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Marine Ecology Progress Series

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MEPS 654:67-78 (2020)  -  DOI:

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

Brenton A. Twist1,2,*, Anna Kluibenschedl3, Daniel Pritchard3,4, Matthew J. Desmond3, Roberta D’Archino2, Wendy A. Nelson2,5, Christopher D. Hepburn3

1Institute of Marine Sciences, University of Auckland, Auckland 1142, New Zealand
2National Institute of Water and Atmospheric Research, Wellington 6241, New Zealand
3Department of Marine Science, University of Otago, Dunedin 9054, New Zealand
4Te Ao Tūroa, Te Rūnanga o Ngāi Tahu, Dunedin 9054, New Zealand
5School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand
*Corresponding author:

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.

KEY WORDS: Kelp · Seaweed · Macroalgae · New Zealand · Temperate rocky reef · Species richness · Biomass · Hump-shaped curve · Biomass-diversity · Unimodal relationship

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Cite this article as: Twist BA, Kluibenschedl A, Pritchard D, Desmond MJ, D’Archino R, Nelson WA, Hepburn CD (2020) Biomass and species richness relationships in macroalgal communities that span intertidal and subtidal zones. Mar Ecol Prog Ser 654:67-78.

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