SOLAB website


Plankton interactions, their environmental determinants, and biogeochemical consequences in the Southern Senegal coastal laboratory


General spirit

Coastal ocean environments are subject to intense and multiform anthropogenic pressure, from local origin but also as a consequence of global change. Among them are upper ocean warming, deoxygenation, acidification, eutrophication, overfishing, wastewater discharges, plastics, and heavy metals accumulation.

Anticipating the impacts of these growing perturbations is far from reach. Marine ecosystems are incredibly complex. Many fundamental aspects of ecosystem’s functioning are still poorly understood even for present day conditions, and for an array of reasons.

Ocean physics is variable and heterogeneous on a broad range of scales. The prevailing view that the physics relevant to marine life could be subsumed into large-scale aggregated indicators is increasingly challenged. This is particularly true in coastal upwellings where ecosystem variability is not convincingly captured by the diversity of existing indicators, e.g., seasonal upwelling indices.

The conceptual model of upwelling ecosystems, based on a short food chain, fueled by high nitrate fluxes, and consisting of diatoms feeding copepods, both filtered by SPF, is also challenged. This model fails, for instance, to resolve the Peruvian paradox : under the influence of similar physical processes the four major coastal upwelling systems (the Peru-Chile, California-Oregon, Benguela, Canary systems) experience comparable levels of primary production but, for reasons that are not yet understood, the Peruvian upwelling produces an order of magnitude more fish per unit of primary production than the other systems. The short food chain paradigm also ignores the prevalence of harmful algal blooms in coastal upwelling (Pitcher et al, 2010).

Current knowledge and monitoring gaps in WA would not allow us to identify drivers of changes in fish catch/stock/diversity other than dramatic modifications of fishing pressure, of basic environmental variables (SST), or new species bursts. This leaves vast blind spots in terms of science needed to understand and respond to ecosystem evolutions. For example, subtle abiotic changes with a major but indirect impact on SPFs through modifications of the planktonic ecosystem would certainly go unnoticed with present-day monitoring systems. Such bottom up chains of events have been implicated in a number of ecosystem disruptions affecting diverse parts of the ocean. Knowledge gaps also hamper the development of sustainable marine aquaculture which could provide food, jobs, and relieve fishing pressure on wild stocks.

In this context, (i) hopes that the environment and ecosystem can be understood/managed based on universal and relatively large scales indices with limited concern for region dependant processes and specificities appears illusory to us.

Likewise, (ii) the prospect of being able to anticipate and limit the effects of global changes on marine ecosystems is not, in our opinion, a credible goal to pursue. Justifications for this assertion include: the multiple examples of unanticipated evolutions undergone by marine ecosystems over the past decades (e.g., the slow recovery of Newfoundland cod stock following its collapse in 1992; ); the broad range of biological delicacies (physiological, evolutionary and ecological) that are implicated in ongoing marine ecosystem disruptions by combinations of stressors, with diverse impact modalities; the sheer complexity of marine food webs, the limitations of earth system model projections, particularly at regional scale (uncertainties on oxygen in the North Atlantic). See also Planque, 2015.

Overall, (i) and (ii) have had two essential implications in the design of SOLAB:

  • the focus on past/present state description and undestanding. This increases chances that future system modifications would be detected, properly attributed/understood, and suitable responses implemented.
  • the focus on subregional spatial scales (e.g., inshore versus offshore contrasts or the specific role of Bay de Hann or mangrovian estuaries) and on relatively short time scales (e.g., the modulations of upwelling winds on time scales from days to months). In particular we are interested in localized events that can have disproportionate impacts on the ecosystem and local populations (harmful algal blooms, anoxic episodes, heat waves …).

Overall we also feel that these choices make SOLAB useful on hazard prevention strategies, e.g., oil spill response.