In temperate and cold-water marine environments, corals are a key group of animals that form dense aggregations often referred to as marine “animal forests”. Like tropical coral reefs, these coral-dominated habitats are centers of biodiversity that form lush and colorful communities, providing a wealth of goods and services that contribute to human well-being. From building complex 3-D habitats that serve as nursery, shelter, and feeding grounds for many other species (including species of commercial value) to contributing to nutrient cycling and carbon sequestration, thereby participating in the regulation of natural processes such as climate, corals provide crucial ecosystem services.

Sadly, coral ecosystems have been declining at unprecedented rates worldwide due to the increasing prevalence of human disturbances like pollution, overfishing, habitat destruction, and ocean acidification and warming resulting from human-caused climate change. The magnitude of these impacts is such that in a great many cases active interventions are required to restore and preserve these habitats. The urgency for action is manifested in the United Nations General Assembly recent announcement declaring 2021-2030 as the “decade of ecosystem restoration”.

Our team at the Centre of Marine Sciences in Faro (Portugal) is working with local stakeholders, especially fishing communities, to develop effective tools for the restoration of temperate coral habitats occurring from 30-200 m depth. During their fishing activity with nets deployed on the sea floor, fishermen accidentally capture corals that become entangled in the nets as they are hauled to the boat. We actively collaborate with the fishermen to rescue these corals and test different methods for the restoration of coral habitats. Specifically, we have been using these “corals of opportunity” to refine approaches to outplant them back to impacted areas using various substrates (so-called asexual propagation), as well as to induce them to reproduce in captivity in order to study various aspects of their early-life biology with the goal of using the baby corals in restoration (so-called sexual propagation).

Corals have a two-stage life cycle in which the gametes and larvae released during reproduction are the only free-living stages before the larvae settle onto the seafloor and metamorphose into the sessile polyp stage. One of the challenges with coral sexual propagation is to identify the timing over which reproduction takes place and to replicate the natural conditions that lead to the maturation of the gametes and release and settlement of the larvae in captivity. We have been actively working on that front with a number of different coral species occurring in southern Algarve. Within the scope of RESTORESEAS, we have recently collected larvae from colonies of the sea fan Paramuricea grayi, which were rescued by fishermen and kept in our aquaria system at the Ramalhete Marine Station.

During this event it was possible to determine that the species is a surface brooder, a mode of reproduction in which the embryos and larvae are “brooded” in a film or string of mucus on the surface of the maternal colonies before they are released. PhD candidate Christina Egger has been making detailed observations of their early-life stages as part of her thesis work, including larval development, release and survivorship in culture, as well as the metamorphosis of larvae to a polyp and post-settlement survivorship. Importantly, Christina has been challenging larvae with a number of different substrates to determine settlement preferences, a critical consideration for sexual propagation of corals. In these preliminary experiments, multiple larvae settled on the skeleton of gorgonians, revealing some degree of preference. In future work, we will assess the beneficial properties of this and a wider range of substrates for larval settlement, under varying degrees of conditioning in the field and in culture with bacterial isolates to test for beneficial effects on settlement, growth and survivorship.

Written by Márcio Coelho and Aschwin Engelen, CCMAR