Tripneustes gratilla

3.2.1 | T. g. gratilla View in CoL

In our region of interest, Eastern Australia and across the Tasman Sea, Tripneustes g. gratilla in museum collections demonstrated a largely tropical-to-temperate distribution. The distribution of this taxon ranged from Papua New Guinea (5°13′30″ S) to Jervis Bay (New South Wales, southeastern Australia, 35°7′12″S), encompassing ~30° of latitude. The midpoint of its geographic range in the region investigated was at 20°10′30″ S, around the Whitsundays in Queensland. The furthest east specimen of T. australiae in our region of interest was collected from subtropical Lord Howe Island (31°32′36.6″ S, 159°03′06.6″ E) in the Pacific Ocean (Tables SA2 and SA3). The long-term temperature range across this distribution is 16.3°C–29.97°C, a realised thermal width of 13.67°C. The realised upper and lower limits of T. g. gratilla are 14.7°C and 30.4°C, which represent the average yearly minima and maxima experienced by this taxon at its respective upper and lower range edges (from 2000 to 2020) ( Figure 2 View FIGURE 2 , Table 1 View TABLE 1 ). We note that outside of our region of interest, the western-most collection location from the museum collections we examined was from Cocos (Keeling) Island (12°08′42.7″ S, 96°52′15.6″ E) in the Indian Ocean.

3.3 | Abundance and Distribution of Tripneustes View in CoL in Australia

The RLS survey data for the two Tripneustes spp. were from 7 ecoregions, from the Torres Strait in the north to Cape Howe in the south, at 18 locations and 107 sites from 2003 to 2024. The density of Tripneustes spp. varied significantly among Australian ecoregions (χ 2 = 26.145, df = 6, p <0.001). Peak densities of Tripneustes spp. were in the Lord Howe and Norfolk Island ecoregion, a subtropical ecoregion ( Figure 3 View FIGURE 3 ). Post-hoc pairwise comparisons showed that densities in the Lord Howe and Norfolk Islands bioregion were significantly higher (p> 0.05) than densities in other ecoregions ( Figure 3 View FIGURE 3 , Table SA 6). Densities of Tripneustes spp. were higher in the Tweed-Moreton and Lord Howe and Norfolk Island ecoregions compared to other regions ( Figure 3 View FIGURE 3 ). Consistent with this, the frequency of observation of Tripneustes spp. was lower in the tropical regions of Australia ( Figure 4 View FIGURE 4 ).

3.4 | Model Performance and Habitat

Suitability Maps

3.4.2 | T. g. gratilla View in CoL

The final habitat suitability model for T.g. gratilla (variables:MD and SST) had a high predictive capacity (AUC = 0.926 ± 0.022 SD), indicating the model prediction was reliable. Depth was the dominant predictor of T. g. gratilla habitat suitability (97.1%), and there was some influence of SST (2.9%). This suggests that future habitat suitability for T. g. gratilla will be primarily limited by the availability of habitat at a shallow depth, such as rocky reef or seagrass meadows ( Figure 6 View FIGURE 6 ).