. Introduction
Predation and the understanding of relationships between species play a significant role in our comprehension of the ecosystems that surround us. The Chocolate Chip Starfish (Protoreastor nodosus) is considered the only important sea urchin predator. The purpose of this study is to determine the effects of the vulnerability of sea urchins, such as Tripneustes ventricosus (Tropical Sea Urchin) with respect to predatory and scavenging stimuli. In light of this we may ask, “How does the vulnerability of Tripneustes ventricosus respond to foraging and predatory stimuli?”
1.1 Definition of Sea Urchins and Starfish
A sea urchin is a marine echinoderm that has a mouth on the underside and calcareous jaws with a spherical shell covered in mobile spines. A starfish is also a marine echinoderm with more than four radiating arms. The foundations of the arms have tube feet for movement and for opening the shells of mollusks, predation. It is evidently important to know how sea urchins respond to stimuli because the very response is the origin of their dominance in the marine community.
1.2 Importance of Sea Urchins and Starfish in the Marine Ecosystem
Sea urchins are well known as sea grazers of sea grass beds and coral reefs (2008, p. 1). Reefs with large numbers of grazing sea urchins could become problematic by reducing the abundance of crustose coralline algae. Crustose coralline algae are a species of algae that produce calcium carbonate, thus aiding in coral reef growth ("Sea Urchins Destroy Reef," 2011). Starfish are ecologically important part of marine ecosystems by helping to control the distribution of sea urchins (Duggins, 1983). Sea urchins can erode the coral, remove newly settled corals, and powerfully feed on the corals diminishing the population, like in the Palau Coral Reefs. If sea urchin predators, such as crabs, starfish, snails, were greatly diminished, there would be an imbalance of the marine ecosystem and these urchins would be essentially free to graze and stunt coral reef growth ("Sea Urchins Destroy Reef," 2011). By better understanding the relationship of how sea urchins react to such predators and food sources, we may become well-equipped in preserving the biodiversity important parts of marine ecosystems such as coral reefs.
1.3 Importance of Maintaining Sea Urchin and Starfish Populations
Over-harvesting is referred to as harvesting a renewable supply to the extent of lessening returns. If overexploitation is constant, it can lead to the destruction of the resource. It threatens biodiversity in ecosystems. According to John Rudolf’s article in 2009, “Oyster reefs were once the dominant ecosystem in the world’s temperate bays and estuaries, but destructive dredging by fishermen, pollution and the spread of disease through the introduction of non-native oyster species have led to their widespread decline.” People introduced regulations to try to stop the advancement of over harvesting. Sustainable seafood is seafood that is caught or farmed in methods that reflect the long-term liveliness that harvested species have and the security of the oceans (Sustainable Seafood Guide, 2008).
There are many measurement restrictions to prevent over harvesting of seafood. Foraging behavior helps us understand sea urchins better and how they survive. T. ventricosus commonly are commonly found in the coral reefs of Caribbean. They are ecologically important sea grazers of sea grass beds and coral reefs. In some areas, the sea urchins are dominant invertebrate herbivore (2008, p. 1). Grazing aggregations of the sea urchin, Strongylocentrotus droebachiensis, drive the transition between alternative ecosystem states from productive kelp beds to less productive barrens. Sea urchins can be characterized as very aggressive grazers (2008, p.1). Sea Urchins exhibit a very broad diet. Urchins eat the most preferred foods where is it popular, but are forced to eat other food types when it is rare (Vance & Schmitt, 1979).
Sea urchins also overgraze specific food, which causes the local preferred foods, thereby forcing to add less preferred to their diets. The foraging range promotes evolution of a broad diet by two separate mechanisms. Shelters that cannot be lived in causes more access to different foods. In addition, the overgrazing of sea urchins causes the reduction of abundance of their preferred food (Vance, Schmitt 1979). The sea urchins then have to find other foods to eat to survive.
The purpose of this study is to investigate the effect of vulnerability on responses to foraging and predatory stimuli of Tripneustes ventricosus (Tropical Sea Urchin). This project is significant because it tests how flipping over a sea urchin effects their eating and protecting themselves. Behavior in response to predation involves the Globiferous pedicellariae, venomous defense mechanisms. Varying in position on the either large or small pedicellariae are both tissue and valves with poison glands. After aiding in this defense mechanism, the heads of the pedicellariae close. When this happens, it causes a chain reaction with the pedicellariae of other individuals in the area (Moore, 1966). Spines and tube feet help burrowing, and food-gathering. Generally, urchins have longer spines.
Sea urchins are a major component of recent marine communities where they exert a key role as grazers and benthic predators. Sea stars or starfish are nearly the most important predators in many marine systems such as tropical temperate and polar marine systems (Mauzey, K. P., C. Birkeland, and P. K. Dayton. 1968; Paine 1974). Hartwick B, Smith MJ, Sloan NA. 1983; Lourey. 2000). Both predators and scavengers rest on the awareness of food to angle their movements towards the food source (Moitozoa and Phillips 1979; Himmelman1988; Lapointe and Sainte-Marie 1992). For scavengers, chemoreception is considered to be one of the most important ways to locate food, because radially symmetrical invertebrates receive chemical cues from all directions equally well, sea stars should have an ideal shape for chemosensory perception. A chemo sensor senses chemical stimuli in the environment. Conclusions can be generalized to accommodate predator populations foraging out of shelters, not necessarily in all directions, and to infer the effects of their foraging on prey distributions within habitats. Optimal foraging theory predicts that organisms should seek preys that have a low search/handling time (Sloan, 1982). In Bruce Menge’s research, he was key on distinguishing between a predators preferred food and a predators best or optimal food. Two recurrent themes in many studies are prey selection by predators and the related problem of prey availability (Bruce Menge 1972). Information on the responses of echinoids to attacks by sea stars is scarce in literature. Many scientists have studied sea stars reacting on sea urchins, but not really studied the reactions of sea urchins getting attacked on sea stars.
1.4 Investigating Tripneustes ventricosus’s Vulnerability Response to Starfish
This investigation will use salt water tanks filled with sea water, one containing a Protoreastor nodosus (Chocolate Chip Starfish) (predator); one is empty, and one containing lettuce (prey). Sea urchin will be placed in the tank upside down for ten trials per tank. The increase of vulnerability will increase the speed of how the sea urchin reacts to predation and foraging behavior. The increase of vulnerability will not affect the direction the sea urchin moves to protect and feed itself. The hypothesis is that it will take the longest for the sea urchin to flip over and move when it is alone. When it is alone, it will shift to the right. The researcher considers this because it has nothing to respond to so the sea urchin will not move significantly. When the predator is in the tank, it will take the fastest time for the sea urchin to flip over and it will move away from the predator. In addition, when the prey is in the tank, referring to time it will take the medial amount out of all three experiments and the sea urchin will move towards its prey. The researcher does not infer that chemoreception will be affected since it is a physical change. This topic is very intriguing because you can find out how sea urchins react to their vulnerability.
II. Procedure
First, pour the salt water into the container where it is half way in container and let the water settle. Then, put in the predator/prey into the container; give the organism time to get use to surroundings. Place sea urchin carefully into container, in direct middle. Next, flip over the sea urchin carefully immediately after placed into container. Then, start the timer. When involving prey and predator, one would put them on two opposite sides for 5 trials on each side. Then, observe and wait until sea urchin moves half its size right side up, 2.25cm in a specific direction. When it does this, stop the timer and put sea urchin alone if it already was not. Repeat steps for 9 more trials for each container.
III. Materials & Methods Standard Orientation
Salt water was the natural environment of Tropical Sea Urchin, Chocolate Chip Starfish and the piece of lettuce. The main subject of this investigation was the Tripneustes ventricosus (Tropical Sea Urchin). The predator was the Protoreastor nodosus (Chocolate Chip Starfish) used for the second experimental group. 3 containers held the control group trials and experimental group trials. The prey was the piece of lettuce used for the first experimental group. The ruler and timer were used to measure the dependent variable.
IV. Data
Control- Sea Urchin Alone
Trial # Direction moved Time(mins)
1 Left 8.20
2 Left 10.16
3 Left 15.01
4 Right 7.30
5 Right 10.07
6 Left 9.41
7 Right 5.59
8 Left 6.10
9 Right 6.05
10 Right 7.09
5-Left
5-Right Average: 8.50
Trial # Direction moved Time(mins) Prey’s Side
1 Right 3.33 Left
2 Left 3.06 Left
3 Left 4.58 Left
4 Right 3.58 Left
5 Left 3.17 Left
6 Right 4.50 Right
7 Left 2.57 Right
8 Left 3.08 Right
9 Right 5.51 Right
10 Right 3.21 Right
5-Left
5-Right Average: 3.66
Experimental #1- Sea Urchin with Prey
Experimental 1- Right
Experimental 2-Left
Experimental # 2- Sea Urchin with Predator Experimental 2-Left
Trial # Direction moved Time(mins) Predator’s Side
1 Right 1.27 Left
2 Right 4.06 Left
3 Right 3.23 Left
4 Left 4.36 Left
5 Right 2.45 Left
6 Left 2.06 Right
7 Right 3.36 Right
8 Left 3.16 Right
9 Left 3.06 Right
10 Left 3.00 Right
5-Left
5-Right Average: 3.00
Experimental 2- Right
V. Results
In the control experiment, the sea urchin was flipped vertically over, increasing its vulnerability. The sea urchin moved left and right equally. It did not favor any side of the container. Relatively, the sea urchin turned over into optimal position slowly. In the first experimental group, the sea urchin was in the container with the prey, a piece of lettuce. The sea urchin moved equally left and right. After the experiment, I examined my results again. The sea urchin moved towards the prey six times. In addition, it moved away from the prey four times. Significantly, the sea urchin moved normally towards the target. When regarding at the control as a standard, the first experimental group moved relatively quicker than the control. The first experimental time average was less than half of the time average the sea urchin took to flip over and move 2.25 cm for the control.
The second experimental group was the test with the predator. In coherence with the other experiments, the sea urchin moves in both directions an equal amount of times. Although the sea urchin moved 5 times to the left and right, it moved away from the predator eight times. The sea urchin moved more distinctly away from the predator. On the other hand, the sea urchin the prey moved almost close to equally away and towards the prey. The time it took the tropical sea urchin to go back to optimal position and move in a specific direction 2.25cm was significantly different from the tropical sea urchin with the prey experiment.
VI. Conclusion
For all experiments, there were equal amounts of the sea urchin moving left and right. It did not matter whether the predator and prey was on the left or right. The sea urchin moved five to the right and five to the left for all trials. The control took the longest with an average of 8.5 minutes, for the sea urchin to flip over alone. Experimental two added up to be the fastest with an average of 3.00 minutes, which was when the sea urchin was with the predator. Experimental one was the median time with an average of 3.66 minutes. The sea urchin is vulnerable when it is flipped vertically over. My hypothesis was right to some extent. Regarding the time variable, my hypothesis was right.
However, when it came to the direction the sea urchin moved I was wrong. Furthermore, I observed that when the sea urchin flipped vertically over to optimal position with the predator on its left in the 5 trials when it moved left also, it moved upward left. It was as though the sea urchin realized where it was moving towards and changed its mind. In addition, experimental one with the prey had the same outcome. For example, trial one in experimental one, the sea urchin moved away from the prey. The prey was on the left and the sea urchin moved to the right. However, when the sea urchin moved right it moved downward left, I stopped the timer. Nevertheless, I observed the sea urchin move downward then change direction but not significantly relative to its own size.
Although it moved 5 left and right, the sea urchin with the prey it moved towards more than away. When the tropical sea urchin was with the predator it progressed away more than towards. It seems as though chemoreception was not affected by this type of vulnerability. Chemoreception is the sensory organ bodily responding to a natural stimulus. Vulnerability did not affect the sea urchin’s physiological response to foraging and predatory stimuli because chemoreception was still in effect. The sea urchin still migrated away from the predator and towards the prey more than the abnormally moving towards the predator and away from the prey. I think that the sea urchin’s sense of direction is obscured by increasing its vulnerability in flipping the organism vertically over. Although the sense of the direction is obscured, the sea urchin still senses what it is near whether it is a predator or prey that is the reason why there was time differences.
VII. Future Research
Due to the relevance of chemoreception in this lab study, it is important that future research is involved with chemoreception. Chemoreception is process by which organisms react to chemical stimuli in their locations that mainly depends on the senses, taste and smell. Chemoreception relies on chemicals that act as indications to control cell function, without the chemical being taken into the cell for metabolic purposes (Sloan, 1982). The researcher would advance their research to see how humans can be connected to this experiment. Humans have chemoreception in the nervous system, but does sea urchin have a nervous system? Yes, the nervous system of sea urchins has a rather simple layout. There is not a real brain. A large nerve ring surrounding the mouth is the center. From the nerve ring, five nerves radiate underneath the radial canals of the water vascular system, and branch into numerous finer nerves to innervate the tube feet, spines, and pedicellariae (Moitozoa, 1979). The human nervous system is much more complex than the Tripneustes ventricosus. If the relative size difference of brain between humans and sea urchins is so significant, then does that mean we react faster and normally even through experiencing vulnerability? In a future experiment, I would try to figure this out. The human nervous system is a system of the human's body that directs the voluntary and involuntary actions and communicates signals between different parts of the body. The nervous system has two important parts, the peripheral nervous system and the central nervous system The central nervous system contains the brain and spinal cord. The peripheral nervous system consists of nerves that are long strings that attach the central nervous system to every other part of the body. The peripheral nervous system includes motor neurons (Human Nervous System 2013). Also, it includes mediating voluntary movement, containing the sympathetic nervous system and the parasympathetic nervous system and regulating involuntary functions. The peripheral nervous system has the enteric nervous system, an independent part of the nervous system whose purpose is to control the gastrointestinal system (Human Nervous System 2013). The human has an enormous nervous system, which is the opposite of echinoderms. The sea urchin is part of the echinoderm family. Although echinoderms only have some well-defined sense organs, they are very profound to touch and to changes in many things such as temperature, light intensity, positioning, and the surrounding water (Moore 1963). The researcher would conduct an experiment very similar to this experimentation. The confounding factor to enhancing the experiment to involve humans would be the vulnerability. Humans are very complex. One thing that could affect someone making them vulnerable can mean nothing to someone else. All sea urchins were vulnerable in the mouth/ anus area. Since humans have more brain activity, some subjects may not vulnerability in their mouth or any other private area. The researcher will repeat the experimentation done but will have ethical concerns if it would involve human participants.
VIII. Limitations/Errors
There are some limitations to my experiment. The research was not done in a natural environment. It was not a controlled laboratory either. The researcher could not control the light orientation. As stated before, Tripneustes ventricosus is very sensitive to light intensity. The sea urchin could have sensed the light, which could have affected his perception to its surroundings. Since the experiment was not done in a controlled environment, the temperature could have changed between the different trials or different experimental groups. The sea urchin is profound to temperature. The Tripneustes ventricosus could have moved faster because of the temperature getting colder. On the other hand, the sea urchin could have moved slower due to the temperature becoming warmer. In the tanks, there was a marking that showed the middle of the length of the tank.
There were some complications with orientation in the investigation. When the researcher placed the sea urchin on the middle marking, it was difficult to balance the sea urchin vertically upside down. The Tripneustes ventricosus could have been placed slightly to one side of the tank, which gave the sea urchin a minor bias to go to that same side. This concern gives the sea urchin a higher probability that it will flip vertically over to optimal position on the side it was slightly was placed towards. In the experimental group one, the lettuce was the prey in the salt water. The lettuce kept moving in the water because it was light in mass. Eventually, the researcher achieved in keeping the lettuce very still. The lettuce was moving even though it was very still. It is not significant enough to alter the results. However, the sea urchin hesitated in trial nine. It took the longest for the sea urchin to move. For trial nine, the researcher recorded 5.51 minutes. Hesitation is the sudden halt of the Tripneustes ventricosus after flipping back vertically over to optimal position, then moving again but slower than the rate of the flip to the original position. The movement of the prey could have caused the sea urchin’s hesitation.
The time was measured by the amount of minutes it took the sea urchin to flip vertically over to optimal position and then to move in a direction 2.25 centimeters (half of its own body size). After the sea urchin flipped over, it was hard to take down its exact spot. The researcher did not want to complicate the trial in any way. A ruler was kept on top of the tank to measure how much the sea urchin moved. Although the researcher may not have realized the exact stop every trial, the sea urchin moved drastically enough to tell the side it intended to move.
IX. References
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