Effect of metals on zooplankton abundance and distribution in the coast of southwestern Taiwan

Linking seasonal plankton succession and cellular trace metal dynamics in marine assemblages

Factors affecting trace metal dynamics in marine plankton still need to be fully understood. Underlying mechanisms affecting cellular metal distribution, seasonal changes, and the influence of plankton community structure are poorly explored. This study comprehensively analyzed the seasonal changes in environmental factors, plankton community structure, and their impact on plankton cellular metal dynamics. Plankton samples were isolated, and trace metals (Cr, Mn, Fe, Co, Ni, Cu, As, Cd, Hg, and Pb) were analyzed with an inductively coupled plasma mass spectrometer (ICP-MS). Plankton community structure significantly changed with seasons (p < 0.05), which were mainly driven by temperature (seasonal change) and nutrients (eutrophication). Mean plankton cellular trace metals did not significantly change (p > 0.05) in the study area but were higher along estuaries likely due to differences in metal influx from rivers. However, their distribution patterns significantly differ between the wet and dry seasons, likely influenced by the changes in community structure and anthropogenic influx. Cellular trace metals, particularly in phytoplankton, strongly correlated with selected species suggesting the impacts of community structure in trace metal distribution. Hence, the influence of environmental factors in driving plankton succession may have caused a ripple effect on cellular trace metal distribution, especially in phytoplankton. However, both blooming species Skeletonema and Chaetoceros (diatoms) showed a contrasting relationship with cellular metals, suggesting the cooccurrence of bioaccumulation or biodilution mechanisms. This study shows the potential influence of community structure in cellular trace metal dynamics for marine plankton assemblages. However, more than plankton abundance and functional diversity, i.e., species diversity, might be needed to assess the community-level impacts on cellular metals.

Heavy metals concentration in zooplankton (copepods) in the western Bay of Bengal

Along the coastline, urbanisation and industrialization pose significant challenges to marine habitats and biodiversity. Most wastewater that reaches the marine environment contains toxic metals, which, as they are non-biodegradable, accumulate in the biota and enter the marine food chain. This study presents the concentration of nine heavy metals (Fe, Zn, Cu, Co, Cr, Mn, Ni, Pb, and Cd) in zooplankton (copepods) during the Spring Intermonsoon/Pre-Monsoon (April 2019) in the western Bay of Bengal (BoB). Higher Fe concentrations were found in copepods both nearshore (42,352 µg/g) and offshore (9835 µg/g). However, the relative amounts of heavy metals in copepods from 16 locations (eight nearshore and eight offshore) varied in the order of Fe > Zn > Cu > Co > Cr > Mn > Ni > Pb > Cd. The copepods in the nearshore locations had higher concentrations of heavy metals than those offshore. Compared to earlier data on heavy metals, particularly those that are physiologically non-essential and toxic, the current study demonstrates higher amounts of these metals in copepods in the inshore BoB [Ni (avg. 58.7 ± 5.5 µg/g), Pb (avg. 25.6 ± 4.7 µg/g), and Cd (avg. 16.4 ± 0.9 µg/g)]. Considering the strong East India Coastal Currents in the western BoB, trace metal-concentrated copepods could be transported too far along the Indian coastline from the current study area.

Non-proportional distribution and bioaccumulation of metals between phytoplankton and zooplankton in coastal waters

Metal concentrations were concurrently quantified in seawater, phytoplankton, and zooplankton from a heavily impacted coast of southern Taiwan. Combined size and density fractionation were used to accurately quantify metal concentrations in phytoplankton. Cr, Co, Ni, Cu, As, and Pb were analyzed using an inductively coupled plasma mass spectrometer (ICP-MS). As expected, metals significantly increased with an order of seawater < phytoplankton < zooplankton (p < 0.05); but did not differ between estuarine, nearshore, and offshore sites (p > 0.05). Metals were higher along Kaohsiung Harbor and marine outfall diffusion sites, highlighting their major impacts on plankton metal contamination. Notably, phytoplankton (Cr BCF > 100; half of the sites) significantly accumulated more metals contrary to zooplankton (BAF < 10). Metal concentrations and bioaccumulation factors between phytoplankton and zooplankton showed significant negative correlations. This demonstrates a non-proportional distribution and bioaccumulation of metals in phytoplankton and zooplankton-corroborating laboratory findings on zooplankton ability to control metals, irrespective of significantly high bioaccumulation in phytoplankton.

Factors Affecting Water Quality and the Structure of Zooplankton Communities in Wastewater Reservoirs of the Right-Bank Sorbulak Canal System (South-Eastern Kazakhstan)

This work aims to assess the main factors that determined the variability of environmental and biological variables in wastewater reservoirs of the Right-Bank Sorbulak Canal system (South-Eastern Kazakhstan). We used standard methods for the collection and analysis of data, as well as the principal components analysis (PCA) to assess the relationship between environmental and biological indicators. The average depth of the surveyed reservoirs was 4.1–10.0 m, temperature—21.7–25.7 °C, pH—9.41–10.00, permanganate index—16.22–19.07 mgO/dm3, N-NO2—0.03–0.13, N-NO3—1.28–3.00, N-NH4—0.30–0.53, PO4—0.14–0.39, Si—3.69–8.26, Mn—0.03–0.07, Fe—0.34–0.38 mg/dm3. The content of Cd, Co, Pb, Zn, and Cr was low, Cu—0.012–0.036 mg/dm3. The water quality is influenced by the wastewater composition, chemical interactions, morphometric and physical-chemical conditions of the reservoir, pollution of the coastal area, and secondary water pollution. Changes in the species composition and zooplankton abundance reflected the instability of external conditions. PCA showed the priority influence of carbonates, bicarbonates, magnesium, temperature, nutrients, and heavy metals on zooplankton structure. The results obtained demonstrate the indicator significance of zooplankton, and the methodological approaches can be used to assess water bodies with the complex pollution located in other regions.

Comparative trace metal assessment in phytoplankton using size and density fractionation

Trace metal assessment in marine phytoplankton is challenging due to complex assemblages and variable amounts of abiogenic suspended particulates. Using aliquots, this study were able to compare trace metal concentrations in plankton samples subjected to size and density fractionation. Elements including Cr, Mn, Fe, Ni, Cu, Zn, As, Sr, Hg, and Pb were analyzed by inductively coupled plasma mass spectrometer (ICP-MS). Trace metals were found to be significantly higher in size fractionated than density fractionated plankton for both small (1.2-50 μm) and large (50-120 μm) fractions. Metals from abiogenic sources (61-88%) also significantly contributed to trace metals detected in 1.2-120 μm suspended particulates collected from Kaohsiung Harbor. Results suggest that size fractionation can potentially overestimate trace metals in phytoplankton. It is therefore recommended combining the two methods by first isolating different size fractions followed by density fractionation to separate phytoplankton from zooplankton, and abiogenic particulates from phytoplankton assemblages, respectively.

Cement and oil refining industries as the predominant sources of trace metal pollution in the Red Sea: A systematic study of element concentrations in the Red Sea zooplankton

The Red Sea is exposed to metals from a large variety of natural and anthropogenic sources. In this study, we analyzed 19 common element concentrations in 14 Red Sea zooplankton samples using inductively coupled plasma-optical emission spectrometry (ICP-OES). The average metal or metalloid concentrations of the Red Sea zooplankton were: Ca > Sr > Fe > Al > Zn > As > Cu > Mn > Cr > Mo > Ni > Pb > Cd. The As, Ca, and Cu concentrations significantly increased with increasing latitude, while Cd concentrations decreased (p < 0.01). Our study indicated that anthropogenic activities (i.e., cement factories and oil refining industries) might be the predominant sources of significantly high Cr (1718 mg/kg), Fe (11,274 mg/kg), Mn (57.3 mg/kg), Mo (286 mg/kg), Ni (226 mg/kg), Pb (332 mg/kg), and Zn (17,046 mg/kg) concentrations that recorded in the Central to North Red Sea zooplankton.

Metal and metallothionein levels in zooplankton in relation to environmental exposure: spatial and temporal variability (Saronikos Gulf, Greece)

Metal and metallothionein (MT) in mixed zooplankton were investigated as means of monitoring metal availability regarding environmental exposure. Spatial and temporal variability of Cd, Cu, Ni, Zn, Fe, Mn and Pb in zooplankton and seawater were studied in Saronikos Gulf (Aegean Sea, Eastern Mediterranean), once every second month during an annual cycle (2011-2012). Particulate organic carbon and chlorophyll α were also measured in seawater samples. Median zooplankton metal concentrations were 0.65, 32.4, 7.1, 864, 1420, 40.2 and 26.8 μg g^-1 dw for Cd, Cu, Ni, Zn, Fe, Mn and Pb, respectively, and 109 μg g^-1 ww for MTs. Metal levels in zooplankton and MTs were higher at sites influenced by human-derived pressures. Additionally, metal concentrations in pelagic fish flesh from the Greek MED-POL data base were used for bioconcentration and biomagnification factors calculation. Bioconcentration from water to zooplankton was higher than metal transfer from either seston to zooplankton or zooplankton to fish.

Heavy metal and organic load in Haripur creek of Gopalpur along the Bay of Bengal, east coast of India

Accumulation of heavy metals in zooplanktons is used as an essential tool for the evaluation of health of an ecosystem. Such data are used to set further monitoring strategies especially in (coastal) water bodies. In the present study, seasonal bioaccumulation of heavy metals such as Cu, Zn, Pb, Cd and Hg, organic loads such as nitrite and phosphate, contents loads and physicochemical parameters in Haripur creek along the Bay of Bengal in east coast of India is measured in zooplanktons. Coastal organisms are considered an integral part of marine ecosystems and their frequent massive die-off events along the coast of the Bay of Bengal are correlated with the obtained pollutant data. The levels of heavy metals were also correlated with several extrinsic environmental factors such as water transparency, dissolved oxygen, salinity, pH and temperature. Discriminant function analyses and standardised coefficients for canonical variables for the obtained data indicate that the studied environmental factors and organic loads varied as a function of season. Bioaccumulation of the studied heavy metals in zooplanktons was seasonal and infrequently noticed above the standard limit. The computed bioaccumulation factor of the five metals showed that accumulation of Zn was higher in zooplanktons as compared to that of the other studied metals. So, the entry of heavy metals through the food chains or via direct exposure (to organic loads also) to the other inhabiting organisms including fish may be assumed. This could be one of the possible reasons for the observed frequent (fish) die-off events at Gopalpur Coast along the Bay of Bengal and may be considered a clue for future investigations.

n-3 PUFA biosynthesis by the copepod Apocyclops royi documented using fatty acid profile analysis and gene expression analysis

The cyclopoid copepod Apocyclops royi (Lindberg 1940) is one of two dominant mesozooplankton species in brackish Taiwanese aquaculture ponds. Periodically low n-3 polyunsaturated fatty acid (PUFA) content in seston could potentially be a limiting factor for zooplankton diversity. Apocyclops royi’s potential ability to biosynthesize n-3 PUFA was investigated through a short-term feeding experiment on four species of microalgae. Furthermore, we analyzed the expression of genes encoding putative fatty acid elongase (ELO) and desaturase (FAD) enzymes in A. royi on long-term diets of the PUFA-poor Dunaliella tertiolecta and the PUFA-rich Isochrysis galbana. The copepods exhibited high contents of docosahexaenoic acid (DHA, C22:6n-3) (>20% of total fatty acid) even when DHA-starved for two generations, and no significant differences were found in absolute DHA content between treatments. Transcripts correlating to the four enzymes Elovl4, Elovl5, Fad Δ5 and Fad Δ6 in the n-3 PUFA biosynthetic pathway were identified. Gene expression analysis revealed a significantly higher expression of two desaturases similar to Fad Δ6 in copepods fed PUFA-lacking algae compared to copepods fed algae with high PUFA content. These findings suggest a highly active n-3 PUFA biosynthesis and capability of DHA production in A. royi when fed low-PUFA diets.

Summary: Here, we demonstrate n-3 PUFA biosynthesis in the copepod Apocyclops royi from Taiwanese aquaculture pond systems using fatty acid profiling and gene expression analysis.