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Halophila decipiens

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Taxonomy [top]

Kingdom Phylum Class Order Family
PLANTAE TRACHEOPHYTA LILIOPSIDA HYDROCHARITALES HYDROCHARITACEAE

Scientific Name: Halophila decipiens
Species Authority: Ostenf.
Common Name(s):
English Paddle Grass, Species code: Hd
Taxonomic Notes: This species has often been confused with Halophila ovalis. Halophila decipiens is monoecious, has serrate leaf tips and hairs on both sides of its leaves.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2010
Date Assessed: 2007-10-23
Assessor(s): Short, F.T., Carruthers, T.J.R., Waycott, M., Kendrick, G.A., Fourqurean, J.W., Callabine, A., Kenworthy, W.J. & Dennison, W.C.
Reviewer(s): Livingstone, S., Harwell, H. & Carpenter, K.E.
Justification:
Halophila decipiens occurs mostly in the tropics and is circumglobal, widespread and locally abundant. It is found in deeper waters. Halophila decipiens has no major threats partly because it is found in deeper waters. Coastal development can locally affect seagrass beds in more shallow areas, as can reduced water quality. The global population trend for this species is expected to be stable as it is increasing in some regions, although some localized declines have been observed due to sedimentation (limitation of light). Halophila decipiens is listed as Least Concern. However, because of its deep water habitat more research is needed.

Geographic Range [top]

Range Description: Halophila decipiens occurs mostly in the tropics and is circumglobal.

In the Atlantic, this species occurs in the Gulf of Mexico, throughout the Caribbean Sea, Bermuda and eastern Brazil. It also occurs on the northwest coast of Africa and in the Canary Islands.

In the Pacific, H. decipiens is found from southern Japan and the coast of China throughout Southeast Asia and extending east across the Coral Sea to Fiji. It occurs from the Great Barrier Reef across northern Australia. It is also found in the Hawaiian Islands, Midway, and French Polynesia as well as in Mexico at the southern end of the Baja Peninsula (Santamaria-Gallegos et al. 2006).

In the Indian Ocean, H. decipiens is found from southwestern Australia through the Timor Sea, along the coast of Indonesia, Thailand and southern Myanmar (Novak et al. 2009). It is also present in India, on the southeast and mid-west coasts. It is present in the Chagos Archipelago, in the northern Red Sea, and in Yemen. Halophila decipiens also occurs also in the Seychelles and Kenya (McMahon and Waycott 2009) and Madagascar (F. Short pers. obs.).
Countries:
Native:
Australia; Barbados; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Brazil; China; Colombia; Costa Rica; Cuba; Curaçao; Dominican Republic; Egypt; French Polynesia; Grenada; Guadeloupe; India; Indonesia; Jamaica; Japan; Malaysia; Mauritius; Mexico; Myanmar; New Caledonia; Panama; Papua New Guinea; Philippines; Puerto Rico; Saint Martin (French part); Saint Vincent and the Grenadines; Seychelles; Sint Maarten (Dutch part); Spain; Sri Lanka; Thailand; Trinidad and Tobago; United States; United States Minor Outlying Islands; Vanuatu; Venezuela, Bolivarian Republic of; Virgin Islands, U.S.
FAO Marine Fishing Areas:
Native:
Atlantic – southwest; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Pacific – eastern central; Pacific – northwest; Pacific – western central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Halophila decipiens is widespread and locally abundant. It can have dense cover but low biomass. This species is often not collected or recorded, as the leaves can be obscured by sediments, and it is found in deeper water. Its global population trend is thought to be stable as it is increasing in some regions, although some localized declines have been observed in other regions due to localized threats.

The Midway Atoll (Hawaiian Islands) population forms dense patches with an average of 24,000 blades per square meter (McDermid et al. 2002).

The Costa Baja population displayed a total biomass of 5.2 ± 1.6 g dry weight (dw)/m² with a leaf-pair density of 2964 ± 778 during the winter months, a total biomass of 8.5 ± 2.2 g dw/m² and a leaf-pair density of 4016 ± 599 during the summer months (Santamaria-Gallegos et al. 2006).

In the west Florida shelf, this species covers an estimated 20,000 km² with an average coverage of 20%. During June of 1999, percent coverage was estimated at 45% in 10 m of water, 4% in 15 m, and 18% in 20 m. During the month of October, 1999, percent coverage was estimated at 74% in 10 m of water, 39% in 15 m, and 10% in 20 m. Biomass ranged from 0.02 to 2.64 g dry weight/m² . This species tends to follow typical sub-tropical seasonal cycles with lower biomass during the fall and winter months (Hammerstrom et al. 2006).

During 1972 to 1973, this species was reported to have a mean dry biomass  of 0.14 g/m² along the northwest Cuban shelf at depths of up to 24.3 m. It was reported to be the least abundant seagrass studied, and accounted for 0.1% of total angiosperm biomass in the 2,000 km² range along the Cuban northwestern shelf (Buesa 1975).

Iverson and Bittaker (1986) reported H. decipiens occurring in small monotypic stands and sometimes occurring among H. wrightii in the northern offshore areas along the Big Bend, Florida in water deeper than five m. Data collected in 2000 showed no occurrence of H. decipiens along the Big Bend, Florida (Hale et al. 2004).

Halophila decipiens is not abundant or common in Bermuda: out of 55 sites sampled 3.6% had this species present; of these, 50% of sites sampled had less than six shoots per m2 (Murdoch et al. 2007).
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: Halophila decipiens is typically found on coarse sediments, sand, and muddy bottoms. It is a deep water species but is also found in shallow water under docks and in turbid areas. Halophila decipiens can grow in areas with high sedimentation. Halophila decipiens is monoecious, with male and female flowers occurring on the same spathe. Female flowers produce approximately 30 seeds.

In the Caribbean it can be found to a depth of around 30 m, but in the Indo-Pacific may be found to 58 m (Lee Long et al. 1996). This species tends to be in monospecific seagrass beds (but in the Indo-Pacific it is found with Halophila spinulosa, and in the Caribbean occasionally with H. baillonii). It can be seasonal and has a large seed bank (Zieman 1982, Hemminga and Duarte 2000, Green and Short 2003, Larkum et al. 2006). It is a rapid re-colonizer when beds are disturbed by grazing or trawls.

Halophila decipiens can propagate through budding, but primarily relies on a buried seed bank for population re-establishment in seasonally fluctuating or high disturbance environments (Hammerstrom et al. 2006). It is a highly fecund, annual and opportunistic species (Kenworthy 1993) that may be favoured by disturbance (McMillan 1988), but unable to compete once the other species are established (Preen et al. 1995).

In Thailand, this species was previously thought only to occur in waters 9-36 m in depth but has been found in the intertidal areas where it is exposed during low tide down to the depths of five m. In Malaysian Peninsula, depth limit ranged from 6-24 m in clear water of the east coast, while only about 1.5-3.1 m in the turbid water of the west coast. In the Philippines, it grows primarily at depths of 11-23 m. In Cuba, it was found at a depth of 24.3 m with a biomass of 0.14 g/m². In Veracruz, Mexico it was found in the deeper parts down to 10 m. In the Caribbean, it was found in deep water up to 30 m. In South America, this species is associated with deeper reefs, algal and marl beds, and deeper soft-bottomed vegetative areas.

The first specimen of H. decipiens found in southwestern Australian was collected from the Hardy Inlet near the mouth of Blackwood River in late December 1991 (Kuo and Kirkman 1995). Halophila decipiens is frequently mixed with H. ovalis at a depth of 35 m, as well as in rock pools at the mid-tide level. Dense meadows of this species may cover the entire, gently sloping edge of the river channel. The mature plant produces flowers which fruit in the autumn. Seagrass meadows of this species disappear from the sites during winter (Kuo and Kirkman 1995).

Halophila decipiens is found 3-15 m deep along the Midway Atoll and forms dense patches with an average of 24,000 blades per m2. At the O'ahu Island depth ranges from 1-2 m and along Hawai'i Island, this species is found at depths of 40 m and forms monospecific patches adjacent to, yet not interacting with, Halophila hawaiiana at Midway and O'ahu. Halophila decipiens is the only seagrass to form pure stands in deep waters at the island of Hawai'i (McDermid et al. 2002).

The Costa Baja population was found mainly in subtidal waters with high leaf-pair density and a low biomass with seasonal biomass levels. Highest biomass and plant development were observed during the summer months (Santamaria-Gallegos et al. 2006).
Systems: Marine

Threats [top]

Major Threat(s): Halophila decipiens has few major threats partly because it is found in deeper waters. Coastal development can locally affect seagrass beds in more shallow areas, as can reduced water quality. Trawls can disturb beds in deeper areas, but these are usually recolonized rapidly.

This species has numerous natural grazers such as turtles, dugongs and fish, and if in high numbers these can reduce biomass considerably.

Conservation Actions [top]

Conservation Actions: No specific conservation measures are in place for H. decipiens, party due to its habitat in deeper waters. It is found in some protected areas (e.g., Belize, GBR) but it is often outside Marine Protected Areas (MPAs) because of its depth range. Currently, a seagrass management plan is being developed in Bermuda (Sarkis pers. comm. 2007).

Research on the biology of this species is recommended because of its deep water habitat.

Citation: Short, F.T., Carruthers, T.J.R., Waycott, M., Kendrick, G.A., Fourqurean, J.W., Callabine, A., Kenworthy, W.J. & Dennison, W.C. 2010. Halophila decipiens. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 18 December 2014.
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