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Impacts of marine heatwaves and acute hypoxia on the short-snouted seahorse metabolism and behaviour
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Resumo(s)
Seahorses are teleost fish with unusual anatomical and behavioural characteristics, that make them
one of the most unique and enigmatic animals. They are recognized as flagship species for several
conservation issues. Unfortunately, seahorses’ populations have been declining worldwide, mainly due
to anthropogenic pressure. Their unique lifestyle, namely, their reduced swimming ability, small
distribution, high site fidelity and monogamy, constrains their ability to migrate, adapt and evolve in
future climate scenarios, especially when exposed to short-term extreme events such as marine
heatwaves and acute hypoxia. Yet, seahorses inhabit shallow coastal waters that display daily or seasonal
fluctuations of temperature and oxygen, which suggests that these animals may show some phenotypic
plasticity to these environmental changes. Within this context, the objective of this dissertation was to
test the individual and combined effects of a category II (strong) marine heatwave (21.5°C) and an
extreme hypoxia exposure (~27% dissolved oxygen) on the metabolism, behaviour and food intake of
the temperate seahorse Hippocampus hippocampus. Concomitantly, the impact of the marine heatwave
on the number and size of seahorses oocytes was also examined. Regarding metabolism, hypoxia
exposure, alone or accompanied by the marine heatwave, led to a significant reduction in metabolic and
ventilation rates. The metabolic rates under the combined treatment were slightly higher than that of
those exposed to hypoxia, which may indicate a temperature compensation in relation to oxygen
depletion. The marine heatwave treatment led to a significant increase in ventilation rates and food
intake, but did not change seahorse behavioural patterns. In contrast, seahorses showed signs of
movement lethargy whenever there was oxygen depletion. The number and size of the oocytes increased
significantly with increasing temperature. The results show that, although seahorses may have some
adaptation elasticity to heat stress, an extreme decrease in dissolved oxygen results in metabolic and
behavioural changes that may jeopardize the development and survival of these iconic organisms. The
two stressors together have similar impacts to those observed in the hypoxia treatment, which suggests
that oxygen depletion elicits greater biological effects than strong marine heatwaves.
Descrição
Tese de mestrado, Ecologia Marinha , 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Hippocampus hippocampus onda de calor marinha hipóxia comportamento metabolismo Teses de mestrado - 2023