Analysis of algal growth- and morphogenesis- promoting factors in an integrated multi-trophic aquaculture system for farming Ulva spp.

Abstract

The marine green macroalgal genus Ulva (Chlorophyta) requires the presence of a combination of regulatory morphogenetic compounds released by their associated epiphytic bacteria in addition to nutritional parameters. The activity of algal growth- and morphogenesis-promoting factors (AGMPFs) derived from bacteria was determined in a land-based integrated multitrophic 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 mutabilis during 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 restore the normal growth and morphology of the macroalga under axenic conditions. The results highlight the presence of a sufficient chemical cocktail of AGMPFs in this IMTA system required for growth and morphogenesis of the sea lettuce Ulva spp. In addition, the water from fish farming increased the nutrient availability (nitrate and ammonium) needed for macroalgae production at low concentrations of metal contaminants. Interestingly, the abundances of known morphogenesis-inducing bacteria (e.g. Maribacter mutabilis, Sulfitobacter spp.) were enriched in the Ulva aquaculture water compared to the water from the lagoon. We thus conclude that sustainable growth and development of Ulva spp. can benefit from multitrophic aquaculture systems and shallow-water systems, due to the naturally enriched AGMPFs and their in situ production by bacteria in intensive algal aquacultures.