358
K.Reise
loop from suspension feeders back to the nutrient supply for further primary
production. The combination of high grazing pressure with high release rates
of nutrients may shift the phytoplankton towards smaller cell sizes. Dense
assemblages of suspension feeders are a major agent in the bentho-pelagic
coupling of the coastal ecosystem. They also resemble rocky shores by providing settlement sites, crevices and solid surfaces for algae and their grazers.
Reefs of mussels, oysters, vermetid gastropods and polychaetes also constitute
a transition to reefs of clonal cnidarians. The latter are regarded as hardbottom structures, and thus are outside the scope of this volume on sedimentary shores.
The occurrence of dense suspension-feeder assemblages may be limited by
the supply of planktonic food to a coastal region. Alternatively, new establishment of beds or reefs may depend on the rare coincidence of several factors
required to initiate a new dense assemblage. Thus, there may be a spacious
capacity of suitable but empty habitat. The recent proliferation of mussel and
oyster cultures seems to indicate that many coasts can support more suspension feeders than naturally occur. However, crashes of oyster stocks by
disease could be a sign of local over-cultivation.
Over-exploitation of natural oyster beds on sandy bottoms near the island
of Sylt in the North Sea prompted Mobius (1877) to sketch the first ecological
community concept. He saw the oyster population in the context of its
predators, competitors, diseases, and the relevant physical factors, showing
that the millions of eggs produced are necessary to sustain the natural stock
and are not just a surplus for the benefit of the oyster market. His recommendation for modest and prudent use of this natural resource was in vain. Dense
beds of suspension feeders have since then been recognized as habitats to a
diverse community of associated species (Commito and Dankers, Chap. 2). In
this respect, mussel beds on soft-bottoms from both sides of the North
Atlantic are compared (Fig. O. Barnacles are common epifaunal associates,
while oligochaetes with their direct development and tolerance to enriched
sediments and low oxygen concentrations dominate the infauna. Field experiments have revealed the significance of grazing snails for the control of algal
epigrowth. Algae may enhance suffocation of mussels by accumulating mud.
The interaction between the flow regime and the physical structure of mussel
aggregates is a key variable for associated species as well as for the performance of the mussels themselves. The complex spatial structure and the
dynamics can be quantified by means of fractal geometry.
Sandy beaches are subject to strong physical forcing (Jaramillo and Lastra,
Chap. 3). Their biota show a high degree of similarity between continents and
climatic zones. At the more exposed beaches, the top contributors to the
biomass are very often mobile suspension feeders, composed of anomuran
crabs (Emerita spp.) and bivalves (Mesodesma and Donax spp.; Fig. 2). These
occur in aggregates with the juveniles more up shore and the adults more
K.Reise
loop from suspension feeders back to the nutrient supply for further primary
production. The combination of high grazing pressure with high release rates
of nutrients may shift the phytoplankton towards smaller cell sizes. Dense
assemblages of suspension feeders are a major agent in the bentho-pelagic
coupling of the coastal ecosystem. They also resemble rocky shores by providing settlement sites, crevices and solid surfaces for algae and their grazers.
Reefs of mussels, oysters, vermetid gastropods and polychaetes also constitute
a transition to reefs of clonal cnidarians. The latter are regarded as hardbottom structures, and thus are outside the scope of this volume on sedimentary shores.
The occurrence of dense suspension-feeder assemblages may be limited by
the supply of planktonic food to a coastal region. Alternatively, new establishment of beds or reefs may depend on the rare coincidence of several factors
required to initiate a new dense assemblage. Thus, there may be a spacious
capacity of suitable but empty habitat. The recent proliferation of mussel and
oyster cultures seems to indicate that many coasts can support more suspension feeders than naturally occur. However, crashes of oyster stocks by
disease could be a sign of local over-cultivation.
Over-exploitation of natural oyster beds on sandy bottoms near the island
of Sylt in the North Sea prompted Mobius (1877) to sketch the first ecological
community concept. He saw the oyster population in the context of its
predators, competitors, diseases, and the relevant physical factors, showing
that the millions of eggs produced are necessary to sustain the natural stock
and are not just a surplus for the benefit of the oyster market. His recommendation for modest and prudent use of this natural resource was in vain. Dense
beds of suspension feeders have since then been recognized as habitats to a
diverse community of associated species (Commito and Dankers, Chap. 2). In
this respect, mussel beds on soft-bottoms from both sides of the North
Atlantic are compared (Fig. O. Barnacles are common epifaunal associates,
while oligochaetes with their direct development and tolerance to enriched
sediments and low oxygen concentrations dominate the infauna. Field experiments have revealed the significance of grazing snails for the control of algal
epigrowth. Algae may enhance suffocation of mussels by accumulating mud.
The interaction between the flow regime and the physical structure of mussel
aggregates is a key variable for associated species as well as for the performance of the mussels themselves. The complex spatial structure and the
dynamics can be quantified by means of fractal geometry.
Sandy beaches are subject to strong physical forcing (Jaramillo and Lastra,
Chap. 3). Their biota show a high degree of similarity between continents and
climatic zones. At the more exposed beaches, the top contributors to the
biomass are very often mobile suspension feeders, composed of anomuran
crabs (Emerita spp.) and bivalves (Mesodesma and Donax spp.; Fig. 2). These
occur in aggregates with the juveniles more up shore and the adults more