Yesterday, the Virginia Aquarium rescued its first cold stunned turtle of the season in Virginia waters. Earlier this week, they took in 8 turtles that were stranded in New England. Officials in Delaware also sent out a warning yesterday to be on the lookout for cold stunned sea turtles after hundreds washed ashore in the Outer Banks.While an official in Maryland is not as worried about turtle cold stuns, there has been one suspected case so far this season.
The sudden chill last weekend, and expected chill this weekend, is certainly a concern for lover’s of these cold blooded critters, especially after this warm start to winter.
Word of the Day: Phenology
Timing is everything.
This doesn’t just apply to comedy or to a dinner date. In nature, timing is incredibly important.
In nature, we call event timing phenology. Phenology includes many events that you have probably witnessed: when the cherry blossoms bud in the spring, when Canadian geese migrate south for the winter, when blue crabs move to deeper waters and burrow for the winter…and many more.
The cues for the events are often related to temperature. For example, blue crabs move to deeper water to burrow when water temperatures dip below 50°C.
Phenology and Cold Stuns
So what does phenology have to do with cold stuns? This extra warm autumn and early winter is a perfect example of how changes to phenology can potentially increase the occurrence of a cold stun event.
To demonstrate this, I will use an example from my home garden.
Every year, I grow garden nasturtium in a container. Nasturtium are easy to grow, help promote butterflies, and are edible. Yes, you can put these colorful flowers into a salad for a peppery taste!
Typically, my nasturtium are done blooming by Halloween. This year, however, I had blooms to New Year. On December 28th, I took a picture of my beautiful nasturtium.
This “delayed” winter allowed my plant to continuing blooming. But, when temperatures finally dipped so that the average temperature was below freezing on January 4th, my nasturtium quickly wilted and died.
My garden demonstrated a cold stun. This plant when from being healthy to irreversibly harmed overnight due to a sudden dip in temperatures. But, if we take a step back, we realize that these nasturtium where set-up for failure. Normally, this annual plant’s lifespan would have gracefully run its course months ago. The warm autumn kept the plant stable into winter when inevitably temperatures would dip. Even the warmest winters still have cold days.
Warm winter or longer autumn?
The growing season is getting longer in Chesapeake Bay, which suggests that our seasonal windows are changing. That is, winter is more delayed. This will most likely affect phenology. Many of these cold stun events occur when the warm period is in the beginning of winter; so a delayed winter could increase the chance of having a cold stun event.
Major cold stun events, such as the 2011 juvenile spot fish kill and the 2010 brown pelican scare occurred in early January. In both these cases, it is hypothesized that a warm autumn caused these organisms not to migrate and when temperatures inevitable dipped down, bad things happened.
Let’s look at our data
One of the strongest historical climate trends in Chesapeake Bay is a lengthening of the growing season (Figure 4). While I am still working on this analysis, this growing season extension appears to from an earlier start date and later end date. In other words, our falls are ending later and our springs are starting earlier.
To test this idea, I created a very simple stressor model. Table 1 shows the indices I used, but in a nutshell, I added a +1 every time a late autumn (November into December) had a high percentage of warm days and/or a low percentage of cool days. So, the peaks in Figure 6 represent either autumns with a high percentage of warm days or a low percentage of cool days (or a combination of both).
What you can see is that warm autumns modestly first occurred in the mid-1920’s to 1960’s. Around the 1970’s, warm autumns started to become more frequent. And starting in the 1990’s, autumns became even warmer. Thus, this simple test suggests that we have indeed experienced more years with a delayed winter.
While more work is needed, it appears that phenology has changed in Chesapeake Bay.
But homework for all you readers: be on the lookout for cold stunned critters!
PS: starting next week, posts will go up on Mondays instead of Fridays. Our annual stats have shown that Monday around noon is the most popular time for views. We will try this out!