Interacting effects of habitat structure and seeding with oysters on the intertidal biodiversity of seawalls

RESEARCH ARTICLE Interacting effects of habitat structure and seeding with oysters on the intertidal biodiversity of seawalls Elisabeth Marijke Anne StrainID1,2☯¤a*, Vivian Ruth Cumbo3‡, Rebecca Louise Morris4¤b‡, Peter David Steinberg1,2‡, Melanie Jane Bishop3☯ 1 Sydney Institute of Marine Science, Mosman, New South Wales, Australia, 2 Centre for Marine Science and Innovation, School of Biological, Earth and Environmental Sciences University of New South Wales, Sydney, New South Wales, Australia, 3 Department of Biological Sciences, Macquarie University, Macquarie Park, New South Wales, Australia, 4 Centre for Research on Ecological Impacts of Coastal Cities, School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia ☯ These authors contributed equally to this work. ¤a Current address: Institute for Antarctic and Marine Science, University of Tasmania, Tasmania, Australia ¤b Current address: National Centre for Coasts and Climate, School of Biosciences, University of Melbourne, Victoria, Australia ‡ These authors also contributed equally to this work. * strain.beth@gmail.com Abstract The construction of artificial structures, such as seawalls, is increasing globally, resulting in loss of habitat complexity and native species biodiversity. There is increasing interest in miti- gating this biodiversity loss by adding topographic habitat to these structures, and/or seed- ing them with habitat-forming species. Settlement tile experiments, comparing colonisation

of species to more and less complex habitats, have been used to inform eco-engineering interventions prior to their large-scale implementation. Most studies have focused on apply- ing one type of intervention (either adding habitat structure or seeding with native organ- isms), so it is unclear whether there are greater benefits to biodiversity when multiple interventions are combined. Using a fully orthogonal experiment, we assessed the indepen- dent and interactive effects of habitat structure (flat vs. crevice/ridges) and seeding with native oysters (unseeded vs. seeded) on the biodiversity of four different functional groups (sessile and mobile taxa, cryptobenthic and pelagic fishes). Concrete tiles (flat unseeded, flat seeded, complex unseeded and complex seeded) were deployed at two sites in Sydney Harbour and monitored over 12 months, for the survival and colonisation of oysters and the species density and abundances of the four functional groups. The survival of seeded oys- ters was greater on the complex than flat tiles, at one of the two sites, due to the protective role of crevices. Despite this, after 12 months, the species density of sessile invertebrates and the percentage cover of seeded and colonising oysters did not differ between complex and seeded tiles each of which supported more of these variables than the flat unseeded tiles. In contrast, the species density of mobile invertebrates and cryptobenthic fishes and the MaxN of pelagic fishes, at 1 month, were only positively influenced by seeding with oys-

ters, which provided food as well as habitat. Within the complex seeded and unseeded tiles, there was a greater species density of sessile taxa, survival and percentage cover of oysters PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0230807 July 16, 2020 1 / 21 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Strain EMA, Cumbo VR, Morris RL, Steinberg PD, Bishop MJ (2020) Interacting effects of habitat structure and seeding with oysters on the intertidal biodiversity of seawalls. PLoS ONE 15(7): e0230807. https://doi.org/10.1371/journal. pone.0230807 Editor: Christopher W. McKindsey, Maurice Lamontagne Institute, CANADA Received: August 5, 2019 Accepted: May 20, 2020 Published: July 16, 2020 Copyright: © 2020 Strain et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the manuscript and its Supporting Information files. Funding: We thank The Ian Potter Foundation (PS), Harding Miller Foundation (PS, ES, MB) and The New South Wales Government Office of Science and Research (PS, ES, MB) for their financial support. We also thank Reef Design Lab Pty Ltd for designing and producing the tiles used during the study. This study was part of the World Harbour Project. The funders provided support in the form