Abnormally high ocean temperatures are impacting Biscayne, Dry Tortugas, and Everglades national parks/NPS file

The New York Times recently summed up one of the biggest climate-change stories of the year so far: The planet’s average sea surface temperature spiked to a record high in April and the ocean has remained exceptionally warm ever since, the paper reported. In July, widespread marine heat waves drove temperatures back up to near-record highs, with some hot spots nearing 100 degrees Fahrenheit, or nearly 38 Celsius, the paper continued.

In late July things got worse, as water temperatures off the southern tip of Florida surpassed 100° Fahrenheit. What are the impacts of these hot waters to Biscayne, Dry Tortugas, and Everglades national parks? Traveler Editor Kurt Repanshek sat down with Dr. Steve Davis, the chief science officer for the Everglades Foundation, to discuss that topic for this week's podcast. What follows is their conversation.

Kurt Repanshek: Welcome back to the Traveler, Steve.

Dr. Steve Davis: Thanks Kurt, good to be here.

KR: So, before we get into some of the impacts, could you explain how the ocean waters are getting so hot? I mean, mention the Atlantic Ocean and even the Gulf of Mexico, and your mind envisions these enormous bodies of water that one would think would be pretty difficult to heat up so much.

SD: Well, it really takes years and decades to heat up large areas of water, whether the Great Lakes, Lake Okeechobee, something significantly smaller, or even a place like the Gulf of Mexico and coastal waters around Florida. It takes a while for that water to heat up. It absorbs an enormous amount of energy. But especially with the heat that we've had this summer, the lack of cloud cover in certain areas, and also with a calming of winds that we normally rely upon in the afternoon here in South Florida. Those calmer conditions have allowed that water to heat up as well.

KR: What would be normal? Or what was the normal water temperature in the summer in the Gulf of Mexico?

SD: Well, of course, it depends on where you are, and what what depth you are. The Florida shelf, which extends about 50 miles off Florida's West Coast and down to the Florida Keys and where the Dry Tortugas are, that's a relatively shallow body of water that is quite a bit warmer than the deeper open water areas of the Gulf of Mexico. And it's not uncommon for that to get up to the upper 80s in the height of summer. But as you mentioned, we've seen some near-shore temperatures, especially in the shallower zones and especially for waters that don't flush very well in places like Florida Bay and lower Biscayne Bay, they have exceeded in some cases what we're measuring in the atmosphere. Those waters just sit and heat up from day to day to day.

KR: I imagine it takes an equally long or maybe longer period of time for them to cool down.

SD: It does, and this year, as hot as it's been, it's a little bit hotter than what we've seen previously. And I think back to 2015, when we had a seagrass die-off in Florida Bay, we saw temperatures well in excess of 93°, 94° and even had a recorded temperature of 100° in an area that suffered seagrass die-off that year. We're seeing the same kind of temperatures this year. So it's not, you know, that extraordinary. The problem is this year it seems to be a longer duration. Florida Bay, Everglades National Park, as an important point of reference, it's such a shallow system that the bay temperatures roughly track the temperatures in the atmosphere. So as the air starts to cool down, we'll see the bay cool down, and so we're obviously looking forward to that as we head into late summer and into the fall.

KR: Now these 100°, 100°+ readings are they right along the shoreline or do they extend out quite a bit into the bay?

SD: They do sort of hug the shoreline. One area in particular, Garfield Bight, which is an area roughly 10-12 miles to the east of Flamingo. So for folks that have been to Everglades National Park, you drive that main park road down to the very end, you end up in Flamingo. And so it's an area that hugs the shoreline, and it's an area that doesn't flush very well with the tides. So it's kind of confined and isolated and is vulnerable to that extreme heating. It's also vulnerable to variations in freshwater flow. We know that in 2015, that area, not only was it incredibly hot, but the salinity levels were about double that of ocean water. And that kind of speaks to the vulnerability of that area, and how poorly it flushes with the tide. So the water just sits there and evaporates and becomes very salty, but it also absorbs an enormous amount of heat.

KR: Are you seeing warming temperatures on the east coast of Florida, similar temperature in the water?

SD: Yeah, we're seeing similar extreme heat in areas of Biscayne Bay that, again, don't flush very well with the tide. So areas where you have a lot of mixing and circulation, the temperatures don't get that high. It's the water that sits there and basically stews, day after day. And so upper Biscayne Bay, lower Biscayne Bay, those areas don't flush well. And so we're seeing upper 90s in those areas as well. And I think it's important to note that it's not so much the daytime highs that are a concern. It's the nighttime lows that are a concern. We're seeing nighttime temperatures some days not dipping below 90 degrees. So it really does not cool off sufficiently, which certainly has an impact on the physiology of the organisms in the water. But most importantly, it affects the ability of that water to hold oxygen overnight, when everything living is depending on that oxygen to get through the night before photosynthesis kicks in the next day.

KR: One of the most publicized impacts of this ocean warming, at least that I've heard of, is coral bleaching. Could you explain the process of coral bleaching? And what happens to make the corals go white. Does it does it take a great rise in temperature to occur?

SD: Well, I'm truly not an expert in coral biology. What I do know is that as temperatures get above a certain threshold, it causes the organisms that sort of make the coral skeleton to become stressed and ultimately eject from that reef body, and therefore leads to the bleaching of that coral. But I don't consider myself an expert on coral. So I feel uncomfortable speaking to that.

KR: I'm certainly no expert, that's for sure. I like to scuba and snorkel around coral reefs and admire the colorful reefs. And, you know, that's one of the threats that we're losing. And it's not just loss of biodiversity in the oceans, but obviously, you know, tourism dollars with all the divers and the reef fishes, which we're going to get into. There have been many stories about efforts to save corals by creating nurseries with fragments. I've heard that many of these projects have been pretty successful, but also believe that some of them damaged by the warm water, some of these nurseries.

SD: They would be equally vulnerable because many of the, quote unquote, gardens where they're growing coral fragments are in the same waters and growing under that extreme heat. And so in some of these areas, they've actually gone out and tried to harvest some of those coral fragments to take them back to the lab in a more controlled setting to get them through some of this extreme heat. Anything that we're concerned about in our coastal waters would be affected by this heat to the same degree. And again, it has to do with the organism's ability to physiologically tolerate that heat, but also their demand for oxygen. Under those warmer water conditions, and recognizing the physical constraints of that water to hold oxygen as it gets warmer, it's sort of the tipping point for really the health of a lot of things, whether it's coral, whether it's seagrasses, you know, oysters, sponges. We're seeing impacts to all of these ecosystems as the waters heated up. 

KR: You know Steve, the Florida Reef stretches 350 miles, roughly, from Dry Tortugas National Park, farther south of Key West, up to Martin County I believe, on the east coast of Florida. That has a lot of exposure to these ocean temperatures. Any insights into how that that reef is faring under these temperatures?

SD: Well, it's a massive reef system as you point out. The third-largest reef system in the world. And it's connected from the Dry Tortugas, as you mentioned, all the way up to Martin County with the Florida Straits. That current of water that flows out of the Gulf Stream and all the way up our East Coast. So they're all —whether you're in the Lower Keys, the middle keys, or all the way up the lower East Coast— they're experiencing the same water quality conditions for the most part. In terms of temperature, there are some areas where there might be more nutrient-related problems. But in terms of temperature, they're experiencing the same issues. And of course, that current that carries that same water out of the Gulf is also carrying larval forms of organisms that settle in many of these reef areas and depend on the quality of water and the quality of that reef for them to be able to grow up into adults. Some of these are recreationally important species. So it's all experiencing the same conditions from top to bottom.

KR: That's incredible. You mentioned I believe it was back in 2015, maybe, that you saw similar ocean water temperatures, but for a shorter duration. Were there any obvious impacts to the reef from those temperatures?  

SD: Well, the impacts that were observed on the reef were in part related to the problems that we saw take place in Florida Bay. And again, that's about an 800-square-mile estuary in Everglades National Park, just sandwiched between the Florida Keys and the mainland. And we saw similar temperatures developing in Florida Bay at that time. But the problem then was more related to extreme high salinities that developed in the central part of the bay because of a lack of freshwater flow. So that seagrass die-off that ensued, not only led to algae blooms, but that hyper-saline water was carried out of the bay through the Florida Keys and impacted the reef in that way. So, the reef then was exposed to extremely salty, and because it's excessively salty, it's dense, and that water holds an enormous amount of heat. So that hot, salty water got transmitted offshore into some areas of the middle keys' reef tract. I didn't see significant documentation of impact, but we know that that super salty hot water had an impact locally.

KR: I recall the seagrass die-off in the bay. I don't recall any great mention of coral bleaching.

SD: No, no. And certainly not to the extent, because the duration of those high temperatures was such that it didn't affect the offshore water temperatures as much as it did the near-shore temperatures in Florida Bay. But I would also add that that seagrass die-off lead to several years of algae blooms in Florida Bay. So without that grass there to stabilize the bottom, to take up nutrients, it led to algae blooms that there were several well-publicized satellite images showing this green plume of water getting carried offshore into the reef tract.

KR: Now, when coral bleaching occurs, the corals as I understand it are losing the colonies of life, so to speak, that inhabit them. That has to have downstream impacts, so to speak, by the reef fishes that depend on the coral reefs,

SD: Everything from the smallest of fish and the grazers up to the predatory, more recreationally sought after species. So it has a cascading effect throughout the food web. And, you know, we associate our reefs with being incredibly diverse, incredibly productive. But that starts with the health of the coral itself, and the connection to healthy ecosystems like sea grasses and mangrove. So as those dominoes start to fall, you see the cascading effect throughout the food web.

KR: Because Florida Bay is a very important nursery, so to speak, for reef fishes and shellfish and whatnot?

SD: Incredibly so, and I mentioned the larval fish transport. The studies show very clearly that these larvae get transported along the keys, and the small eddy currents that spin off of that force these microscopic fish into seagrasses, into mangroves. And so it's the communication, the connections between those habitats that really boost their productivity overall. And again, as one of those sorts of systems starts to break down, that connection, and the overall productivity starts to break down.

KR: Are we seeing stagnation in the Florida Bay to go along with these really, really warm water temperatures?

SD: Well, there are some areas that are vulnerable to stagnation naturally, because Florida Bay is not like an open bay system like the Chesapeake. It's actually more like an ice cube tray, where you have a series of basins that are intermittently connected to one another, either through wind events or high freshwater inflow events from the Everglades, hurricanes. But generally, the water in each of the basins across that ice cube tray are isolated from one another to some extent. And it promotes the evaporation, the salt concentration when we're not getting enough fresh water flow, or during really hot periods like we've experienced over the past month-and-a-half. It allows for these basins, some of them that don't exchange with tides or freshwater, to heat up extraordinarily. And that's what we're seeing. So those areas are naturally vulnerable. But having said all that, it's fortunate that we're seeing the benefits of Everglades restoration playing out because we don't see the excess salinity across some of these areas that we've seen in the past that led to seagrass death. The temperature is there, it's just that the salinity is not to that critical level that would lead to a massive seagrass die-off.

KR: And that's due to the inflows coming down the river of grass?

SD: Because of the bridges that have been built on Tamiami Trail, some of the other infrastructure that helps to keep that water in the park, send it all the way down to Florida Bay, we're absolutely seen the benefits of that right now. But it really now depends on how long we're going to see this extreme heat as to the health of that ecosystem beyond the summer.

KR: Is there any forecast for how long it'll continue?

SD: I've heard that August is going to be equally warm. But at the same time, our August in South Florida is generally the wettest month of the year, certainly wetter than July. July is traditionally quite dry. And I don't understand what what drives all that. But if August is an average wet August we're going to have more cloud cover. We're going to have more rainfall. We're going to have more wind. All the above will help to lower the temperatures from what we saw in July. So even if the air temperature is equally warm, I think we're going to see conditions subside. Some of these extreme heat conditions subside around our coastline.

KR: Central Florida. Did it receive a significant amount of rainfall during July? Were there a couple of big storms that moved through and led to some greater releases from Lake Okeechobee?

SD: No, we have not seen significant discharge this year, even though the lake is still quite high as a carryover from Hurricane Ian last year that devastated our southwest coast. We had record rainfall north of Lake Okeechobee, the lake shot up 4 feet in elevation. And there was concern through the dry season because we couldn't send large volumes south, that we would have to see massive discharge of polluted Lake Okeechobee water to our east and west coasts. We haven't seen that yet. And I think in part it's because July was quite dry.  So we're watching that very closely. And really, that's one of the major motivations for Everglades restoration, is to help us control lake levels better and send more of that water south. And we know it's polluted, so we've got to have the storage capacity and the treatment capacity to send those volumes south so that we're not dumping it to our east and west coast. So, we're making great progress there. And the key to that is the big Everglades agricultural area storage reservoir that's now under construction and is slated to be completed by 2030. So we're watching that, but we're also watching lake levels from day to day in hopes that we don't have to see those polluted discharges. Because that's really adding insult to injury, when you've got these incredibly, extremely hot conditions in the estuaries and our coastal waters and to dump polluted water on top of that would really make things worse.

KR: What's the cause of the pollution in the lake waters? Is it agricultural runoff?

SD: It's largely agricultural. Three-quarters of our pollution around the Everglades comes from agricultural pollution that in part has to do with the attempts to straighten the meandering Kissimmee River into a canal, and draining the floodplain and farming that floodplain and then to the south, draining that Everglades agricultural area that's now primarily farmed as sugarcane. The contributions from the north and south led to the pollution of Lake Okeechobee because they used to back-pump water from the south back into the lake. So that pollution has really impaired the lake to the point where now, every summer, we're seeing toxic blue-green algae form on the lake. Not too long ago, more than 75 percent of that 700-square-mile Lake Okeechobee was covered in toxic blue-green algae. That's subsiding a bit, but the concern is when those gates open to the east and west, it's not only carrying enormous volumes of polluted freshwater, but it's carrying those toxins along with it. 

KR: So Steve, as we were talking earlier about the warm ocean waters and the Florida Reef extending all the way down to Dry Tortugas National Park, which is roughly I want to say 70 miles south of Key West. Is Dry Tortugas seeing the same water temperatures as you are closer to Florida Bay and Everglades National Park?

SD: Not as hot, but probably as extreme relative to the long-term conditions that those patch reefs and seagrasses around the Tortugas are accustomed to seeing. So I think relatively speaking, yes, as extreme.

KR: Are we seeing any obvious impacts to marine life, fish kills?

SD: Well, the coral bleaching, the documentation of that, has been pretty eye-opening. What we're seeing in places like Florida Bay, sponge die-off, large sponges dying back. Seagrass die-off. Patchy, not large scale, but some patchy seagrass die-off. We're witnessing that. Fish kills in different areas of our really hot near-shore coastal waters, we're certainly seeing the impacts of that. And, you know, I communicate regularly with fishing guides that are out on the water. They send me pictures of things, and I've spent a little bit of time out there myself and you really get the sense that things are on the edge and just holding on, trying to get through. And it really speaks to how fragile nature is. And when we throw these types of extreme conditions at our environments, whether it's extreme heat, or nutrient loading, or things that lead to algae blooms, or lack of freshwater flow, it really not only stresses them, but it sets back their condition to the point where they don't fully recover in many cases. So I think some of these impacts are yet to play out with regard to larval fish production and growth into a size class that we can observe. We may not know the impacts of that for another year or two. We don't know how much of the reef will recover. That will take some time. So the impacts we're seeing are still sort of playing out and are yet to be documented.

KR: Nature can also be very resilient, and adaptive. Every now and then there's a story that pops up about this section of coral seems to be immune from the higher water temperatures, or has figured out how to cope with it. So you always have to hold out some hope for that type of scenario arising.

SD: Yeah, and we do see an enormous amount of resilience here across our ecosystems in South Florida. In some years, we've had rainfall and just the right amount at the right time, and that's led to record-breaking wading bird nesting. Wading birds are among our most iconic species along with the American alligator and the Florida panther. And we see that if we can get the water right, the species will respond. We've also seen that those estuaries on our east and west coast that get pummeled with polluted Lake Okeechobee discharge because we don't have the capacity to send that south, that if we go a couple of years without those discharges, we start to see habitat recovery. The seagrass has come back, the oysters come back in those bays and estuaries. So the resilience is there. It's just a matter of getting the conditions as close to ideal as possible. And again, that's largely what Everglades restoration is about, at least for our inshore and freshwater ecosystems.

KR: Now, Biscayne National Park, 95 percent of it is underwater. So what is happening to that park with these high water temperatures?

SD: Well, it's equally vulnerable. And some of the hottest temperatures we've seen have been in southern Biscayne Bay. And, you know, the Everglades historically was connected to Biscayne Bay, not only through periodic surface water connections, but also through groundwater. With that massive volume of water sitting on the south Florida peninsula and our porous geology, there was a lot of groundwater discharge, fresh groundwater discharge into Biscayne Bay and one of the goals of Everglades restoration. There's actually a project that's being planned right now as part of Everglades restoration called the Biscayne Bay Southeast Everglades Ecosystem Restoration. It's a mouthful of a project. But one of the objectives of that project is to improve near-shore salinities, which means we're spreading out freshwater flows into Biscayne Bay as opposed to just dumping it out a canal. And if you've been out into some of these areas when the canals are releasing, and thinking about the heat that we're experiencing right now, those canal release points, that's cooler water coming off the land, or coming out of the groundwater into some of those near-shore zones that are experiencing extreme heat right now. And so spreading out that freshwater flow will certainly help to mitigate some of these types of temperature-related impacts that as of right now, we don't have the capacity to do

KR: It's probably too early, I would guess, to say that Biscayne is really endangered because of these hot waters and what they're doing to the marine life and the coral structures.

SD: We have concerns about the reef that's just outside of Biscayne Bay, but also the patchy coral heads and also sea grasses that cover much of Biscayne Bay. But as you know, we have problems related to heat, we also have problems related to nutrient-loading in Biscayne Bay. And so those are also issues that need to be addressed because temperature's really just sort of a catalyst in affecting a lot of these problems that already exist, whether it's nutrient-related or problems with algae growth. Temperature just exacerbates the issues around that. A lot of it has to do with oxygen, a lot of it has to do with the physiology and the metabolism of these organisms. So, temperature itself doesn't necessarily kill. It's all these other surrounding circumstances in our coastal bays and estuaries.

KR: I'm wondering how extreme or how large this problem is. Do you have colleagues in the Virgin Islands who are documenting the same type of conditions, say around Virgin Islands National Park, Buck Island reef?

SD: I don't in the Virgin Islands, but I've got colleagues that work in terrestrial ecosystems and Arizona, they're experiencing the same types of [hot weather] problems. I've got colleagues in the upper Gulf of Mexico, they're experiencing similar problems. And again, it's not just heat, it's the combination of heat and nutrient-loading, or reductions in freshwater flow that are affecting those ecosystems.

KR: Do those problems creep ashore, so to speak? I mean, you've seen the die-offs of the grasses, the seagrasses in Florida Bay. What about the mangrove groves? That last stand, so to speak, on the shoreline buffer?

SD: The short answer is exactly. I talked about the seagrass die-off we saw in in 2015. That also was so extreme, we saw mangroves dying because the salinity was so high. And again, temperature does play a role in the recovery of those mangroves that died back. And a good example is after Hurricane Irma, we saw a pretty substantial area of mangrove around Flamingo that has since yet to recover. And in fact, Hurricane Ian knocked many of those snags down. And those soils, highly organic mangrove soils, could support new mangrove growth, but in some areas, those soils are breaking down and collapsing. In other areas, the soils are accumulating so much toxic, hydrogen sulfide, and the heat plays a role in that as well, that you're not able to get new mangrove regrowth. So our concern is that some of these areas where we've lost mangroves, we may never get them back we can see those areas collapse into open water embayments into the future.

KR: This summer, hopefully it's an anomaly. But looking back over the past two decades, can we say it's an anomaly? I mean, in the West we're seeing longer shoulder seasons crop up as winters get shorter. And so there's related impacts associated with that. Are you seeing longer periods of these really hot water spells, or is this just an anomaly that hopefully it's a one off?

SD: I think this year, based on what I'm seeing, is kind of a shifting baseline. It's obviously an extremely hot year. We're breaking records all over the place. It's likely that the next year or two will be a little bit cooler. But I think we're clearly on a long-term trajectory with regard to climate change. As a scientist, I ascribe to the science, and the experts in this area say very clearly that the heat that we're experiencing this year is largely related to climate-change greenhouse gas emissions. There might be some fraction of that that is attributable to the strong El Nino conditions that are developing. And therefore, as that El Nino subsides, and might be a little bit cooler next year, the following year, but I think what we're seeing is this upward trajectory of warming that isn't sort of perfectly linear over time. As with anything, it goes through these spurts and retreats. We see the same thing with sea level rise. We go back few years ago, we saw a significant jump in sea levels. That relaxed a little bit. It's a very complicated interaction of factors that's at play. But I think we're just continuing on that upward trajectory.

Traveler footnote: Listen to this conversation on National Parks Traveler Podcast Episode 235 | Hot Waters Wash Florida's National Parks