Jellyfish are gelatinous marine animals that drift through the world’s oceans. Their presence washed ashore is a common sight on many coastlines. Understanding why these organisms end up out of their watery habitat involves examining powerful oceanic forces and various aspects of their biology and life cycles.
Oceanic Forces at Play
Oceanic forces play a significant role in the stranding of jellyfish. Tides, the rise and fall of sea levels, carry jellyfish closer to shore during high tide. When the tide recedes, jellyfish unable to swim back into deeper water quickly enough become trapped on the exposed sand. Their passive movement makes them particularly vulnerable to these tidal shifts.
Ocean currents also exert a strong influence on jellyfish distribution and movement. These continuous, directed movements of ocean water can transport vast numbers of jellyfish over long distances. Strong currents, especially those that run parallel to or directly towards coastlines, can effectively push entire populations of jellyfish into shallow waters or directly onto beaches. Jellyfish generally have limited swimming capabilities, relying more on currents for transport.
Wind is another atmospheric factor that contributes to jellyfish stranding. Persistent onshore winds create surface currents that can drive jellyfish towards land. Given their buoyant, bell-shaped bodies and relatively weak propulsion mechanisms, jellyfish are easily pushed by wind-driven surface water.
Severe weather events, such as storms, amplify the effects of tides, currents, and winds. Storms generate powerful waves, strong currents, and intense winds that can disorient and overwhelm jellyfish, forcing them towards the coastline in large numbers. The increased turbulence and water movement during a storm make it exceedingly difficult for jellyfish to maintain their position or swim away from the shore, leading to more frequent and extensive stranding events.
Natural Factors and Life Cycles
Beyond the direct influence of oceanic forces, natural biological and environmental factors also contribute to jellyfish stranding. One prominent reason is the occurrence of “jellyfish blooms,” which refer to a rapid increase in jellyfish populations within a specific area. When a bloom occurs, the sheer number of jellyfish in the water makes it statistically more likely that a greater proportion will be carried ashore, even under normal tidal and current conditions. These blooms can be influenced by factors such as warmer ocean temperatures, increased nutrient availability from runoff, and a reduction in natural predators.
Jellyfish also have a natural lifespan, which varies depending on the species but generally ranges from a few months to a year. As jellyfish reach the end of their life cycle, they die, and their remains can then be passively carried by ocean currents and tides towards the shore. This natural mortality contributes to the overall number of jellyfish found washed up on beaches, as their decaying bodies become subject to the same physical forces that affect live ones.
Environmental stressors can also weaken jellyfish, making them more prone to stranding. Sudden or significant changes in water temperature, salinity, or oxygen levels can stress these delicate organisms. For example, a rapid drop in water temperature or a sudden change in salinity due to heavy rainfall can impair a jellyfish’s ability to regulate its internal environment or swim effectively. Such stressors can lead to a decline in their health, rendering them less capable of resisting currents and more susceptible to being pushed onto beaches.
What Happens After They Strand
Once jellyfish wash ashore, their survival chances diminish rapidly. They are primarily composed of water, with some species being over 95% water. This high water content means that when removed from their aquatic environment, they quickly begin to dry out, a process known as desiccation. Without water to support their delicate structures and maintain their cellular functions, they cannot survive for long on land and typically die within hours or even minutes.
After desiccation, the stranded jellyfish begin to decompose. Their soft bodies break down relatively quickly due to the action of bacteria and other microorganisms. The organic matter from their bodies is then reabsorbed into the beach ecosystem, contributing nutrients to the sand and surrounding environment. This process is a natural part of the coastal nutrient cycle, where marine life returns its components to the terrestrial system.
Even after a jellyfish appears dead or dried out, caution is warranted. The stinging cells, called nematocysts, located on their tentacles, can remain active for hours or even days after the jellyfish has died and washed ashore. Contact with these cells can still cause skin irritation, pain, and other reactions.
What to Do When Encountering Stranded Jellyfish
When encountering jellyfish on the beach, the most important rule is to avoid direct contact. Even if a jellyfish appears lifeless or dried out, its stinging cells can remain potent and capable of delivering a painful sting. Therefore, it is safest to observe them from a distance and resist the urge to touch them with bare hands or feet.
Maintaining a safe distance is also important for pets. Dogs and other animals exploring the beach may be curious about stranded jellyfish and could suffer stings if they sniff or mouth them. Pet owners should keep their animals on a leash and away from any jellyfish encountered on the sand.
If a large number of jellyfish are washing ashore, or if you encounter a species known to be particularly dangerous, it can be helpful to report the sighting. Notifying local lifeguards or beach authorities can help them assess the situation and issue warnings to other beachgoers. This proactive step contributes to public safety by informing others about potential hazards on the beach.