Synthesis: Comparative Ecology of Sedimentary Shores
369
General Conclusions
Comparisons show that sedimentary shores constitute ecotones which receive
significant organic subsidies from the sea and locally also from the land. The
latter is governed by modern land-use practices. Coastal upwelling and nearshore circulations, onshore winds and pronounced seasonality may enhance
the seaside supply. The amount of this supply directly accounts for the abundance of suspension feeders, which in turn may affect the pelagic system in
lagoons and estuaries. After remineralization of the organic import, the
released nutrients support a rich microphytobenthos. This in turn provides
food for grazers and deposit feeders.
Suspension feeders tend to dominate the zoobenthos of the more exposed
shores, provided the adjacent sea is a productive source region. Grazers and
deposit feeders, on the other hand, tend to dominate at the more sheltered
shores. Intermediate sedimentary shores with respect to hydrodynamics and
sand-mud composition are supposed to be the richest in production, zoomass
and diversity of the organisms. Superimposed on these are the gradients in
salinity and climate: species richness in the benthic communities generally
increases with salinity and mean temperature.
Important are transformations of the sedimentary environment by the
organisms at the sheltered shores, and increasingly towards lower latitudes. Sediment-consolidating and sediment-disturbing organisms occur in
dynamic patterns of alternating zones perpendicular to the shore and in
distinct patches. Biotic interactions often determine whether accretion or
erosion prevails. Reef-like structures of suspension feeders, beds of seagrasses
and salt marsh plants not only stabilize and accrete sediment but also modify
nearshore hydrodynamics. This has cascading effects on habitat structure and
the biotic composition. Therefore the worldwide decline in seagrass beds,
ultimately caused by anthropogenic habitat deterioration, has far-reaching
consequences for the ecology of sedimentary shores.
The mobility of benthic organisms by passive drift or active migrations is a
major agent in spatio-temporal dynamics of the biota of sedimentary shores.
This mobility has regular tidal, diurnal, lunar and seasonal components, and
the recovery after disturbances is governed by differential dispersal. The
vagaries, ranges and directions of dispersal need further investigations to include such processes in large-scale comparisons.
Large animals are usually not residents on sedimentary shores but are
flood-tide, ebb-tide or seasonal visitors that exploit opportunistically the
food resources where these are rich. They mostly export their gains out of the
ecotone. Global patterns on the amount of their gains and on their impact on
the resident organisms need more attention in future studies. The flood-tide
visitors have rarely been quantified sufficiently. The larger these organisms
369
General Conclusions
Comparisons show that sedimentary shores constitute ecotones which receive
significant organic subsidies from the sea and locally also from the land. The
latter is governed by modern land-use practices. Coastal upwelling and nearshore circulations, onshore winds and pronounced seasonality may enhance
the seaside supply. The amount of this supply directly accounts for the abundance of suspension feeders, which in turn may affect the pelagic system in
lagoons and estuaries. After remineralization of the organic import, the
released nutrients support a rich microphytobenthos. This in turn provides
food for grazers and deposit feeders.
Suspension feeders tend to dominate the zoobenthos of the more exposed
shores, provided the adjacent sea is a productive source region. Grazers and
deposit feeders, on the other hand, tend to dominate at the more sheltered
shores. Intermediate sedimentary shores with respect to hydrodynamics and
sand-mud composition are supposed to be the richest in production, zoomass
and diversity of the organisms. Superimposed on these are the gradients in
salinity and climate: species richness in the benthic communities generally
increases with salinity and mean temperature.
Important are transformations of the sedimentary environment by the
organisms at the sheltered shores, and increasingly towards lower latitudes. Sediment-consolidating and sediment-disturbing organisms occur in
dynamic patterns of alternating zones perpendicular to the shore and in
distinct patches. Biotic interactions often determine whether accretion or
erosion prevails. Reef-like structures of suspension feeders, beds of seagrasses
and salt marsh plants not only stabilize and accrete sediment but also modify
nearshore hydrodynamics. This has cascading effects on habitat structure and
the biotic composition. Therefore the worldwide decline in seagrass beds,
ultimately caused by anthropogenic habitat deterioration, has far-reaching
consequences for the ecology of sedimentary shores.
The mobility of benthic organisms by passive drift or active migrations is a
major agent in spatio-temporal dynamics of the biota of sedimentary shores.
This mobility has regular tidal, diurnal, lunar and seasonal components, and
the recovery after disturbances is governed by differential dispersal. The
vagaries, ranges and directions of dispersal need further investigations to include such processes in large-scale comparisons.
Large animals are usually not residents on sedimentary shores but are
flood-tide, ebb-tide or seasonal visitors that exploit opportunistically the
food resources where these are rich. They mostly export their gains out of the
ecotone. Global patterns on the amount of their gains and on their impact on
the resident organisms need more attention in future studies. The flood-tide
visitors have rarely been quantified sufficiently. The larger these organisms