Distribution and aspects of the production and biomass of eelgrass, Zostera marina L., at Roscoff, France

We examined the patch dynamics of the intertidal seagrass Zostera novazelandica on 2 reef platforms in order to understand the processes governing the establishment, maintenance and mortality of patches. The size distribution of patches at 3 tidal heights (low, mid and high shore) was assessed. Eighty patches, ranglng in initial size from 0.1 to 2.4 m2 surface area, were tagged and video image analysis was used bi-monthly for 14 mo to calculate rates of expansion and contraction of these patches. Permanently marked 150 m2 areas of reef were monitored monthly to record patch recruitment and mortality. Initially, 75% of patches were <0.5 m2 All patches decreased in size during winter, probably due to increased wave action, and expanded during spring and summer. The proportional expansion and contraction of patches was independent of initial patch size. At the end of the study the size distribution of patches was similar to the initial distribution. Patch mortality was restricted to those <0.4 m2, of which 60% disappeared during the study. Larger patches suffered partial mortality through fragmentation. No large patches were formed through the amalgamation of smaller patches. Seedlings recruited into small sediment pockets in tidepools during spring, but few survived through summer because of removal by wave action. Experimental perturbation of patches resulted in increased erosion followed by decreased growth rates and, in many small patches, mortality. Removing only seagrass blades, however, resulted in increased production of new shoots relative to controls. Overall, seagrass patches are susceptible to disturbance, successful rclcruitment by seedlings may be rare or at least episodic, and populations are probably long-Lived and depend on slow vegetative growth for maintenance and expansion.

Section: Discussionsupporting

confidence: 72%

Section: Discussionmentioning

confidence: 52%

Patch dynamics and response to disturbance of the seagrass Zostera novazelandica on intertidal platforms in southern New Zealand

Ramage¹,

Schiel²

1999

“…On the average, a new leaf pair emerged about every 1.7 d, whereas most other seagrasses have leaf emergence rates on the order of 9 to 16 d (Patriquin 1973, Zieman & Wetzel 1980, Thayer et al 1984a, Fonseca et al 1987). H. decipiens leaves begin to show senescence and substantial deterioration when they are only 10 to 11 d old, while most other seagrass leaves live and remain attached to the shoot for more than 25 d and frequently for as many a s 40 to 50 d (Sand-Jensen 1975, Zieman 1975, Jacobs 1979, Thayer et al 1984a). …”

Section: Heterotrophic Activity; [3h]-thyrnidine Incorporation In Litmentioning

confidence: 99%

Production, decomposition, and heterotrophic utilization of the seagrass Halophila decipiens in a submarine canyon

Kenworthy¹,

Ca²,

Fonseca³

et al. 1989

ABSTRACT-We examined the net production, decomposition, and microbial utilization of the seagrass Halophila decipiens during a 6.5 d period in May 1985 in the Salt River Canyon, St Croix, US Virgin Islands. H. decipienscovered 37 % of the Canyon floor between depths of 14 and 32 m with a biomass of 9.15 g dry \vt m-'; its net productivity was ca 0.145 g C m-' d -' Turnover time, estimated by 2 independent methods, was 10.7 d. After 6.5 d H decjpiens incubated in lltterbags buried in the sediment lost 5 6 % of their original ash free dry weight (AFDW) while litterbags incubated on the sediment surface lost only 28 % of their original AFDW. Bacteria grew rapidly on the detritus, doubling in 3.1 d in the surface bags and 3.7 d in the buried bags. Per-cell thymidine incorporation rates peaked within the first 13 h in both treatments but declined thereafter. Final incorporation rates were highest in surface bags. Mean bacterial cell size and bacterial abundance associated with degrading H. decipiens were larger in the buried litterbags. Bacterial biomass, however, was only 29.3 mg cell C g -' AFDW in buried bags and 17.5 mg C g-' AFDVV in surface bags Using bacterial production averaged for the 6.5 d, we estimate that only about 0.26 "10 of the daily detntal input from H. declplens is converted daily into bacterial biomass attached to the degrading plant material. We conclude that, unless the bacterial community on H. decipiens detritus were to use the organic matter more efficiently and were heavily grazed upon, attached bacteria would not make a significant contribution to a deposit-feeding detritivore's energy demands.

“…Leaf growth of this plant can be measured using a leaf-marking technique, first described over a decade ago (Sand-Jensen 1975) and based on earlier work with a tropical seagrass species (Zieman 1968). Since its introduction, this method has been widely used for Z. marina (eelgrass) and related species in Europe, North America and Asia (Jacobs 1979, Mukai et al 1979, Nienhuis & De Bree 1980, Bulthuis & Woelkerling 1983, Robertson & Mann 1984, Wium-Andersen & Borum 1984. In general, leaf-marking represents a robust, highly interpretable method for estimating seagrass net production (Zieman & Wetzel 1980).…”

Section: Introductionmentioning

confidence: 99%

Diel growth in eelgrass Zostera marina

Kemp¹,

Murray²,

Borum³

et al. 1987

Growth of eelgrass Zostera marina leaves was determined by sequential measurements of leaf length at time intervals of 4 to 12 h. Leaf growth rates at night were consistently lower (30 to 40 %) compared to daytime rates, and night-time rates were highly correlated with growth during the previous day. Diel patterns of O2 metabolism (measured at 2 to 4 h intervals) and leaf growth (at 4 h intervals) generally followed the daily irradiance cycle, with maximum growth and 0 2 production rates both occurring near midday. Rapid (hours to days) responses to changes in environmental conditions such as light and sediment fertility were detected using this leaf growth method. Quantitative comparison of diel integrals of growth (increases in leaf, root, and rhizome biomass) and net O2 production indicated that the 2 processes were in relative balance. Although eelgrass leaf growth was determined readily here on short time-scales, measurement of total plant growth required a longer study period approaching the plastochrone interval (leaf formation time). It was demonstrated, however, that separate cahbration studies relating root-rhizome growth to leaf growth can be conducted (over 1 to 2 wk) to allow estimates of short-term (4 to 12 h) responses of total plant growth to changes in environmental conditions.