In our last blog post, we talked about different methods of underwater surveys and long-term data collection. These monitoring activities are extremely important to understand what’s going on in our marine ecosystems and help to protect them.
What’s the point of monitoring reefs?
Natural habitats exist in a delicate balance. Within the food web, every species from the smallest fungus to the largest predator plays an essential role to keeping this balance intact. On top of that, countless environmental processes (for example nutrient cycles) as well as human activities play into the system. While some of these interactions can be observed on a daily basis, some slower cycles take place over years, decades, or even centuries – and everything is interconnected. Pretty complex, right?
Ecological monitoring compares parameters such as temperature, pollution levels, population sizes, reproduction rates, and many more over time. That way, we can identify trends and patterns within these complex interactions. Especially when it comes to the impact of human activities and related conservation efforts, long-term observation and measurements are key.
What do we monitor?
Depending on your interest and research objective, pretty much anything can be monitored.
As mentioned before, one could measure surface and bottom water temperature over a period of time. This may give us a better idea of daily or seasonal variations compared to consistent trends of rising (or falling) water temperatures. Other options are to measure the levels of certain nutrients or chemicals in the water, survey the amount of plastic and garbage in a specific area, observe current patterns, examine abundance and diversity of plant and animal species, track the extent of fishing or other recreational activities, and many more.
Combining these findings can help us understand the changes we observe in our ecosystems and how they are related to each other. Although it may sometimes be difficult to make sense of these complex interactions, previous research by others can give us some pointers of how to put the pieces together.
What does a healthy reef look like?
As divers, we are mostly interested in coral reefs, which sustain 25% of all marine life and are thus extremely important marine ecosystems. Although every reef might be different, there are some common indicators to determine whether it is healthy or not. Even if you are not a scientist, it’s pretty easy to assess the situation if you watch out for the following things:
First and foremost, healthy reefs are usually vibrant in color and buzzing with activity, as they host different fish species of all sizes, as well as a variety of invertebrates.
Abundance of Herbivorous Fish
Grazers such as Parrotfish and Surgeonfish, feed on different kinds of algae and make sure they do not overgrow. This is important, as algae often compete with corals for sunlight, nutrients and space. One of our favourite herbivores is the Blue Tang (Paracanthurus hepatus) – you may also know this fish is Dory from Finding Nemo! They use their small teeth to pull algae from rocks and corals. Did you know that these fish can live for over 30 years in the wild?
A somewhat complicated indicator, sea urchins can be both beneficial and harmful for coral reefs. Some people like to compare them to lawnmowers, as they feed on algae and seagrass. In small numbers, sea urchins can help slowly growing corals to compete for living space; if there are too many, urchins tend to overgraze and have a rather destructive effect. Here in Pondy, we sometimes spot Black Diadema Sea Urchins (Diadema antillarum). Like other urchins, they are sensitive to light, chemicals, and touch, but on top of that they also have eyes, which helps them direct their spines at potential threats!
Large Fish and Apex Predators
The presence of predators like Barracudas, Groupers, or Jackfish indicates a healthy reef balance. Feeding on sick or weak individuals, they keep other fish populations down the food chain in check and increase health and fitness of the remaining fish. Our favorite predators are octopuses and cuttlefish. Cephalopods are highly intelligent species which mostly feed on shellfish, clams, and molluscs. Some smaller species have adapted smart strategies for their protection. The Coconut Octopus (Amphioctopus marginatus), for example, carries around coconut or sea shells and uses them as armour!
As apex predators, the presence of sharks is a prime indicator of a thriving reef. Despite their bad reputation in movies and media, they are extremely cautious and intelligent, and will mostly avoid interacting with humans. Sadly, shark populations have critically declined in the last decades, as they are heavily overfished. Missing sharks and other predators causes major imbalances down the food chain, so it’s essential to appreciate and protect them more! Consider yourself lucky if you get to see sharks on your dive! 🙂
Have you ever heard of Wobbegong Sharks? These small, bottom-dwelling species with the funny name belong to the family of Carpet Sharks (Orectolobidae) and can be found in shallow tropical waters.
Abundance of Giant Clams, Conches, and Molluscs
Clams and molluscs are quite sensitive to changing water conditions, which means that their presence is a great indicator of good water quality. Not only do they serve as food and fish nurseries, they also sustain invertebrates and shrimp and serve as substrate for sponges, coral, and algae. As filter feeders, they keep the water clear. Crustaceans, such as cleaner shrimp, eat parasites off other fish and remove detritus from the ocean floor.
Last but not least, the absence of coral bleaching is an important indicator for healthy reefs. Did you know that corals are also animals? Most of them live in a symbiotic relationship with small algae (zooxanthellae), which are their main source for food and also give them their color. Corals are extremely sensitive to changing water conditions; when temperatures rise, they have to let go of their zooxanthellae. This means a bleached coral is a starving coral! If they have to go without food for too long, bleached corals will eventually die. Here in Pondy, we get to see Giant Gorginian Fan Corals (Annella mollis) at our deep dive sites!
All of the species mentioned above play a crucial role in their ecosystem, and whenever one of them is overfished, weakened or completely removed, it has an effect on the entire reef. Next time you go on a dive, make sure to take a look and watch the different interactions around you!
If you want to learn more about reef monitoring, fish identification, or artificial reefs, shoot as a message at firstname.lastname@example.org.