About the project

The why, what, how, where, when and who




First, let me introduce you to our dear target system: Seagrasses…

Seagrasses are marine flowering plants (and no algae or seaweed!) that have evolved from freshwater macrophytes to subsist in saline conditions. They can be found along the coast from shallow/intertidal to deeper/subtidal areas, in both tropical and temperate regions. With a total of 12 genera, there are over 50 referenced seagrass species of different shapes and sizes found worldwide.

What makes them so great?

Seagrasses represent one of the most valuable resources in the coastal landscape for the ecosystem services they provide. They are defined as ecosystem engineers, as their presence can modify the physical and chemical characteristics of their environment to create complex habitats, called seagrass meadows. For instance, they will create a shelter for fish juveniles, be a source of food for many organisms, attenuate the effect of waves and currents, etc., the list is long!

Examples of the services seagrasses provide: particle trapping, wave and current attenuation, nursery, shelter, carbon sink, release oxygen, and many others… (©LauraSoissons)


Seagrasses are nowadays under serious threat all around the globe. Threats come from many different sources, from climate change to human activities. The documented and worldwide decline of seagrass meadows is leading to the loss of the services they provide, raising the need to undertake effective conservation measures to protect them. However, our capacity to succeed in this task largely depends on our aptitude to anticipate their potential decline.

And this is where the HEALSEA project comes in…



With the HEALSEA project we propose to test whether the theories established mostly from mathematical models on the resilience of complex ecological systems might apply to seagrasses, and to use them to develop effective conservation measures.

For this we consider:

  • Resilience, as the capacity of a system to resist to and to recover from threats.
  • Response patterns, based on theories inspired from mathematical models suggesting that ecosystem engineers such as seagrasses may respond in two different ways to increasing threats: smoothly, through a linear change of their biological properties; or abruptly, through a sudden decline of their biological properties below a threshold.
  • Indicators of resilience, as developed after those theories to indicate how close a system is to decline. The most recognized indicator of resilience in studies that we will be testing is based on a potential critical slowing down of a system close to a threshold. This critical slowing down is a generic phenomenon during which a degrading system displays a slower recovery time after a disturbance. When detected, a critical slowing down might indicate that the resilience of the system is dramatically reduced.
Conceptual representation of the response patterns and indicators of resilience tested in the HEALSEA project. Left graph: Response patterns along a stress gradient: through a smooth change in the monitored variable (orange line) or abrupt change and sudden decline below a threshold (blue line). Two right graphs: Example of indicators of resilience and CSD: in situation 1, i.e. far from a threshold, the variance of the monitored variable is low while in situation 2, i.e. close to threshold, an increase in variance is measured; after a disturbance, recovery time is short in situation 1, when resilience is still high; however in situation 2, i.e. close to a threshold and at lower resilience, recovery time increases. (Figures inspired from Scheffer et al. 2009; Dakos et al. 2011)


More specifically…

The overall goal of the proposed research is to contribute to the preservation of seagrass health and prevent from their loss by providing a comprehensive understanding of their response to changing conditions, and tools to evaluate their resilience, based on a new approach inspired from mathematical studies. To reach this goal, the objectives of the proposed research are to:

(1)    Identify what are the response patterns of seagrass biological and functional traits to a gradient of stress;

(2)    Test for the existence of indicators of resilience in seagrasses;

(3)    Propose a protocol of action to undertake in order to prevent seagrass decline in the form of a framework for the monitoring of seagrass meadows.



To answer these objectives, different approaches will be combined:

  • a systematic review
  • a field manipulative experiment
  • a model simulation
  • a framework for seagrass monitoring programs





The field experiment will be implemented in the Thau lagoon, near Sète, western French Mediterranean, in meadows of the dwarf eelgrass Zostera noltei Horneman (1832).

Localisation of the Thau lagoon in the Western French Mediterranean (©Google Earth images)


Zostera noltei is a temperate and fast-growing species characterised by a quick response to stress. It grows in intertidal and shallow subtidal areas of temperate and sub-tropical regions. In the Thau lagoon, Z. noltei meadows are found in several shallow subtidal areas and defined as Natura 2000 sites for their importance in sustaining biodiversity, providing shelter and nursery habitats for a variety of commercially important species.


DSCN1442 - Version 2
Zostera noltei  (©LauraSoissons)



The project started in April 2018 and will last until the end of summer 2020. The field experiments will start in 2019 and will continue for the whole growing season (spring & summer).

Updates on the experiment and overall project will be uploaded regularly here. Check it out!



Check out the research institutes and people involved in the project here.



Additional readings and literature used to write this text (in alphabetical order):

  • van Belzen, J. et al. Vegetation recovery in tidal marshes reveals critical slowing down under increased inundation. Commun. 8, 15811 (2017).
  • Benedetti-Cecchi, L. et al. Experimental perturbations modify the performance of early warning indicators of regime shift. Biol. 25, 1867–1872 (2015).
  • Chisholm, R. A. & Filotas, E. Critical slowing down as an indicator of transitions in two-species models. Theor. Biol. 257, 142–9 (2009).
  • Connell, S. D. et al. Testing for thresholds of ecosystem collapse in seagrass meadows? Biol. 1–12 (2017).
  • Dakos, V. et al. Slowing down in spatially patterned ecosystems at the brink of collapse. Nat. 177, E153-66 (2011).
  • Les, D. H. et al. Phylogenetic studies in Alismatidae, II: Evolution of Marine Angiosperms (Seagrasses) and Hydrophily. Bot. 22, 443–463 (1997).
  • Maxwell, P. S. et al. The fundamental role of ecological feedback mechanisms for the adaptive management of seagrass ecosystems – a review. Rev. (2016).
  • Orth, R. J. et al. A global crisis for seagrass ecosystems. Bioscience 56, 987–996 (2006).
  • Rindi, L. et al. Direct observation of increasing recovery length before collapse of a marine benthic ecosystem. Ecol. Evol. 1, 153 (2017).
  • Scheffer, M. et al. Early-warning signals for critical transitions. Nature 461, 53–9 (2009).
  • Short, F. et al. Global seagrass distribution and diversity: A bioregional model. Exp. Mar. Bio. Ecol. 350, 3–20 (2007).
  • Waycott, M. et al. Accelerating loss of seagrasses across the globe threatens coastal ecosystems. Natl. Acad. Sci. U. S. A. 106, 12377–12381 (2009).
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