Ecological and economic assessment of the role of seaweeds in abalone integrated multi-trophic aquaculture - a South African case study.
Abstract South Africa (SA) is the world's third largest abalone producer. The industry is now challenged by restrictions on access to wild kelp, which is the natural food for abalone. Abalone farmers in SA have recently begun implementing integrated multi-trophic aquaculture (IMTA) with the seaweed Ulva lactuca L. and the abalone Haliotis midae L. The positive aspects include: (1) better abalone growth when fed with mixed algae diet, (2) farm effluent reduction, (3) avoidance of contaminated seawater during red tides/oil spills, (4) promoting employment in rural coastal communities. This case study presents a quantification exercise that compares the ecological-economic costs/benefits associated with the seaweed-culture integration into the abalone industry. Data from an abalone farm from the Western Cape with annual production of 240 metric tonnes (MT) was used. The ecological-economic performance of abalone production in monoculture using a water flow-thorough system was compared against two IMTA scenarios, with water recirculation through a seaweed culture unit that replaces part of the wild kelp consumption. The comparison of monoculture with IMTA scenarios indicates an overall economic gain of between 1.1-3.0 million US$ per year. This range of values reflects the effects of adopting IMTA on the farm's profit and the environmental gains, which represent 80% of the estimated overall benefits and includes: avoided kelp bed restoration, reduced nutrient discharge and avoided greenhouse gas emissions (due to energy savings). This analysis is particularly important in informing the SA industry and regulators about the value of the implementation by the abalone farmers of IMTA systems. For this particular case study the message is that the IMTA approach provides substantial economic incentives to the abalone farmers and even larger benefits to the public, compared with the abalone monoculture production.