Complex seasonal patterns of primary producers at the land-sea interface

Seasonal fluctuations of plant biomass and photosynthesis are key features of the Earth system because they drive variability of atmospheric CO₂, water and nutrient cycling, and food supply to consumers. There is no inventory of phytoplankton seasonal cycles in nearshore coastal ecosystems where forcings from ocean, land and atmosphere intersect. We compiled time series of phytoplankton biomass (chlorophyll a) from 114 estuaries, lagoons, inland seas, bays and shallow coastal waters around the world, and searched for seasonal patterns as common timing and amplitude of monthly variability. The data revealed a broad continuum of seasonal patterns, with large variability across and within ecosystems. This contrasts with annual cycles of terrestrial and oceanic primary producers for which seasonal fluctuations are recurrent and synchronous over large geographic regions. This finding bears on two fundamental ecological questions: (1) how do estuarine and coastal consumers adapt to an irregular and unpredictable food supply, and (2) how can we extract signals of climate change from phytoplankton observations in coastal ecosystems where local‐scale processes can mask responses to changing climate?     

A coordinated coastal ocean observing and modeling system for the West Florida Continental Shelf

The evolution of harmful algal blooms, while dependent upon complex biological interactions, is equally dependent upon the ocean circulation since the circulation provides the basis for the biological interactions by uniting nutrients with light and distributing water properties. For the coastal ocean, the circulation and the resultant water properties, in turn, depend on interactions between both the continental shelf and the deep-ocean and the continental shelf and the estuaries since the deep-ocean and the estuaries are primary nutrient sources. Here we consider a coordinated program of observations and models for the West Florida Continental Shelf (WFS) intended to provide a supportive framework for K. brevis red-tide prediction as well as for other coastal ocean matters of societal concern. Predicated on lessons learned, the goal is to achieve a system complete enough to support data assimilative modeling and prediction. Examples of the observations and models are presented and application is made to aspects of the 2005 red-tide. From an observational perspective, no single set of measurements is adequate. Required are a broad mix of sensors and sensor delivery systems capable of describing the three-dimensional structure of the velocity and density fields. Similarly, models must be complete enough to include the relevant physical processes, and data assimilation provides the integrative framework for maximizing the joint utility of the observations and models. While we are still in the exploratory stages of development, the lessons learned and application examples may be useful to similar programs under development elsewhere. One scientific finding is that the key to understanding K. brevis red-tide on the WFS lies not at the surface, but at depth.     

Factors controlling long-term changes of the eutrophicated ecosystem of Pärnu Bay,Gulf of Riga

Phytoplankton, mesozooplankton, mysids and fish larvae were studied during 15–29 annual cycles measured weekly to monthly in Pärnu Bay, the Gulf of Riga. The monthly variability of the biological data was related to temperature, ice conditions, salinity, influx of nutrients, the North Atlantic Oscillation (NAO) index, cloudiness and solar activity. Phytoplankton development was mainly a function of the NAO index. For the whole study period the abundance of zooplankton increased with increasing water temperature and solar activity. Significant correlations between phytoplankton and zooplankton densities were found until 1990. After the invasion of the predatory cladoceran Cercopagis pengoi in 1991, the zooplankton community was likely to be regulated by the introduced species rather than phytoplankton dynamics. The increased abundances of rotifers and copepods triggered the increase in mysid densities. The development of herring larvae was positively affected by the high density of copepods and rotifers but also by increased eutrophication. Until 1990 there was no significant relationship between the density of zooplankton and herring larvae. A negative relationship between the density of zooplankton and herring larvae in the 1990s suggests that the major shift in zooplankton community resulted in food limitation for herring larvae. The results indicated that (1) atmospheric processes in the northern Atlantic explain a large part of the interannual variation of the local phytoplankton stock, (2) trophic interactions control the development of pelagic communities at higher trophic levels, and (3) the introduction of an effective intermediate predator has repercussions for the whole pelagic food web in Pärnu Bay.     

Fortuitous Encounters between Seagliders and Adult Female Northern Fur Seals (Callorhinus ursinus) off the Washington (USA) Coast: Upper Ocean Variability and Links to Top Predator Behavior

Behavioral responses by top marine predators to oceanographic features such as eddies, river plumes, storms, and coastal topography suggest that biophysical interactions in these zones affect predators'' prey, foraging behaviors, and potentially fitness. However, examining these pathways is challenged by the obstacles inherent in obtaining simultaneous observations of surface and subsurface environmental fields and predator behavior. In this study, migratory movements and, in some cases, diving behavior of 40 adult female northern fur seals (NFS; Callorhinus ursinus) were quantified across their range and compared to remotely-sensed environmental data in the Gulf of Alaska and California Current ecosystems, with a particular focus off the coast of Washington State (USA) – a known foraging ground for adult female NFS and where autonomous glider sampling allowed opportunistic comparison of seal behavior to subsurface biophysical measurements. The results show that in these ecosystems, adult female habitat utilization was concentrated near prominent coastal topographic, riverine, or inlet features and within 200 km of the continental shelf break. Seal dive depths, in most ecosystems, were moderated by surface light level (solar or lunar), mirroring known behaviors of diel vertically-migrating prey. However, seal dives differed in the California Current ecosystem due to a shift to more daytime diving concentrated at or below the surface mixed layer base. Seal movement models indicate behavioral responses to season, ecosystem, and surface wind speeds; individuals also responded to mesoscale eddies, jets, and the Columbia River plume. Foraging within small scale surface features is consistent with utilization of the inner coastal transition zone and habitats near coastal capes, which are known eddy and filament generation sites. These results contribute to our knowledge of NFS migratory patterns by demonstrating surface and subsurface behavioral responses to a spatially and temporally dynamic ocean environment, thus reflecting its influence on associated NFS prey species.     

Seasonal succession of phytoplankton in an ice-free pond warmed by a thermal power plant

In a pond receiving warmed cooling waters from a thermal power plant, the physical and chemical properties of the water, phytoplankton, periphyton and zooplankton were monitored on a weekly sampling schedule. In winter the phytoplankton growth was limited by poor light conditions. In mid-February a rapid phytoplankton growth started, simultaneously with increasing light energy, high nutrient concentrations and small herbivorous zooplankton populations. The increase of phytoplankton biomass was stopped by lack of free nutrients and silica at the end of March. From May until August the phytoplankton standing crop was mainly regulated by herbivorous zooplankton. The autumnal maximum of phytoplankton occurred with decreasing zooplankton populations, increasing nutrient concentrations, a turbulence favourable for diatoms and high water temperature.     

Intraspecific variation in a predator drives cascading variation in primary producer community composition

Predation has important cascading impacts on primary producer biomass and community composition in many ecosystems. While most studies have focused on the consequences of interspecific or density differences in predators, it is recognized that phenotypic variation within species can have strong and cascading community and ecosystem consequences at lower trophic levels. In coastal New England lakes, both the presence and life history form of the zooplanktivorous fish alewife, Alosa pseudoharengus, have strong influence on the biomass, size structure and community composition of crustacean zooplankton communities. Here we test the hypothesis that alewife presence and life history will have cascading impacts on phytoplankton biomass and community composition in a mesocosm experiment that previously reported strong biomass and compositional differences of crustacean zooplankton communities among alewife treatments. We show that alewife life history led to small but statistically significant differences in phytoplankton community composition among treatments. This compositional difference was driven primarily by an increase in the density of two edible phytoplankton genera associated with lower zooplankton biomass in the anadromous alewife treatment. Our results show that intraspecific variation in a predator can have cascading effects on primary producer communities. However we did not observe significant differences in total algal biomass.     

Applications of Satellite Ocean Color Sensors for Monitoring and Predicting Harmful Algal Blooms

The new satellite ocean color sensors offer a means of detecting and monitoring algal blooms in the ocean and coastal zone. Beginning with SeaWiFS (Sea Wide Field-of-view Sensor) in September 1997, these sensors provide coverage every 1 to 2 days with 1-km pixel view at nadir. Atmospheric correction algorithms designed for the coastal zone combined with regional chlorophyll algorithms can provide good and reproducible estimates of chlorophyll, providing the means of monitoring various algal blooms. Harmful algal blooms (HABs) caused by Karenia brevis in the Gulf of Mexico are particularly amenable to remote observation. The Gulf of Mexico has relatively clear water and K. brevis, in bloom conditions, tends to produce a major portion of the phytoplankton biomass. A monitoring program has begun in the Gulf of Mexico that integrates field data from state monitoring programs with satellite imagery, providing an improved capability for the monitoring of K. brevis blooms.     

三门湾健跳港网箱养殖区浮游生物多样性的夏季调查

调查了三门湾健跳港海水养殖区夏季浮游生物的种类组成、密度和多样性指数,并将浮游生物群落指标与水质理化因子进行相关分析。共发现浮游生物29种,其中浮游植物14种,第一优势种为中勒骨条藻(Skeletonema costatum);浮游动物15种,第一优势种为太平洋纺锤水蚤(Acartia pacifica)。表层浮游植物的平均密度为43 328ind·L^-1,Shannon-Weiner多样性指数为0.826;浮游动物平均密度为389ind.m^-3,Shannon-Weiner多样性指数为2.964。相关分析结果表明:无机氮、无机磷促使了浮游植物大量繁殖,并使浮游动物多样性指数提高。网箱养鱼区水体富营养化指数与浮游植物多样性指数之间有一定的正相关关系,与浮游动物多样性指数之间呈显著的正相关关系。     

Can export of organic matter from estuaries support zooplankton in nearshore,marine plumes?

Marine and terrestrial ecosystems are connected via transfers of nutrients and organic matter in river discharges. In coastal seas, such freshwater outflows create prominent turbidity plumes. These plumes are areas of high biological activity in the pelagos, of which zooplankton is a key element. Conceptually, the increased biomass of zooplankton consumers in plumes can be supported by two alternative trophic pathways—consumption of fresh marine phytoplankton production stimulated by riverine nutrients, or direct trophic subsidies through the uptake of terrestrial and estuarine organic matter flushed to sea. The relative importance of these two pathways has not been established previously. Isotopic tracing (carbon and nitrogen) was used to measure the extent of incorporation of marine versus terrestrial matter into mesozooplankton consumers in the plumes off a small estuary in eastern Australia. Replicate zooplankton samples were taken during baseflow conditions with minimal freshwater influence to the sea, and during pulsed discharge events that generated turbidity plumes in coastal waters. Food sources utilized by zooplankton differed among locations and with the strength of freshwater flow. Terrestrial and estuarine carbon only made a sizeable contribution (47%) to the carbon demands of zooplankton in the lower estuary during pulsed freshwater flows. By contrast, in plumes that developed in nearshore marine waters, phytoplankton supplied up to 90% of the dietary carbon of zooplankton feeding in the plumes. Overall, it was “fresh” carbon, fixed by marine phytoplankton, the growth of which became stimulated by fluvial nutrient exports, that dominated energy flows in plume regions. The trophic role of terrestrial and estuarine organic exports was comparatively minor. The trophic dynamics of plankton in small coastal plumes is closely linked to variations in freshwater flow, but this coupling operates mainly through the enhancement of in-situ phytoplankton production rather than cross-boundary transfers of organic matter to marine food webs in the pelagos.     

The impact of Indonesian peatland degradation on downstream marine ecosystems and the global carbon cycle

Tropical peatlands are among the most space‐efficient stores of carbon on Earth containing approximately 89 Gt C. Of this, 57 Gt (65%) are stored in Indonesian peatlands. Large‐scale exploitation of land, including deforestation and drainage for the establishment of oil palm plantations, is changing the carbon balance of Indonesian peatlands, turning them from a natural sink to a source via outgassing of CO₂ to the atmosphere and leakage of dissolved organic carbon (DOC) into the coastal ocean. The impacts of this perturbation to the coastal environment and at the global scale are largely unknown. Here, we evaluate the downstream effects of released Indonesian peat carbon on coastal ecosystems and on the global carbon cycle. We use a biogeochemical box model in combination with novel and literature observations to investigate the impact of different carbon emission scenarios on the combined ocean–atmosphere system. The release of all carbon stored in the Indonesian peat pool, considered as a worst‐case scenario, will increase atmospheric pCO₂ by 8 ppm to 15 ppm within the next 200 years. The expected impact on the Java Sea ecosystems is most significant on the short term (over a few hundred years) and is characterized by an increase of 3.3% in phytoplankton, 32% in seagrass biomass, and 5% decrease in coral biomass. On the long term, however, the coastal ecosystems will recover to reach near pre‐excursion conditions. Our results suggest that the ultimate fate of the peat carbon is in the deep ocean with 69% of it landing in the deep DIC pool after 1000 years, but the effects on the global ocean carbonate chemistry will be marginal.     

Water,nitrogen and phosphorus in freshwater Plankton

Summary Mixed phytoplankton, zooplankton and Thermocyclops hyalinus collected from Fort Moat, at Aligarh (U.P.) India, were analysed for water, nitrogen and phosphorus. Results are generally in agreement with observations of earlier investigators.Phosphorus values are found to be very high. Nutritional condition of zooplankton is noticed to have improved during phytoplankton maxima in the lake.     

Spatial and temporal heterogeneity of trophic variables in a deep lake as reflected by repeated singular samplings

Approaches to compare the strength of pelagic trophic cascades often use singular sampling programs for measuring trophic variables, thus potentially neglecting the spatial and temporal heterogeneity in the distribution of fish, zooplankton and phytoplankton. Here, we compared the composition of six trophic variables from three trophic levels in a deep oligotrophic lake within temporal (diel and seasonal) and spatial (horizontal and vertical) sampling resolutions. Mean values and ratios between the variables were compared between day and night, in three sampling months, four lake basins, and three water depths. Factor analysis was used to determine abiotic variables which may explain the heterogeneous distribution of the trophic variables. All six trophic variables were strongly heterogeneously distributed between the sampling months and the water depths, whereas horizontal and day–night differences were lower. Distribution of fish, zooplankton and phytoplankton correlated with water temperature and nutrient concentrations. Accordingly, for the use in comparative and meta-analyses, singular sampling programs in deep lakes have to integrate the entire water depth and are best repeated over several seasons. Alternatively, mean water temperature and nutrient concentrations may be used as covariates to diminish the unexplained variance between samples from different lakes.     

The annual cycles of phytoplankton biomass

Terrestrial plants are powerful climate sentinels because their annual cycles of growth, reproduction and senescence are finely tuned to the annual climate cycle having a period of one year. Consistency in the seasonal phasing of terrestrial plant activity provides a relatively low-noise background from which phenological shifts can be detected and attributed to climate change. Here, we ask whether phytoplankton biomass also fluctuates over a consistent annual cycle in lake, estuarine–coastal and ocean ecosystems and whether there is a characteristic phenology of phytoplankton as a consistent phase and amplitude of variability. We compiled 125 time series of phytoplankton biomass (chlorophyll a concentration) from temperate and subtropical zones and used wavelet analysis to extract their dominant periods of variability and the recurrence strength at those periods. Fewer than half (48%) of the series had a dominant 12-month period of variability, commonly expressed as the canonical spring-bloom pattern. About 20 per cent had a dominant six-month period of variability, commonly expressed as the spring and autumn or winter and summer blooms of temperate lakes and oceans. These annual patterns varied in recurrence strength across sites, and did not persist over the full series duration at some sites. About a third of the series had no component of variability at either the six- or 12-month period, reflecting a series of irregular pulses of biomass. These findings show that there is high variability of annual phytoplankton cycles across ecosystems, and that climate-driven annual cycles can be obscured by other drivers of population variability, including human disturbance, aperiodic weather events and strong trophic coupling between phytoplankton and their consumers. Regulation of phytoplankton biomass by multiple processes operating at multiple time scales adds complexity to the challenge of detecting climate-driven trends in aquatic ecosystems where the noise to signal ratio is high.     

Jelly-falls historic and recent observations: a review to drive future research directions

The biological pump describes the transport of particulate matter from the sea surface to the ocean’s interior including the seabed. The contribution by gelatinous zooplankton bodies as particulate organic matter (POM) vectors (“jelly-falls”) has been neglected owing to technical and spatiotemporal sampling limitations. Here, we assess the existing evidence on jelly-falls from early ocean observations to present times. The seasonality of jelly-falls indicates that they mostly occur after periods of strong upwelling and/or spring blooms in temperate/subpolar zones and during late spring/early summer. A conceptual model helps to define a jelly-fall based on empirical and field observations of biogeochemical and ecological processes. We then compile and discuss existing strategic and observational oceanographic techniques that could be implemented to further jelly-falls research. Seabed video- and photography-based studies deliver the best results, and the correct use of fishing techniques, such as trawling, could provide comprehensive regional datasets. We conclude by considering the possibility of increased gelatinous biomasses in the future ocean induced by upper ocean processes favouring their populations, thus increasing jelly-POM downward transport. We suggest that this could provide a “natural compensation” for predicted losses in pelagic POM with respect to fuelling benthic ecosystems.     

Relations among heterotrophic bacteria, chlorophyll-a, total phytoplankton, total zooplankton and physical and chemical features in the Paranoá reservoir, Brasília, Brazil

The plankton community, chlorophyll-a, heterotrophic bacteria and physical and chemical features of the Paranoá Reservoir were studied at monthly intervals at seven stations from March 1988 to March 1989. Thermal structure had a circulation period from May to July and stratification during the other months. The phytoplankton consisted of 76 taxa, was dominated by the cyanophyte Cylindrospermopsis raciborskii and attained concentrations ranging from 7,759,000 up to 98,160,000 org. l^–1. The zooplankton consisted of 36 taxa and was present in densities between 8 and 8,056 org. l^–1. In stations, or seasons with highly eutrophic conditions, there was a decrease in total phytoplankton and an increase in bacteria and total zooplankton. The results had spatial and temporal variations. Spatial variation demonstrated the existence of water quality deterioration at two or three sampling points. Temporal variation showed the influences of water column stability and the dry versus rainy seasons on nutrient concentrations and the planktonic community.     

Fluctuating deposition of ocean water drives plant function on coastal sand dunes

Sea‐level rise will alter the hydrology of terrestrial coastal ecosystems. As such, it becomes increasingly important to decipher the present role of ocean water in coastal ecosystems in order to assess the coming effects of sea‐level rise scenarios. Sand dunes occur at the interface of land and sea. Traditionally, they are conceived as freshwater environments with rain and ground water as the only water sources available to vegetation. This study investigates the possibility of ocean water influx to dune soils and its effect on the physiology of sand dune vegetation. Stable isotopes are used to trace the path of ocean water from the soil to the vegetation. Soil salinity, water content and δ¹⁸O values are measured concurrently with stem water and leaf tissue of eight species during the wet and dry season and from areas proximal and distal to the ocean. Our results indicate the dune ecosystem is a mixed freshwater and marine water system characterized by oceanic influence on dune hydrology that is spatially heterogeneous and fluctuates temporally. Ocean water influx to soil occurs via salt spray in areas 5–12 m from the ocean during dry season. Accordingly, vegetation nearest to the sea demonstrate a plastic response to ocean water deposition including elevated integrated water use efficiency (δ¹³C_leaf) and uptake of ocean water that comprised up to 52% of xylem water. We suggest physiological plasticity in response to periodic ocean water influx may be a functional characteristic common to species on the leading edge of diverse coastal habitats and an important feature that should be included in modeling coastal ecosystems. Rising sea level would likely cause a repercussive landward shift of dune species in response to encroaching maritime influences. However, human development would restrict this process, potentially causing the demise of dune systems and the protection from land erosion they provide.     

Does stocking of filter-feeding fish for production have a cascading effect on zooplankton and ecological state? A study of fourteen (sub)tropical Chinese reservoirs with contrasting nutrient concentrations

Stocking of filter-feeding fish is a common tool used in Chinese reservoirs to increase fish production because of low natural recruitment. Whether such stocking has important negative effects on zooplankton with cascading effects on phytoplankton is debated. We compared the zooplankton communities in fourteen reservoirs with different nutrient concentrations and fish densities. Both chlorophyll a (Chla) and fish catch were positively related with total phosphorus (TP), whereas zooplankton biomass did not show a similar relationship with TP. Zooplankton seemed to be influenced by fish as high fish catches coincided with a low proportion of calanoids of the total copepod biomass, a high proportion of rotifers of the total zooplankton biomass, a low zooplankton:phytoplankton biomass ratio, and the absence of Daphnia irrespective of TP concentration. Both zooplankton biomass and most of the zooplankton:phytoplankton biomass ratios were among the lowest reported in the literature for the nutrient range studied. Furthermore, the Chla:TP ratio was higher than what is typically observed in temperate lakes. We conclude that top-down control of zooplankton is of key importance in reservoirs in South China where frequent stocking of filter-feeding fish seems to contribute to poor water quality in the form of higher algal biomass and reduced clarity.     

Pheopigment dynamics,zooplankton grazing rates and the autumnal ammonium peak in a Mediterranean lagoon

The dilution technique was used to estimate chlorophyll and pheopigment, net and gross production as well as zooplankton grazing over a 12-month period in a coastal lagoon in Southern France. Chlorophyll a (Cha) based gross growth rates of phytoplankton ranged from undetectable in February to 2.6 day⁻¹ in June, corresponding to 3.8 divisions per day. Cha-based grazing rates ranged from undetectable in February to 1.1 d⁻¹ in June. The seasonal growth pattern of picoplankton was similar to that of the whole community, with a peak in July, corresponding to four divisions per day. Grazing processes represented from 20 to 150% of the phytoplankton daily growth, and the grazing pressure was stronger on small phytoplankton cells than on larger cells. Gross growth rates of phytoplankton were related to zooplankton grazing rates, and both were related to water temperature. Mesozooplankton which escaped sampling or oysters had to be also invoked as additional sinks for the primary production. In the fall, pheopigment concentrations greater than chlorophyll concentrations coincided with high ammonium levels in the water column. Pheopigment a production rates were highly correlated to chlorophyll -based microzooplankton grazing rates. The pheopigment a to chlorophyll a ratio was correlated with ammonium concentrations and could be used an index of the balance between ammonium supply (degradation) and demand (uptake by phytoplankton). In addition, pheopigment degradation rates in absence of grazing could be related to irradiance, indicating photo-degradation of these compounds.     

Long-term changes in zooplankton abundance and water transparency in Lake Geneva

The water quality of Lake Geneva has declined steadily since the 1960s, due to a continuous increase of external phosphorus loading. Average P level in the lake increased steadily to a peak in 1979, and even 1981 in the case of P content in the trophogenic layer. Since then, reduced external inputs related to the delayed effects of phosphorus removal from waste waters initiated many years previously has led to a decrease in P level, and resulted in present stabilization and even improvement in water quality. Long-term changes in zooplankton abundance correspond quite closely to eutrophication level changes. After increasing since the 1960s, maximum zooplankton biomass was recorded for the first time in 1971; a second main peak appeared in 1981 together with the highest eutrophication level. Over the last seven years, zooplankton abundance has decreased continuously, while water transparency has decreased and phytoplankton production has remained at a high level.