Abrupt shifts in the Gironde fish community: an indicator of ecological changes in an estuarine ecosystem

Abstract

For decades, global climate change has directly and indirectly affected the structure and function of ecosystems. Abrupt changes in biodiversity have been observed in response to linear or sudden modifications to the environment. These abrupt shifts can cause long-term reorganizations within ecosystems, with communities exhibiting new functional responses to environmental factors. Over the last 3 decades, the Gironde estuary in southwest France has experienced 2 abrupt shifts in both the physical and chemical environments and the pelagic community. Rather than describing these shifts and their origins, we focused on the 3 inter-shift periods, describing the structure of the fish community and its relationship with the environment during these periods. We described fish biodiversity using a limited set of descriptors, taking into account both species composition and relative species abundances. Inter-shift ecosystem states were defined based on the relationship between this description and the hydro-physico-chemical variables and climatic indices defining the main features of the environment. This relationship was described using generalized linear mixed models on the entire time series and for each inter-shift period. Our results indicate that (1) the fish community structure has been significantly modified, (2) environmental drivers influencing fish diversity have changed during these 3 periods, and (3) the fish−environment relationships have been modified over time. From this, we conclude a regime shift has occurred in the Gironde estuary. We also highlight that anthropogenic influences have increased, which re-emphasizes the importance of local management in maintaining fish diversity and associated goods and services within the context of climate change.

Toward a phenological mismatch in estuarine pelagic food web?

“…Our study examined the evolution of phenological patterns for juveniles of several fish species and their prey in the changing climatic and hydrological environment of the Gironde estuary. Chaalali [46] and Chevillot [10] highlighted abrupt ecological shifts in the Gironde estuarine ecosystem over the last three decades. The periods between these shifts (inter-shift periods) exhibited significantly different ecological communities in terms of relative abundance, diversity and functioning.…”

“…Over the last few decades, many authors have reported ongoing biological effects of climate change [1–6] impacting species and their habitats and shaping the structure of ecological communities as well as overall functioning of ecosystems [1,7–10]…”

“…Chaalali [46], implementing a multivariate analysis of time series (Principal Component Analysis), described two abrupt ecosystem shifts between 1979 and 2009 (circa 1987 and 2001), in relation with hydro-climatic parameters. Chevillot [10], who focused on estuarine fishes, implemented both a multivariate and STARS (Sequential algorithm for testing climate regime shift) [47] approach on a 1985–2014 time series, which allowed to specify shifts times, circa 1988 and 2002, and to define 3 inter-shift periods with significant differences in ecological dynamics and functioning.…”

“…In this context, moving further from Chevillot et al [10], the present article aims at depicting phenological modifications between the aforementioned intershift periods for fish and zooplankton species and at assessing the potential resulting mismatches at a community scale. We focused on the 1985-2010time series.…”

The need for a protean fisheries science to address the degradation of exploited aquatic ecosystems

“…The degradations of both structure and functioning of aquatic ecosystems due to overfishing, contamination, habitat fragmentation and degradation or water extraction are now widely recognised and documented (Postel and Richter 2003;Lotze et al 2006;Worm et al 2006;Chevillot et al 2016; in this symposium: Brind'Amour et al ; Chevillot et al; Kaimuddin et al; Le Luherne et al; Olmos et al; Vogel et al). Among the drivers of global change, climate change is a major threat for ecosystems affecting all biological scales (Gattuso et al 2015): primary productivity, species distributions, and community and food web structure .…”