Is the South-Mediterranean Canopy-Forming Ericaria giacconei (= Cystoseira hyblaea) a Loser From Ocean Warming?

Abstract

Canopy-forming brown algae support highly productive ecosystems whose decline has been attributed to the interplay of several anthropogenic disturbances. Climate change could have disruptive effects on the biology of these species, but the role of temperature in the development of early life stages is poorly understood. The aim of this study was to assess the response of Ericaria giacconei, a winter-reproducing Southern–Mediterranean endemic species, to thermal stress by testing five temperatures (12, 15, 18, 24, and 28°C) on adults and early stages. Chlorophyll a fluorescence of adult plants was measured at 0, 24, 72, and 120 h on nine fronds in each of the three aquaria per treatment. To assess egg release, zygote settlement, and embryo growth rate, approximately 1,200 receptacles were cultured on six Petri dishes per temperature treatment, and 10 random subsections of 2 ×2 mm were examined in three Petri dishes at 0, 20, 44, and 92 h after fertilization. Adult plants showed a plastic physiological response, and thermal stress had no significant effect on PSII efficiency. Embryos fully developed only at 12 and 15°C. Mortality increased at 18 and 24°C, and no zygotes survived at 28°C. In a scenario of further increasing temperatures, the effects of warming could affect the recruitment of E. giacconei and increase its vulnerability to further stresses. These effects on the survival of early stages, which are the bottleneck for the long-term survival of the species, should be taken into account in conservation and restoration measures to maintain canopy-forming macroalgal populations and associated biodiversity and ecosystem services.

Climate change and species facilitation affect the recruitment of macroalgal marine forests

“…Our results showed that the temperature, pH and the presence of potentially facilitating species had substantial effects on the density of recruits of Cystoseira compressa. The warmer temperature had, in agreement with our initial hypotheses, the largest negative effect on both the density and the size of recruits, as already observed on other forest-forming species, both on recruits 21,26,71 and adults 28,57,73,74 . Warmer temperatures not only affect the survival and growth of Cystoseira but also affect their metabolism 56,75,76 .…”

“…Seawater pH affected both the density and size of recruits in opposite ways, as density was negatively affected by the low pH, whereas size was positively affected. Low pH has been shown to negatively influence the settlement and early life stages of other key species such as the giant kelp 25,79 , corals and molluscs 38 which has led to the paradigm that early life stages could be more sensitive to global change and therefore could constitute a bottleneck 21,57 . However, in our experiment, lower pH levels positively affected the size of C. compressa, potentially showing a better performance as reported in some studies for the giant kelp 80,81 .…”

“…In Mediterranean rocky bottoms, Cystoseira sensu lato species (including the genera Cystoseira, Ericaria and Gongolaria, hereafter referred to as Cystoseira) are the main representatives of marine forests 13,55 . However, only a few studies have investigated the effect of climate change on this taxon and even fewer have focused on their early stages 21,[56][57][58] . Most studies show a negative impact of OW for both recruits and adults of Cystoseira on their survival 26,57,59 , resilience 21 and phenology 60,61 .…”

“…However, only a few studies have investigated the effect of climate change on this taxon and even fewer have focused on their early stages 21,[56][57][58] . Most studies show a negative impact of OW for both recruits and adults of Cystoseira on their survival 26,57,59 , resilience 21 and phenology 60,61 . In contrast, decreasing pH increased the productivity, antioxidant activity and production of photoprotective compounds of adult Cystoseira 56,58 .…”

Thermal vulnerability of the Levantine endemic and endangered habitat-forming macroalga, Gongolaria rayssiae: implications for reef carbon

“…However, studies conducted on other representatives of the Cystoseira s.l. group such as Ericaria zosteroides (Capdevila et al, 2019), E. crinita (Verdura et al, 2021), and E. giacconei (Falace et al, 2021) reported important negative warming effects on sensitive life stages of the species.…”