Biomass calibration of nine dominant native and non-native Levantine seaweeds

Seaweeds provide important ecosystem functions in shallow temperate rocky reefs including carbon uptake. The macroalgae communities in shallow reefs off the south-eastern Mediterranean shores have shifted dramatically due to bioinvasions and possibly ocean warming over the past few decades. These changes have likely caused and will continue to shift the ecosystem functionality and carbon sequestration capacity of these reefs. In order to assess the potential changes in carbon sequestration capacity, it is important to determine the organic reservoir contained in the biomass of the native as well as the increasingly dominant alien algal species, for which biometric relationships can serve as good proxies. Between 2017 and 2020, we collected samples of nine species of native and non-native seaweeds that currently dominate the hard substrate of shallow reefs along the northern Israeli Levantine coast. For each species, we provide the biometric relationships between wet weight, dry weight and ash-free dry weight and report the equations for the conversions between the different mass-calibrations. Comparison between species, indicate that organic matter content in Ochrophyta is generally greater than Rhodophyta. Furthermore, seasonality was detected in some metrics of the tested species. Our results provide basic tools for assessing the impacts of climate change and bioinvasions in terms of carbon sequestration potential in shallow water seaweed communities of the Levantine and possibly other regions.