Turnover-driven β-diversity reveals conservation priorities in Antarctic intertidal benthic communities

Abstract Antarctic sedimentary intertidal habitats remain among the most understudied and least represented within protected areas designated under the Antarctic Treaty System. Understanding how biodiversity varies across space and time within these habitats is therefore essential for effective conservation planning. We examined benthic community structure, total abundance and biodiversity (α-, β- and γ-diversity) on sedimentary shores of Deception Island (South Shetland Islands, northern Antarctic Peninsula), using data collected across three intertidal height levels (low, mid and high) at seven beach sites over five austral summers (2004, 2005, 2009, 2010 and 2011). Within each year, we partitioned multiple-site Jaccard β-diversity into turnover and nestedness components. We compared their relative contributions across years to assess whether species replacement or ordered species loss consistently predominated among sampled beaches. We found that local community structure, total abundance and α-diversity varied markedly across sites and years, suggesting that these patterns may be consistent with the influence of habitat heterogeneity, seasonal processes and episodic events such as phytoplankton blooms and biological introductions. β-diversity was consistently high across the sampled beaches and dominated by species turnover, showing that island-scale γ-diversity reflected the contribution of distinct local assemblages. This turnover-dominated β-diversity pattern indicates that protecting only the most species-rich sites would not adequately conserve the distinct local assemblages underpinning island-scale γ-diversity. Conservation planning should therefore prioritise multiple, spatially distinct sedimentary intertidal habitats across Deception Island. Including these habitats in the Antarctic Specially Protected Area (ASPA) network would strengthen the representation of sedimentary intertidal biodiversity within Antarctic conservation planning.