1.  Introduction


Please take action to protect these unique and wonderful reefs and visit the website of the Canadian Parks and Wilderness Society, B.C. Chapter for more details.

 

Siliceous sponge reefs or mudmounds occur several times in Earth history and they culminate in the Late Jurassic where they formed a discontinuous deep-water reef belt extending more than 7000 km. This reef system was the largest biotic structure ever built on earth. The largest reef of today, the Great Barrier Reef in Australia (2000 km), is relatively small compared to the Jurassic sponge reef belt.

(click the thumbnail to enlarge; 182k)

Reef belt

In 1991 a group of Canadian scientists (J.Vaughn Barrie, Kim Conway, John L. Luternauer and Bill Austin) described a modern analogue to the fossil reefs from the shelf off the west coast of Canada for the first time (Conway, K.W., Barrie, J.V., Austin, W.C. & Luternauer, J.L. (1991): Holocene sponge bioherms on the western Canadian continental shelf. - Continental Shelf Research, 11:771-790; London). Prior to this work it was presumed that this type of reef had died out a long time ago. The only known occurrence of these hexactinellid sponge reefs, worldwide, is off British Columbia, Canada.

(click the thumbnail to enlarge; 80k)

Coastline

Hexactinosidan sponges form extensive silicate mounds on the low angle, sediment starved continental shelf off western Canada. The reefs occur in water depths between 165 and 240 m and are often situated along iceberg furrows carved into the seafloor during late Wisconsinan glaciation (13000 years ago). Today the sponge reefs cover an area of about 1000 km2.


The largest sponge mounds are up to 21 m high and show remarkably steep slopes, up to 90, on the flanks. In addition to the mound, or biohermal structures, there are also large biostromal structures ("meadows") which cover many square kilometres of seafloor. These reach thicknesses from 2 to 10 m in southern and central Queen Charlotte Sound.


Since 1999, a team of German and Canadian scientists explored these unique reefs, and for the first time anywhere, hexactinellid reefs were studied by direct observation. The submersible DELTA, a ROV and the research vessels CCGS JOHN P. TULLY and CCGS VECTOR were employed to examine the geology, biology and the ecology of the sponge reefs (see also "2. Methods"). A detailed investigation of these modern reefs will help to provide a means of understanding the paleoecology and structure of the fossil reefs, as well as provide a window to observe the paleoenvironment which supported incredibly prolific sponge reefs during the Age of Dinosaurs. The project will use the present day shelf off B.C. as a key to the past environments that existed during the time of formation of the vast sponge reef belt during the Age of Dinosaurs. The present is the key to the past, and the past is the key to our future.


Why are the hexactinosidan sponge reefs so fascinating?


Known since the Late Proterozoic, the siliceous sponge group Hexactinellida are the very first metazoans which can be related to an extant animal group. The first representatives of the Order Hexactinosida appeared in the Devonian and during the Mesozoic these sponges became important reef building organisms in deeper water due to their fused rigid skeleton.


In the Late Jurassic, siliceous sponges facies was widely spread throughout the the north tethyan realm as mentioned above. Outcrops are known from the Caucasian Mountains, from Romania, Poland, Germany, Switzerland, France, Spain, Portugal, off Newfoundland and Oklahoma. After Jurassic time there is a dramatically decline in the distribution of these reefs and today they have completely disappeared, world wide, with one very remarkable exception off the coast of British Columbia, Canada.


These globally unique modern sponge reefs are very similar to those of the Late Jurassic. A thorough study of the modern reefs will provide us with detailed information about the biological, sedimentological, ecological and paleoenvironmental processes going on in these reefs today and in the geological past. Recent investigations by manned sumersible, ROV and high resolution geophysical surveying, reveal that large areas of these reefs are being heavily impacted by the mobile fishing gear. Sponge reefs in many places have sustained extensive and well-documented damage and destruction by groundfish trawling from 1988 through 2002. These fascinating sponges are found nowhere else in the world but British Columbia's continental shelf. In July 2002 the research team studying the sponges discovered damage to the most pristine of the sponge reefs. Shortly thereafter, fishing closures were imposed on the four sponge reef locations, yet these provide only short-term protection. Marine Protected Area as well as UNESCO World Heritage status is needed to ensure the long-term protection of the globally unique sponge reefs from all damaging human activities.

(click the thumbnail to enlarge; 116k)

trawlarea.html

 

Without protection from this damage the prospects for survival of these unique reefs are bleak. The last known occurrences in the evolution of this ultra-conservative reef type may well be destroyed by irresponsible human activities on the continental shelf. So, today we have an exceptional opportunity and maybe a last chance to learn more about these "living fossil reefs" and their (paleo)environment and therefore we should use it!


       

top 


copyrights

contact the webmaster

last changes 27.05.2008