the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Wet and dry seasons modulate coastal coccolithophore dynamics off South-western Nigeria (Gulf of Guinea)
Abstract. Coccolithophores are calcifying unicellular phytoplankton at the base of the marine food web, playing a key role in pelagic calcium carbonate production. While their sensitivity to environmental change is well established, their ecological importance in tropical coastal systems remains underexplored, particularly along the African coastline. Here, we present the first multi-seasonal assessment of living coccolithophore communities off Lagos, southwest Nigeria, in the Gulf of Guinea. Periodic sampling was conducted at three coastal stations from December 2018 to April 2021 to evaluate species composition, standing stocks, diversity, and ecological drivers. Coccolithophore abundances showed clear seasonal patterns, with significantly higher (p < 0.05) standing stocks and diversity during the wet season. Total abundances ranged from 0.3 × 10³ cells L⁻¹ in the dry season to 5.5 × 10³ cells L⁻¹ in the wet season, with Gephyrocapsa oceanica dominating dry periods and Emiliania huxleyi prevailing during the wet season. Seasonal changes were linked to the migration of the Inter-tropical Convergence Zone (ITCZ), which modulates precipitation and current direction along the Gulf of Guinea. Interestingly, chlorophyll-a concentrations appeared decoupled from coccolithophore abundance, suggesting other phytoplankton groups may drive primary productivity in this region. Despite regional differences in oceanographic settings, the observed standing stocks fall within the global range of coastal coccolithophore assemblages, supporting the hypothesis that these communities are shaped by a set of common ecological constraints. As tropical coastal regions al-ready face multiple pressures from climate change, projected southward shifts of the ITCZ could alter precipitation regimes and current dynamics, with potential implications for coccolithophore community composition and coastal biogeochemical cycling.
- Preprint
(1787 KB) - Metadata XML
-
Supplement
(80 KB) - BibTeX
- EndNote
Status: open (until 22 Sep 2025)
-
CC1: 'Comment on egusphere-2025-3201', Xiaobo Jin, 13 Aug 2025
reply
The authors presented seasonal changes in living coccolithophore community off the coastal Nigeria. They found E. huxleyi dominated in wet seasons, and G. oceanica in dry seasons. This finding is interesting, with significant implications for coccolithophore ecology and biogeography.
Here I would present some comments for such alternating occurrences of the species. The authors found higher chlorophyll-a and silicate concentrations in the dry seasons, which may suggest a dominance of diatom in the phytoplankton community. Therefore, I speculate that the occurrence of E. huxleyi may result from their competition with diatoms. E. huxleyi cannot outcompete against diatoms in the dry seasons, and they would be found in the wet seasons. In contrast, G. oceanica may be a more efficient nutrient assimilator, and they would be co-exist with diatoms. A similar case can be found in the South China Sea as reported in Jin et al. (2019, JGR-BG) and Jin et al. (2022, JGR-BG). The biogeography and seasonal production succession of E. huxleyi and G. oceanica can be governed by their competition with diatoms.
Citation: https://doi.org/10.5194/egusphere-2025-3201-CC1 -
RC1: 'Comment on egusphere-2025-3201', Anonymous Referee #1, 23 Aug 2025
reply
The manuscript, "Wet and dry seasons modulate coastal coccolithophore dynamics off South-western Nigeria (Gulf of Guinea)" by Falilu Adekunbi et al., presents a valuable dataset acquired from three coastal stations between 2018 and 2021. The study's objective is to enhance our understanding of living coccolithophore dynamics, particularly in coastal environments, by examining their relationship with environmental variables and oceanographic settings in the Gulf of Guinea. The authors effectively use a statistical analysis approach to highlight and clarify the key relationships between taxa and environmental variables.
The data acquisition is described in detail, and the findings are well-illustrated with an adequate number of high-quality figures. The references are up to date.
All my comments and suggestions are intended to improve the quality of the paper by clarifying specific sections of the text. I recommend the manuscript for publication after minor revision.
Minor Suggestions
Hyphenation: Several instances of hyphenated words appear to be incorrectly divided across lines (e.g., line 29). The authors should carefully check the entire text to correct all such instances.
Absence of Holococcolithophores: Lines 78-79 state, "Only heterococcolithophores were identified in all the samples (15 taxa, Table S1), as no holococcolithophore could be observed." While this is an interesting result, the authors do not provide an explanation for the absence of holococcoliths in the studied sites. Without this clarification, a reader (such as myself) might question the sampling strategy. For instance, the storage conditions mentioned in line 110 ("The seawater samples for coccolithophore community composition were stored shortly (<5 hours)") are critical and could be a contributing factor (e.g., exposure to sunlight or high temperatures). The authors should address this to rule out potential sampling issues and provide a more complete scientific explanation.
Citation: https://doi.org/10.5194/egusphere-2025-3201-RC1
Viewed
HTML | XML | Total | Supplement | BibTeX | EndNote | |
---|---|---|---|---|---|---|
526 | 17 | 10 | 553 | 13 | 13 | 9 |
- HTML: 526
- PDF: 17
- XML: 10
- Total: 553
- Supplement: 13
- BibTeX: 13
- EndNote: 9
Viewed (geographical distribution)
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1