Environmental Factors and Ethnobiological Cues Influencing Plankton Trophic Distribution In a Creek Channel, Niger-Delta, Nigeria

1. Introduction

Plankton communities, comprising phytoplankton (e.g., Diatoms, Melosira, Navicula, Closterum, Spirogyra) and zooplankton (e.g., Copepods, Rotifers, Cladocerans), underpin aquatic food webs through nutrient cycling and energy transfer (Dexter & Bollens, 2020; Wu et al., 2022). Phytoplankton act as primary producers, while zooplankton link primary production to higher trophic levels, regulating biodiversity and ecosystem stability (Baumgartner et al., 2020; Uwadiae, 2020). Their dynamics in inland waters reflect hydrological, physicochemical, climatic, and anthropogenic drivers, including oil pollution, dredging, and land-use change (Qu et al., 2018; Yang et al., 2021; Edegbene et al., 2020).

Pollution remains a persistent stressor in the Niger Delta, with contaminants like hydrocarbons and heavy metals suppressing plankton growth, survival, and reproduction (Ogamba et al., 2021; Sikoki & Zabbey, 2017). Reports from the Nun and Orashi rivers highlight declines in phytoplankton diversity and fish production following oil spills (Davies & Ugwumba, 2019; Zabbey & Tanee, 2019). Dredging, common in the creeks of the Niger Delta, elevates turbidity and disrupts habitats, reducing plankton abundance and altering community composition (Ohimain et al., 2019; Abowei & Sikoki, 2017).

Seasonality further modulates plankton distribution. Wet-season runoff enriches nutrients, driving phytoplankton blooms, while dry-season flows concentrate pollutants and reduce habitat quality (Edegbene et al., 2021; Akinyemi & Nwankwo, 2020). Similar patterns in the Ogun and Imo rivers suggest that climatic variability strongly influences community structure (Ugbomeh & Atubi, 2019). Intensifying rainfall and flooding linked to climate change may exacerbate these effects (Nwankwoala & Mmom, 2019).

The ecological vulnerability of the Niger Delta is amplified by socio-economic reliance on artisanal fisheries. Plankton declines reduce fish yields, undermining food security and local livelihoods (Akintoye & Obi, 2021; Udo & Akpan, 2021). Despite evidence that over 60% of communities depend on fisheries, ethnobiological and socio-economic consequences remain poorly quantified (Ogamba et al., 2021; Nwankwoala & Mmom, 2019).

Plankton therefore represent sensitive bioindicators of environmental change. Understanding their dynamics under combined anthropogenic and climatic stress is essential for developing community-based conservation and sustainable management strategies in the inland drainages of the wider Niger Delta (Zabbey & Uyi, 2018; Ekubo & Abowei, 2019).

2. Materials and Methods

Study Area

The study was conducted in Otuoke Creek (Lat. 4.75° N, Long. 6.50° E), a freshwater body in Ogbia Local Government Area, Bayelsa State, Nigeria. The creek supports diverse aquatic organisms, including plankton, and is influenced by spatial changes, temporal changes and by anthropogenic activities (like fishing and domestic use). The study area is characterized by distinct wet (April to October) and dry (November to March) seasons (Edegbene et al., 2021; Akinyemi and Nwankwo, 2020).

Sampling, Collection and Identification

The study was a mixed-method observational study design (descriptive-observational-field and cross sectional study design) employing the use of ecology, field observations, and questionnaires. Sample locations were chosen at random with three sampling locations selected, namely: Community, Otuaba, and Azikiel Watersides (Table 1). Field sampling was conducted in the early hours between 07:00hrs and 10:00hrs. Water samples were collected using standard conical plankton net (55 µm mesh, 30 cm mouth diameter) by slanting the net in the opposite direction of water currents, towing the plankton net horizontally for 3 to 5 minutes and transferring the water samples into 500ml dark water sampling bottles.

At the laboratory, water samples were allowed to settle, gently allowing particles to concentrate. An aliquot was placed directly onto a glass slide using a pipette and observed under a compound microscope (100× to 400× magnification) for any plankton species. Detailed Identification to genus and species level was done using identification guides and standard keys for easy observations of individuals per taxon. Questionnaires (21) were organized and distributed to respondents in the three locations respectively (7 questionnaires per location). This was done to gather data on ethnobiological activities, cues and orientations relating to the creek and anthropogenic impacts.

Water Physicochemical Analysis

Water physicochemical characteristics were measured for each sampling location to assess underlying conditions. The parameters included temperature (^oC), pH, conductivity (COD), total dissolved solids (TDS), biological oxygen demand (BOD), turbidity (TURB) and dissolved oxygen (DO). Temperature was estimated using a digital thermometer, pH using a digital pH meter, conductivity using a digital conductivity meter, TDS using a total solid concentration meter, while dissolved oxygen was estimated using Winkler titration method.

Environmental Diversity Indices

Estimation of diversity indices was used to evaluate ecological health, plankton diversity and community structure based on identified taxa. These was achieved using: Shannon-Wiener Index (H’), Margalef’s Richness Index (D), Pielou’s Evenness Index (J), and Simpson’s Dominance Index.

Data and Statistical Analysis

Organized data were illustrated and represented as tables. Microsoft-Excel was used to compute data, estimate statistical data and to also convert data to illustrations.

3. Results

Results were cumulated and presented in tables. Table 1 details sampling locations, their descriptions while Table 2 meteorological conditions where water samples were collected. Table 3a posits an account of the abundance, diversity, and trophic levels of phytoplankton and zooplankton across various locations (L1, L2, and L3; Figure 1). Table 3b gives an account of all phytoplankton species and individuals (autotrophs) observed while Table 3c gives account of the zooplankton species (heterotrophs), individuals observed and their various trophic levels. Based on the observed plankton species data, diversity indices were calculated (Table 4) for both phytoplankton (P) and zooplankton (Z) in all three locations. The indices estimated, include: Shannon-Wiener Index (H’), Margalef’s Richness Index (D), Pielou’s Evenness Index (J), and Simpson’s Dominance Index (1-D). Water physicochemical parameters were estimated to assess hydrologic conditions affecting plankton diversity (Table 5). This section explores awareness and investigation through ethnobiological questionnaire survey (Table 6a-d). Questionnaire data on demographic responses, ethnobiological knowledge and investigation, responses to change, domestic activities carriedout within and around the creek channel.

4. Discussion

Field observations (Table. 1.) and ethnobiological surveys (Table 6a-d) revealed that Otuoke Creek is central to community life, supporting transport, fishing, and domestic activities, but also subjected to waste disposal and other anthropogenic pressures. Such interactions are consistent with reports that human settlements and socioeconomic activities significantly alter habitats like aquatic ecosystems, often leading to pollution and long-term ecological stress (Issaksson, 2018).

Meteorological variables such as temperature, humidity, and wind speed emerged as important drivers of plankton dynamics (Table 2.). Temperature influenced species richness by favoring heat-tolerant taxa while reducing sensitive ones, whereas wind-driven mixing enhanced productivity up to a threshold but reduced stability under excessive turbulence. High relative humidity stabilized aquatic conditions, supporting plankton persistence. Uzoekwe et al. (2025), also posited atmospheric mositure as media for contaminant introduction into aquatic ecosystems. These findings agree with previous reports on climate-linked variability in freshwater plankton communities (Righetti et al., 2022; Jacob et al., 2024; IPCC, 2021).

Community composition (Table 3a, b and c) showed a dominance of phytoplankton (76.6%) followed by phyto-zooplanktivores (21%), phytoplanktivores (1.4%), and zooplanktivores (1%). Such trophic structuring, with phytoplankton dominance and limited higher-level consumers, suggests environmental perturbation and reduced resilience (Ugbomeh & Atubi, 2019; Akinyemi & Nwankwo, 2020). Diversity indices (Table. 4) further highlighted spatial variation: Station 2 exhibited the highest Shannon-Wiener and Simpson values, reflecting stable conditions and even distribution of species, whereas Station 3 recorded the lowest indices, indicating ecological stress likely associated with anthropogenic perturbation, nutrient limitation or pollution inputs.

Physicochemical parameters (pH 6.5–6.8, DO 4.2–4.3 mg/L, BOD 2.4–2.5 mg/L, turbidity 23–24 NTU, and TDS 15–28 ppm; Table. 5) indicated moderately supportive water quality, though values suggested potential for organic loading and light limitation. These conditions align with earlier observations that physicochemicals like moderate BOD and turbidity sustain productivity but can impair sensitive taxa when elevated (Pandey et al., 2014; Inyang et al., 2022).

Ethnobiological data (Table 6a, b, c, and d) confirmed that local communities are aware of ecological changes and pollution sources, including oil spills, defaecation, and waste disposal. However, the persistence of harmful practices such as refuse dumping and bathing within the creek underscores a gap between awareness and sustainable action. Similar studies have shown that integrating traditional ecological knowledge with scientific monitoring enhances biodiversity conservation and promotes culturally relevant management strategies (Rodrigues et al., 2022; Lee, 2025).

The observed variability in plankton abundance and diversity across the three creek locations reflects the combined influence of multiple stressors, including natural dynamics, crude oil pollution, domestic effluents, dredging activities, and fluctuating physicochemical parameters. According to Heys et al. (2016), these drivers of change often interact in complex ways, producing additive, antagonistic, or synergistic effects on aquatic communities. In some cases, the impacts might be additive and cause reductions in phytoplankton density. The combined contributions of stressors like elevated turbidity and petroleum hydrocarbons, each exert a measurable but predictable share of the decline. Conversely, antagonistic interactions could elevate turbidity from dredging activity. This can reduce photosynthetic efficiency, may simultaneously shield phytoplankton from direct oil toxicity and solar radiation, thereby moderating the expected degree of mortality or affecting photosynthetic species.

More critically, synergistic interactions could occur. Low dissolved oxygen levels could co-occur with hydrocarbon contamination or other stressors, producing disproportionate reductions in zooplankton abundance. The joint stress of hypoxia and petroleum toxicity can likely amplify the vulnerability of sensitive taxa, accounting for the sharper biodiversity declines observed in some stations relative to others. This complex interactions and ecological perspective underscores the importance of adopting multistressor management approaches in accounting for the ecological consequences, mitigating the risks to biodiversity and sustaining ecosystem services in oil-producing creeks of the Niger Delta.

Overall, the findings suggest that plankton communities in the creek reflect the combined influence of physicochemical variability, climatic fluctuations, and anthropogenic pressures. The observed patterns reduced trophic balance, spatial heterogeneity in diversity, and ethnobiological drivers indicate that the ecosystem is under moderate stress but could worsen with further perturbation. Research is continuous and can not be exhausted. Continued monitoring, coupled with the incorporation of community knowledge into management frameworks, is essential to safeguard ecological integrity and ensure sustainable use.

5. Conclusion

This study elucidates how ecological, physicochemical, meteorological, and ethnobiological factors collectively shape plankton diversity in Otuoke Creek. Marked spatial differences in plankton community structure were closely tied to fluctuations in temperature, dissolved oxygen, pH, and nutrient loads, influenced by both climatic variability and anthropogenic pressures. Seasonal rainfall amplified contaminant inputs, with waste disposal, agricultural chemicals, effluents, leachates, crude oil spills, and domestic activities identified as key pollution drivers. These stressors likely act through additive, antagonistic, or synergistic interactions, altering plankton abundance and diversity, thereby signaling ecosystem stress.

Ethnobiological practices emerged as critical determinants of ecosystem health. Communities engaged in sustainable fishing, pollution control, and habitat management maintain higher trophic diversity, whereas unsustainable practices reduced biodiversity. Plankton thus serve as sentinels of ecological integrity, reflecting the interplay between natural and anthropogenic stressors.

Conclusively, findings emphasize the need for integrated management approaches that combine environmental monitoring with community participation. Strengthening traditional ecological knowledge alongside scientific assessments can enhance conservation outcomes. Long-term monitoring and adaptive strategies are essential to safeguard biodiversity, sustain ecosystem services, and guide resource management in Otuoke Creek and comparable freshwater systems.