Nine-armed sea stars were heavily impacted by cold temperatures on Sanibel this week. 

Nine-armed sea stars were heavily impacted by cold temperatures on Sanibel this week. 

With high temperatures in the 50s and lows in the low 40s this week, we are currently experiencing a cold spell in Southwest Florida. It may sound like no big deal, especially compared to the “bomb cyclone” affecting much of the northeastern United States, but we’re used to highs in the 70s in January, and we Floridians are known for our low cold tolerance. As we bundle up in our winter layers, it turns out some of our local creatures are feeling the chill as well. We sat down with Doc Bruce to learn more about how unusually cold temperatures can impact the sea and its residents.

How unusual is it for Southwest Florida to experience cold spells in the winter? How cold is "cold", in Southwest Florida terms? 

I think that cold is cold when it gets close to, or below, the 40°F mark. It seems like at about that point, we tend to find more stressed animals, both in the sea and on land. The last significant cold spell was about 10 years ago. If I recall correctly, temperatures reached the high 30s, and there was a significant snook die-off.

How fast does the water temperature change, in relation to the air temperature?

Much more slowly. Water absorbs (and loses) heat relatively slowly. Right now, the Gulf temperatures are in the low 60s to high 50s. The change is more profound for all of our embayments, where the water is much shallower and temperature changes occur much more rapidly. 

Is wind or cold worse for sea creatures? What role do tides play?

It’s hard to say if one is worse than the other, and they are often found together. The cold fronts almost always come with wind. Wind produces waves, and the creatures in the shallows, especially those that live attached to the bottom, are less able to hold on in the cold to begin with. The combination of waves and low temperatures means they can become detached from the bottom, which leaves them prone to being blown into unfavorable environments – many are washed up on the beach.

Which creatures are impacted the most by cold temperatures? 

Almost all of them, in our region. Manatees are very cold intolerant, which is why they migrate out of the ocean to rivers in the winter. Sand dollars and sea stars are commonly dislodged from the bottom and are blown or rolled onto the beaches. Some fish are much less tolerant than others. Snook are especially susceptible. 

Are there things we don't know, but are trying to learn, about how cold weather impacts marine life in subtropical regions? 

I think that most of us forget that the natural ranges of animals (and plants too) are not static lines on maps. They are created by tolerance to certain environmental variables, like cold. We are at the very northern range of many species, and it is episodic cold intrusions that kill many individuals and restrict the species from being able to live in more northern locations.

Does unusually cold weather mean global warming isn't happening?

No, and this is why we don't refer to it a global warming any more. We call it climate change. Although the overall global surface temperatures are increasing, the most immediate effect is climate change and variability. We find cold in warm places, warm in cold places, increasingly frequent large storm events, and more intense storm events. The variation in local climate factors is increasing, and that will produce more extremes on both sides.

Is there anything else we should know about temperature changes in the ocean? 

During winter storm events, the times that are the worst for our sea creatures are when we have extremely low tides. The animals are exposed to air, which is 20 degrees colder than the water, and most of these creatures are cold-blooded. This means their metabolic pathways slow down significantly, and they are less able to fend for themselves and do the things they normally do. In many cases, when they are exposed to cold air, they are faced with an additional challenge if it is raining. They are very highly adapted to life in salt water and being immersed (or rinsed) in fresh water is a real challenge. The systems they have in place to help tolerate those changes isn't working very well because they are cold. 

Thank you, Doc Bruce!

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