Abstract
Seagrass meadows are disappearing at rates comparable to those reported for mangroves, coral reefs, and tropical rainforests. One of the main causes of their decline is the so-called cultural eutrophication, i.e., the input of abnormal amounts of nutrients derived from human activities. Besides the impact of eutrophication at a local scale, the occurrence of additional stress factors such as global sea warming may create synergisms in detriment of seagrass meadows’ health. In the present study, we aimed to evaluate if plants undergoing chronic cultural eutrophication and plants growing in relatively pristine waters are more (or less) sensitive to heat stress, nutrient load and the combination of both stressors. To address this question, a mesocosm experiment was conducted using Posidonia oceanica collected from two environments with different nutrients load history. Plants were exposed in controlled conditions to high nutrient concentrations, increased temperature and their combination for 5 weeks, to assess the effect of the single stressors and their interaction. Our results revealed that plants experiencing chronic cultural eutrophication (EU) are more sensitive to further exposure to multiple stressors than plants growing in oligotrophic habitats (OL). OL and EU plants showed different morphological traits and physiological performances, which corroborates the role of local pressures in activating different strategies in response to global environmental changes. EU-plants appeared to be weaker during the treatments, showing the greatest percentage of mortality, particularly under increased temperature. Temperature and nutrient treatments showed opposite effects when tested individually and an offset response when combined. The activation of physiological strategies with high energetic expenses to cope with excess of nutrients and other stressors, could affect plants present and future persistence, particularly under eutrophic conditions. Our results represent a step forward in understanding the complex interactions that occur in natural environments. Moreover, unraveling intraspecific strategies and the role of local acclimation/adaptation in response to multiple stressors could be crucial for seagrass conservation strategies under a climate change scenario.
Highlights
Seagrasses are important aquatic angiosperms that form meadows of great ecological and economic value for marine and global ecosystems
Our results revealed that plants undergoing chronic cultural eutrophication (EU) are more sensitive to a further increase of nutrients, when in presence of a temperature increase, than plants growing in oligotrophic water conditions (OL)
We found antagonistic interactions resulting from the combination of chronic nutrient increase and temperature rise for chlorophyll content and total non-structural carbohydrates in rhizomes, only in plants growing in eutrophic conditions
Summary
Seagrasses are important aquatic angiosperms that form meadows of great ecological and economic value for marine and global ecosystems. The productivity of seagrass meadows and their ability to capture carbon are comparable to those of terrestrial forests (Fourqurean et al, 2012). These macrophytes are considered ecosystem engineers due to their habitatforming capacity, providing food and shelter for a range of organisms such as finfish, shellfish, waterfowl, and herbivorous mammals (Boudouresque et al, 2009). There is strong evidence that seagrasses are disappearing at rates comparable to those reported for mangroves, coral reefs, and tropical rainforests (Waycott et al, 2009) Such decline has been reported worldwide especially in populations occurring in sheltered embayments and lagoons, where water recirculation is low and prone to nutrient loading from neighboring human population, the socalled “cultural eutrophication” (Touchette and Burkholder, 2000). Little is known about the potential interplay between multiple sources of stress and the response that meadows growing in different environmental conditions may have
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
