Seasonal Changes In Abundance Research Articles

Seasonal Changes in Abundance, Biomass, and Species Composition of Zooplankton Communities in the Open Sea near the Crimean Coast of the Black Sea and Sea of Azov

Seasonal Changes in Abundance, Biomass, and Species Composition of Zooplankton Communities in the Open Sea near the Crimean Coast of the Black Sea and Sea of Azov

Seasonal Changes in Abundance, Biomass, and Species Diversity of Zooplankton in Areas Offshore the Crimea (Black and Azov Seas)

Seasonal Changes in Abundance, Biomass, and Species Diversity of Zooplankton in Areas Offshore the Crimea (Black and Azov Seas)

Floating Riverine Litter Flux to the White Sea: Seasonal Changes in Abundance and Composition

Arctic rivers bring litter from their basins to the sea, but accurate data for the Arctic do not exist yet. This study presents the first assessment of floating macro litter input (>2.5 cm) from the Northern Dvina and Onega rivers to the White Sea. The observations were performed based on the European Marine Strategy Framework Directive (MSFD) methodology and using the mobile application of the Joint Research Centre (Ispra, Italy). The results of observations from May 2021 to November 2021 show that 77% of floating objects were of natural origin (mainly leaves, wood and bird feathers). Of the particles of anthropogenic origin, 59.6% were represented by various types of plastics, 27.7% were processed wood, 8.5% paper/cardboard, 2.7% metal, 1.1% were rubber and <1% textiles. The average monthly input of anthropogenic macro litter by the Northern Dvina varies from 250 to 1700 items/hour, and by Onega from 520 to 2350 items/hour. The level of pollution of the studied rivers was found to be higher than in some Europeans rivers but lower than in China. The mass discharge of macroplastics in the Northern Dvina River was compared with the estimates of the discharge of meso- and microplastics; that allowed us to show that the discharge of macroplastics in mass units is much higher than of micro- and mesoplastics.

Seed bank dynamics and quality in the seagrass Halophila ovalis along estuarine salinity gradients—a case in the Swan-Canning Estuary

The seed bank of Halophila ovalis is crucial for resilience to disturbance through re-establishment. Understanding seasonal changes in abundance and quality of seeds in natural seed banks is critical for seed-based restoration. We selected an estuary in southwestern Australia and investigated the seasonal changes of seed distribution and viability in H. ovalis seed banks. We also adapted an X-ray viability test used for terrestrial seeds to test the viability of H. ovalis seeds. We then simulated the effect of low salinity on seed viability through a short-term indoor experiment. Seed density was significantly different between sites and seasons (0 to 43590 seeds·m-2), and the highest seed density in the seed banks was found after the reproductive season (May). The proportion of viable seeds in the seed bank was less than 22%, and was not subjected to substantial seasonal variability. The density of seeds in the seed bank decreased in spring, which indicated winter conditions were not prompt seed loss. We also predicted that extreme rainfall events and the resulting extremely low salinity would significantly reduce seed viability, and could decrease in seed germination; limit population recruitment. As it rapidly colonizes marine sediments from seeds, H. ovalis was considered an ideal seagrass for restoration purposes. Our results provide physiological information for H. ovalis seed banks to support seed-based restoration plans. Such understanding would enable accurate predictions about seagrass population resilience to extreme climate events in estuaries, where variable and extremely low salinity may limit seagrass population recovery from seeds through decreasing their viability.

Abundance of Lutzomyia longipalpis and Nyssomyia whitmani, the Leishmania spp. vectors in northeastern of Argentina: Are spatial and temporal changing patterns consistence?

Lutzomyia longipalpis and Nyssomyia whitmani were incriminated as vectors of Leishmania sp. Spatial heterogeneity together with seasonal changes in abundance constitute important elements for the understanding of the dynamics of vector populations, and there are fundamental for the development of adequate prevention and control strategies. The aim of this work was to compare the spatial and seasonal abundance of Lu. longipalpis and Ny. whitmani at a city spatial scale between two periods separated by three years. To study the spatial distribution, we compared the abundance distribution of these species at two warm times, 2011 with 2014. Respect to inter-annual seasonal abundance changes, we compared the four seasons of the year between two periods (2011–2012 vs 2014–2016). The spatial distribution for both species were found to be distributed mainly in the same areas of the city in both periods. We change for: Respect to the seasonal pattern of abundance, we observed that seasonal patterns showed changes between periods. Our study defines the ‘where’ and ‘when’ implement the actions to mitigate leishmaniasis cases.

Temporal design for aquatic organismal sampling across the National Ecological Observatory Network

Abstract The National Ecological Observatory Network (NEON) is a continental‐scale research platform designed to assess the impacts of climate change, land‐use change and invasive species on ecosystem structure and function at field sites distributed across 20 ecoclimatic domains (or regions) from Alaska to Puerto Rico. Aquatic sites within the NEON network include 24 streams, 7 lakes and 3 rivers among 19 domains. A significant challenge to this effort is defining standardized methodology for sampling at sites with substantially variable geomorphology and hydrology. The aquatic temporal sampling design provides timing windows for seasonal sampling to best assess organismal diversity and abundance. The need to establish a rule set for temporal sampling was addressed via site‐specific seasonal sampling windows, defined using a suite of environmental variables collected from publicly available meteorological data. Variables integrated into the design include stream flow, growing degree days and riparian phenology. Thresholds for these variables were determined using published literature and used to create three sampling windows for each sample site. Sampling windows target biological community diversity and seasonal changes in abundance, and roughly align with spring, mid‐summer and autumn. NEON‐generated organismal data from 2014 to 2021 were analysed for inter‐ and intra‐annual variability to quantify community‐scale variability among seasonal sampling windows and years at each site. Algae, macroinvertebrate and zooplankton community structure was significantly different within sites across sampling windows, supporting the sampling design of three separate windows per year. Moreover, 93% of sampling windows were completed from 2014 to 2021. An analysis of macroinvertebrate data at 14 sites shows that seasonal β‐diversity represents an important attribute of the stream community, even if interannual trends among sites may differ. We conclude that the temporal sampling design for NEON aquatic biological sampling is justified in having three sampling windows per site and is achievable at most NEON aquatic sites. Although sampling windows have been adjusted at a select number of sites, the original sampling windows are used successfully at the majority of NEON aquatic sites. Sampling windows will be updated with NEON continuous sensor data from each site once sufficient (>3 years) data are available.

Seasonal changes in abundance and feeding ecology of an endemic, keystone predator following the introduction of large rainbow trout Oncorhynchus mykiss

Despite documented negative effects on aquatic ecosystems, management agencies commonly receive requests to stock non-native rainbow trout Oncorhynchus mykiss (Walbaum). We used a multinomial N-mixture model and a suite of diet analyses to evaluate effects of large (265–530 mm) rainbow trout on reach-scale abundance and feeding ecology of an important endemic, keystone species, Neosho bass Micropterus velox (Hubbs and Bailey). We evaluated potential changes by seasonally sampling multiple reaches of an Ozark Highlands stream before and after the introduction of 10,800 rainbow trout. Results suggest that rainbow trout altered the distribution of Neosho bass, as indicated by a negative relationship between rainbow trout density and Neosho bass abundance. Trophically, rainbow trout and Neosho bass <101 mm were equivalent, but rainbow trout diets significantly overlapped with larger Neosho bass. High rainbow trout abundance in the spring post-stocking period changed Neosho bass diets by altering predator–prey dynamics with crayfish. Controlling for fish size revealed Neosho bass consumed larger crayfish than rainbow trout, although rainbow trout and Neosho bass between 200 and 299 mm consumed equal-sized crayfish. Outcomes of rainbow trout stockings are likely density- and size-dependent, but caution is warranted for introductions in warmwater streams.

Does microhabitat use affect population differentiation? A test with southwestern Palaearctic forest birds

We tested whether microhabitat use affects dispersal and population differentiation in forest birds of the southwestern Palaearctic, a link previously suggested in Neotropical birds. To approach this, the number of subspecies within 32 species was used as a metric of population differentiation and was related to their feeding substrata and seasonal changes in abundance (a surrogate of dispersal) in a mountain range (Guadarrama Mountains, Central Spain). Multivariate analyses in which the effect of range size (a main correlate of within-species diversification) and phylogeny relatedness were considered, showed that those birds adapted to exploit the tree canopy had lower seasonal changes in abundance and more subspecies than ground-dweller birds. Our results support a cause-effect link between the use of stable resources in the canopy, seasonal movements and population differentiation of birds from temperate forests of the southwestern Palaearctic.

Altitudinal seasonality as a potential driver of morphological diversification in rear-edge bird populations

Populations at the low latitude limits of a species range (rear-edge populations) are often considered more vulnerable to climate change. However, their ability to track different environmental settings at a regional scale has been widely overlooked, although this may be relevant to accurately assess their adaptive capacity to cope with ongoing changes. Here we tested whether the endemic African Chaffinch (Fringilla coelebs africana) tracks environmental changes (e.g. decreasing temperatures, snow cover) by rearranging their numbers between seasons (spring vs. winter) along the altitude gradients of its northwestern African range. We additionally tested whether these seasonal changes in abundance were paralleled by morphological variation, suggesting a process of population diversification. We assessed African Chaffinch abundance in tree covered farmland and woodland sites distributed along an altitude gradient in spring and winter. In addition, we captured and measured chaffinches within the study gradient to explore the patterns of morphological variation. Our results showed that chaffinches shifted to lowlands from snow covered highlands during winter. In addition, highland individuals showed longer and more concave wings than their lowland counterparts. These morphological traits are usually related to flight efficiency in migratory birds, which suggest the presence of altitudinal movements aimed to track the environmental seasonality caused by orography. These results suggest a potential role of altitudinal seasonality as a driver of regional diversification within the African Chaffinch populations, which could be occurring in other North African avian species given their relatively high endemicity in the region. The evolutionary and conservation implications of these displacements have been often overlooked despite they can shape the adaptive capacity of rear-edge bird populations to face the ongoing environmental changes in this peripheral area of the Palearctic.

Juvenile migration of Japanese dace Pseudaspius hakonensis revealed in a tributary of Lake Biwa with seasonal changes in abundance and stable isotope ratios

Migration patterns of Japanese dace Pseudaspius hakonensis in and around Lake Biwa, Japan are unknown, although fluvial–lacustrine life history has been known in most tributaries, the many mature individuals migrating upstream into tributaries in early spring. Field surveys and stable isotope analyses were used to clarify the migratory history of Japanese dace in the Ishida River, inflowing to Lake Biwa. In the field surveys, the number of young of the year (YOY) individuals caught per unit effort (CPUE) by hand net and casting net in the tributary and lake-shore area was calculated. The CPUE peaked from May to July, after the spawning season, thereafter decreasing rapidly, suggesting that YOY Japanese dace migrated downstream to Lake Biwa immediately after emerging, possibly due to the abundant food resources there. From September to November, the CPUE of YOY individuals increased in the lower reaches of the stream, although their stable nitrogen isotope values were variable, in some cases being similar to those recorded in the upper reaches and the lake-shore area. This suggests that some YOY individuals migrate upstream from the lake in autumn. In the present study, the juvenile migration pattern of fluvial–lacustrine Japanese dace in Lake Biwa was described using a CPUE survey and δ15N and δ13C analyses.

Differential responses of small mammals immediately after clearcutting in forest plantations: Patterns and mechanisms

Clearcutting can have important effects on wildlife. However, the mechanisms by which different species are affected by clearcutting are poorly understood. Here, we performed two experiments to test whether movement behavior influences how a species responds to clearcutting at both individual (survival) and population levels (demographic change). We studied the impact of clearcutting on two rodent species in Pinus radiata plantations in south-central Chile. The study involved a very mobile (Oligorozomys longicaudatus) and a more sedentary (Abrothrix longipilis) species. To study the individual-level response to clearcutting, we radio-tracked 92 (67 A. longipilis and 25 O. longicaudatus) adult male mice from before to after clearcutting and recorded individual survival and movement. To evaluate the population-level response, we recorded the abundance for each species before (winter) and after clearcutting (spring, summer and fall). We also included abundance data in uncut mature stands (controls) to detect seasonal changes in abundance not caused by clearcutting. At the individual-level, we found that after clearcutting >80% of O. longicaudatus remained alive, while only 48% of A. longipilis survived. All A. longipilis that survived clearcutting stayed in the stand (“refuge response”), whereas 77% of O. longicaudatus evacuated the stand and relocated to undisturbed sites (“evacuate response”) allowing them to survive in neighboring areas. At the population-level, the abundance of A. longipilis showed a significant decline after clearcutting that continued towards spring and summer, but in fall we found no differences between clear-cut and uncut mature stands. O. longicaudatus tended to decrease toward spring and summer in both harvested and uncut mature stands, but this trend was not significant. The abundance increased significantly in fall, where the increase in abundance in harvested stands was significantly higher than in uncut mature stands. Our results demonstrate that the short-term effects of clearcutting on abundant small mammal species are species-specific and strongly dependent on the species' movement behavior. Additionally, they showed a rapid population recovery (around 1 year) after high mortality by clearcutting over the less mobile species.

Autumn to spring microbial community in the northern Baltic Sea: temporal variability in bacterial, viral and nanoflagellate abundance during the cold-water season

Marine microbial communities undergo drastic changes during the seasonal cycle in high latitude seas. Despite the dominance of microbial biomass in the oceans, comprehensive studies on the seasonal changes of microbial plankton during the complete winter period are lacking. To study the seasonal variation in abundance of the microbial community, water samples were collected weekly in the Northern Baltic Sea from October to May. During ice cover from mid-January to April, samples from the sea ice and the underlying water were taken in addition to the water column samples. Abundances of bacteria, virus-like particles, nanoflagellates, and chlorophyll a concentrations were measured from sea ice, under-ice water, and the water column, and examined in relation to environmental conditions. All studied organisms had clear seasonal changes in abundance, and the sea-ice microbial community had an independent wintertime development compared to the water column. Bacteria were observed to have a key role in the biotic interactions in both ice and the water column, and the dormant period during the cold-water months (October–May) was limited to before ice formation. Our results provide the first insights into the temporal dynamics of bacteria and viruses during the whole cold-water season (October–May) in coastal high latitude seas, and demonstrate that changes in the environmental conditions are likely to affect bacterial dynamics and have implications on trophic interactions.

Winter decrease of zooplankton abundance and biomass in subalpine oligotrophic Lake Atnsjøen (SE Norway)

Despite the rapidly changing winter conditions in temperate ecosystems, little attention has been devoted to the effects of these changes on lake ecology. Few studies on the seasonal changes in abundance and biomass of the major groups of the metazooplankton community (i.e. rotifers, cladocerans and copepods) in northern oligotrophic lakes include data from the ice-covered winter months. This study reports monthly variation in zooplankton abundance and biomass from June 2010 to October 2011, including winter, in an oligotrophic, subalpine lake in southeastern Norway (Lake Atnsjøen). Changes in rotifer, cladoceran, copepod, and total zooplankton abundances and biomass were related to seasonal variation in water temperature and phytoplankton biomass by means of ordination analysis. The zooplankton abundance and biomass were much lower in winter than during the open water season. However, an under-ice phytoplankton bloom occurred during the final winter months, when snow cover and ice thickness were reduced and (presumably) light penetration increased, leading to an increase in abundance of copepod nauplii. Winter zooplankton abundance was dominated by copepods and rotifers, while winter zooplankton biomass was dominated by copepods and cladocerans. Both phytoplankton and zooplankton had two biomass peaks in 2010 and one peak in 2011. Rotifers dominated zooplankton abundance with a peak in August and total zooplankton abundance followed a similar pattern. In contrast, cladocerans dominated zooplankton biomass with a peak in July and total zooplankton biomass also peaked at this time. Rotifer and total zooplankton abundance and rotifer biomass were most closely correlated to water temperature. However, cladoceran biomass and total biomass were most closely correlated with phytoplankton biomass, but also appeared to be dependent on other carbon sources. Estimates of non-phytoplankton particulate organic carbon indicated that this part of the carbon pool could be an additional food source for zooplankton particularly in early and mid-winter. The longer growing season in 2011 than in 2010, owing to earlier ice-off in 2011, may have contributed to higher phytoplankton and zooplankton biomass in 2011. With climate warming, this is an expected change in temperate lake ecosystems.

Seasonal changes in Abundance of Soil Litter Sap-sucking Insects (Hemiptera) and its Relationship with Edaphic Factors in a Tropical Evergreen Forest

This study presents a review on the dynamics of seasonal variation of insects like Hemiptera in response to different edaphic factors, which include temperature, moisture, pH, organic carbon, inorganic nitrogen, phosphorus, sodium and potassium contents of an anthropogenous tropical forest, in West Bengal. The variation in abundance of Hemiptera is significant during the study period. The order showed its maximum population during summer (April) in 1st study year and in Monsoon (July) in 2nd study year, whereas it showed its minimum representation during winter (December and February) both in 1st and 2nd study year. Insects are generally well adapted to average condition during different season, but extremes can cause problem. From Pearson’s correlation of study, it is observed that the population abundance of a few species is significantly correlated with the concentration of temperature, moisture, pH, sodium, potassium and carbon. But according to the transformed results of Canonical Correspondence Analysis (CCA), it had appeared that increased concentration of temperature, sodium, potassium and carbon content had positive effect on increased Hemipteran population abundance but the concentration of moisture, pH, nitrogen and phosphorus could not affect the population abundance, which ware more specific. The present study helps to distinguish the actual cause of seasonal variation of Hemipteran populations, i.e., the effect of particular edaphic or other factors on them. Keywords: Hemiptera, population abundance, seasonal variation, Pearson’s Correlation study, Canonical correspondence analysis Cite this Article Pradip Kumar Dey, Seasonal changes in Abundance of Soil Litter Sap-sucking Insects (Hemiptera) and its Relationship with Edaphic Factors in a Tropical Evergreen Forest. Research & Reviews: A Journal of Life Sciences . 2019; 9(1): 1–9p.

Changes in the soil meso‐ and micro‐fauna community under the impacts of exotic Ambrosia artemisiifolia

AbstractSuccessful establishment of invasive plant species may exert important effects on soil organisms and processes. To investigate the response of the soil meso‐ and micro‐fauna community to Ambrosia artemisiifolia L. invasion and its age of colonization, samples were collected from three different depths in sites with and without the presence of A. artemisiifolia during the period of October, 2009 to July, 2010. Soil fauna were grouped into four categories, that is, Nematoda, Acarina, Collembola and other meso‐ and micro‐fauna species. Seasonal changes in abundance and distribution patterns in relation to soil biochemical properties were then compared and examined. In general, invasion of A. artemisiifolia into native plants significantly increased the soil fauna densities, especially nematodes. Effects of invasion on soil fauna groups were seasonally variable with density peaking in autumn. Short‐term invasion of A. artemisiifolia could weaken accumulation of soil fauna groups in the top layer. Vertical distribution of soil meso‐ and micro‐fauna communities changed seasonally with the trend of remarkable upward migrations in the period from winter, summer to spring and autumn, though the degrees of upward migration in the invaded and noninvaded sites differed among the fauna groups. Responses of soil fauna communities may be associated with the enhancement of soil nutrient conditions and microbial activities in the presence of A. artemisiifolia. That is, the colonization of A. artemisiifolia, irrespective of colonization age, may exert an important influence on soil meso‐ and micro‐fauna community over time and thus may be beneficial to its successful colonization.

Microalgal diversity of a tropical estuary in south India with special reference to isolation of potential species for aquaculture

The present study unravels the microalgal diversity and dynamics of a tropical estuarine ecosystem (Muttukadu, of Indian south east coast) and applies tools like isolation of useful species to utilize in aquaculture as well as to conserve the native strains. The study was carried out for a period of 18 months. Selected diversity indices (Simpson index, Dominance index, Shannon- Weiner index, Pielou’s evenness index and Margalef richness index) were used to describe the trends of diversity in the estuary during the study period. Spatial and temporal changes in microalgal diversity in the estuary were analysed. Sixty three species of microalgae belonging to Chlorophyceae, Bacillariophyceae, Cyanophyceae, Dinophyceae, Euglenophyceae, Eustigmatophyceae, Prymnesiophyceae, Prasinophyceae and Zygnematophyceae were identified. Out of these, members of Bacillariophyceae formed the dominant flora (48.5%) with twenty six species, followed by Cyanophyceae (29.2%) and Chlorophyceae (13.6%). The species diversity was increased after the flood during December-2015 in south east coast of India. More than two dozens of microalgal strains useful for larval nutrition in aquaculture were isolated during the study period. Nutrient profiling of isolates revealed the presence of essential fatty acids (EPA & DHA) in high percentage in some of the isolates. Altogether, the present study is the first report of this kind from Muttukadu which gives the insight on a) the seasonal changes in abundance of microalgae species in a tropical estuary and b) suitable time for the isolation of potential species for aquaculture and conservation of various species in the laboratory conditions.

Seasonal changes in abundance of four Acartia species (Copepoda, Calanoida) in the coastal waters of Peninsular Malaysia; relationship with monsoon transition

The seasonal variation of Acartia copepods from the waters of Peninsular Malaysia was studied via monthly observations at 2 fixed stations on the west coast (Pulau Pinang and Port Dickson) and 2 fixed stations on the east coast (Kijal and Penyabong) from October 2012 to March 2014. In situ temperatures recorded during this period were relatively constant (mean 29.6±0.7°C) at all stations. Salinity measurements were also fairly constant (mean 30.3 ± 1.1 PSU) for all stations during this study except at Penyabong where the salinity during the northeast (NE) monsoon season was significantly lower (p<0.05) (mean 23.2 ± 7.9 PSU) than during the southwest (SW) monsoon season. Concentration of chlorophyll a at Pulau Pinang during the SW monsoon period was significantly higher (p<0.05) (mean 14.6±5.4μg/L) than during the NE monsoon period. Four species of Acartia were identified at all stations: A. amboinensis, A. erythraea, A. pacifica and A. spinicauda. At Kijal, Acartia erythraea population was significantly higher (p<0.05) (mean 695.7 ± 618.4 inds/m3) compared with the other stations. Acartia species composition at Port Dickson was similar to Penyabong, while Kijal was similar to Pulau Pinang. Small-sized species, Acartia pacifica and A. spinicauda were dominant at Port Dickson and Penyabong, while the larger-sized species, Acartia amboinensis and A. erythraea were dominant at Kijal. Generalized additive mixed models (GAMMs) were applied to abundance data to describe the environmental preference associated with population recruitment of these species, and the results identified a relative contrast in environmental envelopes occupied by the larger and smaller-sized species. The large-sized species preferred colder and more saline water while the small-sized species preferred warmer and lower salinity water. The succession and co-occurrence of similar sized species is suggested to be a result of the combined effect of species-specific preference to varying temperature–salinity regimes.

Seasonal variation in a diverse beetle assemblage along two elevational gradients in the Australian Wet Tropics

Altered abiotic conditions resulting from human-induced climate change are already driving changes in the spatial and temporal distributions of many organisms. For insects, how species are distributed across elevations is relatively well known, but data on their seasonality at different elevations are lacking. Here we show seasonal variation in beetle abundance and species richness along two spatially-distinct elevational transects (350–1000 m and 100–1000 m asl) in the rainforests of northern Australia. Temperature was the best predictor of temporal abundance and species richness patterns, while rainfall had little influence. Elevation had little effect on seasonal changes in abundance or diversity. Adults of most beetle species exhibited long season-lengths (>6 months of the year) with distinct peaks in abundance during the summer wet-season. We found evidence of phenotypic variation among the more widespread species, with seasonal peaks in abundance often not coinciding across elevations or transects. Due to the wide elevational range of most species, and the lack of consistency in the seasonality of wide-spread individual species, we suggest that many beetles inhabiting the low to mid-elevation mountains in the Wet Tropics, and potentially other tropical rainforests, are not as vulnerable to extinction due to climate change as many other organisms.

An exploratory study of heterotrophic protists of the mesopelagic Mediterranean Sea

Abstract Is there a mesopelagic protist fauna composed of species different from that of the overlying surface community? Does the mesopelagic community show seasonal changes in abundances and species composition? We addressed these questions by considering three distinct groups in which species identification is relatively unambiguous: tintinnid ciliates, phaeodarian radiolarians, and amphisolenid dinoflagellates. We sampled weekly at 250 m and 30 m depth from January to June a deep-water coastal site characterized by seasonal changes in water column structure; notably, in winter the mixed layer extends down into mesopelagic depths. We found a deep-water community of tintinnid ciliates comprised of forms apparently restricted to deep waters and species also found in the surface layer. This latter group was dominant during the winter mixis period when tintinnid concentrations were highest and subsequently declined with water column stratification. Phaeodarian radiolarians and the amphisolenid dinoflagellates were regularly found in deep samples but were largely absent from surface water samples and showed distinct patterns in the mesopelagic. Phaeodarian radiolarians declined with water column mixing and then increased in concentration with water column stratification whilst amphisolenid dinoflagellates concentrations showed no pattern but species composition varied. We conclude that for all three protists groups there appear to be both distinct mesopelagic forms and seasonal patterns.

Seasonal changes in abundance, lipid and fatty acid composition of Calanus euxinus in the South-eastern Black Sea

Seasonal changes in abundance, lipid and fatty acid composition of Calanus euxinus Hulsemann, 1991 were analysed monthly during the period from March 2012 to February 2013. The highest abundance of C. euxinus was recorded in February (847 ind. m-3) during the sampling period. Female and male C. euxinus peaked in February (587 ind. m3, 169 ind. m-3, respectively). However, copepodites peaked in November (107 ind. m-3). Average total lipid content was determined as percentage (%) and per individual (mg ind-1). It was proportionally highest in February (7.03%) and lowest in September (3.02%). However, average lipid content per individual was highest in February (0.11 mg ind-1) and lowest in September and November (0.04 mg ind-1). Major fatty acids in C. euxinus were identified as 16:0, 16:1 n-7, EPA and DHA. ΣSFA, ΣMUFA, ΣPUFA and ΣHUFA were observed to be correlated with temperature. ΣSFA and ΣMUFA increasedwith the rise in temperature (r2=0.74, r2=0.73, p&lt;0.05, respectively) whereas ΣPUFA and ΣHUFA increased as temperature decreased (r2=-0.73, r2=-0.80, respectively, p&lt;0.05). Additionally, while ΣPUFA and ΣHUFA increased (r2=0.61, r2=-0.68, respectively, p&lt;0.05), ΣMUFA decreased (r2=-0.68, p&lt;0.05) as chlorophyll-a increased. It was observed that the degree of unsaturation increased as temperature decreased. Results of the study revealed that C. euxinus has rich lipid content as well as fatty acid composition and it plays an important role in the South-eastern Black Sea ecosystem functionalities especially having key role in energy fluxes to higher trophic levels.