Natural Food Availability and Assimilation in the Bivalve Choromytilus meridionalis

ABSTRACT-The tropical pearl oysters Pinctada margaritifera (Linnaeus) and P maxima Janieson are suspension feeders of malor economic importance. P margaritifera occurs in coral reef waters characterised by oligotrophy and low turbidity. P. maxima habitats are generally characterised by high terrigenous sediment and nutrient inputs, and productivity levels. These differences in habitat suggest that P. margaritifera will feed more successfully at low food concentrations, while P. maxima will cope with a wider range of food concentrations and more silty conditions. The effect of varying concentrations of natural suspended particulate matter (SPM) on clearance rate (CR), pseudofaeces production, absorption efficiency (abs.eff.), respired energy (RE) and excreted energy (EEJ was determined for P. margantifera and P maxlma. The resultant scope for growth (SFG) was deterrmned and related to habitat differences between the oysters. There was no selective feeding on organic particles in either species. P. rnargaritifera had higher CR at low SPM concentration (<2 mg I-'), while P. maxima had higher CR under turbid conditions (SPM: 13-45 mg 1-'). The latter species produced less pseudofaeces in relation to its filtration rates; consequently, this species ingested more SPM than P. margaritifera. P. maxima had positive SFG over a wider range of SPM concentrations (up to 30-40 mg I-') while P. margaritifera maximised SFG under low SPM conditions (<3 mg I-'). Thus feeding responses and energy balance reflected the typical habitats of each species. P, margaritdera retained smaller particles than P. maxima, enabling it to consume a wider particle size range of SPM at low food levels. P. maxima was adapted to its environments of greater SPM load through greater ingestion rates and higher digestive ability. The optimum SPM concentrations and particle size range for P. margaritifera (SPM < 5 mg I-', size > 3 pm) and P. maxima (SPM = ca 3 to 15 mg I-', size > 4 pm) may be used for selection of optimum pearl culture sites.

Section: Discussionsupporting

confidence: 92%

Feeding adaptations of the pearl oysters Pinctada margaritifera and P. maxima to variations in natural particulates

Yukihira¹,

Klumpp²,

Lucas³

1999

“…However, in the present study, site-specific differences in AE are confounded to some small extent by the dietary enrichment resulting from pseudofaecal production at Mahanga Bay and the absence of such at Island Bay. Regardless of this, bivalve AE is strongly dependent upon food quality (Bricelj & Malouf 1984, Bayne et al 1987, Navarro et al 1991, in particular, upon the ratio of organic to inorganic matter (Griffiths 1980, Bayne et al 1987. Net AE values typically range from about -60 % up to about 60% (Bayne & Hawkins 1990).…”

Section: Discussionmentioning

confidence: 99%

Where are the mussels on Cook Strait (New Zealand) shores? Low seston quality as a possible factor limiting multi-species distributions

Gardner¹

2000

116

Exammation of the physiological ecology of 3 sympatncally occurring mytilids (the ribbed, blue and greenshell mussels, Aulacomya maoriana, ivlytilus galloprovincialis and Perna canalicdus, respectively) was carned out during summer and winter at 2 sites which differ markedly in their environmental characteristics (Mahanga Bay inside Wellington Harbour, where mussels are abundant, and Island Bay on the exposed Cook Strait shore, where mussels are absent). Seston components (particle counts per rnl in the size range 2.5 to 63 pm, total particulate matter [TPbI], particulate organic matter [POM], and percent organic matter [PCOM]) all varied significantly between sites and between seasons. Mahanga Bay seston exhibited characteristics typical of productive temperate coastal waters. whereas Island Bay seston was characterised by low POM and low PCOM values. Weight-standardised clearance rate (CRS), net absorption efficiency (AE) and Scope for Growth (SFG) values were determined for all 3 mussel species at both sites during both seasons. At Island Bay there was no evidence of seasonal differences in CRs whereas at Mahanga Bay species-specific CRs values were all highest in the winter. Regardless of season, CRs estimates for all 3 species were higher at Mahanga Bay than at Island Bay. At both sites, AE estimates were highest in the w~nter, and AE estimates were higher at Mahanga Bay than at Island Bay during each season SFG estlrnates mirrored AE estimates, with SFG at both sites being highest in winter, and higher at Mahanga Ray than at Island Bay dunng each season. The SFG data support the hypothesis that mussels are absent from sites along Cook Strait shores because they do not enjoy a positive energy balance for long periods of time, consistent wlth the low seston organic matter levels at such locations. The SFG data also indicate that mussels lnside Wellington Harbour can maintain a large, positive net energy balance throughout the year, consistent with the considerable biomass and very large size of all 3 species in this environment.

“…Large amounts of TPM (up to 152 mg 1-') were reported by Griffiths (1980) for Bailey's Cottage, South Africa, although much of it was sand and the POM fraction was considerably lower. At Tromso, Norway, Vahl (1980) recorded values similar to ours, with POM in the range 1 to 4 mg 1-', although TPM was considerably higher (5 to 12 mg 1-') than in Logy Bay.…”

Section: Poc and Ponmentioning

confidence: 94%

Seasonal fluctuations in the size spectra, biochemical composition and nutritive value of the seston available to a suspension-feeding bivalve in a subarctic environment

Jm¹,

Rj²

1995

Seasonal changes In the size spectrum and biochemical composition of the suspended particulate matter were recorded for 2 yr in Logy Bay, southeast Newfoundland. Canada. The seston load was lower than in many shalloiv marine bays, owing partly to a relatively small terrigenous input and little silt, and the quantity of the parhculate organic matter primarily depended on phytoplankton productivity. The ratio chlorophyll a:phaeopigments was high during the phytoplankton bloom, due to the living nature of the organic seston at this time, compared with the rest of the year, when lower values were associated with the highly degraded suspended material. The size-frequency distribution of the suspended particulate matter reflected the succession of the phytoplankton community throughout the year. The spnng peaks were composed mainly of single diatoms and chain-forming diatoms in the size range 20 to 60 pm (equivalent spherical diameter). Variations in carbohydrate, lipid and protein in the seston were primarily associated with the periods of high and low standing stocks of phytoplankton observed in this environment. The seasonal trends were very similar for each biochemical component. and values were highly correlated with those for other properties of the seston, such as organic matter, chlorophyll a and particulate organic carbon and nitrogen. The nutritional quality of the seston was expressed by a food index, calculated as the ratio of food material (protein + carbohydrate + lipid) to total seston. This index followed the cycle of the phytoplankton bloom, with maximum values during spring and summer, and much lower values during winter. The results suggest that the gross analysis of the suspended particulate matter or the measurement of a single chemical variable cannot describe fully the nutritive value of the seston to a suspension-feeder. An analysis of the size spectrum and biochemical composition of the material is required for this purpose.