Part of our job at Extension is to help enhance science literacy. Often we write about natural history topics of interest to community that focus on interesting wildlife or an environmental issue or on topic we think the public should know more about. These articles have good science in them but are often written in a way as to not be too “sciencey” so that public will not be lost in the message. But sometimes there is a need for “sciencey” articles. Ones that may explain things using concepts and terms that go deeper than the public usually like to go. Not that the public cannot understand this, it is just too much like a science class from high school and not everyone enjoyed science when they were in school. A topic they may not enjoy. We are going to try a “sciencey” topic for this article.
What is salinity?
Most have heard the term and usually associate it with how much salt is in the water. They are not incorrect, and for the most part this definition will suffice when using it in conversation. But it actually goes a bit deeper than that. We will start with what is a salt.
Salt crystals used to de-ice roads. Photo: University of South Florida
A salt is the product of an acid and a base. For example, when you combine hydrochloric acid and sodium hydroxide you get sodium chloride (salt) and water.
HCl + NaOH – HOH (H2O) + NaCl
Most recognize sodium hydroxide as common table salt. But to better understand the point let’s combine sulfuric acid and sodium hydroxide.
H2SO4 + NaOH – H2OH (H2O) + NaSO4
Sodium sulfate (NaSO4) would also be a salt. There are numerous salts found in the environment. They are found in rock and mineral forms from land and the seafloor and will eventually make their way into the ocean – where of course they meet water.
Water has been described as the “universal solvent” and that is because water is a polar molecule and dissolves most things. What does “being polar” that mean?
We understand that “polar” means opposite ends, and in this case one end is positively charged, and the other is negative. This has to do with the alignment of the element’s hydrogen and oxygen in the molecule. To explain the alignment would require more chemistry than we want to go into here. But let’s just say the outer suborbital requires eight electrons to be considered stable – even that will take more discussion.
We know that atoms are made of protons, neutrons, and electrons. The protons and neutrons combine to form the nucleus of the atom while the electrons orbit around the nucleus like the moon orbits around the earth. Well, not exactly like that but that description will suffice to get the idea across. The orbit closest to the nucleus can only hold two electrons, any additional electrons will be forced to another orbit further away. If there are no additional electrons there are no additional orbits.
These orbits are identified by letters. The one closest to the nucleus is an s orbital. S orbitals can only hold two electrons. The next orbit out will have an s orbital and a p orbital. Again, the s can hold two, but the p can hold six. So, the second orbit can hold a total of eight electrons – 2 in the s orbital of the second orbit and another 6 in the p orbital of the second orbit (there is not a p orbital in the first orbit). If the atom has more than 10 electrons (2 in the first orbit and 8 in the second) then there will be a third orbit that has an s orbital (holding 2 electrons), a p orbital (holding 6 electrons) and a new orbital called d (which can hold 10 electrons). And so, it goes. Large atoms with lots of electrons will have lots of orbits with several orbitals holding a fix number of electrons. This may be getting more “sciencey” than we wanted, but we will continue to plow forward to help better understand salinity.
Here is the kicker. The s and p orbitals together hold a total of 8 electrons and the s and p orbitals of the orbit farthest from the nucleus MUST be filled for the atom to be stable. If they are not, then the atom is looking to gain or lose electrons to do so. Let’s look at water, we will start with oxygen.
Oxygen has the atomic number of 8. This means it has eight protons and eight electrons. Protons are positively charged, and electrons are negatively charged. Thus, oxygen has eight protons (+8) and eight electrons (-8). The charges cancel each other out and the atom is neutrally charged. But let’s look at how those eight electrons fill the orbits.
Remember the orbit closest to the nucleus only had an s orbital and can hold two electrons, which is does. But this leaves six electrons to place. The second orbit has an s and an p. S can only hold 2 electrons, so 2 of the 6 will go there. The p can hold 6, but now the oxygen atom only has 4 electrons left (after filling the first two s orbitals). So, it places those remaining four in the p orbital. But the p orbital is not full. It will hold 6 but only has 4. It has two empty orbitals and those MUST be filled. It needs 2 electrons from somewhere. (see below).
Filled s12 s2 2 p26
Oxygen s12 s2 2 p24 – it needs two electrons
Where does it find two electrons to become stable?
Let’s look hydrogen.
Hydrogen has the atomic number of 1. It has one proton (+1) and one electron (-1). Its orbit configuration would look like this:
Filled s12
Hydrogen s11 – it needs one electron to fill
Remember if you do not have enough electrons for a second orbit, there is no second orbit. BUT as you see the first orbit of hydrogen (which needs 2) only has 1 electron. It is not full.
Let’s look at another example to first understand how MOST atoms deal with this problem.
Sodium has the atomic number of 11. Eleven protons (+11) and eleven electrons (-11)
Chlorine has the atomic number of 17. Seventeen protons (+17) and seventeen electrons (-17). They would fill their orbits, and orbitals, as follows.
Na s12 s2 2 p26 s31
Cl s12 s2 2 p26 s32 p36 s41
You can see that the last sp for both are not full. However, if sodium “gives” the electron in s3 to chlorine then it’s s3 orbital is gone and the sp2 for the second orbit of sodium would be full – stable. Likewise, if chlorine “accepted” that electron its s4 orbital would be full – stable. And this is what happens. However, this throws the electronic balance off.
If sodium is (+11) (-11) and gives away an electron it is now (+11) (-10) – no longer neutral. It becomes positively charged (+1) and charged atoms are called ions (Na+1). Likewise, chlorine accepting the electron (+17) (-18) would form a negative ion (-1) (Cl-1). Opposite charges attract with Na+1 and Cl-1 combine to form NaCl – salt. This is known as an ionic bond. Two oppositely charged ions combining to form a compound.
Water is a bit different.
Hydrogen s11
Oxygen s12 s2 2 p24
You can see oxygen needs 2, but hydrogen does not have 2 to give AND if it gives the ONLY electron, it has it will no longer exist. So, it SHARES its 1 electron with oxygen. The hydrogen atom will allow its lone electron to orbit the last orbital of oxygen BUT it must circle back and orbit the hydrogen nucleus as well. To get the required 2 electrons that oxygen needs to fill its sp2 it will need another hydrogen atom to do so – hence H2O. When sharing electrons to form a compound we call this a covalent bond.
Now comes the alignment part.
To graphically illustrate how the electrons fill the last sp orbitals of an element they use what is called the electron-dot. It would be laid out as follows:
S **
p Na p if full would look like this ** Na **
p **
The first two electrons would fill the s orbital. Then any additional electrons filling the p’s BUT you would first place an electron in each p and then come back and fill (two max) in clockwise form. The number AND ALIGNMENT of the electrons would be represented by dots.
In the example just given – sodium – the atomic number is 11. The eleven electrons would be placed as follows
s1 – (2) s2 (2) p2 (6) s3 (1) The electron dot would look like *
Na
Chlorine (17) would look like this…
s1 (2) s2(2) p2 (6) s3(2) p3 (5)
**
Cl **
**
You can see the open space for one electron to fill this and complete the two for each. Sodium would GIVE it’s one electron to chlorine (having a full s2p2 with eight dots all around) forming an ionic bond known as sodium chloride (NaCl) or salt. The next inner orbit of sodium would have its sp orbitals filled and would be stable but charged due to having more protons than electrons.
Oxygen (8) would look like this…
s1 (2) s2(2) p2(4)
**
O **
*
This alignment would force the two hydrogen atoms SHARING electrons to do so NEXT to each other.
Water would appear like this…
**
H** O **
H **
The water molecule. Image: Florida Atlantic University
In the sharing of the electrons to form water the oxygen molecule holds the electrons longer than the hydrogen (it is larger). This makes hydrogen slightly positive and oxygen negative. Due to this alignment with both hydrogens at one end of the water molecule gives it a positive and negative end – it is polar – it has opposite poles – a positive and negative one. It acts like a magnet.
The first impact of this situation is that water molecules attach to each other. The positive hydrogen end of one water molecule attaches to the negative oxygen end of another. All of the water molecules bond together and form a lattice of water molecules – like they are all holding hands. These bonds are weak and can be easily broken if a creature is trying to swim through them, but attached they are.
A second impact is that they will disassociate (dissolve) ionic compounds that they come in contact with, like salts. The ionic bond we know as salt – sodium chloride (Na+Cl–) will dissolve in water. The positive ion Na+ is attracted to the negative end of the water molecule. The opposite is true for the chlorine ion.
So, what is actually “drifting” around in the water are dissolved ions – not the salts themselves. Which salts and ions are drifting in seawater? All of them. All 92 natural elements found on the planet are dissolved in seawater – not just sodium and chloride. It is true that the sodium and chloride ions make up about 85% of all the dissolved ions in seawater, but not all. So “sea salt” looks and taste like table salt but it is different.
Salinity then is the measure of dissolved solids (or ions) in the water – not exactly salt.
How salty is the water? What is its salinity?
We can measure this several ways.
Conductivity meter. Photo: Iowa State University
Being that you are measuring the amount of dissolved charged ions in the water you can use a conductivity meter. Conductivity is the measure of the ease of which an electric charge (or heat) can pass through a material. The more ions dissolved in the water the higher the conductivity. This can be measured easily with the conductivity meter. Though conductivity is NOT a measure of the amount of ions in the water, but rather the measure of how easily an electric current passes through the water, it is still very closely related to the amount (or salinity) and is often used (making corrections) to determine the salinity of the water.
Hydrometer. Photo: University of Queensland
Another method is measuring the density of the water. The more dissolved ions in the water the denser it is. A hydrometer is a glass tube filled with a fixed amount of lead shot with a calibrated stem (you can get them with different amounts of lead to measure salinity at a wider range). As you place it in the sample, the density of the water holds the hydrometer in specific position and you can read the salinity from the calibrated stem.
Refractometer
Playing off the density game. The denser the water is the more it will refract light passing through it. A refractometer is an instrument that uses a calibrated scale to measure salinity based on much light passing through refracts (or bends). The volunteers monitoring salinity in our citizen science project are using this method.
Salinity is measured in parts per thousand – parts of salt to 1000 parts of water. Using any of these instruments, or one called a salinity meter which works similar to a conductivity meter but is calibrated to salinity not conductivity, you can determine the salinity of the water.
0 parts per thousand (ppt, ‰) would be freshwater water.
35 ‰ would be seawater.
Salinities between 0 and 35 ‰ would be brackish water.
These values are not set in stone.
Many scientists argue that anything above 0 ‰ is not freshwater. I have read salinities in Perdido River as high as 4 ‰ and it did not taste like salt water. Some would say that up to 5 ‰ could still be considered freshwater – but again, not everyone agrees. One must also understand that in nature there are always SOME dissolved ions in the water. It is just their concentrations are SO low that our instruments cannot detect and give a reading of 0 ‰.
Likewise, the salinity of the Gulf of Mexico can run between 30 – 38 ‰, the average is 35 ‰.
Usually, the salinities in the lower parts of the Pensacola Bay system run between 20-30 ‰.
The bayous are typically between 10-20 ‰.
And the upper portions of the bay run between 0-10 ‰.
There are exceptions.
Bayou Chico usually runs between 0-10 ‰ but readings above 10 ‰ are found near the lower end of the bayou.
Perdido Bay is lower than Pensacola Bay. Lower Perdido Bay averages between 10-20 ‰.
Note: The tide plays a role in what the salinity is at any given moment. High tide brings in more saline water, to any system that experiences tides, and the salinity will be higher at that time.
For reasons we will not go into here, many of the plants and animals that call our waters home have specific salinities they prefer. There is a range they can tolerate, but also a smaller range they prefer. The biology of the upper and lower bays can be very different. The seagrass known as tape grass, or eel grass (Vallisneria) prefers low salinities, typically under 10 ‰, and are found in the upper reaches of the bay. Whereas shoal grass (Halodule) and turtle grass (Thalassia) prefer it above 20 ‰ and more common in the lower reaches. Some species, like turtle grass, have a small range of salinity they can tolerate and are called stenohaline species. Others, like shoal grass or widgeon grass (Ruppia), have a much broader range and can be found in many waterways within the bay system. These are called euryhaline.
Sea Grant is currently looking at the salinity across the bay area (from shore) to determine how (if at all) the excessive amount of rain we have been receiving in the Pensacola area in recent years is impacting the salinity of the system. As we described above, this could impact those stenohaline species who cannot tolerate it. We hope to conduct a more robust salinity monitoring project in the future.
Hopefully this was not too “sciencey” and that you learned something new about the salinity of our bay.
We used to find them here. I have heard stories of folks who could fill a 5-gallon bucket with them in about 30 minutes right by Morgan Park. An old shrimper told me that back in the day when shrimping in Santa Rosa Sound they often found scallops along the points. They would drop a grab and collect them for sale. This was when both commercial scallop harvest, and shrimping, were allowed in Santa Rosa Sound. Neither are today. There are numerous tales of large beds of scallops in Big Lagoon and scientific reports of their presence in both locations and in Little Sabine. I myself have found them at Naval Live Oaks, Shoreline Park, Big Sabine, and in Big Lagoon.
Bay scallops need turtle grass to survive. Photo: UF IFAS
But that was a long time ago. The reports suggest the decline began in the 1960s and today it is rare to find one. What happen is hard to say but most believe it began with a decline in water quality. A decrease in salinity and an increase in nutrients from stormwater runoff degraded the environment for both the scallops and the turtle seagrass they depend on. Overharvesting certainly played a role.
But they are not all gone. There is still turtle grass in our system and occasionally reports of scallops. They are trying to hang on. There have also been attempts to improve water quality by modifying how stormwater is discharged into our bay, though there is much more to do there. Each year Florida Sea Grant Agents at our local county extension offices provide volunteers an opportunity to survey our bay for both species. We have a program called “Eyes on Seagrass” where volunteers monitor sites with seagrass once a month from April through October. We partner with Dr. Jane Caffrey from the University of West Florida to assess this. We also hold our annual “Pensacola Bay Scallop Search” each July.
In the Scallop Search volunteers will snorkel four different 50-meter transects lines either in Santa Rosa Sound or Big Lagoon searching for scallops. These surveys are conducted at the end of July. There are 11 survey grids in Big Lagoon and 55 in Santa Rosa Sound extending from Gulf Breeze to Navarre. To volunteer you will need a team of at least three people and your own snorkel gear. Some locations do require a boat to access. If you are interested in searching along the north shore of Santa Rosa Sound contact Chris Verlinde at chrismv@ufl.edu (850-623-3868). If you are interested in searching along the south shore of Santa Rosa Sound, or Big Lagoon, contact Rick O’Connor at roc1@ufl.edu (850-475-5230).
Volunteers conducting the great scallop search. Photo: Molly O’Connor
Reminder, harvesting scallops in Escambia and Santa Rosa counties is still illegal. Please give them a chance to recover.
This fish is a classic example of why scientists use scientific names. There are numerous common names for this species and multiple ones even in the Gulf region. Ling, Cabio, Lemonfish, Cubby Yew, Black kingfish, Black salmon, Crabeater, and Sergeant fish to name a few. The Cajun name for the fish is Limon – possibly where the name Lemonfish came from. Based on the references, Cobia seems to be the most accepted name, but Ling is often used here along the Florida panhandle. Again, this is a great example of why scientists use scientific names when writing or speaking about species. There is less chance for confusion. I say less because at times the scientific names change as well, and some confusion can still occur.
The Cobia
Photo: NOAA
The scientific name for this fish is Rachycentron canadum. The genus name refers to the sharp spines of the first dorsal fin, which are sharp. The species name may refer to Canada. It is a common practice to give a species the name of the area/location in which it was first described. But it seems that Carlos Linnaeus, the biologist who first described it, used a specimen from the Carolinas to do so. So, not sure why the name was given4. It is the only North American fish in the family Rachycentridae and its closest relative are the remoras of the shark sucker family.
Some state that cobia have only one dorsal fin, but in fact they have two. The first is a series of 7-9 spines spaced with no membrane connecting. They are small, sharp, and somewhat embedded into the body. This is very similar to how the remoras and shark suckers first dorsal spines work, albeit remora’s first dorsal is softer. Cobia have a low depressed head that gives them the appearance of a shark when viewed from the side. It is often confused with sharks because they can get quite large – an average of five feet in length and up to 100 pounds in weight. The small juveniles resemble remora quite a bit. They are darker in color with pronounced lighter colored lateral stripes and their caudal fin (tail) is more lancelet and less lunate than the adults.
Biogeographically they are listed as worldwide, albeit tropical to subtropical – they do not like cold water. In the United States they are found all along the east and Gulf coast, but are absent from the west coast – again, a dislike for cold water. The literature states that there are two population stocks of cobia here. The Atlantic group and the Gulf of Mexico group all head south towards the Florida Keys for winter. However, breeding appears to take place in the northern parts of their range and so no genetics are exchanged while the two groups co-exist in the Keys. If this is the case, and it seems to be, there is a reproductive barrier, or behavioral barrier, that could, over time, isolate these two groups long enough that the gene pools could become different enough that attempts to breed between the groups would not produce viable offspring. If this were the case then they could be listed as subspecies, possibly the Atlantic and Gulf Cobia. But this has not happened. There are also studies that suggest in the Gulf there may be isolated groups. One comment is that there are cobia along Florida’s Gulf coast that migrate inshore and offshore but do not make the run to the Keys and back4. There are also studies that show a similar behavior with a group over near Texas. Obviously, there is a lot of work to be done on the movement and genetics of these possible subgroups to completely understand the biogeography of this animal. And don’t forget, there are cobia along the European/African coast of the Atlantic as well as the Indian and western Pacific.
Cobia resemble both shark suckers and sharks.
Photo: University of Florida
But migrate they do. The “Ling Run”, as it known in the Pensacola area, is something many anglers wait for early in the year. We even have some local bait and tackle shops monitoring water temperature to announce when the run will begin. When water temperatures warm to 67°F it is time. Local anglers flock the Gulf side piers and head out on their boats with high ling towers to search for them. At the beginning of the ling run I have seen the inshore Gulf of Mexico littered with hundreds of boats covering the surface like small dots as far as you can see. One boat I remember was about 20 feet long and had precariously placed a large step ladder in the center as a “ling tower”. The angler was perched at the top of the ladder, holding on in the chop, searching the waters for his target.
Cobia will travel alone or in groups of up to 100 and are often attracted to objects in the water. Flotsam like Sargassum weed, or marine debris are places that anglers focus on. They are known to shadow sharks, manta rays, and sea turtles. I know anglers when they see a sea turtle begin throwing bait in that direction in hopes that a cobia is nearby. To the west of us in Alabama they seem to visit the offshore gas rigs and are attracted to the fishing piers many communities have extending into the Gulf – hence the large crowds of non-boating anglers visiting them during the run. Many anglers are known to drop FADs (Fish Attracting Devices) into the water to attract cobia, though these are not allowed during cobia/ling tournaments – which also pop up across the panhandle during the run.
Despite this apparent heavy fishing pressure, it is considered a sustainable fishery. Cobia mature at an early age, 2 years for males and 3 for females – and they live for about 12 years. They mass spawn in the northern waters. A typical season will find females breeding 15-20 times and producing 400,000 – 2,000,000 per spawn event. There is no evidence that this fishery is overfished, and there is commercial fishery for them as well. Due to their quick growth rates, large size, and high-quality flesh, there is interest in offshore aquaculture of this species.
It is an amazing fish. One of the best fish sandwiches I have ever had was a fresh ling sandwich. It is also a very interesting species from a biographical point. Enjoy the next “Ling Run” along the panhandle – or “cobia run”, or “lemonfish run”, which ever you wish to call it.
One of the programs I focus on as a Sea Grant Extension Agent in Escambia County is restoring the health of our estuary. One of the projects in that program is increasing the encounters with estuarine animals that were once common. Currently I am focused on horseshoe crabs, diamondback terrapins, and bay scallops. Horseshoe crabs and bay scallops were more common here 50 years ago. We are not sure how common diamondback terrapins were. We know they were once very common near Dauphin Island and are often found in the Big Bend area, but along the emerald coast we are not sure. That said, we would like to see all of them encountered more often.
Horseshoe crabs breeding on the beach. Photo: Florida Sea Grant
There are a variety of reasons why species decline in numbers, but habitat loss is one of the most common. Water quality declined significantly 50 years ago and certainly played a role in the decline of suitable habitat. The loss of seagrass certainly played a role in the decline of bay scallops, but overharvesting was an issue as well. In the Big Bend region to our east, horseshoe crabs are also common in seagrass beds and the decline of that habitat locally may have played a role in the decline of that animal in our bay system.
Salt marshes are what terrapins prefer. We have lost a lot of marsh due to coastal development. Unfortunately, marshes often exist where we would like houses, marinas, and restaurants. If the decline of these creatures in our bay is a sign of the declining health of the system, their return could be a sign that things are getting better.
Seagrass beds have declined over the last half century. Photo: Rick O’Connor
Salt marshes have declined due to impacts from coastal development. Photo: Molly O’Connor
For over 10 years we have been conducting citizen science monitoring programs to monitor the frequency of encounters of these creatures. All three are here but the increase in encounters has been slow. An interesting note was the fact that many locals had not heard of two of them. Very few knew what a horseshoe crab was when I began this project and even fewer had heard of a terrapin. Scallops are well known from the frequent trips locals make to the Big Bend area to harvest them (the only place in the state where it is legal to do so), but many of those were not aware that they were once harvested here.
I am encouraged when locals send me photos of either horseshoe crabs or their molts. It gives me hope that the animal is on the increase. Our citizen science project focuses on locating their nesting beaches, which we have not found yet, but it is still encouraging.
Volunteers surveying terrapin nesting beaches do find the turtles and most often sign that they have been nesting. The 2022 nesting season was particularly busy and, again, a good sign.
It is now time to do our annual Scallop Search. Each year we solicit volunteers to survey a search grid within either Big Lagoon or Santa Rosa Sound. Over the years the results of these surveys have not been as positive as the other two, but we do find them, and we will continue to search. If you are interested in participating in this year’s search, we will be conducting them during the last week of July. You can contact me at the Escambia County Extension Office (850-475-5230 ext.1111) or email roc1@ufl.edu or Chris Verlinde at the Santa Rosa County Extension Office (850-623-3868) or email chrismv@ufl.edu and we can set you up.
Bay scallops need turtle grass to survive. Photo: UF IFAS
Volunteers participating in the Great Scallop Search. Photo: Molly O’Connor
Final note…
Each June I camp out west somewhere and each year I look for those hard-to-find animals. After 10 years of looking for a mountain lion, I saw one this year. Finding these creatures can happen. Let’s hope encounters with all three become more common in our bay.
“Bluefish!” … “It’s just a school of bluefish!” So yelled the lifeguard in Jaws II when Chief Brody had mistaken a school of bluefish for the rogue great white shark that was plaguing the town. He would not have been the first to mistake these large schools for a larger fish, particularly a predatory shark, but as some know, bluefish are quite predatory themselves.
Bluefish Image: University of South Florida
Growing up along the Florida panhandle we heard little about this species. We had heard stories of large bluefish schooling along the Atlantic coast killing prey with their razor-sharp teeth and, at times, biting humans. But not much was mentioned about them swimming along our shores. But they do, and I have caught some.
Bluefish are one of several in a group Hoese and Moore refer to as “mackerel-like fish” in Fishes of the Gulf of Mexico. They differ in that they lack the finlets found along the dorsal and ventral sides of the mackerel body and mackerels lack scales having a smoother skin. Bluefish are the only members of the family Pomatomidae. They can reach three feet in length and up to 30 pounds. They travel in large schools viciously feeding on just about anything they can catch and seem to really like menhaden. They move inshore for feeding and protection from larger ocean predators but do move offshore for breeding.
Bluefish landed from the Gulf of Mexico are much smaller than their Atlantic cousins, rarely weighing in more than three pounds. They do have a deep blue-green color to them and thin caudal peduncle and forked tail giving them the resemblance of a mackerel or jack. Some say they are bit too oily to eat while others enjoy them quite a bit. There is a commercial fishery for them in Florida and, as you would expect, it is a larger fishery along the east coast. Most of the panhandle counties have had commercial landings, albeit small ones.
Biogeographically, the blue fish are found all along the Atlantic seaboard and into the Gulf of Mexico. It is listed as worldwide but seems to be absent from the Caribbean and other tropical seas. This could be due to a distaste of warmer waters, or the lack of their prey targets.
They are an interesting and less known fish in our region. Swimming in a school of them should be done with caution, there are reports of nips and bites from these voracious predators.
