Colouring coral larvae for tracking dispersal

O_LIEcologists have long sought to understand larval dispersal characteristics of benthic marine invertebrates. Direct quantification of coral larvae dispersal has proven challenging, in part due to their complex life-history, minute size, and widespread dispersal at the scale of kilometres. Instead, indirect methods such as particle modelling, chemical signatures, and genetic correlation are often used in dispersal studies. C_LIO_LIHere, we develop a direct method of quantifying larval dispersal by applying vital stains to coral larvae, allowing differentiation and direct tracking of millions of larvae from the pelagic dispersal stage through to the sedentary stages of attachment and metamorphosis on coral reefs. C_LIO_LINeutral red and Nile blue stains were extremely effective at staining coral larvae, while alizarin red and calcein blue showed no visible results. Differences in toxicity to vital stains was noted among species, with Acropora spp. exhibiting decreased larval survival and settlement, while Merulinidae spp. were unaffected. By experimenting with different incubation times and concentrations, our results indicate that neutral red can be effectively applied for short periods (60 minutes) at higher concentrations (100-1000 mg l-1). C_LIO_LIThe strong colour of both neutral red and Nile blue stains was retained by newly settled larvae in lab settings upwards of five days following settlement, providing a direct method of differentiating between newly settled larvae on reefs. Field-validation of Nile blue applied to coral larvae from wild-captured coral slicks demonstrates the efficacy of staining across a diverse range of coral taxa. C_LIO_LIVital staining provides a simple, rapid (<60 mins), and low cost (<AUD$0.00001 per larva) method of colouring coral larvae that allows for direct tracking of dispersal and recruitment in studies of reef connectivity and restoration. C_LI