Seagrass collapse due to synergistic stressors is not anticipated by phenological changes

Abstract

Seagrasses are globally declining and often their loss is due to synergies among stressors. We investigated the interactive effects of eutrophication and burial on the Mediterranean seagrass, Posidonia oceanica. A field experiment was conducted to estimate whether shoot survival depends on the interactive effects of three levels of intensity of both stressors and to identify early changes in plants (i.e., morphological, physiological and biochemical, and expression of stress-related genes) that may serve to detect signals of imminent shoot density collapse. Sediment burial and nutrient enrichment produced interactive effects on P. oceanica shoot survival, as high nutrient levels had the potential to accelerate the regression of the seagrass exposed to high burial (HB). After 11 weeks, HB in combination with either high or medium nutrient enrichment caused a shoot loss of about 60%. Changes in morphology were poor predictors of the seagrass decline. Likewise, few biochemical variables were associated with P. oceanica survival (the phenolics, ORAC and leaf δS). In contrast, the expression of target genes had the highest correlation with plant survival: photosynthetic genes (ATPa, psbD and psbA) were up-regulated in response to high burial, while carbon metabolism genes (CA-chl, PGK and GADPH) were down-regulated. Therefore, die-offs due to high sedimentation rate in eutrophic areas can only be anticipated by altered expression of stress-related genes that may warn the imminent seagrass collapse. Management of local stressors, such as nutrient pollution, may enhance seagrass resilience in the face of the intensification of extreme climate events, such as floods.

Assessment of the ecological structure of Posidonia oceanica (L.) Delile on the northern coast of Lazio, Italy (central Tyrrhenian, Mediterranean)

“…These studies should include the changes of private (neutral) allelic in order to control the population demography vs genetic relationship stability necessary to reinforce their resilience as we have observed in other protected areas in the Mediterranean (Micheli et al 2015;. Finally, since seagrasses are globally declining, and their loss is often due to synergies among stressors (Ceccherelli et al 2018), the ecological implication of the results obtained here, such as the genetic features and the environmental conditions, could be further aspects to be considered in the monitoring surveys.…”

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

“…Even if additional researches are necessary to define thresholds for classifying the different level of perturbation, the obtained results open interesting perspectives on the application of the phenol content in Cystoseira sensu latu and P. oceanica as possible biomarkers of environmental quality. In monitoring surveys, the assessment of health marine ecosystems should make provision for multidisciplinary investigations [161,162] and multiparametric approaches, including physiological biomarkers, biomarkers of general stress and more specific biomarkers [131], but also molecular ones [16,27,140,163].…”

“…Recently, the MFSD (2008/56/EC) [58] selected P. oceanica as representative species of the angiosperm quality elements for the Mediterranean marine environment. Despite all that, P. oceanica habitats are experiencing decline or loss throughout the Mediterranean, often due to synergies among multiple stressors, mainly of anthropogenic origin, which are particularly threatening slow-growing species, such as seagrasses [27,116,117].…”

Effect of Seagrass on Current Speed: Importance of Flexibility vs. Shoot Density

“…For example, in light-limited environments, shoot density varies positively with light intensity (Short et al, 1995;Ruiz and Romero, 2001;Krause-Jensen et al, 2003). Furthermore, increasing sediment organic content or nutrient availability can lead to increases in shoot density (e.g., Koch, 2001;Holmer et al, 2008;Howard et al, 2016;Ceccherelli et al, 2018). These factors are in turn affected by the deformation of shoots by hydrodynamic drag, the formation or closure of gaps in the canopy in flowing water, and the transport of dissolved nutrients and sediment by water moving around and through a grass canopy.…”