WAVE on Wheels Outreach

WAVE on Wheels Outreach

Ray Cart Presentation

Grades 9-12

Time requirement

1 Hour

Group size and grade

Up to 50 students maximum

Materials

2Yellow Stingrays – in large transport cooler

1 or 2 water coolers (depending on the length of trip and need for a water change)

Mobile Ray Cart

Blue basket (including Pump, Ray Net, Electrical Cord, Paper towels)

Thermometer

Ray Artifacts Bin

Ray Emergency Water

WAVE Tablecloth

Goal

Through a live ray encounter, students will be excited, engaged, and educated about the wonders of aquatic life and the importance of conservation.

Objectives

1. Students will be able to list 5 adaptations aray has for aquatic life including a combination of internal and external body parts as well as behaviors.
2. Students will be able to define natural selection and discuss its effects on ray adaptations.
3. Students will be able to list at least 3 species related to rays and identify a unique characteristic to that species.
4. Students will be able to discuss biological factors relating to ray population numbers, individual growth rates, and reproductive success.
5. Students will be able to discuss social behavior strategies among rays.
6. Students will be able to discuss ray conservation efforts as well as how they can help save rays and other aquatic animals.
7. Students will be able to design and describe a method for monitoring and minimizing human impacts on ray environments.

Theme

Rays are often misunderstood animals that play an important role in their environment.

Kentucky Core Academic Standards – Science

High School. Interdependent Relationships in Ecosystems

HS-LS2-7. Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity.

HS-LS2-8. Evaluate the evidence for the role of group behavior on individual and species’ chances to survive and reproduce

High School. Natural Selection and Evolution

HS-LS4-4. Construct an explanation based on evidence for how natural selection leads to adaptation of populations.

HS-LS4-5. Evaluate the evidence supporting claims that changes in environmental conditions may result in: (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species.

LS4.C: Adaptation

High School. Human Sustainability

HS-ESS3-4. Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.

ESS3.C: Human Impacts on Earth Systems

Background

Stingrays are Fish

Stingrays are a type of fish. They live underwater, breath water through gills, have a protective layer of scales covering their body, and are cold-blooded, or ectothermic. Worldwide there are more than 22,000 species of fish. Stingrays fall into a special group of fish known as cartilaginous fish including sharks, rays, skates, and guitarfish. This group has a skeleton made of cartilage rather than bone like most fish known as bony fish. Bony fish have gas-filled swim bladders that allow vertical movement in the water column. On the other hand, stingrays do not have swim bladders. They either swim in the open water using their large wing-like fins or use their flat bodies to hide under the sand. Using these wide fins, they also have the ability to glide for long distances through the water. Looking at the cart below, you can see the differences between cartilaginous fish and bony fish.

Cartilaginous fish (Chondrichthyes) / Bony fish (Osteichthyes)
Skeleton / Cartilage / Wholly or partially ossified
Gill slit cover / Open gill slits / Gill cover
Swim bladder / Not present / Present
Skin surface / Covered in dermal teeth / Covered in scales

Ray Adaptations

Stingrays have several unique adaptations that help them survive in their environment. In general, stingrays are darker on top and lighter below. This is a type of camouflage known as countershading. Countershading aids many aquatic animals, including stingrays, as they are more difficult to see because their light undersides blend in with the sunlight. The darker upper body blends in with the ocean depths, which are black as sunlight completely, dissipates. Stingrays also have the ability to blend in with their environment, being able to change their colors when burrowing to hide from predators and prey. This ability to change colors may also be used for communicating between individuals, for breeding or territorial purposes. A flat body gives them the ability to not only hide from potential predators, but to also hide form their prey. Stingrays also have specialized sensory organs that detect electrical fields. These organs, called ampullae of Lorenzini, aid stingrays in locating their prey by detecting tiny electrical signals from the prey’s muscles. Stingrays have a protective spine at the base or middle of their tail. This is usually venomous so it inflicts a painful jab as well as administering potentially lethal venom. This is strictly used for the animal protecting itself. Injuries to a human from stingray barbs are very rare, and it is even rarer to die from this injury. This is due to the location of most injuries, being someone’s legs or feet which is not usually life threatening. If one was allergic to the venom, or to be impaled in an artery, this could lead to death.

Stingray bodies come in a variety of shapes and sizes. These are adaptations to the environment of that stingray species. A depressiform, or flattened, is adapted for living on the bottom of the ocean,while a fusiform, or torpedo shape, is adapted for open water. Almost all stingray species and relatives have this depressiform body shape. While a related animal like a guitarfish have more of a shark like body, other species like a skate will have a diamond shaped body and a long un-forked tail that aids in maneuverability as well as living near the bottom.

Stingrayscan be solitary or in groups, usually for breeding and migration. Many larger species will migrate all over the world, some migrate once a year in the thousands, and others will stay in one reef or sand flat for their whole life.

Growth rates in rays, just like sharks, are a bit of a mystery. Studies show that even though their cartilage structure is very similar to ours, it has a much different growth rate and pattern. These studies also include the fact that it is hard to truly compare two types of animals when they are vastly different. The closest comparison for their growth rates are those of small mammals, like rats. The changes based on age and their cellular densities are rather similar. As a rat or ray grows, they have a higher cellular density to help grow their skeletal structure. When growing, they need less and less cellular density to help keep the skeleton growing. For elasmobranchs it never truly stops, but greatly slows down.

Figure 1:

This is the current hypothesis on how the skeletal structure of a stingray mineralizes. Cellular density slows down as the animal ages, showing that once the tesserae, which is the matrix that makes the cartilage strong, form fewer cells are necessary. In mammals, these cells would completely disappear, but because elasmobranchs constantly grow more cells are needed over time.

- figure-viewer-f6

This means that sharks and rays do grow their whole lives. It is well documented that growth rates in ectotherms are significantly affected by the amount of food intake. Radio carbon dating could tell us more information about the ages of these animals, but it is sometimes difficult to do and not always accurate.More recent studies are also showing that water temperature and carbon dioxide levels may also affect the growth rate and potential as these factors can effect metabolic rates. There is even some evidence that ocean acidification and warmer temperatures may reduce the olfactory capabilities in elasmobranchs decreasing their hunting capability.

Rays have one type of reproduction, called Ovoviviparity, or aplacentalviviparity. This means the rays have embryo sacs within the uterus, but bear live young. The young rely on the yolk of the egg until it runs out. After this, the mother will produce uterine milk, with the fetus either absorbing or ingesting it. Some rays have extra finger-like projections that increase the surface area for absorbing the uterine milk. Internal fertilization, which is what rays do, increases the sperm retention. This insures that nothing is wasted and the fertilization process is more efficient. Sperm retention can also occur, if the female wishes to wait to be pregnant until her life conditions improve. During times of little food or shelter, this occurs. Ovoviviparity differs from viviparity and oviparity by being more of a combination of both processes. Viviparity is live birth where the embryo reaches complete development before birth occurs and oviparity is egg laying.

Other related species, like sharks and skates, can undergo a different type of reproduction. These animals will sometimes lay eggs, which will be held inside the mother until a thick, protective case builds. Similar to a newborn ray, they hatch as exact replicas of an adult, only needing to grow in size. One of species that displays this is the Bowmouth Guitarfish, or sharkray, which can be found at the Newport Aquarium.

Stingray Diets

Animal diets closely related to the dentition, or teeth, of those animals. Stingrays have a very unique tooth structure. This aids them in eating what we believe is their normal diet. Unfortunately, there is not a lot of information on what exactly stingrays and related species eat, but we can infer that from their morphology and mouth placement about what they most likely eat. Small fish, crustaceans, bivalves, worms, and other small animals living in the sand or pelagic areas are thought to be common prey items. Stingrays and other related species have flat, rough teeth that sit on a tooth band. They do replace these teeth similarly to how sharks lose theirs. This is mainly because of the types of animals they feed on, which usually have very hard shells to crunch through. Cartilage is not a very strong material, so the jaw of a stingray, shark, skate, or guitarfish should not be that strong. Scientists discovered that when a stingray’s skeletal system is forming, there is calcium added to the structure. Usually, calcium cannot be moved unless there is blood present, but young rays have been found with large amounts of calcium near their skeletal system as they grow. This calcium is added to the cartilaginous structure as they age. It makes the cartilage strong enough to be rigid at adulthood.

Figure 2:

These are examples of a stingray’s teeth, or mouth plates.

Relationships

Stingrays have mutualistic, parasitic, and commensal relationships with other animals in the ocean. Their mutual relationship comes in the form of fish that swim above them as they search for food. When stingrays eat, they do not always consume everything that they find. The fish that follow them eat the leftover fish that the stingray did not want. This benefits the fish, but does not alter the stingray’s life in any way. Parasites can be found on or in almost any animal on earth, so the stingray is no exception. Parasites feed while harming the host in some way. Whether this be feeding from the host or laying eggs in them, it is deteriorating and in some cases ends in the death of the host. The commensal relationship is also with a species of fish called cleaner wrasses and other smaller species. Stingrays are not particularly clean animals, and cannot remove the parasites or mucus that covers them. These small fish will create cleaning stations to help remove unwanted guests on the stingrays. This benefits both parties, with the fish getting a meal and the stingray being cleaned off. These are all symbiotic relationships between two or more animals.

Natural Selection

Ray ancestry is a difficult field as cartilaginous fish leave very few clues. There are estimates that raysmay have been found as far back as 100 million years ago, possibly farther.Heliobatisand Asterotrygon are the only two extinct genus of stingrays known today. While these have been found since the late 1800’s, it is extremely difficult to find a full fossil. Cartilage is more organic than bone;therefore, it deteriorates much quicker than a bony skeleton. Comparing the fossil skeletons to a close relative shows how little they have changed over 50 to 100 million years.

On the left, there is an xray of a extant species of ray, and on the right is an Heliobatis radiens ray fossil. The small cartilaginous structures on the sides are identical, but some morphology is different. The main structure in the middle is almost identical, with a curvy ‘H’ shape. Though it is difficult to tell in the fossil photo, the mouth structure has also barely altered in over 50 million years. Rays have kept their iconic long, thin tail along with the single or multiple protective barbs at the end.

Most ancient, extinct rays species were not larger than 35-40 inches across, which is about the size of a full grown cownose ray. The development of their young is almost identical to that of our modern rays. Fossil evidence of the same Asterotrygon species of differing ages showed that development has not changed.

Stingray Species

The Newport Aquarium currently displays a southern stingray, a honeycomb whiptail ray, a mangrove ray, freshwater river rays, cownose rays, and yellow stingrays. Our largest tank is not suitable for any manta species, as they can get well over 10-15 feet across. The smallest stingrays stay right around a foot long and are desirable for the aquarium trade. Ours are called yellow stingrays, which for maximum size might get around 2 feet across. Altogether, there are around 500 species of stingrays and skates across 18 separate families.

Food Web Connections

Within food chains, there are many levels, from producer to apex predator. Stingrays sit right in the middle. They are predators, but not top tier, apex predator. This puts them in a place where they eat prey but also regularly become prey. Apex and secondary predators eat stingrays. Apex predators consume tertiary and/or secondary consumers, which consume primary consumers, which consume producers, which produce energy from the sun through photosynthesis. The main source of energy for all ecosystems initiates from the sun in the form of solar energy. Through the process of photosynthesis, plants convert this energy into oxygen and glucose. Because of this conversion, green plants, some bacteria, an algae are labeled as producers. An animal, such as an herbivorous fish, who consumes the plant, is known as a primary consumer, because it receives the energy from the plant, which converted the energy from the sun. The stingray who eats the fish that feeds on the plant that converted the sunlight is known as a secondary consumer, hence a process that directly relates back to the sun as the primary energy source. Stingrays help keep the balance within ecosystems predator and prey relationships.

A stingray’s most sophisticated predator is that of the hammerhead. Hammerheads have a special head shape that allows them to scan for rays, skates, and guitarfish hiding under the sand. Though a ray is flattened to give them a hiding place, hammerheads developed a cephalofoil with extra sensory organs to locate any living creature around them. The head shape of a hammerhead gives them the ability to pin down animals, like rays, on the ocean floor to consume them. Hammerheads actually have a weaker bite force than other sharks of a similar size, like a great white or sandbar. Their head shape keeps them from having an extremely strong jaw, which means that evolutionarily speaking, the cephalofoil structure was more important than jaw strength.

Stingray Conservation

Stingrays are vital to the ecotourism and education opportunities available in the Cayman Islands. Here, snorkelers have the chance to feed, touch, and swim with them. Not only does this give guests a chance to interact with an amazing animal, but they get to learn about their importance in the ecosystems and why we should protect them. The Sandbar and Stingray City both are home to large amounts of southern stingrays (Hypanusamericana) which granted an opportunity to further study stingrays. At these locations, they learned that there are six times more females than males visiting these places, along with an estimated group size of around 150 individuals. In addition, they discovered much about their breeding habits, habitat size varying from male to female and genetic data to further our comparison to other species.

The Inernational Union for Conservation of Nature deems most stingray species as DD, or data deficient. This means there is not enough known about a species to say that there is a risk of extinction. More groups need to be studying stingrays and their behaviors in the wild to help us better understand what is happening with them.

Finally, WAVE is assisting the O’Seas Conservation Foundation in Shark Science and Youth Education. By integrating shark tagging with youth education, this innovative approach will enhance our knowledge pertaining to an understudied species and will help to secure our future through the education and motivation of our environmentally conscious youth. Due to the similarities between many sharks and stingrays, this information can help out more than just shark conservation.