Moving fluids for live – a sponge perspective

Sessile filter feeding animals, including sponges (Porifera), rely on efficient fluid transport systems tokeep energy expenditure for water processing low. As a consequence of the sponge canal systemcomplexity only limited data on flow velocities and transport rates are available. This restricts ourunderstanding of this central anatomical structure and related physiological processes, functionalmorophological principles and ecology. Obtaining experimental measurements from internal parts ofthe canal system is almost impossible for most species. Therefore data are mainly based ontheoretical assumptions. This is linked to the limited availability of detailed morphometric andquantitative data on canal system architecture. Here I discuss experimental and in silico results onflow studies in marine and fresh water sponges. Canal system models based on SR-µCT data allowedfor the setup of finite element models to study flow inside the aquiferous system and the influence ofspecific canal system elements (bypasses and cellular structures). In order to calibrate the model andverify results flow velocity measurements by particle tracking velocimetry have been performed.Observed flow velocities in canal segments of diverse hierarchical orders differ from predictions basedon the classical hierarchical model of flow for sponges which reported much higher and fasterincreasing flow velocities towards the osculum. This is a consequence of the aquiferous systemarchitecture which displays a compensating increase in available canal volume. With the ability toactively change canal diameters and aperture openings in the canal system sponges are most likelyable to fine tune internal flow velocities and perfusion rates of specific areas of their body