Comparative assessment of seafloor sampling platforms.

Abstract

The Australian Marine Parks are the largest network of marine protected areas in the world, and their establishment means that Australia is now tasked with managing an area almost 3.3 million km2. In addition, Australia has the third largest exclusive economic zone in the world, with an extensive geographic area on which to report for State of Environment. The vastness of Australia’s marine estate means that appropriate, efficient, and comparable sampling methods are crucial to meet management and reporting obligations. The overarching objectives of environmental monitoring are to assess condition and detect trends, and numerous marine sampling platforms exist to acquire data to meet these needs. It is daunting to consider all marine sampling platforms in the context of a single monitoring program and to ensure that the most appropriate methods are used for a given purpose. There is thus a need to synthesise and compare these platforms as they relate to the design and implementation of monitoring programs. The purpose of the current study is to describe and comparatively assess common seafloor sampling platforms. We do this by conducting a qualitative assessment and comprehensively reviewing the available literature to identify their potential limitations and advantages. For the purposes of this report, marine sampling platforms include those that acquire seafloor data using underwater equipment or methods. We focus on sampling platforms near (i.e. demersal) or at (i.e. benthic) the seafloor because the habitat and associated biota targeted by these platforms are usually fixed and can be revisited, making them well-suited to monitoring activities. This report is divided into four sections, as well as an introduction (Section 1): • Section 2 describes each major benthic and demersal biological sampling platform, including their advantages, disadvantages, and innovations. These include acoustics platforms (e.g. multibeam echosounder (MBS), sidescan, single-beam), visual methods (e.g. autonomous underwater vehicle (AUV), baited remote underwater vehicle (BRUV), towed imagery, underwater visual census (UVC)), and direct sampling (e.g. ROV, sleds, dredges, corer, grabs). • Section 3 describes the use and perceptions of six benthic and demersal sampling platforms (AUV, BRUV, MBS, towed imagery, sleds/trawls, grabs/box corers) via results from an online questionnaire released on 15 Dev 2016 to gauge use and perceptions of common marine sampling platforms in Australia. A total of 49 people completed the questionnaire, and three platforms were frequently used by a large proportion of respondents: MBS (42.5%), grabs/boxcores (41%), and towed imagery (40%). Highest perceptions of cost and deployment effort were associated with the AUV and MBS. • Section 4 presents results from a literature review in which we searched for studies that used two or more marine benthic or demersal biological sampling platforms, excluding acoustics methods. We then refined this search to include studies that either i) directly compared methods (50 studies) or ii) tested for similar ecological relationships among two or more gear types (42 studies). Based on direct comparisons, the platforms with the least similarity between them may be operator-based direct sampling and sled/trawl, operator-based imagery acquisition and UVC, and UVC and BRUVs. Based on ecological congruence, data from sleds/trawls and grabs/corers showed similar ecological patterns, while UVC and BRUV and UVC and grabs/corers may be the least ecologically congruent. • Section 5 relates our results to marine monitoring by linking each sampling platform to its capability to measure global indicators (Essential Ocean Variables, Essential Biodiversity Variables). We also provide further advice on choosing an appropriate sampling platform as related to monitoring program objectives, target environment, and available resources including cost. Our study confirms that marine surveys are undertaken to acquire baseline environmental data, identify important habitats or taxa, or detect change (including quantifying impacts), each of which is associated with optimal survey designs and sampling platforms. A comprehensive marine monitoring program can include aspects of all of these goals. For example, seafloor acoustic methods provide a baseline map of the seabed from which a powerful and appropriate survey design can then be implemented. On subsequent surveys to detect change, however, such methods may not be needed unless an assessment of seabed stability and geohazards is required. Direct sampling yields valuable biological specimens, particularly in unexplored areas, from which a species inventory can be derived to inform subsequent change detection. Non-extractive methods such as underwater imagery and visual censuses are currently the most appropriate methods to detect change and quantify benthic impacts due to their capacity to collect true repeat observations, which increases efficiency when estimating the trend. Imagery also provides a permanent record of a snapshot in time with minimal interference, compilations of which can then be used to detect trends. There is no universal method appropriate for all marine sampling; a one-size-fits-all approach is neither feasible nor desirable in monitoring programs. For surveys collecting baseline or descriptive information, a diversity of gear may be more appropriate, while for monitoring surveys, fewer platforms capable of repeatable sampling would be more appropriate. This comparative assessment provides information that can be used to guide marine sampling activities as they relate to monitoring objectives. Such information is crucial to ensure cost-effectiveness and efficacy of marine monitoring activities, specifically that the best methods are being used with appropriate knowledge of limitations and challenges. In addition to the marine sampling platforms that are chosen, robust survey designs and standard operating procedures are crucial to ensure consistency of data and comparability over time and space.