The SEAS Team
October 4, 2013
Sargassum Seaweed Wrack Scale
Sargassum seaweed is a common site in the Gulf of Mexico and often ends up as wrack
on the shores of the gulf coast. The amount and frequency of the seaweed washing up on shore is
related to the Sargassum loop current, an annual trek of the algae from the Sargasso Sea to the
nutrient-rich waters of the Gulf and back. The Sargassum Early Advisory System (or SEAS)
Team has generated a method of monitoring and forecasting the presence of seaweed with an
accuracy of 97%, however the classification of quantity has always been elementary,
categorizing the algae’s landfall as ‘low, medium, or high.’ This is because there is no existing
scale to classify the amount of Sargassum wrack once it has hit the coast. This paper aims to
create a hierarchy of the intensity of Sargassum landings, ranking from 0.00), ‘None to
Scattered’ to 9.100), ‘Multiple Massive Landings.’
There are countless dimensions in which one could measure the quantity of seaweed
wrack, however, for the sake of measuring, some aspects are more practical to obtain than others.
For instance, at a glance, determining the weight of Sargassum on the beach sounds like an
optimal way to represent the quantity, however, too many variables affect the weight. Seaweed’s
composition consists of mostly water, so as it desiccates and degrades, it loses mass. Also, the
act of gathering and weighing the algae is strenuous and the weight’s accuracy would be affected
by the presence of sand. Because of variables like degradation, beach width, and beach cleaning
all affect the length of time the wrack remains on the beach, the SEAS Team has determined the
best way to determine a scale is to measure a function of the depth of the seaweed line and
visible coverage.
The seaweed line, also known as a windrow, is a common feature seen in Sargassum
wrack, as the seaweed is pushed ashore by wave action, it is stacked on top of previously
beached seaweed, creating a ‘windrow.’ In order to measure the windrow, one will simply
measure, from the center of the windrow, the height in feet, from beach to the crest. Ground
coverage will be measured in feet from the mean crest of the wash zone inland. The distance in
feet describes the intensity of the seaweed wracks over a period of time, the longer the distance,
the most occurring. Once a windrow of seaweed has been washed ashore, it quickly degrades,
spreads or becomes buried by natural means, this flattens the crest of Sargassum across the areal
beach. Once it hits the beach, it is there to stay until it is cleaned up, buried, naturally dispersed,
or degraded. Since the macro algae takes several days to degrade once it has made landfall, the
increased ground coverage is more of a function of frequent seaweed beachings, rather than one
large seaweed wrack.
To most efficiently exemplify the different levels of intensities at which the seaweed has
amassed on the beach, the SEAS Team has established a number scale comprised of two
components. The first element is height of the windrows on the shoreline. This component is
measured numerically from nominal (0) to over 9 feet tall (9). Windrows are a common sighting
of recently beached wrack, after some duration, the windrow formation degrades and spread
across the beach, increasing coverage while decreasing the height of the windrow. The second
element of the scale is the ground coverage and ranges from none to scattered (0) to over 100 ft
of Sargassum (100). This component identifies the frequency in which seaweed reaches the
beaches over several days.
The most effective way to exhibit the scale is by displaying the windrow number (W)
followed by the ground coverage number (CG), formatted as so: #.## or W.CG. An example
would be, if there was a windrow height of 2 feet, and the aerial beach is covered in up to 20 feet
of wrack starting from the swash zone extending toward the dunes, the scale would read “2.20.”
The scale can be seen below.
Windrow Height
Designated Scale Number
0
1
2
3
4
5
6
7
8
9
Description
There is little to no windrow present. There could be a seaweed
windrow of up to 6” present, but it has been spread and degraded
to where its height is nominal
The Windrow is on average 0.5-1.5 feet in height
The Windrow is on average 1.5-2.5 feet in height
The Windrow is on average 2.5-3.5 feet in height
The Windrow is on average 3.5-4.5 feet in height
The Windrow is on average 4.5-5.5 feet in height
The Windrow is on average 5.5-6.5 feet in height
The Windrow is on average 6.5-7.5 feet in height
The Windrow is on average 7.5-8.5 feet in height
The Windrow is on average 8.5 feet or higher
Ground Coverage
Designated Scale Number
00
10
20
30
40
50
60
70
80
90
100
Description
There is no little to no seaweed wrack (0-2 feet) scattered
across the beach
There is approximately a 2-10 ft span of seaweed from mean
high tide line toward inland
There is approximately a 10-20 ft span of seaweed from mean
high tide line toward inland
There is approximately a 20-30 ft span of seaweed from mean
high tide line toward inland
There is approximately a 30-40 ft span of seaweed from mean
high tide line toward inland
There is approximately a 40-50 ft span of seaweed from mean
high tide line toward inland
There is approximately a 50-60 ft span of seaweed from mean
high tide line toward inland
There is approximately a 60-70 ft span of seaweed from mean
high tide line toward inland
There is approximately a 70-80 ft span of seaweed from mean
high tide line toward inland
There is approximately a 80-90 ft span of seaweed from mean
high tide line toward inland
There is more than a 100 ft span of seaweed from mean high
tide line toward inland