Larkin, M.F., Davis, T.R., Harasti, D. et al. A glimmer of hope for an Endangered temperate soft coral: the first observations of reproductive strategies and early life cycle of Dendronephthya australis (Octocorallia: Malacalcyonacea). Mar Biol 170, 146 (2023). https://doi.org/10.1007/s00227-023-04298-x
Coral in Peril
Cauliflower soft coral (Dendronephthya australis) is an important coral species in rapid decline. Native to Southeast Australia and resembling the vegetable sharing its name, it provides important habitat for local marine life. However, over the last decade its population has rapidly declined due to sediment movement from coastal development and intense storms. This sediment can accumulate on the coral, reducing its ability to exchange gasses, leading to injury or death. Cauliflower soft coral has become a priority species for the federal government to protect, but its reproduction method and larval stage have never been formally described.
Corals have evolved a wide variety of ways to reproduce with some species using both sexual and asexual methods. This makes predicting reproduction strategies difficult as it must be observed to confirm what methods are used. Therefore, researchers set out to complete the lifecycle of cauliflower soft coral by documenting its reproductive strategies and larval development to inform future conservation projects.
Pulling Back the Curtain
In the lab, cauliflower soft coral demonstrated broadcast spawning. This is a form of sexual reproduction where the male and female release gametes into the water column at the same time. The gametes use ocean currents to move and interact with one another, eventually fertilizing and settling back to the sea floor.
Using observations in the wild and photographs from the prior 2 decades, spawning occurs at or around the neap tide during the summer when water temperatures reach above 66 °F (19.1 °C). Neap tides produce slower water flow due to the influence of the sun and moon on the ocean. This gives the gametes the greatest opportunity to interact and produce viable larvae.
These larvae settled to the bottom and transformed into the adult form, known as a polyp, within 18 days of fertilization. Coral larvae typically exhibit preferences for certain sea floor conditions, planting on particular rocks or skeletons of dead coral. It is widely accepted this is done through chemical signaling originating from the surface, but this process is not completely understood yet. Cauliflower soft coral larvae did not display a preference. This possibly indicates the surface it fastens to is not significant to its survivability.
Asexual reproduction was also observed via autonomous fragmentation. This is when a fragment breaks away from the main colony, creating a new individual. No seasonality was associated with fragmentation, indicating it can be a year-round strategy for cauliflower soft coral to reproduce.
This study helped close the life cycle for cauliflower soft coral, identifying broadcast spawning and autonomous fragmentation as sexual and asexual reproduction methods respectively. High larval survivability and settlement in the lab coupled with successful transplantation of juveniles to the wild shows promise for future transplantation conservation projects. Transplantation is a strategy employed for at-risk coral populations where larvae are raised in an artificial environment until they are juvenile polyps. Once old enough, they are moved to the wild where they can establish themselves at an age that experiences a significantly lower death rate. Once enough individuals return to an area, they can become self-sufficient and establish a new population. Without these beautiful coral, a critical habitat is lost for important marine life in the region.
I am a recent MSc graduate in marine biology from Bangor University, where I studied population dynamics of elasmobranchs off the coast of Wales. My interests lie in ecological data analysis to understand environmental processes and identify natural patterns. However, nothing beats being in the field and interacting directly with the marine life.