TEACHER NOTES

Green turtles and corals have changed little since the age of the dinosaurs, yet many species, with which they were contemporaneous, species became extinct. Early in their evolution turtles evolved a simple and successful formula for survival. They are “living fossils”. The following notes are written to provide teachers with potential classroom “Teachable Moments” following their student’s visit to see Turtle Reef 3D. The purpose of these notes is to highlight some of the underlying stories within Turtle Reef 3D that may be explored or expanded upon.

Overall Themes

  • Life on Earth is conducted to astronomical cycles
  • Human economic market systems follow the same rules as evolution
  • Life is formed from associations of interdependent genes
  • Ecosystems are organized around association of mutually beneficial genes contained within different organisms

Opening Preface

  • Scleractinian corals or stony corals that evolved in the middle Triassic were the progenitors of reef-building corals. They coincided with the progenitors of turtles in the late Triassic, around 200 mya. At that time corals and the plants that were the ancestors of today’s zooxanthellae began to associate to form coral reefs.
  • Current evidence for the origin of marine turtles indicates a terrestrial reptilian ancestor related to today’s tortoises
  • There is little evidence for the association of marine turtles and coral reefs during this period; therefore our suggestion that they were associated is purely hypothetical.

Opening sequence

  • Green turtles were in recent historical times incredibly numerous. Studies have shown that there may have been as many as 45 million utilizing the Caribbean at the advent of western contact with the New World. Today, their numbers are down to a few hundred thousand in the same region. There are no reliable records for ancient Hawaiian populations of Green Turtles. By 1978 they were facing the prospect of extinction due largely to overfishing. The question is asked, what would have happened to the Hawaiian Green Turtle without our intervention to protect them?
  • Part of the turtle’s longevity as a species lies it its armored body and its ability to gracefully fly through the water. Turtle’s are slightly negatively buoyant in the water so their propulsion does not require the same lift as a bird. However, the physics of their locomotion is similar to marine birds such as penguins.
  • All marine species are adapted to specific ecological niches by maximizing their ability to gather food, avoid predators and reproduce.
  • Since different diurnal species find refuge in multiple locations at night, those that associate during the day gather together in mixed schools to forage at recognizable locations along the reef.
  • Associations between different species that roam the reef are commonplace and have survival benefits.
  • There are many herbivorous species such as damsel and surgeon fishes that defend territories on the reef, to protect the pastures or other food resources within. Such territorial species are aggressive to their neighbors, and other species that pass nearby irrespective of whether or not they are other herbivores. Some like the Hawaiian Gregory are thought to be pillar species because they alter the structure of the reef around them.
  • Spinner dolphins shelter in the shallow waters of coral reefs during the day. They are a deepwater species that ranges widely at night to feed on squid and lantern fish (Myctophidae) from the deep ocean that migrate vertically to the surface to feed in the euphotic zone.
  • Reef building corals are animals with symbiotic plants called zooxanthellae. These corals produce net carbon to the reef’s primary production. At the edge of the reef as light diminishes with depth, the zooxanthellae fix progressively less carbon, until the point at which reef-building corals no longer survive. This depth is dependent upon light penetration - that is in turn a factor of sunlight, latitude and water transparency.
  • In the absence of strong waves or currents, reefs are frequently surrounded by sand and rubble sea-beds derived from the reef. Most of the white coral sand has passed through the gut of reef parrotfishes. A single adult parrotfish may be responsible for consuming and producing 5000 pounds or more of coral sand a year.
  • Garden eels featured in the film (Hawaiian Garden Eels, Gorgasia hawaiiensis, or Puhi) are endemic, or unique to the Hawaiian Islands. Like so many sand dwelling species they form burrows. Their tails are equipped to burrow through the sand and the sides of their burrows are clearly defined. See special section on this species. Approximately 25% of all Hawaiian fish species (around 680 species that live in waters of less than 600 ft) are endemic.
  • Sand and rubble areas of the reef attract herbivores that can feed on filamentous algae and carnivores that catch creatures above or below the sand and under rubble.
  • Rocky and coral reef areas attract a greater diversity of life because the structure of the reef provides a considerably more varied habitat. Much of the life in these areas has evolved specialized strategies, such as the Long-nosed Butterfly fish.
  • Members of the nightshift find shelter in caves or hang around, often in schools, over the coral rock and lava formations that provide them refuge during light hours. The coral and rocky areas in particular provide plenty of cover from predators.
  • Nocturnal fish are frequently colored red. Ocean water absorbs the red end of the light spectrum first so red coloration appears black at night making it the perfect camouflage for nocturnal predators.
  • The two species of goatfish featured in Turtle Reef avoid direct competition by hunting in the same habitat at different times – one during the day, the other at night.
  • Green turtles in coastal waters appear to spend a great deal of their day resting, and are largely inactive at night.
  • Reef animals are constantly repelling all sorts of parasites (isopods, copepods and the like) and infectious agents, such as fungi and bacteria, whose larvae, spores and adults infest the ocean. Additionally, larval life in the ocean is looking for inviting substrates. All these organisms may “foul” other sea life unless taken care of. Typically, the young and even the adults of some marine species serve as opportunistic “cleaners” on the reef. But there are others, obligate cleaners, such as Labroides wrasses and a host of different cleaner shrimp. The latter reside in localized areas and advertise their presence to attract customers. By tending wounds and picking off ectoparasites from their patrons, these cleaners can make a living. Their population density on the reef is indicative of the reef’s biomass.
  • Labroides wrasses featured in Turtle Reef, like most members of their family, are known as protogynous hermaphrodites, meaning that they start life as females. Usually, a single male dominates the group of cleaners at a station. Frequently one male and one female attend the cleaning station. These fish are usually monogamous if not by choice, by necessity.
  • Not all species are strictly diurnal, crepuscular or nocturnal. Some species such as the Raccoon Butterfly fish and Trumpet fish have been reported as active both day and night.
  • Turtles have their own hygiene issues. Their shell and skin makes a perfect substrate for marine life such as algae, diatoms, crustaceans, polychaetes and many other forms of life to settle and foul. While resting, species such as the sharp-nosed puffers frequently tend the turtles and pluck off all sorts of life. Other fish use turtles for rubbing on, or taking the occasional bite of algae off their carapace as they swim past. Since turtles cannot easily scrape off the algal growth on their carapace (they can be seen often ineffectually trying to rub it off on rocks) surgeonfish provide a useful service by grazing on it. As a rule Surgeonfish do not clean turtles. However, at certain locations cleaning stations are established where it appears that turtles and surgeonfish have an informal contract to clean and be cleaned. It would seem likely that the surgeonfish must learn this behavior around these cleaning stations from others. Interestingly, on Turtle Reef the two species most commonly found performing this service – the Goldring Bristletooth and the Yellow Tang – prefer feeding on vegetable matter from different parts of the turtles. Goldrings feed on the hard parts (carapace and plastron), while the yellow tang browse algae from the soft parts. The other interesting point to note here is that surgeonfish are often speared by the locals and are therefore cautious of people and flighty. While cleaning turtles they act as if they are immune from attack and can be approached very closely.
  • The Hawaiian green turtle’s habit of climbing ashore to bask in the sun is rarely reported elsewhere. Apparently, this habit has increased in frequency since they were protected in 1978.
  • Since turtles are herbivores they are faced with the problem of digesting some plant materials (various polysaccharides such as cellulose) that are remarkably resilient to animal digestive enzymes. Within its gut, green turtles host an entire ecosystem of microscopic organisms that help perform that duty for them. Turtle Reef is partly a story about the associations of different life forms that makes up the coral reef community. This is an example of another level in those associations.
  • The Hawaiian sergeant’s protect their nests only during daylight hours. At night, like other diurnal species they find shelter and abandon their nests. The question is, how seriously are these nests ravaged overnight?
  • Almost all of life on Earth is exclusively dependent upon the sun for survival. The influence of our sun and moon is critical for regulating most marine life living in the surface layers of the ocean. Even those that rest in deep waters, and migrate to the surface at night to feed, provide the source of food for such animals as dolphins and big eyes, are directly dependent upon daily solar and monthly lunar cycles.
  • Durgon’s behavior is normally benign. Afterall, consuming plankton seems innocuous enough. Every now and then, however, they appear to be triggered by chemical sources in the water – perhaps spawning invertebrates or fish colonies, such as damselfish, and then their behavior becomes quite aggressive. The scene in the film elicits the feeling of threat that must face the animals living on the reef when a mob of triggerfish attacks. In this case we could not identify exactly what the fish were attacking. It was a violent, amazing and rare spectacle.
  • Damselfish, such as the Hawaiian Sergeants and the Domino Damselfish tend to produce nests that the males protect until the young hatch and drift away in the currents as part of the plankton. The male’s activity continues all day. Like many reef species late afternoon tends to see an increase in reproductive activity, usually, just before twilight.
  • Approximately 60% of coral reef fish species are diurnal and most herbivores fall into this category. Crepuscular predators make up around 10% of coral reef fish. Some 30% of reef fish species are nocturnal, and almost all of these are carnivores.
  • Eels are not exclusively nocturnal, but many of them are. They are extremely successful predators, but they are not omnipotent. Some species, such as certain species of butterfly fish (and they are very spiny), are reported to have aggressive responses to eels in close proximity at night.
  • The world’s ocean is around 1.3 billion cubic kilometers in volume holding some 20,000 species of fishes. Nowadays, fish species targeted by humans have a viable population for approximately 15 years from the start of commercial exploitation to the point of population exhaustion, when they are depleted and no longer fulfill their important role in the ecosystem. Over the past 100 years we have reduced 35%+ of all fished species in the ocean to this point of depletion. A further 35% are currently on their way to that state of depletion. Some 30% of potential fish stocks have yet to be exploited. Our fishing activities have cored out key parts of marine ecosystems. Since ecosystems function in a similar way to market systems, our actions have a similar result to us cutting out say… physicians, plumbers, bankers and dairy farmers from a human society. Such a society would be crippled. So are the world’s marine ecosystems in ways that mean it no longer functions efficiently. The members that supply the food at the bottom of the food web no longer supplies energy to all parts of the ecosystem as they did in the past because of the broken links in the chain, and the ecosystem is no longer functions efficiently. The ocean will become progressively less productive until we rectify this problem. It is no longer acceptable to support policies that drive more and more wild fish to the brink of extinction, perhaps never to recover. It does not serve the fishermen; it cripples the ecosystem; it short-changes the human population. If we did just this one thing and stopped polluting our most productive areas along the coast, the oceans could swiftly return to health, productivity and prosperity. Alaskan fisheries have figured out this issue and yet provides some 40% of the US catch without overexploiting a single species.
  • The Hawaiian Green turtle has turned the corner. By protecting it, its population is on the rise, and its presence provides important values to us all.