This morning I took some photos of the large windrow of sargassum currently floating in HMB just off the southern coast. We first noticed this area beginning to accumulate about 2 weeks ago, and wondered if it was being trapped inside by the barrier. Now that the southern sections of the barrier have been removed, this is a head scratcher – this windrow is still there, is stationary, and is becoming larger. Why isn’t it leaving through the new opening in the south? Have the natural currents of the Bay been impacted enough by the barrier that the sargassum cannot exit? Could the sargassum actually be reproducing and growing within HMB?

Horror of horrors, it would appear the answer is YES, it is growing and thriving within HMB, like a Kudzu of the sea. Resources on hmbsargassumproject.com confirmed that conditions in HMB appear ripe for reproduction: warm, saline water, and plenty of nutrients in the Bay due to failing and non-maintained septic systems. This, along with the lengthy water turnover time (180 days amid normal current circulation) would appear to create a condition for sargassum proliferation.  No wonder it is impossible to keep up with its removal from the beach. The exacerbation of sargassum could be a problem of our own making, locally.

So, a question for the HMB Sargassum Committee: In the approach to solutions, could the causal factor of sewage in HMB be included as one of the considerations in the comprehensive effort to mitigate the sargassum?  i.e., a sewer system is needed, and quickly.

See also: [ Water quality in the eastern karst region of the Yucatan Peninsula: nutrients and stable nitrogen isotopes in turtle grass, Thalassia testudinum | SpringerLink ]

Yes, increased nitrogen in sea water is definitely contributing to the world wide growth of sargassum.  The added nitrogen comes from both sewage and fertilizer run off.  (See below for a terrific about nitrogen in sargassum from an article published on the US National Science Foundation website.)

It is my understanding, however, that live sargassum does not thrive in the very warm waters of our shallow bay.  Once it passes over the reef, sargassum usually begins to rot before it even reaches the HMB Beach. 

Rotting sargassum in the water releases the same toxic elements into the water that it releases into the air when it mounds up on the beach.  But, over time, the airsacs that keep it afloat also start to disintegrate and the rotting bits then sink towards the seafloor where they often get flush back out to sea by the undertow as shown in this photo:

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FROM THE US NATIONAL SCIENCE FOUNDATION WEBSITE:

https://new.nsf.gov/news/surge-nitrogen-has-turned-sargassum-worlds-largest#:~:text=Results%20show%20that%20from%20the,ratio%20of%20nitrogen%20to%20phosphorus.  

"The findings of the U.S. National Science Foundation-funded research, published in Nature Communications, suggest that increased nitrogen availability from natural and human sources, such as sewage, is supporting blooms of Sargassum and turning a critical nursery habitat into harmful algal blooms with catastrophic impacts on coastal ecosystems, economies and human health. Globally, harmful algal blooms are related to increased nutrient pollution."

A few days late perhaps, but just an observation:

A drone video was posted on a Facebook thread about 10 days ago showing a huge buildup of sargassum in HMB: there was a large windrow on the south side hovering just out from LBV to the point, and there was a brown streak across the reef. During this time, the south end of the barrier had been removed as it was deemed to be malfunctioning. The windrow was still hanging there, despite having an exit from the Bay. I made a post in this Forum about the possibility of sargassum actually growing within the Bay – not just floating in but multiplying due to the warm water and nutrients in HMB.

On Monday, 6/26/2023, a decent thunderstorm rolled through. It didn’t bring heavy winds, but it may have disrupted the currents in the Bay, as the following day, that large windrow of sargassum was almost completely gone and the Bay seemed more clear than it has in weeks.

It was a great relief to see HMB almost clear of floating sargassum for a few days afterward, and I am fascinated by this disruption in sargassum behavior which appears to be related to the thunderstorm. But it started coming back … on Sunday, 7/2/2023, I went swimming in front of La Sirena and encountered lots of small floating clumps.

It did not take long for the windrow on the south side to begin to build up again. The south end of the barrier is still down. As of today, 7/4/2023, we can see the flotilla has gained in mass.

It has been said that the currents in HMB are just “weird.” The Sargassum Committee has a plan to study the currents, and I am looking forward to hearing about what is discovered. I believe the CEA has a study related to circulation in HMB (2016? 2015?) and it would be interesting to compare the findings of that pre-barrier behavior to the study being contemplated by the Sargassum Committee.  That may go a long way to determining the best settings for the barrier, and learning whether it is indeed affecting the natural currents.

In the meantime, I am still worried about the sargassum reproducing here in the Bay, and the problem growing right in front of our eyes. Let’s not rule out our own human effects on the problem. I’m in favor of attacking this problem from the shore, also.

Recent news reports have posited that 2023 may not be a year for a tremendous amount of sargassum after all. Let’s hope for the best.