ASTRAL New value chain at IMTA lab South Africa D2.4

This deliverable was created as part of the WP2 ‘New IMTA value chains and production methods’ of the H2020 All Atlantic Ocean Sustainable, Profitable and Resilient Aquaculture (ASTRAL) project and deals with the production value chain of IMTA Lab South Africa (Figure 1; adapted from Bostock et al.1). Other aspects of the value chain are addressed in investigations and reports compiled by other Work Packages in ASTRAL (see ASTRAL deliverables 4.1, 4.4, 6.3, 7.7, etc.). The deliverable provides information on all the trials undertaken for each of the species produced or introduced at IMTA Lab South Africa.
The overall objective of IMTA Lab South Africa was to develop and validate cost-effective IMTA in land-based pump ashore systems with partial recirculation. To achieve this objective, the physical and chemical parameters as well as the microbial community of an existing fully commercial abalone (Haliotis midae)-Ulva lacinulata IMTA system was monitored to provide critical information on biosecurity, species health and system health. The possibility of increasing recirculation rates in the existing IMTA, from 50% to 75% and 100% recirculation, was also investigated. Culture technology for the production of a new high value species, the collector sea urchin Tripneustes gratilla, was developed and optimised in IMTA, and potential for using faecal matter from the Cape sea urchin Parechinus angulosus as a feed/probiotic for juvenile abalone was investigated.
Clear daily rhythms in oxygen, pH, temperature, and nutrients were observed in the integrated abalone-Ulva IMTA. Daytime temperatures and passage of effluent water through Ulva paddle raceways in the IMTA results in warming and increased oxygen in the daytime. Seawater pH was shown to be higher in the day than at night, with maximum dissolved ammonia nitrogen concentrations observed early in the morning (due to the great metabolic activity of abalone at night) — with a strong negative correlation observed between FAN removal and pH. At standard 50% recirculation, total ammonia nitrogen removal across the seaweed biofilters ranged from 65-85% (mean 73%). Total ammonia nitrogen (TAN) and FAN levels were consistently low at 50% recirculation (<1 mg.L-1), variable at 75% recirculation (<1 to >3 mg.L-1) and high (6 mg.L-1) at the end of the 3-day 100% recirculation trial. There were no significant differences between the 50% and 75% recirculation clusters for temperature, pH, TAN or FAN. At 100% recirculation, temperature was consistently 1°C higher in the daytime, and pH was around 1 unit lower throughout. Also at 100%, TAN and FAN increased rapidly. Data indicated that the IMTA could feasibly run for extended periods at 75% recirculation, with relatively little effect on water quality compared with 50% recirculation. Although no adverse health effects were observed on the abalone when the system was run at 100% recirculation for 3-days, ammonia reached critical levels (from literature values) on the third day. The lack of obvious effects on the abalone suggests there is potential to use Ulva’s bioremediation capacity to mitigate the effects of harmful algal blooms over at least 2-3 days of a bloom event.
The microbiome studies revealed that the inclusion of Ulva in IMTA systems results in beneficial changes in the microbiome of water and farmed abalone by reducing the presence of opportunistic pathogens. When assessing the bacterial community dynamics with increasing recirculation rates, the taxonomic composition of the samples varied across sampling points, suggesting that recirculation at higher rates (50%, 75% & 100%) has an effect on the microbiome composition, but does not result in an increase in opportunistic bacteria. Inclusion of Ulva or components of Ulva in formulated feeds for farmed abalone was shown to have a beneficial effect on the abalone gut microbiome, reducing abundance of opportunistic bacteria, with a corresponding increase in beneficial bacteria. Investigations to assess the use of faecal matter from the Cape sea urchin Parechinus angulosus as a feed/probiotic for juvenile abalone revealed that supplementing juvenile abalone diets with sea urchin faecal matter is advantageous for abalone growth and health in their early juvenile stages, possibly as a result of microbial community transfer from the sea urchins.
Trials to optimise culture technology of the collector sea urchin Tripneustes gratilla revealed that deeper baskets result in significantly lower consumption of various feed types — likely the consequence of lower feed accessibility. Furthermore, removal of urchin baskets from tanks for extended periods (5-minutes) or feeding rigid feed types (e.g., E. maxima) results in increased spine loss, suggesting consumption and removal of baskets for extended periods are the primary cause of decreased production in deeper baskets. While higher stocking densities (8 kg.m-2) significantly reduced mass SGR (P<0.044), urchin mortality, cannibalism and gonad size/quality were not influenced at lower stocking densities tested (4 and 6 kg.m-2). Differences in SGR are attributed to spine loss from negative behavioural interactions. To maximise total urchin mass and gonad yield, stocking densities of approximately 20% coverage of the internal surface area of baskets are recommended. Trials showed that it is possible to feed urchins fresh IMTA grown Ulva during the somatic growth phase, and that feeding with protein rich formulated feeds is only required during the gonad enhancement phase to bulk gonads prior to market. To further streamline production and reduce stress on cultured urchins, a computer vision protocol was developed that significantly increases the precision and decreases the time required for estimating average urchin diameter and mass in a commercial setting. Trials further concluded that careful consideration must be made with regards to site selection when farming T. gratilla, as hypo-saline conditions (<30 ppt) increase stress and reduce disease resistance of this species. Therefore, sites located close to estuaries where salinities are either periodically or frequently impacted by rainfall events should be avoided.
In conclusion, trials at IMTA Lab South Africa have provided valuable information on the biosecurity, species health and system health of the existing abalone-Ulva IMTA with 50% recirculation. Critical information on the physical and chemical parameters as well as the microbial community of the IMTA was generated that could promote broader uptake of IMTA by local and international producers and enhance the sustainability of this production species/value chain. Culture technology for commercial scale production of a new high value species, the collector sea urchin Tripneustes gratilla, in IMTA has been development and further optimised, and the benefits of using faecal matter from the Cape sea urchin Parechinus angulosus as a feed/probiotic for juvenile abalone has been clearly demonstrated — resulting in enhanced growth and health of juvenile abalone. These findings have contributed towards the development of new, sustainable, profitable, and resilient value chains for IMTA production within the ASTRAL project and within the framework of existing, emerging and potential Atlantic markets.

Figure 1. Shaded area indicates the section of the aquaculture production value chain covered by IMTA Lab South Africa.