Getting from Sea to Nurseries: Considering Tidal Dynamics of Juvenile Habitat Distribution and Connectivity in a Highly
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Getting from Sea to Nurseries: Considering Tidal Dynamics of Juvenile Habitat Distribution and Connectivity in a Highly Modified Estuarine Riverscape Maria Alp1,2*
and Ce´line Le Pichon1
1
UR HYCAR, Universite´ Paris-Saclay, INRAE, 1 rue Pierre-Gilles de Gennes, 92761 Antony, France; 2UR RiverLy, INRAE, 5 rue de la Doua, 69625 Villeurbanne, France
ABSTRACT Productive and ecologically highly valuable ecosystems, macrotidal estuaries are also characterised by complex habitat and connectivity dynamics driven by tidal and freshwater influence. Organisms living in these constantly changing systems have to match their movement patterns to the shifting habitat mosaic using available windows of connectivity to access habitat patches of interest. This appears particularly important for the juvenile stages of many fish species colonising shallow and intertidal areas of the estuaries as summer nurseries. We apply tools from landscape ecology to investigate the estuarine habitat and connectivity dynamics on the example of juvenile seabass (Dicentrarchus labrax). We test under which conditions spatio-temporal bottlenecks to estuarine nursery colonisation may emerge for this species in a human-modified estuary. Combining a hydrodynamic
model of the Seine estuary with remote sensing data allows us to capture structural changes in habitat availability and connectivity at the estuarine scale and at a fine spatio-temporal resolution. With chronological least-cost modelling of successive tidal steps, we assess patterns of nursery accessibility and estimate tidal colonisation fronts for different mobility scenarios. We show that, at certain hydrological conditions, tidal water level variation causes local disruptions of habitat availability and connectivity, creating temporary bottlenecks for seabass juveniles’ movement. Fish mobility appears determinant for their vulnerability to these connectivity disruptions. Our approach allows for quantitative assessment and visualisation of riverscape complexity related to tidal dynamics. It is applicable to other highly dynamic ecosystems, where the mobile nature of connectivity and habitats needs to be integrated into conservation and management planning.
Received 31 January 2020; accepted 18 July 2020
Key words: least-cost modelling; spatio-temporal hydrodynamics; functional connectivity; habitat patch dynamics; tidal cycle; dispersal; nursery habitats; Seine estuary; European seabass; Dicentrarchus labrax.
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00536-1) contains supplementary material, which is available to authorized users. Author contributions: MA and CLP contributed equally to study design and manuscript preparation. MA led the data preparation and least-cost modelling. *Corresponding author; e-mail: [email protected]
M. Alp, C. Le Pichon
HIGHLIGHTS Tidal estuarine habitat distribution and connectivity change on an hourly scale. Transient bottlenecks to movement emerge in estuaries with modified topography.
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