Effects of ocean warming, eutrophication and salinity variations on the growth of habitat-forming macroalgae in estuarine environments

Henrique Douglas Dos Santos Borburema,George Emmanuel Cavalcanti De Miranda,Ruth Pessoa De Lima

doi:10.1590/0102-33062020abb0303

Henrique Douglas Dos Santos Borburema, George Emmanuel Cavalcanti De Miranda + Show 1 more

Open Access

https://doi.org/10.1590/0102-33062020abb0303

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Abstract

Global change and coastal eutrophication are affecting macroalgae worldwide. We analyzed the effects of increased water temperature (25, 28 and 32 °C) and eutrophication on the growth of Bostrychia binderi and Bostrychia montagnei in a range of salinities (18, 24, 30, 36 and 42 PSU) through three independent multifactorial experiments. Both species had higher growth at 25 °C than at 28 and 32 °C (warming scenario projected by IPCC), suggesting a negative effect of ocean warming. The species showed a broad tolerance to the range of salinities tested, with higher growth at 36 and 42 PSU, as a local adaptation strategy. Oligotrophic seawater significantly affected the growth of both species because the lowest growth was found in this condition, whereas highest growth was found with increased availability of nutrients, which is probably because estuaries are nutrient-rich environments due to continental runoff. High temperatures, low salinities and few nutrients had negative interactive effects on the growth of both species. Our results show that ocean warming can be detrimental to the studied macroalgae, and that both species are tolerant to eutrophication, with B. montagnei being more sensitive than B. binderi. Our results also reinforce the euryhaline characteristic of the genus Bostrychia.

Highlights

The Intergovernmental Panel on Climate Change (IPCC) has demonstrated global increases in anthropogenic emissions of greenhouse gases into the atmosphere, mainly carbon dioxide (CO2), which are inducing global changes such as continental and oceanic warming, ocean acidification and sea level rise (Collins et al 2013; IPCC 2014; Cornwall & Hurd 2020)
Our results show that ocean warming can be detrimental to the studied macroalgae, and that both species are tolerant to eutrophication, with B. montagnei being more sensitive than B. binderi
Bostrychia binderi had the highest relative growth rates (RGRs) (1.80 % day-1) in the treatment where the apical segments were cultivated at 25 °C, 30 PSU and highest concentration of nutrients (N3), whereas the lowest RGR (0.03 % day-1) was at 32 oC, 42 PSU and lowest nutrient availability (N0)

Summary

Introduction

The Intergovernmental Panel on Climate Change (IPCC) has demonstrated global increases in anthropogenic emissions of greenhouse gases into the atmosphere, mainly carbon dioxide (CO2), which are inducing global changes such as continental and oceanic warming, ocean acidification and sea level rise (Collins et al 2013; IPCC 2014; Cornwall & Hurd 2020). Models from the IPCC (2014) project a continuous increase in temperature on all continents and ocean surfaces until the end of the 21st century (2081–2100). These models are projected future scenarios called Representative Concentration Pathways (RCPs). Sea level rise will lead to the expansion of coastal flooding areas, resulting in estuary level rise and physical and chemical changes in estuarine waters (e.g. changes in: temperature, pH, luminosity, salt wedge affecting salinity gradients), because the estuarine systems are strongly affected by the surrounding sea (Rybczyk et al 2012; Couto et al 2014)

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