Oithona Nana Research Articles

Zooplankton community heterogeneity and trophic interactions in response to environmental drivers in a mesotidal estuary on the Brazilian equatorial margin—Lençóis Maranhenses National Park

Abstract This study emphasises the importance of environmental filters in the dynamics of the zooplankton community and the ecological relationships with phytoplankton in three zones of a tropical mesotidal estuary. Thus, sampling was carried out in six different locations strategically positioned along the Preguiças River estuary, with the following objectives: to characterise the abundance of zooplankton and, through this, determine changes in the community's α‐ and β‐diversity indices depending on variables environmental; to define environmental filters that affect the indicator species of ecosystem zones; and to identify the interaction between phytoplankton and zooplankton along the estuarine gradient. The zooplankton community contained 80 species, including 14 phyla, with Arthropoda being the most diverse, followed by Ciliophora and Mollusca. The class Copepoda stood out, with Paracalanus crassirostris, Pseudodiaptomus gracilis, and Oithona nana dominating the community. In total, 21 species were selected as indicators, including Temora turbinata in the coastal zone, Rhizodomus tagatzi in the mixing zone, and Moina micrura in the tidal river zone. The environmental heterogeneity showed significant spatial differences, with variations governed mainly by salinity, temperature, and suspended organic matter, which acted as the principal environmental filters. The coastal zone and mixing zone species demonstrated direct ecological relationships with the blooms of the diatoms Skeletonema costatum and Asterionellopsis glacialis, in which the abundance of zooplankton was favoured by their occurrence, denoting top‐down control of the trophic network. For the partitioning of β diversity, the turnover component was responsible for the diversity value due to environmental heterogeneity, which distinguished communities across zones. Our findings represent the first comprehensive investigation into the relationship between environmental heterogeneity and zooplankton within this tropical ecosystem, subject to mesotides. These discoveries are pivotal in identifying environments highly susceptible to degradation (low β diversity) and those acting as dispersal centres (high β diversity), thereby facilitating targeted conservation efforts and more efficient management of estuarine systems. Therefore, our results provide a crucial basis for the sustainable management of similar coastal ecosystems in different parts of the world.

Relationship Between Environmental Parameters and Manta Ray Occurrence in Raja Ampat Archipelago, Indonesia

Understanding the influence and impact of environmental factors on manta ray sightings is critical to understanding the spatial and temporal ecology of a highly mobile species. Therefore, this study aims to determine the influence and impact of environmental factors as indicated by the parameters of wind speed, chlorophyll-a, SST, salinity, pH, dissolved oxygen, and the number of phytoplankton and zooplankton species. The mapped chlorophyll-a was re-analyzed based on the seasonal period throughout 2021 downloaded from marine copernicus and analyzed by kriging method. The influence and effects of environmental parameters on the short-term appearance of eye rays were studied using an adaptive model (GAM). The analysis showed a significant influence of environmental factors on manta ray sightings in Raja Ampat, namely Calanoid spp, Oithona nana, Acartia clausi, Calanus helgoladicus, and Oithona brevicornis. Based on this model, zooplankton is an important parameter that can describe the influence of environmental parameters on manta ray sightings at observation points in Raja Ampat MPA. The results of the reanalysis of chlorophyll-a concentrations were highest in the eastern to transitional seasons, which were scattered on the west side of Raja Ampat waters. Meanwhile, chlorophyll-a concentrations were low in the west to transitional season on the east side. This mechanism may drive the foraging strategy of manta rays, which visit shallow waters where zooplankton density and biomass are abundant. Adopting the BHS MPA network concept, as it has been implemented, would be in line with broader conservation expectations for the sustainability of manta rays in Raja Ampat.

Identification of Marine Zooplankton in the Maheshkhali Channel, Cox’s Bazar, Bangladesh

The purpose of the study was to identify and characterize marine zooplankton in the Maheshkhali Channel, Cox’s Bazar, Bangladesh. A total of 25 species were identified from the samples collected from the surface water during November, 2022. They were categorized into 4 major groups such as copepoda, crustaceans, ichthyoplankton and meroplankton. Copepods were the most dominant. Among the copepods, Oithona sp., Oncaea sp., Calanus sp., Subeucalanus flemingeri, Cyclops sp., Acartia sp., Labidocera sp. and Canthocalanus pauper were ubiquitous, with Oithona brevicornis, Oithona nana, Acartia tonsa, Subeucalanus sp. being moderately frequent. The presence of Centropages sp., Paracalanus aculeatus, Paracalanus sp., Pseudodiaptomas sp. and Acartia (Odonticartia) ohtsukai were rare. Shrimp larvae, crab zoea and ichthyoplankton were moderately found. Mysid shrimps were found to be highly prevalent whereas ctenophora larvae were less frequent. Copepod, naupliar larvae and copepodites were observed to be consistently present throughout the observed area. The identified species possess great significance in the marine food web. This investigation is the baseline study of marine zooplankton in the Maheshkhali Channel. Further research, therefore, is recommended to identify zooplankton species through microscopic and molecular methods in the coastal waters of Bangladesh.

Diet composition of the Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner, 1868) (Osteichthyes: Carangidae), from the Aegean Sea

Data on feeding habits in aquatic ecosystems are of great importance in determining the role that a certain fish species plays in its habitat and in related ecosystems. In this study, the diet composition of Mediterranean horse mackerel, Trachurus mediterraneus was investigated for 728 specimens from the central Aegean Sea to compare our data with those from other regions of the Mediterranean Sea and throughout all four seasons. Catches from five major groups were identified. Crustaceans (particularly copepods) proved to be the most important food item considering the index of relative importance (IRI). At least 58 different copepod species were identified. Abundant copepod species that occur in every season were Corycaeus sp., Oncaea media, Oncaea spp., Isias clavipes, Euterpina acutifrons and Oithona nana. Isias clavipes occurred only in spring, with all of them appearing in the diet with a %IRI >10. Although found in a relatively smaller quantity, teleost larvae ranked as the second most important prey in the overall diet, with increasing quantities in fish larger than 18.0 cm.

Variations in copepod composition and diversity in relation to eutrophication and hydrology in İzmir Bay, Aegean Sea

Hyrographic and trophic gradient along Izmir Bay used to assess their effects on the copepod composition and diversity. Trophic state of the bay varied from oligotrophic in the outer region to hypertrophic condition in the inner region as stated by trophic index (TRIX). Aegean Sea water entrance and trophic conditions of the bay affected species assemblages. Oithona davisae, Oithona nana and Acartia clausi were associated with hyper-eutrophic conditions whereas the typical Aegean Sea species, such as Oncaea media group, Oithona similis, Paracalanus parvus, A. clausi, Farranula rostrata and Calocalanus styliremis were related to oligotrophic condition. Copepod diversity indices decreased linearly along the trophic gradient, from oligotrophic to hyper-eutrophic conditions, highlighting the substantial impact of eutrophication on the copepod community structure in the inner region. These findings emphasize TRIX's value in assessing eutrophication in anthropized systems, and immense potential for using copepod composition and diversity in monitoring programs for ecological assessments studies.

Effect of Water Circulation on the Distribution of Zooplankton in the Southern Waters of Peninsular Malaysia

The waters of Peninsular Malaysia located between the South China Sea and the Straits of Malacca are greatly influenced by two different monsoons: the Southwest Monsoon (SW) and the Northeast Monsoon (NE). Zooplankton are known to be receptive to any environmental changes. Apart from biotic and abiotic changes, the movement of water currents also has an impact on the distribution and composition of zooplankton, as this group is considered a passive swimmer that is dependent on the movement of water currents. This study was conducted to determine the effect of water movement in the southern waters of Peninsular Malaysia on the distribution of zooplankton. Sampling was done in three main areas: Kukup, Pengerang, and Pulau Besar. A total of 16 stations with three replicates per station were performed using a plankton net with a mesh size of 140µm. Results show that zooplankton in Pengerang recorded the highest with 256.157 ind/ m3, followed by Kukup (132.412 ind/m3) and Pulau Besar (54.066 ind/m3). There were seven dominant species of copepods recorded in this study, namely Acrocalanus gracilis, Bestiolona similis, Euterpina acutifrons, Oithona nana, Oithona similis, Paracalanus aculeatus, and Paracalanus denudatus. Generally, this study has shown a notable relationship between local current circulation patterns and zooplankton distribution.

Feeding strategy and dietary preference shape the microbiome of epipelagic copepods in a warm nutrient‐impoverished ecosystem

AbstractCopepods provide a rich organic microenvironment allowing the settlement and proliferation of microorganisms, forming dynamic microbial hotspots in the oceans. Such symbiotic associations in the plankton were previously hypothesized to be especially developed in warm oligotrophic seas, as they may serve as alternative sources of nutrients in biologically poor waters. Aiming to better understand how copepod microbiomes are shaped in an oligotrophic sea, we characterized microbiota associated with three dominant coastal epipelagic copepod species in the ultra‐oligotrophic Eastern Mediterranean Sea using amplicon sequencing of the 16S rRNA gene. Our results show that copepod‐associated microbial communities were host‐specific rather than determined by seasonal environmental changes. In the filter‐feeding copepod with a tendency to herbivory, Temora stylifera, microbial diversity was low and relatively stable throughout the year. In contrast, omnivorous copepods, the ambush‐feeding Oithona nana, and the mixed‐feeding Centropages ponticus harbored more diverse microbiomes dominated by transient taxa. We suggest that filter‐feeding strategy and narrow food spectrum can limit copepod–microbe interactions, while the ambush and mixed feeding strategies combined with omnivory confer higher microbial diversity. Filter feeders may reduce the recruitment of opportunistic microbes by maintaining high fidelity associations, as indicated by the large number of core taxa in T. stylifera. We underline the importance of the copepod–microbe associations in nutrient‐impoverished ecosystems, based on predicted enrichment of nitrogen metabolism in the core microbiome, mostly during summer when the shallow coastal waters are nitrogen‐depleted.

Mesozooplankton composition and distribution in İzmir Bay, Aegean Sea: With special emphasis on copepods

Mesozooplankton are a diverse group of heterotrophic organisms and an important component of the food web in transferring energy to higher trophic levels. Studies on mesozooplankton composition and distribution in İzmir Bay, Aegean Sea, are scarce and they included mostly the data from early 2000s. The present study provides updated information on the status of this important component of the bay. Mesozooplankton composition and distribution were studied in June and November 2017, February and April 2018 from eight stations situated along a transit from inner to the outer region in İzmir Bay, Aegean Sea. Samples were collected vertically by using WP2 net with 200μm mesh size. The total mesozooplankton abundance varied from 708 ind. m−3 in June to 42045 ind. m−3 in April. The high abundance of polychaeta larvae, cirriped nauplii, copepods and appendicularians were observed in the inner region, while the abundance of echinoderm larvae, chaetognaths, siphonophores and pteropods were high in the central and outer regions. The contribution of copepod to the total mesozooplankton abundance was the highest (≥ 56 %) in February in all regions. The lowest contributions were in November (32 %) in the inner region and in June in the central (27 %) and the outer (29 %) regions. A total of 38 copepod species were identified during the study period. Acartia clausi successively dominated the copepod community in February and April. Oithona nana was the most abundant oithonid in February and April, while O. davisae in November. O. similis, Paracalanus parvus, Oncaea media group, Temora stylifera and Centropages typicus were abundant in the central and outer regions of the bay. Four new species, Parvocalanus crassirostris, Pseudodiaptomus marinus, Centropages ponticus and Oithona tenuis were detected for the first time in the bay. The reported abundance of C. ponticus, P. crassirostris and P. marinus, together with their spatial and temporal occurrence in the present study, indicate that these species have already settled in İzmir Bay. Results indicate that the mesozooplankton distribution and composition were associated mostly with salinity and depth rather than temperature in group and species level. Substantial changes in the copepod species composition have been observed over decades in İzmir Bay. The number and abundance of smaller and egg-sac carrying non-indigenous species appear to be increasing over time in the bay.

Shifts in neritic copepod communities off the Basque coast (southeastern Bay of Biscay) between 1998 and 2015

Abstract The interannual variations in absolute and relative densities of copepods from the neritic waters of the southeastern Bay of Biscay and their relationship to climate teleconnections and local environmental factors were assessed using time series for the 1998–2015 period. Opposite patterns of variation of the absolute densities of spring Acartia clausi and Centropages typicusspecies vs. summer/autumn species, mainly Oncaea media, but also Ditrichocorycaeus anglicus, Oithona nana, Temora stylifera, and Oithona plumifera were detected. This type of opposite patterns were also observed between the relative densities of the spring A. clausi and summer Paracalanus parvus species. These opposite density patterns were positively correlated to all seasons North Atlantic Oscillation (NAO), spring East Atlantic pattern (EA), summer and autumn water temperature and summer chlorophyll a. They were negatively correlated to summer EA pattern, the winter and spring Atlantic Multidecadal Oscillation (AMO) and water temperature, and the upwelling index of all seasons. In these patterns of copepod variation two regime shifts were detected, one in 2008 towards an increase in the spring species and the other one in 2014–2015 towards an increase of summer species. This latter regime shift coincides in time with the abrupt community shifts predicted in the literature for 2014.

Influence of Microalgae Diets on the Biological and Growth Parameters of Oithona nana (Copepoda: Cyclopoida).

Simple SummaryThe success of marine fish farming is primarily determined by diet in early life. While both artemia and rotifers are commonly used as live feed in aquaculture laboratories in Peru, there has been little work studying the use of native food species. Here, we report our research on the use of a native copepod (Oithona nana) for its potential use in Peruvian marine aquaculture. We collected specimens of the native copepod O. nana and performed culturing experiments with two microalgae that have been widely used in aquaculture. Results show that this species adapted positively to our culture conditions, achieving high densities. We also report on the copepod’s reproduction and growth characteristics. Because of these promising results, we recommend that O. nana be studied further and propose it as a species with potential use as a live feed.Several species of the planktonic free-living genus Oithona have been successfully used in the larviculture of marine fish and shrimp. However, few studies have been published that allow us to estimate the potential of Oithona nana culture under controlled conditions. This work evaluated the effect of the microalgae Isochrysis galbana and Chaetoceros calcitrans as single (200,000 cells/mL) and mixed diets (100,000 + 100,000 cells/mL) on population and individual growth, ingestion rate, number of spawnings, fertility, development time by stage, and sex ratio of O. nana. We cultured this copepod at 28 ± 0.5 °C, 35 PSU salinity, 125 lux, and 12:12 photoperiod. Results showed that diet had no effect on the final population level (6273–7966 ind/L) or on individual growth, nor on sex ratio, with less males than females. With C. calcitrans, O. nana had a higher filtration rate (57 ng C/ind/day). On the other hand, a mixed diet induced a higher number of spawns (0.4 events/day) and nauplii per spawn (23 ind). Similarly, a single or mixed diet, containing I. galbana, accelerated the development rate by 6.33–7.00 days. We concluded that O. nana can be cultured with both microalgae, indicating its potential use in an intensive system for production. However, more research is required to improve the productivity of O. nana rearing.

An updated checklist of marine copepoda from Peninsular Malaysia with notes on their functional traits and distributional records

An up-to-date checklist of marine zooplankton copepods from the water of Peninsular Malaysia is presented, there are 235 species of copepods which consists of 89 genera and 44 families. Extensive list of bibliographical references with synonymy, detailed information on their functional groups, and distributional data are provided for each species. The checklist is based on taxonomic and ecological literature until 28 May 2020. Calanoida recorded the most diverse order with 101 species in total, followed by Harpacticoida with 70 species and 61 species from Cyclopoida. As for Canuelloida, Monstrilloida and Siphonostomatoida all recorded with 1 species respectively. There are 192 species of copepod recorded along the west coast (Malacca Strait) and 123 species on the east coast (South China Sea). Endemicity at species level attains 1% for the whole Peninsular Malaysian coast, with 2 genera restricted to the east coast (Kensakia parva and Brachiella malayensis) and one genus to the west coast (Labidocera jaafari). There are six dominant species that can be found along the coast of Peninsular Malaysia (Acartia erythraea, Acartia pacifica, Bestiolina similis, Euterpina acutifrons, Microsetella norvegica, Paracalanus aculeatus, Oithona nana, Oithona simplex and Temora discaudata).

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.

Characteristics and renewal of zooplankton communities under extreme environmental stresses in the oligotrophic hypersaline Arabian Gulf

Impacts of the exceptionally high temperature and salinity on species composition, abundance, biomass and diversity of zooplankton communities were examined in the central Arabian (Persian) Gulf in late winter and summer of 2010 and 2011. Remarkably diverse zooplankton assemblages were characterized with small calanoids (Paracalanus aculeatus and Temora longicornis), cyclopoids (Oithona nana, Oithona plumifera, Corycaeus flaccus and Corycaeus lautus) and harpacticoids (Euterpina acutifrons) with relatively low abundance and biomass. Overall, the low biomass and abundance were not significantly associated with phytoplankton, whereas zooplankton faunal similarities were significantly correlated with water properties measured as environmental distances across sampling sites. Spatially, the lowest abundance, biomass and diversity occurred in extremely saline nearshore waters off the western Qatar peninsula, whereas the highest abundance, biomass and diversity consistently appeared at northeast offshore locations that periodically encounter nutrient and species-rich but low-salinity water entering the Arabian Gulf via the Strait of Hormuz. Numerically, the relative dominance of calanoids along with lower salinity and high chlorophyll-a concentration in the northeast Arabian Gulf implies that zooplankton populations are likely replenished by the seasonal (summer) transport of species from the Gulf of Oman and the Arabian Sea, which may explain partly the high variations of species richness and zooplankton abundance previously reported in the region. Given increasing evidence of climate-change induced responses of zooplankton, our findings suggest that in the semi-closed Arabian Gulf resident populations stressed by the harsh environment are likely to continue to be sustained only by invading water masses during the summer.

Male Differentiation in the Marine Copepod Oithona nana Reveals the Development of a New Nervous Ganglion and Lin12-Notch-Repeat Protein-Associated Proteolysis.

Simple SummaryCopepods are tiny crustaceans and the most abundant animals on Earth; they also play a crucial role in the marine food chain. Among copepods, Oithona is one of most ecologically successful and is known for its differential behavior between males and females. The males adopt the strategy “live fast, die young”: they are constantly in motion to search for females, more vulnerable to predators, feed less, and have a higher mortality rate. In our study, we found the presence of a new male-specific ganglion in Oithona nana probably involved in female cues sensing. We also demonstrate the potential role of new Lin-12 Notch Repeat proteins in the development of this ganglion by interacting with proteins involved in the development of the nervous system. Thanks to our findings, we propose that the “live fast, die young” strategy of the O. nana males is optimized by the explosion of these Lin-12 Notch Repeat proteins in the male proteome involved in the development of the male-specific olfactory ganglion to increase female cue sensing and mating.Copepods are among the most numerous animals, and they play an essential role in the marine trophic web and biogeochemical cycles. The genus Oithona is described as having the highest density of copepods. The Oithona male paradox describes the activity states of males, which are obliged to alternate between immobile and mobile phases for ambush feeding and mate searching, respectively, while the female is less mobile and feeds less. To characterize the molecular basis of this sexual dimorphism, we combined immunofluorescence, genomics, transcriptomics, and protein–protein interaction approaches and revealed the presence of a male-specific nervous ganglion. Transcriptomic analysis showed male-specific enrichment for nervous system development-related transcripts. Twenty-seven Lin12-Notch Repeat domain-containing protein coding genes (LDPGs) of the 75 LDPGs identified in the genome were specifically expressed in males. Furthermore, some LDPGs coded for proteins with predicted proteolytic activity, and proteases-associated transcripts showed a male-specific enrichment. Using yeast double–hybrid assays, we constructed a protein–protein interaction network involving two LDPs with proteases, extracellular matrix proteins, and neurogenesis-related proteins. We also hypothesized possible roles of the LDPGs in the development of the lateral ganglia through helping in extracellular matrix lysis, neurites growth guidance, and synapses genesis.

Linking long-term changes of the zooplankton community to the environmental variability at the EPEA Station (Southwestern Atlantic Ocean)

A significant sea surface temperature increase has been reported for the Southwestern Atlantic Ocean between 20° S-50° S over the last decades. Zooplankton organisms are highly sensitive to temperature rise. They play a very important role in marine ecosystems by providing the main pathway of energy transfer from primary producers to consumers. Seasonal and interannual (2000-2017) variability of metazooplankton in relation to environmental changes, particularly temperature, were analyzed at the EPEA station (38° 28′ S-57° 41′ W). Copepods, appendicularians, cladocerans, chaetognaths, and lamellibranch larvae were identified and quantified. Temperature exhibited a positive interannual trend during the series, whereas the Simpson parameter showed a decreasing tendency and salinity remained almost constant. Adults, copepodites, and nauplii of small copepods belonging to Oithonidae (mostly Oithona nana) and Paracalanidae-Clausocalanidae families dominated the metazooplankton community during the study period. Three groups of taxa with different seasonal patterns of variability were clearly identified. Members of Oithonidae exhibited positive interannual trends, whereas lamellibranch larvae and Calanidae showed negative interannual trends. A direct influence of temperature anomaly on these changes is suggested as well as possible indirect effects of this anomaly upon zooplankton through different phytoplankton fractions. Under the current scenario of climate change, the maintenance of this time-series becomes crucial in order to evaluate the eventual transfer of the environmental variability to the local food webs through planktonic organisms.

Evaluation of the population growth and fatty acid composition of Copepoda, Oithona nana, fed on different diets

The marine Copepoda species Oithona nana , is considered as one of the most Copepoda species that successfully mass cultured in marine hatcheries. This study investigated the effects of four feed diets (soybean, yeast, rice bran, and corn starch) on the population growth, growth rate, population composition, fecundity, and fatty acid composition of Copepoda, O. nana . The experiment was continued for 15 days and the copepods were fed on four feed diets with concentration of 1 g/10 6 individual/day. The results found that O. nana fed on corn starch showed the highest significant population growth (9067 Individual/L) and population growth rate (0.735). For nutritional value, copepods fed on rice bran were detected to have the highest content of monounsaturated fatty acid (MUFA), polyunsaturated fatty acids (PUFA), the lowest saturated fatty acids/unsaturated fatty acids ratio (SFA/UFA ratio) and the lowest SFA. More importantly, the rice bran diet was the only diet that showed eicosapentaenoic acid (EPA; C20:5ω3). Moreover, copepods fed on rice bran showed the highest significant female fecundity (8.33 egg/female), copepodite and nauplii percentages (33.27 and 32.65%, respectively). Finally, regarding to the quantity, corn starch is the most suitable diet for mass culturing O. nana, while, regarding to the quality, rice bran enhances the nutritional value and fecundity of the Calanoida Copepoda O. nana.

Effect of Different Salinity Levels on Population Dynamics and Growth of the Cyclopoid Copepod Oithona nana

Copepods are one of the most abundant and diverse live food sources for mesopelagic and bathypelagic fishes and crustaceans. They could contribute to the overlap of the transition period from live feed to an artificial weaning diet in marine larvae production. However, the culture conditions still need optimization to provide sufficient production to cover the increasing demand for marine hatcheries. Therefore, the present study investigated the effects of different salinity levels (5, 10, 15, 20, 25, and 30 ppt) on the population growth, growth rate, and population composition (males, females, copepodite, and nauplii ratio) of the marine copepod, Oithona nana. The experiment continued for 15 days, under laboratory-controlled conditions of temperature (27 ± 1 °C), pH (7.7 ± 0.15), and continuous gentle aeration in 30 L glass aquaria. The copepod culture aquaria were supplemented with a mixture of soybean and yeast (0.5 g 10−6 individual−1 24-h−1) as a feed source. The highest significant population growth and population growth rate of O. nana were achieved with a salinity level of 20 ppt. Regarding population composition, O. nana cultured at the salinity level of 20 ppt recorded the highest significant percentages of copepodite and nauplii. The results concluded that copepod, O. nana, is capable of withstanding abrupt changes in the salinity, but there are limits to their tolerance, with an optimal salinity level of 20 ppt. This salinity level achieved the highest population growth and the highest percentages of copepodite and nauplii of marine Copepoda, O. nana.

Population Dynamics, Fecundity and Fatty Acid Composition of Oithona nana (Cyclopoida, Copepoda), Fed on Different Diets.

Simple SummaryMarine larval production is the most critical stage in the life of the marine aquacultured species, which depends on the use of different zooplanktonic organisms as live feed. Copepods are high-quality live prey that could be efficiently used to overcome the transition period from live food to weaning with an artificial diet in the post-larval stages. The main culture systems of copepods use microalgae as uni-food, nevertheless for the more sustainable and cost-efficient production of copepods, the development of artificial diets is the core of its production techniques. The present study was conducted to improve the production and nutritional quality of copepod, Oithona nana, using different diets (soybean, yeast, rice bran, and corn starch). Among all diets, corn starch revealed the highest population growth. Meanwhile, animals nourished by rice bran showed the highest percent of copepodite, nauplii, and fecundity. The nutritional quality of copepods referred to fatty acids profile showed a high percentage of unsaturated fatty acids in copepods fed on rice bran. In conclusion, the dry feeds are very applicable, more economic, and simply alternative diets to substitute microalgae and maximize the fecundity and population of O. nana in fish hatcheries.The marine copepod species Oithona nana is considered as one of the most successfully mass cultured Cyclopoida species in marine hatcheries. This study investigated the effects of four feed diets (soybean, yeast, rice bran, and corn starch) on the population growth, growth rate, population composition, fecundity, and fatty acid composition of native isolated Cyclopoida copepod species O. nana. The experiment was continued for 15 days and the copepods were fed on one of the four diets with a concentration of 1 g 10−6 individual day−1. The results revealed that corn starch was found to be the most supportive diet for population growth and population growth rate. For nutritional value, copepods fed on rice bran were detected to have the highest content of MUFA, PUFA, and the lowest SFA and SFA/UFA ratio; more importantly, the rice bran diet was the only treatment that showed C20:5ω3. Moreover, copepods fed on rice bran showed the highest significant female fecundity, copepodite, and nauplii percent. Finally, the protocols described in the current study concluded that the dry feeds, especially corn starch, are very useful and applicable in hatcheries for maximizing the fecundity and density of Cyclopoida copepod species, O. nana.

The non-indigenous Oithona davisae in a Mediterranean transitional environment: coexistence patterns with competing species

The Venice lagoon (VL) has been recognized as a hot spot of introduction of non-indigenous species (NIS), due to several anthropogenic factors and environmental stressors that combined may facilitate NIS invasions. In the last decades an increasing number of zooplankton NIS have been observed in the VL. This work aims to provide a picture of the annual cycle and distribution of the recently recorded non-indigenous copepod Oithona davisae, considering the coexistence patterns with the congeneric resident Oithona nana. Therefore, zooplankton samplings were carried out monthly from August 2016 to July 2017 at five Long-Term Ecological Research LTER stations in the VL. Oithona davisae showed a persistent occurrence throughout the year with the highest abundances in the warm season and in the inner areas, while the congeneric O. nana, showing a different distribution pattern, resulted more abundant near the inlets of the Lagoon, where O. davisae reached the minimum density. Oithona davisae seems to find local conditions that promote its settlement and distribution, especially in the inner and more trophic lagoon sites. In other European coastal embayments or transitional waters, O. davisae occupied the niche left by the indigenous O. nana or can replace this congeneric species through competitive exclusion mechanisms. Our data indicate that, for now, such species replacement has not occurred in the VL. One of the causes is the extreme variety of habitats and niches offered by this environment allowing a balanced coexistence with O. nana and in general with the resident copepod community.

Relationship between environmental factors and zooplankton diversity in the Gulf of Bandırma (the Sea of Marmara)

Zooplankton community and its relationship to environmental variables were investigated seasonally between autumn 2006 and summer 2008 in the Gulf of Bandirma (the Sea of Marmara). In the Gulf, we identified nine Copepoda, three Cladocera, one Hydrozoa, one Cydippida, Appendicularia, Bivalvia, Chaetognatha, Cirripedia, Decapoda, Echinodermata, Gastropoda, Polychaeta, Pisces larvae, and Pisces eggs at three sampling stations. Shannon-Weaver diversity index and Pielou’s evenness value ranged between 0.00–2.72 and 0.00–1.00, respectively. The first two components of the redundancy analysis (RDA) explained 81.9% of the variance as the main factors (generally the longest arrows) affecting the spatial and temporal distributions of zooplankton in the Gulf of Bandirma, with dissolved oxygen (DO), nitrite+nitrate (NO3 + NO2-N) and phosphate (PO4-P). Liriope tetraphylla, Oithona nana, Paracalanus parvus, Penilia avirostris, Appendicularia and veliger larvae (Gastropoda) were positively related to DO and salinity, and negatively correlated with temperature, chlorophyll-a (Chl-a), Trophic State Index (Trix), PO4-P, and NO3 + NO2-N. According to Spearman’s rank correlation analysis, there was a strong positive correlation between the number of zooplankton individuals and temperature, and the number of zooplankton individuals negatively correlated with salinity and Chl-a. In order to determine similarities among seasons in the samples, the Bray-Curtis similarity index was calculated using species diversity and abundance values, while Euclidean distances were calculated using ecological parameters. Overall, the diversity of zooplankton in the Gulf of Bandirma was higher in the first sampling year and decreased due to the effect of mucilage in the second sampling year.