Gerald Herbert / AP

Nesting pelicans fly on Cat Island in Barataria Bay in Plaquemines Parish, La., on April 11, 2012. The island has eroded greatly since the Deepwater Horizon oil spill two years ago.

Associated Press photographer Gerald Herbert says he will never forget what he saw on his first visit to Cat Island, just over a month after the Deepwater Horizon oil spill of April 20, 2010:

Noisy brown pelicans were flying around and swimming in the water, which was carrying waves of newly arrived thick crude. The oil was collecting on the shoreline. Some birds were too coated to fly, looking distressed.

On the lush island rookery, filled with thick mangrove, off-white pelican eggs were smeared with oil from birds sitting on top of them in nests.

I took photographs, documenting the first pelican rookeries affected by the spill. There was a pit in my stomach; I thought this colony may well be doomed.

Gerald Herbert / AP

A pelican sits on the last remaining mangrove remnant on what used to be a small island, as it erodes into the bay next to Cat Island on April 11, 2012.

Herbert decided he had to return to the islands off the coast of Louisiana. A year ago, PhotoBlog published a series of his photographs that showed a dramatically changed ecosystem where land was eroding and vegetation was dead or dying.

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The photographer made a third visit to Cat Island last week, with the disaster now two years distant but its consequences plain to see. "The deterioration was shocking," he writes:

The island had eroded and was much smaller. What was once mangrove so thick only a bird could enter was now black stumps sticking out of the sand. There were fewer pelicans, and they were nesting on bare earth, exposed to the next storm surge.

As I looked out across the water, I got a sick feeling. I thought this may all be gone soon, only a GPS coordinate in the Gulf and a story about what natural beauty was once here.

Gerald Herbert / AP

Pelicans are seen flying over mangrove isolated in the water near the heavily eroded shoreline of Cat Island on April 11, 2012.

Gerald Herbert / AP

The last remnant of what was a small island near Cat Island is seen as it is eroded by the surf on April 11, 2012.

Last year, Associated Press photographer Gerald Herbert covered the Deepwater Horizon oil spill and its aftermath. This month, he returned to see how one impacted area off the coast of Louisiana, Cat Island, is faring a year after the environmental disaster. He discovered a changed ecosystem where land is eroding and vegetation is dead or dying. Biologists from the Louisiana Department of Fish and Wildlife say Cat Island is struggling to recover because the island was completely washed by oil, in part because of poorly maintained oil booms.

Herbert writes: There is no question that Cat Island in Barataria Bay has eroded considerably. Much of the mangrove and marsh grass is gone. The thickets of mangrove, which you could not see through before, now are thinned so much that you can see straight through them. It is quite stunning -- and sad for someone who has seen the previous state of this island -- how much the island has deteriorated both in the accelerated erosion and in the destruction of the flora.

Gerald Herbert / AP

At left, oil smeared pelican eggs are seen in a nest on Cat Island on May 22, 2010 just days after the explosion and subsequent leak began. The island is home to hundreds of brown pelican nests as well at terns, gulls and roseate spoonbills. The photo on right, made at the same spot on April 8, 2011, shows the island significantly eroded and the marsh grass and mangrove trees that pelicans nest on decimated.

Gerald Herbert / AP

At left, oil stained pelicans and baby pelicans are seen on May 23, 2010, on Cat Island. In the image at right, photographed in the same spot on April 8, 2011, the shoreline is heavily eroded and the lush thickets of mangrove trees are mostly dead or dying.

Herbert writes: The pelicans in the region are faring better because they are no longer, for the large part, being contaminated by the oil. The large bands of crude aren't washing onto the nesting shorelines. But, from my unscientific observations, and from reviewing photos and video from then and now, there seem to be fewer pelicans taking flight in the air when we approach the island, probably because there's less real estate to nest there.

Louisiana Wildlife and Fisheries biologists told me that pelicans have a very high nesting fidelity, meaning they nest in the same spots where they were nestlings. As a result, where the mangrove has died on Cat Island, you could see pelican nests on the earthen ground. They used to be safely atop the mangrove, which stand roughly three to six feet tall. Those nests are now exposed to ruin from any storm surge that could come through, even from the many tropical depressions and storms that come through almost yearly.

So the pelicans are faring better because they are not faced with the onslaught of crude that we saw during the oil spill, but their habitat in some places has been severely compromised.

Gerald Herbert / AP

In this two picture combo, nesting terns and pelicans are seen on Cat Island on May 22, 2010, left, as oil from the Deepwater Horizon oil spill impacts the shore. The second photo taken on April 8, 2011 near the same location, shows the shoreline heavily eroded, and the lush marsh grass and mangrove trees mostly dead or dying.

Gerald Herbert / AP

In this two picture combo, pelican eggs smeared with crude oil sit in a nest on on Cat Island in Barataria Bay on May 22, 2010, left. The second photo, taken April 8, 2011, shows newly hatched pelican chicks on the same island.

Gerald Herbert / AP

In this two picture combo, nesting pelicans are seen landing as oil washes ashore on May 22, 2010, left, on Cat Island. The second photo, taken in the same spot on April 8, 2011, shows the shoreline heavily eroded, and the lush marsh grass and mangrove trees mostly dead or dying.

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