November 22nd, 2011 by Marc AuMarc

This year’s sargassum invasion has raised loads of questions: Why is it happening? When will it end? Will the beaches be clear by the time tourists arrive for the high season? Today I’ve been wondering how it will impact the coastal vegetation.

Even in areas where the sargassum seems greatly reduced compared to earlier in the year, it’s secretly still there. Even some beaches that look mostly sandy right now actually have alternating layers of sand and decomposing sargassum built up over the summer and fall. Until it is totally decomposed and washed out to sea by the action of the waves, it seems possible that these nutrients might make the beaches could be more hospitable to the salt-tolerant plants that already live near the shore.

If sargassum floats in continuously or in more frequent waves, perhaps beach sand would gradually turn into something more like a sandy soil. Coastal grasses, beach morning glory, sea grapes, palms and mangroves might be able to move down the beach. If something along these lines did happen, what kinds of impact would it have?

For now, as you can see below, there are just a few small plants sprouting up amongst the sargassum, and perhaps they would have been able to grow in these spots even on a regular year. Only time will tell.

November 10th, 2011 by Marc AuMarc

A couple days ago, thousands of dead fish washed ashore in Salines d’Orient, presumably dead from a hypoxic event. Hypoxia is a lowered level of dissolved oxygen in the water that can kill fish and other animals when they do not have enough oxygen to breathe. Typically, this is caused by an influx of nutrients (e.g., sewage), which causes phytoplankton blooms and increased bacterial activity. This activity reduces oxygen levels in the water, which is what kills the fish.

In this case, there is a large amount of sewage in the water, and the impact was compounded, I have been told, by blockages in the outlets that allow the pond to exchange water with the ocean. Presumably, when the flow of oxygen-rich water into the pond was stopped, the overall oxygen level dropped.

The majority of the dead fish accumulated on the western shore of the pond, which seems natural because the wind would blow the fish in that direction. Above the channel connecting Salines d’Orient to Étang de Poissons I found no dead fish. This makes me think that it is possible that the hypoxic event may not have affected the entire pond, since even with the prevailing easterly wind, there are enough irregularities in the shoreline to catch dead fish floating west.

From what I could tell, there were a minimum of six species of fish dead on the shore, as well as some crabs. There were at least some living fish in the water as well, even near the western shore of the pond. It was unclear what other organisms may have been impacted, such as mollusks, and what the overall impact will be for shorebirds and seabirds that feed on the fish and other animals of the pond.

Overall, it was a pretty gruesome display of our inability to manage our impact on the island. Having just returned from a trip to the British Virgin Islands, I haven’t had a chance to research additional details on the exact triggers of the event, but at the very least it is a clear sign of how fragile our local ecosystems are as they bear the burden of so much human impact. Below are some photos of the pond and the various fish species killed.

October 20th, 2011 by Marc AuMarc

While not yet over, it seems like the sargassum invasion on the island’s east side beaches is losing steam. The New York Times recently published an article about the sargassum, which features a couple photos from yours truly. I’ve personally noticed that there is much less new sargassum on the beaches I frequent, with fresh sargassum often only appearing in isolated spots rather than entire shorelines.

Below are a few photos of the state of the sargassum from early October on Baie de l’Embouchure. The last few photos are from the Le Galion portion of the beach, which was largely spared due to the protective outcrop that shields it from direct easterly swell.

While I was there, I also took a little time to photograph some birds. I even managed to get a few decent shots of barn swallows, which are one of the toughest birds to photograph on the island as they seem to be almost always in flight.

September 6th, 2011 by Marc AuMarc

After figuring out how to find the critters hiding in the sargassum, I couldn’t help but do the same thing again the next day. I didn’t really change my technique, but I figured I would post Sargassum II: Crustacean Bugaloo anyways.

If you’re curious about the technique for photographing them, it was pretty simple. I used a coffee filter to strain the sea water so it was relatively clear and put it into a clear glass bowl with a little flash on each side, triggered by my camera. To get underwater, I just used the flat port from my camera housing, holding it in the water with one hand while I pointed the camera with the other. I think a better approach would be to use translucent container (like tupperware) that would act as a diffuser and put a matte-finish bottom inside the container maybe either black or white. Perhaps I can try this next time.

Below are a whole mess of photos of shrimp and crabs. One thing you might notice on many of the shrimp is a lump on one side of the thorax. These are isopods which parasitize the shrimp. Specifically, they are from suborder Epicaridae, which includes a variety of isopods that parasitize crustaceans (or actually, other crustaceans, because isopods themselves are also crustaceans). The females, which are much larger than the males, attach themselves to the gills of their shrimp hosts and feed on their blood. Often, and it looks to be that case in these photos, the shrimp actually grow their carapace over the isopod, creating the lumps you see in the photos (compared to the symothoid isopods you can see on fish, where the isopod itself is visible). Also, there was one free-swimming isopod that you can see below, it’s dark and curved.

September 5th, 2011 by Marc AuMarc

When the wind changed directions yesterday, it brought to Grand Case the sargassum that has been amassing on St. Martin’s eastern shores for several weeks. In the North Atlantic’s Sargasso Sea, this algae provides shelter for a variety of organisms, such as juvenile fish and invertebrates. So, even though the bay was rough and cloudy, we went out to investigate the floating patches of sargassum.

I found it was possible to find some shrimp amongst the sargassum, although it was tough to do while snorkeling. Instead, I developed another approach, grabbing clumps of sargassum and shaking them out over a plastic bowl. Using this method I was able to to find a variety of creatures, mostly shrimp of different sizes and colors. I also found a few small crabs, including one very strange looking larval crab.

Did they really come all the way from the Sargasso Sea? I’m sure some of the critters could have joined the floating caravan as it has travelled this way, but I would guess many or most of them are, like the sargassum, far from their normal home. Apparently there are a variety of shrimp from the genus Latreutes and others that are residents of the sargassum, often adapted in color and shape to be well camouflaged in that environment.

What is their fate? It would seem that they’re mostly doomed as their homes wash up on the beach. Even if they manage to stay in or get back to the water after their sargassum is gone they would make an easy meal with no place to hide. In the meantime, anyone with a bucket and a little patience can explore an ecosystem that’s traveled hundreds of miles to visit our island.

Below are some photos of crustaceans taken from sargassum, mostly a variety of shrimp. If you look closely, you can see eggs on the underside of some of the shrimp, and organs through their transparent shells.

September 1st, 2011 by Marc AuMarc

For a number of years, the ongoing spread of invasive lionfish in the Atlantic and Caribbean has been the hottest story in marine biology. The invasion has been unprecedented in its speed and impact, from one or more initial introductions probably in the early 1990s to their increasing range and ballooning populations today. Today, they can be found along the east coast of the US from North Carolina to Florida and in most of the Caribbean. In the future, that range may extend to the southern end of the Brazilian coastline.

As the problem has progressed, our ideas about how to address it have changed as well. However, it seems like the lionfish invasion is not only outpacing our efforts to control it, but also our thinking about the problem. As far back as 2003, the NOAA issued a report conceding that elimination of the lionfish was “nearly impossible.” Even back then it occupied much of the southeast US coast, in a wide variety of habitats and in surprisingly high numbers. Still, we held out hope that we could keep it from spreading or manage the population. As it reached each new area, we headed out with nets and spearguns hoping to keep it from becoming established only to fail every time.

To take a step back, humans don’t have a great track record of eradicating invasive species. I think we’ve done it a few times, mostly eradicating goats or rats on uninhabited islands with great effort and expense. The lionfish problem is many orders of magnitude greater. They reproduce quickly and can travel unrestricted throughout the Atlantic and Caribbean. Like many tropical fish, during their larval stage, they are thought to ride the open ocean currents for weeks before settling down. Only a small part of their habitat, shallow reefs visited by snorkelers and divers, is even accessible to humans. At best, eradication could only happen in the tiny sliver of habitat where humans are present and would easily be re-invaded by individuals from the next island or even just a few hundred meters away in deeper water.

To be fair, a typical lionfish plan also includes studying their impact on local ecosystems and raising awareness in the local population. These two goals are worthwhile, and they implicitly assume that lionfish are here to stay. Annual lionfish hunts and the recent push to drive interest in eating lionfish, on the other hand, get much more attention in the press and the public imagination. Biological control, such as attempts to “teach” grouper to eat lionfish are more plausible than going out to catch them all by hand, but at best would only adjust the eventual population equilibrium they reach.

Of course, I would love it if we could eradicate lionfish in the area, and I think it is admirable to give it a shot. At the same time, it seems pretty clear that it won’t work. I think that’s pretty hard to admit, but consensus is bound to move that direction. As we move in that way, the main question will be, how do we preserve marine ecosystems as best we can despite the presence of lionfish?

That’s a harder question to answer. More robust marine ecosystems will probably fare better, so expanding marine protected areas might help offset losses due to lionfish predation. Artificial reefs could increase the total available habitat for reef fish as well. Because small and juvenile fish are particularly vulnerable to lionfish predation, it may be worthwhile to create protected nursery areas. If I were more knowledgeable, I would probably have more or better ideas, but I’m sure those will come as the focus shifts from attempting to control lionfish to doing what we can to save the rest of the ecosystem. It won’t be easy, but at least it won’t be impossible.

Below are some photos taken while snorkeling in Grand Case Bay. There’s a lionfish in the piece of pipe, and the photo after that shows a lionfish marker placed at the site, which is used to make it easier for the marine reserve to find and capture the lionfish. Many of the other photos feature juvenile fish that don’t yet know how threatened they are.

August 24th, 2011 by Marc AuMarc

After being away for a couple weeks, I returned to find the sargassum that had been washing up on the beaches of St. Martin has accumulated to a surprising degree. Sargassum is seaweed, and typically refers to a couple species in the genus Sargassum that live in the open ocean. This is unlike many macroalgae, which are attached to the bottom in shallow waters.

The Sargasso Sea in the North Atlantic Ocean is, of course, named after this alga. For the most part, currents surrounding the Sargasso Sea keep the sargassum in that area. The seaweed provides food and cover for certain marine animals, such as the loggerhead sea turtle.

At this point, I don’t know that there is a definitive answer about why such a large amount of sargassum is showing up in the Caribbean this summer. Some have noted that there are higher than average temperatures in the North Atlantic, which may have increased the amount of sargassum.

On St. Martin, primarily the Atlantic-facing eastern beaches have been impacted. In Grand Case, for example, one would have no idea that anything unusual was going on. Below are some photos from the beach at Grandes Cayes, where there are some pretty significant accumulations. When decomposing, the hydrogen sulfate that is released smells unpleasant and may pose some threat to those with asthma or other respiratory conditions.

What’s next? It’s tough to say. Removal from the beach is difficult without also removing sand, and heavy equipment would likely destroy sea turtle nests. As long as it stops accumulating, which seems likely, then it should biodegrade naturally over time. In the meantime, it’s a boon to isopods and other beach denizens that can eat it.

April 25th, 2011 by Marc AuMarc

Yesterday afternoon I went on a quick expedition to the lagoon area off the north beach of Pinel with Pauline from the Réserve Naturelle. Our goal was to check the elkhorn corals to see if there were broken pieces suitable for transplanting. Elkhorn corals are both prone to breakage and often do well when transplanted.

At the large elkhorn we located we found a very interesting scene. The main colony was large and healthy. There were a couple pieces I had wedged into the dead coral substrate on an earlier visit as well as a number of other pieces on the sea floor. While a few of these were loose, many of them had managed to affix themselves and were growing in the areas down-current from the main colony. Most surprising was one particularly large branch that had affixed itself upside-down with the broken part at the top.

It was encouraging to see how well the coral was colonizing naturally with the broken pieces, but we also planned to visit the site regularly. Even though many pieces had successfully reattached, it is unclear what the percentage of successful reattachment is. It is possible that the dozen successes are just a small subset of the total number of broken pieces. A bit more ominous was the presence of a fair amount of algae in the lagoon, perhaps indicating an excess of nutrients that could be problematic for corals. More news to come!

April 22nd, 2011 by Marc AuMarc

I’m admittedly quite a bit behind in my posting after spending so much time on the Love the Lagoon fundraising event, but I did want to post the article from SXMFaxInfo about our mangrove marine life survey:

March 30th, 2011 by Marc AuMarc

Come to the Love the Lagoon fundraising event Saturday, April 2nd starting at 7pm. The event is at the Sand Bar at Isle de Sol in Simpson Bay, Sint Maarten. Proceeds from the event will go towards buying a sewage pumpout boat that will take sewage from boats on both sides of the lagoon for treatment, rather than it going straight into the lagoon.

There will be music from Simple Stand, exhibits about the lagoon, raffle and much more. There’s additional info on Facebook and the EPIC website. If you can’t make it, find out how to donate on the EPIC site.