Science Advisory Report 2017/026

Glass Sponge Reefs in the Strait of Georgia and Howe Sound: Status assessment and ecological monitoring advice

Summary

• Over the past 15 years, nine glass sponge reef complexes have been mapped by the Canadian Hydrographic Service and the Geological Survey of Canada in the Strait of Georgia and Howe Sound using remote sensing multibeam swath bathymetry imagery.
• In 2015, DFO protected the nine sponge reef complexes via formal bottom-contact fishing closures. In order to monitor these closures, a baseline of reef status is required and a monitoring plan must be developed.
• This work presents the first attempt at comprehensively and quantitatively characterizing the nine sponge reef complexes currently protected by bottom-contact fishing closures in the Strait of Georgia and Howe Sound. The work is based on the results of two Remotely Operated Vehicle (ROV) surveys completed in 2012 and 2013, prior to the implementation of the closures. Although there is insufficient data to form a comprehensive “baseline”, the information presented in this review is considered to be the best available reference for reef status prior to implementation of the closures.
• There is insufficient understanding of glass reef ecology and ecosystem function to define and assess reef “health” at this time. Instead, suites of potential quantitative indices characterizing reef-building glass sponges and associated megafaunal communities were developed and evaluated based on consistency, ability to distinguish between reefs of qualitatively different status, and data processing effort involved. Standardized summaries characterizing reef complex status were derived from a compilation of the most informative indices.
• To support the development of a reef monitoring program, considerations for survey design, sampling methods, and data analyses are provided. In particular, a range of monitoring indices and associated sampling methods are collated to provide options for comparing reef status over time and space. Evaluation of the relative utility of potential indices can only be completed once explicit conservation objectives for the reefs have been established.
• It is recommended that management decisions be based on trend analysis and consider multiple indices in combination, rather than a singular increase or decrease in any one index. A few exceptions exist that could trigger management action. For example, a dramatic, statistically significant decrease in live sponge cover could be viewed as evidence of (an) acute stressor(s) affecting sponge reef health. A diagnostic decision tree to guide monitoring of the sponge reefs is provided as an example.
• The methods developed in this paper can be applied to other reefs in the Strait of Georgia and Howe Sound and could be adapted for assessment of glass sponge reefs in other areas such as Hecate Strait and Chatham Sound.
• Key sources of uncertainty include the natural variability of glass sponge reef communities in comparison with human-caused changes; limited information on functional relationships within a reef ecosystem and on the factors affecting recruitment and growth of glass sponge reefs; and uncertainty as a result of visual survey method limitations (e.g., consistent visual species identification, cryptic species, highly mobile species).
• Ongoing and future research efforts, including field surveys, are needed to address current gaps in understanding of sponge reef biology and ecology and to better understand reef ecosystem function and the key indicators of overall reef “health”. The outcomes of these ongoing efforts will be needed to help develop and refine glass sponge reef monitoring programs.

This Science Advisory Report is from the March 1-2, 2017 regional peer review on Glass sponge reefs in the Strait of Georgia and Howe Sound: status assessment and monitoring advice. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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