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Lake eutrophication and water quality deterioration have become a major environmental problem in urban areas and fertilized basins in developing countries across the world. This paper reviews the characterization, driving factors, and impacts of lake eutrophication as well as the mechanism of preventing and recovering lake eutrophication with case studies of eutrophic lakes across the world including Lake Tana, Ethiopia. In most waterbodies including lakes and reservoirs, total phosphorus concentration, chlorophyll a concentration, and Secchi disk visibility in association with species composition are the common criteria to classify lakes and reservoir as oligotrophic, mesotrophic, and eutrophic. Nutrient-rich runoff from cultivated land and industrialized and urbanized cities concentrated in phosphorus are the critical factors that drove eutrophication in water bodies. Among others, controlling external loading of nutrient, ecological, and mechanical methods were found to be common mechanisms to prevent and recover lake eutrophication. Avoiding the factors that are under human control, i.e., a reduction of external loading of nutrients especially targeted on phosphorus reduction into the water basins, relocates sewage, industrial and domestic waste discharges to be lined out of the catchment of the lake. Furthermore, motivating the community to use less phosphorus-containing fertilizers and promoting phosphorus-free detergents are suggested solutions to sustainably prevent and reduce eutrophication in the long run. These could be some possible measures to safeguard endangered Lake Tana of Ethiopia.

Phytoplankton community structure is crucial to pelagic food webs and biogeochemical processes. Understanding size-based biomass distribution and carbon dynamics is essential for assessing their contributions to oceanic carbon cycling. This study quantifies plankton carbon (C) based size spectra, community composition, living to total particulate organic carbon (POC) and C:Chlorophyll a (C:Chl a ) ratios across biogeographical provinces in the Pacific sector of the Southern Ocean near the Subtropical Front (Chatham Rise, Aotearoa-New Zealand). We analyzed phytoplankton community composition using epifluorescence microscopy and flow cytometry, while quantifying size-fractionated Chl- a and POC to estimate normalized biomass, abundance size spectra, and C:Chl a ratios. On average, subtropical-influenced waters had lower macronutrients, higher total Chl a (1.1 ± 0.2 μg Chl a L -1 ) and were dominated by nanoplankton, which accounted for 45% of the total plankton community (35.2 ± 4.6 μg C L -1 ). In contrast, picoplankton dominated plankton communities within the subantarctic-influenced and accounted for 35% of the total plankton community (18.5 ± 0.9 μg C L -1 ) in these water with higher macronutrient concentrations and lower total Chl a concentrations (0.32 ± 0.06 μg Chl a L -1 ). Subantarctic-influenced regions had steeper (more negative) slopes for the normalized biomass size spectrum (average = -1.00) compared to subtropical-influenced waters (average = -0.78) indicating greater relative dominance of small taxa. The subantarctic-influenced region had ~2-fold higher surface average C:Chl a ratios compared to the subtropical-influenced region with picoplankton consistently having lower C:Chl a ratios, due to low Chl a values, than larger nano- or microplankton. Live plankton carbon contributed a median of 67% of total particulate organic carbon in the euphotic zone (non-living detritus comprises the remaining ~1/3), which is indicative of substantial primary production and rapid recycling by a strong microbial loop. Our study provides important insights into phytoplankton community structure, biomass distribution and their contribution to carbon sequestration in this region, highlighting the important roles of nanoplankton in subtropical productive waters and picoplankton in offshore subantarctic waters as well as a strong variation of C:Chl a across different phytoplankton size classes.

Fishmeal is the most expensive feedstuff in the aquafeed and one of the most environmentally limiting factor of aquaculture development. Therefore, the search for alternative protein sources is a continuous process. The present feeding trial was conducted to evaluate the effects of replacing fishmeal with zooplankton biomass meal (ZBM) on the growth performance, nutrient utilization, intestine, and liver histological changes of grey mullet, Mugil cephalus (initial weight of 0.10 ± 0.01 g). Five isoproteic (35% crude protein) and isolipidic (8% crude lipid) diets were formulated as the control diet (Z0) and the other four diets (Z25, Z50, Z75, and Z100), where 25%, 50%, 75%, and 100% of fishmeal was replaced by ZBM, respectively. After 60 days of feeding, the final weight, weight gain, and daily growth index of the grey mullet fed the Z100 diet were higher than those fed the control diet (p < 0.05). In addition, the better values of feed conversion ratio, protein efficiency ratio and lipid efficiency ratio were recorded in the fish fed with the Z100 diet. Additionally, the intestinal villus length, crypts depth, and muscle thickness were significantly improved with ZBM inclusion (p < 0.05). Meanwhile, there were no histopathological changes observed on the liver when compared with the control group. From the economic point of view, dietary substitution of fishmeal by ZBM (Z100) reduced the cost of diet formulation by 18% and the price per kg weight gain by about 40%. Overall, according to the findings of this study, substituting fishmeal with ZBM up to 100% could improve growth performance, feed utilization, gut health status, and profit ability of rearing M. cephalus juveniles.

Bahia Magdalena is a coastal lagoon located in the Pacific coast of Baja California, a transitional zone between tropical and temperate regions. Its biological and fishing richness is enormous. The objective of this work was to determine the impact of the unusual and consecutive warming events knows as The Blob (TB2013-2015) and 2015-2016 El Niño on the hydrological characteristics and plankton communities, the lower levels of the trophic web. The changes we observed strongly suggested that the warming caused by those phenomena did affect the hydrology and phyto and zooplankton communities. This study included analyses of environmental and biological variables measured in situ and with MODIS-Aqua satellite images, from January 2015 to December 2017. In 2015, the air temperature was very high, upwelling strength decreased and temperature, salinity and water density showed the tropical influence. Additionally, the percentage of oxygen saturation and the nutrients and chlorophyll-a (Chl-a) concentrations were low and showed intra-annual variations different to usual. By April 2015, the chain-forming diatom Eucampia zodiacus bloomed, and we did not record an autumn bloom, but Chl-a fluorescence suggested that smaller phytoplankton fractions were predominant in that season. Zooplankton biomass (ZB) was lower since the second semester of 2015 and showed a negative trend until 2017. Relatively low percentages of dead zooplankton (%ZD) were also recorded. In 2016, when El Niño declined, and the ENSO cold phase (La Niña) started, there were an enhancing of upwellings, nutrients, and Chl-a concentrations. Blooms of diatoms occurred in spring and autumn (Guinardia/Rhizosolenia), whereas the ZB remained low, but %ZD was very high. La Niña finished in 2017, and in contrast to previous years, the upwelling's phenology was close to 1967-2010 average, and upwelling strength increased. Therefore, its rich-nutrients waters input caused several diatoms blooms, whereas ZB remained scarce.

The Ría de Vigo is a semienclosed bay in northwestern Iberia that is affected by seasonal upwelling (spring to autumn) that triggers high levels of primary productivity. Fisheries and aquaculture coexist with other human activities, such as shipbuilding and tourism, in this area. The microbial plankton community in this system was studied to understand how this community is structured and progresses seasonally. Autotrophic biomass (AB) dominated from spring to autumn when upwelling prevailed, while AB and heterotrophic biomass (HB) covaried throughout the year as HB:AB = 0.26 ± 0.04 (r2 = 0.7), indicating a link between the two communities. Diatoms and autotrophic nanoflagellates accounted for 80 ± 18% of the AB, whereas the HB was mainly composed of heterotrophic bacteria (36  11%) and heterotrophic nanoflagellates (30  12%). The AB and HB, as well as their main components, showed a continuous increase during the upwelling season that was attributed to growth. However, a sudden increase occurred in autumn, when downwelling caused the biomass to accumulate before leading to the low values in winter. As upwelling promotes the export of materials to the open ocean, the increase in biomass was possibly due to the existence of a nutrient trap that fueled phytoplankton growth through recycling at the sediment-water interface a substantial portion of the organic matter previously synthetized in the water column. The reorganization of the community that followed the winter decrease in biomass began with the proliferation of small plankton forms.

The distribution and variability of picoplankton and nanoplankton in Admiralty Bay (King George Island, South Shetland Islands, Antarctica) were studied by investigation of five sampling sites during the austral summer of 2010/2011. After a relatively warm winter, the water temperature in the early summer (>0.02 °C) was higher than is normal in December. The spatial–temporal variability of salinity was low, whereas water temperature and chlorophyll a increased significantly ( p  < 0.05) toward late summer. Nitrite and phosphate concentrations increased whereas nitrate and silicate decreased during the summer. Picoplankton increased by late summer and was dominated by heterotrophs (>96 %), with abundance and biomass tenfold (~10 9  cells L −1 ) and twofold (~60 µg C L −1 ) higher, respectively, than were observed in previous studies. In contrast, nanoplankton was dominated by photoautotrophs (>60 %), and values were highest in the early summer, with cell numbers (~10 6  cells L −1 ) and biomass (~90 µg C L −1 ) a factor of two lower than those found in a previous study. Temperature changes, inputs from ice melting, and grazing relationships between planktonic components seemed to have crucially important effects on the distribution patterns of these pico and nanoplankton communities. We suggest that additional study must be performed to develop a better understanding of abiotic and biotic factors that affect the abundance, biomass, and production of plankton smaller than 20 µm, their place in the microbial food web and the possible consequences of environmental changes on higher trophic levels in such Antarctic coastal environments as Admiralty Bay ASMA.

Evaluating how environmental stressor interactions influence ecosystem structure and functioning is critical to understanding the response of ecosystems to global change. We exposed a species-poor planktonic community to P pulses in the absence and presence of solar ultraviolet radiation (UVR). We used a field-mesocosm study in an oligotrophic mid-altitude lake to test the hypothesis that interaction between these factors affects the community’s diversity and composition, but not its biomass-size spectrum, making this community resilient in terms of its C-transfer function. Our findings show that P pulses and UVR affected the relative abundance of different planktonic populations. The abundance of phytoplankton was enhanced strongly by P pulses and secondarily by UVR. The UVR × P interaction affected only the smallest autotrophic species. Chlorococcal abundance increased, whereas chroococcal cyanobacteria decreased. However, UVR had a much more pronounced effect than P on the composition of microcrustaceans, and both factors interactively affected their biomass. Hence, the biomass-size spectrum was not resilient to the UVR × P pulse interaction. The steepness of the slope increased under P-pulse conditions because zooplankton were not able to grow concomitantly with phytoplankton, as confirmed by the low zooplankton to phytoplankton biomass ratio (Z:P). The observed planktonic changes under new foreseeable conditions that include an increase in UVR fluxes and P inputs might decouple the C cycle in inland oligotrophic lakes in the Mediterranean region.

The role of the microbial communities in the classical planktonic food web and its response to eutrophication in shallow lakes is still contradictory. Mediterranean shallow lakes with different eutrophication levels were sampled to study the influence of eutrophication on the microbial food web (MFW) and their contribution to the planktonic food web. Percentage of ciliate biomass in the metazooplankton (MZP) showed a U-shaped trend with eutrophication, with maximum at both ends of the chlorophyll- a (Chl a ) gradient. The MZP to phytoplankton ratio demonstrated a unimodal pattern with minimum values at the two ends of the Chl a gradient and maximum values in the Chl a range 5-10 μg l −1 . In contrast, the MFW to phytoplankton ratio reached its minimum in the central part of the Chl a gradient and maximum values at the extremes of the gradient. These patterns support the hypothesis that the relative importance of bacteria and ciliates is lowest in mesotrophic shallow lakes, and highest in oligotrophic and hypereutrophic systems. These results stress the importance of protozoan in the trophic web, and indicate it is essential to include this group, especially ciliates, when quantifying zooplankton in warm shallow lakes.

Nano-microplankton biomass, mesozooplankton biomass and hydrographic features were measured with mesoscale spatial resolution during 3 surveys in the Bay of Biscay between March and June 2004. Regions of high plankton biomass were associated with mesoscale physical structures. Generalized additive models (GAMs) based upon surface salinity, surface temperature and stratification of the water column explained 83% of the variability in nano-microplankton biomass distributions, 67% for small mesozooplankton, and 41% for large mesozooplankton. The results show that when biological and physical data are collected at the relevant spatial scales, nanomicroplankton and small mesozooplankton biomass distributions can be largely explained using simple hydrographic variables and non-parametric regression models.

Annual examination of net-plankton biomass in dry weight, ash-free dry weight, organic carbon, and nitrogen weight at the Manazuru harbor, central Japan revealed that net-plankton samples from shallow coastal water contained considerable amount of ash (53±13% of dry weight) which would be caused by contamination of inorganic materials from re-suspendion of sediments, terrestrial runoff and chain-forming diatoms. Therefore, in coastal water, dry weight is inadequate fro determination of zooplankton biomass in volving the possibility of over-estimation. Practical estimation of net-plankton biomass in shallow coastal waters, ash-free dry weight, organic carbon, and/or nitrogen are more adequate.