IRD, CNRS, Ifremer, Lemar, SRFC, CSRP, University Brest, Dakar, Senegal.
IRD, CNRS, Ifremer, Lemar, DR Ouest, University Brest, Plouzané, France.
PLoS One. 2024 Sep 6;19(9):e0308083. doi: 10.1371/journal.pone.0308083. eCollection 2024.
The Canary Current Large Marine Ecosystem (CCLME) is one of the most productive Large Marine Ecosystems worldwide. Assessing the abundance, biomass and distribution of zooplankton in the southern part of this system, off the coast of West Africa, remains challenging due to limited sampling efforts and data availability. However, zooplankton is of primary importance for pelagic ecosystem functioning. We applied an inversion method with combined analysis of acoustic and biological data for copepod discrimination using a bi-frequency (38 and 120 kHz) approach. Large copepods with equivalent spherical radii > 0.5 mm were identified using differences in the mean volume backscattering strength (MVBS). Regarding abundance measured by net sampling, copepods strongly dominated the zooplankton community and the large fraction account for 18%. This estimate correlated significantly with MVBS values that were obtained using an inverse algorithm. We confirmed the utility of using 38 kHz for large copepod detection. An epipelagic biomass of large copepod was estimated at 120-850 mg m-2 in March during upwelling season. It is worth noting that this estimation likely underestimates the true biomass due to inherent uncertainties associated with the measurement method. We recommend future investigations in the interest of using only nighttime data to improve the sampling pattern, particularly on the upper part of the water column (< 10 m) as well as on the shallow part of the continental shelf (< 20 m depth) not covered by fisheries vessel. Nevertheless, such high copepod biomass supports high fish production underlining the key role of copepod in the CCLME. Our results open the way to the analysis of the fluctuation and trend of copepod biomass, along with three decades of fisheries acoustics data available in the region. This helps to determine ecosystem changes, particularly under climate change, and to investigate the role of copepods in the southern CCLME carbon pump at the fine scale.
卡纳利洋流大海洋生态系统（CCLME）是世界上生产力最高的大海洋生态系统之一。评估该系统南部、即西非沿海地区浮游动物的丰度、生物量和分布仍然具有挑战性，这是由于采样工作和数据可用性有限所致。然而，浮游动物对浮游生态系统的功能至关重要。我们应用了一种反演方法，结合声学和生物数据进行分析，使用双频（38 和 120 kHz）方法对桡足类进行区分。使用平均体积反向散射强度（MVBS）的差异，识别出等效球半径> 0.5 毫米的大型桡足类。根据网采数据测量的丰度，桡足类在浮游动物群落中占主导地位，其大分数占 18%。这一估计与使用反演算法获得的 MVBS 值显著相关。我们证实了使用 38 kHz 检测大型桡足类的有效性。在上升流季节的 3 月，估计上层浮游动物的大型桡足类生物量为 120-850 毫克/平方米。值得注意的是，由于测量方法固有的不确定性，这种估计可能低估了真实的生物量。我们建议未来的研究仅在夜间使用数据，以改善采样模式，特别是在水柱的上部（<10 米）和渔业船只未覆盖的大陆架的浅部（<20 米深度）。然而，如此高的桡足类生物量支持了鱼类的高产量，突出了桡足类在 CCLME 中的关键作用。我们的结果为分析桡足类生物量的波动和趋势开辟了道路，同时还可以利用该地区三十年来的渔业声学数据。这有助于确定生态系统的变化，特别是在气候变化下，以及研究桡足类在南部 CCLME 碳泵中的作用。
