248
M. Sprung et al.
Sand flat organisms show apparently only a very small degree of omnivory.
For the mud flat organisms, omnivory is attributed principally to the capacity
of suspension feeding in addition to other feeding modes (particularly manifested by the polychaete Nereis diversicolor and the bivalve Scrobicularia
plana). For organisms in the Zostera bed omnivory means to be additionally
herbivorous. For the salt marsh organisms, omnivory is linked to the capacity
to use benthic detritus next to other food sources (plant material and suspension feeding).
In the Sylt-R0m0 area, the main omnivorous capacity for all examined
communities refers to a switch between feeding on benthic detritus and
benthic micro algae. Three dominant macro faunal species are involved in this:
the gastropod Hydrobia ulvae, the lugworm Arenicola marina and the bivalve
Macoma baltica. The latter, and to a minor extent the lugworm, are at times
also suspension feeders (see Chap. 4, this volume).
11.5 Energy Flow and Nutrient Cycle
Energy flow from primary to secondary producers, as focused on in this study
(Fig. 11.3), constitutes only a part of the larger ecological cycle. In a closed
system, primary production will largely depend on the availability of nutrients, which are set free by degradation of organic matter. Macrobenthic
secondary producers do not represent the end of the food chain, but are subject to predation.
From this perspective, both systems are distinctly different with consequences elaborated in this chapter. One essential point is that the Ria Formosa
is more open in terms of water circulation although at first sight geographically more efficiently separated from the sea than the Sylt-R0m0 Bay.
However, water exchange is by many inlets on the longitudinal part. Hydrographically, it represents a chain of small tidal basins. Hence, the subtidal
water volume is much smaller than the tidal prism, water exchange is more
complete and water residence time short (Reise and de Jong 1999). At the
same time nutrient supply from the Atlantic water is much lower. Under these
conditions vascular plants (salt marsh plants and seagrass) with access to
nutrients in the sediment tend to dominate as primary producers. Due to their
morphological and biochemical complexity, vascular plants are rarely degraded directly by herbivorous organisms, but mostly as detritus.
The discrepancy between high primary production and low secondary
production in the salt marshes of the Ria Formosa implies an export of plant
detritus to other lagoon areas. This is contrary to results from studies in North
Sea salt marshes, where plant material is mainly degraded in the marsh (Hemminga et al. 1996) or even imported (Murray and Spencer 1997). Stepwise
M. Sprung et al.
Sand flat organisms show apparently only a very small degree of omnivory.
For the mud flat organisms, omnivory is attributed principally to the capacity
of suspension feeding in addition to other feeding modes (particularly manifested by the polychaete Nereis diversicolor and the bivalve Scrobicularia
plana). For organisms in the Zostera bed omnivory means to be additionally
herbivorous. For the salt marsh organisms, omnivory is linked to the capacity
to use benthic detritus next to other food sources (plant material and suspension feeding).
In the Sylt-R0m0 area, the main omnivorous capacity for all examined
communities refers to a switch between feeding on benthic detritus and
benthic micro algae. Three dominant macro faunal species are involved in this:
the gastropod Hydrobia ulvae, the lugworm Arenicola marina and the bivalve
Macoma baltica. The latter, and to a minor extent the lugworm, are at times
also suspension feeders (see Chap. 4, this volume).
11.5 Energy Flow and Nutrient Cycle
Energy flow from primary to secondary producers, as focused on in this study
(Fig. 11.3), constitutes only a part of the larger ecological cycle. In a closed
system, primary production will largely depend on the availability of nutrients, which are set free by degradation of organic matter. Macrobenthic
secondary producers do not represent the end of the food chain, but are subject to predation.
From this perspective, both systems are distinctly different with consequences elaborated in this chapter. One essential point is that the Ria Formosa
is more open in terms of water circulation although at first sight geographically more efficiently separated from the sea than the Sylt-R0m0 Bay.
However, water exchange is by many inlets on the longitudinal part. Hydrographically, it represents a chain of small tidal basins. Hence, the subtidal
water volume is much smaller than the tidal prism, water exchange is more
complete and water residence time short (Reise and de Jong 1999). At the
same time nutrient supply from the Atlantic water is much lower. Under these
conditions vascular plants (salt marsh plants and seagrass) with access to
nutrients in the sediment tend to dominate as primary producers. Due to their
morphological and biochemical complexity, vascular plants are rarely degraded directly by herbivorous organisms, but mostly as detritus.
The discrepancy between high primary production and low secondary
production in the salt marshes of the Ria Formosa implies an export of plant
detritus to other lagoon areas. This is contrary to results from studies in North
Sea salt marshes, where plant material is mainly degraded in the marsh (Hemminga et al. 1996) or even imported (Murray and Spencer 1997). Stepwise