Energy Flow in Benthic Assemblages: Portugal and North Sea Tidal Basins
251
be severely decimated from intertidal areas not protected by algal or seagrass
cover during late spring/early summer, when recruits of the shore crab
(Carcinus maenas) colonize these zones at quantities of up to 90 specimens
per square metre (Sprung 1994b). Even higher densities of shore crabs have
been reported for the Sylt-R0m0 area (Scherer and Reise 1981) which may
remove 0.4 g C m- 2 a-l of the macrobenthic secondary production.
In summary, main bottom-up and top-down forces act at different components in the systems. Bottom-up forces have their greatest impact on phytoplankton and microphytobenthos in the Sylt-R0m0 Bay, and on macrophytes
in the Ria Formosa lagoon. Main top-down forces will be those on microphytobenthos production in seagrass beds and on macrobenthos in the SyltR0m0 area, and that on phytoplankton (and plankton in general) and on
macrobenthos in the Ria Formosa lagoon.
Contrary to our initial assumption, primary production is lower at Ria
Formosa sites. This is caused by the lower availability of nutrients, which outbalances the potential of higher annual nutrient turnover. Also secondary
production is lower because of lower food availability and high top-down
control. Our data are limited in the sense that only two systems with their
inevitable geographic peculiarities have been examined and warrant further
discussion in a broader context.
Acknowledgements. Natalia Dias kindly furnished unpublished data on salt marsh
invertebrates. Karsten Reise and Justus v. Beusekom improved the text considerably by
their valuable comments.
References
Andrade C (1990) 0 ambiente de barreira da Ria Formosa (Algarve-Portugal). Tese de
Doutoramento, Univ Lisboa, 644 pp
Andrade JP (1990) A importancia da Ria Formosa no cido bio16gico de Solea senegalensis Kaup 1858, Solea vulgaris Ouensel 1806, Solea lascaris (Risso 1810) e Microchirus azevia (Capello 1868). Tese de Doutoramento, Univ Algarve, 409 pp
Anibal J (1998) Impacte da macroepifauna sobre as macro algas Ulvales (Chlorophyta)
na Ria Formosa. Tese de Mestrado, Univ Coimbra, 73 pp
Asmus H (1987) Secondary production of an intertidal mussel bed community related to
its storage and turnover compartments. Mar Ecol Prog Ser 39:251-266
Asmus H, Asmus R (1985) The importance of grazing food chain for energy flow and
production in three intertidal sand bottom communities of the northern Wadden
Sea. Helgolander Meeresunters 39:273-301
Asmus H, Asmus R (2000) Material exchange and food web of seagrass beds in the SyltR0m0 Bight - How significant are community changes on the ecosystem level? In:
Asmus H, Asmus R (eds) Intertidal seagrass beds and algal mats - organisms and
fluxes on ecosystem level. Helgol Mar Res 54:137-150
251
be severely decimated from intertidal areas not protected by algal or seagrass
cover during late spring/early summer, when recruits of the shore crab
(Carcinus maenas) colonize these zones at quantities of up to 90 specimens
per square metre (Sprung 1994b). Even higher densities of shore crabs have
been reported for the Sylt-R0m0 area (Scherer and Reise 1981) which may
remove 0.4 g C m- 2 a-l of the macrobenthic secondary production.
In summary, main bottom-up and top-down forces act at different components in the systems. Bottom-up forces have their greatest impact on phytoplankton and microphytobenthos in the Sylt-R0m0 Bay, and on macrophytes
in the Ria Formosa lagoon. Main top-down forces will be those on microphytobenthos production in seagrass beds and on macrobenthos in the SyltR0m0 area, and that on phytoplankton (and plankton in general) and on
macrobenthos in the Ria Formosa lagoon.
Contrary to our initial assumption, primary production is lower at Ria
Formosa sites. This is caused by the lower availability of nutrients, which outbalances the potential of higher annual nutrient turnover. Also secondary
production is lower because of lower food availability and high top-down
control. Our data are limited in the sense that only two systems with their
inevitable geographic peculiarities have been examined and warrant further
discussion in a broader context.
Acknowledgements. Natalia Dias kindly furnished unpublished data on salt marsh
invertebrates. Karsten Reise and Justus v. Beusekom improved the text considerably by
their valuable comments.
References
Andrade C (1990) 0 ambiente de barreira da Ria Formosa (Algarve-Portugal). Tese de
Doutoramento, Univ Lisboa, 644 pp
Andrade JP (1990) A importancia da Ria Formosa no cido bio16gico de Solea senegalensis Kaup 1858, Solea vulgaris Ouensel 1806, Solea lascaris (Risso 1810) e Microchirus azevia (Capello 1868). Tese de Doutoramento, Univ Algarve, 409 pp
Anibal J (1998) Impacte da macroepifauna sobre as macro algas Ulvales (Chlorophyta)
na Ria Formosa. Tese de Mestrado, Univ Coimbra, 73 pp
Asmus H (1987) Secondary production of an intertidal mussel bed community related to
its storage and turnover compartments. Mar Ecol Prog Ser 39:251-266
Asmus H, Asmus R (1985) The importance of grazing food chain for energy flow and
production in three intertidal sand bottom communities of the northern Wadden
Sea. Helgolander Meeresunters 39:273-301
Asmus H, Asmus R (2000) Material exchange and food web of seagrass beds in the SyltR0m0 Bight - How significant are community changes on the ecosystem level? In:
Asmus H, Asmus R (eds) Intertidal seagrass beds and algal mats - organisms and
fluxes on ecosystem level. Helgol Mar Res 54:137-150