Early life history of the cold-water coral Caryophyllia huinayensis from the Chilean Fjord Region

Cold-water corals (CWC) build complex, three-dimensional habitats for diverse communities of associated species. In spite of their importance, very little is known on their reproductive biology. In the Patagonian fjords of Chile, three caryophylliid CWC abound: Desmophyllum dianthus Es-per 1794 along with the recently described Caryophyllia huinayensis Cairns et al. 2005 and Tethocyathus endesa Cairns et al. 2005. This study reports first in situ and in vitro observations of the early life history of the latter two species along with in vitro growth data of juvenile C. huina-yensis. Both are brooding species with translucent tissues, which allowed us to detect and monitor larval development in the gastrovascular system of living specimens. In situ observations from summer 2017 showed between 15 and 25 milky white reproductive stages in the tentacle portion of the gastrovascular cavity of one adult specimen. Up to five younger, round stages were ob-served in groups in the tips of the tentacles. Small planulae of 1.13-1.28 mm length were observed in the tips of the tentacles or organized radially around the mouth. Observations from C. huina-yensis maintained (> 1 yr) in an aquarium system showed that the 620 µm large orange planulae may swim with a velocity of 230 µm s-1 and thus may move from the tentacle tip to the mouth within less than a minute and thereafter reappear in the same or another tentacle in the similar time. After release larvae were found to be negatively buoyant, crawl along the substrate and settle between four and 16 days. Recently settled juveniles increased their basal disc diameter with a rate of 10 µm d-1. After 30 months of maintenance in the aquarium system (Temperature: 12.5 °C, Salinity 32, pH 8, argonite >1, feed with Artemia salina nauplii twice a week) recruits may gain 4.22 (+/-) 0.03 mm yr-1 in diameter and reach the mean size observed for adults in the field after three years. Research on the early life history of CWC is important to understand larval dispersal and connectivity of populations threatened by a changing climate and increasing eutrophication by expanding salmon farming operations.