Abstract
Two distinct climatic seasons in the tropics generate extreme environmental fluctua- tions in land-based aquaculture and corresponding challenges for integrated aquaculture. Here we assessed the influence of environmental and culture variables on productivity of Cladophora coelothrix at multiple scales, firstly in an operational settlement pond and subsequently in labora- tory and flow-through mesocosm experiments. Classification and regression tree (CART) analyses were used to partition the influence of key variables on growth. In situ productivity correlated pri- marily with nitrogen concentration, position in the pond and stocking density, with a lesser influ- ence of salinity, temperature and the ratio of nitrate-nitrogen (NO3 � -N) and total ammonium nitro- gen (TAN). We subsequently evaluated the resilience of C. coelothrix in laboratory and mesocosm environments by manipulating salinity, temperature and nutrients across a broader range of val- ues derived from a year-long survey of the settlement pond. Here temperature had the greatest influence on growth, followed by nitrogen concentration and salinity. Growth rates of C. coelothrix were high, irrespective of season, except at the extremes of each season, for example, at the lowest annual temperature and with the combination of high temperature and low salinity. Growth was also limited by ~20% when NO3 � -N and TAN were available simultaneously. The use of CART analyses for both in situ and controlled environment data provided a formal dissection of the relative contribution of each environmental variable to growth, demonstrating the year-round potential for bioremediation and identifying the critical combinations of environmental variables for management of this system.
Highlights
High levels of inorganic nutrients are present in many anthropogenically impacted environments, including intensive aquaculture (Sarà 2007, Lin & Fong 2008, Abreu et al 2009)
One pathway for the selection of algae for biomass applications in integrated aquaculture is to utilise species that already exist and opportunistically bloom in aquaculture facilities, including green tide algae. In order for these species to be truly integrated, and become a reliable and commercial source of biomass, it is essential to understand the influence of seasonal changes in environmental conditions on growth, biomass yield and bioremediation potential
We demonstrated that the green tide alga Cladophora coelothrix is tolerant to the concurrent and extreme seasonal fluctuations in temperature, salinity, nitrogen concentrations and sources that are characteristic of tropical land-based aquaculture
Summary
High levels of inorganic nutrients (nitrogen and phosphorus) are present in many anthropogenically impacted environments, including intensive aquaculture (Sarà 2007, Lin & Fong 2008, Abreu et al 2009). This recent emphasis on high-productivity biomass for integrated aquaculture is warranted given a new focus on algal biomass for diverse and innovative bioenergy applications, such as biocrude (Zhou et al 2010) and biochar (Bird et al 2011, 2012) It is unclear, how characteristics unique to tropical land-based aquaculture, in particular monsoonal fluctuations in temperature and salinity with high nitrogen concentrations present in multiple sources (ammonium and nitrate), will influence year-round productivity of green tide algae. Nitrogen source is a driver of productivity, as ammonium can inhibit nitrate uptake even at low concentrations (see Dortch 1990 and Raven et al 1992 for comprehensive reviews) These examples demonstrate the need to understand species-specific responses to interactions between key factors under environmental conditions relevant to land-based aquaculture in order to optimise algal productivity and bioremediation and to produce a reliable supply of biomass
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