Integration of abalone and sea cucumbers in IMTA systems: growth and bioremediation potential.
In order to develop land based IMTA production systems integrating exclusively low trophic species experiments performed as part of the INTEGRATE project, at the IU-ECOAQUA Institute of the University of Las Palmas de Gran Canaria, tested the integrated production of Haliotis tuberculata coccinea, Holothuria sanctori and two species of algae (Ulva rigida and Gracilaria cornea. The studies contributed to determine the adequate biomass of abalone required to provide a food source suitable for sea cucumbers grow out, to determine the amount sediment ingested by the cucumbers and to establish their bioremediation potential in such IMTA production systems.
Two assays were performed at different scales to first estimate abalone faeces production and sea cucumber ingestion and defecation rate and to test their acceptability at pilot scale to estimate the production potential of abalone and sea cucumbers in land based IMTA systems.
During the first assay performed in triplicate in 100 liters tanks, each replicate contained 50 abalone with a total biomass of 717±14 grams, 3 small sea cucumbers with an average weight of 13.09± 0.68 grams and 3 medium size sea cucumbers with an average weight of 22.67±1.39. grams
Sea cucumbers were fed daily, during 15 days, with 15 gr of abalone feces. to estimate sea cucumbers ingestion rate. Sea cucumber faeces and leftover abalone faeces were daily collected weighed on a precision balance and dried in an oven for 48 hours until reaching constant weight to estimate their dry weight and determine sea cucumber ingestion and defecation rates.
Abalone were fed during 15 days on a mixed diet of algae Ulva rigida and Gracilaria cornea (at 28% of their weight) and compound feed (at 2% of their weight).
Faeces were daily collected, weighed on a precision balance and dried in an oven for 48 hours until reaching constant weight to estimate their dry weight and abalone defecation rate.
During the second assay performed in triplicate, in pilot scale 300 liters integrated production systems, each replicate contained abalone with a total biomass of 995±0.33 grams per tank and 1 small sea cucumber with an average weight of 12.08± 0.34 grams together with a medium size sea cucumber with an average weight of 20.37±1.47 grams. Abalone were daily fed at 2% of their weight with compound feed and at 30% of their weight a mixture of Ulva rigida and Gracilaria cornea.
To estimate sea cucumber defecation rate sea cucumber feces were daily collected during 15 days. In the case of abalone feces, they were collected once a week, to ensure enough feeding material remained available to the sea cucumbers. Sea cucumbers and abalone feces were weighed on a precision balance and dried in an oven for 48 hours until reaching constant weight to estimate their dry weight.
Ingestion rate (IR), defecation rate (FPR) and growth performance (SGR & WG) were estimated according to the following formulas:
IR (mg/g/h) = ((Wo − _Wu) / Wsc) / t
Where Wo is dried weight of the offered food (mg), Wu is dried weight of the remaining food (mg), Wsc is the wet weight of the sea cucumber in the tank (g), and t is the duration of the experiment (h).
FPR (mg/g/h) = (Wf / Wsc) / t
Where Wf is dry weight of the faeces (mg), Wsc is wet weight of the sea cucumber or abalone in the tank (g), and t is duration of the experiment (h).
WG (%) = 100 * (Wf − _Wi) / Wi
SGR (%.day-1) = 100 * (lnWf − _lnWi) / number of days
Where Wi is the initial wet weight (g) and Wf is the final wet weight (g).
Significant differences in ingestion rates were observed between small and medium size sea cucumbers while their defecation rates were similar independently of their sizes.
At pilot scale, sea cucumbers ingestion and defecation rates observed sustained the ones observed during the first assay indicating their soundness to be applied and taken into account for larger scale integrated production of these species.
Growth performance of Holothuria sanctori specimens varied according to their initial size; being higher for smaller specimens as previously observed in other studies; and overall was within the range of growth performance observed for other species of sea cucumbers produced using mollusks refuse.
Overall, the integration of sea cucumbers to abalone production units in land-based IMTA systems did not affect abalone growth potential. These results highlight the interesting potential of the two species integration for future production in IMTA systems.