Seagrass (Posidonia oceanica) seedlings in a high-CO2 world: from physiology to herbivory

Abstract

Under future increased CO2 concentrations, seagrasses are predicted to perform better as a result of increased photosynthesis, but the effects in carbon balance and growth are unclear and remain unexplored for early life stages such as seedlings, which allow plant dispersal and provide the potential for adaptation under changing environmental conditions. Furthermore, the outcome of the concomitant biochemical changes in plant-herbivore interactions has been poorly studied, yet may have important implications in plant communities. In this study we determined the effects of experimental exposure to current and future predicted CO2 concentrations on the physiology, size and defense strategies against herbivory in the earliest life stage of the Mediterranean seagrass Posidonia oceanica. The photosynthetic performance of seedlings, assessed by fluorescence, improved under increased pCO2 conditions after 60 days, although these differences disappeared after 90 days. Furthermore, these plants exhibited bigger seeds and higher carbon storage in belowground tissues, having thus more resources to tolerate and recover from stressors. Of the several herbivory resistance traits measured, plants under high pCO2 conditions had a lower leaf N content but higher sucrose. These seedlings were preferred by herbivorous sea urchins in feeding trials, which could potentially counteract some of the positive effects observed.

Climate Change Impacts on Seagrass Meadows and Macroalgal Forests: An Integrative Perspective on Acclimation and Adaptation Potential

“…Experimental simulated heat waves and warming at projected levels in the NW Mediterranean led to reduced growth, increased mortality, leaf necrosis, and respiration in Posidonia oceanica seedlings (Herman and Sultan, 2016;Guerrero-Meseguer et al, 2017), and also increased their susceptibility to consumption by grazers (Hernán et al, 2016). Likewise, experiments with Z. japonica seedlings showed a thermal limit of 29 • C above which seedlings die (Abe et al, 2009), similar to the thermal limit for P. oceanica seedlings.…”

“…However, elevated CO 2 also favors filamentous algae, which can overgrow seagrass seedlings, leading to reduced growth (Burnell et al, 2014). Moreover, lower N content and increased sucrose levels in seedlings growing under high pCO 2 lead to higher herbivory pressure (Hernán et al, 2016).…”

Ecological Function of Phenolic Compounds from Mediterranean Fucoid Algae and Seagrasses: An Overview on the Genus Cystoseira sensu lato and Posidonia oceanica (L.) Delile

“…Since CO 2 can greatly limit primary production in seagrasses [148,149], under high CO 2 scenarios a decrease in phenolics would be expected, following RAH. In P. oceanica plants, a decrease [30,150,151], as well as no changes [147] in phenolic compounds, have been reported, with a consequent increased feeding of a wide range of consumers, including fishes and sea urchins [30,[150][151][152]. Under high CO 2 , a decrease in phenolic compounds was also observed in the seeds of P. oceanica, which were bigger, with higher carbon content and more stored sucrose [152].…”

“…In P. oceanica plants, a decrease [30,150,151], as well as no changes [147] in phenolic compounds, have been reported, with a consequent increased feeding of a wide range of consumers, including fishes and sea urchins [30,[150][151][152]. Under high CO 2 , a decrease in phenolic compounds was also observed in the seeds of P. oceanica, which were bigger, with higher carbon content and more stored sucrose [152]. Having more resources (i.e., CO 2 ) available, they invest less on defense, favoring the storage of more rapidly available carbon-based compounds such as sucrose [153].…”

Contrasting effects of ocean warming on different components of plant-herbivore interactions

“…Shoots of the seagrasses P. oceanica and C. nodosa were collected and stored in either 22°C or 30°C treatment aquaria for 3 weeks to allow changes to plant metabolites. Seagrass traits generally respond within these time frames to changes in environmental conditions (Hernán et al, 2017(Hernán et al, , 2016Jordi F Pagès et al, 2010;Ruiz et al, 2001). The alga C. mediterranea was collected and stored in aquaria at 18°C and 25°C, since thalli could not survive the 30ºC treatment.…”