Ghost (net) Busters Ghost Net Impacts on Coral Reefs Time to complete lesson: 20-30 minutes Purpose of module: This module allows students to simulate the impacts of ghost nets on a coral reef. Students will build a model healthy reef ecosystem, damage it using a ghost net, and then remove it from the reef. Students will conduct a damage assessment caused by the net dragging across the reef using quadrats. Background information: Coral reefs, also known as the rainforests of the sea, are one of the most diverse and ecologically complex marine ecosystems. They are found in warm, tropical waters with high salinity and high light exposure. A coral reef is made up of individual coral polyps that resemble tiny anemones and are attached to the reef. Each coral polyp is less than half an inch in diameter, but they live in colonies which Figure 1: A healthy coral reef system. can expand and take up the size of a small car. Reef building corals have a skeleton made of calcium carbonate, a mineral that is left behind when an individual coral dies. Another coral may settle on that spot and grow on top of the remaining skeleton. This allows a coral reef to grow a few centimeters each year, eventually reaching massive sizes. Coral reefs provide food and shelter for many plants, invertebrates, and fish. It is estimated that at least 25% of all marine life spendCredit: part MostBeautifulThings.net of their life at a coral reef. Coral reefs provide shelter for small fish, and small fish attract larger fish, which in turn attract large predators like sharks. Coral reefs encourage the growth of algae and sponges, which attract sea turtles and other herbivores, increasing the biodiversity of these ecosystems. Coral reefs also protect our coastlines by reducing wave energy up to 95%. Coral extracts can even be used to develop treatments for asthma, arthritis, cancer, and heart disease. The high biodiversity and productivity make coral reefs popular areas for both commercial and recreational fishing. However, coral reefs are very delicate and complex, and are very susceptible to damage by fisheries and derelict (lost or abandoned) fishing gear. When fishing gear, either active or derelict, comes in contact with a reef, it can cause Figure 2: A coral reef entangled in ghost fishing nets abrasions, breakage, and smothering of corals. Further damage can be inflicted when the debris is moved by tides, currents, and storms. Damage to reef-forming or hard corals can cause serious damage to a reef ecosystem and can reduce the integrity of the reef as a whole. Coral reefs are also threatened by pollution, climate change, changing ocean chemistry, and invasive species. Materials & kits: Ghost (net) Busters Ghost Net Retrieval Kit (10 coral reef set ups for groups, each containing: set of 12 reef figurines with magnets, ocean floor tray, 2 ghost nets, reef animals, laminated worksheet, plastic quadrat, dry erase markers, spinner. Detailed materials guide, including where to get supplies, is provided at end of lesson) Instructions: • Start by introducing students to coral reefs, using the following interactive questions as a guide: Who has seen a coral reef before? Where were you? What do all these places have in common? (Warm water, near equator) What is a coral? How do they live and grow? What lives at or in a coral reef? What can impact a coral reef? (climate change, fishing, ghost nets, human interaction) • Through today’s activity, we will answer the question: How can ghost nets impact a coral reef? Review ghost nets if needed: what is a ghost net? (a fishing net that was lost or abandoned at sea) How are fishing nets lost? (usually due to storms, boat traffic, old age, and interaction with large animals) Do fishermen want to lose their nets? (No, they need their nets to make a living) What kinds of impacts do ghost nets have on the ocean? (They can catch and kill many kinds of animals, including fish and marine mammals) • Break students into 9 groups – students will work through the activity in their groups, but we will go through each part as a class one step at a time. 1. Have students start by creating a healthy coral reef model on the “sandy” portion of their tray. Note that the entire tray is under water, but the blue represents deeper water. As they build, explain that as a class today we are representing an entire reef ecosystem, like the Great Barrier Reef, and that each individual group represents a patch in that reef. Review what kinds of Figure 3: Healthy coral reef model. animals are in their coral reefs and how we know the reef is healthy (very colorful, many animals living there). 2. Students will then simulate a ghost net dragging along the reef. Have students look at their green weighted net and make observations about it. Some ghost nets, including sink-gillnets and trawls, have weights on one side and floats on the other allowing them to remain vertical in the water column. When these nets get caught on coral reefs, they will often drag across with the ocean current and cause damage to the reef. (Have students suspend their green weighted net in the blue portion of their tray, and drag the net across slowly as the ocean currents would. The net will dislodge some of the corals.) Discuss observations. 3. Have students hold up the piece(s) of coral that were knocked over the easiest and ask why they chose these ones. (These are the tall and branching corals that have lots of places for the net to become entangled). Scientists have found that these tall branching corals are damaged the most by ghost gear. Ask students if a coral can survive when knocked over or broken. (No, they are animals and they build on each other, so if one is broken nothing else can grow on top of it) Corals only grow a few centimeters a year, so if they are damaged it takes a long time to recover. 4. Next, have students rebuild their coral reef to demonstrate another ghost net impact. Remind students that in real life this would take decades or centuries to happen. 5. Now let’s take a look at what happens when a different ghost nets enter an area. Have students pick up their piece of gillnet and compare/contrast it with the green weighted net. (Have one student hold the net as it slowly sinks down through the water column.) As a net drifts down, some animals would leave the reef and escape. (Other students in group will start to remove some of the animals as the net is drifting down). When a net settles on a reef, it continues to move around with the motion of the ocean, causing the net to become Figure 4: Students placing ghost net on coral reef. tangled around the corals. Coral reefs are often damaged through fragmentation, abrasion, and smothering by nets. (Students will be the “ocean” and entangle their coral reef and animals with the net). 6. When a reef becomes entangled, some animals will continue to use it for shelter and/or food. Some of these fish are small enough to fit through the net, while others become entangled. Entangled sea life may die due to starvation or drowning, and the dead animals will attract other marine creatures to the reef. (Have students use their animals to swim in and out of the net – some will get caught along the way). 7. Wave action around reefs can increase during storms like hurricanes, causing the entangled net to drift back and forth suddenly. This can cause corals to become dislodged or break apart. (Have students simulate a hurricane by moving the net back and forth, knocking over a few corals in the process) 8. Coral reefs and other living creatures often remain entangled indefinitely, but sometimes scuba divers will work to retrieve these ghost nets and free the marine organisms entangled in them. Before removing nets, scientists will collect data on the damage caused by the ghost net, usually using quadrats. (Have students place their quadrat randomly on top of their reef and note the damage the ghost net has caused on that reef system using the directions on the worksheet. They will sample in 3 locations if time allows) 9. Finally, have students carefully remove the net from the damaged reef and put away materials. 10. Have students calculate the percent surface area damaged by the ghost net and the percentage of marine life that died as a result of entanglement using the equations on the back of the worksheet. • Discuss as a class how each reef was impacted by their ghost nets. How is it the same? How is it different? Were certain corals or animals more susceptible to damage by the net? Calculate or estimate the average percent surface area damaged by nets for the entire class. • Discuss current research on coral reefs and ghost nets. Many studies have looked at how coral reefs are damaged by derelict fishing gear, especially in Florida and the Hawaiian Islands. Damage to corals is usually in the form of tissue abrasion, which can cause individual or colony mortality. Corals can also be broken or dislodged, with branching gorgonian corals often the most affected. • Discuss other threats to coral reefs if time allows (coral bleaching, destructive fishing, climate change). • While we can sometimes disentangle a reef, it is not always possible. It is important to try to prevent the entanglement in the first place.