Prey Concentrations Research Articles

On steadyness of stereotypes in conceptions on marine ecology of pacific salmons (Oncorhynchus spp.)

Some conceptions on marine ecology of pacific salmons (Oncorhynchus spp.), established in the second half of the last century, are discussed from critical position, as overemphasizing of the sea surface temperature influence on distribution of salmons and formation of their year-classes strength, deficiency of food (particularly in winter time) and fierce competition for food, pink salmon «suppression» over other salmon species and own adjacent generations, limited carrying capacity of the Subarctic zone for salmons, distortion of the epipelagic communities structure in the North Pacific by mass artificial reproduction of chum salmon, etc. Most of these ideas have not been confirmed by the data of long-term monitoring in complex marine expeditions conducted by Pacific Fish. Res. Center (TINRO) in the Far-Eastern Seas and adjacent North Pacific waters since the 1980s till nowadays. The data show that pacific salmons are very ecologically plastic species with wide temperature range of habitat. Salmons are able to considerable vertical migrations crossing easily the temperature gradient zones and different water masses. They have wide feeding spectra. Migrating dispersed, they successfully get their ration, even in vast areas with relatively low concentration of prey (macroplankton and small nekton). Total biomass of all species of pacific salmons in the North Pacific does not exceed 4-5 million tons (1.5-2.0 million tons in the Russian waters), whereas the stocks of other mass species of nekton are hundreds of millions of tons. The salmons consume 1.0-5.0 % of the total consumption by nekton in the epipelagic layer in the western Bering Sea, 0.5-1.0 % in the Okhotsk Sea, 5.0-15.0 % at East Kamchatka, and less than 1 % in the Pacific waters at Kuril Islands, So, the role of pacific salmons in trophic nets of the Subarctic waters is rather moderate. Therefore, neither pink salmon, nor chum salmon can be seriously considered as the species responsible for reorganization of large ecosystems and fluctuating of other mass nekton species.

A production season of turbot larvaeScophthalmus maximus(Linnaeus, 1758) reared on copepods in a Danish (56°N) semi-intensive outdoor system

Turbot were reared from yolk sack larvae to juvenile in an outdoor semi-intensive system. Three production cycles were monitored from May to September. A pelagic food chain was established with phytoplankton, copepods and turbot larvae. Abiotic and biotic parameters of lower trophic levels together with turbot larval survival, development, prey electivity and growth were monitored. A decreasing larval survival from 18.4% in May to 13.6% in July and just 7.0% in September was observed. The overall phytoplankton and copepod abundance decreased during the productive season. The turbot larval growth showed significant differences between larvae below (isometric) and above (allometric) 7 mm. Larval fish gut content showed no differences with available prey between production cycles. Therefore, it appears that the available prey concentration is governing their growth in this outdoor system. First-feeding turbot larvae exhibited active selection for nauplii whereas developed larvae switched to copepodites and adult copepods. Although developing turbot larva exhibited active selection towards copepod size classes, there was no evidence of selective feeding on either of the two dominant copepod species. The turbot larvae's prey ingestion was modelled together with the standing stock of copepod biomass. The model results indicated that the estimated need for daily ingestion exceeded the standing stock of copepods. Hence, the initially established food web was unable to sustain the added turbot larvae with starvation as a consequence. We therefore suggest several solutions to circumvent starvation in the semi-intensive system.

Modeling Nonresident Seabird Foraging Distributions to Inform Ocean Zoning in Central California.

Seabird aggregations at sea have been shown to be associated with concentrations of prey. Previous research identified Central California as a highly used foraging area for seabirds, with locally breeding seabirds foraging close to their colonies on Southeast Farallon Island. Herein, we focus on nonresident (i.e. non-locally breeding) seabird species off of Central California. We hypothesized that high-use foraging areas for nonresident seabirds would be influenced by oceanographic and bathymetric factors and that spatial and temporal distributions would be similar within planktivorous and generalist foraging guilds but would differ between them. With data collected by the Applied California Current Ecosystem Studies (ACCESS) partnership during cruises between April and October from 2004–2013, we developed generalized linear models to identify high-use foraging areas for each of six nonresident seabird species. The four generalist species are Phoebastria nigripes (black-footed albatross), Ardenna griseus (sooty shearwater), Ardenna creatopus (pink-footed shearwater), and Fulmarus glacialis (northern fulmar). The two planktivorous species are Phalaropus lobatus (red-necked phalarope) and Phalaropus fulicarius (red phalarope). Sea surface temperature was significant for generalist species and sea surface salinity was important for planktivorous species. The distance to the 200-m isobath was significant in five of six models, Pacific Decadal Oscillation with a 3-month lag in four models, and sea surface fluorescence, the distance to Cordell Bank, and depth in three models. We did not find statistically significant differences between distributions of individual seabird species within a foraging guild or between guilds, with the exception of the sooty shearwater. Model results for a multi-use seabird foraging area highlighted the continental shelf break, particularly within the vicinity of Cordell Bank, as the highest use areas as did Marxan prioritization. Our research methods can be implemented elsewhere to identify critical habitat that needs protection as human development pressures continue to expand to the ocean.

Mixotrophy in the newly described dinoflagellate Yihiella yeosuensis: A small, fast dinoflagellate predator that grows mixotrophically, but not autotrophically

To investigate tropical roles of the newly described Yihiella yeosuensis (ca. 8μm in cell size), one of the smallest phototrophic dinoflagellates in marine ecosystems, its trophic mode and the types of prey species that Y. yeosuensis can feed upon were explored. Growth and ingestion rates of Y. yeosuensis on its optimal prey, Pyramimonas sp. (Prasinophyceae), as a function of prey concentration were measured. Additionally, growth and ingestion rates of Y. yeosuensis on the other edible prey, Teleaulax sp. (Cryptophyceae), were also determined for a single prey concentration at which both these rates of Y. yeosuensis on Pyramimonas sp. were saturated. Among bacteria and diverse algal prey tested, Y. yeosuensis fed only on small Pyramimonas sp. and Teleaulax sp. (both cell sizes=5.6μm). With increasing mean prey concentrations, both specific growth and ingestion rates of Y. yeosuensis increased rapidly before saturating at a mean Pyramimonas concentration of 109ngCmL−1 (2725cellsmL−1). The maximum growth rate (mixotrophic growth) of Y. yeosuensis fed with Pyramimonas sp. at 20°C under a 14:10-h light-dark cycle of 20μEm−2s−1 was 1.32d−1, whereas the growth rate of Y. yeosuensis without added prey was 0.026d−1. The maximum ingestion rate of Y. yeosuensis fed with Pyramimonas sp. was 0.37ngCpredator−1d−1 (9.3cellspredator−1d−1). At a Teleaulax concentration of 1130ngCmL−1 (66,240cellsmL−1), growth and ingestion rates of Y. yeosuensis fed with Teleaulax sp. were 1.285d−1 and 0.38ngCpredator−1d−1 (22.4cellspredator−1d−1), respectively. Thus, Y. yeosuensis rarely grows without mixotrophy, and mixotrophy supports high growth rates in Y. yeosuensis. Y. yeosuensis has the highest maximum mixotrophic growth rate with the exception of Ansanella graniferaamong engulfment feeding mixotrophic dinoflagellates. However, the high swimming speed of Y. yeosuensis (1572μms−1), almost the highest among phototrophic dinoflagellates, may prevent autotrophic growth. This evidence suggests that Y. yeosuensis may be an effective mixotrophic dinoflagellate predator on Pyramimonas and Teleaulax, and occurs abundantly during or after blooms of these two prey species.

Differential interactions between the nematocyst-bearing mixotrophic dinoflagellate Paragymnodinium shiwhaense and common heterotrophic protists and copepods: Killer or prey

To investigate interactions between the nematocyst-bearing mixotrophic dinoflagellate Paragymnodinium shiwhaense and different heterotrophic protist and copepod species, feeding by common heterotrophic dinoflagellates (Oxyrrhis marina and Gyrodinium dominans), naked ciliates (Strobilidium sp. approximately 35μm in cell length and Strombidinopsis sp. approximately 100μm in cell length), and calanoid copepods Acartia spp. (A. hongi and A. omorii) on P. shiwhaense was explored. In addition, the feeding activities of P. shiwhaense on these heterotrophic protists were investigated. Furthermore, the growth and ingestion rates of O. marina, G. dominans, Strobilidium sp., Strombidinopsis sp., and Acartia spp. as a function of P. shiwhaense concentration were measured. O. marina, G. dominans, and Strombidinopsis sp. were able to feed on P. shiwhaense, but Strobilidium sp. was not. However, the growth rates of O. marina, G. dominans, Strobilidium sp., and Strombidinopsis sp. feeding on P. shiwhaense were very low or negative at almost all concentrations of P. shiwhaense. P. shiwhaense frequently fed on O. marina and Strobilidium sp., but did not feed on Strombidinopsis sp. and G. dominans. G. dominans cells swelled and became dead when incubated with filtrate from the experimental bottles (G. dominans+P. shiwhaense) that had been incubated for one day. The ingestion rates of O. marina, G. dominans, and Strobilidium sp. on P. shiwhaense were almost zero at all P. shiwhaense concentrations, while those of Strombidinopsis sp. increased with prey concentration. The maximum ingestion rate of Strombidinopsis sp. on P. shiwhaense was 5.3ngC predator−1d−1 (41 cells predator−1d−1), which was much lower than ingestion rates reported in the literature for other mixotrophic dinoflagellate prey species. With increasing prey concentrations, the ingestion rates of Acartia spp. on P. shiwhaense increased up to 930ngCml−1 (7180cellsml−1) at the highest prey concentration. The highest ingestion rate of Acartia spp. on P. shiwhaense was 4240ngC predator−1d−1 (32,610 cells predator−1d−1), which is comparable to ingestion rates from previous studies on other dinoflagellate prey species calculated at similar prey concentrations. Thus, P. shiwhaense might play diverse ecological roles in marine planktonic communities by having an advantage over competing phytoplankton in anti-predation against potential protistan grazers.

Effects of feeding frequency of live prey on larval growth, survival, resistance to hyposalinity stress, Na+/K+ ATPase activity, and fatty acid profiles in black sea bass Centropristis striata

Feeding live prey organisms in a commercial marine fish hatchery requires significant labor and resources. The effects of feeding frequency of live rotifers and Artemia on growth, survival, hyposalinity stress resistance, and Na+/K+ ATPase activity in black sea bass larvae Centropristis striata were evaluated. Newly hatched larvae (day 0 post-hatching=d0ph) were stocked (53larvae/L) into twenty-four 30-L tanks supported by a recirculating seawater (35g/L) system in a controlled-environment laboratory. Temperature (22°C), aeration (225mL/min), light intensity (~1000lx), and photoperiod (18L: 6 D) were constant. Beginning on d3ph, larvae were fed a prescribed daily ration of live prey (enriched s-type rotifers and/or Artemia nauplii), but distributed at different frequencies: (1) 1×/d at 0800h, (2) 2×/d at 0800 and 1600h, (3) 3×/d at 0800, 1200 and 1600h, and (4) 4×/d at 0800, 1200, 1600 and 2000h, with six replicate tanks per treatment. The daily ration of live prey (maximum of 750,000 rotifers and 90,000 Artemia) was divided equally among feedings; therefore, prey density at each feeding (i.e., meal size) decreased at higher frequencies. By d31ph, larvae fed 4×/d showed significantly (P<0.05) greater notochord length and SGR (mean±s.e.=7.05±0.20mm and 20.1±0.467%/d) compared to larvae fed 1×/d (6.02±0.11mm, and 18.1±0.204%/d) or 2×/d (6.08±0.12mm and 18.4±0.399%/d). Feeding frequency had no effect on larval survival (23.8–38.2%) or whole body fatty acid composition. Ability to withstand an acute hyposalinity (10g/L) challenge on d32ph was significantly poorer in larvae fed 1×/d than in those fed 2×/d, 3×/d or 4×/d. Following transfer to a sub-lethal salinity (15g/L) on d32ph, Na+/K+ ATPase activity (μmol ADP/mg protein/h) was higher in larvae fed 3×/d (5.61) than in those fed 4×/d (5.22) or 1×/d (5.20). The largest larvae (4×/d treatment) showed reduced Na+/K+ ATPase activity (vs 3×/d), likely due to accelerated development and a shifting of the Na+/K+ ATPase from a global distribution to specialized osmoregulatory sites. The results demonstrated that, for a prescribed total daily ration, feeding lower prey densities (smaller meals) at higher frequencies (3×/d or 4×/d) improved larval growth and resistance to hyposalinity stress and may increase osmoregulatory ability, without affecting survival. These findings delineate more judicious use of limited live prey resources to maximize larval growth and vitality during hatchery production of pre-metamorphic stage black sea bass. Statement of relevanceLive prey (rotifers and Artemia) are expensive to produce and can limit production of juvenile fish in a commercial marine fish hatchery. The results show that given a prescribed (albeit moderate) total daily ration of prey, feeding lower prey concentrations at higher frequencies optimized larval growth performance and vitality in black sea bass raised from first-feeding through pre-metamorphic stages.

Mixotrophy in the phototrophic dinoflagellate Takayama helix (family Kareniaceae): Predator of diverse toxic and harmful dinoflagellates

Takayama spp. are phototrophic dinoflagellates belonging to the family Kareniaceae and have caused fish kills in several countries. Understanding their trophic mode and interactions with co-occurring phytoplankton species are critical steps in comprehending their ecological roles in marine ecosystems, bloom dynamics, and dinoflagellate evolution. To investigate the trophic mode and interactions of Takayama spp., the ability of Takayama helix to feed on diverse algal species was examined, and the mechanisms of prey ingestion were determined. Furthermore, growth and ingestion rates of T. helix feeding on the dinoflagellates Alexandrium lusitanicum and Alexandrium tamarense, which are two optimal prey items, were determined as a function of prey concentration. T. helix ingested large dinoflagellates ≥15μm in size, except for the dinoflagellates Karenia mikimotoi, Akashiwo sanguinea, and Prorocentrum micans (i.e., it fed on Alexandrium minutum, A. lusitanicum, A. tamarense, A. pacificum, A. insuetum, Cochlodinium polykrikoides, Coolia canariensis, Coolia malayensis, Gambierdiscus caribaeus, Gymnodinium aureolum, Gymnodinium catenatum, Gymnodinium instriatum, Heterocapsa triquetra, Lingulodinium polyedrum, and Scrippsiella trochoidea). All these edible prey items are dinoflagellates that have diverse eco-physiology such as toxic and non-toxic, single and chain forming, and planktonic and benthic forms. However, T. helix did not feed on small flagellates and dinoflagellates <13μm in size (i.e., the prymnesiophyte Isochrysis galbana; the cryptophytes Teleaulax sp., Storeatula major, and Rhodomonas salina; the raphidophyte Heterosigma akashiwo; the dinoflagellates Heterocapsa rotundata, Amphidinium carterae, Prorocentrum minimum; or the small diatom Skeletonema costatum). T. helix ingested Heterocapsa triquetra by direct engulfment, but sucked materials from the rest of the edible prey species through the intercingular region of the sulcus. With increasing mean prey concentration, the specific growth rates of T. helix on A. lusitanicum and A. tamarense increased continuously before saturating at prey concentrations of 336–620ngC mL−1. The maximum specific growth rates (mixotrophic growth) of T. helix on A. lusitanicum and A. tamarense were 0.272 and 0.268d−1, respectively, at 20°C under a 14:10 h light/dark cycle of 20μE m−2 s−1 illumination, while its growth rates (phototrophic growth) under the same light conditions without added prey were 0.152 and 0.094d−1, respectively. The maximum ingestion rates of T. helix on A. lusitanicum and A. tamarense were 1.23 and 0.48ng C predator−1d−1, respectively. The results of the present study suggest that T. helix is a mixotrophic dinoflagellate that is able to feed on a diverse range of toxic species and, thus, its mixotrophic ability should be considered when studying red tide dynamics, food webs, and dinoflagellate evolution.

Observing Extremely Weak Protein-Protein Interactions with Conventional Single-Molecule Fluorescence Microscopy.

Extremely weak protein-protein interactions (PPIs), signified by micromolar or even millimolar dissociation constants, are one of the keys to understanding the rapid responses of cellular systems. Although single-molecule methods are particularly useful in determining kinetics of biological processes, their application is largely limited to rather strong interactions because of the diffraction-limited observation volume. In this study, we report a single-molecule method that allows the characterization of PPIs using a prey concentration 4 orders of magnitude lower than the dissociation constant. Instead of increasing the concentration of diffusing molecules, which is inevitably limited by the optical diffraction limit, we employed an increased density of surface bait protein. The low occupancy of the surface baits permitted determination of the kinetics with single-molecule resolution. We used this approach to study a PPI network consisting of Ras and its downstream proteins including full-length Rafs and catalytic subunits of phosphoinositide 3-kinase.

Wind-dependent beluga whale dive behavior in Barrow Canyon, Alaska

Beluga whales (Delphinapterus leucas) are the most abundant cetacean in the Arctic. The Barrow Canyon region, Alaska, is a hotspot for Pacific Arctic belugas, likely because the oceanographic environment provides reliable foraging opportunities. Fronts are known to promote the concentration of planktonic prey; when Barrow-area winds are weak or from the west, a front associated with the Alaskan Coastal Current (ACC) intensifies. This front is weakened or disrupted when strong easterly winds slow or displace the ACC. To determine if winds influence the diving depth of belugas, we used generalized linear mixed models (GLMM) to examine how the dive behavior of animals instrumented with satellite-linked time-depth recorders varied with wind conditions. When projected along-canyon winds are from the WSW and the front associated with the ACC is enhanced, belugas tend to target shallower depths (10–100m) associated with the front. In contrast, when strong winds from the ENE displaced the ACC, belugas tended to spend more time at depths >200m where the Arctic halocline grades into relatively warmer Atlantic Water (AW). The probability of diving to >200m, the number of dives >200m, and the amount of time spent below 200m were all significantly related to along-canyon wind stress (p<0.01). From these results and known relationships between wind stress, currents and frontal structure in Barrow Canyon and the characteristic vertical distribution of Arctic cod, we infer that the probability of belugas targeting different depth regimes is based upon how wind stress affects the relative foraging opportunities between these depth regimes. Belugas are known to target AW throughout the Beaufort Sea; however, this is the first work to show that the probability of targeting the AW layer is related to wind stress.

Mixotrophic ability of the phototrophic dinoflagellates Alexandrium andersonii, A. affine, and A. fraterculus

The dinoflagellate Alexandrium spp. have received much attention due to their harmful effects on diverse marine organisms, including commercially important species. For minimizing loss due to red tides or blooms of Alexandrium spp., it is very important to understand the eco-physiology of each Alexandrium species and to predict its population dynamics. Its trophic mode (i.e., exclusively autotrophic or mixotrophic) is one of the most critical parameters in establishing prediction models. However, among the 35 Alexandrium species so far described, only six Alexandrium species have been revealed to be mixotrophic. Thus, mixotrophic ability of the other Alexandrium species should be explored. In the present study, whether each of three Alexandrium species (A. andersonii, A. affine, and A. fraterculus) isolated from Korean waters has or lacks mixotrophic ability, was investigated. When diets of diverse algal prey, cyanobacteria, and bacteria sized micro-beads were provided, A. andersonii was able to feed on the prasinophyte Pyramimonas sp., the cryptophyte Teleaulax sp., and the dinoflagellate Heterocapsa rotundata, whereas neither A. affine nor A. fraterculus fed on any prey item. Moreover, mixotrophy elevated the growth rate of A. andersonii. The maximum mixotrophic growth rates of A. andersonii on Pyramimonas sp. under a 14:10h light/dark cycle of 20μEm−2s−1 was 0.432d−1, while the autotrophic growth rate was 0.243d−1. With increasing mean prey concentration, the ingestion rate of A. andersonii increased rapidly at prey concentrations <650ngCml−1 (ca. 16,240 cellsml−1), but became saturated at the higher prey concentrations. The maximum ingestion rate by A. andersonii of Pyramimonas sp. was 1.03ngC predator−1d−1 (25.6 cells predator−1d−1). This evidence suggests that the mixotrophic ability of A. andersonii should be taken into consideration in predicting the outbreak, persistence, and decline of its harmful algal blooms.

독도 인근해역 동물플랑크톤 장기간 특성

2006년부터 2015년까지 동해 독도 인근해역에서 동물플랑크톤 군집의 변동특성을 조사하였다. 동물플랑크톤 시료는 고정정점의 수온약층 상부수층에서 표준네트로 수직예인하여 획득하였다. 평균수온과 염분은 장기적으로 뚜렷한 변화는 없었으나, 2013년과 2015년 여름철에 상대적으로 낮은 염분이 관측되었다. 동물플랑크톤 평균 개체수는 여름철 기준으로 <TEX>$317inds./m^3$</TEX>(2008년)부터 <TEX>$10,242inds./m^3$</TEX>(2015년)까지 증가추세를 나타냈고, 동물플랑크톤 장기간 증가는 먹이생물인 엽록소-a 농도 증가와 잠재적 포식자인 주요 어류(멸치, 꽁치, 오징어, 청어, 전갱이)의 어획생산량 감소와 같이 나타났다. 증가를 주도한 우점종은 점진적으로 증가하는 유형류(Oikopleura spp.), 여름철에 주로 출현하며 2012년 이후 급속히 증가한 야광충(Noctiluca scintillans)과 지각류(Penilia avirostris), 그리고 2010년 여름철에 출현하기 시작하여 빠른 속도로 증가한 요각류(Paracalanus parvus s.l.)로 구분되었다. 본 연구결과는 독도주변해역에서 장기간 증가한 동물플랑크톤 개체수가 먹이농도의 증가와 상위포식자의 포식압 감소와 관련있음을 시사하였다. We investigated the abundance and composition of the zooplankton community around Dokdo in the East Sea from 2006 to 2015. Zooplankton samples were collected in the surface mixed layer by vertical hauls using a standard type net at the monitoring stations. There were no clear long-term trends in the average temperature and salinity, but relatively low salinity was recorded in the summer of 2013 and 2015. The average abundances of zooplankton in the summer increased by two orders of magnitude from <TEX>$317inds./m^3$</TEX> in 2008 to <TEX>$10,242inds./m^3$</TEX> in 2015. This long-term increase was accompanied by a slight increase in the chlorophyll-a concentration and a decrease in the catch of potential crucial predators (anchovy, mackerel pike, squid, herring and horse mackerel) in the study area. The dominant zooplankton, accounting for most of the long-term increase, consisted of appendicularian (Oikopleura spp.), which showed a steady increase since 2012, summer species such as Noctiluca scintillans and the cladoceran Penilia avirostris, which showed an abrupt increase, and the copepod Paracalanus parvus s.l., which showed a rapid increase after its first occurrence in summer 2010. These results suggest that the long-term increase of zooplankton could be related to the increase in the concentration of prey and the decrease in the predation pressure of potential predators around Dokdo in the study area.

Growth, Grazing, and Starvation Survival in Three Heterotrophic Dinoflagellate Species.

To assess the effects of fluctuating prey availability on predator population dynamics and grazing impact on phytoplankton, we measured growth and grazing rates of three heterotrophic dinoflagellate species-Oxyrrhis marina, Gyrodinium dominans and Gyrodinium spirale-before and after depriving them of phytoplankton prey. All three dinoflagellate species survived long periods (>10d) without algal prey, coincident with decreases in predator abundance and cell size. After 1-3wks, starvation led to a 17-57% decrease in predator cell volume and some cells became deformed and transparent. When re-exposed to phytoplankton prey, heterotrophs ingested prey within minutes and increased cell volumes by 4-17%. At an equivalent prey concentration, continuously fed predators had ~2-fold higher specific growth rates (0.18 to 0.55d-1 ) than after starvation (-0.16 to 0.25d-1 ). Maximum specific predator growth rates would be achievable only after a time lag of at least 3d. A delay in predator growth poststarvation delays predator-induced phytoplankton mortality when prey re-emerges at the onset of a bloom event or in patchy prey distributions. These altered predator-prey population dynamics have implications for the formation of phytoplankton blooms, trophic transfer rates, and potential export of carbon.

Effect of the silica content of diatom prey on the production, decomposition and sinking of fecal pellets of the copepod &amp;lt;i&amp;gt;Calanus sinicus&amp;lt;/i&amp;gt;

Abstract. The effects of changing the amount of silica in the cell wall of diatom prey, on the production, decomposition rate and sinking velocity of fecal pellets of the calanoid copepod, Calanus sinicus, were examined. Using different light intensities to control the growth of the diatom Thalassiosira weissflogii also led to the accumulation of different amounts of biogenic silica. Copepods were then fed either low ( ∼ 1600 cells L−1) or high ( ∼ 8000 cells L−1) concentrations of this diatom. Copepods fed a high concentration of diatoms with high-silica content exhibited a lower grazing rate and lower fecal pellet production rate than those fed a high concentration of diatoms with low-silica content. However, there was no difference in either the grazing or fecal pellet production rates at low prey concentrations with high- or low-silica content. The size of the fecal pellets produced was only affected by the prey concentration, and not by the silica content of prey. In addition, the degradation rate of the fecal pellets was much higher for copepods fed a low-silica diet than for those fed a high-silica diet. Significantly lower densities and sinking rates only occurred in the fecal pellets of copepods fed a low-silica diet and a low prey concentration. Calculating the L ratio (the ratio of degradation rate : sinking rate) for each group indicated that the fecal pellets produced by copepods fed highly silicified diatoms are likely to transport both biogenic silica and organic carbon to the deep layer, whereas those produced following the consumption of low-silica diatoms are likely to decompose in the mixing layer.

A mixed hyperbolic-parabolic system to describe predator-prey dynamics

Following [2], a model aiming at the description of two competing populations is introduced. In particular, it is considered a nonlinear system consisting of a nonlocal conservation law for predators coupled with a parabolic equation for prey. The drift term in the equation for predators is in general a nonlocal and nonlinear function of the prey density: the movement of predators can hence be directed towards regions where the concentration of prey is higher. Lotka-Volterra type right hand sides describe the feeding. In [2] the resulting Cauchy problemis proved to be well posed in any space dimension with respect to the L1 topology, and estimates on the growth of the solution in L1 and L∞ norm and on the time dependence are provided. Numerical integrations show a few qualitative features of the solutions.

Feeding by the newly described heterotrophic dinoflagellate Aduncodinium glandula: having the most diverse prey species in the family Pfiesteriaceae

2Advanced Institutes of Convergence Technology, Suwon 16229, Korea To explore the feeding ecology of the newly described heterotrophic dinoflagellate Aduncodinium glandula in the family Pfiesteriaceae, its feeding behavior and prey species were investigated. Additionally, the growth and ingestion rates of A. glandula on the mixotrophic dinoflagellates Heterocapsa triquetra and Akashiwo sanguinea, its optimal and suboptimal prey, respectively were measured. A. glandula fed on prey through a peduncle after anchoring to the prey using a tow filament. A. glandula ate all algal prey and perch blood cells tested and had the most diverse prey species in the family Pfiesteriaceae. Unlike for other pfiesteriacean species, H. triquetra and A. sanguinea support the positive growth of A. glandula. However, the cryptophytes Rhodomonas salina and Teleaulax sp. and the phototrophic dinofla gellate Amphidinium carterae did not support the positive growth of A. glandula. Thus, A. glandula may have a unique kind of prey and its optimal prey differs from that of the other pfiesteriacean dinoflagellates. With increasing mean prey concentration, the growth rates of A. glandula on H. triquetra and A. sanguinea increased rapidly and then slowed or became saturated. The maximum growth rates when feeding on H. triquetra and A. sanguinea were 1.004 and 0.567 d -1 , respectively. Further, the maximum ingestion rates of A. glandula on H. triquetra and A. sanguinea were 0.75 and 1.38 ng C predator -1 d -1 , respectively. There is no other pfiesteriacean species having H. triquetra and A. sanguinea as optimal and suboptimal prey. Thus, A. glandula may be abundant during blooms dominated by these species not preferred by the other pfiesteriacean dinoflagellates.

Reply to comment: Prey perception in feeding‐current feeding copepods

AbstractWe reply to the comments of Paffenhöfer and Jiang () who argues that remote chemical prey perception is necessary for feeding‐current feeding copepods to fulfill their nutritional requirements in a dilute ocean, that remote chemical prey detection may only be observed at very low prey concentrations, and that chemical prey perception is feasible if prey cells release dissolved organic material in short‐lasting but intense bursts. We demonstrate that mechanoreception at a very short range is sufficient to sustain a living, even in a dilute ocean. Further, if chemoreception requires that prey cells have short intense leakage burst, only a very small fraction of prey cells would be available to the copepod at any instance in time and, thus would be inefficient at low prey concentration. Finally, we report a few new observations of prey capture in two species of copepods, Temora longicornis and Centropages hamatus, offered a 45‐μm sized dinoflagellate at very low concentration. The observed short prey detection distances, up to a few prey cell radii, are consistent with mechanoreception and we argue briefly that near‐field mechanoreception is the most likely and common prey perception mechanism in calanoid copepods.

Mass entrapment and lysis of Mesodinium rubrum cells in mucus threads observed in cultures with Dinophysis

The entrapment and death of the ciliate Mesodinium rubrum in the mucus threads in cultures with Dinophysis is described and quantified. Feeding experiments with different concentrations and predator–prey ratios of Dinophysis acuta, Dinophysis acuminata and M. rubrum to study the motility loss and aggregate formation of the ciliates and the feeding behaviour of Dinophysis were carried out. In cultures of either Dinophysis species, the ciliates became entrapped in the mucus, which led to the formation of immobile aggregates of M. rubrum and subsequent cell lysis. The proportion of entrapped ciliates was influenced by the concentration of Dinophysis and the ratio of predator and prey in the cultures. At high cell concentrations of prey (136 cells mL−1) and predator (100 cells mL−1), a maximum of 17% of M. rubrum cells became immobile and went through cell lysis. Ciliates were observed trapped in the mucus even when a single D. acuminata cell was present in a 3.4mL growth medium. Both Dinophysis species were able to detect immobile or partly immobile ciliates at a distance and circled around the prey prior to the capture with a stretched out peduncle. Relatively high entrapment and lysis of M. rubrum cells in the mucus threads indicates that under certain conditions Dinophysis might have a considerable impact on the population of M. rubrum.

Critical perspectives on mercury toxicity reference values for protection of fish

Environmental management decisions at mercury-contaminated sediment sites are predicated on the understanding of risks to various receptors, including fish. Toxicity reference values (TRVs) for interpreting risks to fish have been developed to assess mercury concentrations in fish or fish prey. These TRVs were systematically evaluated based on several lines of evidence. First, their conceptual basis and specific derivation were evaluated, including a close review of underlying toxicity studies. Second, case studies were reviewed to investigate whether TRVs are predictive of effects on fish populations in the field. Third, TRVs were compared with available information regarding preindustrial and present-day background concentrations of mercury in fish. The findings show that existing TRVs are highly uncertain, because they were developed using limited data from studies not designed for TRV derivation. Although field studies also entail uncertainty, several case studies indicate no evidence of adverse effects despite mercury exposures that exceed the available TRVs. Some TRVs also fall within the range of background mercury concentrations in predatory or prey fish. Lack of information on the selenium status of mercury-exposed fish is a critical confounding factor, and the form of methylmercury used in toxicity testing may also contribute to differences between TRV-based predictions and field observations of mercury effects on fish. On balance, the available information indicates that several of the TRVs reviewed are lower than necessary to protect fish populations. The 20% effect concentration from a previously published dose-response analysis appears closer to an effect threshold, based on available laboratory data. Additional research is needed to provide a stronger basis to establish dose-response relationships for mercury effects on fish.

Behavioral and physiological responses to prey match-mismatch in larval herring

The year-class success of Atlantic herring (Clupea harengus) spawning in the autumn/winter in the North Sea (NSAS stock) and in the spring in the western Baltic Sea (WBSS) appears driven by prey match-mismatch dynamics affecting the survival of larvae during the first weeks of life. To better understand and model the consequences of prey match-mismatch from an individual-based perspective, we measured aspects of the physiology and behavior of NSAS and WBSS herring larvae foraging in markedly different prey concentrations. When matched with prey (ad libitum concentrations of the copepod Acartia tonsa) larval growth, swimming activity, nutritional condition and metabolic rates were relatively high. When prey was absent (mismatch), swimming and feeding behavior rapidly declined within 2 and 4 days, for WBSS and NSAS larvae, respectively, concomitant with reductions in nutritional (RNA-DNA ratio) and somatic (weight-at-length) condition. After several days without prey, respiration measurements made on WBSS larvae suggested metabolic down-regulation (8–34%). An individual-based model depicting the time course of these Behavioral and physiological responses suggested that 25-mm larvae experiencing a mismatch would survive 25–33% (10, 7 °C) longer than 12-mm larvae. Warmer temperatures exacerbate starvation-induced decrements in performance. Without Behavioral and metabolic adjustments, survival of 25-mm larvae would be reduced from 8 to 6 days at 7 °C. Our findings highlight how adaptive Behavioral and physiological responses are tightly linked to prey match-mismatch dynamics in larval herring and how these responses can be included in models to better explore how bottom-up processes regulate larval fish growth and survival.

Using Movements and Habitat Utilization as a Functional Metric of Restoration for Estuarine Juvenile Fish Habitat

AbstractResource managers use habitat restoration to offset estuarine habitat loss; however, there is limited information about how functionally successful restorations have been, particularly with respect to their use by mobile marine predators. Restoration monitoring efforts typically use point‐of‐capture metrics to assess fish community recovery and habitat use, but this provides little insight into how fish habitat use changes through time. Using translocation experiments, we integrated the movements of California Halibut Paralichthys californicus, a conservation target species, into a point‐of‐capture monitoring program in a restored tidal creek estuary. Large halibut (&gt;25 cm) were captured more frequently in the main stream channel, while small ones (&lt;25 cm) were typically caught in the innermost marsh creeks. We actively tracked these fish (n = 20; size range = 26.6–60.5 cm TL) acoustically to identify their preferred habitats and challenged these habitat associations by means of translocations to a different habitats. Large fish tended to have small localized convex hull activity spaces, remaining in areas with high water flow and sandy substratum near eelgrass Zostera marina beds. Individuals that were translocated to marshes returned to the channel and exhibited movements over long distances from their initial locations to their last tracked positions; however, fish that were translocated from marshes to the channel remained in channel habitat and moved smaller distances between their first and last tracked points. Large halibut likely selected the channel because higher water flow would lead to higher concentrations of prey. Small halibut used marshes more frequently, likely because marshes have temperatures thought to maximize growth rates. Our study can serve as a proof of concept that linking point‐of‐capture and tracking data provides valuable information for habitat restoration, including the fact that California Halibut utilize estuaries in a size‐segregated manner based on environmental conditions. This suggests that tidal creek estuaries with a variety of channel types and morphologies—like our study site—are well‐suited to support this species.Received August 18, 2015; accepted March 1, 2016