The Leaf Canopy of Seagrass Beds: Faunal Community in a Salinity Gradient
229
the bottom substrate. This has been the subject of many investigations and
has been thoroughly reviewed by Heck and Crowder (1991).
As for the fauna in general, investigations focusing on predators in
Scandinavian Zostera beds are sparse. Mobile epifauna (intermediate and top
predators) has been described in terms of abundance and biomass, but not in
terms of food intake. At three localities in the Gullmarsfjord area (including
locality 3 in this study), monthly quantitative samples were taken from
May-December 1980-1982 (Baden and Pihl 1984). In the Baltic (Aland
Islands) the efficiency of predation on the infauna within and outside Zostera
has been investigated by Mattila (1995), and tested experimentally on
epifauna using artificial vegetation (Bostrom and Mattila 1999). In 1999
different sampling methods for seagrass-associated fish were tested at locality
9 (see Sect. 10.3.3).
In Scandinavian seagrass beds, the main difference is the dominance of
intermediate predators on the Swedish west coast compared to the high proportion oflarger piscivores in the Baltic. Grass shrimp (Palaemon adspersus)
and green crab (Careinus maenas) make up about 90 % of the intermediate
predators on the Swedish west coast, and pipe fish (Syngnathus typhle) and
black goby (Gobius niger) contribute less than 10 % to the annual mean of
both abundance and biomass (Baden 1990). Piscivorous fish like eel (Anguilla
anguilla) and eelpout (Zoarees viviparus) are few. In the Baltic Zostera
meadows the fish fauna is, in addition to pipefish, dominated by larger species
of limnetic origin such as perch (Perea fluviatilis), roach (Rutilus rutilus) and
ruffe (Gymnoeephalus eernuus); in addition, flounder (Platiehtys flesus) is also
common (Table 10.2).
For both areas studied in Scandinavia (Table 10.2), the diversity of
predators is lower than in a Zostera bed off Cape Cod (north eastern USA)
that has about 20 decapod and fish species (Heck et al. 1989). Robertson
(1984) and Ryer (1988) showed that with increasing complexity of seagrass,
larger fish become less important predators, whereas intermediate predators
like shrimps and pipefish are favoured by high-density vegetation, as found
along the Swedish west coast and shown by Nelson (1979, 1981), Heck and
Thoman (1984) and Russo (1987). However, many of the fish species found in
Zostera are generalists and forage in vegetated habitats on both sheltered soft
bottoms (reed belts) and rocky shores (brown and green algal belts), or may
shift habitat depending on time of season. Hence, the quantitative role of
predators in the Scandinavian Zostera food webs is still poorly understood.
229
the bottom substrate. This has been the subject of many investigations and
has been thoroughly reviewed by Heck and Crowder (1991).
As for the fauna in general, investigations focusing on predators in
Scandinavian Zostera beds are sparse. Mobile epifauna (intermediate and top
predators) has been described in terms of abundance and biomass, but not in
terms of food intake. At three localities in the Gullmarsfjord area (including
locality 3 in this study), monthly quantitative samples were taken from
May-December 1980-1982 (Baden and Pihl 1984). In the Baltic (Aland
Islands) the efficiency of predation on the infauna within and outside Zostera
has been investigated by Mattila (1995), and tested experimentally on
epifauna using artificial vegetation (Bostrom and Mattila 1999). In 1999
different sampling methods for seagrass-associated fish were tested at locality
9 (see Sect. 10.3.3).
In Scandinavian seagrass beds, the main difference is the dominance of
intermediate predators on the Swedish west coast compared to the high proportion oflarger piscivores in the Baltic. Grass shrimp (Palaemon adspersus)
and green crab (Careinus maenas) make up about 90 % of the intermediate
predators on the Swedish west coast, and pipe fish (Syngnathus typhle) and
black goby (Gobius niger) contribute less than 10 % to the annual mean of
both abundance and biomass (Baden 1990). Piscivorous fish like eel (Anguilla
anguilla) and eelpout (Zoarees viviparus) are few. In the Baltic Zostera
meadows the fish fauna is, in addition to pipefish, dominated by larger species
of limnetic origin such as perch (Perea fluviatilis), roach (Rutilus rutilus) and
ruffe (Gymnoeephalus eernuus); in addition, flounder (Platiehtys flesus) is also
common (Table 10.2).
For both areas studied in Scandinavia (Table 10.2), the diversity of
predators is lower than in a Zostera bed off Cape Cod (north eastern USA)
that has about 20 decapod and fish species (Heck et al. 1989). Robertson
(1984) and Ryer (1988) showed that with increasing complexity of seagrass,
larger fish become less important predators, whereas intermediate predators
like shrimps and pipefish are favoured by high-density vegetation, as found
along the Swedish west coast and shown by Nelson (1979, 1981), Heck and
Thoman (1984) and Russo (1987). However, many of the fish species found in
Zostera are generalists and forage in vegetated habitats on both sheltered soft
bottoms (reed belts) and rocky shores (brown and green algal belts), or may
shift habitat depending on time of season. Hence, the quantitative role of
predators in the Scandinavian Zostera food webs is still poorly understood.