The photos above and below are from two weeks ago but I'm sure the events are still occurring today.
The Daily Bucket is a regular feature of the Backyard Science group, a place where everyone is welcome to note the observations you have made of the natural world around you. Insects, weather, fish, climate, birds and/or plants: all are worthy additions to the bucket. Ask questions if you have them and someone here may well have an answer.
St Marks National Wildlife Refuge, Wakulla County, Florida
The NWR preserves a large portion of the coast line of the western part of what is known as the Big Bend region of Florida. In the parlance of the Florida tourism industry it is also known as the Nature Coast. From Panacea in the northwest to around Crystal River to the southeast the gulf coast of Florida is almost exclusively salt marsh. Compared to the rest of the state, coastal development is minimal. In fact the number of places you can drive down to the coast is fairly small.
Salt marsh is an important habitat, trapping nutrients and serving as a sheltered location for juvenile fish to grow up and wintering water and shore birds to feed. It can also be a challenging place to live.
Salt marshes are fairly shallow and are affected by both the tides pushing salt water in from the gulf and by freshwater flowing in from the opposite side. Thus the salinity of the water will vary spatially across the marsh and will also vary over time with variation in rainfall and the tide. The warm shallow water and abundance of organic matter can also result in oxygen concentrations.
One of the fish species that is abundant in the salt marshes of the southeastern United States is the Sailfin Molly, Poecilia latipinna. Here is a not very good picture of a couple of them.
Sailfin Mollies are members of the family Poeciliidae or livebearers. In particular they are very closely related to two common aquarium fish species, guppies (
Poecilia reticulata) and black mollies (
Poecilia sphenops). As the name suggests the distinguishing characteristic of this family is that they give birth to live young rather than eggs. The anal fin of the male is modified to form a 'penis' (technically known as a gonopodium) which is used to insert sperm into the female. Most species of livebearers occur from Mexico through the far north of South America.
Other than the sailfin molly the only widespread livebearers in the US are the eastern and western mosquitofish in the genus Gambusia. The livebearers are members of the order Cyprinodontiformes. Other members of this group in North America include the pupfish of the southwest and the topminnows in the east. Members of this group are known for living in physiologically challenging environments such as desert springs and salt marshes. They tend to be most common in environments that have few other fish species.
This is a bit of a digression on salinity and fish. I'm sure many of you know this. The proper functioning of nerve cells, muscles, and so depends on having the cells exist in an environment with the proper concentrations of ions. In most marine invertebrates the cells have the same ion concentrations as sea water and thus they are iso-osmotic. Most marine invertebrates have limited or no ability to control the ion concentrations in their bodies. Intertidal organisms have, at least in some cases, evolved mechanisms to deal with an environment in which salinity changed dramatically. Fiddler crabs can maintain a fairly constant internal ion concentration over a wide range of salinities.
Fishes represent an unusual situation. Fish have ion concentrations considerably higher than those in freshwater but lower than sea water. This is true for other vertebrates as well which is why we can't drink seawater and the vertebrates that do such as marine mammals and reptiles have to excrete excess salt. So freshwater and saltwater fishes have opposite problems. In freshwater fish will tend to lose ions and take on water. In salt water fish will tend to lose water and take up ions. So that portion of their physiology has to run in opposite directions.
So fishes that move between fresh and salt water have to have physiological mechanisms that can change rapidly as they move between environments.
Sailfin mollies are physiologically very tough. They thrive in brackish water but can live in fresh water and even in water that is more saline than the ocean. They can also survive in low oxygen environments. At St. Marks they are by far the most abundant fish species in the marsh. This pdf has a lot of nice info on them.
Being a small fish and living in shallow water does present hazards. Lots of things might consider you a tasty treat.
Blue Crab
Some other kind of crab
Sorry for the poor quality of the crab photos. The blue crab wouldn't hold still and I couldn't get to a spot where the shore vegetation wasn't in the way. The crabs would be vulnerable to predators as well such as...
This great egret turned its head just as I took the picture. Although not as scenic as most egret photos it does show that they have at least some binocular vision which would be important when aiming at small moving targets in the water (such as mollies).
The area where these pictures were taken was within fifty feet of the gulf and was probably pretty saline. There were a number of other small fish species present, mostly just a few of each kind. They also didn't hold still to get photos for ID. This species below was the next most common. Probably many of them were juveniles which would complicate ID.
The most striking fish in the area were a group of about half a dozen juvenile needlefish (family Belonidae). I wasn't able to make a specific ID based on the photos but given the habitat they were most likely Atlantic Needlefish,
Strongylura marina. Needlefish are elongate predatory fish that somewhat resemble gars. I've seen somewhat larger needlefish while snorkeling a few times. These ones were only about six inches long.
The needlefish cruised around slowly in the shallows while I watched them. Two or three times one would make an amazingly fast dart at some of the other fish. These predation attempts were unsuccessful. Unfortunately they also happened far too rapidly for me to catch on film. Given the relative sizes of the fish I was surprised. I would have thought the mollies too large for the needlefish to handle.
Overcast today in Tallahassee. Haven't been outside yet. Let us know what is going on where you are.
"Green Diary Rescue" is Back!
After a hiatus of over 1 1/2 years, Meteor Blades has revived his excellent series. As MB explained, this weekly diary is a "round-up with excerpts and links... of the hard work so many Kossacks put into bringing matters of environmental concern to the community... I'll be starting out with some commentary of my own on an issue related to the environment, a word I take in its broadest meaning."
"Green Diary Rescue" will be posted every Saturday at 1:00 pm Pacific Time on the Daily Kos front page. Be sure to recommend and comment in the diary.