Hurricane Irma made landfall in the US as a Category 4 in Florida in early September. According to Corelogic, an analytics company, damages to commercial and residential areas in Florida could cost between $42.5 and $63 billion. Yet, the damage wasn’t just to homes and buildings. Below the water and along the coastline in places like Miami Dade County, coral reefs, mangroves and seagrass were also affected by the storm.
According to experts, it could take years for the ecosystems to recover completely from the effects of the storm. Most of the damage wasn’t caused by Irma directly, but rather by human debris that was blown into various environments by the storm.
However, it isn’t all bad news. Though destructive, hurricanes can sometimes have positive effects on an ecosystem adapted to periodic storms.
How the Coral Reef Fared
The Florida Reef Tract stretches from Martin County all the way south and west beyond Key West. As Irma sideswiped the west coast of Florida, the reefs were hit by huge currents of water that caused havoc to the branching species.
Professor Diego Lirman from the University of Miami monitors ten coral reef sites along the Florida Keys. He was able to begin assessing the damage to the sites including four coral reef nurseries within a week after Irma hit.
“We saw very variable damage going from a lot to minor damage,” Lirman said. “The reefs that fared worst were in the Miami area. The damage got progressively less as you went towards the south toward North Key Largo.”
The time it will take the coral to recover from Irma’s effects depends on how the age of the broken corals. “Some things will recover faster than others. Small corals will recover faster, but the big corals that are lost will take centuries to recover.”
However, while reefs may be adapted to withstand some hurricanes, the increasing amount of large, man-made debris in the ocean make storms more damaging as the debris slams into reefs. Lirman said, “One of the sources of physical damage that we saw after the storm were broken lobster traps and crab pots. Every single reef I visited, we saw pieces of line, traps and fishing gear,” Lirman said. “Long lines with grates, wood and metal meshes get caught and cause coral to fracture.”
The reefs are already hanging on by just a thread, including threats from impacts such as bleaching, disease, and dredging. “These reefs have been hit by multiple disturbances over time… This storm is just one more thing,” Lirman said.
The Mangroves Benefited from the Storm
Irma was bad news for the coral reefs, but there might be some small silver lining for Miami’s mangroves. Mangroves are groups of trees that grow closely together along coastlines, and hurricanes are practically an essential part of their life cycle. Mangroves depend on strong storms for growth according to Prof. Rafael Araujo, an expert on Mangroves, also from the University of Miami. Although frequent, stronger hurricanes can also be problematic for mangroves.
Araujo said that he was hopeful about the potential growth that will follow the storm's aftermath. “Overall there is a little bit of defoliation. In some places in the Keys, some trees were broken off by the force of the winds. Those will take a little time to recover. The other ones should be fine by the time springs rolls around,” Araujo said.
“With most trees, after they suffer a stressful episode, they go into growing mode. The produce more leaves and shoots and foliage than usual. The hurricane acts as if it prunes the tree and the tree comes back to life after the pruning,” Araujo explained . “In general, mangroves in the Caribbean are adapted to this kind of event.” When the mangroves are defoliated by a giant storm, more light reaches down in between the tree branches and stimulates the growth of new shoots down by the base of the tree cluster. Also, storms like Irma push deposit nutrient filled soil into the patches where the mangroves grow, which creates more surface area for new tree clusters to form. That is especially good since, according to Araujo, mangroves are a natural barrier against storm surges preventing flooding further inland.
However, once again, human intervention changes the equation. Araujo said that he was especially concerned by the amount of debris that the storm forced into the mangroves in Miami-Dade that he monitors.
Despite their resilience, the mangrovesstill aren’t entirely impervious to storms. A strong enough hurricane could create a storm surge so significant that mangroves would either be drowned out or washed away entirely. “The interaction of geology and the change in hydrology is concerning,” Araujo said. Fortunately, nothing like that has occurred after Irma as far as Araujo knows. Araujo noted that repeated hits from increasingly stronger storms could irreparably damage the mangroves.
Araujo has not yet done an official assessment. He only measures the mangrove structures yearly. However, he has been out to do a little cleaning. “With storm surges, you get a lot of garbage, bags and plastic bottles,” Araujo said. “If there is something there that is not natural the seeds will have a tough time recruiting. What we do is clean up that type of debris, and we leave anything that can decompose and create a natural fertilizer for a new forest.”
Possibly a bigger threat to mangroves are humans. Purposely removing mangrove is illegal yet it still occurs. The Miami Herald reported on concerned residents notifying county officials that some cleanups were wiping out perfectly healthy mangroves.
How the Already-Struggling Seagrass Survived Irma
Unlike mangroves and coral reefs, it is not immediately obvious how seagrass ecosystems in Biscayne Bay and Florida Bay were affected by the storm. Like coral reefs, deposits of unwanted sediment from rough waters may have buried and damaged some of the seagrass beds. Lisa Spadafina from the county’s Department of Environmental Resource Management (DERM) said that the county is still in the process of accessing the damage to ecosystems in the bay.
“I think it may be a little early to see any effects, Spadafina said. “It has not been long enough for the seagrass to react yet, and it may not.”
DERM is staying vigilant in case there are any effects on the seagrass or the water quality of the bay. “What we may see in the future are impacts from water quality and turbidity. That is what you expect to see after a large storm,” Spadafina explained. “Increases in chlorophyll can be used to measure algal blooms and increase in turbidity is the sediment being stirred up.”
The Sun Sentinel reported that a power outage caused by Irma allowed 6 million gallons of partially treated sewage to spill into Biscayne Bay. That could spell bad news for seagrass beds that are already suffering from a die-off in the bay. According to reporting by the Miami Herald, experts are not yet sure what specifically is causing the die-off, though there are several factors that they are keeping an eye on, sewage contamination among them.
The other potential culprits are salinity imbalances caused by excess rain or the filling of dredge pits in nearby regions. The reduction could be due to a combination of all those factors. The result is clear, however: a loss of 21 square acres of seagrass according to the Miami Herald.
State of the Environment
Two months after Hurricane Irma, conditions are still not perfect, but things could be worse. The brunt of the damage was done to Florida’s coral reef, already struggling from a range of stressors.
Preparing these ecosystems for next year’s hurricane season is imperative. Reducing the amount of debris that poses a risk to both mangroves and coral reefs, as well as minimizing pollution runoff will help increase the ability of these ecosystems to withstand storms. The chances of something similar to Irma hitting Miami sooner rather than later seem to be rising. According to the Center for Climate and Energy Solutions, storms in the Atlantic are expected to increase in intensity.