Phytoplankton dynamics in relation to seasonal variability and upwelling and relaxation patterns at the mouth of Ria de Aveiro (West Iberian Margin) over a four-year period

Abstract

From June 2004 to December 2007, samples were weekly collected at a fixed station located at the mouth of Ria de Aveiro (West Iberian Margin). We examined the seasonal and inter-annual fluctuations in composition and community structure of the phytoplankton in relation to the main environmental drivers and assessed the influence of the oceanographic regime, namely changes in frequency and intensity of upwelling events, over the dynamics of the phytoplankton assemblage. The samples were consistently handled and a final subset of 136 OTUs (taxa with relative abundance > 0.01%) was subsequently submitted to various multivariate analyses. The phytoplankton assemblage showed significant changes at all temporal scales but with an overriding importance of seasonality over longer- (inter-annual) or shorter-term fluctuations (upwelling-related). Sea-surface temperature, salinity and maximum upwelling index were retrieved as the main driver of seasonal change. Seasonal signal was most evident in the fluctuations of chlorophyll a concentration and in the high turnover from the winter to spring phytoplankton assemblage. The seasonal cycle of production and succession was disturbed by upwelling events known to disrupt thermal stratification and induce changes in the phytoplankton assemblage. Our results indicate that both the frequency and intensity of physical forcing were important drivers of such variability, but the outcome in terms of species composition was highly dependent on the available local pool of species and the timing of those events in relation to the seasonal cycle. We conclude that duration, frequency and intensity of upwelling events, which vary seasonally and inter-annually, are paramount for maintaining long-term phytoplankton diversity likely by allowing unstable coexistence and incorporating species turnover at different scales. Our results contribute to the understanding of the complex mechanisms of coastal phytoplankton dynamics in relation to changing physical forcing which is fundamental to improve predictability of future prospects under climate change.

Discontinuity Analysis Reveals Alternative Community Regimes During Phytoplankton Succession

“…This finding aligns with a previous study that assessed patterns of bloom collapse and reorganization following the adaptive cycle (Angeler et al, 2015), a heuristic of complex system change (Holling, 1986;Gunderson and Holling, 2002). The results are also in agreement with a plethora of taxonomic studies in marine (Edwards and Richardson, 2004;Lindemann and St John, 2014;Vidal et al, 2017) and freshwater (Sommer, 1985;Munawar and Munawar, 1986;Reynolds, 2006) environments that have documented substantial community changes in terms of phytoplankton species composition and biomass as a result of abiotic variability. Although our results need to be interpreted with caution due to low sample size and heterogeneity of sites, the significant "blooms" term in the PERMANOVA model preliminarily supports the interpretation that spring and summer blooms generally comprise alternative phytoplankton community regimes.…”

Disentangling Environmental Drivers of Phytoplankton Biomass off Western Iberia

“…On the one hand, a positive trend was found in certain areas off Galicia and central-Northern Portugal. As seen above, this region is typically influenced by upwelling (Cravo et al, 2010;Pérez et al, 2010;Guerreiro et al, 2013;Wang et al, 2015;Vidal et al, 2017). Thus, it would be expected that such a positive trend would be linked to coastal upwelling.…”

“…During recent years, phytoplankton communities have been investigated in WIC, with several in situ and remote-sensing studies performed. These studies have contributed to a more indepth knowledge of local phytoplankton biomass variability and phenology (e.g., Navarro and Ruiz, 2006;Silva et al, 2009;Krug et al, 2018), community composition and structure (e.g., Lorenzo et al, 2005;Mendes et al, 2011;Goela et al, 2014), as well as its relationship with specific environmental processes, such as riverine discharges (e.g., Moita et al, 2003;Prieto et al, 2009;Guerreiro et al, 2013;Vaz et al, 2015) and coastal upwelling (e.g., Cravo et al, 2010;Pérez et al, 2010;Guerreiro et al, 2013;Vidal et al, 2017). Some investigations (e.g., Navarro and Ruiz, 2006;Krug et al, 2017) were also able to regionalize areas in CHLcoherent regions (i.e., areas with similar CHL variability patterns) to study the environmental drivers of phytoplankton.…”

Combined effects of warming and acidification on accumulation and elimination dynamics of paralytic shellfish toxins in mussels Mytilus galloprovincialis

“…The upwelling decline and consequent less turbulent environment and persistence of stratified conditions may result in an increase in the frequency of toxic dinoflagellates blooms, such as Dinophysis spp. and Gymnodinium catenatum, profoundly impacting shellfisheries (Vidal et al 2017). The bloom-forming dinoflagellates Dinophysis spp.…”