Where Land Meets the Sea

November 4, 2015

The edge of the sea is a place of amazing connections.


Mangrove forests face growing threats from unsustainable land development, pollution, clearing for agricultural use, and climate change. © Carrie Vonderhaar, Ocean Futures Society

It is where the ocean crashes relentlessly against the boundaries of the land, where air interchanges between atmosphere and liquid water, and where life continuously moves with the rhythmic rise and fall of the tides. It is not always a calm, safe, or predictable place. Some species, however, have discovered ways to thrive. One habitat, in particular, plays a crucial role in ocean health, and as scientists continue to discover, an important role in our health and economic security. These mystical, tangled jungle gyms of roots and branches that inhabit the edge of many tropical coastlines are the mangrove forests – regions of rich biodiversity of both terrestrial and marine life, and intricate linkages between the coasts and open sea.

From afar, mangroves may look like ordinary bushes that lie along the edge of the water. But up close, mangrove are actually trees and form forests resembling a web of intricate branches with highly specialized adaptations allowing their roots to survive both above, and below, the salty surface of the sea. A harsh environment unsuitable for most plants, mangroves flourish in the intertidal zone, margins between land and sea. With over seventy species of mangroves around the world, they come in numerous shapes and sizes, but one thing remains: they are immensely important for supporting healthy marine and coastal life in more ways than most people realize. It was on a trip to the Florida Keys that I came to deeply understand how imperative mangroves are to our future.

Expedition to the Florida Keys

When I first arrived at the Dry Tortugas, a small group of islands in the Gulf of Mexico at the bottom end of the Florida Keys, my team and I were eager to explore the natural wonders of the Florida Keys National Marine Sanctuary. We knew there was a breadth of diversity, both above and below the sea. We journeyed here to the southern tip of the Florida Keys for a television series in 2005 to film our PBS Ocean Adventure Series: America’s Underwater Treasures.


The shallow waters around mangrove forests provide juvenile fishes and invertebrates safety from bigger predators. © Carrie Vonderhaar, Ocean Futures Society

The Florida Keys National Marine Sanctuary is home to North America’s only living coral barrier reef, and the third longest barrier reef in the world. Within these waters lie spectacular marine landscapes, including seagrass meadows, mangrove islands and extensive coral reefs. Joining us were marine scientists eager to explain the value of the Florida Keys National Marine Sanctuary, why we must continue to learn more about all of these diverse habitats and how many of these habitats are connected and critical in protecting threatened and endangered species. As we climbed aboard our dive boat and took out across the water, I was filled with questions: do these diverse environments work together? What species need them to survive? Do they all contribute to the richness of this region?

On our first dive in the Florida’s Keys warm, clear blue waters, I remember vividly the many species of hard and soft corals scattering the seafloor, along with colorful sponges and schools of vibrant fishes. And then, as we approached an old shipwreck, I laid eyes on her. She was beautiful, with olive-green skin and dark spots over her body, her large round eyes stared back at me as our dive team slowly approached. It reminded me of my youth in the Mediterranean Sea before large fish were wiped out, particularly, the large, beautiful groupers. Here, I find my fiancé; I like to call her, an adult Goliath grouper, one of now many in Florida Keys, but a species with a rich and troubled history.

Across the world, sensational tales of Goliath groupers stalking and attacking fisherman have been told throughout the centuries. A species that can grow to over 800 pounds, it’s no wonder goliath groupers have forged such an imprint and captured fascination among fishermen and divers alike. As rulers of their home territories, goliath groupers are found in predictable places, around deep water shipwrecks, sink holes and natural ledges that provide them both protection and a place to ambush unsuspecting prey. They also aggregate in huge numbers during certain times of the year to reproduce. This predictable pattern has gotten them into trouble.


Jean-Michel Cousteau and the team explore mangroves forests to learn more about their vital role in keeping our oceans, and people, healthy. © Carrie Vonderhaar, Ocean Futures Society

Due to rising demands for their meat, populations of goliath groupers declined severely during the 1980s, and some populations disappeared altogether. Once listed as critically endangered, goliath groupers have been rebounding in recent years due to increased protection over the last two decades. But it isn’t just protecting goliath groupers from overfishing that is important to the survival of their species. Even though groupers spend their adult lives in deeper waters, their species would not survive if it weren’t for an entirely different ecosystem – the mangrove forests that line the shallow coasts.

Mangroves are the vital link

In fact, many people don’t know mangroves may actually be the bottleneck to the survival of their species, not just for groupers, but also for numerous valuable fish species. They are immensely important habitat for juvenile fishes. As researchers learn more about the life cycle of groupers and other fishes, they are realizing the various life stages and the importance of particular habitats, like mangroves, in supporting new generations of fishes. Because of the intricate branches and roots, mangroves provide the perfect sanctuary for young fishes and invertebrates like crabs and shrimps. Here, they are safe from bigger predators, and can hide and hunt among the complex branching structures of the mangrove roots. For Goliath groupers, juveniles will spend the first five to six years of their lives living among these tangled undersea nurseries. In South Florida alone, it is estimated that up to 90 percent of commercially valuable sea life depends on the mangrove forests for some stage of their life cycle.

Three species of mangroves inhabit south Florida’s coastline: red, black, and white mangroves. Along the edge of the sea, they can form dense aggregations, turning shorelines into forests. To survive this harsh environment, mangroves have special adaptations, including filtration systems that keep salt out and complex roots that anchor mangroves upright in shifting sediments. Their complex root structures help trap and recycle nutrients, as well as filter toxins from the water. Particularly important for us, mangrove forests are responsible for keeping our shorelines intact. They act as buffers, protecting the coastline from erosion due to major storms and hurricanes. And up in the treetops, mangroves provide nesting grounds for hundreds of bird species like brown pelicans, magnificent frigate birds and roseate spoonbills. Without the mangroves, coastlines erode, birds leave, juvenile fish loose their nursery home, and the link between open sea and coastal realm is lost.

Disappearing mangroves around the world

In the Florida Keys, as much as 60 percent of shallow mangrove forests have disappeared from coastlines. Worldwide, the declining trend is alarming. Scientists estimate that nearly half the world’s mangroves are either destroyed or in dangerously poor condition. The greatest threats come from unsustainable development and land clearing for commercial enterprise or agricultural use. As global tourism increases, the demand for coastal development is likely to rise. However, great progress can be made if visitors understand the value of mangroves, and choose travel destinations that conserve and protect mangroves and the rich ecosystems they support.


One of the larger fishes in the sea, Goliath groupers, spend the first five to six years of their lives in the sheltered branching roots of the mangroves. © Carrie Vonderhaar, Ocean Futures Society

As I always say, everything is connected. The relationship between mangroves and the ocean is interconnected within the larger complex oceanic system. It amazes me to know that one of the bigger fish we find in the sea, the magnificent Goliath grouper, first begins its juvenile life swimming around the dangling branches of the mangroves, seeking shelter in the nursery grounds of nature. As our shifting climate leads to more frequent and stronger storms, mangroves are our first line of natural defense, protecting shorelines, homes, and people. We need mangroves to be healthy, strong, and productive so that our fisheries may flourish, our coastlines strengthen, and our natural world rebuilds.

Warm regards,


Jean-Michel Cousteau
President, Ocean Futures Society
with Jaclyn Mandoske