Biomass Size Spectra Research Articles

Direct effect of artificial warming on communities is stronger than its indirect effect through body mass reduction

Theory predicts that morphological and bioenergetic constraints due to temperature‐induced body size reduction can modulate the direct effects of warming on biotic interactions, with consequent effects on trophic cascades and biomass distribution. However, these theoretical predictions have rarely been tested empirically. Our aim was to distinguish the indirect effects of warming‐induced body size reductions from the direct effects of warming on community structure. We conducted a mesocosm experiment manipulating factorially 1) body size reduction in the medaka fish Oryzias latipes using two populations raised for several generations under contrasted climate conditions and 2) warming (+4°C), to test their independent and interactive effects on the structure of prey and primary resource communities, the predator–prey biomass ratio and the biomass size spectra. We further dissected the effects of seasonal temperature variation from the effects of constant artificial warming. We found that the indirect effects of warming (i.e. fish body size reduction) on composition and structure of communities as well as their biomass size spectra were of marginal amplitude compared to the direct effects of seasonal temperature variation and constant warming. There were no changes in community composition in response to fish body size reduction or constant warming. However, the density of macroinvertebrates and zooplankton were maximal at intermediate seasonal water temperatures and lower in constantly‐heated mesocosms. Contrastingly, phytoplankton was not strongly affected by seasonal temperature or warming, but rather responded to grazing effects of zooplankton. Finally, we found a reduction in predator–prey biomass ratio under warming and at the warmest seasonal temperature, inducing a steeper slope of the biomass size spectra under increasing seasonal (but not constant) temperature. We conclude that the direct effects of climate change on freshwater communities are stronger than its indirect effects mediated by body mass reduction.

Relationships Between Plankton Size Spectra, Net Primary Production, and the Biological Carbon Pump

AbstractPhotosynthesis in the surface ocean and subsequent export of a fraction of this fixed carbon leads to carbon dioxide sequestration in the deep ocean. Ecological relationships among plankton functional groups and theoretical relationships between particle size and sinking rate suggest that carbon export from the euphotic zone is more efficient when communities are dominated by large organisms. However, this hypothesis has never been tested against measured size spectra spanning the >5 orders of magnitude found in plankton communities. Using data from five ocean regions (California Current Ecosystem, North Pacific subtropical gyre, Costa Rica Dome, Gulf of Mexico, and Southern Ocean subtropical front), we quantified carbon‐based plankton size spectra from heterotrophic bacteria to metazoan zooplankton (size class cutoffs varied slightly between regions) and their relationship to net primary production and sinking particle flux. Slopes of the normalized biomass size spectra (NBSS) varied from −1.6 to −1.2 (median slope of −1.4 equates to large 1–10 mm organisms having a biomass equal to only 7.6% of the biomass in small 1–10 μm organisms). Net primary production was positively correlated with the NBSS slope, with a particularly strong relationship in the microbial portion of the size spectra. While organic carbon export co‐varied with NBSS slope, we found only weak evidence that export efficiency is related to plankton community size spectra. Multi‐variate statistical analysis suggested that properties of the NBSS added no explanatory power over chlorophyll, primary production, and temperature. Rather, the results suggest that both plankton size spectra and carbon export increase with increasing system productivity.

Long-term oscillations in the normalized biomass-size spectrum reveal the impact of oligotrophication on zooplankton trophic structure in the North Atlantic Subtropical Gyre

Ocean warming of the North Atlantic Subtropical Gyre (NASG) induced oligotrophication and a decrease in integrated net primary production during the 2010s, potentially affecting higher trophic levels. We analyzed long-term records (1994–2019) of daytime and nighttime zooplankton biomass in five size classes from the NASG. Daytime biomass decreased in the three largest size classes during the 2010s, while decrease in nighttime biomass was less evident due to the relative stability in diel vertical migrator biomass. We used the normalized biomass size spectrum (NBSS) to estimate the relative transfer efficiency between trophic levels. The steepness of the NBSS slope at the end of the time series increased by 14% (daytime) and 24% (nighttime) from the maximum observed annual average values (2011 and 2009, respectively). This suggests oligotrophication during the 2010s led to a significant reduction in the transfer of biomass across trophic levels, with negative impacts on the NASG planktonic food web.

Vertical changes in zooplankton abundance, biomass, and community structure at seven stations down to 3000 m in neighboring waters of Japan during the summer: Insights from ZooScan imaging analysis

The imaging device ZooScan is used to examine net-collected zooplankton samples. ZooScan has been applied to regional and seasonal changes in the zooplankton community, but it has rarely been used to characterize vertical changes, especially down to the deep sea. In this study, we report a ZooScan analysis of vertically stratified zooplankton samples collected by collected by Vertical Multiple Plankton Sampler down to 3000 m at seven stations near Japan in the Okhotsk Sea, Japan Sea, East China Sea, and subarctic, transitional, and subtropical North Pacific. Throughout the region, both abundance and biomass, as indicated by aggregate zooplankton volume decreased with increasing depths. ANCOVA analysis revealed that factors linked to vertical changes varied with location. Depth and region were the primary determinants of abundance and biomass, respectively. Cluster analysis based on abundance delineated 8 distinct zooplankton community groups. The occurrence of each group varied regionally and 3–5 groups were vertically stratified at each station. Across all stations, Normalized Biomass Size Spectra (NBSS) and size diversity showed pronounced change around 150–500 m depths. At shallower depths, the NBSS slope was steep, the intercept was high, and size diversity was low while, at deeper depths the opposite was true for each of those parameters. Generalized additive models showed that depth, temperature, and salinity had a significant effect on NBSS and size diversity. This study indicates that the ZooScan imaging approach may be useful in the analysis of deep-sea zooplankton communities.

Zooplankton size-structure dynamics of a lowland tropical floodplain lake

Floodplains are highly complex ecosystems representing high biodiversity and conservation values, but they are also one of the world’s most threatened ecosystems due to extensive development and anthropogenic activities. Lake Tempe is a lowland riverine floodplain lake in Sulawesi Island, Indonesia, that is subject to multiple stressors such as flow alteration, eutrophication and invasive species. In this study, the dynamics of the zooplankton community size structure was investigated in Lake Tempe. Five size-based metrics, including zooplankton mean body size, total abundance, total, biomass, and normalised biomass size spectra (NBSS) slope and intercept were assessed from net-sampled zooplankton collected monthly from March to December 2016, and the role of environmental variables in shaping these size-based metrics were also examined. Zooplankton community size structure is a useful metric as it is less labour intensive than traditional approaches, provides more data accuracy and does not require highly specialised taxonomic expertise. The zooplankton community in Lake Tempe was characterised by high density of small-sized zooplankton with an average mean body size < 500 µm equivalent spherical diameter. While the zooplankton density was characterised by the dominance of the size class 300–700 µm, there was evidence of a significant contribution of the size > 700 µm towards total biomass. Seasonal hydrological regimes, water temperature and eutrophication parameters, as indicated by total phosphorus and chlorophyll-a concentration, had a significant role in driving the variability of zooplankton community size structure in this system. The results of this study are not only a significant step in providing critical baseline information on the zooplankton assemblage of Lake Tempe, but is also a significant contribution to the overall understanding of zooplankton community structure in tropical lakes, and will aid in improving lake management plans in these regions.

乐清湾贝类群落组成及其粒径谱结构特征

PDF HTML阅读 XML下载 导出引用 引用提醒 乐清湾贝类群落组成及其粒径谱结构特征 DOI: 10.5846/stxb202111163221 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划资助（2020YFD0900805）；浙江省重点研发计划（2019C02056）；浙江省海洋水产研究所自选课题（HYS-ZX-202101）；中国水产科学研究院南海水产研究所自选课题项目（2021HZ064） Analysis on community structure of shellfish and its characteristics of biomass particle size spectrum in Yueqing Bay, China Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了解乐清湾贝类资源情况及群落稳定性特征，基于2016-2017年乐清湾定点调查数据，分析了不同季节乐清湾贝类组成、优势种、资源密度、以及物种多样性，并首次建立乐清湾海域贝类生物量粒径谱与标准化生物量粒径谱。结果显示：1）本次共采集到贝类共计45种，隶属于12目，25科，31属。焦河蓝蛤（Potamocorbula ustulata）为乐清湾绝对优势种；2）资源密度表现为夏季最高，其次为春季，秋季与冬季次之；4个季节的丰富度指数（D）、多样性指数（H'）和均匀度指数（J'）平均为3.26、1.61、0.45，3种多样性指数均处于较低水平；3） ABC曲线显示乐清湾贝类的生物群落处于中度干扰状态；4）乐清湾生物量粒径谱谱型复杂，优势种控制着生物量粒径谱的峰值，且与我国其他海域的结果也存在差异；5）标准化生物量粒径谱的斜率范围为-1.5539-0.7373，在我国近海海域中属于偏低水平，表明营养循环水平较低。截距范围在16.673-21.597，高于我国其他海域，说明乐清湾贝类生产力水平较高。 Abstract:The sediment environment is the cultured area for shellfish mudflats, its quality will directly affect the survival of shellfish. Shellfish is a filter feeding animal with powerful filtering ability. In recent years, with the rapid development, the mudflat deterioration of the environment threatens shellfish's living severely. As a result, the shellfish community was changed. Therefore, understanding the resource biomass changes is especially important for policy-makers. The research provides scientific evidence for protecting the marine resources and sustainable development. It discusses the resource and community stability by abundance-biomass curve and size spectra. One point should be noted that the biomass size spectrum (BSS) and normalized biomass size spectra (NBSS) were applied to the shellfish community firstly. In some ways, the BBS method is easier to achieve, in which calculation errors caused by inaccurate shellfish identification may be avoided. In order to understand the marine ecosystems, the fields of application for the BSS theory have been adopted into benthic communities, fish and so on. The species composition, dominance, resource biomass and density and community diversity were studied using data collected from four surveys from May 2016 to February 2017 in Yueqing Bay, Zhejiang Province. The main results showed that 45 shellfish species were identified, which belonged to 12 orders, 25 families and 31genera. The absolute dominant species was Potamocorbula ustulata; the level of resource biomass and density was the highest level in summer, followed by winter, spring and autumn. The average values for species abundance index (D), species diversity index (H') and species evenness index (J') were 3.26, 1.61 and 0.45, respectively, indicating that shellfish community diversity was on a low level. The ABC curve showed that the shellfish community was unstable. The biomass size spectrum was complicated, which dome was controlled by dominant species. Compared with other Chinese offshore areas, it was also different from others results. The slopes of NBSS ranged from -1.5539 to -0.7373, and the intercepts ranged from 16.673 to 21.597. The slope values were lower than those of most other area of Chinese offshore area, and it stood for a lower circulatory efficiency of nutrients in Yueqing Bay. In addition, the intercept values inferred that the production in Yueqing Bay was higher than other Chinese offshore areas. As an ecological research method, biomass particle size spectrum can compare the productivity levels of different ecosystems, describe the trend of biomass change, and is very sensitive to environmental changes, providing a new way to understand the biological law at different levels and environmental monitoring. 参考文献 相似文献 引证文献

Seasonal changes in taxonomic, size composition, and Normalised Biomass Size Spectra (NBSS) of mesozooplankton communities in the Funka Bay, southwestern Hokkaido: Insights from ZooScan analysis

Knowledge about the taxonomic and size composition of mesozooplankton is of critical importance for both fisheries and oceanography. In this study, we collected an annual time series of mesozooplankton samples in Funka Bay and analysed them using ZooScan to reveal the seasonal changes in taxonomic and size structure. Both zooplankton abundance and biovolume peaked in April and were dominated by an appendicularian Oikopleura labradoriensis which has been reported as being are being important food source for flatfish larvae. Furthermore, Noctiluca scintillans was abundant from September to December. The occurrence of this species may be related to the recent increase in the transport of Tsugaru Warm Current water into the bay. The Normalized Biomass Size Spectra (NBSS) was significant for 16 of 21 sampling dates. Insignificant NBSS, with an extremely flat slope, was observed for January–March. Significant NBSS with a flat slope was observed in April. Then, the relatively steep slopes of the NBSS were the case from mid-May to December. These seasonal changes in the slope of NBSS suggest that the energy transfer efficiency for higher trophic levels varied seasonally. The observed slopes of the NBSS in Funka Bay ranged from −1.09 to −0.30, which was flatter than the theoretical value (−1) and the previously reported values for the oceanic region of the western North Pacific. This suggests that the energy transfer efficiency to organisms at higher trophic levels in the Funka Bay is higher than in the adjacent oceanic region.

Testing the usefulness of optical data for zooplankton long‐term monitoring: Taxonomic composition, abundance, biomass, and size spectra from ZooScan image analysis

AbstractThe pelagic ecosystem of the Arctic Ocean is threatened by severe changes such as the reduction in sea‐ice coverage and increased inflow of warmer Atlantic water. The latter is already altering the zooplankton community, highlighting the need for monitoring studies. It is therefore essential to accelerate the taxonomic identification to speed up sample analysis, and to expand the analysis to biomass and size assessments, providing data for modeling efforts. Our case study in Fram Strait illustrates that image‐based analyses with the ZooScan provide abundance data and taxonomic resolutions that are comparable to microscopic analyses and are suitable for zooplankton monitoring purposes in the Arctic. We also show that image analysis allows to differentiate developmental stages of the key species Calanus spp. and Metridia longa and, thus, to study their population dynamics. Our results emphasize that older preserved samples can be successfully reanalyzed with ZooScan. To explore the applicability of image parameters for calculating total mesozooplankton and Calanus spp. biomasses, we used (1) conversion factors (CFs) translating wet mass to dry mass (DM), and (2) length–mass (LM) relationships. For Calanus spp., the calculated biomass values yielded similar results as direct DM measurements. Total mesozooplankton biomass ranged between 1.6 and 15 (LM) or 2.4 and 21 (CF) g DM m−2, respectively, which corresponds to previous studies in Fram Strait. Ultimately, a normalized biomass size spectra analysis provides 1st insights into the mesozooplankton size structure at different depths, revealing steep slopes in the linear fit in communities influenced by Atlantic water inflow.

Movement Shapes the Structure of Fish Communities Along a Cross-Shore Section in the California Current

Pelagic fish communities are shaped by bottom-up and top-down processes, transport by currents, and active swimming. However, the interaction of these processes remains poorly understood. Here, we use a regional implementation of the APex ECOSystem Model (APECOSM), a mechanistic model of the pelagic food web, to investigate these processes in the California Current, a highly productive upwelling system characterized by vigorous mesoscale circulation. The model is coupled with an eddy-resolving representation of ocean currents and lower trophic levels, and is tuned to reproduce observed fish biomass from fisheries independent trawls. Several emergent properties of the model compare realistically with observations. First, the epipelagic community accounts for one order of magnitude less biomass than the vertically migratory community, and is composed by smaller species. Second, the abundance of small fish decreases from the coast to the open ocean, while the abundance of large fish remains relatively uniform. This in turn leads to flattening of biomass size-spectra away from the coast for both communities. Third, the model reproduces a cross-shore succession of small to large sizes moving offshore, consistent with observations of species occurrence. These cross-shore variations emerge in the model from a combination of: (1) passive offshore advection by the mean current, (2) active swimming toward coastal productive regions to counterbalance this transport, and (3) mesoscale heterogeneity that reduces the ability of organisms to return to coastal waters. Our results highlight the importance of passive and active movement in structuring the pelagic food web, and suggest that a representation of these processes can help to improve the realism in simulations with marine ecosystem models.

Zooplankton trophic structure and ecosystem productivity

The number of trophic steps within a plankton food web plays an important role in determining the energy available to support higher-level consumers by affecting trophic transfer efficiency (TE): fewer steps can enhance TE by decreasing respiration and predation losses. In this study, trophic structure within the zooplankton community was investigated using stable isotopes in size-fractionated mesozooplankton, and related to 2 biomass proxies related to TE: the normalized biomass size spectra (NBSS) and the ratio of zooplankton:phytoplankton biomass (log10(zoo:phyto)). Four regions were compared: the California Current Ecosystem (CCE—most productive), the Equatorial Pacific (EqP), the Costa Rica Dome (CRD) and the North Pacific Subtropical Gyre (NPSG—least productive). Compound-specific isotope analysis of amino acids confirmed large differences (~3‰) in the isotopic baseline among ecosystems. EqP and NPSG had low and distinct source δ15N values, while CRD/CCE had high and overlapping values. Trophic differences indicated that the CCE had the lowest number (0) of trophic differences within the 4 zooplankton size classes; NPSG and EqP had the highest number (3), and CRD was intermediate (1). NBSS slopes confirmed the CCE and NPSG as extremes and statistically different from each other. TE patterns estimated from log10(zoo:phyto) suggested EqP was the least efficient, while the other 3 ecosystems (despite large ranges in zooplankton and phytoplankton biomass) had similar TEs. The inverse relationship between food chain length and system productivity, a paradigm originally formulated for microbial food webs, holds for the mesozooplankton assemblage at the productivity extremes.

Spatial, seasonal, and climatic variability in mesozooplankton size spectra along a coastal-to-open ocean transect in the subarctic Northeast Pacific

Biomass size spectra (i.e., the distribution of biomass by body size) are increasingly being used to describe energy flows through pelagic communities. We relate spatial and temporal variability in mesozooplankton normalized biomass size spectra (NBSS) to environmental drivers to understand how climatic variability impacts these energy flows. Seasonally-resolved mesozooplankton samples, collected between 1997 and 2019 along a subarctic Northeast Pacific coastal-to-open ocean transect using a 236 µm Bongo net, were analyzed using microscopy and a laboratory laser optic particle counter to obtain NBSS. NBSS intercepts decreased and slopes flattened along the transect until about 400 km offshore, after which they remained relatively similar. NBSS showed significant seasonality, with steeper slopes and lower intercepts during the winter, and the strongest seasonality near the coast. While there was weak evidence of long-term trends in NBSS, no evidence of gelatification was detected. Seasonality was also evident in the environmental parameters, along with some long-term trends. Stepwise regression analysis suggested that changes in NBSS slope were driven by surface chlorophyll-a concentration, depth-integrated nitrate + nitrite, multivariate ENSO index, number of species, species diversity, and water content (i.e., gelatinous contribution). Surface chlorophyll-a concentration had the greatest effect on NBSS slope, suggesting that future studies may employ satellite-derived estimates of chlorophyll-a to infer changes in mesozooplankton NBSS. This study demonstrates how NBSS may be used to compare and understand the broad implications of climate-induced environmental changes on zooplankton in ecosystems with differing species composition.

Seasonal variation in size diversity: Explaining the spatial mismatch between phytoplankton and mesozooplankton in fishing grounds of the East China Sea

The East China Sea (ECS) is the most important fishing ground in China. Field observations have always found no positive correlation between phytoplankton stocks and zooplankton biomass in the ESC. It has been suggested that under eutrophic conditions, the phytoplankton biomass is too high to limit mesozooplankton growth and lower the energy transfer efficiency from phytoplankton to mesozooplankton. However, this hypothesis does not explain the higher zooplankton biomass supported by lower chlorophyll a in offshore waters. This situation can be referred to as a “mismatch between phytoplankton and mesozooplankton” or “variation of Z/P”. In this study, we used field data covering four seasons to test four hypotheses that (a) flatter slope of normalized biomass size spectrum (NBSS) of mesozooplankton enhances the Z/P; (b) higher mesozooplankton size diversity enhances the Z/P; (c) stronger predatory pressure from zooplanktivorous fish decreases the Z/P; and (d) larger-sized primary producers enhance the Z/P. The results of our study confirm that the size diversity of zooplankton was the most important determinant of spatial variation of Z/P in the ECS in each season except winter. The NBSS slope of zooplankton was also an important factor, but only significant in summer. Other potential mechanisms, including predation pressure from zooplanktivorous fish and larger-sized primary producers, were not determinants. This seasonal change was possibly due to seasonal variations of zooplankton community structure and functional structure in ECS, especially the large-sized and omnivorous Calanus sinicus transported by the stronger ECS Coastal Current during the winter. Our findings highlight the importance of a size diversity approach in the evaluation of the carrying capacity for fish in coastal ecosystems with conspicuous temporal and spatial variations.

Response of Zooplankton Size Structure to Multiple Stressors in Urban Lakes

Urban lakes are important environmental assets that contribute significant ecosystem services in urbanised areas around the world. Consequently, urban lakes are more exposed to anthropogenic pressures. Zooplankton communities play a central role in lake processes and, as such, are very sensitive to the impacts of human activities both through in-lake and catchment processes. Understanding their ecological function in urban lakes and how they respond to urbanisation is essential for environmental sustainability. In this study, we investigated the reliability of zooplankton size structure as indicators of anthropogenic stressors in urban lakes. We examined the relationship between environmental variables and zooplankton community size spectra derived as mean body size, density, and biomass. Our study showed that the overall mean body size was within the small size group ranged from 416 to 735 µm equivalent spherical diameter (ESD). Despite no significant difference in total zooplankton density between lakes, there was variability in the total density of the five different size classes. Total biomass was characterised by a significant proportion of size &gt;750 µm. As the specific parameter of normalised biomass size spectra (NBSS), the slopes of the NBSS varied from moderate (−0.83 to −1.04) for a community with higher biomass of the larger size zooplankton to steeper slopes (from −1.15 to −1.49) for a community with higher biomass of smaller size. The environmental variables, represented by total phosphorus (TP) and chlorophyll a (chl-a), had a strong effect on zooplankton biomass and NBSS, where TP and chl-a were significantly correlated with the increase of total biomass and corresponded well with a less negative slope. Our results indicated that the community metric was sensitive to nutrient input and that size-based metrics have the potential to serve as key indicators for the management of urban lakes.

High Dynamic Range in Entomological Scheimpflug Lidars

Minimizing insecticide use, preventing vector diseases and facilitating biodiversity assessments are suitable applications of recent advances in photonic insect surveillance and entomological lidar. The tools also comprise a new window into fundamental aspect of the fascinating life and ecology of insects and their predators in situ. At the same time, it is evident that lidars are subject to finite detection range given by the instrument noise and saturation levels, and therefore, intervals of the biomass spectra are sectioned at different ranges. The Scheimpflug lidar allows an interesting trade-off between high sample rate and low pulse energy for retrieving wing beat harmonics and slow sample rates with high pulse energy for detecting small species far away. In this paper, we review and revise calibration, sizing and associated deficiencies, and report count rates to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> insects/minute up to 2 km range. We investigate if and how high dynamic range can be exploited in entomological lidar and also how fast and slow sample rates could complement each other and capture a wider span of the biomass spectrum. We demonstrate that smaller insect can be detected further away by long exposures and show consistency between the captured biomass size spectra. However, we find unexpected discrepancies between short and long exposures in the range distributions. We found that vertebrates as well as specular insects can saturate signals. Error sources and limitations are elaborated on.

Finding Approaches to Exploring the Environmental Factors That Influence Copepod-Induced Trophic Cascades in the East China Sea

Copepods have been known to be able to cause an increase in phytoplankton through trophic cascades, as copepods consume heterotrophic protists that feed on phytoplankton. However, how the intensity of copepod-induced trophic cascades varies with environmental conditions remains elusive. We hypothesized that a higher proportion of large phytoplankton in the phytoplankton size distribution, a higher stoichiometric quality of phytoplankton, and a higher temperature could mitigate the intensity of a trophic cascade through increasing direct grazing on phytoplankton by copepods. To explore this issue, we quantified the intensity of a trophic cascade as the difference in phytoplankton concentration reduction by grazing using in situ incubations with and without copepods in the East China Sea. We then investigated the relationship between the intensity of trophic cascades versus the slope of the normalized biomass size spectrum (NBSS) of the phytoplankton community, the C:N ratio of particulate organic matter (POM), and temperature. We found that the intensity of trophic cascades weakly decreased with the NBSS slope and increased with temperature; however, both relationships were not statistically significant. We did not find a clear relationship between the strength of the trophic cascades and the C:N ratio of POM. Our results do not support the hypothesis that the proportion of large phytoplankton, the stoichiometric quality of phytoplankton, and the temperature affect trophic cascades. Instead, we suggest that other critical factors, such as protist abundance, play a role in affecting trophic cascades in the plankton food web in the East China Sea. We further propose some issues which should be addressed when conducting in situ shipboard incubation.

Evaluation of Fish Communities in Daya Bay Using Biomass Size Spectrum and ABC Curve

Based on the data collected by four trawl surveys during 2016–2017, we applied biomass size spectrum (BSS) and abundance–biomass comparison (ABC) curve to assess the status of fish communities’ status in Daya Bay, China. Our findings indicated a unimodal pattern and biomass size ranged from −2 to 10 grain levels and the pattern of the Sheldon-type BSS of fish in Daya Bay. Moreover, fishes in the range of four to eight size class were relatively abundant. The highest peak belonged to the two to four grain level (log2 size bins), mainly consisting of Leiognathus brevirostris, Callionymus meridionalis, Callionymus koreanus, Evynnis cardinalis, Trachurus japonicus, and other small fishes. The curves of the BSS in spring and winter were relatively flat and comprised a large curvature. The summer and autumn curves were comparatively steep, and the seasonal curvature was small. The curvatures of the curve were mainly related to a large number of small Evynnis cardinalis and a small number of large-sized Harpadon nehereus and Leiognathus ruconius. In our study, it was observed that the number and the size of the breeding population, trophic levels, migration habits, and other life history characteristics, as well as anthropogenic disturbances (especially overfishing), significantly affected the peak shape, slope, or curvature of the fish BSS, with overfishing being the main factor. The ABC curve exhibited that Daya Bay was in a critical state of disturbance throughout the year. The spring, summer, and autumn were in severe disturbance, while the winter was in moderate disturbance.

Zooplankton size spectra and production assessed by two different nets in the subarctic Northeast Pacific

Abstract Normalized biomass size spectra (NBSS) are frequently used to describe pelagic communities. However, the underlying structure of NBSS may lead to varying intercepts and slopes when only a portion of the biomass range is sampled. This may be further perpetuated by the sampling efficiency of different gears/mesh sizes. Spatial and seasonal effects of mesh size on zooplankton NBSS and production were evaluated. Zooplankton were collected during winter, spring and summer (2017–2019) between Vancouver Island and Station Papa (50°N, 145°W) using a 64-μm Working Party 2 (WP-2) net and a 236-μm bongo net and analyzed using a bench-top laser optic particle counter. WP-2 and bongo NBSS overlapped in 11 size classes, for which the WP-2 more effectively sampled smaller size classes and converged with the bongo in larger size classes. Differences in NBSS slopes from the two nets were detected, yet no differences in total production. However, the contribution of individual size classes to total production varied spatially and seasonally. Total production in the coastal region exhibited strong seasonal variability. Notably, summer estimates of production in the coastal region were at least 2-fold higher than transitional and open ocean regions. This study suggests that using one mesh size may underestimate zooplankton NBSS and thus production.

Comparison of mesozooplankton production estimates from Saanich Inlet (British Columbia, Canada) using the chitobiase and biomass size spectra approaches

Zooplankton production estimates are necessary to understand the availability and transfer of energy to higher trophic levels in marine food webs. Methods have been developed to quantify zooplankton production; however, they are difficult to compare as they focus on single species, groups, stages, or size classes of zooplankton. We compared 2 methods for estimating crustacean production: the chitobiase method (based on a crustacean moulting enzyme), and 3 empirical growth rate models (Huntley-Lopez, Hirst-Lampitt, and Hirst-Bunker) applied to optically resolved mesozooplankton normalized biomass size spectra (NBSS). Mesozooplankton net samples were collected between March and August of 2010 and 2011 in Saanich Inlet (British Columbia, Canada) and analyzed in the laboratory using microscopy and a bench-top laser optical particle counter (lab-LOPC). Microscope and lab-LOPC estimates of abundance and biomass were in close agreement. Crustacean production estimates were highest using Huntley-Lopez (0.20-185.3 mg C m-3 d-1), followed by Hirst-Bunker (0 .01-18.3 mg C m-3 d-1), chitobiase (0.05-15.6 mg C m-3 d-1), and Hirst-Lampitt (0.03-14.3 mg C m-3 d-1). Hirst-Lampitt-, Hirst-Bunker-, and chitobiase-based estimates of crustacean production and trophic transfer efficiency (TTE) yielded similar patterns/magnitude, while the Huntley-Lopez model was more variable. Estimates showed stronger agreement in 2011 than in 2010, attributed to the shift from El Niño to La Niña conditions. We highlight similarities/differences associated with these techniques and suggest that Hirst-Bunker estimates of production and TTE are most consistent with chitobiase-based values.

Hypoxia changes the shape of the biomass size spectrum of planktonic communities: a case study in the eastern Mediterranean (Elefsina Bay)

AbstractHypoxia is a major stressor on biological communities in many oceanic and coastal ecosystems. Various size-dependent processes (e.g. growth and reproduction rates, predator–prey interactions) are adversely affected by hypoxia. We hypothesized that the impacts of hypoxia on planktonic communities would also be reflected in their Normalized Biomass Size Spectra (NBSS) as steeper slopes and lower intercepts. To explore this hypothesis, we studied the planktonic communities (from bacteria to mesozooplankton) of Elefsina, an enclosed bay that exhibits near bottom hypoxia during summer, and Aghios Kosmas, an adjacent coastal site outside the bay. Bottom layer hypoxia formed during the stratification period in Elefsina Bay significantly altered the distribution of planktonic organisms in the water column. Several unicellular and mesozooplanktonic groups avoided the hypoxic layer, in which the biomass of autotrophic picoeukaryotes was markedly higher. Community changes related to hypoxia were clearly reflected in the NBSS. The slope was significantly steeper in the hypoxic layer (−1.330 vs −1.193) and the intercept was lower (−2.222 vs −0.972, hypoxic vs oxic layer). This result can be interpreted as reduced trophic transfer efficiency to the higher trophic levels due to hypoxia.

Stability of plankton community structure in a long-term biomanipulated eutrophic shallow lake in southeast China: Evidence from particle size spectra

To characterize the plankton size structure and evaluate plankton community stability in Longhu Lake, a shallow eutrophic lake in southeast China that has been biomanipulated for ~20 years, the biomass-size spectra of the plankton were seasonally studied from August 2017 to November 2018. The plankton-size spectra revealed a typical bimodal structure in all seasons. The higher peak consisted of small-sized phytoplankton ranging from 10 to 30 μm, while the lower peak consisted mainly of rotifers and ciliates ranging from 66 to 83 μm. Compared with other eutrophic lakes, the size classes of the bimodal structure in Longhu Lake were relatively smaller, indicating individual miniaturization in the lake's plankton community. There was also a trough in the 90 to 370 μm region of the size spectra, indicating a low biomass for crustacean zooplankton in the lake. The slope (b = −1.27 ± 0.04) of the normalized size spectra was lower than that of the theoretical equilibrium state (b = −1), suggesting high energy transfer from the large phytoplankton (>30 μm) and zooplankton (>90 μm) to the planktivorous silver and bighead carps via filter feeding. Although the seasonal size spectra fluctuated with the water temperature (positively) and nutrients (negatively) in Longhu Lake, their patterns and coefficients of determination did not significantly vary with the seasons (R2 = 0.98 ± 0.01, p < 0.05), indicating the plankton community is stable in this long-term biomanipulated eutrophic lake.