Oxygen dynamics around buried lesser sandeelsAmmodytes tobianus(Linnaeus 1785): mode of ventilation and oxygen requirements

Abstract

SUMMARYThe oxygen environment around buried sandeels (Ammodytes tobianus)was monitored by planar optodes. The oxygen penetration depth at the sediment interface was only a few mm. Thus fish, typically buried at 1–4 cm depth, were generally in anoxic sediment. However, they induced an advective transport through the permeable interstice and formed an inverted cone of porewater with 93% air saturation in front of the mouth. From dye experiments the mean ventilatory flow rate was estimated at 0.26±0.02 ml min–1 (86.9±7.3 ml min–1kg–1) (N=3). Expelled water from the gills induced a 1 cm circular plume with <15% air saturation around the gills. During this quasi-steady ventilation mode, fish extracted 86.2±4.8% (N=7)of the oxygen from the inspired water. However, 13% of the investigated fish(2 of 15) occasionally wriggled their bodies and thereby transported almost fully air-saturated water down along the body, referred to as `plume ventilation'. Yet, within ∼30 min the oxic plume was replenished by oxygen-depleted water from the gills. The potential for cutaneous respiration by the buried fish was thus of no quantitative importance. Calculations derived by three independent methods (each with N=3) revealed that the oxygen uptake of sandeel buried for 6–7 h was 40–50% of previous estimates on resting respirometry of non-buried fish, indicating lower O2 requirements during burial on a diurnal timescale. Buried fish exposed to decreasing oxygen tensions gradually approached the sediment surface, but remained in the sediment until the inspired water reached 5–10% air saturation.