Recruitment of Thalassia testudinum seedlings into physically disturbed seagrass beds (original) (raw)
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Marine Ecology Progress Series, 1994
Population dynamics, including demographic characteristics, of short-shoots of Thalassia testudinum were evaluated within 3 Florida Bay (USA) basins experiencing differing seventies of seagrass die-off. Annual mean plastochrone intervals (PI) ranged from 14.1 to 20.6 d, and they increased from the basin experiencing the most prolonged and extensive die-off to the basin least affected by dieoff. Pls calculated by leaf punching were always shorter than those estimated by cohort analyses. In all 3 basins, overall population age structure changed significantly between April 1989 and April 1990; population half-life, mean shoot age, the age of the oldest shoot, and shoot density declined, whereas rhizome apical density increased. An examination of the population dynamics of the 3 T. testudinum populations revealed that both recruitment and mortality of short-shoots increased between April 1989 and April 1990, but the increase in mortality was proportionately greater. These changes indicated that the T. testudinum populations in Florida Bay were continuing to decline and that the declines corresponded to the increased extent and severity of short-shoot die-off.
A Land-Based Thalassia testudinum Nursery Near Tampa Bay, Florida
Gulf of Mexico Science, 2009
An experimental, land-based seagrass nursery, built near Tampa Bay, FL, produced cultivars of Thalassia testudinum Banks and Solander ex König (turtle grass). The nursery was a rectangular basin measuring 6.1 3 12.2 m that graded from 1.5 to 2.0 m in depth constructed inside a fiberglass-covered pole building. The basin had a vinyl liner covered with 10-20 cm of sand and 1.0-1.3 m of water. The nursery ran for 26 mo and focused on producing cultivars of T. testudinum using differing planting techniques. Survival rates were 84% after 3-12 mo in the first planting and 91% after 4 mo in the second planting because early harvesting was required as a result of leaks in the vinyl liner. The planting method that resulted in the highest survival rate was bare rhizomes with two or more short shoots. The cultivars from the two nursery experiments were used in two mitigation projects in Tampa Bay. The nonrecurring cost of the nursery was 12,081.45overa3−yrperiod,andrecurringcostsareestimatedat12,081.45 over a 3-yr period, and recurring costs are estimated at 12,081.45overa3−yrperiod,andrecurringcostsareestimatedat22,280.00, with a potential production of 2,500 turf-like 20-cm 2 units of T. testudinum that could be sold at $20.00 per planting unit.
Large-scale patterns in seagrass (Thalassia testudinum) demographics in south Florida
2001
An examination of the population age structure of 118 spatially separated subpopulations of Thalassia testudinum over the extent of the Florida Keys National Marine Sanctuary (FKNMS) during a 2-yr period revealed significant spatial variation in short shoot (SS) demographic characteristics and population dynamics. Shoot age was determined for 12,031 SS. The number of leaf scars on individual shoots was converted to shoot age by use of observed seasonally and spatially variable leaf emergence rates. The yearly mean leaf emergence rate was 0.0295 Ϯ 0.0128 leaves SS Ϫ1 d Ϫ1 (Ϯ1 SD), and the median age of counted shoots was ϳ5 yr. A significant relationship between asexual reproductive effort and gross recruitment of SS into the populations (r 2 ϭ 0.15, P ϭ 0.001) and between mortality of SS and gross recruitment (r 2 ϭ 0.72, P Ͻ 0.001) existed. Thus, the greatest risk of mortality occurred in areas where gross recruitment was highest. The net population growth for T. testudinum within the boundaries of FKNMS was stable (mean ϭ Ϫ0.006 Ϯ 0.089 yr Ϫ1). However, areas within FKNMS fluctuated between positive and negative net growth rates (Ϫ0.20-0.50 yr Ϫ1). The power of such large-scale observations is the ability to identify areas of management concern and to frame questions that address the controlling mechanisms that influence these regions of fluctuating population growth.
Regrowth of the seagrass Thalassia testudinum into propeller scars
Aquatic Botany, 1997
Regrowth of turtle grass, Thalassia testudinum Banks ex Konig, into existing propeller scars and artificial cuts was studied in a mangal estuary located in Tampa Bay, Florida. Sediments from scars and cuts and adjacent grass beds were not significantly different in relation to particle size distribution and levels of calcium carbonate. Significantly lower concentrations of total organic matter and extractable ammonium but not phosphate were detected in scars. Increases in ammonium levels coincided with the expansion of T. testudinum into a propeller scar. Seagrass blade morphology and productivity did not significantly differ in short shoots growing along the edges of scars or cuts relative to those in adjacent seagrass beds. Rhizome architectural studies revealed that apical meristems were few in number (19 to 38% of rhizomes) and randomly orientated in undisturbed grass beds (31 to 53% oriented toward center). In contrast, a greater percentage of apical meristems (78 to 88%) along the edges and in scars or cuts were directed towards the center. Full regrowth required an average of 3.5 to 4.1 years in existing propeller scars and could take up to 7.6 years in artificial cuts. The lack of changes in shoot productivity and limited production of rhizome meristems in T. testudinum result in slow regrowth in propeller cuts. The management implication is that turtle grass meadows will show long-term damage from propeller scars if not protected.
Journal of Coastal Research
Seagrasses are important for coastal ecosystem health and have significant economic benefits; however, they are undergoing important negative changes worldwide. The seagrass Thalassia testudinum comprises one of the main elements in submerged aquatic vegetation (SAV) habitats, and it grows in monospecific and mixed meadows along the continental shelf of the Gulf of Mexico. In this study, T. testudinum monospecific and mixed meadows were monitored over a 2 year period to identify the abiotic and biotic conditions that may correlate with population parameters through the plastochron index (PI). Plants found in monospecific meadows had larger rhizomes and more flowers in comparison to those in mixed meadows, while the latter produced more leaves and larger shoots. The annual rate of change in biomass (Br) of T. testudinum in the monospecific meadow was 1.15 6 0.03, which was slightly higher than that in the mixed meadow, with a value of 1.12 6 0.03. T. testudinum in monospecific meadows tended to exhibit increased sexual reproduction, while vegetative growth and clonal reproduction were more common in mixed meadows. The results highlight that T. testudinum life-history strategies and establishment are affected by both biotic and abiotic factors like depth, temperature, and water nutrients.
Marine Ecology Progress Series, 1994
The shoot demography and rhizome growth of Syringodium filiforme Kutz. and Halodule wrightii Aschers. were studied, based on plant dating techniques, to account for their role as pioneer in the succession sequence of Canbbean seagrasses. Results demonstrated that these species are able to develop dense meadows, supporting biomasses in excess of 500 g DW m" They produced more than 2000 g DW m -2 yr-' due to their high leaf (5.0 to 8 5 yr.') and rhizome (2 0 to 3.3 yr-') turnover. Rhizome growth and branch~ng rates were very high, allowing these seagrasses to rapidly occupy the space they colonise. The rapid rhizome turnover involved, however, a high shoot mortality rate and low 11fe expectancy (average shoot life expectancy 100 to 180 d). This implies that, while these pioneer species are able to rapidly occupy the space they colonise, their established shoots cannot occupy that space for a s long a s the more longlived species Thalassia testudinum. We suggest, therefore. that the role of seagrass species a s pioneer or climax species is independent of their capacity to support dense, productive populations, and is closely related to shoot longevity and rhizome turnover.
2009
Seagrass beds are highly productive and valuable habitats, which fulfill a key role in coastal ecosystems. Spatial distribution, biomass, density, productivity and leaf dynamics of the dominant seagrass species Thalassia testudinum were studied at five locations in the Gandoca-Manzanillo National Wildlife Refuge, Caribbean coast of Costa Rica, from November 2005 until March 2006. Seagrass beds within the study area cover approximately 16 ha. Spatial and temporal differences in ecological seagrass parameters were examined along gradients of riverine inputs and related to a range of environmental parameters (depth, grain size distribution, nutrient concentrations, salinity and temperature). Average canopy cover and above-ground biomass of T. testudinum inversely correlated with depth, but did not vary significantly between study sites when compared along depth ranges. Considerable spatio-temporal variations in shoot densities, areal productivity and leaf sizes seem to be related to riverine inputs and wave energy. It appeared that T. testudinum at exposed sites respond to increased environmental disturbance related to the offset of the rainy season with clonal recruitment, whereby shoot densities increase and average leaf sizes are reduced. Lower shoot densities and greater leaf sizes, in contrast, are characteristic for locations with rather consistent environmental conditions, where seagrasses are sheltered. T. testudinum in the refuge has higher shoot densities but shorter leaves and lower productivity compared to sites in 15 other Caribbean countries. The seagrass beds appear to be in a relatively healthy state, however, observations of temporal increased stocks of filamentous epiphytes and macroalgae indicate temporal environmental stress in the system.
Restoration Ecology, 2018
Physical damage by motor vessels is a widespread problem for seagrass meadows, with hull and propeller strikes accounting for thousands of acres of impaired habitat in Florida, USA, alone. Because the excavations can become topographically unstable, and because re-colonization and succession of seagrasses can require decades to reach climax, Thalassia testudinum-dominated communities, there has been increasing efforts to re-grade and stabilize impacted sediments, and to speed succession. A prior project involving 8 vessel groundings in two hydrodynamic settings (high and low energy) examined the relative efficacy of capping injuries with sand-filled fabric tubes or limestone pearock, followed by This article is protected by copyright. All rights reserved. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Restoration Ecology, 2009
Selection of strategies to efficiently utilize limited seed supplies in efforts to restore the seagrass Zostera marina (eelgrass) requires a better understanding of the processes that limit seedling establishment at potential restoration sites. We investigated the effect of seed distribution timing on seedling establishment and tested for interactive effects of seed burial and distribution timing. We also investigated the effect of habitat type on seedling establishment by distributing Z. marina seeds inside and outside of established Ruppia maritima (widgeongrass) patches and examined mechanisms causing habitat differences by manipulating seed position (buried or unburied) and vulnerability to seed predators (unprotected or protected in packets). Seeds distributed on the sediment surface in the summer (July or August) produced fewer seedlings than seeds distributed in fall (October) in five of six trials over 3 years.