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Thalassia testudinum

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Taxonomy [top]

Kingdom Phylum Class Order Family
PLANTAE TRACHEOPHYTA LILIOPSIDA HYDROCHARITALES HYDROCHARITACEAE

Scientific Name: Thalassia testudinum
Species Authority: Banks & Sol. ex K.D.Koenig
Common Name(s):
English Species code: Tt, Turtlegrass

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2010
Date Assessed: 2007-03-20
Assessor(s): Short, F.T., Carruthers, T.J.R., van Tussenbroek, B. & Zieman, J.
Reviewer(s): Livingstone, S., Harwell, H. & Carpenter, K.E.
Justification:
Thalassia testudinum forms extensive dense seagrass beds and is thought to be the most important habitat-forming seagrass species in the Caribbean. This is an abundant species that is relatively robust to disturbance, and the overall population trend is stable. Localized threats to T. testudinum include coastal development, eutrophication and sedimentation, which have contributed to some local declines. This species is listed as Least Concern.

Increased coastal development has the potential to cause more widespread declines. Since this species is a major habitat-forming species that cannot be replaced functionally by another species, its available habitat should be closely monitored.

Geographic Range [top]

Range Description: Thalassia testudinum occurs in the western central Atlantic from Florida, USA to Venezuela, throughout the Gulf of Mexico and the Caribbean Sea. It is also found in Bermuda.
Countries:
Native:
Anguilla; Antigua and Barbuda; Aruba; Bahamas; Barbados; Belize; Bermuda; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Cayman Islands; Colombia; Costa Rica; Cuba; Curaçao; Dominica; Dominican Republic; French Southern Territories; Grenada; Guadeloupe; Guatemala; Haiti; Honduras; Jamaica; Martinique; Mexico; Montserrat; Netherlands Antilles (Bonaire); Nicaragua; Panama; Puerto Rico; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Sint Maarten (Dutch part); 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 – western central; Pacific – eastern central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Thalassia testudinum forms extensive dense seagrass beds throughout its range. This is the most important seagrass habitat-forming species in the Caribbean. There have been some declines in seagrass beds in developing areas, particularly in areas of nutrient enrichment and sedimentation. Generally, however, this species still very abundant throughout its range.

Out of 103 published studies on this species, 29 showed an increase in abundance (mix of biomass, aerial extent, or density), 17 decreased and 57 showed no change (Global Seagrass Trajectories Database, Carruthers pers. comm. 2007). The overall population trend is stable.

Caribbean regional biomass ranges from 3.2 g dw/m² (recorded at the latitude 17.8o in the Virgin Islands) to 820 g dw/m² (recorded along the 28.3o latitude on the Florida coast). These findings are summarized in Gacia (1999) and include data from publications ranging from 1959 until 1996.

The T. testudinum population in the Florida Bay covered 90% of mud bank and basins until a massive die off in 1987. Four thousand hectares were completely lost and 24,000 ha were affected due to primary die off caused by higher water temperatures, hypersalinity and increased biomass, leading to high respiration demands. This was followed by secondary die-off from increased turbidity due to increased phytoplankton beginning the fall of 1991. Between 1984 and 1994, mean short shoot density dropped by 22% throughout the Florida Bay and standing crop biomass dropped by 28%. While light attenuation may have been a factor, the patchy distribution of die-off suggests that primary die-off was the principle reason for the decrease in abundance (Hall et al. 1999). Between the spring of 1995 and spring of 1999, despite individual basins in the Florida Bay exhibiting changes in abundance by between 12-100%, the total abundance throughout the Bay exhibited little change due to declines in abundance in the western part of the Bay being offset by increases in abundance in the central and eastern basins (Durako and Hall 2000). Increases in seagrass coverage along with large occurrences of flowering plants were observed during the spring of 2000; however, primary die-off among high density stands was also observed north of Barneys Key with similar symptoms noted to the 1987 die-off (Nuttle et al.  2003).
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: Thalassia testudinum is the most abundant seagrass in the Caribbean and forms dense rhizome mats below the sediment, creating extensive meadows on shallow sand or mud substrates from the lower intertidal to a maximum 10-12 m depth.  It has also been reported below 20 m. In Cuba, this species was found to a depth of 14 m and accounted for 97.5% of total angiosperm biomass (190 g/m²). Optimum temperatures for this species range between 20-30°C (Phillips 1960).

Thalassia testudinum typically dominates seagrass vegetation in reef lagoons, where it often coexists with Syringodium filiforme, Halodule wrightii and calcareous rhizophytic green algae belonging to the order Caulerpales, amongst which Halimeda spp. are the most conspicuous members. This species plays an important role in production of sediments (Zieman 1982, UNESCO 1998, Hemminga and Duarte 2000, Green and Short 2003, Larkum et al. 2006). It is typically found in low density in oligotrophic areas and replaced by other species when there are continuous high nutrient inputs (Fourqurean and Rutten 2004).

Thalassia testudium is an important food for green sea turtles and manatees, as well as for a number of other fish and invertebrate species.

The dense beds in the Florida Bay are susceptible to primary die-off, which usually occurs during late summer to early winter. Primary die-off is usually followed by reduced water clarity and increase epiphytic growth, which can lead to secondary die-off among neighbouring local seagrass (Nuttle et al. 2003).

Seeds are viviparous and do not form seed banks. After major eradication, recolonization is dependent on import from seeds from other areas or from vegetative fragments (van Tuessenbroek et al. 2006). Seedling success can be variable, and the generation length of this species has been estimated as eight years (for recruitment).
Systems: Marine

Threats [top]

Major Threat(s): The biggest threats to Thalassia testudinum are coastal development, eutrophication, and sedimentation (T. Carruthers, F. Short, B. van Tussenbroek, J. Zieman pers. comm. 2007). Boat traffic, marina development, and sewage pollution from greatly expanded residential and hotel development is a particular problem in Florida. Trawling is also a threat in some parts of the range.

Conservation Actions [top]

Conservation Actions: The range of Thalassia testudinum falls in some Marine Protected Areas (MPAs). In the Caribbean, T. testudinum is included in the 24 fully managed marine protected areas. This species is monitored by the CARICOMP network (Caribbean Coastal Marine Productivity network), including coral reefs and mangroves (Green and Short 2003). Currently, a seagrass management plan is being developed in Bermuda (Sarkis pers. comm. 2007). This species is also listed as Vulnerable (A2a) under the Bermuda Protected Species Act (Sarkis pers. comm. 2007).

This is a major habitat-forming species in the Greater Caribbean and should be monitored (Van Tussenbroek et al. 2006).

Citation: Short, F.T., Carruthers, T.J.R., van Tussenbroek, B. & Zieman, J. 2010. Thalassia testudinum. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 22 October 2014.
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