Above- and below-ground production, biomass and reproductive ecology of Thalassia testudinum (turtle grass) in a subtropical coastal lagoon

Abstract

Above-and below-ground growth, biomass, phenology and reproductive effort in the seagrass Thalassia testudinum were monitored monthly for 2 yr in the Lower Laguna Madre, Texas. Annual whole plant production (953 i 136 g DW (dry weight) m-2 yr-l) was calculated from monthly measurements of leaf and rhizome production made using marking techniques. Leaf growth exhblted a seasonal pattern; monthly production ranged from 8 to 95 g DW m-' mo-', equivalent to 614 * 71 g DW m-' yr-l.Rhlzome growth was seasonal, and area1 below-ground production ranged between 14 and 40 g DW m" mo-', equivalent to 339 2 65 g DW m-' yr-'. On an annual basis, rhizome production accounted for 35% of total plant production. Seasonal leaf and rhizome growth patterns were correlated with underwater irradiance. daylength and temperature. Total biomass ranged between 750 and 1500 g DW with below-ground tissues accounting for 80 to 90 % of the total. There was no seasonal pattern in the belowground biomass of T. testudinum; variability was a result of environmental heterogeneity. Flowering was variable between years; 13 to 30% of the shoots flowered and about 15% of total above-ground biomass was allocated to reproduction. Flowering phenology was positively correlated with underwater daylength. During 1996, maximum fruit abundance ranged between 20 and 70 fruits m-' and on average each fruit contained 2 seeds. The annual flowering event represents a substantial resource (e.g. carbon and nitrogen) investment, whlch may influence individual plant production. Seasonal fluctuations in environmental parameters are the primary factors controlling seagrass growth rates and production. Determination of total plant productivity must take into account seasonal patterns, reproductive costs and the large fraction of production occurring in the below-ground tissues.

Response and recovery dynamics of seagrasses Thalassia testudinum and Syringodium filiforme and macroalgae in experimental motor vessel disturbances

“…As much as 80 to 90% of the dry weight of T. testudinum is belowground biomass (Van Tussenbroek 1998, Kaldy & Dunton 2000, and the belowground fraction may extend deeper than 1 m into the sediment (Marba et al 1994). Shallow disturbances (≤10 cm) likely damaged very little of the belowground biomass and rhizome apical or basal shoot meristems and thus the experimental plots recovered quickly due to regrowth of intact short shoots.…”

Comparing Productivity and Biogeochemistry of Native and Transplanted Thalassia testudinum and Halodule beaudettei in Big Lagoon, Florida, USA

“…Productivity of seagrass beds in Big Lagoon was also comparable to that of prior studies that took place in Mississippi (Moncreiff et al, 1992), Virginia (Murray and Wetzel, 1987;Hume et al, 2011), south Florida (Nagel, 2007;Yarbro and Carlson, 2008), and Australia (Eyre and Ferguson, 2002;Eyre et al, 2011b), but much higher than rates measured in H. beaudettei patches in the region (Stutes et al, 2007) (Table 2). Since short-term studies can overestimate actual productivity rates, especially if they are performed in very productive times of the year, such as summer, during which seagrass productivity can be as much as 90% higher than in winter (Kaldy and Dunton, 2000), it is necessary to adjust for seasonal changes when estimating annual productivity rates of seagrass communities (Herzka and Dunton, 1997). Our study was conducted between May and Oct. and does not include either the early spring portion of the growing season or winter and fall, when the plants are dormant.…”

Epiphytes mediate the trophic role of sea urchins in Thalassia testudinum seagrass beds

“…Therefore, the relative availability of green and decaying leaves, as well as the herbivore's choice of leaf type, may be important factors determining sea urchin effects within seagrass meadows. This issue has been inadequately investigated, although it can have important consequences for the functioning of ecosystems, depending on the dif ferent interactions between grazers and seasonal changes in the standing plant biomass, production (Duarte 1989, Kaldy & Dunton 2000, and leaf loss dynamics (Francour 1990, Romero et al 1992. Previous studies have suggested that sea urchins preferentially feed on epiphytes (Verlaque & Nédelec 1983, Shepherd 1987, Tomas et al 2005a, Vergés et al 2011, possibly due to their C:N ratios and the absence of refractory plant material.…”