220
S.P. Baden and C. Bostrom
fresh water after having been frozen and detritus, fauna and epiphytes were
scraped off and sieved on a 250-flm mesh. Zostera biomass dry weight (12h at
60°C) and leaf area per m- 2 were measured and the fauna classified to species
(except for harpacticoids and insect larvae). The epiphytic fouling at localities
1-5 was sorted under a dissecting microscope into three fractions, namely
detritus, fauna and filamentous epiphytes, before weighing and drying. For
detailed information on the procedure, see Baden et al. (2000). At localities
6-9, the epiphytic covering was practically absent.
10.3.2 Predators
Sampling of predators does not allow for quantitative comparisons but gives
an indication of the relative importance and composition of the mobile predatory faunal assemblages. Besides predators caught in the net bag and the
visual observations made during sampling, the most reliable quantitative
samples from fully marine Zostera meadows (locality 3) were taken with a
drop-trap covering 0.5 m 2 (1.5 m high) released from a boat and emptied with a
hand-net (method described in detail by Baden and PihI1984). On the Aland
Islands, a survey comparing methods for catching seagrass associated fish
(Sillanpaa 2001) was used to evaluate the importance of fish in brackish water
Zostera meadows. Data presented here are based on results from the site used
for collection of leaf fauna (locality 9). Gear used were drop-trap (area 1 m 2 ,
height 80 cm), survey nets (10-50 mm), haul seine, push net, passive non-baited
traps and visual observation by SCUBA along transects.
10.4 Results
10.4.1 Zostera marina: Standing Stock and Leaf Area
The leaf canopy of Zostera meadows provide both substrate and hiding places
for special faunal communities. Generally, this three-dimensional habitat
supports higher species diversity and animal abundances than nearby on
vegetated habitats (Heck and Thoman 1984; Orth et al. 1984; Moller et al. 1985;
Mattila et al. 1999). Some type of linear or stepwise relationship between the
standing stock and the leaf area of Zostera and different categories of fauna is
found in many areas (Adams 1976; Stoner 1980; Orth et al. 1984; Baden 1990;
Mattila et al. 1999).
On the Swedish west coast Zostera starts growing in May and reaches a
maximum shoot (turion) density of 1000-2000 m- 2 at 0.7 m depth in August.
S.P. Baden and C. Bostrom
fresh water after having been frozen and detritus, fauna and epiphytes were
scraped off and sieved on a 250-flm mesh. Zostera biomass dry weight (12h at
60°C) and leaf area per m- 2 were measured and the fauna classified to species
(except for harpacticoids and insect larvae). The epiphytic fouling at localities
1-5 was sorted under a dissecting microscope into three fractions, namely
detritus, fauna and filamentous epiphytes, before weighing and drying. For
detailed information on the procedure, see Baden et al. (2000). At localities
6-9, the epiphytic covering was practically absent.
10.3.2 Predators
Sampling of predators does not allow for quantitative comparisons but gives
an indication of the relative importance and composition of the mobile predatory faunal assemblages. Besides predators caught in the net bag and the
visual observations made during sampling, the most reliable quantitative
samples from fully marine Zostera meadows (locality 3) were taken with a
drop-trap covering 0.5 m 2 (1.5 m high) released from a boat and emptied with a
hand-net (method described in detail by Baden and PihI1984). On the Aland
Islands, a survey comparing methods for catching seagrass associated fish
(Sillanpaa 2001) was used to evaluate the importance of fish in brackish water
Zostera meadows. Data presented here are based on results from the site used
for collection of leaf fauna (locality 9). Gear used were drop-trap (area 1 m 2 ,
height 80 cm), survey nets (10-50 mm), haul seine, push net, passive non-baited
traps and visual observation by SCUBA along transects.
10.4 Results
10.4.1 Zostera marina: Standing Stock and Leaf Area
The leaf canopy of Zostera meadows provide both substrate and hiding places
for special faunal communities. Generally, this three-dimensional habitat
supports higher species diversity and animal abundances than nearby on
vegetated habitats (Heck and Thoman 1984; Orth et al. 1984; Moller et al. 1985;
Mattila et al. 1999). Some type of linear or stepwise relationship between the
standing stock and the leaf area of Zostera and different categories of fauna is
found in many areas (Adams 1976; Stoner 1980; Orth et al. 1984; Baden 1990;
Mattila et al. 1999).
On the Swedish west coast Zostera starts growing in May and reaches a
maximum shoot (turion) density of 1000-2000 m- 2 at 0.7 m depth in August.