Abstract
Phytoplankton phenology and size structure are key ecological indicators that influence the survival and recruitment of higher trophic levels, marine food web structure, and biogeochemical cycling. For example, the presence of larger phytoplankton cells supports food chains that ultimately contribute to fisheries resources. Monitoring these indicators can thus provide important information to help understand the response of marine ecosystems to environmental change. In this study, we apply the phytoplankton size model of Gittings et al. (2019b) to 20-years of satellite-derived ocean colour observations in the northern and central Red Sea, and investigate interannual variability in phenology metrics for large phytoplankton (>2 µm in cell diameter). Large phytoplankton consistently bloom in the winter. However, the timing of bloom initiation and termination (in autumn and spring, respectively) varies between years. In the autumn/winter of 2002/2003, we detected a phytoplankton bloom, which initiated ~8 weeks earlier and lasted ~11 weeks longer than average. The event was linked with an eddy dipole in the central Red Sea, which increased nutrient availability and enhanced the growth of large phytoplankton. The earlier timing of food availability directly impacted the recruitment success of higher trophic levels, as represented by the maximum catch of two commercially important fisheries (Sardinella spp. and Teuthida) in the following year. The results of our analysis are essential for understanding trophic linkages between phytoplankton and fisheries and for marine management strategies in the Red Sea.
Highlights
The Red Sea is the world’s northernmost tropical sea (Figure 1), and hosts one of the longest coral reef ecosystems on Earth, which supports high levels of marine biodiversity [1] and provides essential ecosystem services, including coastal protection, tourism, and fisheries [1,2,3,4]
Interannual Variability of Phenology Anomalies Attributed to Large Phytoplankton
To the best of our knowledge, the analysis presented in this paper comprises the first attempt to assess the linkages between the interannual variability of satellite-derived ecological indicators and fisheries dynamics in the Red Sea
Summary
The Red Sea is the world’s northernmost tropical sea (Figure 1), and hosts one of the longest coral reef ecosystems on Earth, which supports high levels of marine biodiversity [1] and provides essential ecosystem services, including coastal protection, tourism, and fisheries [1,2,3,4]. The northern half of the Red Sea has been the subject of recent research efforts, as phytoplankton dynamics in this region have been shown to follow a typical tropical biological regime, with a winter (October–April) phytoplankton growth indicators such as size structure and phenology (the timing of phytoplankton growth periods) is essential for understanding how energy is transferred through the marine food web [12,42] This is important in the Red Sea, where commercial and traditional fisheries constitute an essential source of sustenance for coastal communities [43]. Interannual variations in phenology metrics are compared with historical fishery landings reported in the region, to explore links between phytoplankton blooms and trophic energy transfer
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