Temperate Coastal Environments Research Articles

Assessment of model projections of climate‐change induced extreme storms on the south‐east coast of Australia

AbstractGeneral circulation models (GCMs) and their downscaled regional‐scale equivalents have been important tools for climate‐change studies. However, there has been limited assessment of the performance of GCMs and downscaled models in simulating extreme storms in temperate coastal environments. This study assesses the model characterization of extreme storms on the heavily populated coast of south‐east Australia. Twenty‐year average recurrence interval (ARI) storm intensities derived from generalized extreme value (GEV) distributions based on observed and large‐scale atmospheric model data are compared. Changes in extreme storms from past climate to a high‐emission future scenario are also investigated. Simulations of storm minimum surface pressures compared favourably with measured data. Both the GCMs and downscaled models reproduced the observed decrease with increasing latitude along the coast in the 20 year ARI of minimum surface pressure. Both indicated that the minimum storm surface pressure should change negligibly in a high‐emission future. Although the models underestimated the maximum daily precipitation significantly, models are improving significantly with CMIP epoch and downscaling. In the high‐emission future scenario, the GCMs and NARCliM projected the 20 year ARI maximum daily precipitation would increase in the order of 25%. GCMs and the corresponding downscaled products presently do not represent the extreme value distributions of historical wind speed data well, overestimating at smaller values of ARI and significantly underestimating in larger values of ARI. Significant changes in the magnitude of the 20 year ARI maximum daily‐average onshore wind speed are not projected for the high‐emission future.

Annual recurrence of prokaryotic climax communities in shallow waters of the North Mediterranean.

In temperate coastal environments, wide fluctuations of biotic and abiotic factors drive microbiome dynamics. To link recurrent ecological patterns with planktonic microbial communities, we analysed a monthly-sampled 3-year time series of 16S rRNA amplicon sequencing data, alongside environmental variables, collected at two stations in the northern Adriatic Sea. Time series multivariate analyses allowed us to identify three stable, mature communities (climaxes), whose recurrence was mainly driven by changes in photoperiod and temperature. Mixotrophs (e.g., Ca. Nitrosopumilus, SUP05 clade, and Marine Group II) thrived under oligotrophic, low-light conditions, whereas copiotrophs (e.g., NS4 and NS5 clades) bloomed at higher temperatures and substrate availability. The early spring climax was characterised by a more diverse set of amplicon sequence variants, including copiotrophs associated with phytoplankton-derived organic matter degradation, and photo-auto/heterotrophic organisms (e.g., Synechococcus sp., Roseobacter clade), whose rhythmicity was linked to photoperiod lengthening. Through the identification of recurrent climax assemblages, we begin to delineate a typology of ecosystem based on microbiome composition and functionality, allowing for the intercomparison of microbial assemblages among different biomes, a still underachieved goal in the omics era.

Stable Carbon and Nitrogen Isotope Composition in Suspended Particulate Matter Reflects Seasonal Dynamics of Phytoplankton Assemblages in the Gulf of Riga, Baltic Sea

The ratio of stable carbon and nitrogen isotopes in the suspended particulate matter has been widely used to study processes occurring in the marine ecosystem. At the same time, the signals provided by isotope ratios in coastal ecosystems can be difficult to interpret, due to several, often contradictory processes taking place simultaneously. In this study, we hypothesized that the carbon and nitrogen isotopic variation is predominantly affected by seasonally occurring phytoplankton species succession in the Gulf of Riga, Baltic Sea. Cyclical seasonal patterns were observed for carbon and nitrogen isotopic compositions of both SPM and phytoplankton data. Enrichment of heavy isotopes in the Gulf of Riga took place during spring phytoplankton bloom (from on average between + 7.1 and + 8.8 ‰, and between − 23.7 and − 21.9 ‰ for δ15N and δ13C, respectively) and pooled at significantly lower values (from + 3.1 to + 5.1 ‰ and from − 28.7 to − 25.1 ‰ for δ15N and δ13C, respectively) for the rest of the year. At the same time, the spatial gradient of isotope ratios was sporadic and inconclusive. The results showed that terrestrial and anthropogenic input to particulate matter is negligible from spring to autumn. Multivariate analysis revealed that the observed seasonal variability was indeed driven by variation in phytoplankton species composition. The diatoms, dinoflagellates, and the ciliate Mesodinium rubrum facilitated enrichment of 15N and 13C in spring. In contrast, atmospheric nitrogen fixation by cyanobacteria and the assimilation of their released nutrients by other organisms resulted in lower δ15N values during summer. This variability requires careful considerations for conducting food web studies in temperate coastal and estuarine environments during high phytoplankton biomass periods.

The Role of Recovery Phases in Mitigating the Negative Impacts of Marine Heatwaves on the Sea Star Asterias rubens

During recent years, experimental ecology started to focus on regional to local environmental fluctuations in the context of global climate change. Among these, marine heatwaves can pose significant threats to marine organisms. Yet, experimental studies that include fluctuating thermal stress are rare, and if available often fail to base experimental treatments on available long-term environmental data. We evaluated 22-year high-resolution sea surface temperature data on the occurrence of heatwaves and cold-spells in a temperate coastal marine environment. The absence of a general warming trend in the data may in parts be responsible for a lack of changes in heatwave occurrences (frequency) and their traits (intensity, duration, and rate of change) over time. Yet, the retrieved traits for present-day heatwaves ensured most-natural treatment scenarios, enabling an experimental examination of the impacts of marine heatwaves and phases of recovery on an important temperate predator, the common sea star Asterias rubens. In a 68-days long experiment, we compared a 37- and a 28-days long heatwave with a treatment that consisted of three consecutive 12-days long heatwaves with 4 days of recovery in between. The heatwaves had an intensity of 4.6°C above climatological records, resulting in a maximum temperature of 23.25°C. We demonstrate that heatwaves decrease feeding and activity of A. rubens, with longer heatwaves having a more severe and lasting impact on overall feeding pressure (up to 99.7% decrease in feeding rate) and growth (up to 87% reduction in growth rate). Furthermore, heatwaves of similar overall mean temperature, but interrupted, had a minor impact compared to continuous heatwaves, and the impact diminished with repeated heatwave events. We experimentally demonstrated that mild heatwaves of today’s strength decrease the performance of A. rubens. However, this echinoderm may use naturally occurring short interruptions of thermal stress as recovery to persist in a changing and variable ocean. Thus, our results emphasize the significance of thermal fluctuations and especially, the succession and timing of heat-stress events.

Temporal escape-adaptation to eutrophication by Skeletonema marinoi.

Diatoms commonly set off the spring-bloom in temperate coastal environments. However, their temporal offset may change in regions subject to nutrient enrichment, and by peaking earlier, such populations can maintain their position in the vernal plankton succession. We tested whether the marine keystone diatom Skeletonema marinoi can accomplish this through thermal evolutionary adaptation. Eight geographically separated subpopulations, representing hydromorphologically and climatologically similar inlets displaying a range of trophic states, were compared in a common-garden experiment. At early-spring temperatures, both doubling times and variation coefficients thereof, correlated negatively with the trophic state of the environment of origin, indicating selection for fast growth due to eutrophication. At mid-spring temperatures, the relationships were reversed, indicating selection in the opposite direction. At late-spring temperatures, no significant relationships were detected, suggesting relaxed selection. Subsequent field observations reflected these findings, where blooming temperatures decreased with trophic state. Natural selection thus moves along with eutrophication towards colder temperatures earlier in the spring, favouring genotypes with the capacity to grow fast. The thermal niche shift demonstrated herein may be an evolutionary mechanism essentially leading to trophic changes in the local ecosystem.

Decadal patterns and trends in benthic-pelagic exchange processes

In marine environments, the exchange of particles and solutes between the seafloor and overlying water column, known as benthic-pelagic (B/P) coupling is an important component in many biological and biogeochemical cycles. Key processes and drivers involved in this exchange display strongly seasonal variability, especially in temperate coastal environments. The magnitude and timings of these seasonal patterns however are not identical year-on-year, and the influence of this inter-annual variability on the rate and direction of B/P exchange, as well as the influence of longer term, multi-year trends, are less well understood. In this current study, multi-year temporal patterns of benthic-pelagic solute and particle exchange were investigated on the examples of particulate organic carbon and dissolved inorganic nitrogen time series data, to assess connections between inter- and multi-annual processes and characterize their nature and what drives them. To this end, a decadal (2009–2018) time-series dataset that combines biological, physical, meteorological and chemical measurements from the Western Channel Observatory, Plymouth, UK was analysed in combination with supplementary data from several environmental monitoring agencies. Time-series decomposition using seasonal decomposition with locally estimated scatterplot smoothing revealed that the main causes of inter-annual variability were extreme outlier events, some of which were influential enough to cause multi-annual trends. Stochastic meteorological and biological extremes, such as exceptional storms and phytoplankton blooms explained a large proportion of outlier events in the time series. Global-scale climatic fluctuations, such as North Atlantic Oscillation (NAO) and Southern Oscillation Index were reflected in benthic-pelagic exchange trends when they co-occurred in an additive manner (e.g. positive NAO and El Niño). The importance of multi-parameter long-term observatories, such as the Western Channel Observatory, is highlighted, and the use of transdisciplinary time-series datasets to identify individual events which have large ecosystem-level impacts is demonstrated. In order to identify and monitor long-term effects, such as climate trends or decadal global ocean cycles, multi-decadal sustained observations are of vital importance.

Phylogenetic morphometrics, geometric morphometrics and the Mexican fossils to understand evolutionary trends of enchodontid fishes

Enchodontids were a diverse and abundant fish marine clade that during the Upper Cretaceous became common inhabitants of temperate coastal environments around the world. The recent studies on Mexican enchodontid species have contributed to better understand their evolutionary relationships; however, the phylogenetic significance of the morphological variability of some bones in these fishes is unclear. Here, we explore the morphological variation and the phylogenetic implications that the preopercle, and lower jaw have throughout the geological time; these bones were selected because usually are well-preserved in fossils belonging to the group. Our results indicate that temporally, the enchodontid species herein studied can be divided into two main groups, one present in the early-Upper Cretaceous group and the other in the late-Upper Cretaceous. Additionally, our results indicate that body size in Enchodontidae seems to adjust to the phyletic increase of size or Cope's rule. The shapes of the preopercle and lower jaw of enchodontids are highly variable that it is hard to use these as supra-specific distinctive features. Among these fishes, the most differentiated shapes correspond to those that developed an elongated and shallow lower jaw, and those with preopercles that bear a posteroventral well-developed spine, as in Eurypholinae and Unicachichthys. The phylogenetic relationships of enchodontid fishes defined by the configurations of these two skeletal structures provide a glimpse of the biogeographical relationships of the family; however, these patterns should be analyzed considering a most complete and inclusive phylogeny.

The role of kelp in the transport and fate of negatively buoyant marine plastic

We report observations of negatively buoyant plastics washed up on the shores of a beach in southwest England in association with deposits of kelp. Items retrieved included polyethylene terephthalate (PET) bottle fragments, polyvinyl chloride toys, electrical casings, construction plastics, polycarbonate goggles, carcass tags, pot rubber, fishing float fragments and PET textiles, with an upper estimate of 24 t of plastic deposited during a single kelp beaching event. It appears that after kelp becomes detached from the bed during strong winds or tides or through senescence, biological debris becomes associated with or acts to transport benthic plastic landwards through entrainment, entanglement and rafting and, sometimes, attachment to the holdfast. Observations provide evidence of significant local and regional ecological transportation of plastics in temperate coastal environments that is not driven directly or solely by buoyancy, and afford a convenient, non-invasive insight into the makeup of plastic that is encountered in the benthic environment.

Parasite-mediated increase in prey edibility in the predator-prey interaction of marine planktonic protists

In planktonic predator-prey interactions, predation pressure could be affected by several factors associated with prey, including cell size, shape, nutritional quality, presence of chemical deterrents, and movement behaviors. In addition, parasitism may also play an important role in predator-prey interaction by infecting one or both partners involved in the biological interaction. In this study, parasite mediation in predator-prey interactions of planktonic protists was addressed using model organisms commonly observed in temperate coastal environments, namely, a phototrophic dinoflagellate Akashiwo sanguinea as a potential host and prey, a heterotrophic dinoflagellate predator Luciella masanensis, and a dinoflagellates-infecting parasitoid Parvilucifera infectans. Parasite mediation permitted L. masanensis to exploit the prey A. sanguinea that the predator was otherwise unable to use or did not prefer. However, parasite-mediated exploitation seems to be dependent on the infection cycle of P. infectans. Although zoospores and mature sporangium produced from infected A. sanguinea were not ingested by the predator L. masanensis, both newly infected (i.e., cells that zoospores had just penetrated) and infected (those containing early to late trophocytes) A. sanguinea cells attracted numerous L. masanensis cells and were rapidly ingested by the predator, leading to the predator's positive growth. The results from mixed culture experiments of the three protists showed that the presence of P. infectans at low density led to co-occurrence of the three protists. Thus, the parasitoid seems to play the role of a mediator in either inedible prey- or predator-dominated environments, leading to co-occurrence of the three protists.

Intra-Annual Patterns in the Benthic-Pelagic Fluxes of Dissolved and Particulate Matter

In coastal temperate environments, many processes known to affect the exchange of particulate and dissolved matter between the seafloor and the water column follow cyclical patterns of intra-annual variation. This study assesses the extent to which these individual short term temporal variations affect specific direct drivers of seafloor-water exchanges, how they interact with one another throughout the year, and what the resulting seasonal variation in the direction and magnitude of benthic-pelagic exchange is. Existing data from a multidisciplinary long-term time-series from the Western Channel Observatory, United Kingdom, were combined with new experimental and in situ data collected throughout a full seasonal cycle. These data, in combination with and contextualized by time-series data, were used to define an average year, split into five ‘periods’ (winter, pre-bloom, bloom, post-bloom, and autumn) based around the known importance of pelagic primary production and hydrodynamically active phases of the year. Multivariate analyses were used to identify specific sub-sets of parameters that described the various direct drivers of seafloor-water exchanges. Both dissolved and particulate exchange showed three distinct periods of significant flux during the year, although the specific timings of these periods and the cause-effect relationships to the direct and indirect drivers differed between the two types of flux. Dissolved matter exchange was dominated by an upward flux in the pre-bloom period driven by diffusion, then a biologically induced upward flux during the bloom and an autumn downward flux. The latter was attributable to the interactions of hydrodynamic and biological activity on the seafloor. Particulate matter exchanges exhibited a strongly hydrologically influenced upward flux during the winter, followed by a biologically induced downward flux during the bloom and a second period of downward flux throughout post-bloom and autumn periods. This was driven primarily through interactions between biological activity, and physical and meteorological drivers. The integrated, holistic and quantitative data-based analysis of intra-annual variability in benthic/pelagic fluxes presented in this study in a representative temperate coastal environment, demonstrates not only the various process’ inter-connectivity, but also their relative importance to each other. Future investigations or modeling efforts of similar systems will benefit greatly from the relationships and baseline rules established in this study.

How zooplankton communities are shaped in a complex and dynamic coastal system with strong tidal influence

Temperate coastal marine environments are typified by strong seasonality and highly productive annual spring phytoplankton blooms. However, in areas of strong tidal activity, coastal waters may remain in a state of low productivity year-round due to light limitation induced by deep mixing. Such high-nutrient low-chlorophyll (HNLC) environments can be found in British Columbia, Alaska, Argentina, and the United Kingdom. This study aimed to examine how zooplankton communities are shaped by tidally mixed environments through direct comparison of adjacent stratified and mixed regions on the British Columbia coast. Stations located in five distinct regions of coastal BC were sampled during the most productive months (April to July) over two years. The most seasonally stratified station was characterized by a higher biomass of large zooplankton species, including calanoid copepods and euphausiids. In contrast, the mixed regions had a higher abundance of small (<2 mm) zooplankton species and a prevalence of meroplankton taxa. Zooplankton communities in tidally mixed regions had indicator species that reflected source waters in an adjacent stratified area. However, despite different source waters, tidally mixed regions showed a convergence of community structure pointing to a common community modification process. It may be the result of a combination of advective processes, zooplankton vertical migration behavior, enhanced predation due to close contact with bathymetry and daytime transport to the surface, and a large contribution of meroplankton. In areas with strong tidal exchange, zooplankton communities were more similar than expected based on the physical and chemical characteristics of the water column alone. The mosaic of primary productivity regimes on the BC coast therefore translates into similar spatial scale variation in zooplankton communities, resulting in a spatially heterogenous prey field for zooplankton consumers.

The Origin and Spread of Locally Adaptive Seasonal Camouflage in Snowshoe Hares.

AbstractAdaptation is central to population persistence in the face of environmental change, yet we seldom precisely understand the origin and spread of adaptive variation in natural populations. Snowshoe hares (Lepus americanus) along the Pacific Northwest coast have evolved brown winter camouflage through positive selection on recessive variation at the Agouti pigmentation gene introgressed from black-tailed jackrabbits (Lepus californicus). Here, we combine new and published whole-genome and exome sequences with targeted genotyping of Agouti to investigate the evolutionary history of local seasonal camouflage adaptation in the Pacific Northwest. We find evidence of significantly elevated inbreeding and mutational load in coastal winter-brown hares, consistent with a recent range expansion into temperate coastal environments that incurred indirect fitness costs. The genome-wide distribution of introgression tract lengths supports a pulse of hybridization near the end of the last glacial maximum, which may have facilitated range expansion via introgression of winter-brown camouflage variation. However, signatures of a selective sweep at Agouti indicate a much more recent spread of winter-brown camouflage. Through simulations, we show that the delay between the hybrid origin and subsequent selective sweep of the recessive winter-brown allele can be largely attributed to the limits of natural selection imposed by simple allelic dominance. We argue that while hybridization during periods of environmental change may provide a critical reservoir of adaptive variation at range edges, the probability and pace of local adaptation will strongly depend on population demography and the genetic architecture of introgressed variation.

The effect of temperature and meal size on the aerobic scope and specific dynamic action of two temperate New Zealand finfish Chrysophrys auratus and Aldrichetta forsteri.

Shallow coastal and estuarine habitats function as nurseries for many juvenile fish. In this comparative study, metabolic profiles of two New Zealand finfish, snapper (Chrysophrys auratus) and yellow-eyed mullet-YEM (Aldrichetta forsteri) that as juveniles share the same temperate coastal environments, were examined. Metabolic parameters (routine and maximum metabolic rates, and specific dynamic action-SDA) were investigated at a set of temperatures (13, 17, 21°C) within the range juveniles both species experience annually. SDA was also determined for a range of different feed rations to investigate the effects of meal size on postprandial metabolic response. Temperature was a strong modulator of snapper and YEM metabolic profile (routine and maximum metabolic rates, and absolute and factorial aerobic scope). Metabolic rates increased with temperature in both species as did absolute scope in YEM, though for snapper, it was only greater at the highest temperature. Factorial scope behaved in the same fashion for the two species, being greatest at 13°C. Both absolute and factorial scope were ~ twofold greater in YEM than in snapper across the entire temperature range. Temperature also affected SDA response in snapper, while in YEM, SDA parameters were largely unaffected when temperature increased from 17 to 21°C. Snapper were able to consume a large range of meal sizes (0.5-3.0% body mass-BM) with meal sizes > 1% BM having a pronounced effect on numerous SDA parameters, whereas mullet appeared to consume more limited ration sizes (≤ 1.0% BM). In both species, rations ≤ 1% BM produced similar changes in SDA parameters identifying comparable digestive bio-energetics. Overall, our metabolic characterisations demonstrate that both species can adjust to the variable temperate environmental temperatures and manage the energetic costs of digestion and feed assimilation. Yet, despite these general similarities, YEM's greater aerobic scope may point to better physiological adaptation to the highly variable temperate coastal environment than were observed in snapper.

Characterisation of shallow groundwater dissolved organic matter in aeolian, alluvial and fractured rock aquifers

Groundwater organic matter is processed within aquifers through transformations such as the adsorption of dissolved organic matter (DOM) to minerals and biodegradation. The molecular character of DOM varies according to its source and this can impact its bioavailability and reactivity. Whilst the character of DOM in riverine and oceanic environments is increasingly well understood, the sources, character and ultimately the fate of groundwater DOM remains unclear. Here we examine groundwater DOM from contrasting hydrogeological settings in New South Wales, Australia. For the first time, we identify the distinct molecular composition of three groundwater DOM end-members including a modern terrestrial input, an aged sedimentary peat source, and an aged stable by-product pool. We also identify and characterise the processing pathway of DOM in semi-arid, low sedimentary organic carbon (OC) environments. Based on size exclusion chromatography, ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), isotopic analyses (13C, 14C and 3H) and principle component analysis (PCA), we show that in higher rainfall temperate coastal peatland environments, large amounts of aged sedimentary organic carbon can leach into groundwater resulting in higher molecular weight (500 g mol−1 < molecular weight > 1000 g mol−1) and highly aromatic groundwater DOM with high O/C ratios and low H/C ratios. We show that in semi-arid environments with low rainfall rates and high groundwater residence times, groundwater dissolved organic carbon (DOC) is processed into increasingly low molecular weight (<350 g mol−1), low aromaticity DOM with low O/C ratios and high H/C ratios by subsurface processing mechanisms such as biodegradation and adsorption. We provide the first comprehensive study of groundwater DOM characterisation based on multiple analytical techniques, and highlight the impact of source inputs and processing on groundwater DOM composition at a molecular level.

Performance and reliability of active acoustic biotelemetry to best track marine pelagic species in temperate coastal waters

Acoustic tracking is a commonly used method to study the movement ecology of marine species. The characteristics of the data collected are not simply functions of the location of the tagged animal as they are also influenced by the method of data collection and its sampling frequency. In particular, since the data are acoustically driven, the significance of any result hinges not only on the accuracy of the equipment but also on the reliability of the information received. While passive acoustic telemetry requires an evaluation of the detection efficiency of receivers moored in different habitats (or sites) to obtain reliable data, active acoustic telemetry requires more field-related information on how to best track tagged animals without impacting on their natural behaviour. This study aimed to evaluate the reliability of active acoustic telemetry data in a temperate coastal environment. This was achieved by conducting a series of field experiments to assess (i) the use of signal strength-to-infer distance to the tracked animal under different tracking conditions, (ii) what signal strength threshold can be used to obtain reliable bio-telemetered data, (iii) whether the behaviour of a tracked animal would be a main concern in terms of data reliability, and (iv) the best filtering option to reduce the data to be analysed. The findings yielded a signal strength-to-distance relationship to improve the accuracy of the positional fixes of actively tracked animals, which can be used as a practical reference for future tracking studies on pelagic species in temperate coastal environments.

Elevated salinity blocks pathogen transmission and improves host survival from the global amphibian chytrid pandemic: Implications for translocations

Abstract Emerging infectious diseases are one of the greatest threats to global biodiversity. Chytridiomycosis in amphibians is perhaps the most extreme example of this phenomenon known to science. Translocations are increasingly used to fight disease‐induced extinctions. However, many programmes fail because disease is still present or subsequently establishes in the translocation environment. There is a need for studies in real‐world scenarios to test whether environmental manipulation could improve survival in populations by generating unfavourable environmental conditions for pathogens. Reintroductions of amphibians impacted by chytridiomycosis into environments where the disease persists provide a scenario where this paradigm can be tested. We tested the hypothesis that manipulating environmental salinity in outdoor mesocosms under near‐identical environmental conditions, present in a nearby translocation programme for an endangered amphibian, would improve survival and determine the mechanisms involved. One hundred and sixty infected and 288 uninfected, captive‐bred, juvenile frogs were released into 16 outdoor mesocosms in which salinity was controlled (high‐ or low‐salinity treatment). The experiment was run for 25 weeks from the mid‐austral winter to the mid‐austral summer of 2013 in a temperate coastal environment, Australia. Increasing salinity from c. 0.5 ppt to 3.5–4.5 ppt reduced pathogen transmission between infected and uninfected animals, resulting in significantly reduced mortality in elevated salt mesocosms (0.13, high‐salt vs. 0.23, low‐salt survival at 23 weeks). Increasing water temperature associated with season (from mean 13 to 25°C) eventually cleared all surviving animals of the pathogen. Synthesis and applications. We identified a mechanism by which environmental salinity can protect amphibian hosts from chytridomycosis by reducing disease transmission rates. We conclude that manipulating environmental salinity in landscapes where chytrid‐affected amphibians are currently translocated could improve the probability of population persistence for hundreds of species. More broadly, we provide support for the paradigm that environmental manipulation can be used to mitigate the impact of emerging infectious diseases.

Recurrent patterns of microdiversity in a temperate coastal marine environment

Temperate coastal marine environments are replete with complex biotic and abiotic interactions that are amplified during spring and summer phytoplankton blooms. During these events, heterotrophic bacterioplankton respond to successional releases of dissolved organic matter as algal cells are lysed. Annual seasonal shifts in the community composition of free-living bacterioplankton follow broadly predictable patterns, but whether similar communities respond each year to bloom disturbance events remains unknown owing to a lack of data sets, employing high-frequency sampling over multiple years. We capture the fine-scale microdiversity of these events with weekly sampling using a high-resolution method to discriminate 16S ribosomal RNA gene amplicons that are >99% identical. Furthermore, we used 2 complete years of data to facilitate identification of recurrent sub-networks of co-varying microbes. We demonstrate that despite inter-annual variation in phytoplankton blooms and despite the dynamism of a coastal–oceanic transition zone, patterns of microdiversity are recurrent during both bloom and non-bloom conditions. Sub-networks of co-occurring microbes identified reveal that correlation structures between community members appear quite stable in a seasonally driven response to oligotrophic and eutrophic conditions.

Large-Scale Differences in Community Structure and Ecosystem Services of Eelgrass (Zostera marina) Beds Across Three Regions in Eastern Canada

Eelgrass (Zostera marina) forms extensive beds in temperate coastal and estuarine environments worldwide and provides important ecosystem services, including habitat for a wide range of species as well as nutrient cycling and carbon storage. However, little is known about how eelgrass ecosystem structure and services differ naturally among regions. Using large-scale field surveys, we examined differences in eelgrass bed structure, carbon and nitrogen storage, community composition, and habitat services across three distinct regions in Eastern Canada. We focused on eelgrass beds with low anthropogenic impacts to compare natural differences. In addition, we analyzed the relationships of eelgrass bed structure with environmental conditions, and species composition with bed structure and environmental conditions, to elucidate potential drivers of observed differences. Our results indicate that regional differences in eelgrass bed structure were weakly correlated with water column properties, whereas differences in carbon and nitrogen storage were mainly driven by differences in eelgrass biomass. There were distinct regional differences in species composition and diversity, which were particularly linked to temperature, as well as eelgrass bed structure indicating differences in habitat provision. Our results highlight natural regional differences in ecosystem structure and services which could inform spatial management and conservation strategies for eelgrass beds.

Mortality on fruit in citrus orchards caused by naturally occurring enemies of red scale Aonidiella aurantii: relation to spatial distribution of patch density and season

AbstractThe efficacy of biological control agents depends on the amount of mortality they impose on pests in the field. Quantifying their impact on a pest is critical for guiding decision‐making in its management. Here, we quantify the relation of population levels of natural unmanipulated populations of a pest to mortality rates imposed by naturally occurring enemies. Mortality beyond first instar caused by natural enemies of Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) on fruit was studied in four unsprayed citrus orchards in a warm temperate coastal environment in New South Wales, Australia, over approximately three pest generations in the course of a year. The percentage of hosts on fruit suffering parasitism and predation was usually independent of host density. There was no consistent evidence that one parasitoid influenced another, nor that parasitism and predation rates were related. At the orchard scale, it was apparent that parasitism and predation over a time series were related to current or previous host numbers and could become high enough in relation to fecundity rates to cause pest numbers to decline. Temporal feedback to density could be causing the pest populations to fluctuate between limits at economically sustainable levels given additional mortality of the first instars due to expected rates of dispersal and subsequent pre‐ and post‐settlement failures.

Improved methodology for measuring pore patterns in the benthic foraminiferal genus Ammonia

Abstract Benthic foraminiferal pores are considered to play an important role in facilitating the gas exchange between the organism and the environment, with pore size and density supposed to be related to gas exchange intensity. Recent studies have therefore attempted to establish relationships between pore patterns and redox conditions, such as bottom water oxygen and nitrate concentrations. However, a prerequisite for such an attempt is the development of a practical and reliable methodology for measuring pore patterns. The aim of this study is to present a semi-automated pore measurement method for Ammonia , a dominant taxon of temperate coastal environments that are increasingly affected by seasonal hypoxia (bottom water oxygen concentration In order to demonstrate the efficiency of the method, we applied it in two case studies. Firstly, a study of living Ammonia in Lake Grevelingen (Netherlands) revealed a clear difference in pore patterns between three studied stations characterised by different seasonal bottom water oxygenation patterns. Secondly, a sediment core from the same site clearly showed the presence of two morphotypes of Ammonia ; one with numerous, small pores and the other with fewer but much larger pores, resulting in a higher porosity (larger part of the test covered by pores). Since the man-made closure of Lake Grevelingen in 1971, the latter morphotype has progressively replaced the former one. Finally, a summary of the measurements on 870 specimens with both pore patterns shows a strong relationship between pore density and pore surface area, suggesting a physical control of the interaction between these two parameters.