By Mathew Monroe and Nikki Dix

For the past few years on the first week of each month with good morning low tides, we have taken a 20-mile boat ride throughout GTM NERR to track settlement of oyster spat.

Spat is the stage of an oyster’s life cycle at which the mobile journey as larvae through the estuary ends and the sedentary life begins.

After they settle, spat stay in the same spot for the rest of their lives. To collect these “baby oysters”, we use what is referred to as the spat tree method. It is kind of what it sounds like; a PVC T with recycled oyster shells suspended from each arm just above an oyster reef. Each month the shells are collected and swapped out for a new set.

Looking at the shells under a microscope, we count each spat that has settled on the collected shell that month.

Spat, settled oysters, on an adult oyster shell

Spat tree

Tracking these trends helps us and those who care about our local oysters understand seasonal reproduction patterns and the associated environmental conditions. From an oyster restoration stand point, understanding when larval oysters are most abundant and ready to settle is very important for timing the installation of new reefs. If you try to start an oyster reef too early or late in the year, your substrate will get silted and spat won’t be able to attach themselves. You’ll be left with a slimy substrate and no oyster reef. In the past few years, spat has been most abundant in May and June, when temperatures start to rise and phytoplankton (oyster food) start to grow.

We are still working on counting the spat from this year and hope to add the data from the current year into our report in the near future!