Vertical gradients in the fauna and oxidation of two exposed sandy beaches

Abstract

Vertical profiles of oxygenation and fauna were measured in two exposed sandy beaches. At the less exposed site the whole upper metre of sediment was oxidized although the redox potential discontinuity started at 85 cm. Meiofauna were concentrated in the upper 40 cm and protozoa in the upper 55 cm, but bacteria showed no distinct vertical drop-off in numbers. On a more exposed beach the upper 1,3 m was highly oxidized, with meiofauna concentrated in the upper 80 cm and protozoa in the upper 115 cm. Meiofauna and protozoan numbers correlated with oxygen tensions and redox values and with each other. It is suggested that small protozoans are an important food source for the meiofauna.

Vertikale profiele van suurstofkonsentrasie en fauna is in twee oop sandstrande bepaal. By die meer beskutte strand was die hele boonste meter sediment geoksideer alhoewel die redokspotensiaal-diskontinu'rteit by 85 cm begin het. Meiofauna was in die boonste 40 cm gekonsentreer en protozoa in die boonste 55 cm, maar daar was nie 'n duidelike - afname in bakteriegetalie op dieper vlakke nie. In die geval van die meer blootgestelde strand was die boonste 1,3 m hoogs geoksideer. Meiofauna was in die boonste 80 cm en protozoa in die boonste 1,15 m gekonsentreer. Meiofauna- en protozoa- getalle het met suurstofkonsentrasies en redokswaardes sowel as met mekaar gekorreleer. Daar word voorgestel dat klein protozoa 'n belangrike voedselbron vir die meiofauna is.