Reproduction and recruitment of the seagrass Halophila stipulacea
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770; e-ISSN 1879-1522, more
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| Keywords |
Ecosystem disturbance
Germination
Population functions > Recruitment
Reproduction
Seagrass
Seedlings
Stress (biological)
Halophila stipulacea (Forsskål) Ascherson, 1867 [WoRMS]
ISW, Red Sea [Marine Regions]
Marine/Coastal |
| Author keywords |
UVR; PAR; stress; disturbance; seedling and germination |
| Abstract |
The small seagrass species, Halophila stipulacea is abundant in the subtidal zone of the Bay of Eilat, Red Sea, southern Israel. Early life history characteristics of this species were investigated in summer 2002 by means of field surveys and outdoor experiments. Monospecific stands were found at depths of between 2 and 20 m. Reproduction began in late May and ripe pericarps were found for 1 month starting from the beginning of August. The ratios of female versus male plants were 0.9 at depths of between 2.5 and 10 m and 0.5 at depths of between 12.5 and 15 m. The proportion of reproductive branches was significantly larger in the shallow (2-5 m) than in the deep (7-15 m) populations, i.e., 20 ± 11% versus 6 ± 10%, respectively. Ripe seeds were predominantly produced at depths of between 2 and 5 m. Experimental studies demonstrated that full sunlight completely inhibited seedling growth at a depth of 30 cm; no macroscopic seedlings could be observed after 40-day exposure to full sunlight. If exposed to 90% photosynthetic active radiation (PAR) but protected from ultraviolet radiation (UVR), the number of macroscopic seedlings increased to 7.4 ± 2.3% of the planted seeds. If protected from both UVR and 80% of the PAR, the number of macroscopic seedlings increased to 22.5 ± 4.0% of the planted seeds. UVR exclusion and 80% PAR reduction also significantly increased the rhizome growth rates of seedlings in the first month after germination (0.14 ± 0.04 mm day-1) compared with only UVR exclusion (0.04 ± 0.02 mm day-1). The absence of H. stipulacea from the uppermost part of the subtidal zone (depths of 0-2 m) may be due to light inhibition of germling growth and uprooting by occasional storms. |
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