About 50 stings each year in the Great Barrier Reef region send people to hospital with a bizarre constellation of symptoms known as 'Irukandji syndrome'. At least 10 species of jellyfish have been linked with the syndrome. The initial sting is typically mild, and is followed after a 5-40 minute delay by any or all of the following: severe lower back pain, nausea and vomiting, cramps, spasms, muscular restlessness, difficulty breathing, profuse sweating, or a feeling of impending doom. Irukandji syndrome is not usually fatal, but it can be; more frequently it resolves entirely or, rarely, results in permanent heart damage.
The best prevention against Irukandji stings is a full-body lycra suit (or neoprene wet suit), which provides good protection for about 80% of the body's skin surface. It is still possible to be stung on the hands, feet, or face, but this rarely happens compared to the larger body surfaces. For those wishing additional protection, gloves, booties, and hood are recommended.
Irukandjis are more prevalent on days with dense 'jelly button' or 'sea lice' blooms, especially if salps are present (see Chapter 14). These sorts of days only occur a few times a year, but it is wise to avoid the water if possible.
Treatment priorities for known or suspected Irukandji stings:
1. If the person is already feeling systemic symptoms, call '000' for an ambulance, then douse the sting well with vinegar. Rest and reassure the patient.
2. If systemic symptoms have not yet onset, douse the sting site well with vinegar and monitor the patient for 30-40 minutes to see if symptoms develop; if so, call '000' for an ambulance.
Treatment priorities for box jellyfish stings:
1. Call for help dial '000' for ambulance or get a lifeguard
2. Treat the victim provide emergency care (CPR if necessary)
4. Seek medical aid transport to hospital distributions. Box jellyfish, for example, are generally restricted to coastal and near-shore island localities. In contrast, stings from Irukandji jellyfishes have been reported from nearly every coastal and island/reef locality where recreational activities take place throughout the GBR (Box. 18.2). Curiously, the moon jellyfish (Aurelia spp.) is one of the commonest species globally, but is only sporadically found in the GBR region, where it may occur in dense but short-lived blooms. However, the majority of jellyfish species have only been reported from one reef or island but this is probably more due a paucity of studies than a reflection of their true abundance. In general, the dangerous species have received the most attention but some are yet to be formally classified.
A hot topic of modern jellyfish research is bloom dynamics, or the cycles and triggers of jellyfish blooms. Most jellyfish are capable of exploiting perturbed ecosystems, whether through pollution (especially eutrophication), overfishing, species introductions, or climate change. They have changed little in design in over 600 million years, suggesting that they are tolerant of changes in pelagic assemblages and environmental change. Water quality conditions that threaten the survival of some organisms may facilitate the development of jellyfish blooms. Numerous examples exist around the world where jellyfish have essentially 'flipped' the local ecosystem, becoming the dominant predator. In this capacity, jellyfish can have direct and indirect effects on other species. For example, they may eat the larvae of other species as well as the food of these larvae (that, in turn, influences larval survival).
■ PREDATION AND DEFENSE
Most medusae and ctenophores will eat a diversity of plankton and some nekton. They are typically carnivorous, preferring zooplankton prey rather than phytoplankton. Their own kind can be also be on the menu. Cyanea spp. (lions mane) eat Aurelia and other medusae, while the ctenophore Beroe preys on other ctenophores such as Pleurobrachia. Some species of ' blubbers' (Order Rhizostomeae) have symbiotic algae (zooxanthellae) in their tissues, similar to those of corals. These symbiotic jellyfishes are typically found in warm shallow waters, where they 'farm' their algal symbionts; the jellyfish may obtain a significant portion of its nutritional requirements from its algae.
Some jellyfish have definite feeding preferences. For example, one species of box jellyfish from the GBR region has been demonstrated to change its dietary habits as it grows, starting out preferring prawns, and switching to fish later in life.
While the huge appetites of jellyfish make them fearsome predators, their soft bodies also make them an easy meal. Turtles, crabs, many fishes, such as sunfish and triggerfish, and seabirds actively hunt jellyfishes.
All cnidarian jellyfishes have venomous stinging organelles (nematocysts, Fig. 18.12), which they use for defence and prey capture. The ctenophores lack nema-tocysts, and instead, they have strange organelles called colloblasts, which lack venom but ensnare prey with adhesive. A nematocyst might be thought of as a tiny harpoon with poison, while a colloblast is more like a rope covered in honey.
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