Stronger storms are bad news for coastal ecosystems

Satellite image from NASA of Hurricane Katrina over the Gulf of Mexico showing sea surface temperatures.

Each year hurricanes, large and small, form over warm waters with many moving inland, causing great amounts of damage along coastlines. Currently, there is much debate over how climate change will affect tropical storms. While monitoring suggests there has been little to no increase in the amount of storms, recent evidence indicates that warming oceans are leading to more powerful storms [1, 2]. Since 1975, the overall number of hurricanes has not risen, but the number of category 4 and 5 events, the most devastating types of storms, has increased [2].

Katrina costs

Hurricanes that reach land can have devastating effects. In 2005, Hurricane Katrina hit the coast of Louisiana in the US, killing 1,836 people, affecting millions, and causing billions of dollars in damage. When a category 4 or 5 hurricane reaches land, homes are lost, people become displaced, and businesses are ruined. As cities and towns are devastated, the surrounding ecosystems are also affected by waste and refuse that flow from the hurricanes destruction [3]. Hurricane Katrina was one of the most destructive storms observed in the last several centuries, and the impacts on the surrounding ecosystems are predicted to last for decades [3, 4].

Mangrove roots support a unique community of organisms that are devastated by tropical stroms that wash sand over the roots.

Coastal environments are altered severely by storms

Hurricanes are accompanied by strong winds, tornadoes, storm surges, and large amounts of rainfall that can damage and sometimes destroy the many ecosystems that are found along the coast. Mangrove stands are coastal ecosystems where many specialized groups of marine organisms thrive. During storms, vegetation is ripped out and sand washes in, scouring and damaging the mangrove roots, harming the animals that live there. In 1992, in the Bahamas and Southern Florida, Hurricane Andrew stripped old mangrove stands down to stumps, devastating this diverse ecosystem [5].

Threatened barriers

Barrier islands are low lying offshore deposits of sand and other sediments found on coastlines all over the world. Sheltering near-shore habitats, they act as natural barriers against wind and waves, and are greatly impacted by large storms. When hurricanes hit, barrier islands often are submerged and begin to erode [6]. Seagrass beds are also threatened by increased exposure to the open ocean, which are found between barrier islands and the mainland. Such seagrass beds are critically important to many fish species, sea turtles and marine mammals, which depend on them for food and habitat [3]. In large storms entire seagrass beds can be uprooted and destroyed. Delicate in nature, seagrass habitats are already in need of protection and have been severely degraded by industrial developments along the planet's coastlines. In many parts of the world as much as 80% of the seagrass beds have been destroyed [7-10].

Seagrass and eelgrass beds are found in sandy bottom habitats that are particularly at risk from tropical storms.

Eroded ecosystems

Erosion caused by massive storms can also be harmful to coastal ecosystems. Large influxes of eroded sediments can reduce habitat for coastal birds, mammals and numerous invertebrate species [3]. Hurricane Iniki in Hawaii caused beach face erosion 300 meters inland, creating mounds of sand 9 meters high [11]. Shorebirds that nest along coastlines are frequently injured or killed during large storms due to wind and rain, and birds that do survive are often left without a home [12].

Contaminated wetlands

Coastal and inland wetlands are also threatened by powerful storms. After hurricane Katrina, marshes and swamps were inundated with saltwater and polluted runoff from the flooded cities and towns. Massive tree blow-downs also occurred. Collectively, these threats translate into habitat loss for entire suites of animals, including threatened species such as the Brown Pelican [3].

Over the long-term, high salt levels in wetlands may change plant community structure, altering the entire ecosystem [12]. Salt levels in wetlands and terrestrial soils may remain elevated for up to a year after a hurricane [12]. Amphibians and reptiles in these areas are at risk due to their sensitivity to toxins and disturbances, and are slow to return to impacted areas [4]. In places such as Louisiana that have been hit particularly hard by severe hurricanes over the last decade, the wetlands are being lost at a rate of 40 km² per year [11].

Reef grief

Hurricanes also have devastating effects on coral reefs, another ecosystem already under threat. When hurricanes hit coral reefs, pieces of the beds are ripped, sand scours the entire area and whole parts of the reefs are flattened. Animals that live in coral reefs, such as sea urchins, snails and fish, ultimately suffer population reductions. In 1980, Hurricane Allen left many reefs in Jamaica devoid of any damselfish, algae grazing animals that have been found to keep corals nicely groomed and healthy [5].

May get worse with climate change

Surface temperatures around the world on the rise.
Prepared by Robert Rohde for Global Warming Art.

This trend of intensifying hurricanes is likely to continue with a 5% increase in storm intensity expected for every 1°C increase in tropical ocean temperature [1]. We have already observed a 0.4°C increase in sea surface temperatures since 1950 in some of the world's oceans, with even warmer waters predicted for the future[13]. Coastline ecosystems are already compromised by habitat loss, pollution, and invasive species – they don't need the added headache of stronger hurricanes! Unfortunately, these fragile ecosystems may be up against more than they can handle.

Coastal Ecosystems Connections lesson plan

1. Emanuel, K., Increasing destructiveness of tropical cyclones over the past 30 years. Nature, 2005. 436 : p. 686-688.

2. Webster, P., et al., Changes in tropical cyclone number, duration, and intensity in a warming environment. Science, 2005. 309 : p. 1844-1846.

3. Sheikh, P.A., The Impact of Hurricane Katrina on Biological Resources, in CRC Report for Congress . 2005, CRS Report for Congress. p. 12.

4. Donaldson-Evans, C., Southeastern Loisuana's ecology slowly retunrs following hurricane Katrina. 2006, Fox News.

5. Woodley, J.D., et al., Hurricane Allen's Impacts on Jamaican Coral Reefs. Science, 1981. 214 (4522): p. 749-755.

6. Llanos, M., Louisiana loses chunk of natural storm buffer. 2005, MSNBC.

7. Kendrick, G.A., et al., Changes in seagrass coverage in Cockburn Sound, Western Australia between 1967 and 1999. Aquatic Botany, 2002. 73 : p. 75-87.

8. Walker, D. and A. McComb, Saegrass degradation in Australian coastal waters. Marine Pollution Bullentin, 1992. 25 (5-8): p. 191-195.

9. Changes in eelgrass (Zostera marina) in sourthern Gulf of St. Lawrence estuaries. 2006, Fisheries and Oceans Canada.

10. Baden, S., et al., Vanishing seagrass (Zostera marina, L.) in Swediah coastal waters. Ambio, 2003. 32 (5): p. 374-377.

11. Sallenger, A., Hurricane impacts on the coastal environment. 2004, USGS.

12. Michener, W.K., et al., Climate change, hurricanes and tropical storms, rising sea level in coastal wetlands. Ecological Applications, 1997. 7 (3): p. 770-801.

13. Bratcher, A.J. and B.S. Giese, Tropical decadal variability and global warming. Geophysical Research Letters, 2002. 29 (19): p. 24-1 to 24-4.