Biomass and species richness relationships in macroalgal communities that span intertidal and subtidal zones

Abstract

Investigations of the strong environmental gradients within intertidal and subtidal rocky reefs have contributed significantly to our understanding of ecological processes, but studies exploring how algal community structure responds to the extreme environmental transition of the intertidal-subtidal interface are rare. Our objective was to examine patterns in macroalgal distribution and species richness with depth on temperate rocky reefs. Standing algal biomass and richness were measured on 6 representative reefs in southern New Zealand, across 5 depth strata from the high intertidal zone, 1.5 m above mean low water (MLW), to the subtidal zone, 10 m below MLW. We found a unimodal relationship between algal richness and biomass across the depths, where maximum species richness occurred at intermediate levels of biomass. These results are consistent with many terrestrial plant studies across strong environmental gradients. Biomass decreased down the shoreline, with the exception of the high intertidal where the lowest biomass was recorded, whilst species richness increased down the shoreline. Additionally, strong patterns of dominance were observed, with a single species (not always the same species) contributing >56% of the total biomass across all depth strata examined. This dominance could have important implications for ecosystem provisioning across this system, particularly if dominant species are found to be vulnerable to the impacts of local and/or global change. The strong environmental gradients that characterise the intertidal-subtidal transition on rocky reefs over relatively small and experimentally tractable spatial scales enable opportunities to further advance our understanding of the mechanisms controlling the distribution of biodiversity.

Small-scale species richness of plant communities with similar biomass: the influence of habitat types in the context of historical hypothesis (Western Caucasus and Ciscaucasia, Black and Azov Seas, Russia)

“…1989, Garsia et al 1993, Waide et al 1999, Cornwell & Grubb 2003, Adler et al 2011, Ma et al 2010, Bhattarai et al 2004, Pärtel et al 2007, Zobel & Pärtel 2008, Fraser et al 2015, Bhattarai 2017, Twist et al 2020. According to "species-energy theory", monotonic increase in richness from low to intermediate level of production (biomass) reflects a decrease in the harshness of the environment and in crease in resources available.…”