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Exploring the beautiful nature of California


California Nature:  Seagrass


There are four prerequisites for a seagrass:
(1) It must be adapted to saline water
(2) it must be able to grow completely submersed
(3) it must be securely anchored with perennial rhizomes or "holdfasts" to withstand wave action and tidal currents
(4) it must be water pollinated.

At least ten aquatic species in the Pacific states satisfy the above criteria, although only five are native to rocky shores and sandy or muddy bays: Phyllospadix torreyi, P. scouleri, Zostera marina, Z. pacifica, and Z. nana.

Four additional species, including Ruppia maritima, Zannichellia palustris, Potamogeton pectinatus, and Najas marina live submersed in brackish water of salt marshes, ditches and estuaries.
seagrass meadows off the coast of California help fish live and grow These latter species have cosmopolitan distributions and can survive very sudden and large fluctuations in salinity. In spite of their enormous salt tolerance they seldom penetrate the purely marine habitat. A tenth species that certainly ranks as a true marine seagrass, Halodule wrightii, was naturalized in the Salton Sea and may occur in the Gulf of California.

Salt-loving plants (halophytes), such as the seagrasses and mangroves, generally have a lower concentration of water molecules (lower water potential) in their root cells so they can take in water. They maintain lower water potentials in their roots by having higher internal salt concentrations than seawater and by losing water at the leaf surface. Since high internal salt concentrations can be lethal to plant cells, some halophytes can excrete excess salt through their leaves and stems.

Compared to terrestrial flowering plants the seagrasses are not well-known to most naturalists, and yet they play a major role in marine ecosystems. They are an intriguing and marvelously adapted group of seed plants. What they lack in showy blossoms and fragrant scents they more than make up for by their picturesque habitats, exposed only at low tides when sunlight reveals their emerald green masses.
Seagrasses were created from  land flowering plants adapting to the sea  about 100 million years ago, which indicates a relatively early appearance of seagrasses in the overall evolution of flowering plants. Seagrasses are assigned to two families, Potamogetonaceae and Hydrocharitaceae,  Most seagrass meadows are monospecific, but may develop multispecies, with up to 12 species, meadows in subtropical and tropical waters.

Seagrasses occur in all coastal areas of the world, except along Antarctic shores. Seagrass meadows enhance the biodiversity of coastal waters. They harbor more animals and more species than nearby unvegetated areas. The fish fauna of seagrass meadows can be of considerable diversity, typically reaching more than 100 species in any one region, often dominated by juvenile specimens, as seagrass meadows often play a nursery role.

sea grasses live grow and breed in saline water The largest animals that are associated with the seagrass habitat are the green turtle, and the West Indian manatee. These animals are the largest marine herbivores, and forage over seagrass meadows.

The fish fauna of seagrass meadows can be of considerable diversity, typically reaching more than 100 species in any one region, often dominated by juvenile specimens, as seagrass meadows often play a nursery role.

The largest animals that are associated with the seagrass habitat are the green turtle, and the West Indian manatee. These animals are the largest marine herbivores, and forage over seagrass meadows.

Seagrass meadows have other important ecological functions. They improve water quality by reducing the particle loads in the water and absorbing dissolved nutrients. Seagrass stabilize sediments, diminishing sediment re-suspension while promoting sedimentation.

Seagrass meadows dissipate wave energy and protect coastlines. In addition, a significant fraction of seagrass production accumulated in the beach, as beach-cast detritus, where they deliver carbonate materials that nourish the beach and contribute to dune formation.

Seagrass meadows are believed to be experiencing a world-wide decline, with global loss rates estimated at 2-5% year, compared to 0.5% year for tropical forests. The causes for seagrass loss are multiple and include disease, extreme events, such as hurricanes and typhoons, burial by shifting sand, excess nutrient inputs to coastal waters and a reduction of water and sediment quality. Climatic extremes, such as heat waves and associated hypoxic events; and displacement by invasive species have also played a key role in the decline of seagrass meadows.
Marine Algae      Seagrass      Coral
 
 
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