Reproduction Under Stress: Acute Effect of Low Salinities and Heat Waves on Reproductive Cycle of Four Ecologically and Commercially Important Bivalves

Abstract

The impacts of climate change on the structure and functioning of estuaries is a major focus of concern, even more when the affected species support important fisheries as the bivalves Ruditapes decussatus, Ruditapes philippinarum, Venerupis corrugata, and Cerastoderma edule in Europe. Their reproductive performance, in the context of climate stressors, had not been investigated so far. Our objective was to experimentally evaluate acute stress effects over gonad development after 6 days of low salinity stress in autumn, winter and spring as well as 4 days of heatwave stress during emersion in summer. These are the most probable extreme events that bivalves should face in our latitudes. Four different salinity ramps (5–20, 10–25, 15–30, 30–30) were created during simulated tidal cycles in mesocosms for the low salinity experiments. Also four sediment heatwaves at emersion (20–20, 20–27, 20–32, 20–37°C) were done during simulated tidal cycle. Both low salinity and heatwave stresses over such short periods compromised reproduction; the acute response was species-specific and varied with the time of the year, and therefore, with the stage of the gametogenic cycle. In December, during sexual resting and the beginning of gametogenesis, a delay in gametogenesis at lower salinities was recorded in the four species. However, at the peak of the reproductive period (March and May), different responses were observed: abnormal oocytes in R. decussatus and resorption of gametes with haemocytic infiltration in R. philippinarum and V. corrugata. Likewise sediment temperatures higher than 32°C provoked gonadal resorption and severe haemocytic invasion in V. corrugata, R. decussatus, and C. edule but had no effect in R. philippinarum. These responses to both environmental stressors might be related to the allocation of energy from reproduction toward defense and repair mechanisms to ensure survival. Contrastingly, low salinities triggered massive spawning in C. edule that could lead to a mismatch between the presence of larvae and phytoplankton, causing potentially starvation and thus reducing recruitment success. Reproduction of theses bivalves would be compromised if low salinity episodes in winter and spring, even for short periods of time such as those in these experiments, are followed by a heatwave in summer. Furthermore the impact would be magnified if this situation happens during consecutive years preventing replenishment of the shellfish beds.

Resilience and Social Adaptation to Climate Change Impacts in Small-Scale Fisheries

“…Fishers also demonstrated strong local environmental knowledge and awareness about the impacts of climate change on their activity, which is also consistent with previous research (Shaffrill et al, 2017;Pita et al, 2020). Our findings also showed that all fishers agreed with the expert opinion (Peteiro et al, 2018;Domıńguez et al, 2020;Domıńguez et al, 2021;Vaźquez et al, 2021) about the new scenarios of climate change for the future of shellfish, and noted that these scenarios would be negative for their activity.…”

“…-Part C (Climate change impacts and future scenarios): the interviewees were asked their opinion about predictions, suggesting that abundance of shellfisheries (except the Manila clam) will decrease in the near future (Domıńguez et al, 2020;Domıńguez et al, 2021;Vaźquez et al, 2021), and what fishers would do if these predictions come true;…”

“…The recent increase in the minimum salary in Spain (from 707,7 € in 2017 to 965 € in 2021) (Ministry of Labour and Social Economy, 2021) could change the perception of the fishers about the minimum income needed to maintain the activity. Taking into account the trend of future increases of minimum salary, abandonment of the fishery seems to be the most likely reaction in the medium term, considering the current quotas and trends of declining catches and abundance of most of commercial shellfish species (Pita et al, 2019;Domıńguez et al, 2020;Domıńguez et al, 2021;Vaźquez et al, 2021).…”

“…In general, how individuals and communities adapt to climate change depends on a diverse range of social-ecological factors including social norms and values, local environmental conditions, socio-economic status and processes of marginalization and inequality (Savo et al, 2017). However, focusing on only a few species such as the Manila clam, which is more resistant to changes in environmental conditions (Domıńguez et al, 2020;Domıńguez et al, 2021;Vaźquez et al, 2021), can be a high-risk adaptation strategy. Manila clam (native to the Pacific), was introduced for culture in Europe in the 1970s because of its high adaptability (Latrouite and Claude, 1976;Peŕez-Camacho and Cuña, 1985;Drummond et al, 2006).…”

“…Nevertheless, the threats are numerous and growing. Variations in temperature and/or salinity, even within the limits of tolerance of each species, can constrain most physiological processes, such as growth and reproduction (Macho et al, 2016;Peteiro et al, 2018;Domıńguez et al, 2020;Domıńguez et al, 2021;Vaźquez et al, 2021), and also behavior (Woodin et al, 2020). The associated constraints may lead to a recruitment failure in adult populations or delays in the time required for the species to reach commercial sizes.…”