Lesson 2: Parasites, YUM! An example of mutualism and its effects on coral reefs

1. Lesson 2: Parasites, YUM! An example of mutualism and its effects on coral reefs Researcher: Thomas Adam Doctoral Student University of California, Santa Barbara

2. In this lesson, we will be exploring the symbiotic relationships found between parasites, host fish, and cleaner fish, and how this may affect the surrounding environment. Gnathiid Parasite. Feeds on fish blood (like a mosquito) Cleaner Wrasse Cleaner fish. Feeds on invertebrates, especially gnathiids Parrotfish Host fish. Herbivore, feeds on algae it scrapes off the reef

3. Background • “Cleaner fish” remove and eat parasites found on the scales, fins, or mouths of other fish. They are said to eat about 1,200 parasites a day!² • The parasites are mostly small crustaceans called gnathiid isopods. • Many different kinds of fish visit the “cleaner station” to have parasites removed. The station is usually located in front of a reef that an individual “cleaner fish” rarely leaves. • The different kinds of fish that visit a “cleaner fish” are called “client fish” because they get cleaned.

4. Key Term: Parasitism Parasitism is a relationship between two organisms in which one organism benefits at the other organism's expense. The gnathiid isopod (right) is a parasite to fish because it sucks the fish’s blood and could transmit diseases. Only the gnathiid benefits from the interaction.

5. Key Term: Mutualism On the other hand, cleaner fish and client fish have a mutualistic relationship because they both benefit from the cleaning interaction. CLEANER FISH benefit client fish because they get rid of their parasites. CLIENT FISH benefit cleaner fish because they provide them with a food source (parasites).

7. Organism of interest: Bluestreak Cleaner Wrasse Species name: Labroides dimidiatus • Bluestreak Cleaner Wrasses are commonly found in the tropical Pacific. The study we discuss in this lesson was conducted in Moorea, French Polynesia. • Cleaner Wrasses use the coral reef as a habitat, and find a territory that they rarely leave. • Cleaner Wrasses are often seen alone or in pairs.

8. Developing a Scientific Question • Since the Bluestreak Cleaner Wrasse stays in small territories where it is visited by many different kinds of fish, Tom (lead researcher) began asking questions, such as: Do the visiting client fish have an effect on the coral reef habitat near the cleaner station?

9. A Question for YOU: What are some ways these visiting “client” fish might affect the coral reef? Hint: Think of all the different kinds of fish in the ocean. How could they positively or negatively effect the coral reef? Take some time to brainstorm and record your ideas.

10. POSITIVE EFFECTS Client fish might eat algae from the reef so the coral can have access to sunlight to grow (photosynthesis). Client fish might release feces (waste) which could be food for some coral reef dwellers. Some client fish might travel in schools, bringing more yummy parasites for the cleaner fish. NEGATIVE EFFECTS Some client fish might be corallivores and feed on the coral itself! Some client fish might be carnivores and feed on the cleaner fish and/or other client fish. Some client fish might be so large that they damage the reef as they pass through a cleaner station. I hope you got creative! Some examples might include…

11. Further Developing a Scientific Question Tom observed various species of butterflyfishes being cleaned at cleaner stations. Many of these butterflyfishes prey on coral polyps (corallivores), including the ornate butterflyfish shown below.

12. Main Research Question Do cleaner fish have a negative effect on corals by attracting and concentrating coral predators? Assignment: Create an educated prediction (hypothesis) of what you would expect the results of this experiment to be and explain WHY you are making that prediction.

13. Compare your Hypothesis to the Scientist’s Hypotheses… • The bluestreak cleaner wrasse is attracting butterflyfishes. 2) The increase in the abundance of butterflyfishes at reefs with cleaner fish has a negative impact on coral because the butterflyfishes are feeding on the corals. Did you notice that Tom needs to go beyond his initial observations and actually quantify whether butterflyfish are being attracted to the reef by cleaner wrasses? Then he can go on to investigate his main question.

14. How would you TEST these hypotheses? Assignment: Write a step by step PROCEDURE that would allow you to investigate these questions. Be detailed and creative. When you are done writing a procedure, create a MATERIALS LIST of supplies you would need to conduct the experiment. Teachers: Please give students ample time to brainstorm and develop their ideas. This is an excellent group activity.

15. Tom’s Materials Listto investigate question #1 • Scuba gear (including dive buddy) • Underwater paper/pencil to record data • Small nets to catch fish • Clove oil (slows down fish so they are easier to catch but does not harm them) • Ruler or calipers to measure fish • Ziploc bags/buckets to transport fish • Watch/Timer

16. EXPERIMENTAL REEFS: Bluestreak cleaner wrasses were caught from another reef and transferred to this reef. CONTROL REEFS: 1) The patch reef had no cleaner fish to begin with. 2) The cleaner fish was removed from the patch reef.

17. Tom’s Methodsto investigate question #1 To test whether cleaner wrasses were attracting corallivores to their cleaning stations, Tom IDENTIFIED, COUNTED and took SIZE ESTIMATES of every fish that passed both experimental and control patch reefs. Patch reefs are small, isolated reefs that are often cleaning stations for cleaner fish. The patch reef in the background photo is one of Tom’s study sites.

18. EXPERIMENTAL: The abundance of butterflyfish visiting reefs INCREASED when a cleaner was added to the reefs. CONTROL: The abundance of butterflyfish visiting the reefs with no cleaner wrasses stayed CONSTANT throughout the experiment Results for Experiment #1 This means that the increase in butterflyfish abundance was caused by the addition of a cleaner!

19. Tom’s Materials Listto investigate question #2 • Scuba gear (including dive buddy) • Small pieces of Porites rus coral • Numbered square tiles • Z-SPAR (clay-like substance, used to stick coral to tiles) • Mass balance for buoyant weight • Ziploc bags, buckets and coolers to transport corals

20. Tom’s Methodsto investigate question #2 • Porites rus was used because it is a species of coral that is particularly important in reef-building. • Pieces of this coral (240 total!) were placed on tiles using sticky Z-SPAR and then buoyant weighed. • Twenty reefs were used for the experiment: Ten EXPERIMENTAL reefs WITH a cleaner wrasse Ten CONTROL reefs with NO cleaner wrasse • At each reef, the coral pieces were either: CAGED (6 corals): NO access for corallivores PARTIALLY CAGED (6 corals): corallivores CAN access coral • After a month, all of the same corals were buoyant weighed again to see if their weight increased, decreased, or stayed the same.

21. A Questions for YOU: Tom used 240 corals total. He surveyed 20 reefs, each with 12 corals. Why would he use so many corals and reefs? Hint: Why not just test two corals, one at an experimental reef and one at a control reef?

22. And the winning answer is… Science is so much fun that Tom wanted to spend ALL of his free time on his project… What, you don’t believe me? Okay, the real reason is that REPETITION is very important in science. Scientists must repeat their experiments over and over again to be sure they get similar results every time. If a hypothesis statement holds true for each experimental trial, the statement can develop into a scientific LAW or THEORY. If another study can prove the statement wrong, then usually a new hypothesis must be written and tested before it can become a law or theory.

23. BUOYANT WEIGHING • This method is used because it allows scientists to measure corals in seawater. Since corals are mainly tissue, their weight changes drastically if exposed to air. Here is how it is done: • Individual coral piece is placed in a wire basket. • The wire basket is attached to fishing line by a hook that hangs from the bottom of the scale. • The basket is placed in seawater so that coral is fully submerged and the weight is recorded digitally.

24. A Question for YOU: What is the difference between the words “mass” and “weight”? Hint: Think about why the method shown in the previous slide provides us with “weight” data instead of “mass” data.

25. Mass vs. Weight Mass: A measure of the amount of “stuff” or matter in an object. Example: When you place an object on a mass balance, the scale is balanced by the mass of another object that is already known. Weight: A measure of the pull of gravity on an object. Example: In buoyant weighing, the object (coral) is attached to fishing line that was hanging from the scale. Gravity is pulling the line and the object. There is no balancing! So, the weight of an object changes when the pull of gravity changes, but the object’s mass remains the same. FURTHER DISCUSSION: If you were in outer space, where you are not subjected to Earth’s gravitational force, would it be more productive to collect data on the mass or weight of an object?

26. Results for Question #2 • Corals left in PARTIAL CAGES grew more slowly when placed at cleaner stations than at a similar reef without cleaner wrasses. DOES THIS SUPPORT TOM’S HYPOTHESIS? • YES! This means more corallivores were attracted to the experimental reefs, most likely because of the presence of cleaner wrasses. The corallivores probably found the open sides of the cage and ate some or all of the coral inside, so they ARE negatively affecting the coral reef. • FULLY CAGED corals did equally well at cleaner stations and control reefs. DOES THIS SUPPORT TOM’S HYPOTHESIS? • YES! The corallivores could not get inside the cage at any of the reefs, so there should be no change to the weight of the corals. • Tom’s evaluation: The difference between the growth rate of the fully and partially caged corals was positively related to the abundance of butterflyfish, strongly suggesting that butterflyfish were responsible for the decrease in the growth rate of corals at cleaner stations.

27. Conclusions • Cleaners can actually have a negative effect on the corals that provide habitat for them and many other fishes. However, this is likely only one of many effects that cleaners have. For example, it is possible that cleaners also benefit corals by attracting fish that eat algae (herbivores), which leaves behind less algae that will compete for space with the corals. • Further research on cleaner-client interactions will help us to better understand some of the processes that are important for structuring coral reef communities.

28. End of lesson Hey, wait up! Dude, you’re coated in parasites. It’s LUNCHTIME! Cleaner Wrasse Parrotfish (herbivore)

29. VOCABULARY CHECK • Parasitism: A relationship between two organisms in which one organism benefits at the other organism's expense. • Mutualism: A relationship between two organisms in which they both benefit from the interaction. • Organism: Any living thing. • Photosynthesis: The process in which green plants combine carbon dioxide and water in the presence of light energy and chlorophyll to produce carbohydrates (see lesson 1). • Schooling: Bunching or grouping of fish all orienting in one direction and keeping equal spacing. • Corallivore: An organism that feeds primarily on coral polyps. • Carnivore: An organism that feeds on other consumers (“meat eater”). • Hypothesis: An educated prediction. • Hypotheses: More than one hypothesis. • Quantify: To express observations as a number or measure. • Calipers: An instrument used to accurately measure length or thickness of an object. • Buoyant Weigh: A technique used to find the weight of an object while submerged. • Repetition: Repeating a scientific experiment until there is enough data to support the validity of the outcome. • Theory: A former hypothesis that has been tested with repeated experiments and observations and found to always have the same result. • Law: Similar to a theory. Usually describes, but does not explain, one phenomena. Laws often include a mathematical equation. • Mass: A measure of the amount of “stuff” or matter in a thing. • Weight: A measure of the pull of gravity on an object. • Herbivore: An organism that feeds on producers (“plant eater”).

30. Work Cited Text • Adam, Thomas, researcher. Personal contact. • Grutter, A. S. Mar. Biol. Prog. Ser. 130, 61–70 (1996). Photos • Laman, Tim. www.nationalgeographic.com (slide 11). • Parks, Peter. www.lexagrutter.com (slide 4) • Pelc, Robin. University of California, Santa Barbara (slides 1, 2, 3, 6, 7, 11, 28). • Withy-Allen, Kira. University of California, Santa Barbara (slides 15, 17, 19, 23).