Martin Sprung

Nutrient fluxes in intertidal communities of a South European lagoon (Ria Formosa) – similarities and differences with a northern Wadden Sea bay (Sylt-Rømø Bay)

During an annual cycle, flux rates of oxygen, nitrate, nitrite, ammonium, phosphate and silicate were measured in light and dark bell jars at three sites in Ria Formosa (Algarve, Portugal) enclosing either a natural macrophytic community (macroalgae on sand or mud, a seagrass bed of Zostera noltii) or bare sediments. The results are compared with a preceeding study in which the same bell jar technique has been applied in the Sylt-Rømø Bay of the northern Wadden Sea. Nitrate flux was mainly directed from the water column to the benthic communities in Ria Formosa, as well as in the Sylt-Rømø Bay. However, nitrate uptake was higher in the northern, more eutrophic study area. In Ria Formosa, nutrient concentrations were lower than in the Sylt-Rømø Bay possibly due to strong water exchange with Atlantic waters. High temperatures and strong insolation had a greater impact on nitrate fluxes in Ria Formosa than in the Sylt-Rømø Bay. Bioturbating macrofauna increased ammonium efflux in the Sylt- Rømø Bay while this effect was not as pronounced in the Ria Formosa study sites. Benthic phosphate uptake dominated in the Ria Formosa and was correlated to initial phosphate concentrations in incoming waters. At both study sites, oxygen and nutrient fluxes were correlated with temperature. Additionally, flux rates were strongly influenced by biotic components and levels of eutrophication. A literature survey showed that mainly in temperate regions, material fluxes increase with temperature, whereas in warmer areas, ammonium and phosphate fluxes between sediment and water were generally lower.

Larval abundance and recruitment of Carcinus maenas L. close to its southern geographic limit: a case of match and mismatch

In the Ria Formosa lagoon (S. Portugal), Carcinus maenas larvae have been observed only during the cold part of the year (October–May), when the water temperature stays below 23 °C. Larvae suffer high mortality during day time (about 80% during 6 h). Hence, they will only develop outside the lagoon, as proved by the observation of zoea I stages exclusively. Main recruitment starts in April, i.e. much later than the first larvae appear. Small crabs prefer Zostera noltii patches and colonize other sites when the carapace width exceeds about 5 mm. A reserve of some small crabs is found in Zostera noltii patches nearly all year round. It is postulated that one of the key factors for successful propagation of the species is a match between physiological reactions (here in particular temperature effect on reproductive cycle and larval release), and the ecological conditions for larval survival and recruitment, such as predator impact, food availability or currents.

Energy Flow in Benthic Assemblages of Tidal Basins: Ria Formosa (Portugal) and Sylt-Rømø Bay (North Sea) Compared

Tidal areas are zones of steep physical and biologically determined gradients. Gradients develop vertically in sediment profiles, horizontally along intertidal transects, temporally with respect to temperature, oxygen, nutrients, light with diurnal, tidal and seasonal periods. It is a special feature of tidal systems that these gradients reveal a high small-scale variability in space and time caused primarily by the hydrodynamics. The energy flow in intertidal areas should be high due to the proximity of sea bottom and surface water, the concomitant good supply of light, and the tidal flow. This leads to a close spatial coupling not only between water column and sea bottom processes, but also between the landward and seaward parts of the coastal system and to a distinct distribution of primary and secondary producers (Jorgensen 1983; Reise 1985; Kjerfve 1994b).

Does the energy equivalence rule apply to intertidal macrobenthic communities

Energy equivalence assumes equal contribution of large and small species to production and energy flow in communities. As in a double logarithmic plot, physiological rates decline with body weight by −0.25, log biomass should increase by 0.25 and log abundance decline by −0.75 with log species weight, when this concept is valid. This was tested with annual data sets of the macrobenthos of 4 intertidal sites in the German Wadden Sea (Königshafen) and 3 sites in a south Portuguese lagoon (Ria Formosa). Only abundance data from two of these sites displayed significantly negative slopes with mean body size of the species. Biomass and secondary production data were significantly positively correlated with mean body size for all Ria Formosa sites and also for the biomass of a mussel bed in Königshafen. However, high variation in body size of the individuals of a species limits interpretation of these plots.It is preferable to test this concept by body weight classes regardless of its species composition. At Königshafen, biomass and production displayed two distinct peaks. One peak at small body size was caused by browsing species. The other peak at larger body size was caused by animals which potentially extract their food from the water column. This bimodality was only vaguely reflected at one station in the Ria Formosa, possibly because of a dominance of detritus feeding species. In a normalized form (log biomass or production / width of size classvs. log size class), these spectra imply a dominance of small individuals in biomass and production at all sites (except for a mussel bank at Königshafen). This is interpreted as a consequence of permanent disturbances.

Converse effect of flooding on intertidal macrobenthic assemblages in the Guadiana estuary

macrobenthic assemblages in the Guadiana estuary anxo conde, jose’ calva’rio, martin sprung2,†, ju’ lio m. novais and jorge domi’nguez IBB-Institute for Biotechnology and Bioengineering, Center for Biological and Chemical Engineering, Instituto Superior Tecnico (IST), 1049-001, Lisbon, Portugal, Centro de Ciencias do Mar (CCMAR), Faculdade de Ciencias do Mar e do Ambiente, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal, Departamento de Ecoloxia e Bioloxia Animal, Universidade de Vigo, Vigo E-36310, Spain, †Deceased