Influences of food availability and abiotic factors on growth and survival of the lion's paw scallop Nodipecten nodosus (Linnaeus, 1758) from a subtropical environment

Rupp, Guilherme Sabino (2003) Influences of food availability and abiotic factors on growth and survival of the lion's paw scallop Nodipecten nodosus (Linnaeus, 1758) from a subtropical environment. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The lion's paw scallop Nodipecten (=Lyropecten) nodosus is the largest native pectinid in Brazil and has great potential for aquaculture. Cultivation of postlarvae, which is initially carried out in land-based facilities and subsequently in the sea, is an essential step in scallop husbandry, usually involving high costs and high mortalities. The influence of food availability on postlarval growth and survival early after metamorphosis, have been controversial. After deployment in the sea-based culture, postlarvae are subject to uncontrolled environmental variables, which in the subtropical study region display an unusual pattern of variation. The importance of food availability and abiotic environmental factors on growth, survival and byssal attachment of postlarval N nodosus at its southern distribution limit was examined using laboratory and field approaches, aiming to resolve some of the existing controversies and to provide biological information to facilitate the development of scallop farming in Brazil. -- The presence of epiflora on the spat collectors enhanced settlement, but not growth. Availability of suspended algae begins to support growth 3-5 days after settlement (230-250 μm shell height), but larval energy reserves were sufficient to meet metabolic demand during the period in which suspension feeding is not functional, with no indications of food deprivation-induced mortality. -- After the postlarvae were deployed in the sea, temperature was the major environmental factor affecting growth, with food availability having a negligible influence. Scallops deployed in the sea-based nursery at a size of 0.5 mm (2 weeks post- set), grew faster and had similar percentage retrievals than those deployed 2-3 weeks later and retrieved simultaneously from the sea. -- Sub-surface intrusions of cold and phytoplankton-rich waters from South Atlantic Central Water influenced a near-shore(< 0.51an) site in late summer-early autumn, resulting in oscillating temperatures and high PIM, reducing postlarval growth. Such a phenomenon was not observed in late autumn-early winter. -- N. nodosus is eurythermal but stenohaline tropical species, adults being less tolerant of high temperature and low salinity than spat. Survival was maximized at salinities above 29 psu and at temperatures between 15 and 28°C. At ambient salinity, the maximum rate of byssal attachment occurred at 19-27°C and 23-27°C for spat and juveniles, respectively. These are the suggested temperatures most favourable for growth. -- There is a large potential for growing postlarval and juvenile N. nodosus in coastal areas of southern Brazil, where growth and retrievals can be maximised by adjusting the size and season of deployment, culture depth, and by selecting an adequate site.

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