Inexpensive Video Drop-camera for Surveying Sensitive Benthic Habitats: Applications from Glass Sponge (Hexactinellida) Reefs in Howe Sound, British Columbia

Abstract

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.

Formation, Persistence, and Recovery of Glass Sponge Reefs: A Case Study

“…Temperatures at large sponge reefs on the continental shelf of Hecate Strait were from 5.5 to 7.3°C [9]. Those reefs occur at depths of 140-240 m, much deeper than the Howe Sound reefs at 24-96 m [8]. It is unlikely that the majority of bioherms experience such high summer temperatures as were recorded for the present study site.…”

“…The depth of the present study site is 24 m at the shallowest point. The Passage Island reef is at 24 m, the Defence Island offshore reef at 31 m, and the Halkett Pinnacle reef at 32 m [8]; all other Howe Sound sponge reefs are significantly deeper (38-96 m) [8]. The temperature data (Figure 2) indicate that spikes in temperature exceeding 10.5°C occurred at around the heightening of the 2015/2016 El Niño in summer of 2015.…”

Invertebrate settlement and diversity on a glass sponge reef

“…Our study occurred at the Halkett Point glass sponge reef in Howe Sound, Salish Sea on the southwest coast of British Columbia (BC), within the Halkett Bay Provincial Marine Park northwest of the city of Vancouver (Figure 1a). The glass sponge reef was first discovered by G. Dennison in 1996 and first formally described by Clayton and Dennison (2017). The reef was federally protected from all bottomcontact fishing activities in 2019, but at the time of our study, in 2017, fishing restrictions were not yet in place (DFO 2019).…”

“…The reef was federally protected from all bottomcontact fishing activities in 2019, but at the time of our study, in 2017, fishing restrictions were not yet in place (DFO 2019). The main sponge reef occurs between 22-90 m on a pinnacle that is irregular in shape with a relatively flat top and gently sloping sides (Figure 1b; Clayton and Dennison 2017;DFO 2018). Glass sponge reefs are naturally patchy with areas of live, erect dead, and buried dead sponge present throughout the reef (Dunham et al 2018).…”

“…While remote video surveys allow us to describe large fauna (≥4 cm) associated with the reefs, smaller organisms (hereinafter referred to as macroinvertebrate fauna), such as polychaetes and bryozoans, are typically missed. Several of the reef complexes recently discovered in Howe Sound (Clayton and Dennison 2017;Dunham et al 2018) are significantly shallower than other known reefs (22-127 m compared to 90-300 m), occurring within safe recreational SCUBA diving limits. The discovery of these shallow reefs allowed us, for the first time, to examine macrofaunal community structure and settlement timing on a glass sponge reef in the Salish Sea using diver-deployed settlement plates.…”