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Halodule wrightii

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Taxonomy [top]

Kingdom Phylum Class Order Family
PLANTAE TRACHEOPHYTA LILIOPSIDA NAJADALES CYMODOCEACEAE

Scientific Name: Halodule wrightii
Species Authority: Asch.
Common Name(s):
English Shoalgrass, Species code: Hw
Taxonomic Notes: Halodule wrightii is a well established species. However, the taxonomy of the other species of Halodule in the Atlantic is less certain (Larkum et al. 2006) and there are questions about its taxonomy in the Indo-Pacific as well (Green and Short 2003).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2010
Date Assessed: 2007-03-21
Assessor(s): Short, F.T., Carruthers, T.J.R., van Tussenbroek, B. & Zieman, J.
Reviewer(s): Livingstone, S., Harwell, H. & Carpenter, K.E.
Justification:
Halodule wrightii has a disjunct global distribution. The main part of its range is in the Atlantic, although it is also found in the eastern tropical Pacific and the Indian Ocean. It is the dominant species in Brazil and West Africa. Halodule wrightii is a widespread species and is locally abundant. The overall population trend for this species is stable, and possibly increasing in some parts of its range. It is highly tolerant to a range of environmental conditions, however, it is affected locally by coastal development and destructive anthropogenic activities. This species is listed as Least Concern.

Geographic Range [top]

Range Description: Halodule wrightii has a disjunct global and predominantly tropical distribution. The main part of its range is in the Atlantic: the western tropical Atlantic from northern Florida (USA) to Venezuela including the Gulf of Mexico and the Caribbean Sea; also in Bermuda and North Carolina (USA). In the southern Atlantic, it is present on the coast of Brazil. In the eastern Atlantic, it occurs from southern Morocco on the coast of Africa and the Canary Islands, to the northern part of Angola.

Halodule wrightii is found in the eastern tropical Pacific from the Gulf of California to the Gulf of Panama. In the Indian Ocean it is found from the northern extent of the Bay of Bengal to along the Coromandel Coast as well as Oman. Also from southern Somalia to the north part of South Africa including the Mozambique Channel,  Mauritius and Madagascar.
Countries:
Native:
Angola (Angola); Antigua and Barbuda; Aruba; Bahamas; Barbados; Belize; Bermuda; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Brazil; Cayman Islands; Colombia; Costa Rica; Cuba; Curaçao; Dominica; Dominican Republic; Grenada; Guadeloupe; Guatemala; Guinea-Bissau; Haiti; Honduras; India; Jamaica; Kenya; Madagascar; Mauritania; Mexico; Montserrat; Mozambique; Netherlands Antilles (Bonaire); Nicaragua; Panama; Puerto Rico; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Sao Tomé and Principe; Sint Maarten (Dutch part); Tanzania, United Republic of; Trinidad and Tobago; Turks and Caicos Islands; United States; Venezuela, Bolivarian Republic of; Virgin Islands, British; Virgin Islands, U.S.
FAO Marine Fishing Areas:
Native:
Atlantic – eastern central; Atlantic – northwest; Atlantic – southeast; Atlantic – southwest; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Pacific – eastern central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Halodule wrightii is a widespread species which is locally abundant. It is the dominant species in Brazil and West Africa. In other areas it may be found in mixed beds with other seagrass species. Its presence on the western side of Central America appears to be a migration through the Panama Canal and therefore its range appears to be expanding and there is potential for future range extension if it is introduced into other areas.

According to the Global Seagrass Trajectories Database, (Carruthers pers. comm. 2007) there are 64 published studies that monitored this species over time and of these 40 had no change, 15 decreased in coverage, and nine increased in coverage (all aerial extent, density, biomass, or cover). The overall population trend for this species is increasing (2% increase). Data from 2000 shows a 28% occurrence when sampling 188 stations at Big Bend, Florida. This is a 23% increase from the data reported by Iverson and Bittaker (1986). Despite the increase in occurrence, maximum depth range decreased from 10.6-8.3 m (Hale et al. 2004). Research by Hall et al. (1999) show a significant widespread decrease in the Florida Bay with a bay wide short shoot density off about 267.5 shoots/m² in 1984 to about 22.5 shoots/m² in 1994. Decrease in abundance was most likely cause by increased light attenuation due to primary die-off off Thalassia testudinum. Reduction can also be linked to a decrease in phosphorus availability caused by reduction in freshwater input (Hall et al. 1999). Global average maximum biomass is estimated to be 253.5 g dw/m² above ground (from 19 observations) and 193.3 g dw/m² below ground (from 12 observations) (Duarte and Chiscano 1999).
Population Trend: Increasing

Habitat and Ecology [top]

Habitat and Ecology: Halodule wrightii is typically found on sandy to muddy bottoms and can be found in mixed seagrass species beds. It is highly tolerant to a range of environmental conditions including wide ranging salinity (hypersaline), high temperatures, turbidity, and eutrophication (Zieman 1982, UNESCO 1998, Hemminga and Duarte 2000, Green and Short 2003, Larkum et al. 2006). Optimum temperatures for H. wrightii range between 20-30°C (Phillips 1960).

This species is ephemeral with rapid turn-over and high seed set and forming effective seedbanks, well adapted to high levels of disturbance. It is a pioneer species in Mozambique in exposed sandy areas close to the coastline. It is the dominant species in Texas (USA). It is established along both the eastern and western margins of the lagoon in Tamaulipas (Mexico). In Veracruz (Mexico), it is found in the shallower areas where it tolerates changes in temperature and salinity. In the Caribbean, it is found growing on sand and mud from the intertidal zone to five m. It is the most widely distributed seagrass in Brazil. In South America, it is associated with shallow habitats without much freshwater input, such as reefs, algal beds, coastal lagoons, rocky shores, sand beaches, and unvegetated soft-bottom areas and nearby mangroves  (Green and Short 2003).

After a complete destruction of seabeds, a rapid recovery was observed with early recovery characterized by small patches suggesting recovery through fragments. Studies show that fragments stay viable for up to four weeks in the spring months and up to two weeks during the autumn months. High viability of fragments suggests a high dispersal distance (Hall et al. 2006).

This is usually an early colonizing species yet studies in Florida Bay shows that with increased nutrient levels, Halodule wrightii becomes the dominant species as it is able to out-compete Thalassia testudinum for light resources, suggesting that areas in  Florida Bay with high nutrient availability will be dominated by Halodule wrightii while areas with low nutrients will be dominated by T. testudinum (Fourqurean et al. 1995).

Halodule wrightii can rapidly and densely recolonize denuded areas in warm months. Most bed maintenance and new shoot production probably occurs through rhizome elongation (Phillips 1960).
Systems: Marine

Threats [top]

Major Threat(s): Halodule wrightii is a tolerant species to most disturbances. It replaces less tolerant species under conditions of habitat deterioration, eutrophication, and increased turbidity, and therefore general threats are not considerable except in localized situations. Localized threats include trawling activities, coastal development, habitat destruction and mechanical damage from anchoring and recreational and commercial boating.

Conservation Actions [top]

Conservation Actions: Halodule wrightii is protected in numerous marine protected areas throughout its range.

Citation: Short, F.T., Carruthers, T.J.R., van Tussenbroek, B. & Zieman, J. 2010. Halodule wrightii. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 September 2014.
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