The behaviour of giant clams (Bivalvia: Cardiidae: Tridacninae)

Abstract

Giant clams, the largest living bivalves, live in close association with coral reefs throughout the Indo-Pacific. These iconic invertebrates perform numerous important ecological roles as well as serve as flagship species—drawing attention to the ongoing destruction of coral reefs and their associated biodiversity. To date, no review of giant clams has focussed on their behaviour, yet this component of their autecology is critical to their life history and hence conservation. Almost 100 articles published between 1865 and 2014 include behavioural observations, and these have been collated and synthesised into five sections: spawning, locomotion, feeding, anti-predation, and stress responses. Even though the exact cues for spawning in the wild have yet to be elucidated, giant clams appear to display diel and lunar periodicities in reproduction, and for some species, peak breeding seasons have been established. Perhaps surprisingly, giant clams have considerable mobility, ranging from swimming and gliding as larvae to crawling in juveniles and adults. Chemotaxis and geotaxis have been established, but giant clams are not phototactic. At least one species exhibits clumping behaviour, which may enhance physical stabilisation, facilitate reproduction, or provide protection from predators. Giant clams undergo several shifts in their mode of acquiring nutrition; starting with a lecithotrophic and planktotrophic diet as larvae, switching to pedal feeding after metamorphosis followed by the transition to a dual mode of filter feeding and phototrophy once symbiosis with zooxanthellae (Symbiodinium spp.) is established. Because of their shell weight and/or byssal attachment, adult giant clams are unable to escape rapidly from threats using locomotion. Instead, they exhibit a suite of visually mediated anti-predation behaviours that include sudden contraction of the mantle, valve adduction, and squirting of water. Knowledge on the behaviour of giant clams will benefit conservation and restocking efforts and help fine-tune mariculture techniques. Understanding the repertoire of giant clam behaviours will also facilitate the prediction of threshold levels for sustainable exploitation as well as recovery rates of depleted clam populations.

Molecular cloning, characterization, and the response of Cu/Zn superoxide dismutase and catalase to PBDE-47 and -209 from the freshwater bivalve Anodonta woodiana

“…Bivalve molluscs are ubiquitous, sedentary filter feeders, which can bio-accumulate pollutants to a high degree [16,17]. The Chinese pond mussel (the Eastern Asiatic freshwater clam or swanmussel), bivalve Anodonta woodiana functions as a main criteria required for a bio-indicator organism [18,19].…”

Captive Bred, Adult Giant Clams Survive Restoration in the Wild in Seychelles, Indian Ocean

“…The transplant month was critical to ensure clams had enough time to self-attach before heavy swells of the Southeast Monsoon (May to October) began. Giant clams can be toppled by strong waves during storm conditions, even roll laterally for a short distance across the reef, and regain their upright position (Soo and Todd, 2014). In juvenile Tridacna maxima, (1-3 years old) byssal re-attachment occurs within 4 days (Waters et al, 2013).…”

“…Giant clams host Symbiodinium clades A, C, and D (DeBoer et al, 2012). Symbiodinium clade D is known as thermally stress-tolerant (Baker et al, 2004;Stat and Gates, 2011), so some resistance to thermal stress in giant clams is possible (Soo and Todd, 2014). Perhaps in bleaching events that only affect corals, giant clams can accelerate the recovery of nearby bleached corals by making live symbionts available through their normal physiological functions.…”

“…They are the largest living bivalves found in close association with coral reefs throughout the Indo-Pacific (Lucas, 1988). With their large size and stunning colors ranging from electric blue, green, pink, and purple to gold, giant clams are equivalents of "charismatic megafauna" that can act as flagship taxa, drawing attention to the ongoing destruction of coral reefs (Soo and Todd, 2014). Giant clams have ecological significance as reef builders, contributing to the calcium carbonate framework of coral reefs (Barker et al, 1988;Gilbert et al, 2006), as food for 75 known predators and a scavenger guild, shelter for juvenile and adult coral reef fish, shell surfaces for epibionts and as hosts for ectoparasites and commensals (Neo et al, 2015).…”

Larval ecology of the fluted giant clam, Tridacna squamosa, and its potential effects on dispersal models

“…Swimming speeds of T. squamosa veligers were comparable to those of other bivalves (see Chia et al, 1984;Emlet, 1990). Bivalve veligers, including T. squamosa veligers, use their prototroch (ciliary bands) for propulsion, usually moving along helical paths while swimming (Soo and Todd, 2014). Even though ciliated larvae may not be fast enough swimmers in the horizontal plane to alter their distribution (Shanks, 1995;Young, 1995), this type of locomotion can facilitate the occupation of different depths (Shanks, 1995), hence exposing them to alternative current conditions.…”