This phenomenon, which can sometimes disrupt swimming and cause discomfort for tourists and residents , is due to natural processes linked to the life cycle of these animals, wind patterns, and ocean currents. Although their presence is striking and requires extra caution, experts remind us that they have been part of the marine ecosystem for millions of years.
Causes of massive jellyfish blooms
Jellyfish that congregate in large numbers along the coast typically do so when several factors coincide: water rich in plankton for food, favorable temperatures, and specific wind and current patterns . Under these conditions, swarms that drift out to sea eventually end up being swept toward the shore.
Marine ecosystem researchers point out that these concentrations are not isolated events, but rather recurring episodes that are more striking in some years due to the magnitude of the blooms. When food is abundant during the juvenile stages, the population grows rapidly and the phenomenon becomes much more visible.
Another key factor is marine circulation in gulf or bay areas , where currents can act as a "funnel" and accumulate large quantities of jellyfish in relatively small areas, right where bathers congregate.
Furthermore, changes in the water column throughout the seasons have a direct influence: in spring and summer, the ideal conditions arise for jellyfish to enter their most visible phase , which coincides perfectly with the peak tourist season.
Life cycle: why they appear right in summer
Jellyfish have a unique life cycle that helps explain why they are only seen in large numbers at certain times of the year. Throughout the year, they alternate between a microscopic phase, attached to the seabed, and a free-floating phase in the water , which is the one we see with the naked eye.
During autumn and winter , polyps predominate ; these small structures remain attached to the seabed. At this stage, they go largely unnoticed, but they prepare the ground for the next step: the production of juvenile jellyfish when temperatures rise and food availability changes.
With the arrival of spring and summer, these polyps release jellyfish that grow rapidly. In many parts of the South Atlantic, large concentrations are typically observed starting in December, peaking in January and February , coinciding with the holiday season at the beaches.
From the early autumn months, the number of specimens visible on the surface decreases significantly. In practice, this means that, although the species is present in the area year-round, coastal "invasions" are concentrated in a couple of months and then disappear from the sight of swimmers and recreational fishermen.
The featured species: Chrysaora plocamia
In various locations in the South Atlantic, including gulfs and open bays, the most commonly observed species in these blooms is the jellyfish Chrysaora plocamia , belonging to the scyphozoan group. It is characterized by its relatively large size and striking tentacles.
Scientific records indicate that this jellyfish has been documented regularly since the 1970s , with particularly noticeable episodes of abundance in several specific years and an almost continuous presence in recent times during the summer season.
This organism is considered an "R-strategist," meaning it has rapid growth, a high reproductive rate, and produces a large number of larvae . This allows it to quickly take advantage of periods of abundant food and multiply its population in a short time.
Research suggests that many of these jellyfish complete their entire life cycle within the gulf or bay itself , from the benthic stages attached to the seabed to the adult jellyfish observed by swimmers. This ability to complete the cycle in the same location allows the phenomenon to repeat itself year after year.
Risks to bathers and possible inconveniences
Despite their striking and often intimidating appearance, most jellyfish involved in these blooms are not considered extremely dangerous to healthy people. However, they can cause noticeable discomfort and, in some cases, require medical attention.
Jellyfish like Chrysaora plocamia have tentacles equipped with stinging cells that release venom to capture prey. When they come into contact with human skin, they usually cause burning, itching, and localized irritation, which is especially bothersome for children and those with sensitive skin.
The most common effect is a burning sensation and redness , which, although it doesn't usually lead to serious injury, can be very uncomfortable for several hours. In most cases, the discomfort subsides with simple measures and leaves no lasting effects.
Experts insist that, even though these species are not among the most dangerous in the world, it is essential to maintain respect and not minimize their effects , since allergic people, small children or bathers with pre-existing health problems could react worse to a sting.
What to do about a jellyfish sting
If you come into contact with a jellyfish and experience sting symptoms, experts recommend remaining calm and following a few basic steps. The goal is to reduce pain, prevent further activation of the stinging cells, and avoid infection.
First, it's advisable to get out of the water immediately to avoid further contact with the tentacles and to calmly assess the extent of the injury. Once on shore, it's important not to rub the area, as this could break any stinging cells still attached to the skin and worsen the reaction.
If any tentacle fragments are visible, remove them with an object such as a card, a shell, or tweezers, avoiding using your bare hand . Afterward, rinse with seawater , never fresh water, as the sudden change in salinity can activate more nematocysts.
Many first aid guides recommend applying local cold, either with ice packs wrapped in a cloth or cold compresses, to relieve pain and inflammation. In some cases, the use of vinegar or specific solutions is suggested , depending on the area and the type of jellyfish, as well as dermatological creams with an anti-inflammatory effect, always under medical supervision.
If the discomfort is intense, extends beyond the contact area, breathing difficulties or dizziness appear, or if the affected person is a child, an elderly person or someone with pre-existing conditions, it is essential to go to a health center as soon as possible or consult the emergency services.
Safety and coexistence tips on beaches with jellyfish
When a high presence of jellyfish is detected near the shore, rescue organizations and authorities usually issue specific recommendations and, sometimes, partial restrictions on swimming . Following these guidelines is key to reducing risks.
Experts recommend avoiding direct contact with jellyfish, both in the water and on the sand , even if they appear inert. A stranded jellyfish can retain its stinging ability for some time, so it's best not to handle it or use it as a "toy" on the beach.
Before entering the sea, it is advisable to pay attention to the flag signs and warnings , as well as listen to the instructions of lifeguards and surveillance personnel, who usually have up-to-date information on the state of the water.
On days when a significant concentration of fish has been reported, many people choose to stay in shallower areas or reduce their time in the water . In particularly affected areas, some beaches may consider installing nets or buoys to create relatively safer swimming areas, provided conditions allow.
A natural phenomenon that repeats itself every year
Although it may seem like an exceptional situation at first glance, the massive presence of jellyfish in certain coastal areas is, according to experts, a natural, cyclical phenomenon that is expected at certain times of the year. Scientific records accumulated over decades show that these episodes have been recurring regularly.
In many cases, the years in which their presence is particularly striking coincide with periods of highly favorable environmental conditions for their reproduction and with a high availability of food in the water column. This makes the blooms more intense and visible from the coast.
Experts point out that, although the public perception may be that the problem is new or increasing unexpectedly, much of this effect is due to greater media coverage and increased attention from residents and tourists . The same beaches that decades ago experienced episodes of jellyfish blooms now have many more people observing and sharing images.
This context does not diminish the importance of the inconveniences they cause for leisure and some recreational activities, but it helps to put the phenomenon in its proper perspective: it is not a sudden irruption of an organism foreign to the environment , but the visible expression of ecological processes that have been occurring for a long time.
The sight of beaches with large concentrations of jellyfish can be unsettling for those seeking a peaceful swim, but according to available scientific data, it is a natural process linked to the life cycle of these animals, the dynamics of the ocean, and recurring environmental patterns . With clear information, caution in the water, and respect for the instructions of lifeguards, it is possible to continue enjoying the coast while minimizing risks and accepting that sharing space with jellyfish is increasingly becoming a part of our summers.