24
R.F. Dame et al.
lagoon has large inputs of raw and secondarily treated sewage from the
metropolitan area of Tunis. The organic input coupled with poor flushing and
circulation supports highly productive phytoplankton populations that in
turn feed the dense serpulid reefs. Using static mesocosms, Keene (1980)
determined that oxygen uptake and nutrient remineralization by the reefs
were high with the latter enhancing system productivity. In the second study,
serpulid reefs in a coastal marina near Cape Town, South Africa, were studied
(Davies et al. 1989). Here F. enigmaticus was found to be capable of filtering
the entire bay in about a day and removing approximately 130 kg of suspended particulate material per hour. Thus, these studies support the notion
that, in poorly flushed, organically loaded, shallow coastal systems, the
structural and functional aspects of serpulid reefs indicate their ability to
transform the ecosystem.
1.3 Encrustations
In addition to mono specific reefs, benthic suspension feeders, such as
ascidians (Petersen and Riisgard 1992; Petersen et al. 1995, 1997), barnacles
(Crisp 1979; Crisp and Southward 1961; Hily 1991), sponges (Riisgard et al.
1993) and bryozoans (Buss 1979), are also found as living layers or encrustations on rocks or other firm substrates. Further, dense populations of suspension-feeding animals are sometimes found on unconsolidated substrates,
i.e., solitary polychaetes (Riisgard 1991; Vedel and Riisgard 1993), clams
(J0rgensen 1990), and echinoderms (Hily 1991).
One of the few studies of an encrusting suspension feeder that showed
these animals to have an impact at the ecosystem level is that of the ascidian
Ciona intestinalis (Table 1.1) living on the surfaces of seagrass blades in
Kertinge Nor, Denmark (Petersen and Riisgard 1992; Riisgard et al. 1995).
Observations on Kertinge Nor indicate that, depending on the season, there is
sufficient filtration capacity by C. intestinalis to filter the water volume of the
fjord in 1 to 10 days (Petersen and Riisgard 1992) potentially allowing the
tunicates to control phytoplankton densities within the system.
1.4 Species Groups
When found in sufficient numbers, a group of species (Hily 1991; Lemmens et
al. 1996) may also have a large enough effect to be considered ecosystem
transformers. Water flow appears to be a major factor in determining the
location, structure, and growth of suspension feeders in dense aggregations.
R.F. Dame et al.
lagoon has large inputs of raw and secondarily treated sewage from the
metropolitan area of Tunis. The organic input coupled with poor flushing and
circulation supports highly productive phytoplankton populations that in
turn feed the dense serpulid reefs. Using static mesocosms, Keene (1980)
determined that oxygen uptake and nutrient remineralization by the reefs
were high with the latter enhancing system productivity. In the second study,
serpulid reefs in a coastal marina near Cape Town, South Africa, were studied
(Davies et al. 1989). Here F. enigmaticus was found to be capable of filtering
the entire bay in about a day and removing approximately 130 kg of suspended particulate material per hour. Thus, these studies support the notion
that, in poorly flushed, organically loaded, shallow coastal systems, the
structural and functional aspects of serpulid reefs indicate their ability to
transform the ecosystem.
1.3 Encrustations
In addition to mono specific reefs, benthic suspension feeders, such as
ascidians (Petersen and Riisgard 1992; Petersen et al. 1995, 1997), barnacles
(Crisp 1979; Crisp and Southward 1961; Hily 1991), sponges (Riisgard et al.
1993) and bryozoans (Buss 1979), are also found as living layers or encrustations on rocks or other firm substrates. Further, dense populations of suspension-feeding animals are sometimes found on unconsolidated substrates,
i.e., solitary polychaetes (Riisgard 1991; Vedel and Riisgard 1993), clams
(J0rgensen 1990), and echinoderms (Hily 1991).
One of the few studies of an encrusting suspension feeder that showed
these animals to have an impact at the ecosystem level is that of the ascidian
Ciona intestinalis (Table 1.1) living on the surfaces of seagrass blades in
Kertinge Nor, Denmark (Petersen and Riisgard 1992; Riisgard et al. 1995).
Observations on Kertinge Nor indicate that, depending on the season, there is
sufficient filtration capacity by C. intestinalis to filter the water volume of the
fjord in 1 to 10 days (Petersen and Riisgard 1992) potentially allowing the
tunicates to control phytoplankton densities within the system.
1.4 Species Groups
When found in sufficient numbers, a group of species (Hily 1991; Lemmens et
al. 1996) may also have a large enough effect to be considered ecosystem
transformers. Water flow appears to be a major factor in determining the
location, structure, and growth of suspension feeders in dense aggregations.