Syringodium filiforme

Syringodium filiforme

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Overview

Brief Summary

Manatee Grass (Syringodium filiforme) is a prominent component of seagrass beds in shallow warm waters from Florida and the Gulf Coast of the United States south through the West Indies to northern South America (Haynes 2000). It typically grows at depths ranging from around one to three meters (Duarte et al. 2007). It  is found in the sublittoral zone (the region between the low tide mark and the edge of the continental shelf) of marine waters with sandy or muddy bottoms (Haynes 2000).

Manatee Grass is dioecious (i.e., there are separate male and female plants) and pollination occurs underwater. Pollen is expelled in strands and forms clumps over several hours. Submarine pollination occurs when the pollen clumps collide with the stigmas (female parts) of the female plants. However, Syringodium pollen released on the water surface floats and coalesces, forming snowflake-like rafts, suggesting the possibility that surface pollination may occur as well during very low tides in populations growing in shallow water. (Cox et al. 1990)

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Conservation and Management

Trends

Murdoch et al. (2007) documented the decline of many large seagrass meadows in Bermuda and discussed the results of several unpublished studies that provide information regarding the environmental, biological and anthropogenic causes and characteristics of these habitat changes. Of a total of about 900 hectares of lagoon and offshore meadows documented in 1997,  by 2004 about 475 hectares were either reduced to sandy areas with dead and decaying rhizomes or had only very sparsely distributed shoots of Turtle Grass (Thalassia testudinum), Manatee Grass (Syringodium filiforme) or Shoal Grass (Halodule wrightii). Among the likely factors contributing to these widespread declines are anthropogenic (i.e., human-caused) nutrient input, chemical pollution, physical damage by moorings, dredging, boat propellers, and increased sedimentation (Murdoch et al. 2007 and references therein). According to Murdoch et al., however,  the lagoonal and offshore meadows in Bermuda (in contrast to inshore and nearshore meadows) have not been exposed to obvious anthropogenic disturbance. Thus, the causes of the recent decline and factors preventing re-establishment of the lagoonal and offshore meadows remain unclear, although the large scale of the decline suggests that factors operating over large spatial scales, such as region-wide climate, water quality, and environmental management practices probably played an important role in the decline.

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Ecology

Habitat

Manatee Grass typically grows at depths ranging from around one to three meters (Duarte et al. 2007). It  is found in the sublittoral zone (the region between the low tide mark and the edge of the continental shelf) of marine waters with sandy or muddy bottoms (Haynes 2000).

Lirman and Cropper (2003) investigated the sensitivity of several seagrass species (Turtle Grass, Shoal Grass and Manatee Grass) to varying salinity and its apparent impact on distribution and abundance. Manatee Grass was the most susceptible of the three species; maximum growth rates for this species were observed at 25 parts per thousand and dropped dramatically at higher and lower salinity.

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Ecology

In an experimental study in the Virgin Islands, Manatee Grass was found to be an early colonizer of exposed seabed, following pioneering rhizophyic algae. Manatee Grass later declined over time as a result of competition with Turtle Grass, which propagated and established more slowly, but outcompeted Manatee Grass for nutrients as well as light. Although the frequency and magnitude of disturbance seemed insufficient to prevent complete replacement by Turtle Grass, coexistence of Manatee Grass, Turtle Grass, and other seagrasses and rhizophytic algae was often observed and is apparently facilitated by partitioning of sediments (and the nutrients they contain), with Turtle Grass utilizing sediments deeper than those used by Manatee Grass. (Williams 1990 and references therein) DiCarlo and Kenworthy (2008) found a less clear cut pattern of species succession. Although they did observe rapid colonization by Manatee Grass and/or Shoal Grass (Halodule wrightii) in recovering beds in the Florida Keys (at two sites shifting from previous dominance by Turtle Grass and at 5 other sites ending up with mixed Turtle Grass and Manatee Grass), at their 3 Puerto Rico sites they did not see a succession of species, instead seeing Turtle Grass replaced by Turtle Grass after recovery.

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Distribution

Manatee Grass is found in Florida, Louisiana, Mississippi, and Texas; eastern Mexico; the West Indies; Bermuda; Central America (Belize, Nicaragua, Costa Rica, Panama); and northern South America (Colombia, Venezuela) (Haynes 2000).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Reproduction

Manatee Grass flowering and fruiting occurs from February to June (Haynes 2000).

Cox et al. (1990) studied pollination in Manatee Grass in the Virgin Islands. Manatee Grass is dioecious (i.e., there are separate male and female plants) and pollination occurs underwater. Pollen is expelled in strands and forms clumps over several hours. Submarine pollination occurs when the pollen clumps collide with the stigmas (female parts) of the female plants. However, Syringodium pollen released on the water surface floats and coalesces, forming snowflake-like rafts, suggesting the possibility that surface pollination may occur as well during very low tides in populations growing in shallow water. Cox et al. found that fruit set was higher where staminate (i.e., pollen-producing) inflorescences were present nearby and lower in plots lacking staminate inflorescences. (Cox et al. 1980)

The floral morphology and development of Manatee Grass are described by Tomlinson and Posluszny (1978).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Evolution and Systematics

Systematics and Taxonomy

Syringodium filiforme was at one time known as Cymodocea filiformis (Haynes 2000).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

References

Cox, P. A., Elmqvist T., & Tomlinson P. B. (1990).  Submarine Pollination and Reproductive Morphology in Syringodium filiforme (Cymodoceaceae). Biotropica. 22, 259-265.
DiCarlo, G., & Kenworthy W. J. (2008).  Evaluation of aboveground and belowground biomass recovery in physically disturbed seagrass beds. Oecologia. 158, 285-298.
Duarte, C. M., Marba N., Krause-Jensen D., & Sanchez-Camacho M. (2007).  Testing the Predictive Power of Seagrass Depth Limit Models. Estuaries and Coasts. 30, 652-656.
Haynes, R. R. (2000).  Cymodoceaceae: Manatee-grass Family. (of Committee F., Ed.).22, 86-89. New York: Oxford University Press.
Murdoch, T. J. T., Glasspool A. F., Outerbridge M., Ward J., Manuel S., Gray J., et al. (2007).  Large-scale decline in offshore seagrass meadows in Bermuda. Marine Ecology Progress Series. 339, 123-130.
Tomlinson, P. B., & Posluszny U. (1978).  Aspects of Floral Morphology and Development in the Seagrass Syringodium filiforme (Cymodoceaceae). Botanical Gazette. 139, 333-345.
Williams, S. L. (1990).  Experimental Studies of Caribbean Seagrass Bed Development. Ecological Monographs. 60, 449-469.