The interplay of temperature, light, and substrate type in driving growth and reproduction of an important tropical crustose coralline alga

Updated: 2024-07-19

This study examined the influence of light, temperature, and substrate types on growth and reproduction responses of Titanoderma cf. tessellatum, an important crustose coralline alga to settle coral larvae. The experiment was at the National Sea Simulator of the Australian Institute of Marine Science, Townsville, Australia in August–October 2023. Fragments of Titanoderma cf. tessellatum were cultured at two temperatures (27.5 vs. 30 °C) and two light levels (mean maximum midday irradiance of 10 PAR vs 40 PAR) on three different tile materials (calcium carbonate [CaCO3], concrete, or polyvinyl chloride [PVC]). Fragments were photographed every two weeks for 12 weeks to assess growth, changes in reproductive structures (i.e., conceptacles), sporeling settlement, and recruitment of juveniles. Newly germinated spores, or sporelings (< 1 mm in size), were counted from week 6 onwards to determine sporeling settlement rate. As sporelings continued to grow and expand laterally to become juveniles (~1–5 mm in size), individuals coalesced. Therefore, as a proxy for recruitment, which took into account spore settlement and post-settlement survivorship and growth, we measured the total area covered by Titanoderma juveniles at week 12.