Normalized Biomass Size Spectra Research Articles

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.

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.

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.

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.

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.

Response of size and trophic structure of zooplankton community to marine environmental conditions in the northern South China Sea in winter

Abstract The South China Sea (SCS) is a semi-enclosed marginal sea. And in the northern SCS (NSCS), the Pearl River plume, mesoscale eddies and Kuroshio intrusion may influence the structure of pelagic ecosystems. Here, based on mesozooplankton samples collected in the NSCS from December 2014 to January 2015, spatial variations of mesozooplankton biomass, abundance, normalized biomass size spectra (NBSS), size structure and trophic structure were analyzed to study the response of mesozooplankton community to the influence of highly variable oceanographic environment. High biomass, abundance and intercept of NBSS for the mesozooplankton community were observed in highly productive regions (net primary production > 400 mg C m−2 day−1), such as river plume and cold eddy. No consistent spatial variation was observed for the slope of NBSS, probably because of highly dynamic marine environment in the NSCS. For the trophic structure of mesozooplankton community, the ratio of total chaetognaths biovolume to herbivores/omnivores biovolume (RTCH) was significantly high in river plume and Kuroshio intrusion. The high RTCH indicated unstable trophic structures, which may be due to extreme high proportion of smaller size individuals supported by discharge of river and transport of warm water species from the tropical western Pacific by Kuroshio intrusion, respectively.

Size Spectra Modeling of Mesozooplankton over a Tropical Continental Shelf

de Souza, C.S.; da Conceicao, L.R.; Freitas, T.S.S.; Aboim, I.L.; Schwamborn, R.; Neumann-Leitao, S., and Mafalda, P.d.O., Jr., 2020. Size spectra modeling of mesozooplankton over a tropical continental shelf. Journal of Coastal Research, 36(4), 795–804. Coconut Creek (Florida), ISSN 0749-0208.Size spectra analysis is a useful way of studying biomass and energy flow in ecosystems across trophic levels. The size spectrum reflects a balance of energy and matter between gains through growth and recruitment and losses though mortality in a size-structured community. Therefore, changes in biomass and normalized biomass size spectrum (NBSS) slope and intercept between time or environment can be used to assess the energy transfer efficiency within ecosystems. Linear models were developed to analyze zooplankton biomass and community size structure for the narrow continental shelf and shelf break off Salvador, Brazil, using samples that were collected during 10 oceanographic cruises, from April 2013 to October 2014, and analyzed with a ZooScan. Three descriptors of zooplankton size spectra were examined: size diversity, NBSS slope, and intercept. Copepods were always dominant in abundance. Size spectra varied considerably along a short coast-to-offshore transect of 17 km. The pattern of spatial change presented a predominance of larger size fractions nearshore (flat NBSS slope, –0.56) and the predominance of smaller sized organisms in oceanic waters (steep NBSS slope, –0.88). This gradient was mostly due to the higher abundance of large (>5 mm equivalent spherical diameter) gelatinous organisms (mainly hydromedusae) nearshore. The results suggest that the tropical zooplankton community at the continental shelf off Salvador was characterized by low productivity and low trophic efficiency, especially offshore. Although copepods were dominant in numbers, large-sized gelatinous predators were the key structuring zooplankton taxon in this area.

Empirical correspondence between trophic transfer efficiency in freshwater food webs and the slope of their size spectra.

The density of organisms declines with size, because larger organisms need more energy than smaller ones and energetic losses occur when larger organisms feed on smaller ones. A potential expression of density-size distributions are Normalized Biomass Size Spectra (NBSS), which plot the logarithm of biomass independent of taxonomy within bins of logarithmic organismal size, divided by the bin width. Theoretically, the NBSS slope of multi-trophic communities is exactly -1.0 if the trophic transfer efficiency (TTE, ratio of production rates between adjacent trophic levels) is 10% and the predator-prey mass ratio (PPMR) is fixed at 104 . Here we provide evidence from four multi-trophic lake food webs that empirically estimated TTEs correspond to empirically estimated slopes of the respective community NBSS. Each of the NBSS considered pelagic and benthic organisms spanning size ranges from bacteria to fish, all sampled over three seasons in 1 yr. The four NBSS slopes were significantly steeper than -1.0 (range -1.14 to -1.19, with 95% CIs excluding -1). The corresponding average TTEs were substantially lower than 10% in each of the four food webs (range 1.0% to 3.6%, mean 1.85%). The overall slope merging all biomass-size data pairs from the four systems (-1.17) was almost identical to the slope predicted from the arithmetic mean TTE of the four food webs (-1.18) assuming a constant PPMR of 104 . Accordingly, our empirical data confirm the theoretically predicted quantitative relationship between TTE and the slope of the biomass-size distribution. Furthermore, we show that benthic and pelagic organisms can be merged into a community NBSS, but future studies have yet to explore potential differences in habitat-specific TTEs and PPMRs. We suggest that community NBSS may provide valuable information on the structure of food webs and their energetic pathways, and can result in improved accuracy of TTE-estimates.

Seasonal variability of zooplankton size spectra at Mombetsu Harbour in the southern Okhotsk Sea during 2011: An analysis using an optical plankton counter

To evaluate the temporal changes in zooplankton size spectra, optical plankton counter (OPC) measurements were made of high-frequency time-series zooplankton samples collected at approximately 3.5-day intervals in Mombetsu Harbour, which is located in the southern Okhotsk Sea, from January to December 2011. Based on biomasses of 47 equivalent spherical diameter (ESD) size classes binned at 0.1 mm intervals across 0.35–5 mm, the Bray–Curtis similarity index separated the zooplankton community into six groups (A–F). The occurrence of each group was separated seasonally. Thus, groups A and B were observed during the ice-covered season and summer season, respectively. During March and June, groups C–F were observed. Their occurrence varied in the short term in relation to the exchange of water masses. Groups A and C, which were observed from January to April, showed flatter normalized biomass size spectra (NBSS) slopes (−0.85 to −1.1), which indicate low productivity. In contrast, the other groups showed steeper slopes (−1.31 to −1.52) from May to December, with high productivity. Throughout the year, the frequency of highly productive groups occurred at a high level (95.2%). Although the seasonal variability in zooplankton size and productivity in Mombetsu Harbour was mainly governed by water mass exchanges, the productivity was continuously high throughout nearly all of the one-year study period.

Seasonal benthic patterns in a glacial Patagonian fjord: the role of suspended sediment and terrestrial organic matter

Complex marine-terrestrial interactions characterize Chilean fjords, where benthic communities influence the distribution of organic matter (OM). We examined spatial and seasonal changes in the hydrography, sediment conditions and soft-bottom macrobenthic, meiobenthic, and total microbial biomass in a glacial Patagonian fjord (Martinez Channel, Chile). The transport of a high load of glacial mineral and particulate OM to the fjord in the austral summer coincided with low total live benthic biomass. Multivariate analysis evidenced temporal-related macrofaunal groups influenced by the different environments produced by the advection of sediment transport and terrestrial OM from the Baker River, Chile. The relationships between density/biomass and respiration versus body size varied considerably with distance from major riverine inputs, but the slopes of density size spectra and normalized biomass size spectra were less negative in summer than in winter. Occasional large-scale advective processes in the water column affected sediment conditions and removed surface macrofauna, influencing the slope and intercept of the regression models. In the outer fjord, lateral advection and subsequent sedimentation of terrestrial OM contributed a significant fraction to total OM sediments (<14.76%). Stable carbon isotopes measured in benthic organisms suggest that benthic communities in the inner fjord may assimilate a significant fraction of terrestrial OM via heterotrophic bacteria in contrast to the minor input of terrestrial OM in the outer fjord.

Seasonal and interannual variability of zooplankton vertical distribution and biomass size spectra off Ubatuba, Brazil

The analysis of plankton size distributions in response to physical and biological forcing is relevant to the understanding of marine ecological processes. In this study, we evaluated the influence of seasonal intrusions of the South Atlantic Central Water (SACW) on zooplankton vertical distribution and normalized biomass size spectra (NBSS) on the inner shelf off subtropical Brazil. Monthly sampling was performed at a fixed station for 5 years and zooplankton samples were analyzed with a ZooScan system. SACW intrusions led to increases in nitrate, chlorophyll and zooplankton biomass in different depth strata. NBSS slopes and intercepts varied between SACW intrusion and retraction phases and stratification was a key factor explaining seasonal fluctuations in NBSS parameters. The zooplankton interannual variability was related to the changing strength of SACW intrusions during the time series, as indicated by surfacing 18 and 208C isotherms in certain years and intrusion phases, indicative of transient upwelling. We conclude that the temporal components of zooplankton variability in this subtropical coastal ecosystem were governed by SACW intrusions, affecting the vertical distribution of zooplankton biomass and size structure.

Spatial and temporal changes in zooplankton abundance, biovolume, and size spectra in the neighboring waters of Japan: analyses using an optical plankton counter.

An optical plankton counter (OPC) was used to examine spatial and temporal changes in the zooplankton size spectra in the neighboring waters of Japan from May to August 2011. Based on the zooplankton biovolume of equivalent spherical diameter (ESD) in 45 bins for every 0.1 mm between0.5 and 5.0 mm, a Bray-Curtis cluster analysis classified the zooplankton communities into six groups. Thegeographical distribution of each group varied from each of the others. Groups with a dominance of 4 to 5 mm ESD were observed in northern marginal seas (northern Japan Sea and Okhotsk Sea), while the least biovolume with a dominance of a small-size class (0.5 to 1 mm) was observed for the Kuroshio extension. Temporal changes were observed along the 155° E line, i.e., a high biovolume group dominated by 2 to 3 mm ESD during May shifted to other size spectra groups during July to August. These temporal changes were caused by the seasonal vertical descent of dominant large Neocalanus copepods during July to August. As a specific characteristic of the normalized biomass size spectra (NBSS), the slope of NBSS was moderate (-0.90) for the Neocalanus dominant spring group but was at -1.11 to -1.24 for the other groups. Theoretically, the slope of the NBSS of the stable marine ecosystem is known to settle at approximately -1. Based on the analysis by OPC, zooplankton size spectra in the neighboring waters of Japan were separated into six groups. Most groups had -1.11 to -1.24 NBSS slopes, which were slightly higher than the theoretical value (-1). However, one group had a moderate slope of NBSS (-0.90) caused by the dominance of large Neocalanuscopepods.

Polychaete Annelid Biomass Size Spectra: The Effects of Hypoxia Stress

Quantitative benthic samples were taken during spring and summer at three locations on the Louisiana continental shelf from 2004 to 2012 to assess the influence of hypoxia on the mean sizes (wet weight) of polychaete annelid worms. While the mean body size over the entire study of 64 samples was 3.99 ± 4.66 mg wet weight per individual, the mean ranged from 2.97 ± 2.87 mg during consistently hypoxic conditions (&lt;2 mg/L) to a high of 7.13 ± 7.60 mg (p&lt;0.01) under oxic conditions (&gt;2 mg/L). The variations in size within assemblages were estimated from conventional biomass size spectra (BSS) and normalized biomass size spectra (NBSS) across a broad range of oxygen concentrations. The decline in size was due to the elimination of large species under hypoxic conditions (&lt;2 mg/L), not a reduction in size within species. At “severe” levels of hypoxia (&lt;1 mg/L), the smallest species also declined in abundance, whereas the ubiquitous “medium-sized”Paraprionospio pinnataflourished. These results suggest that there will be enhanced selection for small sizes and species with enlarged branchial palps such as those inP. pinnataif, as predicted, hypoxia becomes more commonplace in time and space worldwide.