Results of a lab experiment to determine the range of pelagic larval duration in massive Porites larvae in Palau in 2023

The period of time that larvae spend in the water column, the pelagic larval duration (PLD), has a profound impact on dispersal distance. Characterizing variations in PLD across a population is critical for refined estimates of dispersal, yet this work is rarely done. We conducted an experiment to characterize the PLD of massive Porites larvae in April 2023. Adult massive Porites corals were collected from six sites in Palau immediately prior to their spawning, around the full moon. Collected corals were held in individual plastic containers in ambient unfiltered flow-through seawater tanks at the Palau International Coral Reef Center (PICRC). Larvae from two bulk crosses were pooled for this experiment. Each cross included sperm from 3 males and eggs from one female . Three-dpf larvae (n=20 individuals) were added to clear plastic culture dishes (~200 mL) with ambient seawater (ASW) at three different filtrations: unfiltered, 5 μm filtered, or 0.5 μm filtered (n=10 per treatment). No additional settlement cues were provided. Culture dishes were maintained in flow-through ASW tanks at PICRC, and ~80% water changes were conducted every 2 days. Temperature and light experienced by larvae during the experiment were recorded using Hobo pendant loggers in an identical culture dish in the same seawater tank. Immediately prior to water changes, all larvae and settlers in each culture dish were counted. Settlement was defined as a larva attaching itself to the bottom of the dish, remaining attached after mechanical disturbance (i.e., gently shaking the dish), and visually beginning to undergo metamorphosis.