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

Abstract

Marine forests are shrinking globally due to several anthropogenic impacts including climate change. Forest-forming macroalgae, such as Cystoseiras.l. species, can be particularly sensitive to environmental conditions (e.g. temperature increase, pollution or sedimentation), especially during early life stages. However, not much is known about their response to the interactive effects of ocean warming (OW) and acidification (OA). These drivers can also affect the performance and survival of crustose coralline algae, which are associated understory species likely playing a role in the recruitment of later successional species such as forest-forming macroalgae. We tested the interactive effects of elevated temperature, low pH and species facilitation on the recruitment of Cystoseira compressa. We demonstrate that the interactive effects of OW and OA negatively affect the recruitment of C. compressa and its associated coralline algae Neogoniolithon brassica-florida. The density of recruits was lower under the combinations OW and OA, while the size was negatively affected by the temperature increase but positively affected by the low pH. The results from this study show that the interactive effects of climate change and the presence of crustose coralline algae can have a negative impact on the recruitment of Cystoseira s.l. species. While new restoration techniques recently opened the door to marine forest restoration, our results show that the interactions of multiple drivers and species interactions have to be considered to achieve long-term population sustainability.

Keep It Simple: Improving the Ex Situ Culture of Cystoseira s.l. to Restore Macroalgal Forests

“…Cystoseira s.l. species will have no choice but to try to adapt to the multiple impacts of climate change that are already affecting most marine ecosystems [ 108 ], but regulation of herbivorous fish populations must be considered an extremely urgent step to be implemented in areas of the Mediterranean where they have been shown to play a major role in the regression of brown algal forests.…”

Changes in threats to macroalgal forests (Cystoseira sensu lato) at three restoration sites in the Mediterranean Sea

“…Significant reductions in settlement of various Cystoseira s.l . species have been observed after a few days of exposure to abnormally high temperatures (Capdevila et al, 2015; Verdura et al, 2018; Monserrat et al, 2022). Moreover, photosynthetic efficiency of adults was also proven to be reduced after 2 weeks of exposures at 28°C, while after 25 days even the tissues were damaged in the population of Port de la Selva (Verdura et al, 2021).…”

Invasive Fish and Sea Urchins Drive the Status of Canopy Forming Macroalgae in the Eastern Mediterranean

“…Recent experiments have shown that sea level rise in the region may expose intertidal macroalgal populations to grazing by rabbitfish, leading to reduced algal cover in very shallow waters in the long term [ 97 ]. Further, the species forming the forests may be vulnerable to the effects of ocean warming and ocean acidification [ 26 , 27 ]. For instance, Gongolaria rayssiae , a species endemic only to Israel and Lebanon, completely loses its branches in early summer and its optimum temperature matches spring temperatures [ 98 ].…”

“…forests has been reported in the Mediterranean Sea over the past few decades [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. These declines result from both direct anthropogenic pressures, such as water quality decrease and habitat destruction [ 21 , 22 , 23 , 24 , 25 ], and indirect anthropogenic pressures, such as climate change through global warming and ocean acidification [ 26 , 27 ] and overgrazing by herbivores (mainly in the southeast basin due to biological invasions of rabbitfish or trophic cascades caused by overfishing that lead to an increase in sea urchin populations) [ 28 , 29 , 30 , 31 ]. It is essential to prioritize effective management actions to halt the loss of Mediterranean marine forests and conserve these keystone rocky reef habitats.…”