“Green caviar” and “sea grapes”: Targeted cultivation of high-value seaweeds from the genus Caulerpa – Progress Report

Progress report on the Australian Flora Foundation funded project:

Nicholas Paul, Rocky de Nys and Symon Dworjanyn
School of Marine & Tropical Biology, James Cook University, Townsville Qld 4811
Progress report 1/1/10

The project aims to identify edible seaweeds from the tropical and sub-tropical coastline of eastern Australia for potential commercial production. The project has three main components: 1) collection and acclimation of the sea grape varieties, 2) taste evaluation by restaurants and other relevant entities, and 3) targeted cultivation of varieties based on taste test results. This work has so far identified and collected 5 species of Caulerpa (sea grapes) from eastern Australia and successfully propagated two of these for extended periods in culture. Product packaging methods and microbial analyses indicate suitable shelf-life periods and show promise for the commercial viability of the different sea grapes. The next task in 2010 is the formal taste experiment, which will provide sufficient data for publication as well as direction for the cultivation of specific varieties and traits.

1) Collection and acclimation
All species of Caulerpa identified in the proposal (C. lentillifera, C. racemosa var laetevirens, C. racemosa, C. geminata, C. hodgkinsoniae) have been sourced. However, seasonal difference in biomass and inter-annual variation have meant that some species have been propagated for use in the taste test whereas others must be collected for immediate use.

We have successfully adapted our previous propagation techniques for Caulerpa lentillifera to C. racemosa var laetevirens. This means that at least two sea grape varieties can be propagated (harvest with re-growth) in tank-based aquaculture. However, Caulerpa racemosaconsistently reaches sexual maturation before sufficient biomass per unit area is achieved, resulting in the loss of all viable biomass after gametes are expelled. Furthermore, Caulerpa geminata from Coffs Harbour has been temperamental in culture, growing poorly after winter collections. Both C. racemosa and C. geminata will be collected from the wild in summer 2010 and acclimated briefly prior to use in the taste test. C. hodgkinsoniae was not abundant in 2009 and collected individuals had poor growth. For this reason it will no longer be considered in the project.

2) Taste evaluation
Before the taste test could be conducted, the method of harvest, type of packaging and the absence of food pathogens and harmful bacteria were assessed for the two species available after propagation, Caulerpa lentillifera and C. racemosa var laetevirens.

i) Packaging: The packaging materials and shelf life of the new products are important for the commercial viability of the food. Post-harvest regimes indicated that picked fronds (edible portions of the algae) were more viable than whole plants. The fronds maintained their structural integrity and their vitality, the latter assessed using measurements of yield from pulse amplitude modulated (PAM) fluorometry. Using a short post-harvest healing time (<24 hours) and packing picked seaweed into containers with absorbent spun-bonded polyethylene pads (used in meat packaging) allowed shelf life to extend beyond 3 days, the milestone required for taste tests.

ii) Microbial analysis: Common food pathogens have been conducted by Department of Primary Industries QLD NATA-accredited food laboratory in Cairns. These assays (n=2) indicated that there were no detectable Listeria or Salmonella, E. coli was <3/g, and Staphylococcus spp. were <10/g sample. Furthermore, each seaweed species used in the taste test will be analysed immediately prior to the test.

iii) Taste test: The formal comparison of taste using subjects from different restaurants in various cities can now proceed with the packaging and microbial analyses finalised. This taste assessment will be completed early in 2010, providing sufficient time for data analysis and interpretation before proceeding with cultivation steps. These data will provide the basis for the first publication of the grant.

3) Cultivation
Propagation of select species and morphologies will comprise the remainder of the grant.

4) Other Developments
A final development is that our (Paul & de Nys) original work on green caviar (Caulerpa lentillifera) has contributed to the recent formation of the first Australian seaweed aquaculture company, South Pacific Seaweeds. We are optimistic that the subsequent taste test and information generated on the new sea grape varieties in the remainder of the AFF grant will provide additional opportunities for commercialisation of these new varieties.