Coral reefs are vital for coastal protection as well as a having a huge influence on marine ecology. Without reefs, fish populations would be in severe decline, reducing the amount of food available to humans and also causing considerable harm to the marine ecosystem. All in all, corals are more important than you may give them credit for.
Staghorn Coral (Corpora cervicornis) is considered a keystone species for reefs and is found throughout the Caribbean and the Great Barrier Reef. Its importance is due to its role in providing structural support to coral reefs. Its fast growing and complex structure provides the perfect natural defence against storms. Its also critical to the ecology of reefs, creating protection by acting as a nursery for many species of juvenile fish and is fundamental for the entire ecosystem. Over the past few decades, a combination of white-band disease and increased human activity has caused a severe decline in the number of Staghorn and Elkhorn coral, two species from the genus Acropora sp., throughout the greater Caribbean.
To combat this decline in coral populations, coral nurseries have been the primary response to increase rates of growth and recovery. Simply put, this method is marine agriculture, whereby coral fragments are extracted and grown in protected areas with optimum conditions. This allows the monitoring and management of coral growth, with the intention of reintroducing these into natural colonies to boost reef infrastructure, speeding up recovery.
At the moment, a huge focus is placed on genetic studies of populations throughout the Caribbean. This identifies areas of gene flow to locate potential recruits for coral nurseries and is vital for the recovery of this ecologically crucial coral.
The coral species have two forms of reproduction: sexual reproduction which occurs in August/September and asexual fragmentation. The most common form of reproduction is by fragmentation due to naturally damaged corals in storms becoming new genetically-identical colonies. Sexual reproduction is limited by oceanographic conditions such as water speeds and currents, so local populations have low genetic variation making non-native recruit an issue. Due to this, the question being asked is: where can recruits be taken from to boost rapidly declining Staghorn colonies?
The general consensus from multiple studies is that there is a very low level of genetic exchange between populations within the Caribbean. A Caribbean-wide study of genetic connectivity demonstrated that long distance dispersal by sexual reproduction is limited (>500km), with a high level of local genetic structure. This is seen in the Florida Keys despite having the highest levels of variation, demonstrating a recent geologically halt in gene flow. Around the island of Puerto Rico, highly developed genetic structure of different reefs of different regions, and even within populations, shows that sexual reproduction is extremely limited with little genetic connectivity between populations.
Due to the limited genetic connectivity between populations, using non-native recruits poses various issues such as local adaptation to the specific conditions. Studies have shown how the mortality rate of Staghorn Coral fragments is heavily affected by the link between the local conditions of the nursery and the coral’s original position. This has caused issues whereby the donor colony ocean conditions have to match the conditions of the nursery site. The high levels of genetic structure within different regions demonstrates how populations have become highly adapted to the conditions of their origin.
The introduction of non-native staghorn corals from nurseries to boost population declines is an appealing solution, however studies advice against this. This is due to low levels of genetic connectivity causing high levels of genetic structure in each population. Management plans should therefore be set up to boost local populations using local coral nurseries sites. Without the presence of a genetically-connected, protected marine site for these corals the best alternative is to concentrate conservation efforts on protecting individual populations. Once the recovery of individual declining populations has been achieved, efforts should be turned to increasing genetic connectivity throughout the Caribbean
In terms of recovering coral population declines, coral nurseries are our best bet! In Mexico, Expedition Akumal are a group creating coral nurseries for Staghorn Coral and more information can be found here.