Copepod Concentrations Research Articles

Resolving abrupt frontal gradients in zooplankton community composition and marine snow fields with an autonomous Zooglider

AbstractAn autonomous Zooglider navigated across the California Current Front into low salinity, minty waters characteristic of the California Current proper in both summers of 2019 and 2021. Diving to 400 m depth, Zooglider transited another near‐surface frontal gradient somewhat inshore. These frontal gradients were generally associated with changes in intensity, size composition, and Diel Vertical Migration responses of acoustic backscatterers. They were also associated with pronounced changes in zooplankton community composition, as assessed by a shadowgraph imaging Zoocam. Zoocam detected a decline in concentrations of copepods, appendicularians, and marine snow in the offshore direction, and an overall shift in community structure to a higher proportion of carnivorous taxa (and, in 2019, of planktonic rhizaria). No taxon was consistently elevated at all the peak frontal gradients, but appendicularians, copepods, and rhizarians sometimes showed front‐related increases in concentration. Such frontal gradient regions represent relatively abrupt transitions to different communities of planktonic organisms and suspended marine snow particles, with consequences for predator–prey relationships and the dominant vectors of particle export into subsurface waters.

Ingestion of microplastics by copepods in Tampa Bay Estuary, FL

Microplastics have been recognized as an emerging contaminant. Copepods are abundant primary consumers in marine food webs. Interactions between copepods and microplastics can lead to negative health effects to the individual and may have implications for populations and ecosystems through biomagnification. Laboratory and field studies have observed various species of zooplankton ingesting microplastics, however, this is the first study to observe microplastic-copepod interactions in Tampa Bay. Over 2 years (November 2017-January 2020), 14 sampling cruises were conducted with seven stations throughout Tampa Bay. At each station copepods were collected by towing a 200 μm mesh ring net (0.5 m diameter) for 3 min. 1,000 individual Acartia tonsa copepods were picked from each sample and digested to release gut contents. Gut contents were stained in a Nile Red solution and then visualized using epifluorescent microscopy, quantified, photographed and sized using image analysis. In Tampa Bay, A. tonsa consumed fragments over fibers, ranging from 0.018 to 0.642 mm, with an average particle size of 0.076 mm. An overall average of 15.38 particles were ingested per 1,000 copepods, or 6.48 particles m–3 when normalized for environmental copepod concentrations. While significant differences were detected between stations and months, no clear spatial (from head to mouth of estuary) or temporal (between wet and dry seasons) trends in ingestion rate or ingested particle size were evident. These results show that A. tonsa ingested microplastics throughout Tampa Bay. These robust baseline data, for a copepod species that dominates estuarine zooplankton communities around the world, set the stage for valuable comparisons between estuaries with different physical mechanisms and levels of anthropogenic impact, allowing for exploration of how the environmental conditions impact ecological interactions.

Identification and observations of parasitic isopod larvae (Isopoda: Epicaridea) from the northeastern Pacific: pelagic distribution and association with copepod intermediate hosts

Abstract Zooplankton samples from the northeastern Pacific, USA were analyzed to identify and determine the abundance and distribution of parasitic isopod larvae and copepod hosts. Vertically stratified samples were collected at stations spanning the continental shelf off Oregon, USA. Two species of epicarideans were identified: Hemioniscus balaniBuchholz, 1866 (endoparasite of barnacles) and Argeia pugettensisDana, 1853 (ectoparasite of shrimps). Cryptoniscus larvae of these species can be distinguished based on the antennae (four basal and five flagellar articles in H. balani, four basal and four flagellar articles in A. pugettensis), tooth-like structures on the antennules and coxal teeth (present in H. balani, lacking in A. pugettensis), and pereopods (1, 2 gnathopodal and 5, 6 ambulatory in H. balani, all gnathopodal in A. pugettensis). Epicaridean larvae were rare in zooplankton samples with concentrations up to 10 m–3. Larvae were often found within 10 km of shore, with highest concentrations below the Ekman layer at 20–50 m depth near the bottom and between the 8 and 10°C isotherms. Likely as a result of dislodgment, only 26 copepods with epicaridium or microniscus larvae attached were confirmed. Larvae were mostly (78%) found attached to two species of Acartia, suggesting they were the preferred host, but five other genera of copepods were documented as hosts. The concentration of copepods and larvae exhibited a significant positive correlation when the analysis was limited to stations where both larvae and copepods were caught. The distribution of host copepods was significantly shallower than epicaridean larvae and generally closer to shore. The planktonic phase of the life cycle of epicarideans remains a black box for most of the +860 known species. Future work should include molecular data to link their larval and adult life cycle stages and connect the parasites with their intermediate hosts.

Winter zooplankton dynamics in the English Channel and southern North Sea: trends and drivers from 1991 to 2013

Abstract Winter has long been regarded as a period of minor importance in marine zooplankton ecology with static, low concentrations and growth rates of organisms. Yet, there is growing evidence that winter conditions influence spring bloom strength. With rising water temperatures, growing importance of fish larvae survival during winter and the lack of data to parameterize ecosystem models for this period, research focus shifted on winter zooplankton ecology. To enable looking into past changes in winter zooplankton ecology, we established a new winter zooplankton time series based on samples collected in the eastern English Channel and southern North Sea by the International Herring Larvae Survey since 1988. Four areas of the study region were identified containing different congregations of zooplankton. Overall, zooplankton size decreased while total zooplankton abundance increased, reaching its maximum in 2011. Zooplankton abundance dynamics were mainly related to temperature, chlorophyll a concentration and North Atlantic Oscillation index. Depth and Atlantic water inflow strongly influenced zooplankton size. Increased chlorophyll a concentration and high abundances of small copepods indicated bottom-up controlled secondary production since 2010 and a possible winter bloom in 2011. Based on the analysed parameters, no relation between herring larvae abundance and zooplankton or environmental drivers was determined.

Eddy‐Like Features Near St. Matthew Island, Eastern Bering Sea Shelf: Observations From the Oculus Coastal Glider

AbstractThe eastern Bering Sea Shelf is characterized by high biological productivity, seasonal sea ice, and commercially important fisheries. Enhanced productivity is often associated with small‐scale oceanographic features. Our objective was to use an autonomous underwater vehicle to examine features typically missed by ~20‐km spaced shipboard sampling. A coastal glider (Oculus) sampled ~3 dives hr−1 with horizontal spacing of ~300 m per dive in August/September 2017. In the north‐south transition zone near St. Matthew Island, the glider sampled four eddy‐like features associated with weaker vertical stratification. These features had diameters of 15–20 km and were associated with higher surface chlorophyll. Shipboard data collected in the same region approximately a month later showed that a similar feature was associated with high concentrations of small copepods. Incorporating higher resolution sampling available with gliders into the Bering Sea observing network will improve our understanding of ecosystem response to patchiness in the system.

Prey and predator overlap at the edge of a mesoscale eddy: fine-scale, in-situ distributions to inform our understanding of oceanographic processes

Eddies can enhance primary as well as secondary production, creating a diverse meso- and sub-mesoscale seascape at the eddy front which can affect the aggregation of plankton and particles. Due to the coarse resolution provided by sampling with plankton nets, our knowledge of plankton distributions at these edges is limited. We used a towed, undulating underwater imaging system to investigate the physical and biological drivers of zoo- and ichthyoplankton aggregations at the edge of a decaying mesoscale eddy (ME) in the Straits of Florida. Using a sparse Convolutional Neural Network we identified 132 million images of plankton. Larval fish and Oithona spp. copepod concentrations were significantly higher in the eddy water mass, compared to the Florida Current water mass, only four days before the ME's dissipation. Larval fish and Oithona distributions were tightly coupled, indicating potential predator-prey interactions. Larval fishes are known predators of Oithona, however, Random Forests models showed that Oithona spp. and larval fish concentrations were primarily driven by variables signifying the physical footprint of the ME, such as current speed and direction. These results suggest that eddy-related advection leads to largely passive overlap between predator and prey, a positive, energy-efficient outcome for predators at the expense of prey.

Fewer Copepods, Fewer Anchovies, and More Jellyfish: How Does Hypoxia Impact the Chesapeake Bay Zooplankton Community?

To understand dissolved oxygen deficiency in Chesapeake Bay and its direct impact on zooplankton and planktivorous fish communities, six research cruises were conducted at two sites in the Chesapeake Bay from spring to autumn in 2010 and 2011. Temperature, salinity, and dissolved oxygen were measured from hourly conductivity, temperature, and depth (CTD) casts, and crustacean zooplankton, planktivorous fish and gelatinous zooplankton were collected with nets and trawls. CTD data were grouped into three temperature groups and two dissolved oxygen-level subgroups using principal component analysis (PCA). Species concentrations and copepod nonpredatory mortalities were compared between oxygenated conditions within each temperature group. Under hypoxic conditions, there usually were significantly fewer copepods Acartia tonsa and bay anchovies Anchoa mitchilli, but more bay nettles Chyrsaora chesapeakei and lobate ctenophores Mnemiopsis leidyi. Neutral red staining of copepod samples confirmed that copepod nonpredatory mortalities were higher under hypoxic conditions than under normoxia, indicating that the sudden decline in copepod concentration in summer was directly associated with hypoxia. Because comparisons were made within each temperature group, the effects of temperature were isolated, and hypoxia was clearly shown to have contributed to copepod decreases, planktivorous fish decreases, and gelatinous zooplankton increases. This research quantified the direct effects of hypoxia and explained the interactions between seasonality and hypoxia on the zooplankton population.

Distribution of calanoid copepods across the mesoscale frontal zone of tropical-subtropical convergence off México

The distribution of calanoid copepods was investigated in the convergence zone between the California Current Water and Transitional Tropical Water in June 2010 to understand how this zooplankton community responds to mesoscale environmental structure. Hydrographic conditions and zooplankton profiles were measured along two transects which crossed a mesoscale front and adjacent structures, visible in sea surface temperature and ocean color satellite images. The hydrographic structure showed strong temperature (~2 °C) and oxygen (50 μmol kg−1) gradients in the frontal zone (~90 km) associated with a sinking of the thermocline and oxycline, from ~30 m depth in the Transitional Tropical Water, to ~ 90 m depth in the California Current Water. The front was marked by a salinity minimum (<34.3 g kg−1) that sank along the sloping thermocline. High chlorophyll-a concentrations associated with the thermocline were detected in the Transitional Tropical Water, where a cyclonic eddy was defined. These concentrations decreased as the thermocline depth increased. Multivariate analysis defined three calanoid copepod habitats related to the hydrographic structure. A habitat with the highest copepod concentration (24,704 copepods 1000 m−3) was found on the tropical water side associated with a cyclonic eddy. Subeucalanus subtenuis and Centropages furcatus, indicator species, were concentrated between the thermocline (~30 m depth) and the sea surface. On the subtropical water side, where the thermocline was deeper, a habitat with the lowest copepod concentration (3304 copepods 1000 m−3, an order of magnitude smaller), characterized by Euchaeta indica and Centropages elongates, was observed. As an unexpected result, the habitat located in the frontal zone, characterized by Scolecithrix bradyi and Heterorhabdus papilliger had low copepod concentration (4453 copepods.1000 m-3). This low concetration could be due to the steep thermocline slope in the frontal zone, which could cause the thermocline depth to rapidly exceed the photic zone depth, and therefore affect the availability of food for calanoid copepods. It is concluded that the definition of the calanoid copepod habitats, was not only caused by the front itself, but by its interaction with other fine-scale mechanisms that generate oceanographic conditions leading to development of different food webs depending on the structure of water column.

A comparison between Zooglider and shipboard net and acoustic mesozooplankton sensing systems

Abstract Some planktonic patches have markedly higher concentrations of organisms compared to ambient conditions and are &lt;5 m in thickness (i.e. thin layers). Conventional net sampling techniques are unable to resolve this vertical microstructure, while optical imaging systems can measure it for limited durations. Zooglider, an autonomous zooplankton-sensing glider, uses a low-power optical imaging system (Zoocam) to resolve mesozooplankton at a vertical scale of 5 cm while making concurrent physical and acoustic measurements (Zonar). In March 2017, Zooglider was compared with traditional nets (MOCNESS) and ship-based acoustics (Simrad EK80). Zoocam recorded significantly higher vertically integrated abundances of smaller copepods and appendicularians, and larger gelatinous predators and mineralized protists, but similar abundances of chaetognaths, euphausiids, and nauplii. Differences in concentrations and size-frequency distributions are attributable to net extrusion and preservation artifacts, suggesting advantages of in situ imaging of organisms by Zooglider. Zoocam detected much higher local concentrations of copepods and appendicularians (53 000 and 29 000 animals m−3, respectively) than were resolvable by nets. The EK80 and Zonar at 200 kHz agreed in relative magnitude and distribution of acoustic backscatter. The profiling capability of Zooglider allows for deeper high-frequency acoustic sampling than conventional ship-based acoustics.

Physical controls on phytoplankton size structure, photophysiology and suspended particles in a Norwegian biological hotspot

The impact of the physical environment and phytoplankton size on particle types (zooplankton, biogenic matter or phytodetritus) in the water column is poorly understood. Here, we investigate how hydrography (e.g. water column stratification) impacts phytoplankton size and photophysiology across a productive coastal bank area. Additionally, we investigate how the physical environment and phytoplankton size structure influence the concentrations of plankton (e.g. copepods and diatom chains), biogenic forms (fecal pellets) and other particles (minerals, aggregates or phytodetritus) using discrete samples and in-situ optical instruments. Microphytoplankton (>20 µm), including many chain-forming diatoms, dominated (average > 90% of total size fraction) in un-stratified waters of the bank. Phytoplankton within the bank region also required more irradiance to saturate photosynthesis, as indicated by the onset light saturation parameter (Ek, average 297 µmol photons m−2 s−1), suggesting high plasticity to a dynamic light environment. Conversely, the contribution of nano- and picophytoplankton (<20 µm), such as flagellates increased (up to 36% of total phytoplankton size fraction) towards stratified off-bank waters. The phytoplankton community from off-bank had lower Ek (average 199 µmol photons m−2 s−1) and presented higher concentrations of photoprotective pigments, such diatoxanthin – used in the xanthophyll cycle to cope with light stress and potential photo-damage. Higher concentrations of copepods (>1 × 103 counts m−3), fecal pellets (>1 × 104 counts m−3) and ammonium (>0.5 µM) within the bank compared to off-bank regions, indicated that copepods were actively grazing in this region. Low stratification (average stratification index (SI) < 6 × 10−3 kg m−4) allowed for intensive mixing, which might have promoted the high concentration of aggregates (>5 × 105 counts m−3) within the bank when compared to off-bank (SI off-bank > 10 × 10−3 kg m−4). Our results, obtained using automated techniques measured in-situ, represent an innovative approach to demonstrate that phytoplankton size and stratification influence the nature of particles found in the water column (including aggregates, fecal pellets and grazer abundances).

Пространственно-временные изменения видового состава и плотности популяций веслоногих ракообразных (Crustacea: Copepoda) в дальневосточном морском заповеднике ДВО РАН (Японское море)

Дальневосточный государственный морской заповедник ДВО РАН (ДВГМЗ) является самым богатым по разнообразию населения районом морей России, но сведений о пространственно-временной изменчивости зоопланктона в его акватории чрезвычайно мало, а последние наблюдения проводились более 20 лет назад. В данной работе приведены результаты современного исследования видового состава, плотности популяций и распределения веслоногих ракообразных — основных представителей зоопланктона в ДВГМЗ. Работа основана на сборах планктона, которые выполнялись ежемесячно на 10 станциях в акватории ДВГМЗ в пределах 50-метровой изобаты в июне — сентябре 2012 г. В этот сезон в заповеднике отмечается наибольшая изменчивость температуры воды. Обнаружен 21 вид копепод из двух отрядов (Calanoida — 17 видов и Cyclopoida — 4 вида). Наибольшее видовое богатство отмечено для родов Acartia и Oithona (по 4 вида). Преобладали морские виды — 80 % общего числа видов в пробах, а по отношению к биотопу — неритические (58 %). Широкобореальные виды составляли 55 % общего числа, тропические и субтропические — 45. Наибольшее количество видов копепод (16) отмечено в июне, наименьшее (5) — в сентябре. В июне — июле доминировали Oithona similis и Pseudocalanus newmani, в августе — Paracalanus parvus, Oithona brevicornis и Oithona similis, в сентябре — Paracalanus parvus и Oithona brevicornis. С июня по сентябрь происходило постепенное снижение обилия и разнообразия копепод во всех районах заповедника. Средняя плотность популяций копепод была максимальной в июне, в период развития холодноводных видов Oithona similis, Pseudocalanus newmani, Acartia hudsonica и Eurytemora pacifica, а минимальной — в сентябре. Наибольшие концентрации копепод отмечены в июне в западном районе заповедника в зал. Посьета (Посьетский рейд) над горизонтом глубины не более 10 м. По результатам кластерного анализа станций на акватории ДВГМЗ на основе коэффициента видового сходства Брэя — Кёртиса на уровне сходства 60 % выделены три комплекса планктонных копепод, видовой состав которых формируется под влиянием различных водных масс. Наибольшее видовое богатство и плотность копепод отмечены в комплексах западного и восточного районов заповедника. В мелководном комплексе западного района высокая плотность видов солоноватоводных родов Acartia, Eurytemora, Centropages, Tortanus и Pseudodiaptomus свидетельствует о присутствии там эстуарных и прибрежных вод. Наличие тропических и субтропических видов копепод (O. nana, Mesocalanus tenuicornis, Pseudodiatomus inopinus) подтверждает возможность проникновения в западный район тёплых вод из области Восточно-Корейского течения. В глубоководном комплексе восточного района совместное присутствие летом холодноводных и тепловодных видов копепод указывает на выраженную стратификацию водной толщи, где на глубине влияние оказывала холодная глубинная водная масса из Японского моря, а в верхнем слое — её более тёплая поверхностная модификация. В комплексе южного района заповедника, где доминировали панталассные и неритические виды, отмечены минимальные показатели видового богатства и плотности копепод. Обилие летом в этом комплексе холодноводных O. similis и P. newmani свидетельствует о поступлении холодных вод в придонный слой, а показатели численности копепод могут характеризовать степень влияния холодных вод на южную часть акватории заповедника. Особенности распределения копепод, их стабильно низкие показатели обилия и разнообразия в исследованной акватории к югу от ДВГМЗ могут быть вызваны опресняющим воздействием речных вод и возможным негативным влиянием загрязняющих веществ. Видовой состав и количественные характеристики копепод возможно использовать для оценки экологического состояния акватории морского заповедника.

Linking nutrient inputs, phytoplankton composition, zooplankton dynamics and the recruitment of pink snapper, Chrysophrys auratus, in a temperate bay

Survival of larval fish is often linked to production of preferred prey such as copepods, both inter- and intra-annually. In turn, copepod production depends not only the quantity of food, but also on the nutritional quality, edibility and/or toxicity of their micro-algal food. Hence, larval fish survival can become de-coupled from levels of nutrient input depending on the resulting composition of the plankton. Here we use a plankton dynamics model to study nutrient input, phytoplankton composition and copepod, Paracalanus, production in relation to interannual variation in recruitment of snapper, Chrysophrys auratus, in Port Phillip Bay, Australia. The model was able to simulate the ratio of diatoms to flagellates in the plume of the main river entering Port Phillip Bay. Interannual variability in the copepod, Paracalanus, abundance during the C. auratus spawning period over 5 years was accurately predicted. The seasonal peak in Paracalanus production depended on the timing and magnitude (match-mismatch) of nutrient inputs and how these were reflected in temporal change in the diatom:flagellate ratio. In turn, the model-predicted Paracalanus abundance was strongly related to inter-annaul variability in abundance of snapper, C. auratus, larvae over 7 years. Years of highest larval C. auratus abundance coincided with a matching of the spawning period with the peak in Paracalanus abundance. High freshwater flows and nutrient inputs led to an early seasonal dominance of diatoms, and consequently reduced abundances of copepods over the C. auratus spawning period with correspondingly low abundances of larvae. Conversely years of very low rainfall and nutrient input also led to low phytoplankton and copepod concentrations and larval C. auratus abundances. Highest abundances of larval C. auratus occurred in years of low to intermediate rainfall and nutrient inputs, particularly when pulses of nutrients occurred in the spring period, the latter supporting the match-mismatch hypothesis.

Commercial Diets in Phase I Palmetto Bass, Morone saxatilis × Morone chrysops , Production in Plastic-lined Ponds: Fertilizer or Feed?

The role of offering a commercial pelleted diet has been characterized as both an expensive organic fertilizer and as a selected food item for larval hybrid striped bass (palmetto), Morone saxatilis × Morone chrysops, culture operations. In this study, we examined the effects of providing a commercial diet on fish production and zooplankton dynamics during phase I culture in plastic-lined ponds. We also sought to estimate relative dietary contribution of a commercial fish feed relative to natural pond biota using stable isotope tissue analysis. Palmetto bass were stocked into six 0.04-ha plastic-lined ponds at a rate of 125,000/ha. During the 31-d culture period, ponds were fertilized with alfalfa pellets at a rate of 112 kg/ha/wk. At 14 d post-stock (dps), Silver Cup Trout Fry diet was offered at a rate of 13.6 kg/ha/d and fertilization was discontinued in three ponds. Although mean final fish length was significantly greater within the fed treatment, no other production parameters were found to be different (P < 0.1). Following feed application, copepod concentrations within the fed ponds were greater in magnitude by 24 dps. Through stable isotope tissue analysis, we found a significant enrichment in both 13C and 15ν of fish, zooplankton, and Chironomidae larvae within the fed ponds (P < 0.10). Using a three-source mixing model, the mean (±SE) percent composition of feed in the fish's isotopic signature increased from 5% ±2 to 20% ±6 within 16 d. Although fish production was not greatly affected through the addition of a commercial fish feed, enriched 13C and 15ν of fish tissue indicate that palmetto bass fingerlings increasingly utilized the prepared diets over time. However, based on the isotopic values of fish and potential food sources, it can be estimated that natural pond biota likely accounted for up to 80% of nutrient assimilation in the hybrid striped bass.

Ecological characteristics of core-use areas used by Bering–Chukchi–Beaufort (BCB) bowhead whales, 2006–2012

The Bering–Chukchi–Beaufort (BCB) population of bowhead whales (Balaena mysticetus) ranges across the seasonally ice-covered waters of the Bering, Chukchi, and Beaufort seas. We used locations from 54 bowhead whales, obtained by satellite telemetry between 2006 and 2012, to define areas of concentrated use, termed “core-use areas”. We identified six primary core-use areas and describe the timing of use and physical characteristics (oceanography, sea ice, and winds) associated with these areas. In spring, most whales migrated from wintering grounds in the Bering Sea to the Cape Bathurst polynya, Canada (Area 1), and spent the most time in the vicinity of the halocline at depths <75m, which are within the euphotic zone, where calanoid copepods ascend following winter diapause. Peak use of the polynya occurred between 7 May and 5 July; whales generally left in July, when copepods are expected to descend to deeper depths. Between 12 July and 25 September, most tagged whales were located in shallow shelf waters adjacent to the Tuktoyaktuk Peninsula, Canada (Area 2), where wind-driven upwelling promotes the concentration of calanoid copepods. Between 22 August and 2 November, whales also congregated near Point Barrow, Alaska (Area 3), where east winds promote upwelling that moves zooplankton onto the Beaufort shelf, and subsequent relaxation of these winds promoted zooplankton aggregations. Between 27 October and 8 January, whales congregated along the northern shore of Chukotka, Russia (Area 4), where zooplankton likely concentrated along a coastal front between the southeastward-flowing Siberian Coastal Current and northward-flowing Bering Sea waters. The two remaining core-use areas occurred in the Bering Sea: Anadyr Strait (Area 5), where peak use occurred between 29 November and 20 April, and the Gulf of Anadyr (Area 6), where peak use occurred between 4 December and 1 April; both areas exhibited highly fractured sea ice. Whales near the Gulf of Anadyr spent almost half of their time at depths between 75 and 100m, usually near the seafloor, where a subsurface front between cold Anadyr Water and warmer Bering Shelf Water presumably aggregates zooplankton. The amount of time whales spent near the seafloor in the Gulf of Anadyr, where copepods (in diapause) and, possibly, euphausiids are expected to aggregate provides strong evidence that bowhead whales are feeding in winter. The timing of bowhead spring migration corresponds with when zooplankton are expected to begin their spring ascent in April. The core-use areas we identified are also generally known from other studies to have high densities of whales and we are confident these areas represent the majority of important feeding areas during the study (2006–2012). Other feeding areas, that we did not detect, likely existed during the study and we expect core-use area boundaries to shift in response to changing hydrographic conditions.

Effects of Grazer Presence on Genetic Structure of a Phenotypically Diverse Diatom Population

Studies of predator-prey systems in both aquatic and terrestrial environments have shown that grazers structure the intraspecific diversity of prey species, given that the prey populations are phenotypically variable. Populations of phytoplankton have traditionally considered comprising only low intraspecific variation, hence selective grazing as a potentially structuring factor of both genetic and phenotypic diversity has not been comprehensively studied. In this study, we compared strain specific growth rates, production of polyunsaturated aldehydes, and chain length of the marine diatom Skeletonema marinoi in both grazer and non-grazer conditions by conducting monoclonal experiments. Additionally, a mesocosm experiment was performed with multiclonal experimental S. marinoi populations exposed to grazers at different levels of copepod concentration to test effects of grazer presence on diatom diversity in close to natural conditions. Our results show that distinct genotypes of a geographically restricted population exhibit variable phenotypic traits relevant to grazing interactions such as chain length and growth rates. Grazer presence affected clonal richness and evenness of multiclonal Skeletonema populations in the mesocosms, likely in conjunction with intrinsic interactions among the diatom strains. Only the production of polyunsaturated aldehydes was not affected by grazer presence. Our findings suggest that grazing can be an important factor structuring diatom population diversity in the sea and emphasize the importance of considering clonal differences when characterizing species and their role in nature.

Tidal and subtidal currents affect deep aggregations of right whale prey, Calanus spp., along a shelf-basin margin

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 479:263-282 (2013) - DOI: https://doi.org/10.3354/meps10189 Tidal and subtidal currents affect deep aggregations of right whale prey, Calanus spp., along a shelf-basin margin Kimberley T. A. Davies*, Tetjana Ross, Christopher T. Taggart Department of Oceanography, Dalhousie University, 1355 Oxford Street, Halifax, Nova Scotia B3H4R2, Canada *Email: kim.davies@dal.ca ABSTRACT: North Atlantic right whales Eubalaena glacialis foraging on deep (>100 m) populations of diapausing Calanus spp. in the Roseway Basin right whale Critical Habitat (south of Nova Scotia, Canada) are most often located along the southern margin of the basin. We investigated the physical and biological oceanographic characteristics that make this margin a lucrative feeding ground. Bottom-moored acoustic Doppler current profilers equipped with conductivity, temperature, and depth sensors were deployed cross-isobath on the southeastern slope of the basin to simultaneously measure variation in Calanus spp. concentration, current velocity, and water mass characteristics in time and space. Variation in upslope tidal advection of deep-basin water with densities >1026 kg m-3 and containing highly concentrated copepod aggregations was the most important process influencing cross-isobath variation in copepod concentrations on the slope. The aggregations were maintained in the slope region through time despite extensive along-isobath advection, implying the existence of copepod re-supply mechanisms to the southern margin. Proposed mechanisms include immigration from surface populations, horizontal advection, and gyre-like re-circulation within the basin. A simple empirically-driven particle tracking model illustrated tidally-forced particle convergence between the 100 and 140 m isobaths on the southeastern slope, followed by upward and along-isobath advection. Cross-isobath ‘compression’ of copepods coupled with the maintenance of their vertical position through neutral buoyancy is proposed as a mechanism resulting in accumulation on the slope, making the area uniquely beneficial to right whales feeding at depth along the slope margin. KEY WORDS: Calanus · Water mass density · Acoustic Doppler current profiler · Tides · Roseway Basin · Right whale · Sloped margin Full text in pdf format Supplementary material PreviousNextCite this article as: Davies KTA, Ross T, Taggart CT (2013) Tidal and subtidal currents affect deep aggregations of right whale prey, Calanus spp., along a shelf-basin margin. Mar Ecol Prog Ser 479:263-282. https://doi.org/10.3354/meps10189 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 479. Online publication date: April 08, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Influence of environment on walleye pollock eggs, larvae, and juveniles in the southeastern Bering Sea

We examined the influence of environmental conditions on walleye pollock (Theragra chalcogramma) early life history in discrete stages at two ecological scales using a 17-year time series from the southeastern Bering Sea. Generalized additive models (GAMs) were used to quantify relationships between walleye pollock stages (eggs, yolksac larvae, preflexion larvae, late larvae, and juveniles), the fine-resolution environment (temperature, wind speed, salinity, and copepod concentration), and the broad-resolution environment (annual spawning stock biomass, temperature, zooplankton biomass, and wind mixing). Early stages (eggs, yolksac larvae, and preflexion larvae) were associated with high spawning stock biomass, while late stages (late larvae and juveniles) were not associated with spawning stock biomass. The influence of temperature increased with ontogeny: high egg abundance was associated with temperatures from −2 to 7°C and negative annual temperature anomalies and high juvenile abundance was associated with temperatures from 4 to 12°C and positive temperature anomalies. Winds enhanced the transport of early stages from spawning locations to shallower sampling depths, but did not affect feeding stages (preflexion larvae, late larvae, and juveniles) in a manner consistent with the encounter-turbulence hypothesis. Feeding stages were positively associated with localized copepod concentrations but not zooplankton biomass anomaly, suggesting that the localized measurements of potential prey is a better indicator compared to broad-scale conditions measured in areas where these stages do not necessarily occur. Broad-resolution covariates, however, explained a greater portion of the overall variation than did fine-resolution models. Of the environmental conditions examined, temperature explained more variation in abundance of walleye pollock early life stages than any other covariate. Temperature is likely a major driving force structuring variability in populations of walleye pollock in their first year of life, acting directly upon them and indirectly upon their physical habitat and prey community.

Use of flubendazole as a therapeutic agent against rotifers (Brachionus plicatilis) in intensive cultures of the harpacticoid copepodTisbe holothuriae

Copepods are well known to be the optimal live feed for most species of marine fish larvae. Still copepods are rarely used in marine hatcheries worldwide. Lack of efficient production techniques are among the reasons for this. Consequently, Artemia and rotifers are utilized in commercial settings. One problem in intensive production of copepods is contamination with rotifers. Rotifers have higher growth rates than copepods and consequently will compete out the copepods when accidentally introduced to the copepod production systems. Once contamination has occurred, the only cure has been to shut down production and subsequently use a therapeutic agent to eliminate all zooplankton in the system before restart with a stock culture free of rotifers. We tested flubendazole as a mean of controlling rotifers (Brachionus plicatilis) in intensive laboratory cultures of the harpacticoid copepod (Tisbe holothuria). Flubendazole was lethal to rotifers in concentrations as low as 0.05 mg L−1. There was no significant effect on the concentration of copepods, even at the highest concentration tested, i.e. 5.0 mg L−1 flubendazole. We conclude that flubendazole is an effective drug for control of B. plicatilis in T. holothuriae batch cultures.

Upslope transport of near-bed zooplankton

Abstract Zooplankton residing just above the deep-sea floor is an important component of the benthic/benthopelagic food chain. Consuming planktonic particulates and organisms, holoplankton and meroplankton are prey for fish and large invertebrates. Mechanisms controlling their abundances have been explored over relatively long time scales (months to years). Here, zooplankton were sampled every 2 h for 2.2 d using a moored, automated, serial zooplankton pump. The physical regime (currents and temperature) 1–100 m above bottom was measured during an inclusive 24-d period. The study site was located on the upper continental slope (750 m) of the Mid-Atlantic Bight, between the productive shelf and more impoverished rise and abyss. The coupled biological and physical records indicated tidally driven, net upslope transport of the holoplankton. The copepod (74.5% of collections) time series showed marked periodicity with a peak frequency of ∼13 h, approximately the diurnal tide (Fourier analysis). Local maxima corresponded with minimal water temperatures. Moreover, tidal cross-slope flow was highly coherent and 90° out of phase with temperature. Thus, maximal copepod concentrations, originating in colder deeper water, would be transported up the slope by the tide. Estimated net displacement of ∼1 km/d would deliver the animals to continental-shelf depths within a couple weeks. Time series of the much less abundant larvaceans (urochordates) (15.3%) and polychaete larvae (8.9%) showed periodicities with peak frequencies of 8–9 h. Statistical significance of the periodic signals could not be determined due to low numbers. Revealing holoplankton dynamics on scales of hours, this study may contribute to understanding of, for example, copepod feeding and aggregation near the deep-sea floor.

Regional-scale mean copepod concentration indicates relative abundance of North Atlantic right whales

Management plans to reduce human-caused deaths of North Atlantic right whales Eubalaena glacialis depend, in part, on knowing when and where right whales are likely to be found. Local environmental conditions that influence movements of feeding right whales, such as ultradense copepod patches, are unpredictable and ephemeral. We examined the utility of using the regional-scale mean copepod concentration as an indicator of the abundance of right whales in 2 critical habitats off the northeastern coast of the United States: Cape Cod Bay and Great South Channel. Right whales are usually found in Cape Cod Bay during the late winter and early spring, and in the Great South Channel during the late spring and early summer. We found a significant positive relationship between mean concentration of the copepod Calanus finmarchicus in the western Gulf of Maine and the frequency of right whale sightings in the Great South Channel. In Cape Cod Bay we found a significant positive relationship between the mean concentration of other copepods (largely Pseudocalanus spp. and Centropages spp.) and the frequency of right whale sightings. This information could be used to further our understanding of the environmental factors that drive seasonal movement and aggregation of right whales in the Gulf of Maine, and it offers a tool to resource managers and modelers who seek to predict the movements of right whales based upon the concentration of copepods.