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Tropical seagrass species tolerance to hypersalinity stress
Koch, M.S.; Schopmeyer, S.A.; Kyhn-Hansen, C.; Madden, C.J.; Peters, J.S. (2007). Tropical seagrass species tolerance to hypersalinity stress. Aquat. Bot. 86(1): 14-24. dx.doi.org/10.1016/j.aquabot.2006.08.003
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

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Keywords
    Osmotic adaptations; Salinity; Sea grass; Halodule wrightii Ascherson, 1868 [WoRMS]; Ruppia maritima Linnaeus, 1753 [WoRMS]; Thalassia testudinum K.D.Koenig, 1805 [WoRMS]; Marine

Authors  Top 
  • Koch, M.S.
  • Schopmeyer, S.A.
  • Kyhn-Hansen, C.
  • Madden, C.J.
  • Peters, J.S.

Abstract
    The long-term sustainability of seagrasses in the subtropics and tropics depends on their ability to adapt to shifts in salinity regimes, particularly in light of present increases in coastal freshwater extractions and future climate change scenarios. Although there are major concerns world-wide on increased salinity in coastal estuaries, there is little quantitative information on the specific upper salinity tolerance of tropical and subtropical seagrass species. We examined seagrass hypersalinity tolerance under two scenarios: (1) when salinity is raised rapidly simulating a pulsed event, such as exposure to brine effluent, and (2) when salinity is raised slowly, characteristic of field conditions in shallow evaporative basins; the first in hydroponics (Experiments I and II) and the second in large mesocosms using intact sediment cores from the field (Experiment III). The three tropical seagrass species investigated in this study were highly tolerant of hypersaline conditions with a slow rate of salinity increase (1 psu d−1). None of the three species elicited total shoot mortality across the range of salinities examined (35–70 psu over 30 days exposures); representing in situ exposure ranges in Florida Bay, a shallow semi-enclosed subtropical lagoon with restricted circulation. Based on stress indicators, shoot decline, growth rates, and PAM florescence, all three species were able to tolerate salinities up to 55 psu, with Thalassia testudinum (60 psu) and Halodule wrightii (65 psu) eliciting a slightly higher salinity threshold than Ruppia maritima (55 psu). However, when salinity was pulsed, without a slow osmotic adjustment period, threshold levels dropped 20 psu to approximately 45 psu for T. testudinum. While we found these three seagrass species to be highly tolerant of high salinity, and conclude that hypersalinity probably does not solely cause seagrass dieoff events in Florida Bay, high salinity can modify carbon and O2 balance in the plant, potentially affecting the long-term health of the seagrass community.

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