Oyster Spat: Reflecting on 2019

BY ALEE KNOELL

If you are familiar with this blog, you are likely familiar with the grand journey of the oyster as well. How after weeks and weeks of floating through the water column, the microscopic oyster larvae find themselves a surface they deem worthy enough to make permanent residence. Subsequent to this attachment, the larvae are collectively known as spat. And that is where we at the Guana Tolomato Matanzas National Estuarine Research Reserve (GTM NERR) come in.

This year marks the GTMs fifth year of partaking in this Spat Monitoring project, and my what an adventure it has been! When we started back in 2015 we had a mere 12 reefs to monitor, tacking on collectors (or trees) in 3 more reefs in the Tolomato River (TR) by the end of the year and adding another one to the Saint Augustine (SA) region halfway through 2016. Aside from Guana River (GR), which did not see much of an increase until last year, the average spat per shell (sps) has been gradually increasing over the course of this study. However, in 2019 all regions except for Salt Run (SR) doubled in sps during peak settlement from the past year alone. 2019 is also the first year the average sps has exceeded 200 (300 in the case of the Tolomato region)!

So how else do the regional trends of 2019 compare to those of past years? Well for one thing, the average sps during peak settlement- the period that sees the highest amount of spat settlement in the year- for each region (except Salt Run) doubled that of last year, increasing up to 210 little guys per shell. If that doesn’t sound crazy, imagine counting those suckers under a scope and you may just reconsider! Structurally, these trend lines follow a somewhat similar pattern to 2017; each region hit their minor peaks in the same months as they did in 2017 and all peaked in September. In contrast, in 2018 the trees in Tolomato River, Fort Matanzas (FM), and Salt Run regions all peaked in October, following several more high and low points than last year (Figure 1)

Figure 1. Mean spat per shell for each region over the course of the study

Even viewing the trends of 2019 alone (Figure 2) can give us a little insight on some characteristics of spat settlement in our pristine Intracoastal Waterway. For one, while the regions may vary on when they experience their midsummer peak, they all see significantly more sps in the middle of fall (in the case of 2019, September). Second, our free-floating friends seem to consistently settle in the highest numbers on the Tolomato River trees. Note that there are few points in the year where any other region presents a higher sps average. This has been the case since Tolomato reefs were introduced to the project.  

Figure 2. Mean spat per shell for each region in 2019

This is quite a bit of information- believe me, I know! But to sum it up, 2019 has so far seen the highest number of spat in all the years this monitoring has been going on. As we are still in the collection phase of this program, we are not entirely sure why that is, so we certainly have a lot of questions! And given the myriad of ecosystem services our little spat will grow to provide, we are pretty excited to see such high recruitment.

An enthusiastic spat tree collection

We have by now collected enough data to conclude that there is not really much to look at between the months of December and February, so starting next year we will cease to collect during that time. Until then, wish our oyster babies good luck on their travels; judging from the yearly regional graph (Figure 1), next month will likely be a minor peak in settlement, and I have already seen a substantial amount of sps from the month of June!

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