Functioning Of Estuarine Ecosystems Research Articles

Continuous Monitoring Reveals Drivers of Dissolved Oxygen Variability in a Small California Estuary

Estuarine ecosystem diversity and function can be degraded by low oxygen concentrations. Understanding the spatial and temporal patterns of dissolved oxygen (DO) variation and the factors that predict decreases in DO is thus essential to inform estuarine management. We investigated DO variability and its drivers in Elkhorn Slough, a shallow, well-mixed estuary affected by high nutrient loading and with serious eutrophication problems. Long-term (2001–2012), high-resolution (15 min) time series of DO, water level, winds, and solar radiation from two fully tidal sites in the estuary showed that hypoxia events close to the bottom are common in the summer at the more upstream estuarine station. These events can occur in any lunar phase (spring to neap), at any time of the day, and both on sunny or cloudy days. They are, however, short-lived (lasting in average 40 min) and mainly driven by momentary low turbulent diffusion around slack tides (both at high and low water). Tidal advective transport explains up to 52.1% of the daily DO variability, and the water volume (or DO reservoir) contained in the estuary was not sufficient to avoid hypoxia in the estuary. Solar radiation was responsible for a positively correlated DO daily cycle but caused a decreased in the averaged DO in the summer at the inner station. Wind-driven upwelling reduced the average DO at the more oceanic station during spring. The approach we employed, using robust techniques to remove suspect data due to sensor drift combined with an array of statistical techniques, including spectral, harmonic, and coherence spectrum analysis, can serve as a model for analyses of long-term water quality datasets in other systems. Investigations such as ours can inform coastal management by identifying key drivers of hypoxia in estuaries.

Rising tides, cumulative impacts and cascading changes to estuarine ecosystem functions

In coastal ecosystems, climate change affects multiple environmental factors, yet most predictive models are based on simple cause-and-effect relationships. Multiple stressor scenarios are difficult to predict because they can create a ripple effect through networked ecosystem functions. Estuarine ecosystem function relies on an interconnected network of physical and biological processes. Estuarine habitats play critical roles in service provision and represent global hotspots for organic matter processing, nutrient cycling and primary production. Within these systems, we predicted functional changes in the impacts of land-based stressors, mediated by changing light climate and sediment permeability. Our in-situ field experiment manipulated sea level, nutrient supply, and mud content. We used these stressors to determine how interacting environmental stressors influence ecosystem function and compared results with data collected along elevation gradients to substitute space for time. We show non-linear, multi-stressor effects deconstruct networks governing ecosystem function. Sea level rise altered nutrient processing and impacted broader estuarine services ameliorating nutrient and sediment pollution. Our experiment demonstrates how the relationships between nutrient processing and biological/physical controls degrade with environmental stress. Our results emphasise the importance of moving beyond simple physically-forced relationships to assess consequences of climate change in the context of ecosystem interactions and multiple stressors.

The importance of benthic-pelagic coupling for marine ecosystem functioning in a changing world.

Benthic-pelagic coupling is manifested as the exchange of energy, mass, or nutrients between benthic and pelagic habitats. It plays a prominent role in aquatic ecosystems, and it is crucial to functions from nutrient cycling to energy transfer in food webs. Coastal and estuarine ecosystem structure and function are strongly affected by anthropogenic pressures; however, there are large gaps in our understanding of the responses of inorganic nutrient and organic matter fluxes between benthic habitats and the water column. We illustrate the varied nature of physical and biological benthic-pelagic coupling processes and their potential sensitivity to three anthropogenic pressures - climate change, nutrient loading, and fishing - using the Baltic Sea as a case study and summarize current knowledge on the exchange of inorganic nutrients and organic material between habitats. Traditionally measured benthic-pelagic coupling processes (e.g., nutrient exchange and sedimentation of organic material) are to some extent quantifiable, but the magnitude and variability of biological processes are rarely assessed, preventing quantitative comparisons. Changing oxygen conditions will continue to have widespread effects on the processes that govern inorganic and organic matter exchange among habitats while climate change and nutrient load reductions may have large effects on organic matter sedimentation. Many biological processes (predation, bioturbation) are expected to be sensitive to anthropogenic drivers, but the outcomes for ecosystem function are largely unknown. We emphasize how improved empirical and experimental understanding of benthic-pelagic coupling processes and their variability are necessary to inform models that can quantify the feedbacks among processes and ecosystem responses to a changing world.

Heavy Metals Pollution Influence the Community Structure of Cyanobacteria in Nutrient Rich Tropical Estuary

Anthropogenic inputs influence the community structure and activities of microorganisms, which may impinge the functioning of estuarine and coastal ecosystem. The aim of the present study was to understand the influence of dissolved heavy metals (Cr, Mn, Fe, Ni, Cu and Zn) on community structure of cyanobacteria in a nutrient rich tropical estuary, Cochin Estuary (CE), across the southwest coast of India. Dissolved heavy metals were higher in CE during dry season, with Zn as major pollutant. The level of dissolved Zn was higher in stations near river head during dry (130 μg L-1) and wet seasons (105 μg L-1). The community structure of cyanobacteria was higher in CE during wet season (H’ index: 1.4 to 3.1) compared to that in dry season (H’ index: 1.1 to 2.2). The 16S rRNA gene sequence analysis showed the prevalence of Synechococcus sp in CE. PCA analysis indicated the positive influence of Zn and nutrients on community structure of cyanobacteria. We postulate that the Zn pollution may be a critical factor to be monitored and controlled in nutrient rich estuaries, otherwise it may accelerate the eutrophication and associated ecological constraints.

An estimation of the effects of Ensis directus on the transport and burial of silt in the near-shore Dutch coastal zone of the North Sea

This paper describes the distribution of the razor clam Ensis directus in the Dutch coastal zone with emphasis on its relation to sediment grainsize, in particular silt. The study includes a spatial survey along the coast of North Holland (Netherlands) and an in-situ experiment for the burial of silt. Densities of E. directus appeared highest close to the coast in the siltiest sediment, where also the highest body mass index values (BMI) were found suggesting the best conditions for growth. The largest specimens with the lowest BMI were found at the less silty, outermost off-shore stations.In the shallow (10m) zone a “lander” frame was deployed at the seabed containing ~100 pvc tubes filled with silt free sand that each hosted either a living E. directus, an empty shell, or bare sand. After three 3-weeks periods the silt content in the different tubes was determined and compared. The silt content around a living E. directus appeared 34% (spring) and 12% (autumn) higher than around an empty vertical shell, and 56% (spring) higher than in bare sand.We discuss the different pathways along which silt is brought into subsurface sediment layers and speculate about the potential role of E. directus in the coastal sediment and silt dynamics. It is estimated that E. directus facilitates the (temporal) burial of up to 6Mton of fine particles in the coastal zone annually. This equals up to 27% of the annual SPM transport along the Dutch coast and is between 45 and 85% of the annual influx into the western Wadden Sea.The results show that the coastal E. directus population has a large impact on mass balance and behaviour of SPM, and on the ecological functioning of Dutch coastal and estuarine ecosystems.

Average vs. extreme salinity conditions: Do they equally affect the distribution of macroinvertebrates in estuarine environments?

AbstractSalinity is a key variable used to explain the distribution of species within estuaries and the functioning of estuarine ecosystems. Despite the relevance of average conditions and extreme events, the existing schemes of zonation are only based on average values; the extreme values obtained through high‐resolution long‐term data have not been still integrated in an appropriate methodology capable of recognizing salinity types. Therefore, the background variability of salinity has been frequently underestimated in ecological studies. The primary goal of this research is the identification of ecologically significant salinity zones capable of encompassing the entire estuarine regime. A two‐step methodological approach was developed: (1) the reconstruction of long‐term salinity series using the Deflt3D hydrodynamic model, the analog method and a subset of short‐term representative states of river flow and tidal level and (2) the identification of different zones using eight descriptors of the salinity regime (i.e., the median, the range and the intensity, duration and frequency of extreme events) and the application of a combination of two clustering techniques of unsupervised learning (Self‐Organizing Maps (SOM) and K‐Means). Thus, five ecologically significant salinity types that are representative of estuarine variability were identified based on a salinity series reconstructed using a validated method. Differences in the mean values of salinity among typologies allow explaining patterns in the general descriptors of benthic macroinvertebrates assemblages (i.e., richness and diversity). If extreme salinity conditions are also considered, typologies increase their ecological significance and they are able to recognize differences in species composition.

The Influence of Benthic Macrofauna on the Erodibility of Intertidal Sediments with Varying mud Content in Three New Zealand Estuaries

Fine sediment inputs can alter estuarine ecosystem structure and function. However, natural variations in the processes that regulate sediment transport make it difficult to predict their fate. In this study, sediments were sampled at different times (2011–2012) from 45 points across intertidal sandflat transects in three New Zealand estuaries (Whitford, Whangamata, and Kawhia) encompassing a wide range in mud (≤63 μm) content (0–56 %) and macrofaunal community structure. Using a core-based erosion measurement device (EROMES), we calculated three distinct measures of sediment erosion potential: erosion threshold (Ʈ c ; N m−2), erosion rate (ER; g m−2 s−1), and change in erosion rate with increasing bed shear stress (m e ; g N−1 s−1). Collectively, these measures characterized surface (Ʈ c and ER) and sub-surface (m e ) erosion. Benthic macrofauna were grouped by functional traits (size and motility) and data pooled across estuaries to determine relationships between abiotic (mud content, mean grain size) and biotic (benthic macrofauna, microbial biomass) variables and erosion measures. Results indicated that small bioturbating macrofauna (predominantly freely motile species <5 mm in size) destabilized surface sediments, explaining 23 % of the variation in Ʈ c (p ≤ 0.01) and 59 % of the variation in ER (p ≤ 0.01). Alternatively, mud content and mean grain size cumulatively explained 61 % of the variation in m e (p ≤ 0.01), where increasing mud and grain size stabilized sub-surface sediments. These results highlight that the importance of biotic and abiotic predictors vary with erosion stage and that functional group classifications are a useful way to determine the impact of benthic macrofauna on sediment erodibility across communities with different species composition.

Phytoplankton blooms in estuarine and coastal waters: Seasonal patterns and key species

Phytoplankton blooms are dynamic phenomena of great importance to the functioning of estuarine and coastal ecosystems. We analysed a unique (large) collection of phytoplankton monitoring data covering 86 coastal sites distributed over eight regions in North America and Europe, with the aim of investigating common patterns in the seasonal timing and species composition of the blooms. The spring bloom was the most common seasonal pattern across all regions, typically occurring early (February–March) at lower latitudes and later (April–May) at higher latitudes. Bloom frequency, defined as the probability of unusually high biomass, ranged from 5 to 35% between sites and followed no consistent patterns across gradients of latitude, temperature, salinity, water depth, stratification, tidal amplitude or nutrient concentrations. Blooms were mostly dominated by a single species, typically diatoms (58% of the blooms) and dinoflagellates (19%). Diatom-dominated spring blooms were a common feature in most systems, although dinoflagellate spring blooms were also observed in the Baltic Sea. Blooms dominated by chlorophytes and cyanobacteria were only common in low salinity waters and occurred mostly at higher temperatures. Key bloom species across the eight regions included the diatoms Cerataulina pelagica and Dactyliosolen fragilissimus and dinoflagellates Heterocapsa triquetra and Prorocentrum cordatum. Other frequent bloom-forming taxa were diatom genera Chaetoceros, Coscinodiscus, Skeletonema, and Thalassiosira. Our meta-analysis shows that these 86 estuarine-coastal sites function as diatom-producing systems, the timing of that production varies widely, and that bloom frequency is not associated with environmental factors measured in monitoring programs. We end with a perspective on the limitations of conclusions derived from meta-analyses of phytoplankton time series, and the grand challenges remaining to understand the wide range of bloom patterns and processes that select species as bloom dominants in coastal waters.

Contrasting tropical estuarine ecosystem functioning and stability: A comparative study

A comparative study of the Sine-saloum (Senegal) and Gambia (The Gambia) estuaries was performed based on trophic model outputs that describe the system structure and functioning. These trophic models were constructed such as to differentiate main energetic flows in the systems and express how climate change may have impacted ecosystem resilience to change. Estuarine fish assemblages are highly resilient despite exposure to vast hydrodynamic variations and stress. Coupled with strong anthropogenic-driven stresses such as fisheries and climate change, ecosystems may undergo severe regime shifts that may weaken their resilience and stability. Taxonomically related and morphologically similar species do not necessarily play similar ecological roles in these two ecosystems. Biomass and production in the Sine-saloum are concentrated at trophic levels (TLs) 2 and 3, while for the Gambia, both are concentrated at TL3. Higher TL biomasses in Gambia compared to Sine-Saloum may be explained by the latter ecosystem being characterized by inverse hypersalinity. Higher TL of production in Sine-Saloum is due to higher exploitations compared to Gambia where fishing activities are still less developed. High production and consumption rates of some groups in both ecosystems indicate high system productivity. Elevated productivity may be due to higher abundance of juvenile fishes in most groups that utilize the latter as refuge and/or nursery zones. Both ecosystems are phytoplankton-driven. Differences in group trophic and ecological roles are mainly due to adaptive responses of these species to seasonal and long-term climate and anthropogenic stressors. System indicators suggest different levels of ecosystem resilience and stability as a function of biodiversity. Relevance of other observations on ecosystem functioning and indicators in relation to perturbation is discussed.

Worldwide patterns of fish biodiversity in estuaries: Effect of global vs. local factors

The main ecological patterns and the functioning of estuarine ecosystems are difficult to evaluate due to natural and human induced complexity and variability. Broad geographical approaches appear particularly useful. This study tested, at a worldwide scale, the influence of global and local variables in fish species richness in estuaries, aiming to determine the latitudinal pattern of species richness, and patterns which could be driven by local features such as estuary area, estuary mouth width, river flow and intertidal area. Seventy one estuarine systems were considered with data obtained from the literature and geographical information system. Correlation tests and generalized linear models (GLM) were used in data analyses. Species richness varied from 23 to 153 fish species. GLM results showed that estuary area was the most important factor explaining species richness, followed by latitude and mouth width. Species richness increased towards the equator, and higher values were found in larger estuaries and with a wide mouth. All these trends showed a high variability. A larger estuary area probably reflects a higher diversity of habitats and/or productivity, which are key features for estuarine ecosystem functioning and biota. The mouth width effect is particularly notorious for marine and diadromous fish species, enhancing connectivity between marine and freshwater realms. The effects of river flow and intertidal area on the fish species richness appear to be less evident. These two factors may have a marked influence in the trophic structure of fish assemblages.

REVIEW: Chemical contaminant effects on marine ecosystem functioning

Summary Ecosystem functioning underpins the ecosystem services upon which humans rely. Critical functions, such as primary and secondary productivity, are, however, increasingly threatened by a range of anthropogenic stressors. Although the extent of the threat of contamination is large and has been increasing, pollution is one of the least‐studied stressors in ecology. We did a systematic review and critical synthesis of the effects of contaminants on marine and estuarine ecosystem functioning. No other stressors besides toxic chemicals were included in this review. We identified 264 relevant studies across a range of contaminants. Toxic contaminants generally altered marine ecosystem functioning by reducing productivity and increasing respiration. Effects varied, however, according to the type of contaminant and the component(s) of the system studied (e.g. particular trophic levels, functional groups or taxonomic groups). Toxicity studies that included a measure of ecosystem function were strongly biased towards planktonic communities in contrast to studies of biodiversity, which have been dominated by work on soft‐sediment communities. Toxicant studies that included measures of ecosystem function rarely included a measure of biodiversity and rarely interpreted their findings within an ecosystem function context. Studies that included multiple components of an ecosystem, that is more than one functional group of organisms, were more likely to find no effect of contamination, possibly due to ecological interactions. Studies that suffered from unclear or flawed methodology were more likely to find a significant impact of contaminants on some endpoints of ecosystem functioning than studies with appropriate designs. Synthesis and applications. Up to 70% of studies found negative impacts of contaminants on primary production. Toxic contaminants therefore have the potential to greatly affect the ecosystem services and benefits provided by these systems. Our findings will help managers and policymakers to determine whether contaminants are affecting both biodiversity and ecosystem functioning in a given context, therefore helping to prioritize areas for remediation. There is still, however, much to understand about the relationships between biological diversity and ecosystem functioning. Our understanding of chemical contaminant effects will remain patchy until direct measures of both variables are undertaken within multiple ecosystems. We therefore recommend the adoption of functional endpoints, such as productivity and respiration, in ecological studies, routine toxicological studies and ecological risk assessment.

Discovery of a Katablepharis sp. in the Columbia River estuary that is abundant during the spring and bears a unique large ribosomal subunit sequence element

Heterotrophic protists play significant roles in pelagic food webs as bacterivorous and herbivorous consumers. However, heterotrophic protists—unlike autotrophic ones—are often difficult to track since they tend to lack features such as photosynthetic pigments that allow for remote sensing or for bulk characterization. Difficulty in the identification of heterotrophic protists has often resulted in lumping them into broad groups, but there is a strong need to develop methods that increase the spatial and temporal resolution of observations applied to particular organisms in order to discover the drivers of population structure and ecological function. In surveys of small subunit rRNA, gene (SSU) sequences of microbial eukaryotes from the Columbia River to the Pacific Ocean, the heterotrophic flagellate Katablepharis sp. were found to dominate protist assemblages (including autotrophic and heterotrophic fractions) in the spring, prior to the freshet. We discovered a 332 base pair unique sequence element (USE) insertion in the large subunit rRNA gene (28S) that is not present in other katablepharids or in any other eukaryote. Using this USE, we were able to detect Katablepharis within mixed assemblages in river, estuarine, and oceanic samples and determine spatial and temporal patterns in absolute abundance through quantitative PCR and fluorescence in situ hybridization. Given their high abundance and repeatable temporal patterns of occurrence, we hypothesize that the Columbia River Estuary Katablepharis (Katablepharis CRE) plays an important role in estuarine biogeochemical and ecosystem function.

Threat of predation alters the ability of benthic invertebrates to modify sediment biogeochemistry and benthic microalgal abundance

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 494:29-39 (2013) - DOI: https://doi.org/10.3354/meps10561 Threat of predation alters the ability of benthic invertebrates to modify sediment biogeochemistry and benthic microalgal abundance Katherine M. Premo, Anna Christina Tyler* Program in Environmental Sciences, School of Life Sciences, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, New York 14623, USA *Corresponding author. Email: actsbi@rit.edu ABSTRACT: Benthic invertebrates alter estuarine ecosystem function by moderating benthic microalgal production and sediment biogeochemistry. While lethal predation eliminates the effect of invertebrates, non-consumptive effects of predation through trait-mediated indirect effects on behavior may reduce prey control of ecosystem function. Using microcosms, we investigated how chemical cues from the predatory mud crab Panopeus herbstii changed prey behavior and thereby affected the ability of the grazing-deposit feeding gastropod Ilyanassa obsoleta and filter-feeding bivalve Mercenaria mercenaria to regulate benthic ecosystem function. Sediment-water column fluxes of oxygen and nutrients, microscale profiles of sediment oxygen, benthic chlorophyll a, porewater ammonium and organic matter were measured after exposure to predator effluent. Both species had significant effects on sediment processes, with higher sediment oxygen consumption and release of ammonium to the water column, and lower porewater ammonium. However, individual effects were altered in the presence of chemical cues from P. herbstii. The negative effect of M. mercenaria on porewater ammonium was diminished by 26% in predator treatments, suggesting less movement and therefore less sediment oxidation and nitrogen removal. For I. obsoleta, there was a 30% increase in microalgal biomass and a 35% decrease in sediment ammonium release in the predator treatments, possibly associated with decreased foraging activity. In these experiments, non-consumptive predator effects indirectly altered benthic biogeochemistry, benthic microalgae and nutrient fluxes. These results suggest that experiments conducted without predators may overestimate the impact of benthic fauna on ecosystem processes and that changes in community structure resulting in loss of predators may have indirect effects on benthic ecosystem function, leading to faster nitrogen turnover and release to the water column. KEY WORDS: Trait-mediated interactions · Non-consumptive effects · Benthic invertebrates · Benthic microalgae · Sediment biogeochemistry Full text in pdf format PreviousNextCite this article as: Premo KM, Tyler AC (2013) Threat of predation alters the ability of benthic invertebrates to modify sediment biogeochemistry and benthic microalgal abundance. Mar Ecol Prog Ser 494:29-39. https://doi.org/10.3354/meps10561 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 494. Online publication date: December 04, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Estuarine ecosystem function response to flood and drought in a shallow, semiarid estuary: Nitrogen cycling and ecosystem metabolism

We quantified sediment‐water interface and water column nitrogen (N) transformation rates seasonally over the course of a year that incorporated a major storm event and a period of prolonged riverine base flow in Copano Bay, Texas, a shallow, productive estuary in the western Gulf of Mexico. We calculated daily rates of gross primary production (GPP), community respiration (CR), and net ecosystem production (NEP) in Copano Bay to examine carbon (C) cycling over the course of the year. These metrics of estuarine ecosystem function indicated that the estuary switched from a net sink for N during floods to a net source of N during droughts while sustaining high rates of primary production throughout the year. The estuary became a net sink for N as a result of increased denitrification rates following a storm event. Both GPP and CR increased immediately following a flood event, and the system was driven to net heterotrophy. Copano Bay became a net source of N during periods of prolonged base flow via increased N fixation rates. Internal N cycling became increasingly important during periods of base flow, including increased rates of dissimilatory nitrate reduction to ammonium. This internal N cycling sustained production during periods of drought, when GPP ≈ CR. Both CR and NEP were linked to nutrient export from the inflowing rivers. N and C cycles were tightly linked but became decoupled briefly as a result of inputs of nutrients and organic matter during the period after a major storm event.

Science and Management of the Introduced Seagrass Zostera japonica in North America

Healthy seagrass is considered a prime indicator of estuarine ecosystem function. On the Pacific coast of North America, at least two congeners of Zostera occur: native Zostera marina, and introduced, Zostera japonica. Z. japonica is considered "invasive" and therefore, ecologically and economically harmful by some, while others consider it benign or perhaps beneficial. Z. japonica does not appear on the Federal or the Oregon invasive species or noxious weed lists. However, the State of California lists it as both an invasive and noxious weed; Washington State recently listed it as a noxious weed. We describe the management dynamics in North America with respect to these congener species and highlight the science and policies behind these decisions. In recent years, management strategies at the state level have ranged from historical protection of Z. japonica as a priority habitat in Washington to eradication in California. Oregon and British Columbia, Canada appear to have no specific policies with regard to Z. japonica. This fractured management approach contradicts efforts to conserve and protect seagrass in other regions of the US and around the world. Science must play a critical role in the assessment of Z. japonica ecology and the immediate and long-term effects of management actions. The information and recommendations provided here can serve as a basis for providing scientific data in order to develop better informed management decisions and aid in defining a uniform management strategy for Z. japonica.

Isolation and connectivity: Relationships between periodic connection to the ocean and environmental variables in intermittently closed estuaries

Morphometric and physicochemical variables are key determinants of biotic community structure in estuaries and are influenced by changes to estuary mouth state (open/closed). This study examined and compared the consequences of intermittent connection to the ocean on environmental gradients among estuaries; specifically, how estuary morphology and hydrology relate to physical connection to the sea, and the influence of this relationship on the physicochemical environment. By sampling 20 estuaries across New Zealand and using historical aerial photographs, a continuous index of estuarine connection to the ocean was developed and independently validated using berm elevation derived from Airborne Laser Scanning (ALS) data. Using published literature, this index was compared to equivalent indices in South Africa and Australia. A clear relationship between connections to the ocean, freshwater flow and productivity indices underlie the environmental differences between permanently open and intermittently closed estuaries. Consistent patterns across the Southern Hemisphere, albeit with regional variations in estuarine characteristics, suggest that remote sensing is useful for predicting the physicochemical environment of small estuaries across regions. Principal components analysis for Otago estuaries showed that 40% of measured variation in the environment could be attributed to the gradient of relative connectivity (EOI), or isolation (berm elevation) to the ocean. Evaluating these relationships is central to understanding how global and local environmental changes may affect estuarine connectivity regimes and, ultimately, the functioning of estuarine ecosystems.

Factors Controlling Phytoplankton Biomass in a Subtropical Coastal Lagoon: Relative Scales of Influence

Patterns in phytoplankton biomass are essential to understanding estuarine ecosystem structure and function and are the net result of various gain and loss processes. In this study, patterns in phytoplankton biomass were explored in relation to a suite of potentially regulating factors in a well-flushed, subtropical lagoon, the Matanzas River Estuary (MRE) in northeast Florida. We examined temporal variability in water temperature, light availability, nutrient concentrations, phytoplankton productivity, and phytoplankton standing stock over 8 years (2003–2010) and explored relationships among variables through correlation analysis. Laboratory experiments in the spring and summer of 2009 quantified phytoplankton growth rates, nutrient limitation potential, and zooplankton grazing rates. The potential influence of oyster grazing was also examined by scaling up population metrics and filtration rate estimates. Results indicated that phytoplankton biomass in the study area was relatively low mainly due to a combination of low temperature and light availability in the winter and consistent tidal water exchange and bivalve grazing throughout the year. Relatively low levels of phytoplankton standing stock and small inter-annual variability within the MRE reflect a balance between gain and loss processes which provide a degree of resilience of the system to natural and anthropogenic influences.

Detecting shifts in ecosystem functioning: The decoupling of fundamental relationships with increased pollutant stress on sandflats

In this study, we investigated the influence of low level contamination by copper, lead and zinc on the functioning of estuarine sandflat ecosystems by comparing the strength and variability of relationships between benthic macrofauna and fluxes (oxygen and nutrients) at three clean and three mildly contaminated sites. Specifically, as indicators of ecosystem functioning, we examined relationships between bivalve biomass, total benthic respiration and ammonium release, and ammonium uptake and benthic primary production. Furthermore, a small amount of organic matter was added to experimental plots at all sites (35g/0.2m2) to evaluate stress-on-stress responses relative to controls. Relationships were strongest at the clean sites (steepest slopes, highest r2 values, lowest p-values) and weakest at the mildly contaminated sites and in organically enriched plots. Our results suggest that changes in ecosystem functioning may be occurring at mild (<ERL) levels of pollution that are unlikely to cause widespread mortality of macrofauna.

Seasonal succession of estuarine fish, shrimps, macrozoobenthos and plankton: Physico-chemical and trophic influence. The Gironde estuary as a case study

Characterization of the structure and seasonal variability of biotic communities is essential for a better understanding of estuarine ecosystem functioning and in order to manage these highly fluctuating and naturally stressed systems. Numerous studies have investigated the role of environmental factors in controlling temporal variations in biotic communities. However, most have concluded that the explanatory power of physico-chemical variables was significant but not sufficient to explain ecological dynamics. The present study aimed to propose the importance of trophic interactions as an additional structuring factor of species seasonal variability by examining simultaneous dynamics of all estuarine biotic communities, using the oligo-mesohaline area of the Gironde estuary (SW France) as a case study. Data on the main biological groups (fish, shrimps, macrozoobenthos and plankton) sampled during a five-year period (2004–2008) at monthly intervals using a well standardized protocol, as well as data on environmental variables, were compiled here for the first time. According to species composition, the Gironde estuary is used as a nursery, feeding, resident and migratory habitat. For almost all species, strong seasonal fluctuations occurred with a succession of species, indicating an optimization of the use of the available resources over a typical year by estuarine biological communities. Multivariate analyses discriminated four seasonal groups of species with two distinctive ecological seasons. A clear shift in July indicated a biomass transfer from a “planktonic phase” to a “bentho-demersal phase”, corresponding to spring and summer–autumn periods, respectively. With regard to the temporal fluctuations of dominant species of all biological groups, this study highlighted the possible influence of trophic relationships, predation in particular, on seasonal variations in species abundance, in addition to the physico-chemical influence. This study enabled us to collate important seasonal data and to discuss their integration into seasonal models of estuarine functioning and/or specific prey–predator models. In a global change context, prey abundance variations could generate changes in the temporal dynamics of their predators (and conversely), and potentially in the functioning of the whole estuarine system.

하구 생태 복원을 위한 생태구역 구분; 남해 고성만 고성천 인근 하구의 예

연안 하구는 인위적인 개발압력이 상존하며 자연적인 변화에도 민감하게 반응하는 지역이다. 따라서 보존과 지속 가능한 이용을 위해서는 하구 생태계의 구조와 기능에 대한 이해가 필요하며, 인위적 혹은 자연적 변화에 어떻게 반응할 것인지를 아는 것이 필요하다. 하구 생태계 변화의 방향과 현 상태를 용이하게 판단하기 위한 노력의 하나로서 비오톱(biotope)과 하구 타입 분류(typology)를 이용하여 "생태 구역"을 정의하였다. 하구댐의 유무, 염분특성, 식생유무에 따라 16개의 생태 구역을 정의하였고, 고성만에 위치한 고성천 인근 4개 하구(배둔, 구만, 마암, 고성) 생태계에서 지형, 하상경사, 퇴적물 특성, 염분 구조, 식생 면적 등을 통해 생태구역 구분을 시도하였다. 고성천 인근 하구에는 총 16개 생태구역 중 7개가 구분되었다. 자연형 하천인 구만천, 마암천, 배둔천의 상류에는 NFB(natural, fresh, bare)가 나타나고 있으며, 기수 지역에는 NLV(natural, low salinity, vegetated)가 그리고 갯벌에는 NHB(natural, high salinity, bare)가 나타났다. 폐쇄형인 고성천의 경우 담수지역에는 CFB(closed, fresh, bare), 이후 하구쪽으로 CFV(closed, fresh vegetated)가 나타났다. 갈대가 넓게 서식하는 하구댐 안쪽지역은 CLV(closed, low salinity, vegetated)가 나타나며, 거산방조제 바깥쪽은 CHB(closed, high salinity, bare)가 나타났다. 고성천의 CHB와 CLV 지역은 방조제가 하구 생태계에 미치는 영향을 잘 보여주고 있다. 염분이 비교적 높고, 수심이 갚은 수로나 갯벌이 존재하던 CHB 지역이 하구둑에 의해 고염분 지역과 단절되면서 염분이 감소하고, 조석의 영향이 줄어들면서 침수가 줄고, 결국 갈대가 서식하기에 적합한 환경으로 바뀌게 되며, CLV로 바뀐 것으로 여겨진다. 국내의 여러 하구에 나타나는 생태구역을 데이터베이스화하여 각 생태구역의 출현 분포를 파악하는 것이 필요하며, 이러한 자료는 인위적, 자연적 변화에 의한 하구 생태계 변동을 예측하고 관리/대응 방안을 마련하는데 이용될 것이다. 생태구역 변화는 생태구조와 가능의 변화를 가져오기 때문에 생태계 역할 및 가치의 변화를 수반하며, 생태 구역 변화를 야기하는 사업의 타당성을 판단하는 근거자료로 이용될 수 있다. Estuarine ecosystem responds sensitively to natural and anthropogenic perturbations. lt is necessary to identify the direction of the change when the perturbation occurs as well as to understand the structure and functioning of estuarine ecosystem for a proper management of the area. In this study, the estuarine habitats were classified into different ecological districts so as to the switch from one district to another district could be related to the environmental change due to the perturbations. Total 16 ecological districts was defined according to the presence of barrage, salinity and vegetation characteristics. The defined ecological districts were applied to small estuaries in Goseong bay, south sea of Korea (Baedun, Guman, Maam, Goseong) to distinguish different regions which might have characteristic bottom topography, inclinations of river bottom, sediment characteristics, salinity structure and area of vegetation. Total 7 out of 16 ecological district was identified in this region; NFB (natural, fresh, bare), NHB (natural, high salinity, bare), NLV (natural, low salinity, vegetated) in natural (without barrage) estuaries and CFB (closed, fresh, bare), CFV( closed, fresh vegetated), CLV (closed, low salinity, vegetated), CHB (closed, high salinity, bare) in closed (with barrage) estuary. A comparison of environmental factors and biota between CHB and CLV demonstrated the effect of barrage on estuarine ecosystem. The height and sediment characteristics of CHB and CLV were similar but the average salinity was lower in CLV than in CHB due to the barrage, which produced favorable condition for the Phragmites australis in CLV. Information regarding the ecological districts in various sizes and location could be useful for predicting the ecosystem change due to natural and anthropogenic perturbations and for preparing management actions.