Pumping Water & Feeding
Glass sponges are purely filter feeders. Sponges subsist on macroscopic detritus material, but also consume cellular material, bacteria, and nonliving particles.
Sponge Water Circulation
Circulation of water through the sponge serves three principal purposes:
- carry food into the sponge
- eject non food particles ingested along with food in sponges with non-selective water intake
- oxygenate cells in the sponge interior
The sponge circulatory system consists of inlet pores called ostia which are typically scattered across the surface or organized into special sieve plates. Water is pumped in canals through the sponge by thousands to millions flagellated cells call choanocytes, acting like tiny pumps.
Food organisms are extracted by specialized phagocyte cells; non-food particles are pumped to one or more exhaust points called oscula or to a central atrial canal in sponges with single or multiple tubular form.
Sponge with oscula Sponge with central atrial cavity
Without some sort of water circulation sponge form would be limited to thin membranes whereas the evolution of a pumping mechanism allowed the evolution of more massive sponges because oxygenated water could reach cells relatively remote from the surface.
Hexactinellids seem to lack selective control over the food they ingest - any food small enough to penetrate the syncytium is ingested. Because of their lack of a continuous outer membrane and their lack of defined ostia, hexactinellids lack control over how much water passes through them. It is believed that the stability of deep-water environments allows hexactinellids to survive despite these shortcomings.
Almost all sponges pump water to obtain nutrients, building blocks for the skeleton ( silicates in the case of glass sponges), and likely oxygen.
We have preliminary estimates of pumping rates for 4 small sponges, 3 in the lab and one in the field. Rates were based on the speed of movement of carmine dyed water along a cm ruler for distances of 1-4 cm.
All were fairly small sponges with a single large exhalent osculum. In the lab pumping rates for each sponge varied considerably from day to day and at times ceased totally. Rates showed no obvious correlation with time in the lab, water temperature, renewed water, light, time of day or night, oxygen or vibrations. However, this needs more detailed study. Maximum rates for the sponges averaged 1cm/sec, 1.7cm/sec and 3cm/sec. This is comparable to the rates obtained in the field for the Boot Sponge, another glass sponge, by Gary Silver, a graduate student at the University of Victoria in the mid 1970s.
Rates for the sponge in the field averaged 1.8 cm/sec.
The area of the osculum was calculated by drawing or photographing the osculum, photocopying the image onto graph paper with appropriate enlargement or reduction, and counting squares.
The volume was calculated from the area x the distance. It yielded values of 1.3 L/min; 1.7 L/min; 3.0 L/min for lab sponges; and 1.8 L/min in the field
If sponges pumped continuously at this rate (which may well not be the case) we are looking at water volumes in the neighborhood of 2-4 tons/day
Pumping capacity is crudely based on the number of flagellated chambers, each operating as a mini-pump. In the Cloud Sponge these chambers are essentially in one plane equivalent in area to the surface area of the sponge (not the volume as in some sponges).
We can extrapolate still further to estimate rates in the largest measured sponge (3.4 meters long by 1.1 meters high by 0.5 meters wide). This sponge has an area some 70 to 100 times that of the small test sponges and IF it pumped with equivalent efficiency, would process 140 to 400 tons of water a day.
These are lots of “ifs” based on limited data but they, perhaps, give some idea of the significance of a population of these sponges in processing water.