A meta-analysis of integrated multitrophic aquaculture: extractive species growth is most successful within close proximity to open-water fish farms

Fish farming in open water releases dissolved and particulate waste (inorganic and organic) into the surrounding marine environment. To reduce this environmental impact, commercial extractive species can be grown alongside to utilize and reduce this waste, a technique known as integrated multitrophic aquaculture (IMTA). Information is lacking on whether (i) IMTA is generally successful with respect to extractive species growth responses and (ii) at what spatial scale they can be cultivated from fish cage nutrient sources. Focussing on bivalves and macroalgae as extractive species, this study uses a meta-analysis approach to summarize and conclude peer-reviewed data on IMTA to address these information gaps. We show that there are clear benefits to integrating bivalves and macroalgae with fish farms. Bivalves grown within, and relatively near, fish cages (0m and 1-60m distance categories, respectively) showed significantly higher biomass production relative to controls compared to those grown at larger spatial scales (61+m). However, biomass production of macroalgae was significantly higher than controls only within close proximity to fish cages (0m). This information shows increased extractive species production is generally greatest at relatively small spatial scales. It also highlights the need for more site-specific information (e.g. seawater parameters, hydrodynamics, food supply, farm capacity) in future studies. The allocation of control sites and locating these at suitable distances (>1-8km) from fish farm effluent sources to avoid fish farm nutrient contamination are also recommended.