Natural Food Availability and Assimilation in the Bivalve Choromytilus meridionalis

Abstract

Samples of seawater overlying a bed of the mussel Choromytilus meridionalis (Kr.) at Bailey's Cottage, False Bay, South Africa, were analysed for organic and inorganic content in the particle-size ranges 2-100 μm and 100-200 μm diameter. Organic matter comprised 10-30 % of total sample weight, the remainder being predominantly sand. Changes in weight of particulate matter in samples taken throughout the year showed no clear seasonal pattern. Particulate organic material considered available as food to the mussels averaged 2.65 mg/L. Particulate inorganic matter averaged twice this amount. The energy value of the organic material averaged 6.1 kJ g-l. Phytoplankton was present in 34 % of the samples and is not considered an important constituent in the mussels' diet. The assimilation efficiency of mussels feeding on natural detritus averaged 40 % over the ration levels 3-18 mg/L dry weight of particulate matter. However, assimilation efficiency on pure Dunaliella primolecta culture declined to zero at a ration of 3 mg/L while pseudofaeces production was initiated at 6 mg/L. It was concluded (論拠が不明だぞ～）that the presence of particulate inorganic matter may be an important dietary requirement, 'diluting' the food and enabling assimilation to continue at the high ration levels experienced in the field. ○ 勉強メモ： Griffiths 1980 EN130502-01 P151 The presence of particulate inorganic matter may be an important dietary requirement of Choromytilus meridionalis (Kr.), 'diluting' the food and enabling assimilation to continue at the high ration levels experienced in the field. ○ 勉強メモ： Griffiths 1980 EN130502-01 P15 フィールドで懸濁物の有機物/無機物比を推定。また、Choroをフィールドから飼育容器にうつして2時間以内の糞を採集し、有機物/無機物比を測定。これらからassimilation efficiency (F-E/F(1-E))を計算。なるほど。 ○ 勉強メモ： Griffiths 1980 EN130502-01 P15 100μm濾過しただけの天然海水を、2L/h の流速でChoro（何個体か、Griffithsは述べていない）に与えて、消化率を調べた（らしい。明記なし）。 ○ 勉強メモ： Griffiths 1980 EN130502-01 Figure 3 & P155L 餌密度（mg/L AFDW）に対する消化率の応答曲線のピークは、室内実験より野外観察において右にずれているように見える。が、possibleな理由として、野外のChoroの実際に吸い取った海水について餌密度をうまく推定できなかったこと、また、Choroが無機懸濁物まじりの餌をなかなか排泄しないこと、を挙げられる。