Sand dollar tests collected by our research team after a tropical storm. 

Sand dollar tests collected by our research team after a tropical storm. 

September 2016 marks one year of Sanibel Sea School conducting sand dollar research on Sanibel. We've had the opportunity to sample the sand dollar populations at two locations, Sundial Beach Resort and Buttonwood Beach, each month except for June and August. 

Researchers measure adult live sand dollars. 

Researchers measure adult live sand dollars. 

We've been collecting data on juvenile size frequency, adult density, and adult size frequency. Over the past year, we've seen changes in the sand dollar distribution at both of our sampling sites, along with changes in the seafloor topography after the tropical storms we've had in the area. 

We've seen a large decrease in the density of juveniles at both locations - meaning there are less juveniles per square meter. We will continue to monitor the growth of last year's settlement.

Soon, we will begin to collaborate with Canterbury School's staff to help with at least 5 science fair projects for both middle and high school Independent Science Research classes. Students will choose a topic of interest related to sand dollars and we will assist them in developing scientific research methods for their projects. 

Below, we share a visual summary of our results. 

Starting in September 2015, the test diameters of a population of sand dollars (M. tenuis) were measured and recorded once a month. Interestingly, it appears our sand dollars have seasonality in their growth; growing fastest in the summer (May, June, and July) and winter (December, January, and February) months.  We also captured the 2016 spring recruitment in May, which is why some very small sand dollars appear as outliers in the figure above. This means a new generation of juveniles was added to the original population, and corresponds with the timing of last year’s recruitment. This year's recruitment appears to be smaller than last year's.

Starting in September 2015, the test diameters of a population of sand dollars (M. tenuis) were measured and recorded once a month. Interestingly, it appears our sand dollars have seasonality in their growth; growing fastest in the summer (May, June, and July) and winter (December, January, and February) months.  We also captured the 2016 spring recruitment in May, which is why some very small sand dollars appear as outliers in the figure above. This means a new generation of juveniles was added to the original population, and corresponds with the timing of last year’s recruitment. This year's recruitment appears to be smaller than last year's.

Over the course of the year, the average test diameter of our sand dollars increased from 23.9 mm in September 2015 to 48.3 mm in August 2016, slightly more than doubling in size. Also, the range of sizes was greater in August than September, possibly indicating a high degree of variation among individual growth rates - put simply, some sand dollars grow faster than others.   

Over the course of the year, the average test diameter of our sand dollars increased from 23.9 mm in September 2015 to 48.3 mm in August 2016, slightly more than doubling in size. Also, the range of sizes was greater in August than September, possibly indicating a high degree of variation among individual growth rates - put simply, some sand dollars grow faster than others.   

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