Trade-offs between defence and competition in gregarious juvenile fluted giant clams (Tridacna squamosa L.)
Bivalves can derive benefits from living in groups, such as reduced predation risk and increased reproductive success, but at the cost of greater competition for resources. Although gregariousness has been observed in giant clams, both experimentally and in the field, the ecological significance of this behaviour has yet to be evaluated. Here we quantified some benefits and costs of aggregation in the fluted giant clam, Tridacna squamosa, through two laboratory experiments that tested (1) growth and ectoparasite (pyramidellid snails) load, and (2) predation rates, of juvenile clams when reared in two configurations: aggregated and dispersed. Aggregated clams showed significantly lowered growth and greater ectoparasite susceptibility. Clams within aggregations were, however, more resistant to predation by the stone crab, Myomenippe hardwickii, as they required more time to handle compared to dispersed clams. As giant clams in the wild are vulnerable to numerous predators, the defensive advantage conferred by aggregation is potentially sufficient to outweigh the growth and ectoparasitism costs. These benefits may only apply to juveniles, as older individuals should have reached a size refuge from most predators and would therefore receive fewer benefits from aggregation.
We thank all members of the Experimental Marine Ecology Laboratory and staff at the St. John’s Island National Marine Laboratory (SJINML) for their support and assistance. Author M. L. Neo acknowledges the National Research Foundation, Singapore for supporting her research endeavours at the SJINML. This research was funded and supported by the National Parks Board CME Grant number R-154-000-568-490.
Compliance with ethical standards
Conflict of interest
All authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
Human and animal rights
Stone crabs were collected in accordance with the guidelines of the National Parks Board (Singapore) and collecting permit NP/RP15-117. Fluted giant clams were obtained from a local mariculture facility on St John’s Island National Marine Laboratory in accordance with the guidelines of the institution.
- Anderson DT (1994) Barnacles: structure, function, development and evolution. Chapman and Hall, LondonGoogle Scholar
- Andréfouët S, Gilbert A, Yan L, Remoissenet G, Payri C, Chancerelle Y (2005) The remarkable population size of the endangered clam Tridacna maxima assessed in Fangatau Atoll (Eastern Tuamotu, French Polynesia) using in situ and remote sensing data. ICES J Mar Sci 62:1037–1048Google Scholar
- Bertram BC (1978) Living in groups: predators and prey. In: Krebs JR, Davies NB (eds) Behavioural ecology: an evolutionary approach, 4th edn. Blackwell, Oxford, pp 64–96Google Scholar
- Cumming RL (1988) Pyramidellid parasites in giant clam mariculture systems. In: Copland JW, Lucas JS (eds) Giant clams in Asia and the Pacific, no 9. ACIAR Monograph, Canberra, pp 231–236Google Scholar
- Cumming RL (1993) Reproduction and variable larval development of an ectoparasitic snail, Turbonilla sp. (Pyramidellidae, Opisthobranchia), on cultured giant clams. Bull Mar Sci 52:760–771Google Scholar
- Ellis S (2000) Nursery and grow-out techniques for giant clams (Bivalvia: Tridacnidae). Center for Tropical and Subtropical Aquaculture Publication, HawaiiGoogle Scholar
- Gofas S (1991) The family Galeommatidae (Bivalvia: Leptonacea) in the eastern Atlantic. Veliger 34:344–353Google Scholar
- Krause J, Ruxton GD (2002) Living in groups. Oxford University Press, OxfordGoogle Scholar
- McMahon RF, Bogan A (1991) Mollusca: Bivalvia. In: Thorp J, Covich A (eds) Ecology and classification of north American freshwater invertebrates. Academic Press, New York, pp 315–399Google Scholar
- McMichael D (1974) Growth rate, population size and mantle coloration in the small giant clam Tridacna maxima (Röding), at One Tree Island, Capricorn Group, Queensland. In: Cameron AM, Campbell BM, Cribb AB, Endean R, Jell JS, Jones OA, Mather P, Talbot FH (eds) Proceedings of the 2nd International Coral Reef Symposium. Volume 1. The Great Barrier Reef Committee, Brisbane, Australia, pp 241–254Google Scholar
- Nash W (1988) Growth and mortality of juvenile giant clams (Tridacna gigas) in relation to tidal emersion on a reef flat. In: Copland JW, Lucas JS (eds) Giant clams in Asia and the Pacific, no 9. ACIAR Monograph, Canberra, pp 183–190Google Scholar
- Neo ML, Wabnitz CCC, Braley RD, Heslinga GA, Fauvelot C, Van Wynsberge S, Andréfouët S, Waters C, Tan AS-H, Gomez ED, Costello MJ, Todd PA (2017) Giant clams (Bivalvia: Cardiidae: Tridacninae): a comprehensive update of species and their distribution, current threats and conservation status. Oceanogr Mar Biol 55:87–388Google Scholar
- Pitcher TJ (1998) Shoaling and schooling behaviour of fishes. In: Greenberg G, Haraway MM (eds) Comparative psychology: a handbook. Garland, New York, pp 748–760Google Scholar
- Stasek CR (1965) Behavioral adaptation of the giant clam Tridacna maxima to the presence of grazing fishes. Veliger 8:29–35Google Scholar
- Suzuki Y (1998) Preliminary studies of locomotion and burrowing by juvenile boring clam, Tridacna crocea. Naga ICLARM Q 21:31–35Google Scholar
- Vulinec K (1990) Collective security: aggregation by insects as a defense. In: Evans DL, Schmidt JO (eds) Insect defenses: adaptive mechanisms and strategies of prey and predators (Animal Behavior Series). State University of New York Press, New York, pp 251–288Google Scholar
- White ME, Powell E, Ray S, Wilson E (1987) Host-to-host transmission of Perkinsus marinus in oyster (Crassostrea virginica) populations by the ectoparasitic snail Boonea impressa (Pyramidellidae). J Shellfish Res 6:1–5Google Scholar