Oysters as sentinels of climate variability and climate change in coastal ecosystems

Abstract

Beyond key ecological services, marine resources are crucial for human food security and socioeconomical sustainability. Among them, shellfish aquaculture and fishing are of primary importance but become more vulnerable under anthropogenic pressure, as evidenced by reported mass mortality events linked to global changes such as ocean warming and acidification, chemical contamination, and diseases. Understanding climate-related risks is a vital objective for conservation strategies, ecosystems management and human health. We provide here a comprehensive study of the historical mortality of adult oysters related to observed climate variability along the French Atlantic coast from 1986 to 2015, and we built on this knowledge to develop hindcast and forecast assessments of the oyster mortality risk from 1900 to 2100. We show that mortality events usually occur several months after winters dominated by the occurrence of positive North Atlantic oscillation (NAO+) atmospheric regimes of circulation. We explain the lagged response by the multiseasonal long-lasting imprint of wintertime NAO+ on biological and environmental factors, which partly structure oyster mortality etiology. Very high wintertime seawater temperature anomalies at the interannual timescale, which were mostly attributable to internal climate variability through NAO+ and which led to pronounced mortality over the observed period, are then treated as 'analogs' in a large ensemble of Intergovernmental Panel on Climate Change emission scenarios and models in order to anticipate future risks. Without any adaptive process, we provide evidence that actual exceptional mortality is likely to become the norm by ∼2035, even if global warming is limited to +2°C relative to pre-industrial levels.

Latitudinal drivers of oyster mortality: deciphering host, pathogen and environmental risk factors

“…Among them, increasing seawater temperature and decreasing salinity were associated with a higher mortality risk in adults, likely reflecting physiological imbalance and increased susceptibility to pathogens 48 . This agrees with the fact that mortality events recorded along the Atlantic coast of France usually occur months after winters dominated by the occurrence of positive North Atlantic oscillation (NAO+) atmospheric regimes of circulation 49 . The NAO+ is characterized by positive anomalies in air temperature and rainfall leading to higher sea surface temperature and higher river flow and lower salinity 48 .…”

Connectivities with shellfish farms and channel rivers are associated with mortality risk in oysters

“…This agrees with the fact that mortality events recorded along the Atlantic coast of France between 1986 and 2015 usually occur several months after winters dominated by the occurrence of positive North Atlantic oscillation (NAO+) atmospheric regimes of circulation (Thomas et al 2018). The NAO+ is characterized by positive anomalies in air temperature and rainfall and locally translates into higher sea surface temperature, higher river flow and lower salinity and higher chlorophyll concentration due to the intrusion of nutrient-rich riverine waters (Thomas et al 2018). Recent mortalities of adult oysters have often been associated with V. aestuarianus (EFSA AHAW Panel 2015, Goudenège et al 2015, Parizadeh et al 2018.…”

“…More specifically, in temperate estuarine ecosystems, mortality of adult oysters was associated with the temporal increase in seawater temperature during the warm season, freshwater out flow from rivers and subsequent drop in salinity, and excessive increase in nutrient and phytoplankton concentrations, which induce metabolic disorders associated with reproductive effort and stress (Delaporte et al 2006, Royer et al 2007, Soletchnik et al 2007, Bushek et al 2012, Go et al 2017. This agrees with the fact that mortality events recorded along the Atlantic coast of France between 1986 and 2015 usually occur several months after winters dominated by the occurrence of positive North Atlantic oscillation (NAO+) atmospheric regimes of circulation (Thomas et al 2018). The NAO+ is characterized by positive anomalies in air temperature and rainfall and locally translates into higher sea surface temperature, higher river flow and lower salinity and higher chlorophyll concentration due to the intrusion of nutrient-rich riverine waters (Thomas et al 2018).…”

Ocean acidification may slow the pace of tropicalization of temperate fish communities

“…Although the most abundant tropical species A. vaigiensis was relatively more abundant in oyster-dominated habitats, it also had high abundances in urchin barren-dominated habitats, which may be explained by the fact that: (1) A. vaigiensis usually forages in the water column and in areas with intense water movement, which may coincide with the same areas where oyster reefs and urchin barrens are found; and (2) oysters and urchins also create hard-substrate habitats that provide refuge for many temperate and tropical fishes that prefer habitats free from algae [47][48][49] . As such, declines in oyster reefs mediated by climate change 50,51 and overfishing in Australia 52 may further reduce the establishment of the most common vagrant tropical fish in temperate ecosystems.…”