Everglades – Invasive Reptiles
Another sunny day, another 8:00am start. Today was the longest of the trip with hours and hours of travelling in the car. Our first stop being the Everglades National Park before moving onto Homestead where we would have a talk on constructed wetlands from Bill Mitsch, who we met a few days previously.
Travelling there we noticed there was a large amount of fencing that ran along large lengths of the roads we were on. Their purpose was to keep Florida panthers (Puma concolor coryi) from being killed on the road.
This would have been put up at great expense but considering that there are only 150-200 animals left in the wild and that last year one was killed on the road every fortnight, it may be vital to their survival.
A serious of underpasses allow them to safely pass underneath the roads. These are common spots for researchers to set up camera traps to track their movements and usage of the underpass.
When we arrived at the Everglades (at what I can only describe as an outpost, needless to say we got lost finding it) we met up with Brian Faulk the resident expert on invasive reptiles with his main focus on Burmese pythons (Python bivittatus).
These pythons had been introduced to Florida through escapees from private collections. Either being released on purpose when they got too large or from pet shops and warehouses that were damaged by hurricanes and tropical storms.
Licenses can be obtained to cull them, but it is very difficult to find them making this process ineffective in controlling their numbers. During the this time of year in the dry season you will find one snake every 40 hours on average, during the wet season it is one snake every three hours.
One of the reasons it is difficult to find them is their low activity levels. As they are ambush predators they sit and wait in the same place and can hide very well in even low level vegetation. It’s possible to be almost standing on a snake that you know is there through radio tracking and have difficulties in finding it.
Traps (baited with prey or pheremones) have been deployed around the local area with very poor success, only three snakes were caught in seven months. Eleven snakes were found in the area after it was mown.
Sniffer dogs are more effective at finding them than humans, but this technique is more useful for eradicating small localised populations.
Large numbers of snakes do get killed on the roads but it does not seem to have a big impact on the population and many larger snakes can even survive being hit by vehicles. In one case a 10ft snake was hit by a truck and had a split trachea but survived.
A biological control is currently being explored by using the inclusion body disease (IBD) which affects snakes in the boid family. Having it is currently unknown what impact it would have on native species.
The only parasite they have found on these snakes is the non native longworm, but it does not appear to have any pathogenic effects.
They are generalist feeders, feeding mostly on birds and mammals but they have had an impact on rabbit populations which is a concern as this is makes the snake a serious competitor to native species.
In an effort to combat the rising snake populations State government has cracked down on their sale and transportation. It is illegal to sell them and it is forbidden to take them across state lines. Unfortunately this is too little too late.
They are not the only large species of snake introduced to Florida, there is now an establishing population of African rock pythons (Python sebae) just north of the Everglades National Park and a population of Boa constrictor just south of Miami, although they do need seem to be spreading.
Genetic studies of the pythons show that they have limited genetic diversity, but that is not necessarily a problem in reptiles. This is not the case for all inroduced species. Brown anoles (Anolis sagrei) have an increasing genetic diversity due to multiple foundings.
In total there are 50+ species of invasive/introduced reptile in Florida. This is due to the subtropical climatic conditions. The only way this works in our favour is that species such as the Burmese python cannot spread any further north because it is too cold.
Most of the invasive species are lizards as there are relatively few native species. This has led to changes in niche occupation.
Where brown anoles (Anolis sagrei) are absent green anoles (Anolis carolinensis) move down trees to occupy that niche. Where they are present the green anoles move back further up as they do where the two species interact in Cuba.
There are novel interactions developing however such as the niche separation of green anoles and chameleons, with chameleons dominating the canopies of trees where present.
A few species do pose direct harm to native species such as the cane toad (Rhinella marina) and the cuban tree frog (Osteopilus septentrionalis) which has been documented to cause diarrhoea in snakes that eat them.
Whilst he was talking about the invasive reptiles he handed round a pet Burmese python for everyone to hold as well as a few jars of preserved specimens on non native lizards found locally.
Afterwards he showed us a wild caught python with which he demonstrated how easy it is for them to disappear into the grass.
We where then allowed to handle it, albeit with a bit more care than the pet one.
Everglades Invasive Fish
After we finished with Bryan we moved onto the Anhinga trail of the Everglades National Park where we met up with another guide who talked to us about invasive fish species.
There are 17 species in the park, 15 established and they are all established in the surrounding canals. Much like the reptiles they arrived from the exotic pet trade.
Some however were introduced on purpose such as the peacock bass (Cichla monoculus) (as a sport fish) and grass carp (Ctenopharyngodon idella) to control vegetation in canals, keeping them clear for a constant flow regime.
Some of the less cold tolerant species such as peacock bass do die off occasionally during unusual cold snaps like the one that occurred in 2o10. However they persist in the warmer canals and reestablish in the following years.
Our guide went into explain how the building of canals and levies had changed the hydrology in Florida. These were built-in an effort to more equally distribute water in the state by moving water from east to west.
The building of these structures did however cut off northern areas, reducing the flow from north to south which in turn increased flow east and west.
In 2000 the Taylor Slough was built-in order to prevent water from draining out of the park. It reconnected areas of freshwater marsh. Unfortunately by reconnecting these areas they facilitated the spread of non native fish.
In order to combat these invasive fish more studies are being made into they requirements and interactions with native flora and fauna.
One way of preventing non native fish from entering new areas is electric fish barriers which are currently being used in Chicago to prevent Asian carp from spreading into the Great Lakes. Currently this technique is not used in the Everglades.
The reconnection of waterways does benefit some native species such as the Long nose gar (Lepisosteus osseus) which is now reestablishing in areas it became extirpated.
As we walked around the Anhinga trail it became clear how prevalent invasive species were. Although we did spot native species like the Florida gar (Lepisosteus platyrhincus) we saw quite a few non native, oscars (Astronotus ocellatus), mayan cichlid (Cichlasoma urophthalmus) and walking catfish (Clarias batrachus) to name a few.
I did notice particular feeding behaviour amongst predatory species, feeding in the margins where the most bait fish were present.
There was also an abundance other species along the trail, mostly birds but reptiles as well, alligators and freshwater turtles.
As was the case elswhere you could get very close to wildlife, the closest were the cormorants (Phalacrocorax auritus) which you could literally stand next to.
However I got really lucky with hsi next photo. I’d fallen a bit behind the group (from taking so many photos) and I suddenly heard some people behind me start shouting. I turn around to see a great blue heron (Ardea herodias) with a walking catfish in its bill.
I’ve also got the a video of the eating behaviour, wasn’t quite what I or anyone else expected.
Although it wasn’t my favourite picture of the trip (that one would come the next day) it was my best of the trip and I was thrilled to have shot it. I just wish I had a better camera to do it justice.
Bill Mitsch Talk
We couldn’t stay as long I would have liked here as we had to move onto Homestead for our talk from Bill Mitsch. I certainly did enjoy the limited time we had here though.
Thankfully Homestead wasn’t too much farther from where we already were and we arrived in good time to sit down and get ready before the talk started.
It was an interesting 45 minute or so talk, the only issue was the constant technical issues as it was being broadcast online for viewers who couldn’t make it to the actual talk. They were connected by phoning in, enabling them to ask questions at the end.
Below is a summary of the talk. It was titled: ‘Using Wetlands to prevent phosphorous and nitrogen pollution in downstream wetlands, lakes, rivers and coastal waters.’
Nitrogen and phosphorous are essential for life, but in modern times they have become pollutants due to excess amounts entering water ways, with more than 750 aquatic ecosystems affected.
Naturally the amount follow the redfield ratio of 41gC:7.2gN:1gP
Non point sources are often the greatest culprits, largely from agricultural run-off.
It is worth noting that CO2 has also increased by 40% compared to the 20th century and global nitrogen fixation has doubled.
Wetlands play a crucial part in reducing excess pollutants and purify water as well as help with flood regulation, increase biodiversity and help in climate regulation.
One of the biggest examples of nutrient pollution in American is the Gulf of Mexico hypoxia, with less than 2mg/L oxygen in the summer. This is caused by excess nitrogen pollution in the US midwest which then flows 1,000 miles south to the Gulf.
Most denitrification in wetlands occurs during summer, but the greater the inflow of nitrogen the lower the retention, meaning a greater area is required. It is estimated that five million acres of constructed wetland would be required in order to cut the Gulf hypoxia by half.
This would require a colossal amount of resources to bring to fruition.
One of the potential solutions to this could be restoring black swamp in Ohio. Large amounts of wetland existed here in 1780 but it has almost disappeared in modern times.
This could also help prevent toxic algal blooms that currently plague Lake Erie. What used to be a clear oligotrophic lake has now become a green eutrophic one.
This is costing the tourism industry there an estimated $11.5 billion and a nearby city, Toledo, effectively shut down for a few days of August in 2014 as the drinking water was deemed unsafe to drink.
The current proposal is to restore black swamp as they are restoring wetlands in North Western Indiana using the Everglades as a model.
The current problems in the Everglades is that historically water flowed from North to South but now flows, due to canal and levee construction, from the centre to East and West, flooding estuaries with too much water and pollution.
Long term the plan is to restore the natural flow regime but at the same time remove the excess nutrients.
So far 23,000 hectares of wetland have been created in the South of Florida known as storm water treatment areas (STAs).
It is the largest area of treatment wetlands ever built and has been very successful in removing excess phosphorous, which has fallen by as much as 50-80%.
The current target retention rate is 1g/m/yr and the wetlands are meeting that.
The inflow rate is 191ppb and the outflow rate is 35ppb. Although this represents an 82% drop it is still above the set goal of 10ppb.
In order to reach this stated goal mesocosm experiment was set up in 2011. 18 experimental plots of 1x6m were set up with six diffeent vegetation communities, with three replicates of each.
Initially the experiment didn’t work with a greater outflow of phosphorous than inflow in 2012. However this was due to the efflux from the original soil before the new soil formed.
The following year the outflow dropped dramatically and the plots with water lily showed levels below the goal of 10ppb. Showing that it was an achievable goal. Although it is worth noting it is an arbitrary goal.
The conclusions (and some of the answers to questions) from his talk were:
- Wetlands can remove significant levels of nitrogen and phosphorous
- 20-300 ppb and 1 ppm nitrogen were reasonable goals but it was possible to push lower
- 10ppb of phosphorous was achievable but required extensive downstream wetlands
- Building more reservoirs or purchasing more water storage is not a good option
- Large land requirements may inhibit progress, landowners still won’t commit to wetlands for non scientific reasons.
- No point building lakes as they will turn green, no point in planting forests as it is too wet, wetlands are the ideal habitat of choice
- Life span of constructed wetlands 20+ years
- Things will get worse before they get better
- Marshes are the best surface flow wetlands
- Forests are the best subsurface flow wetlands due to their large root structures, they are also important for carbon sequestration.
So after all that it was time to jump back onto the bus and head back to the Vester…or was it?
As we were so far south the staff were undecided over whether to a) go home b) go to the Florida keys or c) go to Miami. Unfortunately so were the students.
Eventually it was decided that one bus would go to each location. I opted to go home as it was late in the day and it was going to take a good three hours to get home anyway. Besides if I went to the Keys or Miami it would only be a quick stopover and I decided it wasn’t worth it.
However getting back was a bit trickier than anticipated as we were given faulty directions and got lost pretty much instantly. However once we asked for directions we were on our way and arrived back at the Vester some three hours later.
We then went off to a place called Murphy’s sport bar for a slice of authentic American culture.
All I’m going to say is that it was quite an experience.