Comparison of Methods to Sample Abundance of Estuarine Subtidal Macroalgae: Novel Core Sampling Method, Using Multi-SUBstrate Subtidal (SUBS) Sampler, Versus Standardized Methods

Current protocols for monitoring planktonic algae in water samples are well developed and are applied routinely for all types of waterbodies. However, for waterbodies where benthic macroalgae is predominant, the protocols are not as well developed. Traditional approaches focus on either collecting a limited number of samples in the intertidal zone to represent the entire waterbody or applying tools which are constrained by some limiting variable, such as lack of visibility, need for diver, sampling depth constraints, or use of tools where loss of sample is unavoidable. All of which result in incomplete characterization of the waterbody of interest. The core sampling method, multi-SUBstrate Subtidal sampler (SUBS Sampler; Sorensen et al., in prep), was developed as a standardized method to address some of the challenges of sampling macroalgal biomass in the subtidal zone. In addition, the SUBS Sampler has the capacity to simultaneously collect water, sediment macro and planktonic algae in one core sample. This work describes comparison of the SUBS Sampler to standardized methods recommended for use in the Southern California Bight Regional Monitoring Program (McLaughlin et al., 2019) to evaluate efficacy of use in routine monitoring applications. The overall goal of this study was to compare the utility of the SUBS Sampler to previously used, low-tech methods (e.g., hampers for floating algae and rake method) for sampling both subtidal macroalgae and submerged aquatic vegetation. Method comparison included both a quantitative and qualitative assessment looking at abundance estimates, logistics, ease of use, potential observer biases, and laboratory processing speed. Overall, the SUBS sampling method seemed to provide higher estimates of total biomass across the entire gradient of biomass and scored substantially better than other methods for logistics and ease of field and post-sample processing procedures.