SEAPAID · Seagrass production and isotopic discrimination

Final Activity Report Summary - SEAPAID (Seagrass production and isotopic discrimination)

Experimental work field: - field site selected within Cadiz bay natural park (3 stations selected along a transect of tidal height [deep subtidal to intertidal]. Monitoring environmental variables: - bimonthly measurements of water column nutrient concentrations; - bimonthly measurements carried out within 1 km of the field site by the local management agency (Junta Andalucia) of water column; nitrogen, phosphate, oxygen, chlorophyll, total suspended solids concentrations, temperature, salinity and pH; - continuous measurements of temperature and irradiance at each of the field stations initiated 2006. Seagrass demography and growth: - bimonthly measurements of seagrass (Cymodocea nodosa and Zostera noltii) biomass, morphology and growth. Tissue nutrient and isotopic content and enzymatic activities: - bimonthly measurements of seagrass tissue (C. nodosa and Z. noltii) carbon and nitrogen content; - bimonthly measurements of seagrass tissue (C. nodosa and Z. noltii) d13C and d15N. d13C and d15N of intertidal vs subtidal seagrass populations; - carried out as part of the bimonthly field sampling, i.e. three stations selected along a transect of shore height; - large scale survey carried out in June 2006, stable isotope ratios are still pending, however plan to relate d13C values to growth and ecophysiology of populations inhabiting subtidal and intertidal areas monitor d15N of seagrass leaves along a natural eutrophication gradient; - initial linking between seasonal changes in water column [N] (presumed to indicate anthropogenic inputs) and seasonal changes in seagrass d15N ratios; - large scale survey carried out in June 2006, mapped macrophyte density within a 25 km2 area, samples collected for stable isotopes (results pending). Expect d15N values to be related to distance from anthropogenic (aquaculture) N source; - samples of macroalgal species were collected from a number of areas within the Cadiz Bay region (separated by approx 10 km). Samples analysed for d13C and d15N ratios. Data processed and used as part of Msc. thesis. Effect of environmental variables on seagrass photosynthesis, growth and isotopic discrimination (Laboratory); - investigation into the effect of water flow on the photosynthesis of single seagrass leaves. Description of how the changing boundary layer thickness over single seagrass leaves of two species (Z. marina and C. nodosa) influences the assimilation of carbon and nitrogen. A novel oxygen microelectrode setup and flow chamber were designed and used to measure net and gross photosynthesis as well as respiration within the light at different water flow velocities. Carbon and N assimilation were also simultaneously measured using stable isotope enriched tracers. Experiment completed May 2006, isotope results pending. - investigation into the effect of water flow on the ammonia uptake of a seagrass meadow. Using a flume tank, ammonia uptake within seagrass (C. nodosa and Z. noltii) meadows, was investigated at a range of flow velocities. Particular attention was paid to investigating the possibility of spatial differences in uptake within the meadow in relation to distance from the leading edge. Experiment completed October 2005, all data processed and presented at international conference (ISBW2006-Zanzibar) and submitted for publication in an international peer reviewed journal. Field manipulative experiments; - in-situ N assimilation and transfer between shoots of Z. noltii. A series of seasonal (four times per year) experiments were carried out to measure rates of N assimilation in-situ and the fate of assimilated N. Of particular focus was the role of apical dominance in resource transfer between shoots and how this changes during different seasons. Isotope results pending.

Data: CORDIS, © European Union