic ecosystem certainly carries a substantial loss, not only for the environment but also for human beings who use the goods and services of the environment. Water related problems often cannot be managed and overcome completely because of sectoral approach, monodisciplinary and unintegrated. Trans disciplinary science dealing with the interaction of hydrological processes and the dynamics of biology and/or ecology in various spatial, temporal conditions and human life practices around its environment is called ecohydrology. The ecohydrology concept is agreed to solve water related problems in the world. It is included in one of UNESCO IHP VIII themes to support SDGs achievement. This article aims to demonstrate the concept of ecohydrology in supporting sustainable water resource management. Based on the implementation of ecohydrology concept in three different demonstration sites, the results showed that it has been agreed as the solution to improve and restore river basin and lake ecosystem functions and services. It is important to note that the implementation of ecohydrology should consider economic valuation, political and government support as well as local society involvement in order to get effective and sustainable solutions for managing water resources.

Management pathways for the successful reduction of nonpoint source nutrients in coastal ecosystems

Eutrophication remains a threat to coastal habitats and water quality worldwide. The U. S. Clean Water Act resulted in reductions of nutrient loading from point sources but management of nonpoint sources (NPS) of nutrients remains challenging despite efforts over at least three decades. The hydrological factors, best management practices (BMPs) and regulatory mechanisms that target nutrient NPS and improve coastal ecosystem function are poorly understood. We identified three case study sites in the U.S. with sufficient NPS management and monitoring history to quantify changes in estuarine habitat and water quality following BMP implementation and regulation targeting nutrient NPS. Utilizing publicly available data, we compared sites that are geographically distant and hydrologically distinct. We found that BMPs targeting NPS loads from surface waters into Roberts Bay (Florida) and Newport Bay (California) significantly reduced nutrient concentrations and harmful algal blooms within ∼20 years. Improvements occurred despite concurrent human population growth within both watersheds. Conversely, we found that the majority of BMPs implemented within the Peconic Estuary (New York) watershed targeted surface waters despite a dominance of nitrogen inputs (97%) from groundwater and atmospheric sources. Declines in habitat and water quality in Peconic Estuary may be due to a failure to control the dominant nutrient sources and the long residence time of nitrogen in groundwater. Compared to surface water, reducing groundwater and atmospheric nutrients face greater technical and financial challenges. Improvements to Peconic Estuary may occur with further reductions in surface water inputs and as nutrients leach out of the groundwater. Although the effectiveness of specific NPS BMPs has been examined at small spatial scales, our study is the first to quantify improvements at a watershed scale. We showed that successful NPS management pathways are those which targeted the dominant sources of nutrients to coastal ecosystems and applied multiple BMPs within watersheds.

Laboratory studies on the biodegradation of organisms for estimating carbon storage potential in coastal aquatic ecosystems

ABSTRACT To assess the potential as carbon storages of short-life organisms in shallow coastal areas, refractory carbon fractions were examined using rapid biodegradation experiments. Refractory fractions of primary producers, such as seaweed and phytoplankton represented 31.2%−44.0% of the total carbon content. The seagrass Zostera marina contained a high rate of refractory carbon fraction, with 83.4% of the carbon in the belowground parts of Z. marina remaining as refractory carbon, which suggested that it had a significant function as a carbon storage in the shallow coastal area. The content of refractory carbon in the soft tissues of bivalves and gastropods were approximately 8.5%−31.5%, lower than that in other macrobenthos such as arthropods and echinoderms (29.7%−52.0%). The residual carbon in mollusk shells was mostly particulate inorganic carbon. In addition, 4.0%−19.1% of refractory organic carbon derived from polysaccharides and/or proteins in biominerals, while byssus remained. Considering the amount of shells in the shallow coastal zone, this organic carbon appeared to be a substantial carbon storage. Results suggested that not only primary producers but also macrobenthos and sessile animals have important carbon storage functions in coastal aquatic ecosystems.

Arctic lagoon and nearshore food webs: Relative contributions of terrestrial organic matter, phytoplankton, and phytobenthos vary with consumer foraging dynamics

Characterizing energy flow and trophic linkages is fundamental to understanding the functioning and resilience of Arctic ecosystems under increasing pressure from climate change and anthropogenic exploitation. We used carbon and nitrogen stable isotopes to examine trophic dynamics and the relative contribution of terrestrial organic matter, water column phytoplankton, and phytobenthos (benthic micro- and macro-autotrophs as well as sea ice algae) to the food webs supporting 45 macroconsumers in three Arctic coastal lagoon ecosystems (Krusenstern, Sisualik, Akulaaq) and the adjacent Kotzebue Sound with varying degrees of connectivity in Cape Krusenstern National Monument, Alaska. A two-source (water column particulate organic matter and benthic sediment organic matter), two-isotope trophic dynamics model informed by a Bayesian isotope mixing model revealed that the Lagoon-Kotzebue Sound coastal ecosystem supported consumers along a trophic position continuum from primary consumers, including amphipods, copepods, and clams to trophic level five predators, such as seastars, piscivorous fishes, seals, and seabirds. The relative contribution of the three primary producer end members, terrestrial organic matter (41 ± 21%), phytoplankton (25 ± 21%), and phytobenthos (34 ± 23%) varied as a function of: 1) consumer foraging ecology and 2) consumer location. Suspension feeders received most of their carbon from food webs based on phytoplankton (49 ± 11%) and terrestrial organic matter (23 ± 5%), whereas herbivores and detritivores received the majority of their carbon from phytobenthos-based food webs, 58 ± 10% and 60 ± 8%, respectively. Omnivores and predators showed more even distributions of resource reliance and greater overall variance among species. Within the invertebrates, the importance of terrestrial organic matter decreased and phytobenthos increased with increasing trophic position. The importance of terrestrial organic matter contribution increased with lagoon proximity to major rivers inputs and isolation from Kotzebue Sound. Several taxa with cultural and subsistence food importance to local communities showed significant reliance (30–90% of baseline carbon) on food chains linked to fresh terrestrial organic matter. Our study indicates that terrestrial-marine linkages are important to the function of Arctic coastal lagoon ecosystems and artisanal fisheries. These linkages are likely to strengthen in the future with regional changes in erosion and runoff associated with climate change and anthropogenic disturbance.

Improved chromosome-level genome assembly and annotation of the seagrass, Zostera marina (eelgrass).

Background:Seagrasses(Alismatales) are the only fully marine angiosperms. Zostera marina(eelgrass) plays a crucial role in the functioning of coastal marine ecosystems and global carbon sequestration. It is the most widely studied seagrass and has become a marine model system forexploringadaptation under rapid climate change.The original draft genome(v.1.0)of the seagrass Z. marina(L.)was based on a combination of Illumina mate-pair libraries andfosmid-ends. A total of 25.55 Gb of Illumina and 0.14 Gb of Sanger sequence was obtained representing 47.7×genomic coverage. The assembly resulted in~2000 unordered scaffolds (L50 of 486Kb), a final genome assembly size of 203MB, 20,450 protein coding genes and 63% TE content. Here,we present an upgraded chromosome-scale genome assemblyand comparev.1.0and the newv.3.1, reconfirming previous results from Olsen et al. (2016), as well as pointing out new findings. Methods:The same high molecular weight DNAused in the original sequencingof the Finnish clonewas used.Ahigh-qualityreferencegenome was assembledwiththeMECATassemblypipelinecombiningPacBiolong-readsequencingand Hi-C scaffolding. Results:In total,75.97 GbPacBiodata wasproduced.The final assembly comprisessixpseudo-chromosomesand304 unanchored scaffolds with a total length of 260.5Mb andanN50 of 34.6 MB, showing high contiguity and few gaps (~0.5%). 21,483 protein-encoding genes are annotated in this assembly, of which 20,665 (96.2%)obtained at least one functional assignment based on similarity to known proteins. Conclusions:Asanimportant marine angiosperm,the improved Z. marinagenomeassemblywillfurtherassistevolutionary, ecological,and comparative genomicsat the chromosome level.Thenew genome assemblywillfurther our understandinginto the structural and physiological adaptations from land to marinelife.

Habitat-Diversity Relations between Sessile Macrobenthos and Benthic Copepods in the Rocky Shores of a Marine Protected Area

In rocky shore systems, sessile macrobenthic assemblages may act as “ecosystem engineers” for many smaller benthic organisms. Thus, the influence of macrobenthic coverage on the diversity and assemblage structure of the harpacticoid copepod fauna was investigated in the rocky shores of a Marine Protect Area (MPA) in the Ligurian Sea (NW, Mediterranean Sea). Two sampling sites were investigated in two seasons at three different depths on both sub-vertical and inclined reefs. A total of 61 species of copepods mainly represented by Miraciidae, Laophontidae, Longipediidae and Thalestridae were found. The complex micro-topography of these substrata provided a wide variety of niches for many species with different lifestyles that suggests the important role of rocky shores to ensure the functioning of coastal ecosystems. The harpacticoid assemblage structure seemed mainly influenced by season and depth. The temporal spread observed is likely one of the underlying mechanisms of niche segregation that allows many species to co-occur in this specific environment along with a subordinate spatial segregation corresponding to the depth gradient. The results seem to support the hypothesis that the different species composition of the “ecosystem engineer” (and consequently its structure changes) are relevant in structuring the copepod assemblages. The comparison with previous data on general meiofauna underlines that higher surrogacy of the taxonomic identification could be used to study rocky shore communities, but the rich diversity that these systems host can only be understood at the lower taxonomic levels. The same holds for future evaluations of impact of environmental changes (including MPA regulations) on meiofaunal assemblages.

Chemical contamination alters the interactions between bacteria and phytoplankton

Bacteria and phytoplankton are key players in aquatic ecosystem functioning. Their interactions mediate carbon transfer through the trophic web. Chemical contamination can alter the function and diversity of phytoplankton and bacterioplankton, with important consequences for ecosystem functioning. The aim of the present study was to assess the impact of chemical contamination on the interactions between both biological compartments. Two contrasting marine coastal ecosystems, offshore waters and lagoon waters, were exposed to chemical contamination (artificial or produced from resuspension of contaminated sediment) in microcosms in four seasons characterized by distinct phytoplankton communities. Offshore waters were characterized by a complex phytoplankton–bacterioplankton network with a predominance of positive interactions between both compartments, especially with Haptophyta, Cryptophyta, and dinoflagellates. In contrast, for lagoon waters, the phytoplankton–bacterioplankton network was simpler with a prevalence of negative interactions with Ochrophyta, Cryptophyta, and flagellates. Contamination with an artificial mix of pesticides and trace metal elements resulted in a decrease in the number of interactions between phytoplankton and bacterioplankton, especially for offshore waters. Resuspension of contaminated sediment also altered the interactions between both compartments. The release of nutrients stored in the sediment allowed the growth of nutrient limited phytoplankton species with marked consequences for the interactions with bacterioplankton, with a predominance of positive interactions, whereas in lagoon waters, negative interactions were mostly observed. Overall, this study showed that chemical contamination and sediment resuspension resulted in significant effects on phytoplankton–bacterioplankton interactions that can alter the functioning of anthropogenic coastal ecosystems.

Commensalism, antagonism or mutualism? Effects of epibiosis on the trophic relationships of mussels and epibiotic barnacles

The dynamics determining the establishment and maintenance of epibiotic relationships are fundamental to understand the role of biological interactions in the functioning of marine coastal ecosystems. Epibiosis of barnacles on mussels is a common feature of many intertidal rocky shores. There are several possible explanations for this relationship, but it is unclear whether the association is commensal, antagonistic, or mutualistic. We investigated the diets of barnacles and mussels in an epibiotic relationship (epibiont barnacle and basibiont mussel), and compared them to the diets of conspecifics living on the same rocky shore but independently (free barnacle and free mussel), using stable isotope (SI) and fatty acid (FA) techniques. The SI results indicated that the diet of mussels did not change as a function of epibiosis, while free barnacles were characterized by higher δ15N values than epibiotic conspecifics, indicating that they were feeding on more recycled food sources. This result was, however, supported by data from only one site. Results from FA were partially consistent with those of SI analysis, indicating that mussel FA profiles did not change between basibiont and free mussels, but that epibiotic barnacles were characterized by a lower amount of polyunsaturated FA than free barnacles. This suggests that the diet of epibiotic barnacles is of lower quality. This could be due to competition for food with mussels, driven by the different mechanisms of food assimilation between epibiotic barnacle and basibiont mussel; or by the different sizes of particles ingested by the two species under epibiosis vs free-living conditions. The discrepancy between the FA and SI results observed could reflect the different integration time of the analytical techniques, with FA reflecting shorter term variability than SI. We conclude that epibiosis represents an unfavourable relationship for barnacles due to the lower quality of food available when colonizing mussel shells, whereas mussels neither benefit nor were harmed by this association. Thus, this relationship is amensalistic: negative for barnacles but neutral for mussels.

Rapid Landscape Changes in Plastic Bays Along the Norwegian Coastline

The Norwegian Coastal Current transports natural debris and plastic waste along the Norwegian coastline. Deposition occurs in so-called wreck-bays and includes floating debris, such as seaweed, driftwood and volcanic pumice, and increasing amounts of plastics during the last decades. Deposition in these bays is controlled by ocean currents, tidal movements, prevailing winds and coastal morphology. We have compared soil profiles, analyzed the vegetation and inspected aerial photos back to 1950 in wreck-bays and defined three zones in the wreck-bays, where accumulation follows distinct physical processes. Zone 1 includes the foreshore deposition and consists of recent deposits that are frequently reworked by high tides and wave erosion. Thus, there is no accumulation in Zone 1. Zone 2 is situated above the high tide mark and includes storm embankments. Here, there is an archive of accumulated debris potentially deposited decades ago. Zone 3 starts above the storm embankments. The debris of Zone 3 is transported by wind from Zone 1 and Zone 2, and the zone continues onshore until the debris meets natural obstacles. Plastic accumulation seems to escalate soil formation as plastic is entangled within the organic debris Mapping and characterizing the soil layers indicates that deep soils have been formed by 50 or more years’ accumulation, while the pre-plastic soil layers are thin. The plastic soil forms dams in rivers and wetlands, changing the shape and properties of the coastal landscape, also altering the microhabitat for plants. This case-study describes an ongoing landscape and vegetation change, evidently co-occurring with the onset of plastic accumulation. Such processes are not limited to the Norwegian coastline but are likely to occur wherever there is accumulation of plastic and organic materials. If this is allowed to continue, we may witness a continued and escalating change in the shape and function of coastal landscapes and ecosystems globally.

Changes in Rocky Intertidal Community Structure During a Marine Heatwave in the Northern Gulf of Alaska

Marine heatwaves are global phenomena that can have major impacts on the structure and function of coastal ecosystems. By mid-2014, the Pacific Marine Heatwave (PMH) was evident in intertidal waters of the northern Gulf of Alaska and persisted for multiple years. While offshore marine ecosystems are known to respond to these warmer waters, the response of rocky intertidal ecosystems to this warming is unclear. Intertidal communities link terrestrial and marine ecosystems and their resources are important to marine and terrestrial predators and to human communities for food and recreation, while simultaneously supporting a growing coastal tourism industry. Given that current climate change projections suggest increased frequency and duration of marine heatwaves, monitoring and understanding the impacts of heatwaves on intertidal habitats is important. As part of the Gulf Watch Alaska Long-Term Monitoring program, we examined rocky intertidal community structure at 21 sites across four regions spanning 1,200 km of coastline: Western Prince William Sound, Kenai Fjords National Park, Kachemak Bay, and Katmai National Park and Preserve. Sites were monitored annually from 2012 to 2019 at mid and low tidal strata. Before-PMH (2012–2014), community structure differed among regions. We found macroalgal foundation species declined during this period mirroring patterns observed elsewhere for subtidal habitat formers during heatwave events. The region-wide shift from an autotroph-macroalgal dominated rocky intertidal to a heterotroph-filter-feeder dominated state concurrent with the changing environmental conditions associated with a marine heatwave event suggests the PMH had Gulf-wide impacts to the structure of rocky intertidal communities. During/after-PMH (2015–2019), similarities in community structure increased across regions, leading to a greater homogenization of these communities, due to declines in macroalgal cover, driven mostly by a decline in the rockweed,Fucus distichus, and other fleshy red algae in 2015, followed by an increase in barnacle cover in 2016, and an increase in mussel cover in 2017. Strong, large-scale oceanographic events, like the PMH, may override local drivers to similarly influence patterns of intertidal community structure.

Potential impacts of marine urbanization on benthic macrofaunal diversity

Urbanization and associated human activities have caused numerous changes to natural environments, including the loss of natural habitats and replacement with artificial structures. How these changes impact coastal marine biodiversity and ecosystem functioning is not well known. In this study, we examined the potential impacts of habitat changes by comparing species commonality and community structure (i.e., species richness, abundance, and functional composition) among artificial (a breakwater wall) and natural habitats (eelgrass bed, intertidal flat, and subtidal bottom) within a semi-enclosed coastal sea impacted by marine urbanization. We found considerable species overlap (i.e., high species sharing) among the eelgrass bed, intertidal flat, and subtidal bottom habitats. By contrast, the breakwater wall was a distinctive habitat with little overlap in species and functional groups with the other habitats, and was therefore a poor substitute for natural habitats. Our study suggests that marine urbanization degrades redundancy and inhibits the maintenance of biodiversity in coastal marine zones.

Feedback mechanisms stabilise degraded turf algal systems at a CO2 seep site

Human activities are rapidly changing the structure and function of coastal marine ecosystems. Large-scale replacement of kelp forests and coral reefs with turf algal mats is resulting in homogenous habitats that have less ecological and human value. Ocean acidification has strong potential to substantially favour turf algae growth, which led us to examine the mechanisms that stabilise turf algal states. Here we show that ocean acidification promotes turf algae over corals and macroalgae, mediating new habitat conditions that create stabilising feedback loops (altered physicochemical environment and microbial community, and an inhibition of recruitment) capable of locking turf systems in place. Such feedbacks help explain why degraded coastal habitats persist after being initially pushed past the tipping point by global and local anthropogenic stressors. An understanding of the mechanisms that stabilise degraded coastal habitats can be incorporated into adaptive management to better protect the contribution of coastal systems to human wellbeing.

The effects of afforestation tree species mixing on soil organic carbon stock, nutrients accumulation, and understory vegetation diversity on reclaimed coastal lands in Eastern China

Establishing mixed-species plantations on the reclaimed coastal lands has become a new paradigm in forest management in China, because it increases the provision of ecosystem services. However, the mixing effects of trees with different identities remain largely understudied. In subtropical China, plantations have been historically dominated by monocultures, the conversion of which to mixed plantations are now required considering the need of sustainable forestry development. In this study, we evaluated the soil carbon sequestration, nutrient accumulation, and understory regeneration of three coastal plantations with different compositions established 12 years ago, on a reclaimed area in Eastern China. Plots on two scales (30 m × 20 m for trees and 1 m × 1 m for understory vegetation) were set up to conduct vegetation inventory and soil sampling to compare growth parameters, soil physical and chemical properties, and understory composition. We found that coniferous-mixed forest (CMF) had significantly higher soil available water capacity; both CMF and broadleaved-coniferous mixed forest (B-CMF) had significantly higher soil capillary porosity and soil moisture content at saturation; broadleaved mixed forest (BMF) had a greater soil permeability coefficient. Among soil chemical properties, we observed that CMF had higher soil organic carbon stock and cation exchange capacity in both 0–20 cm and 20–40 cm soil layers. CMF and B-CMF had higher hydrolysable nitrogen and total potassium in both soil layers; BMF had higher available phosphorus contents. Moreover, B-CMF supported better canopy tree growth and higher understory plant species diversity. Therefore, our results showed that the introduction of broad-leaved trees into the coniferous-dominated plantations established on the reclaimed coastal lands produced significant effects on soil properties and understory species diversity. Thus, our study may facilitate the development of new afforestation regimes to mitigate the potential impact of increasing environmental changes by improving our understanding of species composition effects on coastal forest ecosystem functioning.

Boosted fish abundance associated with Posidonia oceanica meadows in temperate shallow CO2 vents

Ocean acidification (OA) may induce major shifts in the structure and function of coastal marine ecosystems. Studies in volcanic CO2 vents, where seawater is naturally acidified, have reported an overall simplification of fish assemblages structure, while some primary producers are likely to increase their biomass under elevated concentration of CO2. Here we used temperate shallow CO2 vents located around the coast of Ischia island (Italy) to assess the effects of OA on necto-benthic fish assemblages associated with the foundation seagrass species Posidonia oceanica in the Mediterranean Sea. We compared P. oceanica meadow structure, its epiphytic community and the associated fish assemblage structure and diversity at vents with low pH sites and reference sites with ambient pH using underwater visual census strip transects, in two seasons (fall 2018 and summer 2019). Data were analysed using both univariate and multivariate statistical techniques. Results showed greater P. oceanica habitat complexity (i.e. shoot density) and lower abundance of epiphytic calcareous species (e.g. coralline algae) at the vents than reference sites. Total abundance of adult and juvenile fish was higher at vents than reference sites, while no differences were found for species richness and composition. Overall, the herbivore Sarpa salpa stands out among the species contributing the most to dissimilarity between vents and reference sites, showing higher abundances under OA conditions. This pattern could be explained by the combined effect of a positive response to the higher structural meadows complexity and the greater seagrasses palatability/nutritional value occurring at the vents, which may help herbivores to withstand the higher energetic cost to live under high pCO2/low pH conditions. Our results indicate that necto-benthic fish assemblages associated with the Mediterranean P. oceanica ecosystem may cope with OA under the CO2 emission scenarios forecasted for the end of this century.

Novel approach to enhance coastal habitat and biotope mapping with drone aerial imagery analysis

Understanding the complex factors and mechanisms driving the functioning of coastal ecosystems is vital towards assessing how organisms, ecosystems, and ultimately human populations will cope with the ecological consequences of natural and anthropogenic impacts. Towards this goal, coastal monitoring programs and studies must deliver information on a range of variables and factors, from taxonomic/functional diversity and spatial distribution of habitats, to anthropogenic stress indicators such as land use, fisheries use, and pollution. Effective monitoring programs must therefore integrate observations from different sources and spatial scales to provide a comprehensive view to managers. Here we explore integrating aerial surveys from a low-cost Remotely Piloted Aircraft System (RPAS) with concurrent underwater surveys to deliver a novel approach to coastal monitoring. We: (i) map depth and substrate of shallow rocky habitats, and; (ii) classify the major biotopes associated with these environmental axes; and (iii) combine data from i and ii to assess the likely distribution of common sessile organismal assemblages over the survey area. Finally, we propose a general workflow that can be adapted to different needs and aerial platforms, which can be used as blueprints for further integration of remote-sensing with in situ surveys to produce spatially-explicit biotope maps.

A place for subterranean estuaries in the coastal zone

Willard S. Moore coined the term subterranean estuary (STE) as that part of the coastal aquifer ‘where groundwater derived from land drainage measurably dilutes seawater that has invaded the aquifer through a free connection to the sea’ more than two decades ago (Moore, 1999). In doing so, Moore was calling attention to the potential importance of this zone, long studied by terrestrial hydrologists, to marine systems. Since then, we have accumulated indisputable evidence of the importance of STEs and their associated submarine groundwater discharge (SGD) in coastal ecosystem function. Yet, subterranean estuaries are often not considered distinct systems in the land-ocean continuum either from an academic viewpoint or for developing integrative monitoring and management. This invisibility means that the impact of STEs on ecosystem state has been neglected when environmental assessments that aim to meet coastal water quality and ecosystem health targets are performed. It is possible that our current broad definition of STEs, as well as misuse and misunderstanding of terminology, partly explain their de-facto transparency to the wider coastal scientific community. Here, we argue for the inclusion of STEs as important, interconnected systems driving water quality, ecology, and biogeochemical cycles in nearby coastal ecosystems. To achieve broader recognition, we first need to address the perceived compartmentalization of surface and groundwater systems, as well as overcome a pigeon-holed approach to research often confined within narrow disciplinary boundaries. The establishment of open-water estuarine science over the last several decades shows that such obstacles are surmountable. A lack of awareness and recognition of STE functions impedes a holistic understanding of coastal ecosystems and slows down the development of cause-effect relationships for a science-based approach to ecosystem management.