A systematic review of floating and beach landing records of Sargassum beyond the Sargasso Sea

Sargassum algal blooms on ocean surfaces and landings of huge Sargassum mats on beaches is an emerging global environmental challenge with wide socio-economic and environmental implications. Literature on Sargassum growth cycles, travel patterns, species and morphotypes, and quantified impacts have tended to focus on a geographic region, or a specific event. Few, if any, publications document long term continuous monitoring of Sargassum blooms in large areas such as the Pacific, or the tropical Atlantic. To address this gap, this paper systematically reviews the global evidence of Sargassum bloom monitoring beyond the Sargasso Sea, and identifies gaps in the evidence base of floating and landing influxes. This systematic review uses combinations of two key terms relating to Sargassum and monitoring, and utilises the resources in ISI Web of Knowledge, Scopus and Google Scholar. The analysis moves us past a classic literature review, and produces an unbiased assessment of empirical research on Sargassum monitoring from 1960 to 2019. We find a significant research focus on open-ocean blooms and floating mats whereas research on beach landings and their associated impacts is comparatively limited. Research is focused within specific countries or water bodies (notably, the Gulf of Mexico, the Caribbean and North Atlantic Ocean) and tends not to comprehensively assess neighbouring or regional shorelines, for example, West Africa and Central America. There was a lack of consistency in the application of methods for quantifying Sargassum biomass volume (including dry/wet weight, unit of measurement, and spatial extent of calculations). Further, in many publications Sargassum species identification was omitted. Given current attempts to understand the drivers and impacts of the exponential growth in Sargassum in some parts of the world, a consistent and replicable research approach to monitoring Sargassum could support creation of a Sargassum evidence database. To move this agenda forwards, we propose a definition for a Sargassum 'event': a continuous bloom of any Sargassum in open oceans, or, an aggregation of landed Sargassum, with the potential to disrupt social, economic or ecosystem functioning, or to impact human health. This review highlights the importance of standardising Sargassum monitoring methods to facilitate improved documentation of temporal and spatial patterns of Sargassum blooms and beach landings