Human Impacts >>
The maps  identify areas that have Cloud Sponges in shallow waters. However, many areas have not been assessed. 


Howe Sound


Jervis Inlet
 

The main skeleton of Cloud Sponges is formed of fused strands of glass. For this reason they are extremely fragile and are at risk of being shattered from human activities such as fishing and diving.

There are a number of ways in which the human impacts on these Sponge Gardens can be greatly reduced.


Are You A Prawn Fisher?

In Saanich Inlet sponges occur only
shallower than 230 ft. Here prawn fishers can avoid damaging sponge
s by keeping their traps below 250 ft. as long as the  water has oxygen.

However, in other inlets sponges may be destroyed at depths down to 400 feet.
 

     On an Easter weekend, biologists mapped the locations of 64 prawn traps (red dots) in the recreational fishery in Saanich Inlet,  B.C.

     Commercial fishermen can each deploy 150 to 300 traps at a time.

 



Are You A Line Fisher?

Please lift up cannonballs and lines to shallower than 100 ft. when near known sponge gardens such as in Saanich Inlet.

 

This sponge received a physical impact from a cannonball or a prawn trap.
 

 

 

It was torn in two
 

 



  It subsequently died and became covered with silt

 
  It is likely the plumbing of  the pumping system had become too disrupted
 
  Most sponges breakdown when they die
 
  However, the mainframe skeleton of a Cloud Sponge remains intact for at least decades.

 

Are you a Crab Fisher?

Please keep traps shallower than 100 ft.
And on soft bottoms

 


Practice outside the
   sponge beds

Avoid flailing kicks

Adjust your buoyancy to
  stay off bottom

Please look, photograph
   but don’t touch

 
       

 

Aerial image of log booms anchored in fjord (Alberni Inlet) 

“Sinkers” from log booms can destroy sponges as they roll

down the walls of fjords

 

 
We noted in the introduction that trawling has destroyed some  of the glass sponge reefs in B.C.  
 
 

 

Not all impacts are physical.  Suspended sediment in the water like smog in air can affect organisms in a variety of ways. 

           
  • The map shows sedimentation rates in blue, in grams per square   meter per year in Saanich Inlet  (after Drinnen 1995)

  •       

  • Note that rates increase toward the mouth of the Saanich Inlet

  •  

  • This is opposite to the condition in most fjords. (e.g., Farrow et al 1983).

  •  

  • The distribution of the Cloud Sponge is shown in red

  •  

  • It does not occur where sedimentation rates exceed roughly 1000  grams per square meter per year

  •  

  •  
 
 
 

High suspended sediment may be

produced naturally such as by glaciers

 

 
 
 

 

         or may be the result of e.g.:

  • stirring up the  bottom by log dumps 

  • removal of cover by clear cutting

  •  

  • exposure of soil by development

  •   loosening soil such as by agriculture

 

 
 
  At Christmas Pt., in Saanich Inlet only 8% of the sponges had dead bases:  
 
 

While at Senanus reef in Saanich Inlet 80% of the sponges  had dead bases

The rate of sedimentation is twice as high here compared to Christmas Pt. 

While amount of sedimentation or associated high suspended particulates may be correlated with % of dead bases,  we cannot exclude some other factor(s).   

How glass sponges respond to artificial addition of sediment is discussed under “keeping clean” in the Natural History Section.

 
 
 
Each year the oxygen in the basin of Saanich Inlet gets used up.
 
The walls of the inlet here are barren
 
 
 
Back in 1982 divers in the PISCES submersible saw sponge skeletons some 30 meters (100 ft) below any living sponges.
 
This means that some time in the past the oxygenated water extended 30 meters deeper into the basin.
 
A likely explanation is that there was less pollution by nutrients from, for example, farming, clear cutting, landscaping, sewage, and maybe global warming.
 
It we could date the sponges; we might be able to identify events which caused lowered oxygen.
 
These dead sponges might also tell us that low or no oxygen water may extend into shallower water in the future.