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National Committee on Marine Sciences (NCMS)

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Author: search.filters.author.Caasi, Olivier Josh C.Ocean Decade Challenge: search.filters.odc.Challenge 3: Sustainably feed the global population

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    Size-dependent predation on juvenile sandfish, Holothuria scabra by seagrass-associated crabs
    Caasi, Olivier Josh C.; Gosselin, Louis A.; Juinio–Meñez, Marie Antonette (Cambridge University Press, 2023-10-23)
    High mortality of juvenile Holothuria scabra in seagrass nursery areas has been attributed to predation. In this study, laboratory and field experiments were conducted to determine the effect of the size of two seagrass–associated crabs, Thalamita crenata and Dardanus megistos, on the survival of juvenile sandfish at different sizes (1–10 g). Small juvenile sandfish (1–2 g) offered in field trials were more preferred by small Thalamita and large Dardanus. Non-lethal damage caused by both crabs were also evident, indicating differences in the mode of attack and consumption. The incidence of non-lethal wounds in medium and large juveniles in the laboratory indicate higher incidences of unsuccessful attacks by the crabs. Differences in consumption rate may be related to cheliped morphology and handling techniques, and activity patterns affecting encounter rates. Mortality rates of juvenile sandfish due to T. crenata (CW: 4.30–7.05 cm) ranged from 10–43%, while those by D. megistos (SL: 0.90–2.3 cm) was even higher at 34–53% after 24 h trials. This is the first report that a hermit crab D. megistos is a significant predator of juvenile sandfish. Results provide new insights on crab–soft-bodied prey interactions in tropical seagrass areas. These are also important considerations in stock restoration and ocean-based culture. Given that juveniles (≤10 g) are very vulnerable to predation by these common crab species, growing sandfish to larger sizes is essential prior to release in the field.
    This study was funded by Australian Centre for International Agricultural Research (ACIAR) through the project FIS/2016/ 122 ‘Increasing technical skills supporting community–based sea cucumber production in Vietnam and the Philippines’ and administrative support from the Marine Environment and Resources Foundation (MERF), Inc. We are grateful to the Bolinao Marine Laboratory of the University of the Philippines Marine Science Institute for the use of facilities and equipment. Special thanks to Tirso Catbagan, Garry Bucol, and Tomilyn Jan Garpa for their assistance with field and laboratory work. We also thank JayR Gorospe and Jerwin Baure for comments on the draft versions of the manuscript.
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    Metamorphic success and production cost of Holothuria scabra reared on microalgae concentrates compared with live microalgae
    Garpa, Tomilyn Jan; Caasi, Olivier Josh C.; Juinio–Meñez, Marie Antonette (Bureau of Fisheries and Aquatic Resources, 2024-03-07)
    The production of live microalgae poses challenges for the expansion of sandfish hatcheries, hindered by high costs and limited technical resources. In relation to this, the use of three imported commercial concentrates (Instant Algae®) - TW1200 (Thalassiosira weisflogii), TISO1800 (Isochrysis sp.), and Shellfish1800 (mixed diatom) - were compared with live Chaetoceros calcitrans (CC). The diet efficacy was evaluated based on larval development, growth, and survival to late auricularia (LA) with hyaline spheres (HS), and the number of post-settled juveniles. Larvae reared with TW did not progress beyond LA, while those fed CC exhibited earlier LA development, larger sizes (1028.43 ± 19.38 µm), and significantly more post–settled juveniles (9,268 ± 2,183.79) compared to SHELL and TISO. Although TISO larvae reached a larger size during LA (855.7 ± 62.67 µm), SHELL resulted in a higher number of post-settled juveniles. The better performance of CC and SHELL may be attributed to their higher carbohydrate content. Despite SHELL and TISO having lower juvenile yields and longer feeding durations, the estimated cost per juvenile using SHELL, TISO, and CC were PHP 2.00, PHP 11.77, and PHP 0.52, respectively. Results showed that microalgae concentrates are not a cost-effective option under the studied conditions. The potential use of microalgae concentrates as supplemental feeds and further research to develop the use of local microalgae concentrates to sandfish larval culture are discussed.
    This study was funded by Australian Centre for International Agricultural Research (ACIAR) through the project FIS/2016/122 “Increasing technical skills supporting community-based sea cucumber production in Vietnam and the Philippines” and administrative support from the Marine Environment and Resources Foundation (MERF), Inc. We would also like to thank the Bolinao Marine Laboratory of the University of the Philippines Marine Science Institute for the use of facilities and equipment. We are grateful to our collaborators, Jon Altamirano and Roselyn Noran, and SEAFDEC AQD for guidance on the methods used for preparation and protocols of microalgae concentrate feeding regimen. Special thanks to JayR Gorospe for comments on the earlier draft and Jerwin Baure for copyediting this manuscript. The assistance of Mr. Tirso Catbagan in the culture of larvae and maintenance of the experimental tanks was invaluable during the experiment.