Distribution Of Mesozooplankton Research Articles

Species Distribution Models for Mesopelagic Mesozooplankton Community

ABSTRACTAimWe aimed to enhance our understanding of the distribution of mesopelagic mesozooplankton (MM) using species distribution models, assess the performance of various modelling techniques, identify key environmental predictors for MM distribution and compute their habitat suitability indices.LocationOur study focused on the mesopelagic zone globally, with data analysed from different oceans.TaxonOur focus was primarily on mesopelagic mesozooplankton, gathering data on 861 different species from the Mesopelagic Mesozooplankton and Micronekton (MMM) Database.MethodsWe used an ensemble of species distribution models, applying 10 different modelling algorithms and three multi‐model ensemble approaches. We explored two important factors that can affect model performance: subsampling and the choice of background points. We also estimated the relative importance of various environmental conditions such as mixed layer depth, temperature, salinity, net primary productivity, euphotic zone depth and dissolved nitrate concentration on the distribution of these species.ResultsEuphotic zone depth, salinity and dissolved nitrate concentration were identified as the most important variables for explaining the distribution of mesopelagic mesozooplankton. The ensemble modelling results were robust in areas with abundant observational records, but high uncertainty was observed in data‐limited regions. We found a patchy habitat suitability map for zooplankton when modelled within their native range, largely due to uneven sampling. Unrestricted range models yielded smoother patterns but could inaccurately project species in areas where they do not occur.Main ConclusionsOur study highlights the need for increased sampling effort in data‐limited regions to improve the accuracy of mesopelagic species distribution models. Despite some inaccuracies, unrestricted range models, assuming ecological equivalence (where different species occupying a similar ecological niche in different geographical regions or different ecosystems exhibit similar adaptations and behaviours), provide a reasonable comparison for habitat suitability maps and model performance. It also confirms the significant impact of certain environmental conditions on mesozooplankton distribution.

Diversity and Distribution of Mesozooplankton in the Coastal Southwestern Mediterranean Alboran Sea, during Summer: What Are the Driving Factors?

Diversity and Distribution of Mesozooplankton in the Coastal Southwestern Mediterranean Alboran Sea, during Summer: What Are the Driving Factors?

Links between the three-dimensional movements of whale sharks (Rhincodon typus) and the bio-physical environment off a coral reef

BackgroundMeasuring coastal-pelagic prey fields at scales relevant to the movements of marine predators is challenging due to the dynamic and ephemeral nature of these environments. Whale sharks (Rhincodon typus) are thought to aggregate in nearshore tropical waters due to seasonally enhanced foraging opportunities. This implies that the three-dimensional movements of these animals may be associated with bio-physical properties that enhance prey availability. To date, few studies have tested this hypothesis.MethodsHere, we conducted ship-based acoustic surveys, net tows and water column profiling (salinity, temperature, chlorophyll fluorescence) to determine the volumetric density, distribution and community composition of mesozooplankton (predominantly euphausiids and copepods) and oceanographic properties of the water column in the vicinity of whale sharks that were tracked simultaneously using satellite-linked tags at Ningaloo Reef, Western Australia. Generalised linear mixed effect models were used to explore relationships between the 3-dimensional movement behaviours of tracked sharks and surrounding prey fields at a spatial scale of ~ 1 km.ResultsWe identified prey density as a significant driver of horizontal space use, with sharks occupying areas along the reef edge where densities were highest. These areas were characterised by complex bathymetry such as reef gutters and pinnacles. Temperature and salinity profiles revealed a well-mixed water column above the height of the bathymetry (top 40 m of the water column). Regions of stronger stratification were associated with reef gutters and pinnacles that concentrated prey near the seabed, and entrained productivity at local scales (~ 1 km). We found no quantitative relationship between the depth use of sharks and vertical distributions of horizontally averaged prey density. Whale sharks repeatedly dove to depths where spatially averaged prey concentration was highest but did not extend the time spent at these depth layers.ConclusionsOur work reveals previously unrecognized complexity in interactions between whale sharks and their zooplankton prey.

Vertically distinct sources modulate stable isotope signatures and distribution of Mesozooplankton in central Patagonia: The Golfo de Penas - Baker Channel connection and analogies with the Beagle Channel

Vertically distinct sources modulate stable isotope signatures and distribution of Mesozooplankton in central Patagonia: The Golfo de Penas - Baker Channel connection and analogies with the Beagle Channel

Local variability of Arctic mesozooplankton biomass and production: A case summer study

The Barents Sea is a highly productive ecosystem within the Arctic Ocean. The overall biological productivity in this region relies heavily on the secondary mesozooplankton production (MZP). Previous research has primarily focused on mesozooplankton abundance (MZA) and biomass (MZB), lacking a comprehensive analysis of the environmental factors that influence MZP in the Arctic marine environment. The primary objective of this study was to examine the key factors responsible for the spatial variability in the community structure and MZP during the summer season. Data were collected from 52 stations in the central Barents Sea, specifically during post-bloom conditions in 2015. Through cluster analysis, two distinct groups of stations were identified, differing in terms of mesozooplankton taxa abundance. Copepods were found to dominate the mesozooplankton assemblages, comprising 89% of total MZA, 83% of MZB, and 68% of MZP. The biomass stocks in the study area varied from 8 to 102 mg dry mass (DM) m−3, with an average of 44 mg DM m−3. MZP rates ranged from 0.34 to 2.33 mg DM m−3 day−1, with an average of 1.16 mg DM m−3 day−1. The highest MZB and MZP values were observed at frontal zones that separated relatively warm and cold waters. Through redundancy analysis, it was determined that the primary environmental factors affected the distribution of mesozooplankton were longitude, latitude, and sampling depth. Temperature, salinity, and chlorophyll a concentration were found to have a less significant impact. These findings emphasize the importance of oceanographic conditions as the main predictors of mesozooplankton distribution during the summer season in the Arctic marine environment. This study highlights the essential role of environmental forcing in determining the productivity of Arctic marine zooplankton. Given the ongoing climatic changes, the results of this report can serve as a valuable tool for monitoring pelagic ecosystems in the Arctic.

Composition patterns of surface mesozooplankton in the zonal fronts of Drake Passage

Abstract Zooplankton is the main food source for higher trophic levels in marine environments. In the Southern Ocean, the distribution of zooplankton is related to the physical gradient of the Antarctic Circumpolar Current (ACC) fronts. Our objective was to determinate the distribution of mesozooplankton in relation to the ACC fronts in the Drake Passage. Samples were collected with the Continuous Plankton Recorder in two transects. Mesozooplankton was associated with environmental variables. High mesozooplankton abundances were recorded in the Subantarctic Front in 2017 and in the Antarctic Zone in 2016. A total of 81 taxa and 23 species in 2016 and 31 in 2017 were identified. Copepoda was the most abundant group (89%), and Centropages brachiatus (3 872 ind. m−3) and Oithona spp. (2 916 ind. m−3) were the most abundant copepod taxa. Mesozooplankton abundance and composition were influenced by front variability. Taxa were contracted northward on 2016 and displaced southward in 2017 and linked to chlorophyll a (Chl a) values recorded in the coastal shelf of South America. Chl a values registered close to Antarctic Peninsula were not linked to mesozooplankton abundance. Changes in abundances of certain taxa may reflect distinct climate events. These changes may impact the availability of prey for higher trophic levels, either through displacement for food or food availability.

Recent Changes in Composition and Distribution Patterns of Summer Mesozooplankton off the Western Antarctic Peninsula

The Southern Ocean has undergone significant climate-related changes in recent decades. As a result, pelagic communities inhabiting these waters, particularly mesozooplankton, have adapted to new conditions. The present study considers the patterns of horizontal and vertical (up to 1000 m) distribution, the composition, abundance, and biomass of mesozooplankton, and the relationships of these parameters to the extreme environmental conditions off the western Antarctic Peninsula throughout the record-warm austral summer season of 2022. Sampling was conducted using the opening/closing Multinet system (0.25 m2 aperture) equipped with five 150-μm mesh nets and a WP-2 net. The mesozooplankton was represented by the three most abundant groups: eggs and larvae of euphausiids such as Euphausia superba, small copepods such as Oithona similis, and large calanoid copepods such as Calanoides acutus, Calanus propinquus, Metridia gerlachei, and Rhincalanus gigas. The composition and quantitative distribution of the mesozooplankton significantly varied: the copepods were abundant in the west, off the Antarctic Peninsula, while eggs and larvae of euphausiids were abundant in the east, off the South Orkney Islands. Most mesozooplankton occurred in the upper 200 m layer, and each taxon showed characteristic depth preference: small copepods, euphausiids larvae, and cirripeds cypris larvae were abundant in the epipelagic layer, while large calanoid copepods, euphausiids eggs, amphipods, pelagic polychaetes, and ostracods were found mostly in the mesopelagic layer. The composition and quantitative distribution of mesozooplankton had clear relationships with environmental factors, particularly with a combination of variables such as water salinity, temperature, and chlorophyll a concentration.

Summer distribution and community structure of surface water mesozooplankton from the eastern Mediterranean Sea

The zooplankton community structure and its relationship with environmental parameters were evaluated in the surface waters (0–50 m) of the eastern Mediterranean (the Aegean Sea’s coastal waters and the Levanine Sea’s coastal and offshore waters), from coastal waters to open sea waters, during the summer for two years. A total of 157 species/groups were registered in the study area. Copepods, cladocerans, doliolids, meroplankton and appendicularians represented the most important zooplankton groups. Five copepod species (Corycaeus [Onychocorycaeus] ovalis, Goniopsyllus clausi, Oncaea scottodicarloi, Sapphirina bicuspidata and Scaphocalanus curtus) have been recorded for the first time in Turkish coastal regions; three species (Centropages bradyi, Goniopsyllus clausi and Oncaea scottodicarloi) had not previously been found in the Aegean Sea; and one species (Goniopsyllus clausi) has been added for the first time to the eastern Mediterranean fauna. Moreover, Pleopis schmackeri was already found to be present in both the Aegean Sea and Mediterranean coasts of Turkey in August 2006. Dominant species varied from the coastal waters to open waters. A small number of species belonging to the coastal community (e.g. Penilia avirostris, Pseudevadne tergestina, Oithona plumifera, Paracalanus parvus and Centropages kroyeri) dominated all coastal areas. In contrast, the open water stations were characterised by the presence of typically epipelagic species of the Mediterranean Sea (e.g. Calocalanus spp., Clausocalanus furcatus, Lucicutia flavicornis, Mecynocera clausi, Farranula rostrata, Oncaea scottodicarloi and Oncaea mediterranea).

Spatial and temporal variation and distribution of mesozooplankton in the Drake Passage sampled with the continuous Plankton Recorder

Zooplankton is the main link between primary producers and higher trophic levels in marine foods webs. In the Southern Ocean, zooplankton could be key in identifying environmental changes, given rapid warming registered in the area in the last decades. The Drake Passage is a choke point of oceanographic processes, since it is the narrowest and most dynamic path of the Antarctic Circumpolar Current (ACC). The objective of this study was to determine the horizontal spatial variations of mesozooplankton in the Drake Passage relative to Southern Ocean oceanographic fronts and zones. Three transects were sampled using a CPR in the Drake Passage during the austral summer of 2009 and 2010. Temperature and salinity were measured at 1-min intervals with a thermosalinograph and Chlorophyll a data extracted from NASA's ocean color web. Organisms were counted and identified to the lowest level, resulting in 53 taxa, with 24 identified to species, eight to genus and 21 to a higher taxonomic level. Four fronts (Subantarctic Front - SAF, Polar Front - PF, South of ACC Front - SACCF and Peninsula Front -PF*) delimiting five zones (Subantarctic Zone - SAZ, Polar Front Zone - PFZ, Antarctic Zone - AZ, Southern Zone - SZ and Transitional Water Zone with Bellingshausen Sea Influence TBW) were registered according to temperature values. Higher mesozooplankton abundances were recorded in the PFZ (412.0 ± 27.9 ind. m−3) in 2009 and in the AZ (128 ± 12.3 ind. m−3) during 2010. Copepoda were the most abundant group (82%), followed by crustacean eggs (4.3%) and Larvacea (4.0%). Within Copepoda, the most abundant taxa were Calanidae copepodites (33.5 ± 53.4 ind. m−3), Oithona spp. (25.4 ± 27.1 ind. m−3) and Calanus simillimus (19.4 ± 26.1 ind. m−3). Differences in community structure were found between zones with C. simillimus and Thysanoessa macrura contributing most to the dissimilarities between the SAZ and the PFZ, Ctenocalanus citer between the PFZ and AZ, Euphausia superba between zones south of the Polar Front and Salpa thompsoni between the SZ and TBW. Some species or taxa are related to or: indicators of a particular zone. The PFZ was the most diverse and had higher mesozooplankton abundances compared to the other zones. Changes in composition are perceptible compared to previous studies, with a decrease of larger organisms and richness, lack of larger copepods, decrease of krill and increase of S. thompsoni abundances.

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.

Spatial and temporal distribution of mesozooplankton in the coastal waters of Cyprus (Eastern Mediterranean)

This study provides elements on the spatial and temporal mesozooplankton variability during a three-year study, encompassing vertical hauls from 50 m deep to the surface from four coastal locations of Cyprus. The total mesozooplankton abundance fluctuated between 190.4 and 882.5 individuals m-3. A total of 90 holoplanktonic and meroplanktonic taxa were recorded. Copepods dominated in the community and accounted for 71.7% of the total mesozooplankton, followed by appendicularians, molluscs, cladocerans, and siphonophores, which contributed 8.04%, 5.48%, 4.60%, and 3.31%, respectively. There were no statistically significant differences among the four sampling sites for any of the mesozooplanktonic taxa, though seasonal and interannual differences were recorded for several of them. The community composition reinforced the evidence for a higher resemblance of the Cyprus mesozooplankton to the offshore communities of the northern and central Levantine Sea and those around Rhodes Island, instead of the northeastern Mediterranean coastal areas. Comparisons of the seasonal abundance variation of the mesozooplankton taxa with other coastal areas of the Levantine Sea are provided. Considering the seasonality of the mesozooplankton, there was a separation of the taxa into distinct groups representing the summer, the winter-spring, and the autumn periods. The temperature was the most important variable that shaped the formation of the distinct seasonal groups of taxa, while chlorophyll-α, dissolved oxygen, and salinity contributed to a lesser extent. Chlorophyll-α concentrations verified the oligotrophic character of the area and seem to be unaffected by inland inputs. The mesozooplankton community showed a spatial consistency, probably as the result of the open sea influence, and seems to be regulated mainly by the properties of the central Levantine pelagic waters and less by terrestrial inputs of inland waters.

Effects of environmental variables on mesozooplankton dynamics in an Amazonian estuary

In the present study, it was analyzed the structure of mesozooplankton community, and their spatio-temporal variations along the Caeté River estuary (northeast of Pará, Brazil). Samples were collected during spring tides conducted in nychthemeral cycles, in three fixed sectors located along the studied estuary (inner-S1, middle-S2 and outer-S3), using conical plankton nets of 200 μm mesh size. Samplings were performed in September 2014 (dry season) and March 2015 (rainy season), totaling 54 samples. A total of 25 mesozooplankton species were recorded, being the copepods the most diversified group (21 species), mostly dominated by estuarine and coastal species. The most abundant mesozooplankton species presented significantly higher densities ( p <0.0001) between the middle ( Pseudodiaptomus richardi , 583.8±956.5 ind m −3 , Paracalanus quasimodo, 108.9±181.4 ind m −3 and Pseudodiaptomus acutus, 23.4±66.6 ind m −3 ) and outer ( Acartia tonsa, 476.9±1,298.8 ind m −3 and Acartia lilljeborgii (407.9±1,038.1 ind m −3 and Parasagitta tenuis , 59.9±117.1 ind m −3 ) sectors. The non-metric multidimensional ordination analysis highlighted that the average density of the main species varied mainly at a spatial scale, with density increasing toward the mouth of the estuary (except for P. richardi ). Spearman's correlation ( rs ) demonstrated that the salinity, turbidity, dissolved nutrients and chlorophyll a concentrations were the prevailing environmental variables associated with significant spatial changes of mesozooplankton distribution in this area. Overall, the results showed that spatial variation in the water physicochemical characteristics of the Caeté Estuary have significant effects on the structure and succession of the mesozooplankton, which may potentially affect the functioning and biodiversity of this coastal ecosystem.

Coastal Mesozooplankton Assemblages during Spring Bloom in the Eastern Barents Sea.

Simple SummaryArctic coastal waters have been strongly influenced by climatic fluctuations during the past decades. Recent studies reported clear warming processes in the Barents Sea and adjacent waters. Plankton assemblages are good indicators of environmental changes, and their composition and production affect all components of pelagic ecosystems. Most of data on the zooplankton in Arctic seas were obtained during summer seasons, and little is known about zooplankton communities in other seasons. Spring is one of the crucial periods in the Arctic marine environment, as primary production may reach the annual maximum. To investigate a spring pattern of Arctic mesozooplankton, we performed a study in the eastern Barents Sea. This research is the first report on the spring coastal zooplankton near the Novaya Zemlya Archipelago. We revealed high diversity and abundance of zooplankton taxa. Environmental variability had a significant impact on the mesozooplankton assemblages, with geographical location and phytoplankton density being the most important. Our data may be useful for future investigations dealing with Arctic plankton communities during the era of global climatic changes.Mesozooplankton play an important role in Arctic shelf ecosystems as a trophic link and a key food source for many larval fish species. The distribution of mesozooplankton in the eastern Barents Sea was studied along a 500 nautical mile-long transect in May 2016 during the spring bloom. Mesozooplankton were sampled using a Juday net hauled from the surface to the bottom at 12 stations. We found good correspondence between the distribution of water masses and mesozooplankton assemblages. Mesozooplankton abundance (mean 73·103 individuals m−2) in Novaya Zemlya coastal water was dominated by Copepoda ova and nauplii, Thyssanoessa spp. nauplii and Oithona similis. Parasagitta elegans and Calanus finmarchicus comprised most of the total mesozooplankton biomass (mean 0.9 g dry mass m−2) in that water mass. A second assemblage (mean abundance 171·103 individuals m−2) was associated with the colder Barents Sea water, with Oithona similis, Copepoda nauplii, Fritillaria borealis and Cirripedia nauplii being the most numerous. In that water mass, C. finmarchicus, Metridia longa, Cirripedia nauplii and Calanus glacialis contributed most to the total biomass (mean 3 g dry mass m−2). The dominance of young stages of Copepoda and a high proportion of meroplankton were typical of spring mesozooplankton assemblages. The spatial distribution of mesozooplankton abundance and biomass was strongly correlated with latitude, longitude and chlorophyll a concentration, which together explained 10% of the total variance in mesozooplankton density. The present investigation is a baseline study for the assessment of the spring mesozooplankton assemblage in the eastern Barents Sea, and for an evaluation of the possible impact of future environmental changes on the Arctic shelf marine ecosystem.

Circulation and distribution of suspended mesozooplankton carcasses in a mid-latitude estuary

The coast of southern Chile, located between 37° and 41°S, has many estuaries, which, together with their wetlands, still comprise a region with high biological richness and a high ecosystem value. The Valdivia River Estuary (VRE) stands out due to its relative size and commercial importance. This study analyses time series of environmental forcings and idealized model output to identify estuarine regimes and the subtidal circulation, and its influence on the distribution of Suspended Meso-Zooplankton Carcasses (SMZC), which may affect the local labile organic carbon input. Field campaigns were conducted in 2014 and 2015, and time series of metocean forcings span from 2012 to 2018. The characteristic regimes of the estuary that control the seasonal suspended particulate matter distribution were identified as Normal, Extreme, Exceptional Rainy, and Exceptional Dry. When mapped on the Geyer & MacCready circulation-stratification diagram, they coincide with partially-mixed, strongly-stratified, salt-wedge, and well-mixed water column structures, respectively. The idealized numerical model allows determining the subtidal circulation patterns induced by the along-channel density gradient, river discharge, and wind. The equilibrium SMZC distribution within the VRE during Normal and Exceptional Dry regimes was determined from the modeled circulation patterns. Model results indicated that, during the austral autumn (April 2014; Normal regime), the SMZC distribution shows a maximum concentration as low as 128 individuals per m3 located near the head of the estuary. This suggests low residence times of suspended carcasses within the estuary. During the austral summer (January 2015; Exceptional Dry regime), the SMZC distribution exhibits its maximum value near the mouth, exceeding 15,000 ind. m−3. These results suggest a massive carcass-derived carbon export towards the estuary mouth during dry seasons. Remarkably, the cross-section where maximum SMZC was predicted during this regime matches the area where large beds of Tagelus dombeii have been reported. Overall, this study highlights the importance of circulation-stratification relationships on the control of SMZC trapping mechanisms and on the identification of hotspots of benthic biomass in mid-latitude estuaries. Other estuaries with similar relationships and regimes might experience similar shifts in suspended meso-zooplankton distribution patterns in response to seasonal changes in forcings.

Mesozooplankton distribution in relation to the salinity gradient in a tropical hypersaline lake

Fluctuations in salinity are known to influence coastal marine communities. In this study, we present the effect of salinity on the distribution characteristics of mesozooplankton in Pulicat lake, the second largest lagoon situated along the south east coast of India. During different seasons of the study period, salinity varied from hyposaline (12.57) to hypersaline (139.74) in the lake. Salinity values were moderate in southern (33.75 ± 0.7) and northern inlets (29.38 ± 4.33), which were connected with the sea; while in the central region of the lake salinity was observed to be higher (52.32 ± 4.57). Mesozooplankton biovolume and abundance were high in the southern and northern inlets whereas a severe reduction in diversity and abundance was observed in the central region of the lake manifesting that increase in salinity is negatively impacting the mesozooplankton distribution. Copepod (Acartia tonsa, Acrocalanus gibber, Paracalanus parvus, Oithona brevicornis and Oithona similis), crustacean and molluscan larvae dominated the mesozooplankton abundance. A. tonsa predominance (79%) over the lake and across different seasons indicates its tolerance to a wide range of salinity fluctuations i.e., brackish to hypersaline environment of the Pulicat. The distribution of euryhaline species A. tonsa in all the sampling locations throughout the study period indicated their prevalence in the lake. Multilinear analysis between biotic and abiotic components through redundancy analysis (RDA) also suggested that salinity is the major constraint factor for the distribution of mesozooplankton. In conclusion, this study showed that the increased salinity levels have profound effects on mesozooplankton community and distribution.

Influence of environmental variables on the distribution and community structure of mesozooplankton in the coastal waters of the eastern Arabian Sea

The spatio-temporal variation of mesozooplankton in response to environmental variables was studied for the coastal waters of southeastern Arabian Sea during the spring inter-monsoon (SIM) and fall inter-monsoon (FIM) of 2014. Overall 84 mesozooplankton taxa belonging to 17 taxonomic groups were identified. The copepod group dominated species richness (58 species) of the mesozooplankton community. Spatial variation of mesozooplankton biomass and total abundance changed significantly in relation to the distribution of sub-surface water (0.5 m) dissolved organic carbon (DOC). Carnivorous and omnivorous mesozooplankton abundance increased substantially with an increasing DOC level. Factor analysis and Mantel test revealed that the distribution of mesozooplankton community, biomass and abundance had significant positive correlation with the distribution of chlorophyll a (Chl-a) and DOC during both the seasons. Distribution of Chl-a had a positive influence on herbivorous mesozooplankton abundance, while DOC had a positive relationship with omnivorous and carnivorous mesozooplankton abundance. Our study indicates that the distribution of Chl-a and DOC influences the spatial variation of mesozooplankton community and abundance in the coastal waters of eastern Arabian Sea during the inter-monsoon seasons (SIM and FIM).

Zooplankton community size-structure change and mesh size selection under the thermal stress caused by a power plant in a semi-enclosed bay

Zooplankton samples were collected using 505, 160 and 77 µm mesh nets around a power plant during four seasons in 2011. We measured total length of zooplankton and divided zooplankton into seven size classes in order to explore how zooplankton community size-structure might be altered by thermal discharge from power plant. The total length of zooplankton varied from 93.7 to 40 074.7 µm. The spatial distribution of mesozooplankton (200 −2 000 µm) populations were rarely affected by thermal discharge, while macro- (2 000 −10 000 µm) and megalo-zooplankton (>10 000 µm) had an obvious tendency to migrate away from the outfall of power plant. Thus, zooplankton community tended to become smaller and biodiversity reduced close to power plant. Moreover, we compared the zooplankton communities in three different mesh size nets. Species richness, abundance, evenness index and Shannon-Wiener diversity index of the 505 µm mesh size were significantly lower than those recorded from the 160 and 77 µm mesh size. Average zooplankton abundance was highest in the 77 µm mesh net ((27 690.0±1 633.7) ind./m3), followed by 160 µm mesh net ((9 531.1±1 079.5) ind./m3), and lowest in 505 µm mesh net ((494.4±104.7) ind./m3). The ANOSIM and SIMPER tests confirmed that these differences were mainly due to small zooplankton and early developmental stages of zooplankton. It is the first time to use the 77 µm mesh net to sample zooplankton in such an environment. The 77 µm mesh net had the overwhelming abundance of the copepod genus Oithona, as an order of magnitude greater than recorded for 160 µm mesh net and 100% loss through the 505 µm mesh net. These results indicate that the use of a small or even multiple sampling net is necessary to accurately quantify entire zooplankton community around coastal power plant.

Zooplankton-Mediated Fluxes in the Eastern Tropical North Atlantic

Zooplankton organisms are a central part of pelagic ecosystems. They feed on all kinds of particulate matter and their egested fecal pellets contribute substantially to the passive sinking flux to depth. Some zooplankton species also conduct diel vertical migrations (DVMs) between the surface layer (where they feed at nighttime) and midwater depth (where they hide at daytime from predation). These DVMs cause the active export of organic and inorganic matter from the surface layer as zooplankton organisms excrete, defecate, respire, die and are preyed upon at depth. In the Eastern Tropical North Atlantic (ETNA), the daytime distribution depth of many migrators (300-600 m) coincides with an expanding and intensifying oxygen minimum zone (OMZ). We here assess the day and night-time biomass distribution of mesozooplankton with an equivalent spherical diameter of 0.39 to 20 mm in three regions of the ETNA, calculate the DVM-mediated fluxes and compare these to particulate matter fluxes and other biogeochemical processes. Integrated mesozooplankton biomass in the ETNA region is about twice as high at a central OMZ location (cOMZ; 11\si{\degree} N, 21\si{\degree} W) compared to the Cape Verde Ocean Observatory (CVOO; 17.6\si{\degree} N, 24.3\si{\degree} W) and an oligotrophic location at 5\si{\degree} N, 23\si{\degree} W (5N). At cOMZ, an in comparison to the other regions particularly strong Intermediate Particle Maximum (IPM) is found, which seems to be related to DVM activity. Zooplankton DVM is responsible for about 29 to 42\% of nitrogen loss from the upper 200m of the water column. Gut flux and mortality make up about \ivall{Perc_DVM_O2_flux_into_OMZ-cOMZ}\% of particulate matter supply to the 300 to 600 m depth layer at cOMZ, whereas it makes up about \ivall{Perc_DVM_O2_flux_into_OMZ-CVOO}\% and \ivall{Perc_DVM_O2_flux_into_OMZ-5N}\% at CVOO and 5N, respectively. Resident and migrant zooplankton are responsible for about 6 to 23\% of the total oxygen demand at 300 to 600 m depth. Changes in zooplankton abundance and migration behavior due to decreasing oxygen levels at midwater depth could therefore alter the elemental cycling of oxygen and carbon in the ETNA OMZ and impact the removal of nitrogen from the surface layer.

Cross-shelf structure and distribution of mesozooplankton communities in the East-Siberian Sea and the adjacent Arctic Ocean

The East-Siberian Sea (ESS) plays a significant role in circulation of surface water and biological production in the Arctic, yet due to its remote location and historically difficult sampling conditions remains the most understudied of all Arctic shelf seas, with even baseline information on biological communities absent in literature. We aim to fill this gap by describing the distribution and community structure of mesozooplankton in the ESS and the adjacent Arctic Ocean based on recent (September 2009, 2015) as well as historical (August–September 1946, 1948) observations. We found that the overall biomass and abundance during our studies were significantly lower than in the adjacent Chukchi Sea, but higher than historical estimates from the ESS, around 25–35 mg DW m−3. The diversity was low and characteristic for other Arctic shelf seas, with increasing number of species in deeper waters. Biomass was highest at the shelf break, where it approached 70 mg DW m−3, and was mainly composed of the large copepod Calanus glacialis. On the shelf, abundance and biomass were low (10–20 mg DW m−3) and was dominated by small copepods and chaetognaths. Several distinct assemblages of zooplankton were identified and related to the physical properties of the water masses present. A striking result was the presence of both Atlantic and Pacific expatriates in offshore waters close to the shelf break, but generally not on the shelf itself. Tracking these advected organisms could be a useful tool in determining the pathways, extent, and transit time of Atlantic and Pacific water entering the Arctic.

Distribution of Mesozooplankton during Spring and Autumn across the Frontal Zone of South Sea, Korea

We investigated the distributional pattern of mesozooplankton and the related environmental characteristics across the frontal zone in the South Sea of Korea during spring and autumn 2016. The frontal zone (FZ) was formed by Korean Southern Coastal Waters and Tsushima Warm Current, and the physical structure of front was more distinct during autumn than spring. The peaks of mesozooplankton abundance were not coincident (p > 0.05) with peaks of integrated chlorophyll-a (chl-a) concentrations (spring: chl-a = 44.5 mg m−2 at FZ, mesozooplankton = 8,198 inds.m−3 at coastal zone (CZ); autumn: chl-a=141.2 mg m−2 at CZ, mesozooplankton = 5,412 inds.m−3 at FZ). Cluster analysis divided the mesozooplankton community into FZ, CZ and offshore zone (OZ) mainly by the dominant copepods (adult and immature) during both seasons that was associated with chl-a based on principal component analysis. All the zones were characterized by temporal difference in occurrence of copepods, which can be explained by the cyclopoid-to-calanoid (Cy:Ca) ratio. Cy:Ca ratio was dependent mainly on the co-occurrence of higher concentrations of chl-a and cyclopoids at each zone between spring and autumn. Paracalanus copepodites dominated at all stations across the FZ during both periods. Cy:Ca ratio at FZ in spring showed a distinctively higher value than that of CZ and OZ, whereas the pattern was the opposite in autumn. These results indicated that the temporal distribution of mesozooplankton across the frontal zone in the South Sea was mainly characterized by the zonal characteristics of FZ, unlike CZ and OZ, and was the result of temporal differences in chl-a concentrations and the associated increase of cyclopoid copepods (Oithona spp.).