Estimates Of Secondary Production Research Articles

Secondary production at the Barents Sea polar front in summer: contribution of different size classes of mesozooplankton

The Barents Sea polar front is characterized by high primary production following the retreat of the ice edge during spring. However, secondary production estimates of mesozooplankton across the front are scarce, despite being essential for understanding energy flow through the food web. We investigated mesozooplankton community composition and production across the Barents Sea polar front (75°-78°N) in June, covering both Atlantic and Arctic water masses with high spatial and taxonomic resolution. We highlight the contribution of small and large groups of mesozooplankton and estimate secondary production by comparing and evaluating 4 commonly used growth rate models. The zooplankton community composition and size distribution changed across the polar front. In the Atlantic region, Rotifera, Chaetognatha and Appendicularia were common, while copepods and their nauplii contributed most across the polar front and in Arctic water masses. Mesozooplankton secondary production took place mainly in the surface and was highest south of the front, declining towards Arctic waters. Considering production by copepods alone, highest values were found in the northern sector of the polar front and in the Arctic region. Young developmental stages (CI-CIV) of Calanus spp. and small-sized taxa contributed most to copepod production in Atlantic waters, while calanoid copepod nauplii contributed considerably to copepod production in Arctic waters. We emphasize that the production estimates were strongly influenced by the growth rate model and conclude that copepod secondary production in a summer situation with non-limiting food concentration was best described using a model that solely considers water temperature and copepod body weight.

Understanding the impact of sand extraction on benthic ecosystem functioning: a combination of functional indices and biological trait analysis

Marine aggregates have been intensively extracted in the North-East Atlantic over the past decades. This study aimed to assess the effect of sand extraction on benthic ecosystem functioning using a combination of biological traits and functional indices (the bioturbation (BPc) and irrigation potential (IPc) and secondary production (SPc) of the macrobenthic community). Data on macrobenthos, sediment properties and extraction intensity were collected over a time period of ten years (2010 – 2019) for three coarse sediment extraction areas in the Belgian Part of the North Sea, each with a different extraction regime. Sediment parameters such as the medium sand fraction (250 – 500 µm) and median grain size showed a significant effect on all functional indices. Whilst sand extraction variables only significantly affected secondary production estimates. The secondary production of the macrobenthic community decreased following a high yearly extraction intensity, whereas a high cumulative (10-year period) extraction intensity resulted in a slightly increased secondary production. Species-specific responses revealed that these high cumulative extraction volumes increased the abundance of opportunistic species, which could have contributed to the higher SPc values observed in cumulative disturbed areas. Response traits such as tube-living and sessile individuals with a pelagic egg development were positively influenced by a long-term disturbance, an indication of a more disturbance-tolerant community. A short-term disturbance rather seemed to favor a macrobenthic community characterized by a higher burrowing capability. In terms of effect traits, both short- and long-term extraction clearly favored deposit feeders, which can structure organic matter distribution and thus indirectly influence nutrient and oxygen fluxes as well. Future in situ measurements in sand extraction areas could help to unravel and strengthen our understanding of the ecosystem processes linked to these trait-based observations.

Effects of incomplete sampling on macroinvertebrate secondary production estimates in a forested headwater stream

Estimates of secondary production depend on the efficiency of sampling methods in capturing abundances and body lengths of the entire macroinvertebrate community. The efficiency of common sampling methods in fulfilling these criteria is poorly understood. We compared the effects of a Surber sampler (250 µm mesh size) and a Freeze corer in capturing abundance, biomass, and secondary production of macroinvertebrates in a forested headwater stream. We then examined how the use of nets with different mesh sizes could affect estimates of secondary production. Macroinvertebrate abundance was three times lower, and biomass was three times higher with the Surber than with the Freeze corer. Neither method captured the entire length distribution, and incomplete sampling of body lengths and abundance resulted in underestimating total secondary production by 48% (Surber) and 49% (Freeze corer). We estimated that reducing the mesh size from 250 to 100 µm would reduce the underestimation of production from ~ 48 to ~ 12% due to the inclusion of smaller individuals. Our results improve the efficiency of common sampling methods, allowing a reliable quantification of the role of macroinvertebrates in stream ecosystem functioning.

The fragmentation of nano- and microplastic particles from thermoplastics accelerated by simulated-sunlight-mediated photooxidation

The plastic debris that washes ashore and litters the shoreline often undergoes weathering under sunlight exposure, such that it fragments to form nanoplastics and microplastics, but the fragmentation rate for many thermoplastics is unknown. In this study, three major thermoplastics were exposed to simulated sunlight in an accelerated weathering chamber to evaluate the speed of photooxidation-induced fragmentation. The initiation of photooxidation-induced fragmentation extrapolated from the accelerated weathering chamber to real sunlight exposure in South Korea followed the order of PS (< 1 year) > PP (< 2 years) > LDPE (> 3 years). The surface cracks created by photooxidation were not directly reflected in the initiation of fragmentation of thermoplastics. The initiation of fragmentation was faster in PS than other polymers, but the total abundance of particles produced, and increasing ratio (exposure/non-exposure) were comparable or lower than those of PP. The increasing ratio pattern between nanoplastics and small microplastics of PP differed noticeably from other polymers. The initiation of nanoplastic and small-microplastic fragmentation determined in this study will be useful for the further estimation of secondary microplastic production by weathering and thus for decision-making regarding methods for the timely removal of plastic litter in the environment.

Linking Historical Changes in Salt‐Marsh Coverage to Lost Production of a Nektonic Bioindicator

AbstractDevelopment reduces the amount of secondary biological production in coastal estuaries. However, the magnitude of this reduction remains largely unknown. We are not aware of studies that have quantified lost secondary biological production in estuaries as a result of interdecadal coastal development of salt‐marsh habitats. Our objective was to demonstrate a technique that combined historical imagery, GIS, and secondary production estimates to quantify the magnitude of lost areal production arising from the development of tidal creeks. We estimated lost production of a dominant salt‐marsh fish MummichogFundulus heteroclitusin Spooners and Pelletier creeks, two second‐order tidal systems in coastal North Carolina. We georeferenced historical (1939) aerial imagery, digitized low‐tide and high‐tide features in historical and contemporary (2019) imagery, and compared the intertidal vegetated area of each creek between periods. The lost intertidal area was then multiplied by creek‐specific published rates of areal production of larval and juvenile age‐0 Mummichog in salt‐marsh cordgrassSpartina alterniflorahabitats. There was a loss of intertidal area and intertidal/subtidal vegetated edge of 72% and 54%, respectively, in Spooners Creek, and 47% and 4%, respectively, in Pelletier Creek. Losses of intertidal area over the last ~80 years translated into estimated annual losses of 44 and 8 kg of dry weight production (~695,000 and 186,500 individuals) for a single cohort in Spooners and Pelletier creeks, respectively. These estimates represent minimum losses, as some in‐stream development was already visible in the historic imagery and a single cohort’s production was used (not multiple cohorts). We encourage other researchers to use historic imagery to determine changes in aquatic habitats and link losses (or gains) in these habitats to the productivity metrics of important fishes.

Biodiversity, community structure and ecosystem function on kelp and wood falls in the Norwegian deep sea

Fjordic systems in temperate and Arctic regions often feature extensive kelp forests at their shallow coastal margins as well as extensive terrestrial forests. Detrital export from these shallow-water and terrestrial ecosystems is an important source of carbon for deep-sea communities in the form of kelp and wood falls. Benthic landers with experimental substrates (wood blocks and kelp parcels) were deployed for 10 mo at a depth of 530 m in a deep Norwegian fjord to investigate and compare macro- and megabenthic community structure, biodiversity and ecosystem functioning on kelp and wood falls. Results revealed that while wood and kelp falls can support a similar number of species and abundance of fauna, they support significantly different faunal communities. Biomass and secondary production on both wood and kelp substrates were significantly greater than in the control samples. Secondary production estimates were similar or higher than those reported from soft-sediment ecosystems at shallower European marine sites. Biological trait analysis showed that macrofaunal assemblages were distinct between the kelp and wood, providing evidence for differences in ecosystem function between the substrates. This case study from a deep-sea fjord in Norway provides clear evidence that while wood and kelp organic falls can support similar abundances of fauna, the associated benthic biodiversity, community structure and ecosystem functioning can be dramatically different between these substrates. The work presented here aims to provide information that is useful in assessing the extent of anthropogenic impacts on deep fjord ecosystems with respect to informing future conservation and management strategies.

Magnitude and direction of stream-forest community interactions change with timescale.

Networks of direct and indirect biotic interactions underpin the complex dynamics and stability of ecological systems, yet experimental and theoretical studies often yield conflicting evidence regarding the direction (positive or negative) or magnitude of these interactions. We revisited pioneering data sets collected at the deciduous forested Horonai Stream and conducted ecosystem-level syntheses to demonstrate that the direction of direct and indirect interactions can change depending on the timescale of observation. Prior experimental studies showed that terrestrial prey that enter the stream from the adjacent forest caused positive indirect effects on aquatic invertebrates during summer by diverting fish consumption. Seasonal and annual estimates of secondary production and organic matter flows along food web pathways demonstrate that this seasonal input of terrestrial invertebrate prey increases production of certain fish species, reversing the indirect effect on aquatic invertebrates from positive at the seasonal timescale to negative at the annual timescale. Even though terrestrial invertebrate prey contributed 54% of the annual organic matter flux to fishes, primarily during summer, fish still consumed 98% of the aquatic invertebrate annual production, leading to top-down control that is not revealed in short-term experiments and demonstrating that aquatic prey may be a limiting resource for fishes. Changes in the direction or magnitude of interactions may be a key factor creating nonlinear or stabilizing feedbacks in complex systems, and these dynamics can be revealed by merging experimental and comparative approaches at different scales.

Experimental N and P additions relieve stoichiometric constraints on organic matter flows through five stream food webs.

Human activities have dramatically altered global patterns of nitrogen (N) and phosphorus (P) availability. This pervasive nutrient pollution is changing basal resource quality in food webs, thereby affecting rates of biological productivity and the pathways of energy and material flow to higher trophic levels. Here, we investigate how the stoichiometric quality of basal resources modulates patterns of material flow through food webs by characterizing the effects of experimental N and P enrichment on the trophic basis of macroinvertebrate production and flows of dominant food resources to consumers in five detritus-based stream food webs. After a pre-treatment year, each stream received N and P at different concentrations for 2years, resulting in a unique dissolved N:P ratio (target range from 128:1 to 2:1) for each stream. We combined estimates of secondary production and gut contents analysis to calculate rates of material flow from basal resources to macroinvertebrate consumers in all five streams, during all 3years of study. Nutrient enrichment resulted in a 1.5× increase in basal resource flows to primary consumers, with the greatest increases from biofilms and wood. Flows of most basal resources were negatively related to resource C:P, indicating widespread P limitation in these detritus-based food webs. Nutrient enrichment resulted in a greater proportion of leaf litter, the dominant resource flow-pathway, being consumed by macroinvertebrates, with that proportion increasing with decreasing leaf litter C:P. However, the increase in efficiency with which basal resources were channelled into metazoan food webs was not propagated to macroinvertebrate predators, as flows of prey did not systematically increase following enrichment and were unrelated to basal resource flows. This study suggests that ongoing global increases in N and P supply will increase organic matter flows to metazoan food webs in detritus-based ecosystems by reducing stoichiometric constraints at basal trophic levels. However, the extent to which those flows are propagated to the highest trophic levels likely depends on responses of individual prey taxa and their relative susceptibility to predation.

Trophic basis of production in tropical headwater streams, Puerto Rico: an assessment of the importance of allochthonous resources in fueling food webs

The relative importance of allochthonous and autochthonous resources in fueling tropical headwater streams remains an open topic. We combined estimates of secondary production and assessment of its trophic basis to determine which resources were responsible for animal production. We studied benthic insect assemblages in two streams in the Luquillo Experimental Forest, Puerto Rico. Habitat-weighted production estimates were similar in both streams (528.5 and 591.5 mg m−2 year−1), but production was over twice as high in pool versus riffle habitats. The mayfly Neohagenulus (Leptophlebiidae) was a major contributor to total production (259.1 and 352.2 mg m−2 year−1). All taxa relied heavily on amorphous detritus and plant tissue. Aquatic insect production was similar to that reported for shrimp assemblages in the same study area, but low relative to temperate region estimates. The trophic basis of production appears to be allochthonous organic matter, which agrees with the small size and closed canopy cover over the study streams. This is the first study quantifying the production and trophic basis of the non-shrimp macroinvertebrate assemblage in tropical island streams. We also provide support for the importance of riparian vegetation as the main energy sources for stream tropical stream food webs.

Secondary Production of Kelp Bass Paralabrax clathratus in Relation to Coastal Eelgrass Zostera marina Habitat in a Southern California Marine Protected Area

Seagrasses are an important refuge for fishes and provide ecosystem services worldwide. Along the Pacific Coast, however, quantitative assessments of the ecological role of seagrass habitats with limited anthropogenic impacts are lacking despite their value to resource management. To address these issues, the ecological function of the eelgrass Zostera marina Linnaeus in a protected area off Santa Catalina Island, California, USA was quantified using estimates of secondary production in the kelp bass Paralabrax clathratus (Girard, 1854). Monthly assessments of Zostera structural complexity, as well as the size and abundance of juvenile kelp bass were used to establish a baseline of fish biomass and recruitment associated with Zostera habitat. The greatest number of kelp bass was recorded in the summer and fall months and the fewest during the winter and spring. Secondary production in kelp bass (0.1 to 0.59 g m–2 mo–1) followed monthly changes in Zostera habitat structure throughout the 24-month study period. Seasonal changes in the structural complexity of coastal Zostera beds may influence the flow of energy to adjacent reef environments through the transfer of fish biomass. These findings help define the potential role of Zostera habitat within the larger context of nearshore coastal ecosystems in the Southern California Bight.

Defining isoscapes in the Northeast Pacific as an index of ocean productivity

AbstractAimWe modelled isoscapes in the Northeast (NE) Pacific using satellite‐based data, with the main objective of testing whether isoscapes defined by a few key parameters can be used as a proxy for secondary productivity.LocationNortheast Pacific; 46–60° N and 125–165° W.Time periodFrom 1998 to 2017 (ongoing).Major taxa studiedZooplankton, with a focus on large herbivores.MethodsApproximately 280 summer zooplankton samples were analysed for carbon (δ13C) and nitrogen (δ15N) stable isotope (SI) ratios. Environmental conditions experienced by zooplankton organisms were extracted from satellite, in situ sensor and model databases. A generalized additive model approach was used to explain the spatial variability of δ13C and δ15N values and to predict isoscapes.ResultsSea surface temperature (SST), sea level anomaly (SLA) and chlorophyll‐a concentration emerged as the significant SI predictors. Modelled isoscapes reproduced patterns observed in δ13C and δ15N value distribution, such as a decrease from the coast to offshore. The contribution of eddies in enhancing local production in the open ocean was also well captured by the models. In the central part of the NE Pacific, higher SI values were correlated with higher large copepod biomass measured by the North Pacific Continuous Plankton Recorder (CPR) survey. However, in the area off the coast of British Columbia, high δ15N variability appeared to be associated with episodic intrusions of coastal waters, demonstrating that caution is needed when interpreting sharp changes in SI ratios.Main conclusionsAlthough the mechanisms driving SI ratio variability are complex, we demonstrate that a few parameters used as a proxy for some of these major mechanisms are able to produce successful isoscape models. This approach was proved useful to provide a qualitative estimate of secondary production, which can be particularly valuable in a region where few data are available.

A global estimate of terrestrial net secondary production of primary consumers

AbstractAimNet secondary production (NSP) emerges from the consumption of net primary production (NPP) by all heterotrophic organisms. There has been sporadic interest in the importance of NSP, but no global estimates have been produced. Here, we examine NSP and attempt a global estimate using contemporary NPP data combined with modern metabolic scaling theory for consumption rates. We distinguish between potential NSP, as the amount of secondary production that could be supported by NPP, and realized NSP, as the amount remaining after anthropogenic habitat disruption.LocationGlobal.Time period2000–2014.MethodsWe present a metabolic model of NSP, implementing a type II functional response for consumption rates, wherein search efficiency and handling time are calculated based on consumer mass and ambient temperature. We solve this model for each 0.05‐decimal‐degree pixel in the global terrestrial biosphere, using as data inputs NPP (MOD17A3) and land‐surface temperature (MOD11C3). We aggregate estimates within global land‐cover classifications (MCD12C1) to obtain cover‐specific and global estimates of NSP. We also correct our estimates based on declines in consumer abundance reported in Living planet report 2014.ResultsWe estimate that potential NSP is 4.74 Pg C/year globally (95% CI: 3.75–5.75). When we correct for global consumer population declines, realized NSP is estimated at 2.37 Pg C/year (95% CI: 1.86–2.89), a loss of 50% in the rate of carbon flux through secondary consumers.Main conclusionsOur estimates should not be viewed as the last word on NSP but are sufficient to suggest that the flux of carbon through consumers is of a similar magnitude to many other fluxes crucial to the global carbon cycle. We view this as a hypothesis to be tested that suggests NSP deserves significantly more attention in Earth systems, macroecology and biogeochemical research.

Spatial variability of macrobenthic production in the Bering Sea

Despite being located at higher latitudes with seasonal ice-cover, the Bering shelves and slope are still one of the most productive regions of the world. Existing reports regarding marine production of the Bering Sea are mainly confined to its high water column production and high biomass of macrobenthos. Compared with biomass, secondary production estimates are more functionally based and have assumed a fundamental role in the quantification of ecosystem dynamics. Based on Brey’s empirical model (in: Brey, Population dynamics in benthic invertebrates. A virtual handbook, Alfred Wegener Institute for Polar and Marine Research, Germany, 2001), macrobenthic production across the majority of the Bering Sea was quantified during the 4th, 5th and 6th Chinese Arctic Scientific Expeditions. Mean total production (TP) and community P/B for the entire survey area were 220.6 ± 341.5 kJ m−2 year−1 and 0.4 ± 0.2 year−1, n = 46, respectively. Higher TP occurred in the shallower shelves and slope with values exceeding 131.0 kJ m−2 year−1, whereas lower TP occurred in the deep basin with values of 1.0 kJ m−2 year−1. Comprehensive analysis revealed that the sediment, water flow, temperature and depth were the major factors affecting the macrobenthic production. Owing to the relatively high biological production in the upper water column and the tight pelagic–benthic coupling, higher production occurred in the shallow shelves and slope, particularly in the northern Bering Sea. In contrast, the high-nutrient, low-chlorophyll characteristic and deficient particulate organic carbon input led to low production in the deep basin. Similar to the conditions in the Arctic and Antarctic, the energy conversion rate of macrozoobenthos was relatively low for the Bering Sea.

Seasonality in coastal macrobenthic biomass and its implications for estimating secondary production using empirical models

AbstractMacrobenthic secondary production is widely used to assess the trophic capacity, health, and functioning of marine and freshwater ecosystems. Annual production estimates are often calculated using empirical models and based on data collected during a single period of the year. Yet, many ecosystems show seasonal variations. Although ignoring seasonality may lead to biased and inaccurate estimates of annual secondary production, it has never been tested at the community level. Using time series of macrobenthic data collected seasonally at three temperate marine coastal soft‐bottom sites, we assessed seasonal variations in biomass of macrobenthic invertebrates at both population and community levels. We then investigated how these seasonal variations affect the accuracy of annual benthic production when assessed using an empirical model and data from a single sampling event. Significant and consistent seasonal variations in biomass at the three study sites were highlighted. Macrobenthic biomass was significantly lower in late winter and higher in summer/early fall for 18 of the 30 populations analyzed and for all three communities studied. Seasonality led to inaccurate and often biased estimates of annual secondary production at the community level when based on data from a single sampling event. Bias varied by site and sampling period, but reached ∼ 50% if biomass was sampled at its annual minimum or maximum. Since monthly sampling is rarely possible, we suggest that ecologists account for uncertainty in annual production estimates caused by seasonality.

Latitudinal variations of zooplankton community structure and productivity in the Barents sea (summer 2013)

The Barents Sea is regarded as one of the world’s most unique regions with its high summer productivity. However, there were a few studies dealing with estimation of daily secondary production in the Barents Sea. The aim of the present study was to conduct an investigation of the pelagic mesozooplankton assemblage in the Barents Sea, to calculate daily production levels of mesozooplankton and to analyze the relationship between the community structure and environmental drivers.Structure of zooplankton communities was investigated within the main water masses of the Barents Sea in the summer 2013 (June–July). Calanus finmarchicus presented as copepodites IV–V dominated in terms of the total zooplankton abundance and biomass in Murmansk Coastal Water and Atlantic Water. Spring phase of zooplankton succession cycle was found in Arctic Water where Copepoda nauplii were the most abundant and Calanus glacialis dominated by zooplankton biomass. Zooplankton of the Barents Sea Water had features of spring and summer phases of zooplankton succession cycle. Spatial variations in the zooplankton distribution were associated with hydrological conditions and phytoplankton density. Maximum of the mean zooplankton biomass was registered in Atlantic Water (30,7 mg dry mass/m3) while the minimum was found in Barents Sea Water (5,4 mg dry mass/m3). Calculated daily production of zooplankton ranged from 0,01 to 1,57 mg dry mass/m3per day. Total zooplankton stock for the study area of 281 000 km2was estimated to be &gt; 740 000 t of dry mass. The obtained values of zooplankton biomass and stock were considerably lower than in previous years, which are probably connected with higher predator pressure — grazing of zooplankton by capelin and other predators as well as with possible climatic influence.

Copepod secondary production in the sea: Errors due to uneven molting and growth patterns and incidence of carcasses

Secondary production of copepods is one of the basic parameters that govern the structure and function of the marine pelagic food web, and it is commonly estimated as cumulative biomass increase through consecutive molting based on short-term molting rate (MR) incubation experiments. The accuracy of the method depends on two underlying assumptions: (1) Even stage duration and inter-molt growth; (2) All copepods in situ are alive. We conducted a year-long study in a coastal bay within the Humboldt Current System to assess the errors in copepod secondary production estimation when these assumptions are violated. Abundances of live and dead individuals of the dominant species: Paracalanus cf. indicus, Acartia tonsa and Calanus chilensis were measured monthly. Concurrent molting rate experiments were conducted to derive copepod secondary production. A modified MR formulation was used to correct the secondary production estimates for error in assumption (1), and the live/dead copepod data were used to correct the estimates for error in assumption (2). Violation of the underlying assumptions caused error in secondary production estimation, most severely in P. cf. indicus. The error was not evenly distributed across the months, and in the case of C. chilensis, it switched between over- and under-estimation repeatedly. The annual average error was −39.2% in P. cf. indicus, 3.1% in A. tonsa, and 5.2% in C. chilensis. The errors also varied in magnitude and in sign among developmental stages, with some stages yielding nearly 70% over-estimation. For copepod species with short generation times, even small errors could quickly propagate and result in highly skewed secondary production projection. Reliable secondary production measurements therefore require careful assessment of species-specific stage duration and between-stage growth when applying the MR method, and quantification of stage-specific live and dead individuals in the field.

Tank bromeliads sustain high secondary production in neotropical forests

In neotropical landscapes, a substantial fraction of the still waters available is found within tank bromeliads, plants which hold a few milliliters to several litres of rainwater within their leaf axils. The bromeliad ecosystem is integrated into the functioning of rainforest environments, but no study has ever estimated the secondary production, nor the biomass turnover rates of bromeliad macroinvertebrates in relation to other functional traits. We estimated secondary production at invertebrate population to metacommunity level in bromeliads of French Guiana. Coleoptera, Diptera and Crustacea with traits that confer resistance to drought had lower biomass turnover, longer generation times, and slower individual growth than species without particular resistance traits, suggesting convergent life history strategies in phylogenetically distant species. Detritivores and predators accounted for 87% and 13% of the overall annual production, respectively, but had similar production to biomass ratios. An average bromeliad sustained a production of 23.93 g dry mass m−2 year−1, a value which exceeds the medians of 5.0–14.8 g DM m−2 year−1 for lakes and rivers worldwide. Extrapolations to the total water volumes held by bromeliads at our field site yielded secondary production estimates of 226.8 ± 32.5 g DM ha−1 year−1. We conclude that the ecological role of tank bromeliads in neotropical rainforests may be as important as that of other freshwater ecosystems.

Life History, Growth, Survival, and Secondary Production of Ancyronyx variegatus (Germar, 1824) (Coleoptera: Elmidae) in Elk Creek, Erie County, Pennsylvania, USA

Abstract Larvae and adults of Ancyronyx variegatus (Germar, 1824) were collected monthly from Elk Creek, Erie County, Pennsylvania, USA. Ancyronyx variegatus has a univoltine life cycle with six instars. Primary recruitment months were April, May, and June, and adults were present throughout the year. The annual secondary production of A. variegata in Elk Creek was 0.55784 g/m2/yr. The mean standing stock biomass was 0.14296 g/m2, and the cohort production/biomass ratio was 3.902. The estimate of secondary production is important because it combines individual growth and population survivorship into a single measurement, which leads to a better understanding of the ecological importance of A. variegatus in the wood-dwelling aquatic insect community.

Population dynamics and secondary production of a key benthic tanaidacean, Monokalliapseudes schubarti (Mañé-Garzón, 1949) (Tanaidacea, Kalliapseudidae), from a tropical coastal lagoon in southeastern Brazil

Estimates of population dynamics and secondary production are important to understand the role of species in ecosystems and the mechanisms that drive life-history trade-offs, contributing to system preservation and monitoring. Population dynamics (growth rate, instantaneous mortality rates and longevity) and secondary production (biomass, production and P/B ratio) of the key marine benthic species Monokalliapseudes schubarti (Mañé-Garzón, 1949) were investigated monthly in a tropical coastal lagoon over 18 months and compared with data from other subtropical and temperate populations. A growth curve was estimated by fitting the Von Bertalanffy growth model. M. schubarti showed latitudinal variation in growth parameters. In tropical areas, M. schubarti generated consecutive cohorts and the growth curve parameters were: , , . A smaller asymptotic length was found for tropical and subtropical areas compared with data from temperate areas, and a lower growth rate was found at the tropical site. The annual mortality rate for the finite population was 0.999 year−1. Longevity, estimated at 10 months, was lower at the tropical site. The secondary production rate of M. schubarti at the tropical coastal lagoon was 10.60 g AFDW m−2 year−1, with a P/B ratio = 5.44. Brief longevity, a high P/B ratio, and high mortality may indicate M. schubarti as an opportunistic species in tropical areas.

RNA:DNA ratios as a proxy of egg production rates of Acartia

Estimates of copepod secondary production are of great importance to infer the global organic matter fluxes in aquatic ecosystems and species-specific responses of zooplankton to hydrologic variability. However, there is still no routine method to determine copepods secondary production in order to eliminate time consuming experimental analyses. Therefore, we determined whether there is a correlation between Egg Production Rates (EPR) and RNA:DNA ratios of Acartia species, by measuring their seasonal and spatial variability and the influence of environmental factors for Acartia sp. collected in the Guadiana river estuary. EPR of Acartia tonsa was positively related with chlorophyll a concentration, freshwater inflow and biomass of dinoflagellates, while Acartia clausi was only related to dinoflagellates. Dinoflagellates seem to be the optimal food item influencing the reproduction of both Acartia species in the studied area. The biochemical index RNA:DNA was positively related to EPR, indicating that it is a good proxy of copepod production and a promising method to use in the future to estimate secondary production.