Diversifying native crop options for Pacific oyster farms in New Zealand: Creating sea gardens for food, medicine and restoration

Abstract

The research presented in this thesis illustrates the process in exploring opportunities for diversifying crop options for the Pacific oyster aquaculture industry in New Zealand. This included an investigation of the potential for coculture of the snail, Lunella smaragdus, with Pacific oysters in baskets, by examining the possible reduction of biofouling of baskets, as well as improvements in survival and condition of oysters, and the growth and survival of the snails. The research also investigated the potential for native bivalve species (Paphies australis, pipi; Austrovenus stutchburyi, cockles), New Zealand sea cucumber (Australostichopus mollis) and seaweed (Hormosira banksii, Neptune’s necklace) as alternative commercial crop options to utilise oyster culture infrastructure left vacant following the loss of the oysters due to OsHV-1 μVar mass mortality episodes. The experiments were conducted on Pacific oyster farms in the Mahurangi and Kaipara Harbours in northern New Zealand operated by Biomarine Ltd. Coculture experiments were conducted with different starting snail biomass and sizes that also varied in relation to the plastic mesh size of the oyster aquaculture baskets. The oyster baskets supported a small number of snails, at 42 g biomass per basket. While not commercially viable as a crop, the snails reduced biofouling (p < 0.001, at 466 days of coculture). Snail treatment did not have a negative impact on oyster survival and growth but had a moderate effect on oyster meat condition (low and high starting snail biomass, M = 4.2 %, SE ± 0.1 and M = 4.3 %, SE± 0.1, respectively), which was higher compared to controls (M = 3.8 %, SE ± 0.1, p =0.005). The potential for the coculture of pipi, cockles, sea cucumber and Neptune’s necklace on the Pacific oyster farms were assessed experimentally, by investigating their growth and survival at different densities, and with Neptune’s necklace, assessing the potential yield of fucoidan. The bivalves had moderate survival but slower growth than in the wild. Pipi: M = 95.4 %, SE ± 2.3; 308 days; cockles: Mahurangi: > 98 %, 93 days and M = 46 - 78 %, 376 days; Kaipara: 88 – 100 %, 89 days). Sea cucumbers grown at high starting biomass showed moderate growth M = 10.6 g (SE ± 5.2, p =0.018) but did not survive beyond 73 days. The oyster baskets were not suitable for seaweed culture (200 and 149 days. However, fucoidan yield was comparable to commercial yield from other species (0.38 -0.77 % of wet biomass). Coculturing other native marine species to those examined in this current study, which are capable of utilising resources at different trophic levels to oysters, may contribute to more efficient use of the farm infrastructure and available nutrients, while potentially having a positive impact on the environment. This would also provide more economic security for farmers through diversifying their crop portfolio. Identifying and assessing the suitability of new species for aquaculture development is complex and challenging, and this thesis addresses the necessary questions that form the foundation to inform further development of native species with potential for culture on Pacific oyster farms in New Zealand.