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Halodule wrightii (Shoal Grass)

Halodule wrightii (Shoal Grass)

Halodule wrightii (Shoal Grass)

Halodule wrightii (Shoal Grass)

Halodule wrightii, or shoal grass is a widespread and locally abundant seagrass species. It has a worldwide distribution predominantly in the tropics. Its main range is in the western Atlantic, Gulf of Mexico and Caribbean Sea, from North Carolina south to Venezuela, and Bermuda, as well as the east coast of Brazil. It is also found in the eastern Atlantic from Morocco south to Angola, in the eastern tropical Pacific from the Gulf of California to the Gulf of Panama and throughout the Indian Ocean.6 This species is commonly misidentified as Halodule beaudettei, however, the distribution for Halodule beaudettei is currently only described in the Caribbean in the Yucatan Penisula of Mexico, Belize and Barbados.5 While there is current debate as to whether these two species are distinct from each other, they are currently distinguished from each other by examining their blades; Halodule wrightii has longer and thinner blades (5-18cm long and 0.3 to 0.8mm wide) with a bidentate tip, whereas Halodule beaudettei has shorter and wider blades (1.5-6cm long and 0.7-1.25mm wide) with a tridentate tip.3 However, immature leaves of Halodule wrightii can resemble a tridentate tip, so this method should only be used on mature leaves.3 Halodule wrightii is a dominant species in Florida, usually found growing with Turtle grass (Thalassia testudinum) and Manatee grass (Syringodium filiforme), although monospecific meadows occur. It is typically found in shallow waters down to 12 meters in depth and is able to withstand prolong period of exposure at low tides. While this species is ephemeral, it is fast growing and has a high turnover rate.4,6

Shoal grass is subject a variety of natural and anthropogenic threats causing decline in local populations. The main anthropogenic threats to shoal grass in Florida is the destruction of habitat from coastal development and motor vessel damage. In Florida Bay, populations have declined due to the natural die off of turtle grass and subsequent increase in light attenuation.1 While subject to these various threats, shoal grass is a pioneer species and is known to colonize banks that have been disturbed or are too shallow for other species of seagrass to grow creating dense meadows and environmentally important habitat for fishes and invertebrates. Research has also shown that shoal grass is efficient at carbon sequestration, using enzymes to convert CO2 to an inorganic carbon source which acts as a blue carbon sink. This process plays a major role in countering the effects of ocean acidification.2

Halodule wrightii (Shoal Grass) Facts

  • Halodule wrightii has a worldwide distribution, predominantly in the tropics.
  • This species is commonly misidentified as Halodule beaudettei, however, Halodule wrightii has longer and thinner blades with a bidentate tip, whereas H. beaudettei has shorter and wider blades with a tridentate tip.
  • Halodule wrightii is a dominant species in Florida usually found growing with Turtle grass (Thalassia testudinum) and Manatee grass (Syringodium filiforme).
  • Shoal grass is typically found in shallow waters down to 12 meters in depth and is able to withstand prolong periods of exposure at low tides.
  • In Florida Bay, populations have declined due to the natural die off of turtle grass and subsequent increase in light attenuation.
  • Shoal grass is a pioneer species known to colonize banks that have been disturbed or are too shallow for other species of seagrass to grow.
  • Shoal grass is efficient at carbon sequestration, using enzymes to convert CO2 to an inorganic carbon source which acts as a blue carbon sink. This process plays a major role in countering the effects of ocean acidification.
  • Leaf Morphology
    • 0.3 to 0.8mm wide and 5-18cm long.
    • Bidentate tip.

Seagrass Species in North America

… | Halodule wrightii (Shoal Grass) | … | …

Seagrass Species in other Continents

Africa | Asia | Australia | Europe | North America | South Amercia

References

1Hall, L.M., Hanisak, M.D., and Virnstein, R.W. (2006) Fragments of the seagrasses Halodule wrightii and Halophila johnsonii as potential recruits in Indian River Lagoon, Florida. Marine Ecological Progress Series, 310: 109-117.

2Kennedy H., Beggins J., Duarte C.M., Fourqurean, J.W., Holmer, M., Marbà, N., and Middleburg, J.J. (2010) Seagrass sediments as a global carbon sink: isotopic constraints. Global Biogeochemistry Cycles, 24: GS4026-GS4034.

3Phillips, R.C. (1967) On the species of the seagrass, Halodule, in Florida. Bulletin of Marine Science, 17(3): 672-676.

4Sargent, F.J., T.J. Leary, D.W. Crewz, and C.R. Kruer. (1995) Scarring of Florida’s seagrasses: assessment and management options. FMRI Tech. Rep. TR-1. Florida Marine Research Institute, St. Petersburg, Florida. 37 p. plus appendices.

5Short, F.T., Carruthers, T.J.R., van Tussenbroek, B. & Zieman, J. (2010) Halodule beaudettei. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1. . Downloaded September 2012.

6Short, F.T., Carruthers, T.J.R., van Tussenbroek, B. & Zieman, J. (2010) Halodule wrightii. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1.. Downloaded September 2012.

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