Exploring the Shallows of Savusavu: SEEING STARS
There is an abundance of tidal pools and reefs that line the shores of Savusavu. In many cases you don’t need a boat to see some amazing marine life in the shallows, only a few steps off the main road and you’ll be at the water’s edge. At low tide the reef flats emerge, and little pools of water full of life dot the coast along the Hibiscus Highway. To avoid harming the beautiful wildlife you have come to see, make sure to tread carefully and avoid picking up anything; some species have defense mechanisms if they are provoked, and many are delicate and sensitive to human contact. The photos in this article were all taken in shallow waters without any contact with the reef or its inhabitants.
Starfish, or sea stars, are common sightings in the shallow reefs and tide pools. Starfish are not a type of fish; rather they belong to the phylum Echinodermata. Echinoderms are marine invertebrates and include sea urchins, sea stars, and sea cucumbers (among many others), and exhibit radial symmetry. This means they have a top and bottom surface, but no discernable left or right sides. Many of the sea stars we’re familiar with have five arms, but some species have up to 40 arms, and many have the ability to regenerate lost arms.
Sea stars may not have a brain, but they are sensitive to their environments. They use their tube feet to locate food, and to eat they invert their stomachs to begin digesting externally. Many sea stars are scavengers, and they help to break down dead animals, and like all reef creatures they have an important role in the ecosystem. They can live for many years in the wild, but are sensitive to touch, temperature, and oxygen levels which means the mortality rate is much higher in aquariums.
Amazing biodiversity in so many shapes and sizes
Fiji is home to a wide variety of the 2,000 or so species of sea stars. Perhaps the most easily recognizable is the blue sea star, which is an interesting species as it can reproduce sexually or asexually, meaning it can clone itself. In addition to the sea stars you can see vibrant crinoids, or ‘feather stars’ which perch on coral or sea fans to feed in the current. If you’re lucky you might spot one free-swimming, using its feather-like appendages in a graceful dance from one coral to another. These beautiful creatures are often referred to as ‘living fossils’ because they are one of Earth’s earliest animals, and their relatives once carpeted the ocean floor.
Related to sea stars are brittle stars, which are found in large numbers in the tidal pools around Savusavu, while many species are deep water dwellers living over 200m below the surface. More than 60 of the 2,000+ species of brittle stars are bioluminescent, producing their own green or sometimes blue light, presumably to deter predators. Some brittle stars have a symbiotic relationship with corals and you may find them wrapped around sea fans and sponges.
Potential threats to coral reefs
One sea star you hope not to see in abundance is the Crown of Thorns (CoT) starfish. These large and spiny sea stars can reach up to 80cm in diameter, have between 8-21 arms, and can be found in a variety of bright colors, alerting potential predators to their toxicity. CoTs are voracious corallivores, meaning they eat coral alive. A single CoT can devour over ten square meters per year, and outbreaks can destroy an entire reef within weeks if numbers are large enough. However, these are naturally occurring animals, and play a role in maintaining coral diversity as they favor faster-growing corals. Healthy reefs can eventually recover from occasional CoT outbreaks, but more permanent problems arise when reefs are facing other stressors and climate change.
During your stay in Fiji you can help prevent future CoT outbreaks by avoiding purchasing the beautiful triton shells which are often sold in the markets. Live giant tritons are one of the few known predators of CoTs, as their large, venomous spines are a deterrent to many fish and invertebrates. Recently, outbreaks of CoTs have become much more frequent. Many iconic reef systems, including the Great Barrier Reef, have experienced prolonged CoT outbreaks that have severely impacted the coral and the myriad of species that rely on healthy coral. It is speculated that agricultural runoff and other nutrient pollution has contributed to CoT outbreaks, and with an extremely high reproductive rate (females may produce 50-60 million eggs in a breeding season), over-fishing of their known predators, and rapid growth rates, outbreaks pose a huge threat to coral reefs around the world, including Fiji. These outbreaks not only affect the coral reefs and their inhabitants, but the people who rely on reef ecosystems for food, income, and livelihood.
Learn more about marine invertebrates such as sea stars, and some of the threats faced by coral reefs globally by joining our South Pacific Coral Reef Ecology eLearning Course.
About the authors: Sara Carlson & Matthew Norman own and operate Ocean Ventures Fiji (www.oceanventuresfiji.com), a PADI Dive Resort that also focuses on conservation education and snorkeling trips in Natewa Bay, Vanua Levu, approximately 40 minutes outside of Savusavu. They can be found on Instagram: @matthewnormanphotography & @divingsara.