Co-culture of sea cucumber Holothuria scabra and red seaweed Kappaphycus striatum

Abstract

Commercially valuable sea cucumbers are potential co-culture species in tropical lagoon environments, where they may be integrated into established aquaculture areas used for seaweed farming. In the current study, wild-caught juvenile sea cucumbers, Holothuria scabra, and red seaweed Kappaphycus striatum were co-cultured on Zanzibar, United Republic of Tanzania. Sea cucumbers (97 g AE 31 SD, n = 52) were cultured in mesh enclosures at initial cage stocking densities of 124 AE 21 SD and 218 AE 16 SD g m À2 under seaweed culture lines. Over 83 days, individual growth rate (1.6 g d À1 AE 0.2 SD) of sea cucumbers at low stocking density was significantly higher (v 2 = 8.292, d.f. = 1, P = 0.004) than at high-stocking density (0.9 g d À1 AE 0.1 SD). Seaweed individual growth rates [6.27 (AE0.3 SE) g d À1 ] were highest in co-culture with sea cucumber at low density but did not differ significantly from high sea cucumber density or seaweed monoculture treatments (v 2 = 3.0885, d.f. = 2, P = 0.2135). Seaweed growth varied significantly (v 2 = 35.6, d.f. = 2, P < 0.0001) with sampling period, with the final sampling period resulting in the highest growth rate. Growth performance for seaweed and sea cucumbers (v 2 = 3.089, d.f. = 2, P = 0.21 and v 2 = 0.08, d.f. = 1, P = 0.777 respectively), did not differ significantly between monoculture and co-culture treatments, yet growth in co-culture was comparable with that reported for existing commercial monoculture. Results indicate H. scabra is a highly viable candidate species for lagoon co-culture with seaweed. Co-culture offers a more efficient use of limited coastal space over monoculture and is recommended as a potential coastal livelihood option for lagoon farmers in tropical regions.

Growth performance of the sea cucumber Holothuria scabra and the seaweed Eucheuma denticulatum: integrated mariculture and effects on sediment organic characteristics

“…Similar results were obtained by Uthicke (2001) and Wolkenhauer et al (2010), who observed that sea cucumbers enhance productivity of primary producers through their burrowing and nutrient recycling activities. In contrast to Beltran-Gutierrez et al (2014), where a low stocking density (154 g m −2 ) of H. scabra yielded higher growth rates of Kappaphycus striatum than either a density of 200 g m −2 or an absence of sea cucumbers, in the current study higher stocking densities of H. scabra (200 and 300 g m −2 ) resulted in the highest growth grates of E. denticulatum. Potential reasons are discussed in the section on the effect of stocking density below.…”

“…For example, co-culture of H. scabra with shrimp Litopenaues stylirostris is not viable and survival of H. scabra in such a system has been observed to be very low (Bell et al 2007). On the other hand, in an integrated system of the seaweed K. striatum and H. scabra, seaweed did not appear to have a negative effect on sea cucumbers (Beltran-Gutierrez et al 2014).…”

“…Twenty fully enclosed cages (1.5 × 1.5 × 0.5 m, L × W × H) were constructed using a 10 mm polyethylene oyster mesh (roof and walls), wood stakes, cable ties and 4 mm nylon ropes following the design described in Beltran-Gutierrez et al (2014). The cages were installed 300 m from the shoreline, where the lowest water level at spring low tide ranged between 0.2 and 0.5 m, and pushed 0.25 m into the sediment.…”

“…Eucheuma denticulatum was planted inside the cages using the off-bottom method, which is commonly used for seaweed farming in Zanzibar (Neish 2003, Fröcklin et al 2012, Msuya & Salum 2012, Beltran-Gutierrez et al 2014. Healthy fronds of seaweed weighing 25 ± 2 g (mean ± SD) were tied onto a 4 mm rope with 1 mm string (tie−tie), maintaining a distance of 20 cm between fronds.…”

“…The optimization of seaweed-sea cucumber integrated systems requires establishment of stocking densities that can yield optimum growth of culture species and best utilise potential nutrient flow synergies between species (Agudo 2006, Li & Qi 2010. Following the design of a previous study that integrated K. striatum and H. scabra in Zanzibar (Beltran-Gutierrez et al 2014), the current study extends research knowledge to the use of Eucheuma denticulatum, a much more widespread seaweed species in Zanzibar and apparently more resistant to environmental conditions than Kappaphycus (Hayashi et al 2010, Msuya 2011b, Msuya & Porter 2014. A wide range of stocking densities (without sea cucumbers, low, medium, high) is applied in order to better understand trade-offs and limiting capacities with different densities and effects on organic matter content in sediments.…”