Introduction

Known for proliferative breeding, the molluscs inject a huge volume of ‘fodder’ into the trophodynamics of aquatic system. In fact, some neretids, limpets and nudibranch (gastropods) annually release so many gametes that weigh more than their own body weight (Hughes, 1971b, Parry, 1982, Todd, 1979). For example, the gastropod Patella peroni releases gametes equivalent to 2.2 times of its own body weight (Parry, 1982) and life time reproductive investment ranges from 2.5 times in the dumpling squid Euprymna tasmanica to 5.5 times in the prosobranch Lacuna pallidula, of their respective body mass (Squries et al., 2013, Grahame, 1977); these values may be compared with the most prodigious pufferfish Canthigaster valentine, producing eggs equivalent to 1.5 times of its body weight (see Pandian, 2010, p 14). In terms of number, Haliotis midae produces up to 25 million eggs (Poore, 1973). In the Coosa River below Jordan Dam, USA, the viviparous snail Tulotoma magnifica produces 163 million young ones (Christman et al., 1996). Amazingly, a 2.6 kg weighing

Near La Jolla, California, Loligo opalescens population spawns 1.76 x 1012 eggs covering half the total 1,600,000 m2 of spawning area with egg capsules (212 eggs per capsule) at the density of 10,400 capsules per m2 (Okutani and McGowan, 1969). In terms of standing biomass, the quantum of gametes released ranges from 12% of assimilated energy in Choromytilus meridionalis (Griffiths, 1977, 1981b) to 80% in Mytilus edulis (Kautsky, 1982). The quantity of gametes released by bivalves is on average an impressive 76% of their weight (Griffiths and Griffiths, 1987). With an estimated production of 8 x 107 eggs per m2 over 160 km2 area (up to 30 m depth) of the Baltic Sea, M. edulis alone contributes more than 50% of the zooplankton (Kautsky, 1982). About 90% of the filtered energy by C. meridionalis is released to other consumers in the form of gametes, feces and pseudofeces (Griffiths, 1981b). The pelagic larval duration of many gastropods lasts for 107, 242 and 320 days in Phalium granulatum, Tonna galea and Cymatium nicobaricum, respectively (Scheltema, 1971). Hence, these larvae serve as food for longer durations to the consumers. Annually, an estimated 100 mt squids serve as feed for spermwhales (Clarke, 1980). Serving as the host, the bivalve Scrobicularia plana provides adequate resources to its trematode parasite Gymnophallus fossarum to release 73,163 cercariae per day (Bartoli, 1974). Whereas molluscan reproductive biology offers considerable scope for ecologists, the amazing tenacity of some snails to successfully survive over long periods from 3 months to 23 years on aestivation (see Hyman, 1967, p 613) provides astounding opportunity to physiologists.