Reference: Canty, S. W. J., Kennedy, J. P., Fox, G., Matterson, K., González, V. L., Núñez-Vallecillo, M. L., Preziosi, R. F. & Rowntree, J. K. 2022. Mangrove diversity is more than fringe deep. Scientific Reports, 12, 1695. https://doi.org/10.1038/s41598-022-05847-y
The Mighty Mangrove
Many of Earth’s most powerful phenomena occur where natural forces meet. Storms and tornadoes form where cold fronts encounter warm fronts. Earthquakes, volcanos, and mountains occur where Earth’s plates interact. Where the land meets the sea is no exception. Here, the mighty mangrove forest plays an essential role as a protector of the coastline and creatures of land and sea alike.
At the frontlines of coastal regions across the world, mangrove trees are experts at dealing with harsh conditions. Changing tides, varying salt content, and oxygen-lacking soil are just some of the artilleries that mangroves face at this intersection. In braving these extreme environments, mangrove forests protect against erosion and tropical storms that ravage the coast and provide home and shelter for the diverse life that occupies these regions. Mangroves are also especially good at reducing carbon dioxide from the air, a major contributor to climate change.
To add to the list of challenges, mangroves have faced drastic declines over the last 60 years due to deforestation for city expansion and shrimp and fish farms. Removing mangroves reduces forest coverage and causes once-continuous forests to be fragmented. Protective measures have slowed the rate of logging, but researchers remain cautious about the future of mangrove forests. A recent study by Steven Canty and colleagues used genetic analyses to see how related trees are between and within mangrove forests – data that can supplement the protective measures. Maintaining genetic diversity could equip these forests to withstand perhaps their greatest battle yet: climate change.
It’s in the Genes
Like animals, trees pass down DNA to offspring from generation to generation. While trees of one species share very similar DNA, there can still be considerable genetic variation between individuals. The more diversity there is in a population, the better that population can adjust to disturbances. Consider a disease that is introduced to a forest that targets trees with a specific genetic makeup. If the entire forest is genetically similar and vulnerable to that disease, the whole forest may be wiped out. If the trees have diverse genes instead, the disease will only impact a small number of trees, and the forest can persist.
By measuring the diversity between trees, researchers can predict how resilient the forest will be to disturbances like disease, climate change, and deforestation. Past studies on mangrove diversity have focused on testing only the seaward edge of the forests because this area takes the greatest hit from tides and storms. Canty and his team of researchers tested genetic diversity within a mangrove forest and among coastal edges of forests separated by sea. The researchers extracted DNA from the leaves of 269 Red Mangroves in the Honduran Caribbean.
The DNA evidence showed that trees within the forest were genetically diverse from trees at the seaward edge. Like past findings, edge trees are closely related to the edge of distant mangrove forests. Here, mangroves were related across distances reaching 115 kilometers, while greater diversity was found just 20 meters into the forest.
Protecting the Protectors
The edges of mangrove forests are often related, sharing similar DNA passed between coastlines. Pollen released by mangroves on the forest’s edge can disperse over thousands of miles, carried by the ocean’s air currents. Scientists still question how the forests have become so diverse internally. The authors speculate that storms damage the frontlines, creating holes in the forest edge for trees at the interior to be pollinated by distant and local sources.
Genetic diversity is essential for dealing with the unpredictable changes brought on by climate change. Mangrove forests carry a great deal of genetic diversity within, suggesting that management and restoration should focus on protecting whole forests rather than exclusively the edge. Genetic analysis at small and large scales will be vital for monitoring mangrove forest health. Completing these tests can also indicate how pollen disperses and where to plant mangroves to facilitate pollination. To protect the protectors of the coast, you can make sustainable choices, support restoration initiatives, and keep updated on mangrove projects. With your help, the mangrove forest can continue to be a force to be reckoned with where ocean and land collide.