Glass Sponges as Water Filters
It has been calculated that a single glass sponge reef can filter an Olympic sized swimming pool of water in a minute and that they remove about 95 percent of bacteria from seawater. This makes glass sponge reefs incredibly important natural water filters, especially in semi-enclosed and highly developed water bodies like the Strait of Georgia.
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 ofmovement of carmine dyed water along a cm ruler for distances of 1-4 cm.
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.
Glass Sponges as Nurseries for other species
Glass sponge reefs also play a very important ecological role as nursery habitats in deeper waters (100meters). The complex structures and large tubes (called ‘oscula’) provide plenty of hiding places, making them ideal nursery grounds for rockfish, crabs, prawns and other marine animals. They are particularly important as rockfish nurseries because rockfish populations have been declining in B.C. largely due to overfishing and accidental bycatch. Rockfish are unable to adjust to pressure changes at the surface because of their closed swim bladder so when they are caught accidentally, they cannot be saved and released.
Sponge Nursery photographed by K. Conway
Feature 3
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