USING MICROSENSORS TO MEASURE SPONGE PHYSIOLOGY

Abstract

Microsensors effectively measure a wide variety of parameters such as chemical concentrations, temperature, light levels and flow. Based on successful investigations of microscale phenomena in sponges we conclude that microsensors are a promising tool for sponge science. We would like to encourage their wider use in sponge physiology (e.g. to measure respiration, pumping activity and its regulation), and of the metabolism of associated microorganisms (e.g. photosynthesis, nitrification, sulfate reduction). We describe our experiences with liquid ion exchange microsensors, Clarke-type microsensors and microoptodes to provide recommendations for their use on sponges. Possible problems include: 1. sponge texture impeding sensor insertion (due to a strong cortex or spongin); 2. with endolithic or encrusting sponges a sensor can break upon touching the underlying substrate; 3. respiration/photosynthesis measurements may be biased by adhering or fouling plant/animal tissue; 4. contraction/expansion of sponge tissue altering the reference depth during measurements; 5. pumping/different flow regimes causing strong variation of data; 6. ruptured cells may influence chemical properties under investigation; 7. heterogeneity of the sponge body can result in patchiness of data. Some problems can either be overcome by adjustments to the equipment (1, 2) or by preparing the investigated sponge for the intended study (1, 3, 4). Other problems require great care in the recording process and good knowledge of adequate replication (5, 6, 7).