Synthesis: Comparative Ecology of Sedimentary Shores
365
(Sprung et aI., Chap. 11; Michaelis and Wolff, Chap. 12). In the coastal waters
along this gradient from north to south, mean temperature, seasonality,
insolation and salinity increase. Nutrient and phytoplankton supply to the
coastal biota, on the other hand, decreases in the same direction. The seagrass
Zostera noltii occurs throughout this latitudinal range but increases in areal
share from north to south. Vascular plants dominate the primary production
in the south. In the Wadden Sea, salt marsh vegetation is marginal. In the Ria
Formosa lagoon in Portugal, Spartina marshes and stands of shrubby
halophytes are extensive. At the Banc d' Arguin in northern Africa, where
seagrasses cover most of the tidal flats, there are only a few stands of Spar tina
and stunted mangroves. Due to the arid climate, unvegetated sebkhas extend
above mean high tide line. Herbivory on the vascular plants is insignificant in
the south, whereas the beds of seagrass and the salt marshes in the Wadden
Sea are seasonally grazed by migrant geese and ducks.
In the benthic fauna, species richness increases and biomass decreases
from north to south. The decrease in biomass and production is most pronounced in the suspension feeders. The dense beds of cockles and mussels in
the Wadden Sea find no analogue in the Ria Formosa and the Banc d' Arguin,
presumably because the food supply from the sea decreases from north to
south on this eastern Atlantic coast. Connolly and Roughgarden (1998)
explain a decreasing coverage at the rocky shore with barnacles and mussels
along the North American Pacific coast from north to south with different
current regimes. In the north, nearshore circulation promotes larval recruitment' in the south this is inhibited by strong offshore currents. It may be
speculated that recruitment to the benthic fauna with pelagic larvae to the
sedimentary shores along the eastern Atlantic coast may follow a similar
trend with positive effects of the oceanographic regimes in the north and
negative ones in the south.
The southern sites also have no equivalent to the large populations of the
lugworm (Arenicola marina) and the mud snails (Hydrobia ulvae) in the
north, which primarily feed on the rich microphytobenthos. The provision of
food to upper trophic levels by the zoobenthos depends on the nutrient
supply to easily digestible unicellular algae in the plankton and in the sediment. Migrant wading birds feed on their flyway on the zoobenthos in all
three regions, particularly in the Wadden Sea and the Banc d' Arguin, and
must cope with these different food provisions. Predation pressure on the
zoobenthos by flood tide visitors has not been quantified sufficiently to allow
comparisons along this latitudinal gradient.
The benthic macrofauna on tidal flats in the temperate zone and in the
tropics is always strongly dominated by sets of a few species. A main difference seems to be that in the tropics total species richness is higher and there
is a greater variety of taxa. Also, within and between regions, there may be a
higher variety in the tropics than in the temperate zones. Suspension feeders
365
(Sprung et aI., Chap. 11; Michaelis and Wolff, Chap. 12). In the coastal waters
along this gradient from north to south, mean temperature, seasonality,
insolation and salinity increase. Nutrient and phytoplankton supply to the
coastal biota, on the other hand, decreases in the same direction. The seagrass
Zostera noltii occurs throughout this latitudinal range but increases in areal
share from north to south. Vascular plants dominate the primary production
in the south. In the Wadden Sea, salt marsh vegetation is marginal. In the Ria
Formosa lagoon in Portugal, Spartina marshes and stands of shrubby
halophytes are extensive. At the Banc d' Arguin in northern Africa, where
seagrasses cover most of the tidal flats, there are only a few stands of Spar tina
and stunted mangroves. Due to the arid climate, unvegetated sebkhas extend
above mean high tide line. Herbivory on the vascular plants is insignificant in
the south, whereas the beds of seagrass and the salt marshes in the Wadden
Sea are seasonally grazed by migrant geese and ducks.
In the benthic fauna, species richness increases and biomass decreases
from north to south. The decrease in biomass and production is most pronounced in the suspension feeders. The dense beds of cockles and mussels in
the Wadden Sea find no analogue in the Ria Formosa and the Banc d' Arguin,
presumably because the food supply from the sea decreases from north to
south on this eastern Atlantic coast. Connolly and Roughgarden (1998)
explain a decreasing coverage at the rocky shore with barnacles and mussels
along the North American Pacific coast from north to south with different
current regimes. In the north, nearshore circulation promotes larval recruitment' in the south this is inhibited by strong offshore currents. It may be
speculated that recruitment to the benthic fauna with pelagic larvae to the
sedimentary shores along the eastern Atlantic coast may follow a similar
trend with positive effects of the oceanographic regimes in the north and
negative ones in the south.
The southern sites also have no equivalent to the large populations of the
lugworm (Arenicola marina) and the mud snails (Hydrobia ulvae) in the
north, which primarily feed on the rich microphytobenthos. The provision of
food to upper trophic levels by the zoobenthos depends on the nutrient
supply to easily digestible unicellular algae in the plankton and in the sediment. Migrant wading birds feed on their flyway on the zoobenthos in all
three regions, particularly in the Wadden Sea and the Banc d' Arguin, and
must cope with these different food provisions. Predation pressure on the
zoobenthos by flood tide visitors has not been quantified sufficiently to allow
comparisons along this latitudinal gradient.
The benthic macrofauna on tidal flats in the temperate zone and in the
tropics is always strongly dominated by sets of a few species. A main difference seems to be that in the tropics total species richness is higher and there
is a greater variety of taxa. Also, within and between regions, there may be a
higher variety in the tropics than in the temperate zones. Suspension feeders