International Journal of Marine Science, 2024, Vol.14, No.5, 321-331 http://www.aquapublisher.com/index.php/ijms 322 The current study constitutes a pivotal component of the ongoing HARP project, focusing on evaluating the efficacy of different coral nursery designs in facilitating the growth and survival of coral fragments at varying depths (⁓2 m and ⁓5 m). Both coral nursery designs are low-cost, adaptable-scale and can be used by both island resorts and community islands. Rope-based and metal table-based nurseries were employed to cultivate coral fragments of Acropora aspera, Acropora muricata, and Montipora digitata sourced from naturally broken colonies within the same location as the nurseries. Fragments from the same colony were evenly distributed between the rope and metal frames for consistency. Bimonthly underwater surveys were conducted over a period of six months to analyze the following parameters: (i) growth, (ii) ecological volume, (iii) health condition, (iv) presence of disease, (v) predation, and (vi) survival rate. Rope nurseries outperformed metal tables in terms of coral survival and overall performance. The absence of predation on ropes significantly enhances survival rates for A. aspera and A. muricata, making rope nurseries a more effective technique for propagating corals in Maldives' lagoons. 2 Results and Analysis Growth rates after 6 months monitoring (Figure 1), A. aspera exhibited a similar growth rate in rope-based and table-based nurseries at ⁓2 meters with no statistically significant difference (Figure 1a). At ⁓5 meters, the growth rate was significantly higher in table-based nurseries compared to rope-based nurseries (P< 0.001). Similar results were reported for A. muricata (Figure 1b), with a higher growth rate on table-based nurseries at ⁓5 meters compared to the rope- based nurseries. No significant differences were found at ⁓2 meters. For M. digitata, the growth rate was significantly higher for corals on rope-based nurseries at ⁓2 meters compared to ⁓5 meters and to table-based nurseries (Figure 1c, P< 0.001). The highest growth was recorded for M. digitata at ⁓2 m on ropes-based nurseries, reaching 4.48 ± 2.04 cm, followed by A. aspera and A. muricata, with 2.21± 0.76 cm and 2.06± 0.89 cm, respectively. High growth rates were also reported on metal-tables based nurseries at ⁓5 meters, where the growth rate for all species exceeded ⁓3 cm over six months. The ecological volume for the different species is reported (Figure 2). The ecological volume was overall higher at ⁓2 meters compared to ⁓5 meters for all the analyzed species (Figure 2a, 2b, 2c), reflecting more favorable conditions for coral growth in shallower depths. No significant differences were found in the bimonthly surveys between rope-based nurseries and table-based nurseries (Figure 2). However, the analysis of EV variation after 6 months shows statistically significant variations (Figure 3). For A. aspera the variation in EV was statistically higher on ropes at ⁓2 meters, compared to ropes at ⁓5 meters (Figure 3a, * P<0.05). No significant differences were found for table-based nurseries. For A. muricata, the variation in EV was not significant influenced by nursery design and/or depth (Figure 3b). M. digitata (Figure 3c) showed a significantly higher EV variation on both ropes (**** P<0.0001) and tables (** P<0.01) at 2 meters, increasing from 2699.6 ± 233.2 to 5808.6 ± 512.8, respectively. No significant differences were found in at 5 meters (Figure 3c). The general health of the coral fragments (Figure 4), Ropes at both ⁓2 and ⁓5 meters had the best health conditions, with only less than 20% of coral fragments showing partially unhealthy colonies (Figure 4a, 4b, 4e, 4f, 4i, 4j). Rope-based nurseries reported no predation over the study period of 6 months. Table-based nurseries presented predation on both A. aspera and A. muricata due to Drupelia spp, especially at ⁓2 meters. No other predator’s species or bite marks were recoded (Figure 4c, 4d, 4g, 4h, 4k, 4l). The survival rate was overall lower in coral grown on tables-based nurseries compared to the rope-based nurseries, for all 3 species. Interestingly, M. digitata displayed the highest survival rate, 80~90% in all the experimental conditions. No statistically significant differences due to depth or nursery design were reported (Chi-square P=0.7192, Fisher's exact test, P=0.7623, n=15, Figure 4).
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