The decomposition of macroalgal detritus (tubular and planar Ulva spp.) was studied in a microcosm under a daily light:dark cycle to simulate the decomposition on intertidal sediment. The consequences of bloom decay were evaluated in the bulk water phase and in the sediment. ), dissolved organic carbon (DOC) and inorganic carbon (DIC) were measured in the inflowing and outflowing seawater. Vertical microprofiles of O 2 , pH and H 2 S at the sediment -water interface, sediment contents of organic matter (OM), inorganic and organic carbon (C org ), total nitrogen (N) and inorganic nutrients were measured before and after addition of macroalgal detritus. Changes in the taxonomic composition of microphytobenthos were studied by optical microscopy and by the analysis of photosynthetic pigments. Macroalgal detritus vanished from the sediment surface in 6 d. Macroalgal decomposition shifted the microcosm net balance to higher releases of DOC, DIC and inorganic nutrients, suggesting rapid release from macroalgal biomass. Besides being released to the water column, a fraction of macroalgal carbon and of nitrogen was incorporated into the sediment as indicated by a transient increase in C org and N. Aerobic mineralization of macroalgal detritus reduced O 2 in the water column and the sediment. Microbenthos photosynthetic activity was initially suppressed but recovered from the third day as macroalgal detritus decomposed. Photosynthetic O 2 production by microbenthos largely determined the fraction of macroalgal detritus that was aerobically mineralised. Decomposition of macroalgal detritus favoured the dominance of cyanobacteria over diatoms in the microbenthos. KEY WORDS: Macroalgal blooms · Microbenthos · Microelectrodes · Macroalgal decomposition · Macroalgal detritusResale or republication not permitted without written consent of the publisher

Long-term ( 4 14 d) and short-term ( 4 9 h) effects of salinity on the dimethylsulphoniopropionate (DMSP) content of the marine benthic diatom Cylindrotheca closterium were investigated. When grown in batch cultures at various salinities, intracellular DMSP increased from 13.8 to 823 mmol g 71 protein at salinities of 11 and 44 psu, respectively, but increasing salinity further did not result in a higher content. Instead, the concentration of the amino acid proline increased from 17.5 to 149.6 mmol g 71 protein when salinity increased from 33 to 55, indicating that this compound is more important than DMSP as an osmoprotectant at higher salinities. In addition, another, hitherto unidentified, compound increased strongly in response to salinity. During salinity up-and down-shock experiments, changes in the DMSP content of C. closterium corresponded with the changes in salinity. DMSP was excreted into the medium after salinity down-shock, while salinity upshock induced a slow synthesis of DMSP. However, C. closterium was also able to take up DMSP from the medium; the amount depended on the salinity difference applied. This is the first report of uptake of DMSP by an alga. The results demonstrate that synthesis of DMSP is too slow to be important for short-term acclimation and that its contribution to the intracellular osmotic potential of C. closterium is probably small. However, the observation that uptake of DMSP was faster after salinity up-shock from 11 to 33 than from 11 to 22, indicates that DMSP does have an osmoprotective function in C. closterium. Uptake of DMSP and other organic osmolytes from the environment may serve as a mechanism of osmoacclimation for diatoms living under highly fluctuating salinities in intertidal sediments.

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Eutrophication in coastal areas promotes blooms of green macroalgae that accumulate on the sediment, affecting the exchange of mass and energy at the sediment -water interface. The effects of macroalgal blooms on the microbenthic net metabolism and on the carbon and nitrogen contents of the sediment were studied during an in situ experiment. Two sediment enclosures (with and without macroalgae) of 1.5 × 1. ). This relatively low macroalgal biomass always suppressed the photosynthetic activity of microphytobenthos, decreased the oxygen availability for the sediment and reduced the oxygen penetration depth in the light and in the dark. The microbenthic community metabolism clearly shifted to heterotrophic, while the photoautotrophic activity was located in the macroalgal canopy. This macroalgal mat was net autotrophic, and more productive than the microphytobenthic community inhabiting the bare sediment. Part of the macroalgal production was buried in the sediment, increasing its carbon and nitrogen contents with respect to bare sediment during all seasons except spring. Concentrations of inorganic nutrients in the sediment were always higher below the macroalgal mat than in bare sediment, likely due to a direct input of inorganic nitrogen and phosphate associated with macroalgal debris.

The lack of space and opportunity for development have been identified as key reasons behind the stagnation of the European aquaculture industry. With the historical loss and degradation of current European wetlands there is an opportunity for harnessing the commercial investment of the aquaculture industry in construction of dual purpose wetlands that incorporate both conservation and extensive aquaculture activities. These wetlands can be used to expand the area available to suitable aquaculture into ecologically sensitive areas, such as Natura 2000 sites. Veta la Palma (VLP) situated in the Doñana Natural Park (and a Natura 2000 site) is an example of such an aquaculture development and a possible model for future opportunities. In the current study some of the important ecosystem services that are provided by VLP are assessed. The provisioning services of VLP were the economic rationale for the investment and more than 820 tonnes yr -1 of fish and shrimp is produced, through a mixture of semi-extensive and extensive aquaculture. The regulating services include nutrient absorption, and the flow of river water through VLP and high primary production results in the absorption of 377 tonnes of dissolved inorganic nitrogen yr -1 , and 516 tonnes of C yr -1 . Supporting services include the provision of habitat for more than 94 bird and 21 fish species. The primary production that supports the birds, extensive and semiextensive aquaculture production was also estimated to be 167,000 t, 50,000 t and 133,000 t yr -1 , respectively. The losses to birds are substantial and these estimates indicate that almost half of the primary production supports the wetland birds which directly consume 249 tonnes of fish and 2578 tonnes of invertebrates per annum. However it is the ecological credentials of the farm that enable premium prices and hence ensure the economic viability of the farm. The study demonstrates the possibility of using aquaculture to mitigate the historical loss of wetlands, provide significant ecosystem services and contribute to achievement of the European environmental legislative goals, and furthers the opportunity for the expansion of aquaculture into sensitive but impacted habitats.

Extensive aquaculture in coastal and estuarine wetlands can support both increased food production and wider ecosystem services when underpinned by effective management to promote productivity and hence food webs that support both commercial species and biodiversity. Changing hydrology, specifically water movement, within wetlands significantly impacts the physico-chemical properties of the water body and hence can be employed to manipulate productivity and alter patterns of recruitment of commercial species and may also transfer non-native species from the supplying water bodies. The reconstructed wetlands of Veta la Palma in the Doñana Natural Park are subjected to either a 1 % or 5 % d -1 water exchange with water drawn from the adjacent Guadalquivir estuary. This site provides an excellent opportunity for examining the effect of water management on the food webs that support both the birdlife and aquaculture activities for which this habitat is managed. Stable isotopes were used to examine food webs in three replicate lagoons under each water management scheme. In lagoons receiving higher water exchange, phytoplankton productivity appeared to be more important than benthic production in supporting food webs. Increased water exchange also changed the shape of the food webs, facilitated the colonisation of at least one non-native species and increased the importance of non-native species in the diets of large commercially harvested fish (> 60 % of seabass diet). Lagoons with high water flows also had between three and four times greater shrimp biomass than those of low flow lagoons. Non-native fauna were opportunistic omnivores, eating marginally more non-natives in lagoons with greater water exchange. Overall non-native cordgrass Spartina densiflora contributed only slightly more to food webs compared with the native reed Phragmites australis, despite the lagoon edge occupancy ratio of 9:1, respectively. Nonnatives also appear to enhance food provision for large predators and wetland birds, by increasing biomass, without competing for resources with native species, supporting the dual management objectives of aquaculture and waterbird conservation.

The present study evaluated productivity under different operational (optical) conditions using the unicellular alga Nannochloropsis sp. (Eustigmatophyta). This alga is often grown in mass algal cultures because it contains high contents of the polyunsaturated fatty acid, eicosapentaenoic acid (EPA, 20:5ω3). We followed biomass, photosynthetic activities and physiological parameters in a 3 d experiment using various photosynthesis techniques in 2 outdoor cultivation systems: a flat panel photobioreactor (FPP) and a high rate algal pond (HRAP). We aimed to detect acclimation behaviour to the different optical conditions, with the FPP having a short light path and the HRAP having a long light path. Both algae cultures showed an afternoon depression of photosynthetic activity, which was more pronounced in the FPP. Therefore, the HRAP culture showed 'classical' shade adaptation behaviour, whereas the FPP algae was high-light acclimated. The FPP showed diurnal changes in the potential rates of photosynthesis and respiration. High temperatures (41°C) on Day 3 in the FPP caused a large reduction in the maximum Photosystem II (PSII) efficiency (F v /F m ) and an over-reduction of the PSII acceptors, which did not recover during the light period. Chlorophyll fluorescence measurements with and without dark adaptation suggested that the decreased photosynthetic activity was due to both chronic and dynamic downregulation. Photodamage was higher in the FPP, but most was recovered during the evening. A comparison between the quantum efficiencies for PSII charge separation and oxygen evolution revealed a close coupling between the 2 processes. We also concluded that the optical absorption cross section of PSII equalled 75% of the total absorption cross section.

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