Brooding coral Porites astreoides colonies were collected on St. John, U.S. Virgin Islands on June 22nd, 2017 and used in an in-situ larval coral settlement experiment. Settlement counts were taken on June 28th, 2017.

Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Deployments
• Project Information
• Funding

Coral collections and spawning
Eight colonies of the brooding coral Porites astreoides were collected on St. John, U.S. Virgin Islands (18.31384N, 64.76439W) on 22 June 2017. The colonies were maintained in a shaded outdoor ambient seawater-supplied aquarium. Corals spawned overnight 22-24 July and larvae were collected each morning and maintained in 0.2m filtered seawater. On 25 July, larvae from all colonies and spawning nights were pooled, and groups of 55 actively swimming larvae were selected. Groups were randomly assigned to one of 9 light or 9 dark 140ml polyethylene chambers (preconditioned with reef water for one month) filled with 0.7m filtered seawater (remove grazers, retains microbes). Each chamber contained two preconditioned settlement surfaces: a clay stilt (3.8cm diameter) and a red cable tie (10.2cm; chosen from previous findings, Mason et al. 2011). Light chambers were transparent, allowing ambient light ingress, while dark chambers were externally covered with black tape to prevent light transmission.

Settlement experiments
Following larval addition, three light and three dark settlement chambers were each affixed to a vertical pole deployed at three sites: Tektite Reef (18.30962N, 64.72218W), Cocoloba Reef (18.31528N, 64.76065W), and a sand site with no reef structure within 100m (18.31789N, 64.75059W) (Table 1). Sites differ in biophysical habitat characteristics (Table 1) known to influence soundscape properties (6). The experimental set-up included acoustic recorders (SoundTrap ST-300, Ocean Instruments NZ), recording continuously at 48 kHz, and temperature/light loggers (HOBO Pendant UA-002, Onset Corporation). The chambers and instruments were secured 0.20.5m above the seafloor in 710m water depth (see Figure 1C). Larvae were completely isolated within settlement chambers, allowing exposure to ambient sounds (polyethelene plastics have high acoustic transparency) while preventing exposure to other water-borne habitat cues (e.g., reef water chemicals).
Chambers were recovered after 62 hours and maintained in seawater tables during the 6-hour processing period in which settled corals were enumerated. Some actively swimming larvae were still present, suggesting that oxygen remained sufficient for larval survival.

NSF Award Abstract:
Coral reef ecosystems host some of the highest biodiversity of life per unit area on Earth and harbor about one-quarter to one-third of all marine animals. Reef-associated animals are a major source of protein for millions of people, and reefs offer shoreline protection and provide a significant source of tourism revenue, especially in developing countries. Factors that influence supply and settlement of young (larval) fish, coral, and associated animals can have large impacts on reef ecosystem and population structure, and learning more about these can help improve understanding of how to maintain the benefits provided by coral reefs. This study will lead to a detailed, mechanistic understanding of how young larvae use natural sounds to orient toward, locate, and select preferred settlement habitat. The approach will combine detailed field measurements and experiments to isolate key soundscape variables that impact coral reef larvae. 

For marine communities, such as those on coral reefs, factors influencing larval supply and settlement can have major impacts on community structure and population replenishment. There are now some indications that sound plays an important role in attracting larvae to suitable settlement habitat. There is little understanding of what soundscape habitat information is available to larvae and how differences and variability in sound can influence settlement. This project will include comprehensive experiments, environmental measurements, and modeling with the goal of understanding the role of sound in influencing larval recruitment and local biodiversity. The investigators will measure in situ settlement of larval fish and coral in relation to different soundscapes and habitat conditions in a marine protected area using traditional larval sampling methods, moored acoustic recorders, and a suite of environmental observations. Controlled and calibrated environmental playback experiments will isolate soundscape components and determine specific and fundamental acoustic cues larvae use to orient and settle. The spatial and temporal variability of soundscape cues and components across reef habitats will be established. Finally, the project will determine the relevant ranges of sound plumes that larvae may encounter through direct measurements of the sound fields of multiple reefs.