Analysis of algal growth- and morphogenesis-promoting factors in an integrated multi-trophicaquaculture system for farming Ulva spp.. Water Microbiome characterization of Ulva aquaculture tanks in the lagoon of Aveiro (PT)

The marine green macroalgal genus Ulva (Chlorophyta) requires the presence of acombination of regulatory morphogenetic compounds released by their associated epiphytic bac-teria in addition to nutritional parameters. The activity of algal growth- and morphogenesis-promoting factors (AGMPFs) derived from bacteria was determined in a land-based integratedmultitrophic aquaculture (IMTA) system of fish and macroalgae (located at the coastal lagoon Ria de Aveiro, Portugal) using a standardised bioassay with axenic cultures of Ulva mutabilisduring a snapshot study. The study thus informs aspects of various potential aquaculture−environment interactions. It was observed that both the water from the lagoon (external to the farm system) and the water from the fish pond (input for algae cultures) could completely restorethe normal growth and morphology of the macroalga under axenic conditions. The results high-light the presence of a sufficient chemical cocktail of AGMPFs in this IMTA system required forgrowth and morphogenesis of the sea lettuce Ulva spp. In addition, the water from fish farmingincreased the nutrient availability (nitrate and ammonium) needed for macroalgae production atlow concentrations of metal contaminants. Interestingly, the abundances of known morphogene-sis-inducing bacteria (e.g. Maribacter mutabilis, Sulfitobacter spp.) were enriched in the Ulvaaquaculture water compared to the water from the lagoon. We thus conclude that sustainablegrowth and development of Ulva spp. can benefit from multitrophic aquaculture systems andshallow-water systems, due to the naturally enriched AGMPFs and their in situproduction bybacteria in intensive algal aquacultures.