Standing Stock Biomass Research Articles

Spatio-temporal patterns in the biomass, species composition and nitrogen content of drift macroalgae in an urbanised coastal embayment

Understanding spatio-temporal variability in the production of drift macroalgae is useful for monitoring and assessing the influence of local anthropogenic nutrient sources on coastal ecosystems. In this study we: (1) assessed how the drift macroalgal community composition and biomass have changed over a 22-year period in Port Phillip Bay (a large coastal embayment in Victoria, Australia); and (2) measured the amount of accumulated nitrogen in drift macroalgae and the contribution of anthropogenic nitrogen sources through isotopic analysis. The surveys revealed little overlap in species composition (<13%) and a significant decrease in standing stock biomass (from 631 to 49 g m-2) between surveys (1995/1996 and 2017/2018). This was associated with a high degree of turnover (β-diversity) at the genus level between surveys (mean – 0.53), resulting in distinct communities at all sites, particularly among red algal genera. In addition, the occurrence of ephemeral macroalgal blooms and a semi-perennial mat of the red macroalga Botryocladia sonderi at 10-15 m depth at locations close to nutrient sources indicate drift macroalgae are important nutrient accumulators in the bay. Isotopic analysis revealed a high contribution of anthropogenic-derived nitrogen (δ15N > 17‰ and ~ 3% N content) at depths and locations close to nutrient sources, particularly at times of the year when large wastewater discharges occur. Harvesting of drift macroalgae could be a cost-effective solution for offsetting nitrogen inputs from anthropogenic sources, but it will be important to first investigate whether harvesting results in negative impacts to associated fauna or nutrient cycling.

An insight into the fishery, biology and population dynamics of Auxis rochei (Risso, 1810) along the south-west coast of India

Auxis rochei is one of the coastal tunnies contributing substantially to the tuna landings inIndia, with an average (2014-2019) annual catch of 7210 t. Kerala stood first, with an annualaverage landing of 3176 t. The fishery comprised 14.5 - 39.6 cm fork length (FL) size groupswith a mean length of 27.64 cm and a major mode of 26 cm FL. The Length-weight (L-W)relationship of pooled fishes was expressed as W= 0.000003 L3.22 (r2= 0.91). The size at firstmaturity was estimated at 25.8 cm FL when the fish was 1.5 years old. The number of eggsper spawning ranged from 84,562 to 1,33,698 and the ova diameter ranged between 0.1and 0.6 mm, indicating asynchronous oocyte development with multiple spawning. Highergonadosomatic index (GSI) was recorded during April, May and June and coincided withthe minimum gastrosomatic index (GaSI). The recruitment pattern was bimodal, with variedintensity ranging from 0.79-17.89%. Growth was allometric and the von Bertalanffy growthequation derived was Lt=43.5(1-e-0.8(t+0.0212)). The growth performance index (ɸ) was 3.18 andthe longevity of the fish was estimated at 3.7 years. One-year-old plus fishes sustained thefishery (22 - 32 cm FL). Total mortality (Z), natural mortality (M) and fishing mortality (F)were estimated at 3.70, 1.40 and 2.30, respectively, with an exploitation rate (E) of 0.62and the exploitation ratio (U) of 0.60. Beverton and Holt yield per recruit (Y/R) and Biomassper recruit analysis indicated that the Emax was at 0.87, much higher than the present levelof exploitation, reflecting the sustainable fishery along the coast. Standing stock biomass(SSB) was estimated at 7215.7 t, and the spawning stock biomass formed 55.5% of the SSB.Thompson and Bell analysis indicated the MSY as 8125 t, at F-factor, 2.6. The biologicalreference points FCURR/FMSY (0.4) and BCURR/BMSY (1.5) were at safe levels, signifying the scopefor fishery enhancement. Keywords:Biological reference point, Fecundity, Growth, GSI,L-W relationship, Mean length, Mortality, SSB

Assessing the carbon storage value of kelp forest restoration in the Hauraki Gulf Marine Park, New Zealand: Lessons from no-take Marine Protected Areas

Anthropogenic CO2 emissions are one of the principal driving forces of climate change. Climate change leads to systematic changes of ecosystems that cause significant impacts on species interactions, ecosystem processes, and result in profound socio-economic consequences. While carbon offsetting of terrestrial forests and their monetary value are well accepted, the carbon offsetting potential and value of coastal and marine ecosystems (Blue Carbon, BC) remains excluded from the international carbon accounting framework. In this study, we estimated the carbon offsetting value of kelp forests (Ecklonia radiata) against urchin barrens (dominated by crustose coralline algae) using the standing stock biomass as a metric. We propose that standing stock biomass is a crucial next step in introducing BC to the general carbon offsetting framework. Our approach is informed by long-term ecological research conducted in a marine reserve, which highlights the potential of utilizing trophic cascades to limit the dominance of urchin barrens in shallow coastal habitats. We found that the value of carbon standing stock in current kelp forests with reforestation in the Hauraki Gulf Marine Park (HGMP) is worth up to $NZ 7.9 million, based on 2021 carbon market pricing in New Zealand. This simple step towards realizing the value of marine conservation and its multiple benefits to society highlights the missed opportunities when policy and plans do not align with ecology and economics. Including the ocean's contributions to carbon storage is a critical step in using monetization techniques to overcome climate change challenges. Monetizing the carbon offsetting value of kelp forests contributes to establishing funding mechanisms to attract diverse investments in marine ecosystem restoration while providing ecological benefits in ocean governance.

Macroalgae maintain growth outside their observed distributions: Implications for biodiversity‐ecosystem functioning at landscape scales

Abstract The spatial insurance hypothesis states that at landscape scales with environmental variability between different places, biodiversity increases ecosystem functioning if species respond asynchronously to environmental variation, and they are highest functioning in places where they dominate the relative abundance. Under this hypothesis, observed species turnover between places in a landscape with environmental variation might suggest that species diversity is an important driver of landscape‐scale ecosystem functioning. However, the spatial insurance implicitly assumes that species found in one place in the landscape will not be able to maintain high functioning in other places. Given this assumption of the spatial insurance hypothesis, we would predict that species' functioning in monoculture should decline if transplanted to a different place on an environmental gradient, away from where they naturally dominate. If this is the case, we would expect that the loss of one species in one place of the environmental gradient could not be compensated through the establishment of another species in that place. We tested this prediction using a model system of marine macroalgae on intertidal rocky shores on the Swedish west coast. We performed a reciprocal transplant experiment with adult individuals of four fucoid seaweeds that dominate the standing stock biomass at different depths on these shores and monitored their relative growth rate over 2 months. Counter to the assumptions made by the spatial insurance hypothesis, growth rates for three of the four species showed limited responses to being transplanted to different depth zones. Spatial insurance may, hence, play a minor role in sustaining landscape ecosystem functioning in this and other systems. Synthesis. The functional consequences of species loss at landscape scales may not be as obvious as observational studies and ecological models suggest. Consequently, natural patterns of species turnover should not be used directly to argue for the role of biodiversity at landscape scales. Instead, how species may or may not be able to compensate for the loss of other species is a critical aspect if we are to understand how changes in biodiversity at the landscape scale affect ecosystem functioning.

Effects of temporal abiotic drivers on the dynamics of an allometric trophic network model.

Current ecological research and ecosystem management call for improved understanding of the abiotic drivers of community dynamics, including temperature effects on species interactions and biomass accumulation. Allometric trophic network (ATN) models, which simulate material (carbon) transfer in trophic networks from producers to consumers based on mass-specific metabolic rates, provide an attractive framework to study consumer-resource interactions from organisms to ecosystems. However, the developed ATN models rarely consider temporal changes in some key abiotic drivers that affect, for example, consumer metabolism and producer growth. Here, we evaluate how temporal changes in carrying capacity and light-dependent growth rate of producers and in temperature-dependent mass-specific metabolic rate of consumers affect ATN model dynamics, namely seasonal biomass accumulation, productivity, and standing stock biomass of different trophic guilds, including age-structured fish communities. Our simulations of the pelagic Lake Constance food web indicated marked effects of temporally changing abiotic parameters on seasonal biomass accumulation of different guild groups, particularly among the lowest trophic levels (primary producers and invertebrates). While the adjustment of average irradiance had minor effect, increasing metabolic rate associated with 1-2°C temperature increase led to a marked decline of larval (0-year age) fish biomass, but to a substantial biomass increase of 2- and 3-year-old fish that were not predated by ≥4-year-old top predator fish, European perch (Perca fluviatilis). However, when averaged across the 100 simulation years, the inclusion of seasonality in abiotic drivers caused only minor changes in standing stock biomasses and productivity of different trophic guilds. Our results demonstrate the potential of introducing seasonality in and adjusting the average values of abiotic ATN model parameters to simulate temporal fluctuations in food-web dynamics, which is an important step in ATN model development aiming to, for example, assess potential future community-level responses to ongoing environmental changes.

Length-Weight Relationship and the Condition Factor of some Important Estuarine Fish Species from Kakum Estuary of Ghana

This study assessed the length-weight relationships and the condition factors of nine commercial and abundant fish species namely Liza dumerilli, Mugil curema, Liza falcipinnis, Mugil bananensis, Lutjanus goreensis, Lutjanus fulgens, Sardinella aurita, Caranx hippos, and Eucinostomus melanopterus from the Kakum River Estuary. This study was conducted from November 2016 to April 2017 to provide primary information about the biometrics, the length-weight model parameters, and the state of well-being of fish species inhabiting the Kakum Estuary. Sampling was done monthly using a mini boat of 9 m long with a depth of 1.5 m for both diurnal (06:00, 10:00, 14:00, 18:00, 06:00 h) and nocturnal (22:00, 02:00 h) periods with a medium-mesh cast net of 20 mm stretched. Sampling was done within thirty (30) minutes on all sampling times. The total length of the species from the estuary ranged from 2.2 cm in Liza dumerilli to 29.8 cm in Mugil curema while the total weight ranged from 0.2 g to 251 g in Mugil curema. The slope b values of the species varied from 2.3787 for Liza dumerilli to 3.1009 for Eucinostomus melanopterus. Three species from the Kakum Estuary exhibited negative allometric growth and 6 species were growing isometrically. The mean condition factors of the fish species ranged from 0.82 ± 0.36 (SD) in Sardinella aurita to 1.82 ± 0.23 (SD) in Lutjanus goreensis. The results of the present study provide essential input parameters for further assessment of the species standing stock biomass.

Annual Summer Submersed Macrophyte Standing Stocks Estimated From Long-Term Monitoring Data in the Upper Mississippi River

Abstract System-scale restoration efforts within the Upper Mississippi River National Wildlife and Fish Refuge have included annual monitoring of submersed aquatic vegetation (SAV) since 1998 in four representative reaches spanning ∼ 440 river kilometers. We developed predictive models relating monitoring data (site-scale SAV abundance indices) to diver-harvested SAV biomass, used the models to back-estimate annual standing stock biomass between 1998 and 2018, and compared biomass estimates with previous abundance measures. We modeled two morphologically distinct groups of SAV with differing sampling efficiencies and estimated each separately: the first category included only wild celery Vallisneria americana, which has long, unbranched leaves and dominates lotic environments, while the second category included 17 branched morphology species (e.g., hornwort Ceratophyllum demersum and Canadian water weed Elodea canadensis) and dominates lentic environments. Wild celery accounted for approximately half of total estimated total biomass in the four reaches, combined branched species accounted for half, and invasive species (Eurasian watermilfoil Myriophyllum spicatum and curly-leaf pondweed Potamogeton crispus), a fraction of the branched species, accounted for &amp;lt; 1.5%. Site-scale SAV estimates ranged from 0 to 535 g·m−2 (dry mass). We observed increases in biomass in most areas between 1998 and 2009 and substantial increases (e.g., from &amp;lt; 10 g·m−2 to ∼ 125 g·m−2) in wild celery in extensive impounded areas between 2002 and 2007. Analyses also indicate a transitional period in 2007–2010 during which changes in biomass trajectories were evident in all reaches and included the start of a 9-y, ∼ 70% decrease in wild celery biomass in the southernmost impounded area. Biomass estimates provided new insights and illustrated scales of change that were not previously apparent using traditional metrics. The ability to estimate biomass from Long Term Resource Monitoring data improves conservation efforts through better understanding of changes in habitat and food resources for biota, improved goal setting for restoration projects and improved quantification of SAV-mediated structural effects such as anchoring of sediments and feedbacks with water quality.

Biological trade-offs underpin coral reef ecosystem functioning.

Human impact increasingly alters global ecosystems, often reducing biodiversity and disrupting the provision of essential ecosystem services to humanity. Therefore, preserving ecosystem functioning is a critical challenge of the twenty-first century. Coral reefs are declining worldwide due to the pervasive effects of climate change and intensive fishing, and although research on coral reef ecosystem functioning has gained momentum, most studies rely on simplified proxies, such as fish biomass. This lack of quantitative assessments of multiple process-based ecosystem functions hinders local and regional conservation efforts. Here we combine global coral reef fish community surveys and bioenergetic models to quantify five key ecosystem functions mediated by coral reef fishes. We show that functions exhibit critical trade-offs driven by varying community structures, such that no community can maximize all functions. Furthermore, functions are locally dominated by few species, but the identity of dominant species substantially varies at the global scale. In fact, half of the 1,110 species in our dataset are functionally dominant in at least one location. Our results reinforce the need for a nuanced, locally tailored approach to coral reef conservation that considers multiple ecological functions beyond the effect of standing stock biomass.

Individual‐level data reveal high prevalence of positive size‐trophic position relationships for vertebrates in temperate streams

Abstract A positive relationship between body size and trophic position is often assumed in ecology, but efforts to confirm the generality of this relationship for freshwater vertebrates have produced mixed results. Some authors have tested for among‐species relationships, using species‐level estimates of average size and trophic position. Others have used individual‐level body size and trophic position data to test for within‐species relationships. However, no study has yet estimated prevalence, defined here as the fraction of total standing stock biomass within a given ecosystem that consists of taxa exhibiting positive size versus trophic position relationships. Individual‐level estimates of body size and relative trophic position (inferred from bulk‐tissue nitrogen stable isotopes) were collected for vertebrates in six temperate streams. In each stream, all locally occurring vertebrate taxa were collected and closed population depletion samples were used to obtain standing stock biomass estimates. Ordinary least squares regression was used with the individual‐level data to test for positive relationships between body size and relative trophic position (r‐STPRs). A separate r‐STPR model was tested for each vertebrate species collected at the six study sites. Linear mixed‐effects modelling was then used to test for differing r‐STPRs among species. Prevalence of the r‐STPR was calculated for each site by summing the standing stock biomass of all taxa that exhibited a statistically significant, positive STPR at a given site, then dividing this number by the total standing stock biomass of vertebrates at the site. Significant, positive r‐STPRs were detected in 15 of 22 species × site regression models. Prevalence of species with positive r‐STPRs ranged from 91 to 100% of the total vertebrate biomass in western streams and from 45 to 66% in eastern streams. Results confirm that positive r‐STPRs are characteristic of many of the vertebrate taxa considered in this study. Furthermore, species that exhibit positive r‐STPRs comprise a clear majority of the standing stock biomass in five of six study streams. By using individual‐level data to account for prevalence, a more complete understanding of size‐dependent trophic dynamics should be possible in freshwater ecosystems.

Clump Structure, Standing Stock Biomass and Carbon Sequestration

Munrochloa ritchiei (Munro) M. Kumar and Remesh, is a perennial, sympodial bamboo species endemic to Western Ghats of Kerala. The present study focuses on the clump structure, standing stock biomass and carbon storage of this species. Clump structure of the species was recorded in the sample plots and the destructive sampling was carried out to study biomass production and carbon sequestration potential. During the first and second observations the average number of culms was found to be 13,801.2 and 20,154.96, respectively. The distribution of culms in different height class followed a normal distribution whereas; Weibull distribution was the best fit for girth classes. The standing stock biomass of M. ritchiei was 70.6±37.9 t ha -1 and culms and rhizome contributed maximum towards total biomass. Carbon sequestration potential of the species was 30.1±14.9 t h -1 . Total soil carbon stock under the bamboo stand up to a depth of 60 cm was to the tune of 84.799±19.202 t ha -1 . The present study exhibits a unique bamboo species which can play major role in the climate change mitigation and provide more opportunity for livelihood on a sustainable basis.

Principles for estimating fish productivity on coral reefs

Coral reefs provide major nutritional inputs to humans through fish production. Yet, our capacity to adequately assess fish productivity in these and other high-diversity aquatic systems is hampered by a lack of computationally accessible methods with realistic data requirements. Standing stock biomass is often assumed to reflect biomass productivity, yet theoretical and empirical evidence question this assumption. These methodological hurdles have stymied progress in managing this critical coral reef function, potentially jeopardising the future of many small-scale tropical fisheries struggling to respond to global changes. Here, we summarise the physiological and ecological processes that lead to the production of fish biomass. We outline principles and present a robust framework for quantifying fish productivity in high-diversity ecosystems that overcomes these shortcomings by integrating readily accessible individual-level data (e.g. from visual counts) with growth trajectories and predicted mortality rates. This framework provides fisheries-independent estimates of multispecies fish productivity without the need to specify often unknown detailed trophic relationships. We delineate five simple steps and provide a critical user-friendly interface (an easy-to-use R package) to make the calculation of fish productivity a readily accessible tool for coral reef scientists and managers.

Antarctic demersal finfish around the Elephant and the South Orkney islands: distribution, abundance and biological characteristics

A research survey for demersal finfish was completed using bottom trawl fishing gear, following a random stratified sampling design, between 50 and 500 m on shelf areas of subarea 48.1 (Elephant Island) and Subarea 48.2 (South Orkney Island). An acoustic survey was simultaneously carried out to enhance knowledge of bathymetry and the distribution of fish and krill in the studied area. The cruise took place between the 6 and 27 January 2018. A total of 36 hauls were carried out, 15 around Elephant Island and 21 around the South Orkney Islands. A total of 37 fish species were caught with a total biomass of 19,112 kg. The main species encountered included Notothenia rossii and Champsocephalus gunnari, with nominal catches weighing 16,204 (85%) and 876 kg (5%), respectively. Other species of fish accounted noticeably for lower amounts (11%), such as Gobionotothen gibberifrons (330 kg), Chaenocephalus aceratus (322 kg), and Pseudochaenichthys georgianus (299 kg). Indicative estimates of standing stock biomass suggested that in this cruise, N. rossii was the most abundant demersal finfish species in the Elephant Island area, followed by C. gunnari. Differently, on the South Orkney Islands shelf, the most abundant species was G. gibberifrons, followed by P. georgianus. The study provides biological data (length frequency distribution, median size, sex ratio, gonad maturity stages, length-weight relationship) on the main species captured during the survey, and the oceanographic characteristics (depth profiles of temperature, salinity, density) obtained with CTD around the South Orkney Islands.

Seasonal habitat use indicates that depth may mediate the potential for invasive round goby impacts in inland lakes

Abstract The round goby (Neogobius melanostomus) is among the fastest‐spreading introduced aquatic species in North America and is radiating inland from the Great Lakes into freshwater ecosystems across the landscape. Predicting and managing the impacts of round gobies requires information on the factors influencing their distribution in habitats along the invasion front, yet this information is not available for many recently invaded ecosystems. We evaluated the seasonal habitat use and biomass of round gobies in an inland temperate lake to define the spatiotemporal scope of biological interactions at the leading edge of the round goby invasion. Using novel statistical approaches, we combined hierarchical models that control for imperfect species detection with flexible smooth terms to describe non‐linear relationships between round goby abundance and environmental gradients. Subsequently, we generated accurate detection‐corrected estimates of the standing stock biomass of round gobies. Our results show seasonally differentiated habitat niches, where suitable round goby habitat in summer months is restricted to shallow depths (&lt;18.4 m) with a mixture of vegetative and mussel cover. We found high round goby biomass of 122 kg/ha in occupied habitats during the summer, with a total lake‐wide biomass of 766,000 kg. In winter, round gobies migrate to deep offshore habitats and disperse, dramatically altering their scope for biological interactions with resident aquatic species across summer and winter seasons. The results of this study indicate that the scope of biological interactions in inland lakes may be seasonally variable, with potential for high round goby biomass in shallow lakes or at the periphery of deep lakes in the summer months. Such shallow‐water habitats may therefore present higher risk of ecological impacts from round gobies in invaded lentic ecosystems. As round gobies expand inland, consideration of seasonal habitat use will be an important factor in predicting the impacts of this pervasive invader.

Phytoplankton in the Tara Ocean.

Photosynthesis evolved in the ocean more than 2 billion years ago and is now performed by a wide range of evolutionarily distinct organisms, including both prokaryotes and eukaryotes. Our appreciation of their abundance, distributions, and contributions to primary production in the ocean has been increasing since they were first discovered in the seventeenth century and has now been enhanced by data emerging from the Tara Oceans project, which performed a comprehensive worldwide sampling of plankton in the upper layers of the ocean between 2009 and 2013. Largely using recent data from Tara Oceans, here we review the geographic distributions of phytoplankton in the global ocean and their diversity, abundance, and standing stock biomass. We also discuss how omics-based information can be incorporated into studies of photosynthesis in the ocean and show the likely importance of mixotrophs and photosymbionts.

Stable Isotope Analysis and Persistent Organic Pollutants in Crustacean Zooplankton: The Role of Size and Seasonality

Zooplankton is crucial for the transfer of matter, energy, and pollutants through aquatic food webs. Primary and secondary consumers contribute to the abundance and standing stock biomass, which both vary seasonally. By means of taxa- and size-specific carbon and nitrogen stable isotope analysis, the path of pollutants through zooplankton is traced and seasonal changes are addressed, in an effort to understand pollutant dynamics in the pelagic food web. We analyzed zooplankton plurennial changes in concentration of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane and its relatives (DDTs) and in taxa-specific δ15N signatures in two size fractions, ≥450 µm and ≥850 µm, representative of the major part of zooplankton standing stock biomass and of the fraction to which fish predation is mainly directed, respectively. Our work is aimed at verifying: (1) A link between nitrogen isotopic signatures and pollutant concentrations; (2) the predominance of size versus seasonality for concentration of pollutants; and (3) the contribution of secondary versus primary consumers to carbon and nitrogen isotopic signatures. We found a prevalence of seasonality versus size in pollutant concentrations and isotopic signatures. The taxa-specific δ15N results correlated to pollutant concentrations, by means of taxa contribution to standing stock biomass and δ15N isotopic signatures. This is a step forward to understanding the taxa-specific role in pollutant transfer to planktivores and of zooplankton enrichment in PCBs and DDTs.

Warmer and browner waters decrease fish biomass production.

Climate change studies have long focused on effects of increasing temperatures, often without considering other simultaneously occurring environmental changes, such as browning of waters. Resolving how the combination of warming and browning of aquatic ecosystems affects fish biomass production is essential for future ecosystem functioning, fisheries, and food security. In this study, we analyzed individual‐ and population‐level fish data from 52 temperate and boreal lakes in Northern Europe, covering large gradients in water temperature and color (absorbance, 420 nm). We show that fish (Eurasian perch, Perca fluviatilis) biomass production decreased with both high water temperatures and brown water color, being lowest in warm and brown lakes. However, while both high temperature and brown water decreased fish biomass production, the mechanisms behind the decrease differed: temperature affected the fish biomass production mainly through a decrease in population standing stock biomass, and through shifts in size‐ and age‐distributions toward a higher proportion of young and small individuals in warm lakes; brown water color, on the other hand, mainly influenced fish biomass production through negative effects on individual body growth and length‐at‐age. In addition to these findings, we observed that the effects of temperature and brown water color on individual‐level processes varied over ontogeny. Body growth only responded positively to higher temperatures among young perch, and brown water color had a stronger negative effect on body growth of old than on young individuals. Thus, to better understand and predict future fish biomass production, it is necessary to integrate both individual‐ and population‐level responses and to acknowledge within‐species variation. Our results suggest that global climate change, leading to browner and warmer waters, may negatively affect fish biomass production, and this effect may be stronger than caused by increased temperature or water color alone.

Ecosystem structure and function of afrotropical streams with contrasting land use

Abstract Land use changes can strongly influence stream ecosystems, yet these effects remain poorly documented in many hotspots of deforestation such as tropical Africa. The few studies conducted in this region have mostly focused on structural aspects of stream integrity; sparse data are available for key ecosystem processes such as ecosystem metabolism and litter decomposition. To address this knowledge gap, we measured multiple ecosystem functions in rainforest and nearby agricultural (farm) streams located in an afrotropical deforestation hotspot. In two farm and forest stream pairs, we quantified the standing stock biomass of basal resources and invertebrate functional feeding groups, measured rates of litter decomposition (microbial and shredder‐mediated) and modelled invertebrate secondary production. We also calculated whole‐stream metabolic parameters over multiple weeks. To test the regional generality of our results, we then reanalysed a published dataset and assessed the functional composition of invertebrate communities from many local streams. We found that farm streams had greater algal standing stocks, gross primary production (GPP) and production‐to‐respiration ratios than forest streams, although they remained strongly heterotrophic with relatively low GPP values. Agricultural land use also led to the almost complete extirpation of invertebrate shredders, resulting in much slower litter decomposition rates at farm than forest sites despite comparable rates of microbial decomposition. Finally, farm streams had lower invertebrate biomass despite abundant basal resources, leading to a 41%–66% reduction in estimated invertebrate production. We speculate that the functional response of our streams to agricultural land use (i.e., a modest increase in GPP but large declines in invertebrate production and shredder‐mediated litter decomposition rates) could be common across the afrotropics due to low fertiliser usage in this region and/or features of the local fauna. Although our study focuses a small number of streams, the large effect sizes that we report suggest that afrotropical streams could be strongly affected by rapid land use changes in the region, highlighting the need for additional research, monitoring, and conservation efforts in this poorly studied area of the world that is under increasing human pressures.

The loss of large wood affects rocky mountain trout populations

AbstractWestern U.S. rivers are currently influenced by legacy effects of reduced large wood (LW) loading and retention that has substantially reduced in‐stream habitat complexity. Large wood is typically associated with streams in undisturbed old‐growth forest and in the correct geomorphic context can drastically alter stream and valley habitat complexity. Streams withLWare typically multichannel and depositional, while streams lackingLW, due to relatively recent wildfire or logging (&lt;200 years ago), are usually single channelled and erosional. We compared population biomass and individual growth rates of Brook TroutSalvelinus fontinalisin streams across a gradient of wood volumes. At both the square metre and valley length scales, standing stock biomass of aquatic invertebrates was the best predictor of trout biomass. However, at the valley scale, the number of pools was important in predicting trout biomass in combination with standing stock biomass of aquatic invertebrates. Individual growth rates of age‐1 Brook Trout were negatively affected by increasing density; however, growth rates for the largest and smallest individuals at each site were unaffected by density. Our results suggest the pool habitat created byLWacts synergistically with prey availability to dramatically increase trout populations. However, in streams lacking LW, negative effects of detrimental land use practices have persisted &gt;100 years, suggesting that recovering lost animal production in mountain stream networks will only occur at decadal to century time scales.

BÀN VỀ ĐIỀU TRA NGHỀ CÁ THƯƠNG PHẨM Ở BIỂN VIỆT NAM

In fish stock assessment, two approaches have been used to collect data: Fisheries independent survey and fisheries survey. Fisheries independent survey provides scientific information on species composition, catch rate, density, distribution, standing stock biomass and biological information of certain species while fisheries survey supplies primary data for a wide variety of statistical analysis of fisheries performance. In Vietnam, fisheries survey was first developed by project “Assessment of the Living Marine Resources in Vietnam” with the support of DANIA since 1998 as the pilot study in 11 coastal provinces with the purpose of establishing the fisheries statistical system in Vietnam. After the pilot stage, it has been extended to all of 28 coastal provinces and worked effectively since 2000. In 2006, when the project ended, the fisheries statistical system collapsed due to no finance support to continue. Since July 2014, the fisheries data collection network has been recovered with the collaboration of Directorate of Fisheries, Research Institute for Marine Fisheries and Provincial Departments of Capture Fisheries and Marine Resources Protection. The survey design was the logbook base with applying the sampling in space and in time method. This is an overview of the capture fisheries survey in Vietnam with its limitations and challenges.

Quantitative risk assessment of salmon louse-induced mortality of seaward-migrating post-smolt Atlantic salmon

The Norwegian government recently implemented a new management system to regulate salmon farming in Norway, aiming to promote environmentally sustainable growth in the aquaculture industry. The Norwegian coast has been divided into 13 production zones and the volume of salmonid production in the zones will be regulated based on salmon lice effects on wild salmonids. Here we present a model for assessing salmon louse-induced mortality of seaward-migrating post-smolts of Atlantic salmon. The model quantifies expected salmon lice infestations and louse-induced mortality of migrating post-smolt salmon from 401 salmon rivers draining into Norwegian coastal waters. It is assumed that migrating post-smolts follow the shortest path from river outlets to the high seas, at constant progression rates. During this migration, fish are infested by salmon lice of farm origin according to an empirical infestation model. Furthermore, louse-induced mortality is estimated from the estimated louse infestations. Rivers draining into production zones on the West Coast of Norway were at the highest risk of adverse lice effects. In comparison, rivers draining into northerly production zones, along with the southernmost production zone, were at lower risk. After adjusting for standing stock biomass, estimates of louse-egg output varied by factors of up to 8 between production zones. Correlation between biomass adjusted output of louse infestation and densities of farmed salmon in the production zones suggests that a large-scale density-dependent host-parasite effect is a major driver of louse infestation rates and parasite-induced mortality. The estimates are sensitive to many of the processes in the chain of events in the model. Nevertheless, we argue that the model is suited to assess spatial and temporal risks associated with farm-origin salmon lice.