The SOLAB project is articulated around three work packages:
1. Observing the southern Senegal upwelling sector
Observations are essential to identify key processes and guide our modelling effort. They cover a wide range of processes, time/space scales and feed WP2 & WP3. Six main research tasks guide our observational efforts:
- SSUS dynamics/hydrology from in situ observations
- Plankton biomass/distribution/diversity from space
- Nutrient and oxygen dynamics from in situ observations
- Functional biodiversity & interactions within the microbial loop from in situ observations/samplings
- Phytoplankton/Zooplankton/SPF interactions from in situ observations
- Impact of SSUS seasonal variability on exploited resources
Generally speaking, we aim to improve the seasonal description of north-to-south/nearshore-to-offshore contrasts in abiotic as well as biotic variables. We are also interested in shorter time scales (synoptic and intraseasonal) in relation to hypoxic/anoxic conditions, harmful algal blooms, jelly fish proliferation …
We use or plan to use a large suite of state-of-the-art instruments, sampling techniques and analyses, e.g.: microstructure measurements to estimate turbulence fluxes of geochemical tracers; chromatography, flow-cytometry, metabarcoding, and image processing for plankton diversity; fatty acids composition and carbon/nitrogen isotope ratios for plankton and fish (Sardinella aurita and maderensis); multi-frequency acoustic.
We go at sea using pirogues and small senegale ships, 26 footer sailing vessel Amouage, and on rare occasions large research vessels. R/V Thalassa will allow us to conduct the SCOPES field experiment (11 Dec. 2022 – 7 Jan. 2023). We also take advantage of the MELAX buoy when it is at sea.
Preliminary work includes Capet et al, 2017 and Machu et al, 2018.
2. Modelling the southern Senegal upwelling sector
Realistic numerical modelling is key to our effort aimed at building an interdisciplinary perspective of the SSUS that integrates physics, biogeochemistry and ecology. SOLAB’s numerical platform consists in physical model CROCO, biogeochemical model PISCES, plankton biodiversity model DARWIN. Lagrangian simulations of small pelagic fish life cycle using the ICHTYOP/EVOL-DEB model framework will also be carried out.
Horizontal resolution (~ 2 km) allows us to represent, with a good degree of realism, the diversity of environmental conditions encountered over the SSUS and the processes that contribute to the connection (or lack thereof) between them: heterogeneous enrichment of the euphotic layer, nearshore retention, turbulent oxygenation of subsurface waters, concentration and dispersion of organisms, shelf-open ocean exchanges …
Our modeling strategy is process-oriented and focused on present conditions (satellite-rich era since 1998). Sensitivity experiments will also be carried out to explore future system evolutions, with 2080 as time horizon. Our main tasks will be aimed at modelling:
- Transport/mixing/aggregation processes including of pollutants (oil, plastics)
- Biogeochemistry and plankton diversity (nutrients, oxygen, plankton classes)
- Parts of the Sardinella aurita and S. maderensis life cycle
- Changes in SSUS functioning associated with future conditions (2080-2100 horizon)
Preliminary work includes Ndoye et al, 2017, Brochier et al, 2018.
3. Results dissemination and benefits to the society and SSUS stakeholders
Scientific guidance on how to preserve/restore SSUS ecosystems is highly needed.
The SSUS is an extreme example of anthropic pressure on a coastal system, with a nearby population of 4 millions greatly relying upon ocean resources. In short, concerns arise from the fact that: the SSUS hosts nurseries that are key to the reproduction of small pelagic fish such as sardinella aurita, sardinella maderensis, ethmalose; many fish stocks are being considered as overexploited; the manifestations and impacts of global changes in this ocean sector are particularly uncertain; water pollution control is extremely weak and most industrial and domestic wastewater are being discharged at sea with no treatment; oil exploitation plans exist in several places of the SSUS (e.g., see 2016 CAIRN report, available at http:// www.cairnenergy.com/index.asp?pageid=856) which raises the prospect of conflicts of usage and further environmental degradation.
In this context, our main objectives are to
- contribute to ocean science capacity building in Senegal (training of 6 PhD students in biogeochemistry, pollutant transport, physical modelling of coastal ocean, environmental signal treatment as part of SOLAB and companion projects)
- help contextualise landing data analyses and SPF stock assessments
- provide environmental information critical to the development of aquaculture (e.g., shellfish in the Sine-Saloum estuary) and algoculture.
- provide recommendations on the design of the Senegalese coastal observatory (to be communicated to DEEC) and proposed strategies for expansion of nearshore MPAs.
- raise the level of Senegalese and international expertise available to the agencies in charge of the Dakar depollution program
- help gain understanding on the SSUS circulation and thus provide potentially useful information in case of oil spill. At this stage our work reveals a seasonally variable but frequently elevated risk of oil transport from offshore exploitation site “Sangomar offshore” to the coastline. This level of risk justifies great anticipation efforts.
The development of ecosystem-based approaches to the management of marine environments (EAMME) is a long-term endeavour that has had limited success so far. SOLAB remains modest with respect to the possibilities of breakthrough in terms of EAMME. On the other hand, we believe that the fundamental knowledge we are gaining will be essential to make sense of and mitigate any ecosystem changes that may occur in the future.