Food Consumption of Pelagic Fish in an Upwelling Area

Secondary production of the benthic community was estimated in the four functional habitats identified in the pristine Pioverna stream (Northern Italy): riffle, pool, transition and bedrock habitats. The instantaneous growth, removal-summation and size-frequency methods were used to estimate production. Twelve taxa reached appreciable densities and presumably accounted for most of total benthic production. Three of them belong to the Plecoptera, seven to the Ephemeroptera and one each to Diptera and Trichoptera. The riffle habitat had the highest secondary production, while bedrock habitat had the lowest. Pool and transition habitats showed intermediate production values. Shredders and predators were the major component of production in pools, with a low contribution of gathering collectors. In riffles, this last category and scrapers had the highest production, with shredders, predators and filtering collectors showing decreasing production values. In general terms, shredders, gathering collectors and scrapers contributed most to total production. The rank-production curves for the habitats are reported. In riffles, a proportionally high evenness of the most productive taxa was noted. In contrast, in the pool habitat a steep curve was recognised. The potential of comparing rank/production curves and changes in reference species production between unaltered and impacted stream habitats and sites is discussed as a means to estimate ecological integrity. For site comparisons of secondary production in the alpine area, the riffle habitat is suggested as the most adequate, as it shows a lower dominance and more taxa contributing to overall production. The calculation of secondary production for indicator and dominant taxa in the different habitats should constitute an effective way to describe some functional aspects of the community to assess the ecological integrity of mountain streams.

The relationship between the food demand of a clam population (Ruditapes philippinarum (Adams & Reeve 1850)) and the isotopic contributions of potential food sources (phytoplankton, benthic diatoms, and organic matter derived from the sediment surface, seagrass, and seaweeds) to the clam diet were investigated. In particular, we investigated the manner in which dense patches of clams with high secondary productivity are sustained in a coastal lagoon ecosystem (Hichirippu Lagoon) in Hokkaido, Japan. Clam feeding behavior should affect material circulation in this lagoon owing to their high secondary productivity (ca. 130 g C m−2 yr−1). Phytoplankton were initially found to constitute 14–77% of the clam diet, although phytoplankton nitrogen content (1.79–4.48 kmol N) and the food demand of the clam (16.2 kmol N d–1) suggest that phytoplankton can constitute only up to 28% of clam dietary demands. However, use of isotopic signatures alone may be misleading. For example, the contribution of microphytobenthos (MPB) were estimated to be 0–68% on the basis of isotopic signatures but was subsequently shown to be 35±13% (mean ± S.D.) and 64±4% (mean ± S.D.) on the basis of phytoplankton biomass and clam food demand respectively, suggesting that MPB are the primary food source for clams. Thus, in the present study, the abundant MPB in the subtidal area appear to be a key food source for clams, suggesting that these MPB may sustain the high secondary production of the clam.

Thailand was proposed to be rich unexplored source of microorganisms, especially bacterial strains. There should be bacteria with high secondary metabolite production potential in the natural resources that are still unidentified. Moreover, they might not produce secondary metabolites in standard laboratory culture condition after isolation, in which coculture condition would help us pursuing the bacteria to produce bioactive metabolites. Here, we aimed to identify new bacterial strains with high secondary metabolite production potential from Thailand's natural resources. To achieve the goal, we performed bacteria isolation, phylogenetic analysis, degenerate PCR of secondary metabolism genes, cocultivation, antibacterial analysis, and HPLC chemical profiling. We isolated distinct 40 bacterial strains, which have over 98% 16S rRNA sequence similarity with known species. There were 22, 31, and 29 strains giving positive PCR amplification of NRPS, PKS, and TPS genes, respectively. Among them, Bacillus licheniformis RSUCC0101 had the highest number of PCR products, 26. In standard single culture condition, crude extracts prepared from Bacillus safensis RSUCC0021 and Bacillus amyloliquefaciens RSUCC0282 could inhibit the growth of Staphylococcus aureus ATCC25923. Furthermore, the cocultivation and HPLC analyses showed that the extracts prepared from 3 pairs of culture between Staphylococcus sp. RSUCC0020, Micrococcus luteus RSUCC0053, Staphylococcus sp. RSUCC0087, and Staphylococcus pasteuri RSUCC0090 could inhibit the growth of Staphylococcus aureus ATCC25923 and produced distinct chemical profiles from their single culture condition. Our study led to the isolation and identification of several promising bacterial strains for production of secondary metabolites that might be useful in biomedical applications.

The chironomids of Lake Mývatn show extreme population fluctuations that affect most aspects of the lake ecosystem. During periods of high chironomid densities, chironomid larvae comprise over 90% of aquatic secondary production. Here, we show that chironomid larvae substantially stimulate benthic gross primary production (GPP) and net primary production (NPP), despite consuming benthic algae. Benthic GPP in experimental mesocosms with 140,000 larvae/m2 was 71% higher than in mesocosms with no larvae. Similarly, chlorophyll a concentrations in mesocosms increased significantly over the range of larval densities. Furthermore, larvae showed increased growth rates at higher densities, possibly due to greater benthic algal availability in these treatments. We investigated the hypothesis that larvae promote benthic algal growth by alleviating nutrient limitation, and found that (1)larvae have the potential to cycle the entire yearly external loadings of nitrogen and phosphorus during the growing season, and (2) chlorophyll a concentrations were significantly greater in close proximity to larvae (on larval tubes). The positive feedback between chironomid larvae and benthic algae generated a net mutualism between the primary consumer and primary producer trophic levels in the benthic ecosystem. Thus, our results give an example in which unexpected positive feedbacks can lead to both high primary and high secondary production.

Agricultural land‐use affects the environmental and biological characteristics of stream ecosystems through multiple pathways including nutrient and pesticide contamination, riparian clear‐cutting and hydromorphological degradation. These changes in the abiotic environment can have a direct effect on the productivity of macroinvertebrate communities through environmental filtering and via altered resource conditions encompassing a shift from allochthonous to autochthonous primary production and changes in elemental stoichiometry and food quality. Additionally, macroinvertebrate productivity can be affected indirectly via biological mechanisms, such as changes in species interactions, richness, competition, and predation. We studied the effects of agriculture on structural and functional descriptors of macroinvertebrate communities by assessing environmental characteristics and macroinvertebrate secondary production (MSP), biomass and density in two forested and two agricultural streams and investigated underlying biotic mechanisms. On average, MSP was 1.6–3.6, biomass 2.8–6.2 and density 5–13 times higher in agricultural than in forested streams. This pattern was associated with higher nutrient concentrations, standing crops of riparian herbaceous vegetation, suspended particulate organic carbon, quantity and quality of epilithic biofilms and chlorophyll‐a concentrations in seston and biofilm of the agricultural streams. Species richness and evenness were significantly lower in agricultural than in forested streams. A negative relationship between MSP and species richness and evenness indicated that density compensation and trait dominance were the prevalent mechanisms facilitating higher MSP in agricultural streams. Our findings suggest that the loss of riparian canopy and excess nutrient conditions are the major environmental drivers contributing to homogenization of ecological niches and dominance of highly productive non‐insect generalist species. This study highlights the importance of an ecosystem approach to understanding how complex aggregate stressors affect the regulation of consumer–resource interactions. There is an urgent need to preserve or restore natural riparian vegetation, fostering habitat and resource diversity and limiting nutrient contamination to stream ecosystems. Read the free Plain Language Summary for this article on the Journal blog.

Coastal vegetated habitats such as seagrasses are known to play a critical role in carbon cycling and the potential to mitigate climate change, as blue carbon habitats have been repeatedly highlighted. However, little information is known about the role of associated macrofauna communities on the dynamics of critical processes of seagrass carbon metabolism (e.g., respiration, turnover, and production). We conducted a field study across a spatial gradient of seagrass meadows involving variable environmental conditions and macrobenthic diversity to investigate (1) the relationship between macrofauna biodiversity and secondary production (i.e., consumer incorporation of organic matter per time unit), and (2) the role of macrofauna communities in seagrass organic carbon metabolism (i.e., respiration and primary production). We show that, although several environmental factors influence secondary production, macrofauna biodiversity controls the range of local seagrass secondary production. We demonstrate that macrofauna respiration rates were responsible for almost 40% of the overall seafloor community respiration. Macrofauna represented on average >25% of the total benthic organic C stocks, high secondary production that is likely to become available to upper trophic levels of the coastal food web. Our findings support the role of macrofauna biodiversity in maintaining productive ecosystems, implying that biodiversity loss due to ongoing environmental change yields less productive seagrass ecosystems. Therefore, the assessment of carbon dynamics in coastal habitats should include associated macrofauna biodiversity elements if we aim to obtain robust estimates of global carbon budgets required to implement management actions for the sustainable functioning of the world's coasts.

Dimethylsulfoniopropionate (DMSP) is a biogenic chemical produced by marine algae that is associated with areas of high primary and secondary productivity in the ocean. In laboratory experiments, DMSP has been shown to be an effective feeding attractant for a variety of fresh and saltwater fishes, suggesting that it might also function as a foraging cue in the natural environment. Here we explore whether free-roaming pelagic fishes associate with periodic elevations of DMSP in their natural foraging habitat. Working in the vicinity of the coral reefs of the Flower Garden Banks in the Gulf of Mexico, we found that daily changes in the number of pelagic jack fishes (Carangidae) were significantly correlated with natural changes in concentrations of DMSP in the water column. These results provide the first evidence of a correlation between variation in the number of pelagic fishes and a specific habitat-associated chemical cue in the ocean.

A benthic survey was carried out from November 1998 to December 1999 in the tidal flats of Bahía Samborombón (Río de la Plata estuary, Argentina), in order to study the population structure, growth and secondary production of Laeonereis culveri. The samples were collected monthly in two intertidal areas with different environmental characteristics (San Clemente Creek and Punta Rasa). Growth was analysed using computer-based methods of length–frequency data (ELEFAN), and the secondary production was estimated by Crisp's and Hynes & Coleman's methods. Laeonereis culveri were recruited throughout the year, with two main peaks during spring and autumn. The autumn cohort showed growth rate (K) of 2 in San Clemente Creek and 1.8 in Punta Rasa. The seasonal oscillation of growth pointed out that worms grow very slowly during winter months. The life span of this cohort ranged from 15 to 17 months. The spring cohort showed higher growth rates in both sampled areas (K=3.3 in Punta Rasa and 3.1 in San Clemente Creek), whereas the growth oscillation showed similar values to those of the autumn cohort. The lowest growth rate was found in January and the life span was 9.5 months. The annual mean biomass in San Clemente Creek was 5.44 g m−2, with a mean production of 40.8 and 43.8 g m−2 y−1, according to the method used, and a production/biomass (P/B) ratio of 7.5 and 8 y−1 respectively. In Punta Rasa, the annual mean biomass (2.69 g m−2) and mean secondary production (19.44 and 23.61 g m−2 y−1, according to the method used) were lower than in San Clemente Creek, nevertheless the P/B ratio (7.2 and 8.7 y−1) was similar. The high secondary production and P/B ratio observed suggest that L. culveri transfer an important biomass to higher trophic levels, pointing out the very important role that this polychaete plays in the energy flux of this coastal estuarine ecosystem.

Dominant animals can indirectly regulate population dynamics and energy flow for many other species in an ecosystem by altering habitat structure and resource availability. However, we know little about the degree to which other taxa can compensate for the loss of these dominant species. By removing animals and measuring responses of other animals as secondary production it is possible to assess how much other taxa can perform similar functions of these dominant taxa. Here we tested the response of aquatic insect secondary production to the loss of a dominant detritivorous fish Prochilodus mariae, in a tropical river, Rio Las Marias, Venezuela. Using an impermeable, plastic curtain, we excluded Prochilodus from one half of a 235-m stream reach for 6 weeks. We measured insect production as biomass times empirically measured body mass-specific growth rates for 8 common taxa constituting 59–74% of insect biomass. Removing Prochilodus increased the standing stock of benthic organic sediment. Biomass of the entire assemblage increased 1.7-fold and insect production for 8 taxa tripled upon exclusion of Prochilodus. Two fast-growing mayfly genera, Tricorythodes and Leptohyphes drove the increased secondary production. Despite low biomass of insects, growth rates were among the highest measured for freshwater insects, and these high growth rates in part caused high secondary production. Although insect production was high in the exclusion reach, insects did not compensate for the loss of Prochilodus in terms of consuming organic sediment showing that the capacity of detritivorous fish to process sediments is higher than that for aquatic insects in this tropical river.

SUMMARY 1. Secondary production of chironomids (Diptera: Chironomidae) in a third‐order northern Indiana stream was estimated using species‐specific, and in most cases cohort‐specific, life‐history data from the field.2. Chironomid life‐history patterns were diverse, ranging from one to four generations per year in addition to asynchronous development. Cohort production intervals (CPI) for all taxa ranged from 56 to 266 days. CPI for cohorts of conspecifics differed up to 3‐fold.3. Annual secondary production was estimated using the instantaneous growth method or the size—frequency method depending on whether cohorts were distinguishable or not. Total annual chironomid production was 29 700 mg dry mass m−2, which is the highest value reported for chironomids from a north temperate stream.4. Eighty per cent of the total chironomid production was attributed to five species: Diamesa nivoriunda (33.9%), Cricotopus bicinctus (16.6%), Pagastia sp. (10.2%), C. trifascia (9.7%) and Orthodadius obumbratus (9.6%).5. The annual P:B ratio ranged from 4.7 to 21.9. Thus, high secondary production was due to high mean annual standing stocks and not to rapid biomass turnover.

Tidal marshes accumulate large quantities of biogenic silica which accumulates in sediments, in plants and in porewaters. Higher salinity tidal marshes lower in the estuary contain higher levels of biogenic silica than those in the upper portion. Vascular plants, Spartina alterniflora and Juncus roemerianus, contain approximately 0.5% (by weight) biogenic silica, which does not vary along the estuarine gradient. The tidal marsh is an efficient biogenic silica trap, concentrating biogenic silica and dissolved silicate above levels found in nearby estuarine waters. High dissolved silicate levels provide ample silicon for benthic diatoms. We hypothesize that diatoms sequester silicate from surface waters supplied by tides and freshwater runoff. These benthic diatoms are eventually consumed and deposited into marsh sediments by macrofauna where their tests are dissolved into the marsh porewater. Vascular plants remove silicate from porewater and deposit amorphous silica into cell walls where it remains until liberated by decomposition into surface water where it can again be taken up by diatoms. Drainage of porewater containing high concentrations of dissolved silicate from marsh sediments is very slow, so flux of dissolved silicate from marsh sediments is uncoupled from the flux of surface water. Most porewater is released when tides are near low or rising resulting in the retention of silicate in the marsh/creek system. High concentrations of biogenic silica in tidal marshes are necessary for maximum benthic diatom production which in turn is necessary for high secondary production of commercial fish and crustaceans. Created tidal wetlands may require many years to concentrate biogenic silica sufficient to maintain high secondary production via the benthic diatom grazing foodchain.KeywordsSalt MarshVascular PlantParticulate Organic CarbonTidal MarshSecondary ProductionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Understanding marine mercury (Hg) biogeochemistry is crucial, as the consumption of Hg-enriched ocean fish is the most important pathway of Hg uptake in humans. Although ocean sediments are seen as the ultimate Hg sink, marine sediment studies on Hg accumulation are still rare. In this context, studying Hg behavior in the marine environment, especially in upwelling environments, is of particular interest due to its importance in these great upwelling regions for the global fishery. There are contradictory statements about the fate of Hg in upwelling regions. Some studies have suggested high biotic reduction of oxidized Hg and gaseous elemental mercury evasion to the atmosphere. More recent work has suggested that in upwelling regions, where productivity is high, evasion of gaseous elemental mercury is diminished due to scavenging and sedimentation of Hg by organic particles. In this study, we compared Hg concentrations and accumulation rates in the past ∼4,300 and 19,400 years derived from sediment cores collected in the Peruvian upwelling region (Peru Margin) and compared them with those of two other cores collected from the sediment fan of the Amazon and a core from the Congo Basin, which is influenced by both seasonal coastal upwelling and discharge from the river. Median Hg concentrations were higher at the Peru Margin (90.7 μg kg–1) and in the Congo Basin (93.4 μg kg–1) than in the Amazon Fan (35.8 μg kg–1). The average Hg accumulation rates in sediments from the Peru Margin (178 μg m–2 yr–1) were factors of ∼4 and ∼39 times higher than those from the Congo Basin (46.7 μg m–2 yr–1) and Amazon Fan (4.52 μg m–2 yr–1), respectively. Principal component analysis (PCA) of the geochemical data set reveals that Amazon Fan sediments are strongly influenced by the deposition of terrestrial material, which is of less importance in the Congo Basin and of minor importance in Peru Margin sediments. Accordingly, Hg export to sediments in upwelling areas largely surpasses that in fans of large rivers that drain large terrestrial catchments. The high Hg accumulation rates in the sediments from the upwelling area and the minor influence of terrestrial Hg fluxes there suggest that atmospheric-derived Hg in upwelling areas is effectively exported to the sediments through scavenging by organic particles.

<em> Abstract.</em>—The region of the outer continental shelf and upper slope, encompassed roughly by 32 and 33°N and 78 and 79°W, is unique within the southeastern Atlantic coast of the United States because of the frequent presence of large (amplitudes of 50-100 km), cyclonic eddies. These eddies develop continuously north of the deflection of the Gulf Stream at the Charleston Bump and decay downstream. The cyclonic circulation of these eddies brings nutrient-rich water from deep and off the shelf edge to near surface and results in enhanced primary production. Succession of Zooplankton assemblages, driven by enhanced primary production, might serve fish production by providing an exceptional, and more continuous food supply for larval fishes spawned in or entrained into eddies. In addition, larval fishes that risk entrainment into the Gulf Stream and consequent loss from local populations, can be retained on, or near, the shelf when embedded within these eddies. The residence of an eddy within the region ranges from a week to a month or two, while the larval period of most fishes ranges from weeks to months. The large-scale eddies in the region develop most frequently in winter when the Gulf Stream is in its strongly deflected mode, coincident with the spawning of a suite of commercially important fishes. Although the region of the Charleston Gyre has the potential to act as an important spawning and nursery habitat, published evidence of usage of the habitat afforded by large scale eddies in this region is weak. High concentrations of larval fishes occasionally occur in the region, but there is no indication of high concentrations of fish eggs. With its high primary and secondary production, succession of Zooplankton assemblages, and retention mechanism, the region of the Gyre may constitute an important spawning and nursery habitat for fishes, but more research aimed at assessing this potential is necessary.

Chapter 22 - Ecosystem Functioning and Sustainable Management in Coastal Systems With High Freshwater Input in the Southern Gulf of Mexico and Yucatan Peninsula

Sediments underneath the high productivity areas of the coastal upwelling and equatorial divergence zones in the Pacific and Indian oceans are enriched in barium, and on this basis the barium content of the sediments has long been suggested as a potential palaeoproductivity indicator. Analyses of sediments from the Peru margin corroborate the pattern of enhanced barium accumulation in areas of high primary productivity in the deep ocean, but also show that this pattern cannot be extended to shallow-water deposits. Sediments from the Peru shelf lack any barium enrichment, whereas this element is significantly enriched in slope and basinal deposits in water columns deeper than 2000 m. This depth effect is further illustrated at Site 682 located in the rapidly subsiding Lima Basin. The Quaternary sequence deposited at water depths >3000 m is enriched in organic carbon, opal and biogenic barium. The Miocene sediments, although deposited under highly productive waters associated with a coastal upwelling centre, do not show an enrichment in the barium record corresponding to the very high organic carbon and opal levels; a pattern that is consistent with deposition in shallow basins. In addition to the effect of water depth on the barium distribution, overprinting of primary signals can be observed in sediments from upwelling areas undergoing strong anoxic diagenesis. Microcrystalline barite is partly dissolved in intervals depleted in interstitial sulphate as shown for sediments from the Peru margin. Dissolution of barite in sulphate depleted intervals of deep water sections leads to high barium concentrations near the termination of the sulphate reducing zone, where downward sulphate and upward barium diffusion foster local barite precipitation in diagenetic fronts. The barium distribution in sedimentary oxic and suboxic environments at deep water depositional sites has a high potential as a palaeoproductivity indicator; however, barium accumulation as a proxy for ocean fertility should be used with caution in areas of varying water depths and in anoxic diagenetic environments where sulphate depletion undersaturates the interstitial waters with respect to barite.