Marine ecoregions and subecoregions within Indo-West Australian waters: A statistical approach based on species distributions

Study area The study area includes nine currently recognised ecoregions within Indo-West Australian waters: Western Sumatra, Southern Java, Lesser Sunda, Bonaparte Coast, Exmouth to Broome, Ningaloo, Shark Bay, Houtman, and Leeuwin. A map of these ecoregions is available from www.marineregions.org. The study area was divided into a 1° grid-cell resolution to create 473 cells, including 83 grid cells in Western Sumatra, 70 in Southern Java, 71 in Lesser Sunda, 46 in Bonaparte Coast, 67 in Exmouth to Broome, 15 in Ningaloo, 25 in Shark Bay, 24 in Houtman, and 72 in Leeuwin. Species occurrence data Species of marine Mammalia, Reptilia, Pisces, Mollusca, Crustacea, Echinodermata, Annelida, Cnidaria, Bryozoa, Porifera, Alismatales, Chlorophyta, Rhodophyta, and Phaeophyceae were selected. Species data from Indonesian and Australian waters were downloaded from the Ocean Biogeographic Information System (OBIS) (https://obis.org) on October 20, 2019. Data were retrieved for 28,923 species and 1,497,347 location records. A total of 14,556 species from 81,968 cell records were extracted after overlaying species data and grid cells. Duplicate species within grid cells were removed. OBIS species names were matched with those in the World Register of Marine Species (http://www.marinespecies.org), and names marked as synonyms in WoRMS were linked to currently accepted names. This data evaluation reduced the number of species from 14,556 to 14,513. Grid cells that contained fewer than five species were excluded to minimise distortion in similarity analyses (Kreft & Jetz, 2010). This reduced the number of grid cells from 473 to 338. The final grid cell counts by ecoregion were 54 in Western Sumatra, 33 in Southern Java, 43 in Lesser Sunda, 42 in Bonaparte Coast, 61 in Exmouth to Broome, 9 in Ningaloo, 25 in Shark Bay, 23 in Houtman, and 48 in Leeuwin. The same approach at both finer (0.5°) and coarser (2°) resolution was conducted as a supplementary analysis. In these analyses, the number of final grid cells was 816 (49.60% of total cells) and 135 (93.75% of total cells), respectively. Environmental data Environmental variables included both surface and benthic environments: salinity, nitrate, dissolved oxygen, current velocity, temperature, pH, photosynthetically available radiation (PAR), and depth. Salinity, nitrate, dissolved oxygen, current velocity, temperature, pH, and PAR data were downloaded from Bio-ORACLE (Tyberghein et al., 2012; Assis et al., 2018), and depth data were downloaded from Global Marine Environment Datasets (IOC et al., 2003). The mean values of environmental variables within grid cells were calculated and used in the analysis.