Freshwater Sponge

In early May of 2021 just after the ice went out on the lake I spotted something unusual while out on the boat exploring.  Due to the hydro-electric dam constructed in the 1930s at Ear Falls and the regular winter “draw-down” of the lake, water levels on Lac Seul are typically quite low in the spring.  However, because of the drought conditions existing in our region over the past nine months, the spring water levels were lower than usual.  Anyway, the item appeared to be some kind of dried out marine vegetation exposed on the shoreline.  It was whitish-tan in colour with many “spikey” branches and looked very similar to dried out chunks of coral.

However, I had seen this stuff on the lake before (just in a different context) and knew it was not a plant.  It was in fact the remnants of a fresh water sponge which is classified as an animal.  I had previously observed fresh water sponges at the bottom of Lac Seul while scuba diving at a different location on the lake.  I sent the above picture to Dr. Andre Martel who is a zoologist at the research and collections branch of the Canadian Museum of Nature.  He in turn forwarded them on to Dr. Sally Leys who is a professor within the department of Biological Sciences at the University of Alberta and one of the few sponge experts in Canada (for additional information please see the following website: https://leyslab.weebly.com/.  Although a definitive identification requires the physical examination of the species, based on the photograph she indicated that it was definitely a freshwater sponge and very likely the species Spongilla lacustris based on its finger-like growth pattern.

This species inhabit freshwater lakes and rivers and is found from North America to Europe and Asia.  Spongilla lacustris filter water to consume their diet that consists of small floating organic particles.  They prefer to reside in lakes that are clear and shallow which is interesting as Lac Seul is very dark water body.  But it is sure cool that this species does live here and it is likely that many people are not aware that they do!