Temperate Northeast Research Articles

Nitrogen addition changed soil fungal community structure and increased the biomass of functional fungi in Korean pine plantations in temperate northeast China

Nitrogen (N) deposition is a global environmental issue that can have significant impacts on the community structure and function in ecosystems. Fungi play a key role in soil biogeochemical cycles and their community structures are tightly linked to the health and productivity of forest ecosystems. Based on high-throughput sequencing and ergosterol extraction, we examined the changes in community structure, composition, and biomass of soil ectomycorrhizal (ECM) and saprophytic (SAP) fungi in 0–10 cm soil layer after 8 years of continuous N addition and their driving factors in a temperate Korean pine plantation in northeast China. Our results showed that N addition increased fungal community richness, with the highest richness and Chao1 index under the low N treatment (LN: 20 kg N ha−1 yr−1). Based on the FUN Guild database, we found that the relative abundance of ECM and SAP fungi increased first and then decreased with increasing N deposition concentration. The molecular ecological network analysis showed that the interaction between ECM and SAP fungi was enhanced by N addition, and the interaction was mainly positive in the ECM fungal network. N addition increased fungal biomass, and the total fungal biomass (TFB) was the highest under the MN treatment (6.05 ± 0.3 mg g−1).Overall, we concluded that N addition changed soil biochemical parameters, increased fungal activity, and enhanced functional fungal interactions in the Korean pine plantation over an 8-year simulated N addition. We need to consider the effects of complex soil conditions on soil fungi and emphasize the importance of regulating soil fungal community structure and biomass for managing forest ecosystems. These findings could deepen our understanding of the effects of increased N deposition on soil fungi in temperate forests in northern China, which can provide the theoretical basis for reducing the effects of increased N deposition on forest soil.

Diversity patterns of echinoids (Echinodermata: Echinoidea) in shallow waters of the Mexican Pacific

The Mexican Pacific hosts a large diversity of echinoids occupying different habitats and ecological niches; nevertheless, the group remains scarcely studied in terms of their spatial patterns of biodiversity and variation in the region. This work evaluated the alpha, beta, and gamma diversity of echinoids living in the Mexican Pacific's shallow waters (0–200 m) at three spatial scales: Operational geographic units (OGUs), ecoregions, and provinces. Alpha diversity was evaluated through the standardized coverage values of 0D, 1D, and 2D, while the contribution of alpha and beta diversity components to gamma diversity was estimated with additive partitioning. Finally, we evaluated whether beta diversity resulted from overlap, species replacement, or richness differences. A total of 45 species and 2,232 incidences were registered in the 150 OGUs distributed throughout the Mexican Pacific. Cluster completeness in the ecoregions of the Warm Temperate Northeast Pacific (WTNP) province was higher (> 95 %) than in the ecoregions of the Eastern Tropical Pacific (TEaP) province. Standardized coverage values of the 0D, 1D, and 2D indices showed differences between the ecoregions Cortezian and Magdalena Transition in the WTNP province. At the ecoregion and province level, alpha diversity might be influenced by sampling techniques and habitat availability, which limits the distribution of regular and irregular echinoids. Gamma diversity is mainly determined by beta diversity at the ecoregion scale, where species overlap and richness differences were the major contributing components, probably resulting from substrate dependence, habitat availability, and mesoscale ocean circulation patterns.

Diversity, distribution and intrinsic extinction vulnerability of exploited marine bivalves

Marine bivalves are important components of ecosystems and exploited by humans for food across the world, but the intrinsic vulnerability of exploited bivalve species to global changes is poorly known. Here, we expand the list of shallow-marine bivalves known to be exploited worldwide, with 720 exploited bivalve species added beyond the 81 in the United Nations FAO Production Database, and investigate their diversity, distribution and extinction vulnerability using a metric based on ecological traits and evolutionary history. The added species shift the richness hotspot of exploited species from the northeast Atlantic to the west Pacific, with 55% of bivalve families being exploited, concentrated mostly in two major clades but all major body plans. We find that exploited species tend to be larger in size, occur in shallower waters, and have larger geographic and thermal ranges—the last two traits are known to confer extinction-resistance in marine bivalves. However, exploited bivalve species in certain regions such as the tropical east Atlantic and the temperate northeast and southeast Pacific, are among those with high intrinsic vulnerability and are a large fraction of regional faunal diversity. Our results pinpoint regional faunas and specific taxa of likely concern for management and conservation.

Did a small thermosensitive intron contribute to the temperate adaptation of Drosophila melanogaster?

Drosophila melanogaster was first used for research in the early 1900's by scientists located in the northeastern corridor of the United States, gaining prominence with the establishment of the famous "fly room" by Thomas Hunt Morgan at Columbia University circa1908. Several reasons for using D. melanogaster in research are well known; easy and inexpensive to breed, short lifespan, amongst others. But why was this insect species flourishing in a temperate northeast region of the New World during the late 1800's when they originated in the tropical forests of sub-Saharan Africa millions of years ago? The purpose of this review is to provide an overview of the experimental underpinnings for a temperature sensitive mechanism that likely contributed to the rather unique ability of Drosophila melanogaster to successfully colonize temperate regions on a global scale. It also furnishes an interesting historical insight into how ancestral genetics serendipitously held the keys to the journey of D. melanogaster becoming such a popular research organism. While numerous papers have been published detailing different aspects of the work, this is the first comprehensive review. Herein, I discuss the discovery of a small thermosensitive intron in D. melanogaster (termed dmpi8) that controls midday siesta levels. Like many day-active animals, Drosophila exhibits a robust genetically based midday siesta that is protective in warm climates. Yet long bouts of daytime inactivity might be counterproductive in temperate climates, especially since daylength in these regions is shorter during the cooler months. Evidence discussed in this review strongly indicates that targeting of dmpi8 splicing efficiency by natural selection enhanced the ability of D. melanogaster to scale daytime sleep levels commensurate with a wide range of local climates. Surprisingly, dmpi8 splicing regulates midday siesta levels in trans by controlling the expression of a nearby anti-siesta gene called daywake. The "fortuitous" genetic arrangement of a thermosensitive intron in proximity to an anti-siesta gene might have contributed to the cosmopolitan nature of D. melanogaster and its historical journey in becoming a popular research organism.

Preliminary Evidence about the Colonisation Process of Kyphosus Species (Perciformes: Kyphosidae) in the Subtropical–Temperate Northeast Atlantic Ocean and Mediterranean Sea

A review of the non-native Kyphosus species historically recorded in Galician waters (north-western Spain) based on morphological and molecular characteristics is carried out. The list is composed of 15 specimens recorded from 2002 to 2022, showing a clearly unbalanced ratio in favour of K. vaigiensis with respect to K. sectatrix (6.5:1). A similar analysis was performed by consulting ichthyological literature on the Kyphosus species reported in the subtropical–temperate Northeast Atlantic Ocean and Mediterranean Sea. The results seem to reflect a more recent and conspicuous appearance of K. vaigiensis in the Northeast Atlantic–Mediterranean area, suggesting a higher invasive capacity than that of its congener K. sectatrix, perhaps related to its greater mobility. DNA barcoding supports the morphological identification of K. vaigiensis from Galicia and confirms the Atlantic–Mediterranean and Indo–Pacific distribution of the species. In addition, the main distinctive morphological characters found in the ichthyological literature have been revised and the taxonomic status of one published record has been changed. The results indicate the need to monitor non-indigenous marine species in the current global warming scenario of the Anthropocene era.

Spotlight on coarse sediments: Comparative characterization of a poorly investigated seafloor biotope in the German Bight (SE North Sea)

Extensive marine benthos surveys have resulted in a solid understanding of the broad distribution pattern of seafloor biotopes in the southeastern North Sea (temperate northeast Atlantic region). However, due to the low spatial resolution of large-scale surveys, specific smaller-scale biotopes with scattered distribution have been insufficiently captured. Consequently, knowledge regarding the environmental characteristics and species inventories of some specific biotopes is still limited. We investigated the habitat characteristics and the macro-infauna (i.e., organisms in samples collected by a sediment grab and retained in a sieve with a mesh size of 1000 μm) of a spatially restricted, patchy coarse sediment (i.e., grain size fraction >500 μm accounting for ≥60% of the total sample mass) biotope in the German Bight over three consecutive years. Habitat and faunal characteristics were contrasted with four other benthic biotopes sampled at the same time to allow for a comparative evaluation. Our study revealed considerable fluctuations in grain size distribution among samples of the coarse sediment, potentially resulting from a frequent redistribution of sediments. A total number of 243 infauna taxa were identified at the 66 stations sampled over three consecutive years (16–33 stations per year) with a considerable proportion of endangered and rare species. The results highlight that previous studies have underestimated the species richness of the biotope. The focus on this previously poorly studied biotope type allowed us to detect species in the study region that were formerly unreported. The macro-infauna in the coarse sediments was characterized by comparatively high abundance and biomass, which may provide a rich food resource for organisms from higher trophic levels. Therefore, coarse sediments likely are an ecologically valuable seafloor biotope despite its limited coverage.

Phenology of Codium cylindricum (Ulvophyceae, Bryopsidales) on the central Pacific coast of Japan

Abstract Codium cylindricum is a large green alga distributed along the temperate Northeast Pacific coasts. Although the species is edible and contains pharmaceutical substances, little is known about its ecology. In this study, we characterized the phenology of C. cylindricum by monthly observations in Tateyama on the central Pacific coast of Japan from March 2018 to February 2019. The average length of attached thalli in three quadrats (2 × 2 m) was 5 cm from April to July. After disappearing in August, recruits appeared in November and the maximum density (1.08 ± 3.5 inds·m−2) was reached in February. On the sea bottom, detached thalli were present from April to October; the biomass monitored in a single quadrat (2 × 20 m) was high from June to August. Based on monthly observations of 50–100 utricles in each of 18–25 thalli, gametangium formation started in June and reached a peak (i.e., gametangia detected in 75% of thalli and 63.4% of utricles) in September, before the disappearance of the detached thalli. These results strongly suggest that C. cylindricum is annual and reproduces mainly while they are drifting. Therefore, growth during detached stage is critically important to increase biomass and dispersal.

Marine Debris Floating in Arctic and Temperate Northeast Atlantic Waters

Floating marine debris is ubiquitous in marine environments but knowledge about quantities in remote regions is still limited. Here, we present the results of an extensive survey of floating marine debris by experts, trained scientists from fields other than pollution or non-professional citizen scientists. A total of 276 visual ship-based surveys were conducted between 2015 and 2020 in the Northeast (NE) Atlantic from waters off the Iberian Peninsula to the Central Arctic, however, with a focus on Arctic waters. Spatiotemporal variations among regional seas (Central Arctic, Barents Sea, Greenland Sea, Norwegian Sea, North Sea) and oceanic regions (Arctic waters and the temperate NE Atlantic) were explored. The overall median debris concentration was 11 items km-2, with considerable variability. The median concentration was highest in the North Sea with 19 items km-2. The Nordic seas, except the Central Arctic showed median concentrations ranging from 9 to 13 items km-2. Plastic accounted for 91% of all floating items. Miscellaneous fragments, films, ropes and nets, packaging materials, expanded polystyrene and straps were the most frequently observed plastic types. Although the median debris concentration in the Central Arctic was zero, this region was not entirely free of floating debris. The variations between regional seas and oceanic regions were statistically not significant indicating a continuous supply by a northward transportation of floating debris. The data show a slight annual decrease and clear seasonal differences in debris concentrations with higher levels observed during summer. A correlation between debris concentrations and environmental and spatial variables was found, explaining partly the variability in the observations. Pollution levels were 500 times lower than those recorded on the seafloor indicating the seafloor as a sink for marine debris. The Arctic was characterised by similar pollution levels as regions in temperate latitudes highlighting that Arctic ecosystems face threats from plastic pollution, which add to the effects of rapid climate change.

Climate-driven shifts in kelp forest composition reduce carbon sequestration potential.

The potential contribution of kelp forests to blue carbon sinks is currently of great interest but interspecific variance has received no attention. In the temperate Northeast Atlantic, kelp forest composition is changing due to climate‐driven poleward range shifts of cold temperate Laminaria digitata and Laminaria hyperborea and warm temperate Laminaria ochroleuca. To understand how this might affect the carbon sequestration potential (CSP) of this ecosystem, we quantified interspecific differences in carbon export and decomposition alongside changes in detrital photosynthesis and biochemistry. We found that while warm temperate kelp exports up to 71% more carbon per plant, it decomposes up to 155% faster than its boreal congeners. Elemental stoichiometry and polyphenolic content cannot fully explain faster carbon turnover, which may be attributable to contrasting tissue toughness or unknown biochemical and structural defenses. Faster decomposition causes the detrital photosynthetic apparatus of L. ochroleuca to be overwhelmed 20 days after export and lose integrity after 36 days, while detritus of cold temperate species maintains carbon assimilation. Depending on the photoenvironment, detrital photosynthesis could further exacerbate interspecific differences in decomposition via a potential positive feedback loop. Through compositional change such as the predicted prevalence of L. ochroleuca, ocean warming may therefore reduce the CSP of such temperate marine forests.

Differentiation patterns of emperor moths (Lepidoptera: Saturniidae: Saturniinae) of a continental island: divergent evolutionary history driven by Pleistocene glaciations.

BackgroundOn the basis of molecular dating, Pleistocene glaciations have been proposed as the major driving force of biota speciation in the Palearctic and the pre-Quaternary origin of Amazonian taxa. However, the major driving factors in East Asia remain unclear. All 16 saturniine species inhabiting Taiwan with congeners of populations, subspecies, or species in East Asia constitute research objects for addressing the mode of speciation because of the repeated formation and disappearance of a landbridge from the Asian mainland to Taiwan during glacial cycles.MethodsThe genetic divergences of mitochondrial cytochrome c oxidase subunit I (COI) and 16S rDNA and the nuclear 28S rDNA of the saturniine species from Taiwan and the Asian mainland were assessed to determine the monophyly of each genus and species of Saturniinae. Moreover, 519 saturniine COI sequences of 114 taxa from adjacent East and Southeast Asian populations and closely related species were retrieved from GenBank and analyzed. The differentiation timing and possible origination of the insular saturniines were elucidated based on phylogenetic relationships, haplotype networks, and lineage calibrations.ResultsApproximately 90% of intraspecific COI divergence was <2%; all divergences exceeding 2% originated from comparisons between allopatric populations or subspecies. Relationship analyses revealed that multiple introductions likely occurred in insular saturniines and that some East Asian saturniines were paraphyletic as deduced by analyzing endemic insular species. Calibration dating revealed that Taiwanese endemic saturniines split from sibling Asian species 0.2–2.7 million years ago (Mya), whereas subspecific-level and population-level splitting events occurred 0.1–1.7 Mya and 0.2–1.2 Mya, respectively. Moreover, phylogenetic patterns combined with geographical distributions revealed that hill-distributed Taiwanese saturniines are closely related to those from southern China and Southeast Asia, whereas saturniines inhabiting altitudes higher than 1,500 m in Taiwan have siblings distributed in temperate Northeast Asia.DiscussionThe Global DNA Barcoding Initiative was successfully applied to study the population genetic structure in species. Most Formosan saturniines are distinct and monophyletic, reflecting the vicariant barrier of the Taiwan Strait; Pleistocene glacial cycles provided opportunities for insular saturniines to experience repeated isolation from and secondary contact with the continental mainland. Each insular saturniine may have evolved with a unique differentiation timing pattern that possibly emerged in the Early, Middle, or Late Pleistocene with these patterns differing from the consistent pattern that occurred in the temperate Palearctic and tropical Amazonian regions. Moreover, multiple migrations or artificial genetic admixtures may have also occurred, as suggested by the coexistence of two divergent lineages in a few Taiwanese saturniines.

East Asian monsoon modulated Holocene spatial and temporal migration of forest-grassland ecotone in Northeast China

Robust forecasts of ecological transformations resulting from ongoing and future climate change are urgently needed. Paleoecological records of vegetation dynamics, combined with records of past climate, can contribute to these forecasts, but the relationship between vegetation and climate is often poorly understood. We synthesized a phytolith dataset using >500 topsoil samples and 6 sedimentary profiles from temperate Northeast China. The modern topsoil dataset was calibrated to quantitatively estimate tree cover and grass cover. Based on the threshold of tree cover, we explored the spatial and temporal variations of the forest-grassland ecotone in NE China as well as possible driving mechanisms. Phytoliths provided reliable quantitative estimates of tree/grass cover, accurately distinguishing sites that are currently forest from grassland in this temperate region. The forest-grassland ecotone expanded westward from 7 to 5 ka, retreated eastward from 4 to 2 ka, and then expanded westward again, migrating <100 km throughout this period. The interval of maximum tree cover varied spatiotemporally from east to west during the Holocene. Precipitation from the East Asian summer monsoon was likely the dominant driver of spatial and temporal variations in the forest-grassland ecotone in NE China, with lesser contributions from the Westerly Jet.

Characterizing energy flow in kelp forest food webs: a geochemical review and call for additional research

Kelp forests are highly productive coastal habitats that serve as biodiversity hotspots and provide valuable ecosystem services. Despite being one the largest marine biomes, kelp forests have been drastically understudied relative to other marine systems. Notably, while the role of kelp as habitat‐forming, or ‘foundation species', is well‐documented, a comprehensive understanding of kelp forest food web structure is lacking, particularly regarding the importance of kelp‐derived energy/nutrients to consumers. Here, we provide a biogeographic perspective on the energetic underpinning of kelp forests based on published literature. We targeted studies which used geochemical proxies – stable isotope analysis – to examine the transfer of carbon from kelp to local consumers. These studies (n = 94) were geographically skewed, with &gt; 40% from Northern European Seas and Temperate Northeast Pacific. Quantitative estimates for the percentage of kelp energy (or kelp + macroalgae if sources were pooled) incorporated by local consumers came from 43 publications, which studied 141 species and 35 broader taxonomic groups. We examined these data for trends among functional groups and across upwelling regimes. No patterns are evident at present, perhaps due to the paucity or variability of available data. However, energetic subsides from kelps clearly support a wide range of diverse taxa around the globe. We also characterized biogeographic patterns in δ13C values of kelps and particulate organic matter (POM, a phytoplankton proxy), to evaluate potential limitations of stable isotope analysis in disentangling the relative contributions of pelagic versus benthic resources to coastal food webs. Globally, kelps and POM differed by &gt; 4.5‰, but there was substantial variation among regions and kelp species. Accordingly, we discuss advances in stable isotope techniques which are facilitating more precise analysis of these complex energetic pathways. We end by proposing four main avenues of critical future research that will shed light on the resilience of these communities to global change.

Tree canopy accession strategy changes along the latitudinal gradient of temperate Northeast Asia

AbstractAimUnderstanding how natural forest disturbances control tree regeneration is key to predicting the consequences of globally accelerating forest diebacks on carbon stocks and forest biodiversity. Tropical cyclones (TCs) are important drivers of forest dynamics in Eastern Asia, and it is predicted that their importance will increase. However, little is known about the impact of TCs on forest regeneration.LocationLatitudinal gradient from south Korea (33° N) to the Russian Far East (45° N).Time periodLast 300 years.Major taxa studiedQuercus mongolica, Abies nephrolepis and Pinus koraiensis.MethodsWe explored the effects of TC activity on canopy accession strategies derived from long‐term tree radial growth patterns along a 1,500‐km latitudinal gradient of decreasing TC activity. We analysed canopy accession strategies for &gt; 800 trees of three widely distributed tree species by dividing them into gap trees (GTs), which established immediately after gap formation, and released trees (RTs), which accessed the upper canopy after a period of competitive suppression.ResultsWe found a substantial decrease in GTs and increase in RTs proportionally along the gradient of decreasing TC activity. Pinus koraiensis and A. nephrolepis exhibited high variability in the proportions of the individual canopy accession strategies along the latitudinal gradient, whereas it was more stable for Q. mongolica. We identified the gradient of TC activity as the main driver influencing canopy dynamics and thus changes in life‐history traits for P. koraiensis and Q. mongolica, whereas maximal growth rate was the main driver for A. nephrolepis.Main conclusionsFlexibility in growth strategies enabled the studied species to cover extensive areas and indicates that they will be able to cope with shifts in disturbance regimes induced by the poleward migration of TCs and increasing TC intensity. Our results highlight the canopy accession strategy as an ecological indicator of past disturbance activity.

Plant diversity and community composition in temperate northeast Atlantic salt marshes are linked to nutrient concentrations

AbstractQuestionStudies in the northwest Atlantic have shown that nutrient enrichment can severely impact salt marshes, undermining their broad range of high‐value ecosystem services. However, biogeographical differences in plant communities may preclude extrapolation of these findings to other regions. The few investigations of such impacts elsewhere, including in Europe, have been strongly localised, restricting generalisations, and have not addressed community‐level properties.LocationSouth and east coasts of Ireland (northeast Atlantic).MethodsWe conducted a field survey of vascular plants and soil properties in fifteen salt marshes representing broad environmental gradients but comparable biogeographical settings, to test if salt marsh plant (a) diversity and (b) community composition are related to soil nutrients.ResultsSpecies richness and Shannon diversity were both negatively related to soil NOx−, and Shannon diversity had a hump‐shaped relationship to labile P. Multivariate community composition was highly significantly related to NOx−, to a lesser degree to P, and marginally significantly to NH4+. This was most clearly evident in the positive association of the ground cover of an evergreen dwarf shrub, Atriplex portulacoides, and a weaker negative association of a forb, Plantago maritima, with NOx−, indicating competition between these key and functionally contrasting mid‐salt‐marsh species. The relationship between community composition and P was most evident through the positive association of P with the invasive cordgrass, Spartina anglica.ConclusionsPhysiognomic and functional differences between the herb‐rich Pl. maritima community and monospecific A. portulacoides stands likely have implications for ecosystem services, as would a continued expansion of S. anglica. Further studies to ascertain causality could determine whether such transitions can be driven by nutrient enrichment.

Above- to Belowground Vegetation Biomass Ratio in Temperate North-East Atlantic Saltmarshes Increases Strongly with Soil Nitrogen Gradient

Saltmarshes provide a broad range of ecosystem services, but have been degraded globally and are further threatened by sea-level rise. Changes in biomass partitioning between above- and belowground components of plant community biomass as a consequence of nutrient enrichment can impact those services profoundly. However, the evidence for such impacts is largely confined to North America, leaving a gap in global understanding of coastal ecosystem resilience. Using field surveys across 15 saltmarshes along the south and east coasts of Ireland, we tested whether aboveground (AG) and belowground (BG) plant biomass allocation across all plant assemblages combined and within individual plant assemblages is related to soil nutrients. AG biomass and AG/BG biomass ratio were positively related, and BG biomass was negatively related to NOx−, both across all assemblages combined and within individual assemblages. AG biomass and AG/BG ratio were also positively related to NH4+ within individual assemblages, but not across all of them combined. The relationships between biomass and labile P were weaker, and their direction varied across the whole P gradient and among individual assemblages. These findings demonstrate broad, community-wide links between biomass allocation and soil nutrients in saltmarshes. The up to 6.6-fold increase in AG/BG biomass ratio along the N gradient, coupled with differential responses among functionally contrasting plants, could have significant implications for multiple saltmarsh functions such as energy fixation for consumers, wave attenuation, sediment binding and carbon storage. Improved understanding of the underlying causalities would help promoting saltmarsh resilience.

Periodic ultraviolet-C illumination for marine sensor antifouling

Ultraviolet light has intriguing potential as a marine antifoulant, targeting almost any species and applicable to almost any surface, while not accumulating in the environment. This study field-tested the effects of periodic ultraviolet-C illumination on marine macrofouling. Across four experiments, several UV illumination duty cycles were tested against controls with no illumination. Duty cycles between 1:2 (time with UV:total time per cycle) and 1:20 were all similarly effective, inhibiting almost all macrofouling at three different temperate Northeast Pacific and Northwest Atlantic sites. Susceptible taxa included barnacles, bryozoans, tunicates (colonial and solitary), and, to a slightly lesser extent, mussels. Duty cycles of 1:30 and 1:60 reduced but did not eliminate biofouling. Measurements of ultraviolet illumination on oceanographic sensors showed similar results. The results suggest further investigation of ultraviolet light as an antifoulant for marine sensors, including susceptibility of other taxa, optimizing illumination patterns, and exploring the potential for evolved resistance.

Gamma-diversity partitioning of gobiid fishes (Teleostei: Gobiidae) ensemble along of Eastern Tropical Pacific: Biological inventory, latitudinal variation and species turnover

Gobies are the most diverse marine fish family. Here, we analysed the gamma-diversity (γ-diversity) partitioning of gobiid fishes to evaluate the additive and multiplicative components of α and β-diversity, species replacement and species loss and gain, at four spatial scales: sample units, ecoregions, provinces and realms. The richness of gobies from the realm Eastern Tropical Pacific (ETP) is represented by 87 species. Along latitudinal and longitudinal gradients, we found that the γ-diversity is explained by the β-diversity at both spatial scales, ecoregions and provinces. At the ecoregion scale, species are diverse in the north (Cortezian ecoregion) and south (Panama Bight ecoregion) and between insular and coastal ecoregions. At the province scale, we found that the species turnover between the warm temperate Northeast Pacific (WTNP), Tropical East Pacific (TEaP) and the Galapagos Islands (Gala) was high, and the species nestedness was low. At the ecoregion scale, historical factors, and phylogenetic factors have influenced the hotspots of gobiid fish biodiversity, particularly in the Cortezian, Panama Bight and Cocos Island ecoregions, where species turnover is high across both latitudinal and longitudinal gradients. At the provincial level, we found that the contributions of the β-diversity from north to south, in the WTNP, TEaP and Gala were high, as result of the high number of unique species. Species turnover was also high at this scale, with a low contribution from species nestedness that was probably due to the low species/gene flow within the provinces. These results highlight the importance and successful inclusion of a cryptobenthic fish component in ecological and biogeographical studies.

Environmental and nutrient controls of marine nitrogen fixation

Biological dinitrogen (N2) fixation by diazotrophic cyanobacteria has great biogeochemical implications in nitrogen (N) cycling in the ocean as this process represents the major source of new N input to the oceans, thereby controlling the marine primary productivity. Numerous factors can affect the extent of N2 fixation. A better understanding of the major environmental and nutrient factors governing this process is highly required. Iron (Fe) and/or phosphorus (P) are thought to be limiting factors in most oceanic regions. Special attention has been given in the present study to evaluate the effects of mineral dust deposition which is believed to stimulate N2 fixation as it increases the availability of both Fe and P. Through three laboratory bioassays (+Fe, +P, +Dust) via incubation experiments performed on Trichodesmium IMS101, we found that each addition of Fe, P or desert dust could stimulate the growth and N2 fixation of Trichodesmium IMS101. Several adaptive nutrient utilization strategies were observed, such as a Fe luxury uptake mechanism, a P-sparing effect and colony formation. In addition, during a field study using natural phytoplankton assemblages from the temperate Northeast Atlantic Ocean the critical role of dissolved Fe (DFe) was again highlighted by the remarkably enhanced N2 fixation rate observed after the addition of DFe under low temperature and P-depleted conditions. At the time of our study no Trichodesmium filaments were found in the studied region, the diazotrophic community was dominated by unicellular cyanobacteria symbiont (prymnesiophyte-UCYN-A1) and heterotrophic diazotrophs, therefore demonstrating that DFe could as well be the ultimate factor limiting N2 fixation of these smaller diazotrophs. Recently, the effects of ongoing climate change (ocean warming and acidification) on N2 fixation drew much attention, but various studies led to controversial conclusions. Semi-continuous dilution growth experiments were conducted on Trichodesmium IMS101 under present-day and future high pCO2 (400 and 800 µatm, respectively) and warming seawater (24 and 28 °C) conditions. The results indicate that higher pCO2 and therefore ocean acidification may be beneficial for Trichodesmium growth and N2 fixation. However, our observations suggest that Fe or P limitation in oligotrophic seawaters may offset the stimulation induced on Trichodesmium IMS101 resulting from ocean acidification. In contrast, ocean warming may not play an important role in Trichodesmium growth and N2 fixation with a 4 °C increase from 24 °C to 28 °C. Nevertheless, ocean warming is predicted to cause a shift in the geographical distribution of Trichodesmium species toward higher latitudes, extending its niche to subtropical ocean regions and potentially reducing its coverage in tropical ocean basins.

1000-Year Quasi-Periodicity of Weak Monsoon Events in Temperate Northeast Asia since the Mid-Holocene

The Holocene variability in the East Asian summer monsoon (EASM) based on speleothem δ18O records has inconsistencies in timing, duration, and expression of millennial-scale events among nearby regions, and even within the same cave. Here, we present another stalagmite δ18O record with multi-decadal time resolution from the temperate Korean Peninsula (KP) for the last 5500 years in order to compare with Holocene millennial-scale EASM events from Southeast Asia. Based on our new stalagmite δ18O record, millennial-scale events since the mid-Holocene were successfully identified in the KP, representing a noticeable cyclic pattern with a periodicity of around 1000 years. We propose that the Holocene millennial-scale events are common hydroclimatic phenomena at least in the East Asian monsoon system. Meanwhile, the shorter periodicity of millennial-scale events than that of the North Atlantic region is likely to decouple the EASM system from the North Atlantic climate system. This observation suggests that weak EASM and North Atlantic Bond events may have been induced independently by direct solar activity (and then possible feedback) and ocean–ice sheet dynamics, respectively, rather than simple propagation from the North Atlantic to the EASM regions.

Assessing the performance of a cost-effective video lander for estimating relative abundance and diversity of nearshore fish assemblages

Rocky reefs in the temperate Northeast Pacific constitute a small portion of the nearshore seabed, yet are highly valued as productive habitat for local fisheries. Surveying these structurally complex, untrawlable habitats requires robust gear that can be deployed in rough sea states. Here, a cost-effective, compact video lander was evaluated for its ability to survey the diversity and abundance of nearshore (<40m), rocky-reef-associated fish populations (e.g. Sebastes, Cottidae, Hexagrammidae). To determine the application and limitations of surveying complex rocky reefs with this new tool, this study sought to (1) determine the frequency of observation of known nearshore fish species, (2) evaluate the influence of baiting the lander on the observed fish assemblage, (3) identify the optimal deployment time to maximize observed species richness and abundance, and (4) evaluate species-specific behavioral responses to the lander characterized a priori as attractive, avoidance, or neutral. Seventy percent of lander deployments met established requirements of visibility, view, and habitat. Seventy-seven percent of observed fishes were identifiable to species. The method observed 15 species belonging to 5 families; 5 species were classified as common (observed in >20% of deployments), the remaining rare. Contrary to lander studies in other regions, bait was not found to improve species-specific identification, increase observed species richness or abundance (at the species or feeding guild level), or shorten deployment duration. A deployment time of 8min on the benthos was determined as optimal for observing maximum species richness and abundance in the nearshore, doubling the previously described lander drop durations evaluated in deeper Oregon, U.S.A., waters. Species-specific behavioral responses to this compact lander were evaluated by viewing trends in species abundance (assessed within 30s bins) over the deployment duration; no attractive or avoidance behaviors were observed. Results confirm that this simple, cost-effective video lander configuration is suitable for sampling the suite of fish species found in the nearshore, including rockfish species federally designated as “overfished” (Sebastes pinniger and Sebastes ruberrimus). Furthermore, this study illustrates the importance of evaluating the performance of survey tools in the specific environment in which the tool will be used to determine best-practices from long-term monitoring.