The effect of swine wastewater on the ecophysiology and stoichiometry of two opportunistic macroalgae

Abstract

The effects of swine wastewater stream of high salinity, ammonia, and organic nutrients collected from a pig farm located in Cyprus on the growth, photosynthetic performance and tissue content (C, N, and P) on two macroalgae (Cladophora sp. and Gracilariopsis longissima) were studied. Two functional indices, the effective quantum yield of photosystem II (ΔF/Fm) and the relative growth rate (RGR, day‐1 ), under constant laboratory conditions (21°C ±1°C, 33.2‐34.5 PSU, 70 μmol photons m‐2 s ‐1 , 14h light per day), after 9 days cultivation were examined. Various experiments with media renewal and measurements on a daily basis were performed using dilutions from 1/20 to 1/500 (sewage:seawater). The results were analyzed performing factorial or repeated two‐way ANOVA. The two species responded significantly different to the effluents with Cladophora sp. showing a better performance than Gracilariopsis longissima in higher effluent concentrations. The limit to perform was on dilution 1/40 for Cladophora sp. and 1/100 for G. longissima. Mean tissue nitrogen content ranged from 7 to 17% (dry weight) and from 7 to 10 % N for Cladophora sp. and G. loingissima, respectively. Maximum N values estimated for Cladophora sp. (17%) at dilution 1:80 and for G. longissima (10%) at dilution 1:400. The N:P ratio between the species’ tissue had no statistical differences, whereas, it was significantly different based on their interaction with the different dilutions. Tissue C content showed no statistical difference amongst the two species and the different dilutions.