Remote sensing in seagrass ecology: coupled dynamicsbetween migratory herbivorous birds and intertidalmeadows observed by satellite during four decades

Marine Diversity
Climatic Events
Remote Sensing
Maria Laura Zoffoli, Pierre Gernez, Simon Oiry, Laurent Godet, Śebastien Dalloyau, Bede Ffinian Rowe Davies & Laurent Barilĺ

Maria Laura ZoffoliPierre GernezSimon OiryLaurent GodetŚebastien DalloyauBede Ffinian Rowe Davies & Laurent Barilĺe


January 1, 2021

Zoffoli et al., 2021

Taking into account trophic relationships in seagrass meadows is crucial toexplain and predict seagrass temporal trajectories, as well as for implementingand evaluating seagrass conservation policies. However, this type of interactionhas been rarely investigated over the long term and at the scale of the wholeseagrass habitat. In this work, reciprocal links between an intertidal seagrassspecies,Zostera noltei, and a herbivorous bird feeding on this seagrass species,the migratory gooseBranta bernicla bernicla, were investigated using an originalcombination of long-term Earth Observation (EO) and bird census data. Sea-grass Essential Biodiversity Variables (EBVs) such as seagrass abundance andphenology were measured from 1985 to 2020 using high-resolution satelliteremote sensing over Bourgneuf Bay (France), and cross-analysed within situmeasurements of bird population size during the goose wintering season. Ourresults showed a mutual relationship between seagrass and Brent geese over thefour last decades, suggesting that the relationship between the two speciesextends beyond a simple grass—herbivore consumptive effect. We provided evi-dence of two types of interactions: (i) a bottom-up control where the late-summer seagrass abundance drives the wintering population of herbivorousgeese and (ii) an indirect top-down effect of Brent goose on seagrass habitat,where seagrass development is positively influenced by the bird population dur-ing the previous wintering season. Such a mutualistic relationship has strongimplications for biodiversity conservation because protecting one species isbeneficial to the other one, as demonstrated here by the positive trajectoriesobserved from 1985 to 2020 in both seagrass and bird populations. Importantly,we also demonstrated here that exploring the synergy between EO andin situbird data can benefit seagrass ecology and ecosystem management.