Seasonal and ontogenetic variability in the photosynthetic thermal tolerance of early life-stages of Fucus guiryi (Phaeophyceae, Fucales)

ABSTRACT

Assessing thermal tolerance of marine organisms is a prerequisite to predict their responses to upcoming warming scenarios, but thermal sensitivities broadly vary among life stages and seasons due to thermal acclimation. This study aimed to identify changes in photosynthetic performance of recruits of the intertidal canopy-forming seaweed Fucus guiryi in relation to seasonality during early ontogeny. Zygotes were isolated from late summer (LS) and late winter (LW) thalli and were exposed to an ecologically relevant thermal range (15, 20, 23 and 25°C) under laboratory-controlled conditions for 3 weeks. Photosynthetic responses were assessed by in vivo chlorophyll a fluorescence measurement. Seasonality had a significant influence on initial zygote morphology, with a decrease in area of 17% from LS to LW. Zygotes from LS and LW exhibited the typical photosynthetic responses of sun and shade plants, respectively, with a greater capacity to dissipate heat via non-photochemical quenching in LW. Late winter embryos showed a wider optimal thermal range for photosynthesis (15–23°C) than late summer ones (20–23°C). Embryos attained maximum photosynthetic responses 1 week after fertilization when they developed the apical meristem. Seasonal differences were more evident during early ontogenesis (0–14 d) than once their photosynthetic apparatus become like that of adult thalli. This study evidenced that zygote traits can vary across seasons, but zygotes are able to acclimate their photosynthetic performance up to 25°C within 3 weeks. Recruits of F. guiryi possessed a wide photosynthetic plasticity and are probably able to persist in populations close to their thermal limits if thermal thresholds are not exceeded.

KEYWORDS:

• Brown seaweeds
• Embryos
• Global change
• Heat stress
• PAM fluorometry
• Rocky intertidal
• Seasonality

ACKNOWLEDGEMENTS

The authors thank Associate Editor E. Tarakhovskaya, Editor-in-Chief A.J. Calado and two anonymous reviewers for their helpful comments and editing of the original manuscript.

AUTHORS’ CONTRIBUTIONS

RSdeP, EB-E, AF-M and MG-S contributed to the conception and design of the study; RSdeP and AFN performed laboratory experiments and statistical analyses; RSdeP organized the database, designed figures and tables and wrote the first draft of the manuscript. All authors contributed to manuscript revision and read and approved the original and revised versions.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

This research was carried out within the European project BiodivERsA3- MARFOR (Functional Variability and Dynamics of Responses of Marine Forests to Global Change), supported by Ministerio de Economía y Competitividad (PCIN-2016-090) and project PID2020-118045-GB-I00 (Ministerio de Ciencia e Innovación, Spain). ANF was financially supported by Sistema Nacional de Garantía Juvenil y del Programa Operativo de Empleo Juvenil 2014–2020 (Contrato personal laboral técnico de apoyo y gestión I+D+i).