Demography of the mussel, an engineering species in the context of climate change

• Main Author: Oliveira, Gabriela Faria
• Publication Date: 2024
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10773/41486
• topic: Population dynamics; Mussel; Mytilus galloprovincialis; Upwelling ecosystem; Fecundity; Larval settlement; Growth; Early mortality; Foundation species

A general decline in foundation species at the rocky intertidal has been observed during the last decades all around the world, and primarily related to climate change. Bivalve relevance for ecosystem functioning and human food security emphasizes the importance of predictions of mussel performance under different climate stressors. Understanding population dynamics of complex life species is crucial to identify the main drivers for population contractions at different spatial scales, and to develop effective management strategies for declining populations, like the Mediterranean mussel (Mytilus galloprovincialis). In this thesis, the use of classic demographic approximations was validated to deepen the understanding of how larval transport, and also reproduction and post-settlement processes are modulated by environmental conditions, determining the persistence of mussel populations along the Portuguese coast. In the second chapter, the effect of a latitudinal gradient of temperature and food availability on the fecundity of the Mediterranean mussel was assessed aiming to parameterize environmental forcing over reproductive output. The results showed that temperature plays an important role, acting as a switching on–off mechanism for gametogenesis, while food availability has a lower influence but also modulates the number of gametes produced. Temperature and food availability also show different effects over fecundity depending on the temporal scale evaluated. The results support the view that gametogenesis responds non-linearly with temperature and chlorophyll concentration, an issue that is largely overlooked in growth, production and energy budgets of bivalve populations, leading to predictive models that can overestimate the capability of the mussel’s populations to deal with climate change future scenarios. The third chapter focused on mussel larval delivery mechanisms inferred from settlement time series and oceanographic variables at contrasting environments along the Portuguese coast, and around two Marine Protected Areas (MPAs). One of the MPAs was an archipelago (Reserva Nacional das Berlengas; RNB) located in front of the exposed rocky coast of Peniche, and the other one (Parque Nacional da Arrábida, PNA) was located in a sheltered bay, characterized as an upwelling shadow. The results indicated that larval delivery at short time scales (days) is dependent on the interaction of upwelling circulation with coastline topography. In the exposed MPA (RNB), the magnitude of mussel larval delivery is limited by the dynamics of an upwelling front and filament that intercepts the island as upwelling increases and decreases. In the sheltered bay (PNA), under an upwelling shadow, the upwelling front promotes recirculation of the water mass, intensifying larval retention and settlement. The results are also consistent with larval transport distances of tens of kilometres and ongoing connectivity between the two MPAs. Finally, in the fourth chapter early-stages mortality and growth patterns were analysed around the three previously mentioned regions, which are characterized by different degrees of protection, larval delivery mechanisms and environmental characteristics (temperature range, availability of food and upwelling exposure) to determine how post-settlement processes influence the decoupling between larval delivery and actual recruitment differently along the Portuguese coast. The results showed again a decoupling between north and south populations, suggesting the avoidance of the most stressful conditions for early development at each region: winter storms and large wave exposure in the north, and summer extreme temperatures and desiccation stress in the south. Nonetheless, common environmental variables control growth and mortality in every region. Considering growth, a positive relationship with the intensification of upwelling over certain thresholds, suggests temperature and food availability as the main environmental variables controlling growth rates. Regarding mortality, a density-dependent effect was detected, as well as a positive effect of intermediate values of UI, which can minorate intraspecific competition by increasing food availability without increasing wave exposure related to intense wind situations. In summary, the general patterns observed in reproduction, larval delivery, and post-settlement development, are deeply influenced by upwelling regimes, confirming the adaptation of mussels to local conditions, even when multiple factors control the population dynamics of this complex-life species.