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Wigeongrass (Ruppia maritima L.):
A Literature Review


Decomposition

Decomposing wigeongrass beds are an important source of organic matter in some estuarine ecosystems (Tenore 1972). Taller stands in temperate climates begin decomposing at stem bases after about three months of exponential growth, which leads to wind "mowing" and the movement of large amounts of plant material to shore. Stunted plants in more inhospitable habitats die from dessication or salinity or are removed from bottom sediments by water turbulence or feeding waterfowl (Verhoeven 1979). Major shoreward movement of detached wigeongrass stems and leaves in late summer can coincide with peak populations of epiphytes and animal grazers (Conover 1958). Verhoeven (1978) estimated that about 44% of the fall decrease in biomass of Ruppia cirrhosa was attributable to leaching and decomposition and the remainder to grazing by birds and invertebrates. Litter bag experiments show that grazing by macroinvertebrates (Gammarus sp. and Sphaeroma sp.) reduces leaves and shoots of Ruppia cirrhosa to particles of < 1 mm in 180 days (Menendez et al. 1989).

In North Carolina impoundments, wigeongrass begins to turn yellow and deteriorate during the hot summer months, but plants recover by fall (Heitzman 1978). Such fall growth does not rapidly decompose, and October-flowering plants can still be used by waterfowl in January.

Indoor cultures of R. maritima were kept in darkness at 20 degrees C in aerated estuarine water and lost 50% mass in 35 days; after 93 days, they showed slightly elevated C and N concentrations and slightly lower amounts of P (Twilley et al. 1986).

Senescence and detachment of stems from the belowground parts of wigeongrass can coincide with an increase in H2S bacteria on the plants and in the substrate (Richardson 1980). Sediment sulfate reduction activity may be an important factor regulating the decrease in wigeongrass and increase in the seagrass Halodule wrightii in subtropical lagoons during hot summer months (Pulich 1989).

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