Temperature Monitoring

Why monitor temperature?

Water temperatures play an important role in marine ecosystems and can explain variability associated with species health, growth, fitness, and survival. Glass sponge reefs are particularly sensitive to warmer temperatures, existing within a narrow optimal temperature range of 9-10⁰C. Prolonged exposure to temperatures greater than 10⁰C has been known to affect feeding, cause tissue damage, and eventually lead to mortality.

This susceptibility to warm temperatures has severe implications for the glass sponge reefs in Átl’ka7tsem/Howe Sound, as the shallow waters they inhabit are more susceptible to warm water events such as those brought about by El Nino, climate change, and ‘heat domes’.

A spike in mortality has already been noted in Átl’ka7tsem/Howe Sound, which coincided with the 2009/2010 and 2015/2016 El Nino events, in which sponges were exposed to temperature spikes greater than 10.5⁰C. If the frequency and severity of El Nino events increase with climate change, and/or the warming of BC waters continue, it can be expected for greater mortality events to occur and for sponge habitat to become restricted to colder, deeper, and/or more northerly waters. This has implications not only for sponge survival, but the ecosystem as a whole. In addition to filtering vast amounts of water on a daily basis, glass sponges provide critical habitat to wide diversity of marine organisms.

Through MLSS monitoring programs, citizen science divers have noted an increased abundance of rockfish species, notably young of the year (baby rockfish), in areas with sponge cover, compared to those without. External scientists have also observed a loss in the abundance and diversity of rockfish species following mortality events (read about it here), while others have noted increased species richness at intact, compared to damaged reefs (Cook et al., 2008).

While these mortality events are deeply concerning, there is evidence that sponges can recover from damage, only if allowed to heal under ideal temperature conditions (see Marliave, 2015). Therefore, in order to ensure reef health, temperature is an essential variable to monitor alongside sponge health indicators, including rockfish counts on the reef, mortality, growth, and recruitment.