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Hydrology 2018, 5(4), 65; https://doi.org/10.3390/hydrology5040065

Submarine Groundwater Discharge Differentially Modifies Photosynthesis, Growth, and Morphology for Two Contrasting Species of Gracilaria (Rhodophyta)

1
Department of Botany, University of Hawaii at Mānoa, 3190 Maile Way, Honolulu, HI 96822, USA
2
Kamehameha Schools, 567 South King St. Honolulu, HI 96813, USA
*
Author to whom correspondence should be addressed.
Received: 12 November 2018 / Revised: 27 November 2018 / Accepted: 29 November 2018 / Published: 2 December 2018
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Abstract

On many tropical reefs, submarine groundwater discharge (SGD) provides a substantial and often overlooked nutrient source to nearshore ecosystems, yet little is known about the impacts of SGD on the biology of reef organisms. To address this, the physiological responses of the endemic rhodophyte Gracilaria coronopifolia and an invasive congener, Gracilaria salicornia, were examined across an SGD gradient in the field and laboratory. Tissue samples of both species were cultured for 16 days along an onshore-offshore SGD gradient at Wailupe, Oahu. G. salicornia tolerated the extremely variable salinity, temperature, and nutrient levels associated with SGD. In marked contrast, half of G. coronopifolia plants suffered tissue loss and even death at SGD-rich locations in the field and in laboratory treatments simulating high SGD flux. Measurements of growth, photosynthesis, and branch development via two novel metrics indicated that the 27‰ simulated-SGD treatment provided optimal conditions for the apparently less tolerant G. coronopifolia in the laboratory. Benthic community analyses revealed that G. salicornia dominated the nearshore reef exposed to SGD compared with the offshore reef, which had a greater diversity of native algae. Ultimately, SGD inputs to coastal environments likely influence benthic community structure and zonation on otherwise oligotrophic reefs. View Full-Text
Keywords: Gracilaria; algae; groundwater; invasive; reef ecology; nutrients; SGD; photosynthesis; salinity; benthic Gracilaria; algae; groundwater; invasive; reef ecology; nutrients; SGD; photosynthesis; salinity; benthic
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Amato, D.W.; Smith, C.M.; Duarte, T.K. Submarine Groundwater Discharge Differentially Modifies Photosynthesis, Growth, and Morphology for Two Contrasting Species of Gracilaria (Rhodophyta). Hydrology 2018, 5, 65.

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