Where marine waters are shallow and bathymetric features are steep, the typically employed multi-beam side scan sonar is not always reliable for identifying complex biological structures. Here, we present a cost-efficient method used in Howe Sound, British Columbia, for bathymetric mapping, exploration, and ground-truthing of glass sponge bioherms. A simple depth sounder and software package was used to produce bathymetric maps. From these maps, prospective sites were selected and surveyed to investigate bioherm presence with a simple drop-camera towed off the bow of a small drifting vessel during calm seas. This method was used during a 4-year citizen science initiative that led to the discovery of 12 glass sponge bioherms in Howe Sound, the first step in protecting these globally unique reefs from the impact of bottom-contact fishing, anchoring, and potential industrial contamination. Before our work using this method, only two glass sponge bioherms had been identified in Howe Sound. The method also proved effective as a means to quantify damage to bioherms from fishing gear.

Glass sponge reefs (bioherms) are known to occur on glacial deposits but have not previously been observed to develop on fjord bedrock ridges. It is assumed that sexual reproduction dominates reef recruitment and that sedimentation can cover intact sponge skeletons. Over a decade of scuba diving research at a small fjordic bioherm, including installation of bar-coded marker stakes, transplants of loose fragments and survey transects of substrate depth with an avalanche probe have led to new insights into the dynamics of bioherm formation and persistence. We present evidence for recovery of sponge growth from scree slopes of collapsed fragments and logged the temporal changes associated with sponge fragmentation and recovery. Bar-coded stakes were installed in 2014 to enable verification of location and sponge identity through time. Photo documentation of growth, collapse, and regrowth is presented. Research on a sponge garden on glacial sediments reveals that earliest sedimentation may center around prostrate boot sponges and bristly tunicates among the cloud and vase sponges. Although hexactinellid boot sponges do not contribute to the geologic base of bioherms, they may take part as a successional community in the substrate conditioning that could result in the genesis of a glass sponge reef or bioherm.

Glass sponge reefs are an ecosystem unique to the continental shelf of the northeast Pacific Ocean. Due to their vulnerability and limited distribution, several sponge reef protection initiatives exist within Canadian waters with the common goal of conserving biodiversity. To date, the biodiversity associated with sponge reefs has largely been assessed using remote video methods that allow us to describe large fauna associated with the reefs. However, small organisms are typically missed, resulting in an underestimate of reef-associated biodiversity. In this study we aimed to further describe invertebrate biodiversity associated with sponge reefs. Sponge reefs recently discovered in Howe Sound, British Columbia are within safe recreational SCUBA diving limits allowing us to examine macrofaunal settlement timing and community structure using diver-deployed settlement plates. We examined the effect of settlement plate material and elevation above the benthos within the reef on invertebrate community structure. A total of 70 taxa settled on the plates representing 10 phyla, including two phyla not previously described on sponge reefs: Nemertea (ribbon worms) and Platyhelminthes (flatworms). There were no significant differences in taxa richness, diversity, or community structure associated with settlement plate material or height above the benthos. Ours is the first report of invertebrate settlement on a sponge reef in the Salish Sea and the first description of larval settlement timing for nine invertebrate species in the northeast Pacific.

No abstract

No abstract