Integrated Responses to Simulated Submarine Groundwater Discharge; Tissue Water Potential, Photosynthesis, and Growth Comparisons for Two Intertidal Algae Species
Date
2012
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Abstract
Marine algae are typically considered ocean plants with their water relations set to
fully saline marine waters. In oceanic islands however, reef algae can be subjected to
periodic to daily fluctuations in osmotic potential of the ambient waters as fresh-water
runoff and submarine groundwater discharges can lower salinities. In contrast, tidal
exposure can increase tissue water potential, even above 34 ‰, as water loss from
evaporation concentrates remaining salts from seawater. With submarine groundwater
discharge, recent studies have shown substantial nutrient influx carried by freshwater
sources. To acquire nutrients required for growth and survival, algae around oceanic
islands must be able to tolerate the osmotic challenges within the algal cells driven by
widely variable changes in external salinity. Here we test the ability of two co-occurring
tidal red algae, Acanthophora spicifera and Laurencia mcdermidiae, to regulate their
tissue water potential in response to simulated diurnal pulses of high nutrient, low salinity
submarine groundwater discharge. The tissue water potential of treated and untreated
specimens will be tested using the Chardakov method, photosynthesis will be estimated
via electron transport rate measurements and changes in biomass will be used to assess
overall fitness. Some algal species may be expected to have more efficient physiological
responses for maintaining a functional intercellular solute potential when exposed to
changes in salinity because this trait has been selected for where large daily salinity
changes have been seen. It is expected that the invasive, bloom forming species, A.
spicifera, will tolerate the experimental lowered salinity, high nutrient pulses because A.
spicifera has developed a unique physiological ability to adapt to this kind of stress. If the
invasive species is more effective in nutrient uptake under extreme conditions this
information could further our understanding of algal bloom dynamics, distributions of
species and how to better manage marine ecosystems.
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algae, marine ecology, biological oceanography
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47 pages
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