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Fig. 1. Effects of temperature and pH on survival of Acanthaster sp. larvae.Larvae were reared in all combinations of two temperatures (26, 30 °C), two pH levels (pH 8.0, 7.6), and three food level treatments (low, switch, high) in a flow-through seawater system. Larvae in present-day treatments (pH 8.0, 26 °C) reached the late brachiolaria stage and began to settle by week 3, so survival was not formally analysed beyond this time point. Survival depended on a significant temperature × weeks interaction and a significant pH × weeks interaction (p < 0.05), with food treatment and all other interactions having little effect (repeated measures ANOVA, Supplementary Table 1). For ease of illustration, data for the a temperature × weeks interaction and b pH × weeks interaction are presented here, and the full data set is presented in Supplementary Fig. 1. At 3 weeks, survival was significantly greater for larvae reared at 30 °C than 26 °C, and greater for larvae grown at pH 8.0 than pH 7.6 (Supplementary Table 1). Survival was calculated using data collected for all living larvae regardless of their morphology (i.e., included abnormal and normal larvae). Solid lines represent the mean for each treatment. Error bars (black) represent the standard error of the mean. For all treatments, n = 42.
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Fig. 2. Effect of temperature, pH, and food on the size of Acanthaster sp. larvae.a Length. b Width. Larvae were grown in all combinations of two temperatures (26, 30 °C), two pH levels (pH 8.0, 7.6), and three food level treatments (low, switch, high) in a flow-through seawater system. Larvae were fed Proteomonas sulcata three times per day at a rate equivalent to 1 × 103 cells mL−1 (low), 1 × 103 cells mL−1 from 3 to 11 dpf (days post-fertilisation) and 5 × 104 cells mL−1 thereafter (switch), or 5 × 104 cells mL−1 (high). Bars represent means. Error bars represent the standard error of the mean. Black dots represent replicates. Measurements of length and width were not made on larvae that displayed abnormal morphology (see Fig. 3). Data on length and width for the 26-7.6-switch and 26-7.6-high treatments at 18 dpf were not presented due to low replication (n < 3) because of high mortality (Supplementary Fig. 1) and a high occurrence of larvae with abnormal morphology in these treatments.
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Fig. 3. Effect of temperature, pH, and food on the occurrence of abnormal Acanthaster sp. larvae.The proportion of Acanthaster sp. larvae that were abnormal when reared in two temperatures (26, 30 °C), two pH levels (pH 8.0, 7.6), and three food level treatments (low, switch, high) in a flow-through seawater system. a 11 dpf (days post-fertilisation). b 18 dpf. Larvae were fed Proteomonas sulcata three times per day at a rate equivalent to 1 × 103 cells mL−1 (low), 1 × 103 cells mL−1 from 3 to 11 dpf and 5 × 104 cells mL−1 thereafter (switch), or 5 × 104 cells mL−1 (high). Bars represent means. Error bars represent the standard error of the mean. Black dots represent replicates. Inset: Examples of abnormal larval morphologies. Scale bar = 100 µm. Photo credit: N. Mesic. Examples of normal larval morphology are provided in Fig. 4.
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Fig. 4. Effect of temperature, pH, and food on the development of Acanthaster sp. larvae.The proportion of larval stages (%) of Acanthaster sp. larvae present when reared at two temperatures (26, 30 °C), three food level treatments (low, switch, high), and two pH levels (pH 8.0, 7.6) for a 11 dpf (days post-fertilisation) and b one pH level (pH 8.0) for 18 dpf, in a flow-through seawater system. Larvae were fed Proteomonas sulcata three times per day at a rate equivalent to 1 × 103 cells mL−1 (low), 1 × 103 cells mL−1 from 3 to 11 dpf and 5 × 104 cells mL−1 thereafter (switch), or 5 × 104 cells mL−1 (high). Data on larval stages at 18 dpf for pH 7.6 treatments were not presented due to low replication (n < 3) because of low survival (Supplementary Fig. 1) and a high occurrence of abnormal larvae in these treatments. Data are means. The number at the base of each bar is the number of replicates for which data was available. Legend: Larval stages appear in scale relative to each other, scale bar = 200 µm. Photo credits: N. Mesic.
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Fig. 5. Effect of temperature, pH, and food on the competence of Acanthaster sp. larvae.Larvae were reared in all combinations of two temperatures (26, 30 °C), two pH levels (pH 8.0, 7.6), and three food level treatments (low, switch, high) in a flow-through seawater system. a Number of replicates in each treatment (out of seven total) where at least one larva developed to the late brachiolaria stage and had a large rudiment indicative of competency to undergo settlement and metamorphosis to post-larval stages. b Minimum larval pelagic duration (PLD); the number of days post-fertilisation (dpf) elapsed before any competent larvae were sighted. X identifies treatments where all larvae died before attaining competence to settle. Bars represent means. Error bars represent the standard error of the mean. The number of replicates in each treatment is shown by the data points and corresponds with the values shown in (a).
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