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4 - Biodiversity, ecosystem services, and the conservation of seagrass meadows
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- By Richard K. F. Unsworth, Swansea University, Leanne C. Cullen-Unsworth, Cardiff University
- Edited by Brooke Maslo, Rutgers University, New Jersey, Julie L. Lockwood, Rutgers University, New Jersey
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- Book:
- Coastal Conservation
- Published online:
- 05 June 2014
- Print publication:
- 27 March 2014, pp 95-130
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- Chapter
- Export citation
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Summary
Introduction
Seagrass meadows are soft sediment intertidal to subtidal benthic habitats that are comprised of a group of plants adapted to life in the sea (den Hartog, 1970; Hemminga & Duarte, 2000). Seagrasses comprise one of the world’s most widespread habitats in shallow coastal waters; they are found on all of the world’s continents except Antarctica. Seagrass habitat can be patchy, but is more commonly comprised of continuous vegetation, which can be thousands of square kilometers in size. It is these large swaths that are referred to as seagrass beds or meadows (terms that are interchangeable). Seagrass meadows occur in sheltered intertidal and shallow subtidal areas on sand or mud substratum (and occasionally in among boulders). Current documented distributions include 125 000 km2 of seagrass meadows; however, recent estimates suggest that these meadows could cover up to 600 000 km2 of the coastal ocean (Duarte et al., 2010).
Seagrasses are marine angiosperms belonging to the order Helobiae and comprising two families – Potamogetonaceae and Hydrocharitaceae (den Hartog, 1970). Seagrass plants are rhizomatous (they have stems extending horizontally below the sediment surface) and modular, composed of repeating units (ramets) that exhibit clonal growth (Hemminga & Duarte, 2000). In contrast to other submerged marine plants (e.g. seaweeds or algae), seagrasses flower, develop fruit, and produce seeds (Ackerman, 2006). They have true roots and internal gaseous and nutrient transport systems (Kuo & den Hartog, 2006). The functional definition for seagrass plants encompasses only 72 species. Three seagrass species are considered endangered and 10 are at elevated risk of extinction; however, the gross majority of species are considered common (Short et al., 2011). It is the common abundance of these species, rather than their rarity, that makes them important. Seagrasses provide habitat, meaning they have a major functional role in supporting various stages in the life cycles of other organisms. For this reason, and with their extensive root–rhizome system and well-developed canopy, seagrasses, like reef-building organisms, are termed foundation species (Hughes et al., 2009).
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