An annual form of eelgrass in Nova Scotia

Pilot experiments in the tidally dominated Dutch Wadden Sea indicated a negative relationship between Zostera marina L. transplantation success and tidal depths. As light availability was sufficient, we hypothesised that water dynamics (particularly waves) and ensuing sediment mobility (movement or resuspension of the sediment) were the major cause for the loss of transplants at larger depths. Transplantation experiments were carried out at intertidal flats and depths under conditions of normal and reduced water dynamics and sediment mobility, using exclosures that reduced water dynamics and shells that stabilised the sediment. To test bioturbation effects, cages that excluded large biota were used. Without protection, Z. marina plants were successfully established in a belt within the intertidal zone (0 to -0.20 m mean sea level, MSL) at 2 out of 3 transplantation sites during the first growing season. Reduced water dynamics by exclosures prevented the loss of plants in the zone -0.40 to -1.15 m MSL; removal of the exclosures after 1 mo resulted in loss of all plants within a few days. Neither light limitation nor bioturbation could explain these results. We conclude that prevalent water dynamics, particularly the relative period of exposure to wave dynamics, were too high for establishment and maintenance of intertidal Z. marina at depths below -0.20 m MSL at these sites of intermediate exposure. At the third, exposed, transplantation site, water dynamics prevented transplantation success along the entire depth gradient studied. Reduction of sediment mobility by shells had a positive effect on transplant survival, particularly at -0.20 m MSL. Shell armour can therefore be recommended in transplantations near the lower limit of potential intertidal habitats of Z. marina. Anchorage of the plants with pegs had no positive effect. Depth limitation of intertidal Z. marina populations by water dynamics can explain zonation patterns that occur in several tidal systems in northwest Europe.

Section: Water Dynamics and Zonation In Naturalmentioning

confidence: 69%

Section: Water Dynamics and Zonation In Naturalmentioning

confidence: 99%

Effects of water dynamics on Zostera marina: transplantation experiments in the intertidal Dutch Wadden Sea

Katwijk¹,

Hermus²

2000

“…scored) seed coats, concluded that both physiological and physical dormancy exist in this species. Published data (Addy 1947, Phillips 1972, Keddy & Patriquin 1978, Churchill 1983, Moore et al 1993) from this species' latitudinal range along the North American coast from North Carolina to Canada shows a progressively later period of seed release with increasing latitude (Fig. 1).…”

Section: Dormancymentioning

confidence: 92%

“…While dormancy is not a life history strategy for several seagrass genera (notably Posidonia, Thalassia, and Amphibolis), dormancy has been demonstrated in others and ranges from a few weeks (Phyllospadix torreyi, Reed et al 1998) 'North Carolina, Phillips (1972); 'Virginia, Moore et al (1993); 3~e w Jersey, Phillips (1972); 4New York, Phillips (1972); 'Rhode Island, Churchill (1983); 6Massachusetts Addy (1947, Phillips (1972; 'Maine, Phillips (1972); 'Nova Scotia, Phillips (1972); 'New Brunswick, Keddy & Patriquin (1978) not been addressed in these studies is whether the environment or some physiological characteristic of the seed is responsible for preventing germination (i. Harrison (1991) used seeds collected from parent plants and from the seed bank (1 mo after seed release) to examine dormancy in Zostera marina. His experiments, conducted under various temperature and salinity conditions with scarified (i.e.…”

Section: Dormancymentioning

confidence: 97%

A review of issues in seagrass seed dormancy and germination:implications for conservation and restoration

Orth¹,

Harwell²,

Bailey³

et al. 2000

183

116

Seagrasses have received considerable attention over the past 2 decades because of the multiple ecological roles they play in estuarine and coastal ecosystems and concerns over worldwide losses of seagrass habitat due to direct and indirect human impacts. Restoration and conservation efforts are underway in some areas of the world, but progress may be limited by the paucity of information on the role of seeds in bed dynamics. Although flowering occurs in most of the 58 seagrass species, seed germination data exist for only 19 of the 42 species that have some period of dormancy, with only 93 published references to field and/or laboratory studies. This review addresses critical issues in conservation and restoration of seagrasses involving seed dormancy (e.g. environmental vs physiological), existence and type of seed bank (transient or persistent), and factors influencing seed germination (e.g. salinity, temperature, light). Results of many earlier published studies relating seed germination to various environmental factors may need re-examination given more recent published data which show a confounding influence of oxygen level on the germination process. We highlight the importance of conducting ecologically meaningful germination studies, including germination experiments conducted in sediments. We also identify questions for future research that may figure prominently in landscape level questions regarding protected marine or estuarine reserves, habitat fragmentation, and restoration.

“…However, several studies have documented the importance of seeds and seedlings in establishing patches in bare areas within and outside of existing beds (Orth & Moore 1983, Harrison 1987, Olesen & Sand-Jensen 1994a,b, Olesen 1999. In addition, in several areas of the world, annual eelgrass populations are maintained entirely by the production of seeds and seedlings (Keddy & Patriquin 1978, Harlin et al 1982, McMillan 1983, Harrison 1991. The production of seeds within an eelgrass meadow is considerable and may reach 70 000 m -2 (van Lent & Vershuure 1994, Fishman & Orth 1996, van Katwijk et al 1998.…”

Section: Introductionmentioning

confidence: 99%

Responses of eelgrass Zostera marina seedlings to reduced light

Bintz¹,

Nixon²

2001

We subjected seedlings of Zostera marina L. to High (72%), Medium (23%), and Low (10%) daily irradiance (mean daily PAR of 24.4, 7.9, and 3.3 E m -2 d -1 respectively) over 12 wk. We measured plant response in terms of survivorship, lateral shoot production, morphology, growth rate, photosynthesis and respiration, and leaf pigment concentration. Decreasing the light available to eelgrass seedlings from 72 to 23% resulted in a reduction of lateral shoot formation, lower plant biomass, and longer and wider leaves. Shoot area, growth rate, and pigment concentrations remained similar. A reduction of incident light to 10% decreased survival to 74% and had a negative effect on shoot growth, size, and above-and belowground biomass. Pigment concentrations increased with respect to seedlings raised at medium light. In general, the responses of seedlings to reduced light are similar to those reported for mature Z. marina. Rapid expansion of seedling patches can only occur at irradiance levels greater than 7.9 E m -2 d -1 . Morphological changes resulting from exposure to mean daily PAR levels of less than 8 E m -2 d -1 such as thinner leaves and low belowground biomass, have serious implications for decreased seedling survival in the field.