Factors affecting Oithona nana and Oithona similis along a salinity gradient

Spatial and temporal variations of reproduction variables of the two cyclopoid copepods Oithona nana Giesbrecht, 1893 and Oithona similis Claus, 1866 were evaluated monthly from September 2007 to August 2008 in four ponds at different salinities in the solar saltern of Sfax, Tunisia, under hypersaline conditions. Along the salinity gradient the abundance of O. nana and O. similis declined from 14,900 ± 15,200 ind. m-3 (A1) to 6,800 ± 7,200 (C31) and from 13,800 ± 17,100 ind. m-3 (A1) to 3,700 ± 5,800 (C31), respectively. The findings showed that the abundance of these Oithona species, particularly the ovigerous females, was positively correlated with the abundance of Diatomeae, and negatively correlated with salinity. The egg production rate (EPR), the egg diameter, the clutch size, as well as the cephalothorax length of mature females, were all negatively correlated with salinity and positively correlated with the abundance of Diatomeae. Along the existing salinity gradient, the EPR decreased from 4.7 ± 0.39 (A1) to 3.2 ± 0.13 (C31) eggs female-1 day-1 and from 5.19 ± 0.46 (A1) to 3.66 ± 0.05 (C31) eggs female-1 day-1 for O. nana and O. similis, respectively, and this could mainly be attributed to the hypersaline conditions. The positive relationship between the abundance of Diatomeae with all traits shows, that these may be a vital component of the diet for the investigated species. The reduction of body size of Oithona along the salinity gradient demonstrates that such a character could mainly be due to a network of causes, related with the confinement and not only to salinity.

Phenology of Oithona similis demonstrates that ecological flexibility may be a winning trait in the warming Arctic

Rapidly warming Arctic is facing significant shifts in the zooplankton size-spectra manifested as increasing numbers of the small-sized copepod Oithona similis. Here we present a unique continuous data set covering 22 months, on its copepodite structure along with environmental drivers in the Atlantic-influenced high Arctic fjord Isfjorden (Spitsbergen). Abundance maxima of O. similis were observed in September when the highest seawater temperature was recorded. A high concentration of the indicator species of Atlantification Oithona atlantica was also observed at that time. The clear dominance of O. similis in the zooplankton community during the dark, theoretically unproductive season emphasizes its substantial role in sustaining a continuous carbon flow, when most of the large herbivorous copepods fall into sleeping state. The high sex ratio observed twice in both years during periods of high primary production suggests two main reproductive events per year. O. similis reproduced even in very low temperatures (< 0 °C) previously thought to limit their fecundity, which proves its unique thermal tolerance. Our study provides a new insight on ecology of this key copepod of marine ecosystems across the globe, and thus confirm the Climatic Variability Hypothesis assuming that natural selection favour species with such flexible adaptive traits as O. similis.

Composition and structure of plankton communities in the Bering Sea

On the data of long-term surveys, mean biomass of plankton in the epipelagic layer of the Bering Sea is evaluated as 821.3 mg/m3 (1058.2 mg/m3 in shelf areas and 760.6 mg/m3 in the deep-water areas) and the stock as 245.1•106 t WW (64.4 • 106 t over the shelf and 180.7 • 106 t in the deep-water sea). By taxa, the average annual portions are: 55.1 % for copepods, 26.3 % for arrowworms, 10.8 % for euphausiids, 3.2 % for medusas, and 2.9 % for amphipods. The dominant species are the arrowworm Sagitta elegans (26.3 %) and the copepod Eucalanus bungii (19.7 %); other mass species are: large-sized copepods Neocalanus cristatus (10.4 %), Neocalanus plumchrus + Neocalanus flemingeri (7.8 %) and Calanus glacialis + Calanus marshallae (5.1 %), euphausiids Thysanoessa raschii (3.5 %) and Thysanoessa longipes (3.4 %), small-sized copepods Metridia pacifica (3.5 %) and Oithona similis (3.5 %), medusa Aglantha digitale (3.2 %).

Western Pacific Zooplankton Community along Latitudinal and Equatorial Transects in Autumn 2017 (Northern Hemisphere)

During the autumn of 2017, a study was conducted to assess the zooplankton community composition in three sections (two latitudinal, going from Japan to the equator, and one longitudinal on the equator) of the Western Pacific Ocean. A total of 384 species of zooplankton adults and 21 groups of zooplankton larvae were identified, with copepods being the predominant taxon. The common dominant species across the three sections were Acrocalanus gibber, Canthocalanus pauper, Oithona similis, Paracalanus aculeatus, and Oncaea venusta. Zooplankton abundance was the highest in the equator section, with a mean abundance of 258.94 ± 52.57 ind./m3. Comparatively, a low abundance was recovered from the Subtropical Countercurrent (STCC) region, while the highest abundance holding stations were located in the eastern equatorial and North Equatorial Countercurrent (NECC) regions. Pearson’s correlation, canonical correspondence analysis, and other methods were used to analyze the relationship between environmental factors and zooplankton. We found that the Shannon–Wiener diversity index and Pielou’s uniformity index were significantly correlated (p < 0.05) with concentrations of nitrite and chlorophyll a. The distribution of zooplankton was also limited by nutrients, chlorophyll a, and dissolved oxygen. In addition, we reveal differences in the abundance of species in the equatorial and latitudinal seas. We found that not only temperature and nutrient salinity, but also ocean currents and the movement of water masses, influence the distribution of zooplankton communities in the Western Pacific.

Organic Feed Enrichment Effects toward Growth Performance and Egg Production of Oithona similis

The optimum condition of culture media and feed diets which fit the necessities of Oithona similis life (ecophysiological) is very important for it to grow and develop in its maximum. The enrichment of O. similis feed can be done by adding fermented organic feed. Providing organic feed with optimum protein content is necessary to support the growth process and reproduction of O. similis. Osmoregulation process of water organism which is influenced by media salinity is related to bioenergetics process as the effort to use feed energy for the growth. This research aimed to examine the effect of different organic feed protein content and to determine the optimum point which may result in the best growth and egg production of O. similis in the optimum condition of culture media. The study used an experimental method with a completely random design consisting of 4 treatments and 4 repetitions each, i.e. O. similis culture with A. 25%; B. 30%; C. 35%; and D. 40% organic feed protein content. The results showed that the difference of protein content in organic feed affects the growth and production of O. similis eggs. The optimum point of protein content in the fermented organic feed is on protein content B, i.e. 30%, which resulted in the best growth performance (70.44 ± 0.43 ind.mL-1 total density, 0.213 ± 0.001.day-1 population growth rate, and 27.38 ± 0.48 eggs.ind-1 egg production. (ttujuan dan pembahasan harus past tense), Tujuan di abstrak minimal harus menggambarkan atau sama denga tujuan di pendahuluan)Keywords: enrichment, Oithona similis, organic feed, protein, reproduction

Zooplankton productivity in the coastal area of the southern Barents Sea in spring

The results of the analysis of zooplankton assemblage state of the southern Barents Sea are presented. Zooplankton samples were collected during the cruise of the RV “Dalnie Zelentsy” in May 2016. Hydrological conditions were typical for Murmansk coastal water this season. A total of 47 zooplankton taxa were identified. Taxa number varied between stations, ranging 18–29, with copepods being a dominant group in zooplankton. The most frequent ones were Calanus finmarchicus, Metridia longa, Metridia lucens, Microcalanus spp., Oithona atlantica, Oithona similis, Pseudocalanus spp., copepod nauplii and ova, as well as cladoceran Evadne nordmanni, larvae of Echinodermata and Polychaeta, chaetognath Parasagitta elegans, and early stages of the euphausiids of the genus Thysanoessa. In populations of common copepod species Pseudocalanus spp. and Oithona similis, early age stages dominated, which indicated their continued reproduction. Total zooplankton abundance ranged from 748 to 6576 ind.·m−3, averaging 3012. Total zooplankton biomass varied from 17 to 157 mg of dry mass per m³, with a mean value of 83. The data obtained were comparable to those registered in Murmansk coastal water in July 2008 and were higher than those in August 2007. The authors suggest that it might be related to the differences in sampling seasons and hydrological conditions. Daily zooplankton production was estimated to be 0.49–4.04 mg of dry mass per m³, averaging (2.17 ± 0.17). These estimates were about twice as high as mean values, registered in Murmansk coastal water during summer period. This seems to be due to higher phytoplankton concentrations in spring. Total zooplankton stock for water area studied (25.8 thousand km²) was estimated to be 425,000 thousand tons of dry mass. Cluster analysis revealed four groups of stations that differ in relative abundance of Calanus finmarchicus, Copepoda nauplii, Oithona similis, larvae of Echinodermata, and appendicularian Fritillaria borealis. Spatial variation of zooplankton abundance was closely related to station location (latitude, longitude, and sampling depth), as well as bottom layer temperature and mean salinity at the station.

Some peculiarities in vertical distribution of metazoan microzooplankton in the Black Sea in spring

Based on material, received in the 84th and 93rd cruises of the RV “Professor Vodyanitsky”, vertical distribution of microplankton fraction of metazooplankton (MM) in the Black Sea in spring was analyzed. A total of 27 stations were examined both in the coastal zone and in the deep sea. The 10-L bottles of the CTD probes “Mark-III Neil Brown” and “Sea Bird 911” were used to collect 4–6 L of water from 4–11 horizons of the water column. The samples obtained were concentrated by the reverse filtration through the plankton net with the mesh size of 10 µm. Quantitative and systematic analysis of all samples was carried out totally in the Bogorov chamber using an MBS-9 stereo microscope. The main factors determining nature of the distribution are MM species composition, physical structure of the water column, and hydrodynamic processes affecting its stability/instability. Nauplii of Black Sea Copepoda and veligers of Bivalvia were the most numerous systematic groups in “spring” MM. Mollusc veligers determined abundance maxima in the lower layers of shallow water habitats, while copepods prevailed over large depths and determined total abundance peaks in the upper and middle water layers. Daily time series experiment showed that advective hydrodynamic processes can significantly affect MM vertical distribution, changing physical structure of the water column. For some species, in most cases, a correlation of their distribution with vertical profiles of temperature and salinity was revealed, which rarely manifested at total MM abundance level. A comparison of two spring seasons (2016 and 2017) showed the relationship between vertical distribution of MM abundance and temperature to be more pronounced in cases of low temperature. A change in the sign of correlation with temperature was detected during spring season for Oithona similis: an initially cold-loving species of Black Sea copepods. This revealed in a more superficial distribution of the maxima abundance of this species at lower seasonal temperatures, which could reflect a shift in temperature optimum for the species population and play the role of an adaptive reaction in conditions of seasonal changes in sea thermal characteristics.

Penngaruh Pemberian Pakan Alami yang Berbeda dari Jenis Zooplankton (Artemia salina, Brachionus rotundiformis dan Oithona similis) terhadap Performa Pertumbuhan Phronima sp.

Phronima sp. merupakan salah satu hyperiid amphipoda yang berpotensi digunakan sebagai pakan alami untuk ikan dan udang. Phronima sp. memiliki habitat persebaran yang sangat luas mulai dari perairan laut hingga estuari. Tujuan dari peneitian ini adalah untuk mengkaji pengaruh pemberian pakan alami yang berbeda dari jenis zooplankton (A. salina, B. rotundiformis dan O. similis) dan mendapatkan jenis zooplankton terbaik sebagai pakan alami terhadap performa pertumbuhan Phronima sp. Penelitian dilaksanakan di Balai Besar Perikanan Budidaya Air Payau (BBPBAP), Jepara. Phronima sp. yang digunakan sebagai organisme uji merupakan koleksi yang dimiliki oleh Balai Besar Perikanan Budidaya Air Payau (BBPBAP), Jepara. Metode yang digunakan dalam penelitian adalah metode eksperimental menggunakan Rancangan Acak Lengkap (RAL) dengan 3 perlakuan yaitu perlakuan A (A. salina), perlakuan B (B. rotundiformis) dan perlakuan C (O. similis) dengan 4 pengulangan. Phronima sp. dikultur dengan kepadatan awal 3 ind/L pada masing-masing perlakuan selama 20 hari dimana setiap 4 hari sekali dilakukan sampling kepadatan populasi. Pakan alami yang diberikan untuk masing-masing perlakuan adalah sama, yaitu berdasarkan bobot biomassa sebesar 720 µg/L. Konversi akhir jumlah pakan yang diberikan pada perlakuan A (A. salina): 240 ind/L, B (B. rotundiformis): 6400 ind/L, dan C (O. similis): 1300 ind/L. Hasil penelitian menunjukkan bahwa pemberian pakan alami dari jenis zooplankton yang berbeda berpengaruh sangat nyata (P<0,01) terhadap populasi total, populasi juvenile, populasi betina bertelur, laju pertumbuhan populasi dan berpengaruh nyata (P<0,05) terhadap populasi Phronima sp. stadia dewasa. Dari ketiga jenis zooplankton yang digunakan sebagai pakan alami tidak ditemukan jenis terbaik, tetapi perlakuan B (B. rotundiformis) menunjukkan hasil tertinggi daripada perlakuan yang lain dengan menghasilkan jumlah individu diakhir pemeliharaan sebanyak 96,30±5,10 ind/L (terdiri dari stadia juvenile 76,84±4,45ind/L, stadia dewasa 15,58±1,77 ind/L dan stadia betina bertelur 3,92±0,57 ind/L), serta laju pertumbuhan populasi sebesar 17,33±0,27 %.Kata Kunci : Phronima sp.; pakan alami; performa pertumbuhan

Temperature-dependent egg production and egg hatching rates of small egg-carrying and broadcast-spawning copepods Oithona similis, Microsetella norvegica and Microcalanus pusillus

Reproductive rates of copepods are temperature-dependent, but poorly known for small copepods at low temperatures, hindering the predictions of population dynamics and secondary production in high-latitude ecosystems. We investigated egg hatching rates, hatching success and egg production of the small copepods Oithona similis and Microsetella norvegica (sac spawners) and Microcalanus pusillus (broadcast spawner) between March and August. Incubations were performed at ecologically relevant temperatures between 1.3 and 13.2°C, and egg production rates were calculated. All egg hatching rates were positively correlated to temperature, although with large species-specific differences. At the lowest temperatures, M. pusillus eggs hatched within 4 days, whereas the eggs from sac spawners took 3–8 weeks to hatch. The egg hatching success was ≤25% for M. pusillus, &gt;75% for O. similis and variable for M. norvegica. The maximum weight-specific egg production rate (μg C μg−1 C d−1) of M. pusillus was higher (0.22) than O. similis (0.12) and M. norvegica (0.06). M. norvegica reproduction peaked at 6–8°C, the prevailing in situ temperatures during its reproductive period. The difference in reproductive rates indicates species-specific thermal plasticity for the three copepods, which could have implications for present and future population dynamics of the species in arctic fjords.