The classic summer image of crowded beaches, umbrellas, and people splashing around in Mar del Plata this year added an unwelcome guest: jellyfish , known locally as aguavivas. Their presence was noticeable at various beaches and caused concern among those who came to the sea to cool off.
In recent days, a proliferation of jellyfish has been recorded near the shore , right in the middle of peak season. Lifeguards and specialists point to one main factor: the sea is behaving warmer than normal, with temperatures above historical averages for this time of year.
Change in sea temperature and jellyfish proliferation
The underlying explanation lies in the temperature of the Atlantic Ocean off the coast of Mar del Plata . Data from the National Institute for Fisheries Research and Development (INIDEP) indicates that, during January, the sea surface registered an average of around 21,6°C , with peaks exceeding 24°C after starting the month at around 18,7°C.
According to this oceanographic monitoring, during the second half of the month the water remained above the climatological average calculated for the period 2013-2023. From January 23 onwards, almost all records were within the upper quarter of the highest values in the historical series, that is, among the 25% of the highest temperatures measured in that coastal strip.
Lifeguards in areas like Punta Mogotes confirm this situation on a daily basis: they report that the sea feels "warmer than usual" and that, under these conditions, jellyfish begin to appear in greater numbers near the swimming area. It's not a new phenomenon, but it is one that is recurring with greater frequency and intensity.
During periods of positive temperature anomalies —that is, when the water is significantly warmer than the area's average—basic ecosystem dynamics change. Jellyfish benefit from this scenario: they reproduce more efficiently, find abundant food in the plankton, and, carried by currents, concentrate in beach areas where people swim.
In addition to temperature, days with calm seas and easterly or southeasterly winds help jellyfish swarms stay close to the coast. On very calm days, the jellyfish disperse less and can accumulate in small areas, increasing the likelihood of contact with beachgoers.
What are jellyfish and why do they wash up on the shore?
The jellyfish found today on the Mar del Plata coast belong to a very ancient group of marine animals , with a body composed almost entirely of water and a simple anatomical structure. Beneath their gelatinous bell or "umbrella" hang tentacles equipped with stinging cells , capable of injecting microscopic toxins.
These organisms are not active predators of swimmers . They lack a developed brain, cannot distinguish large prey, and move with the currents, tides, and winds. Their role in the ecosystem is primarily to feed on small planktonic organisms and, in turn, serve as food for other marine animals.
When the sea surface warms up excessively and remains so for several days, three factors combine to explain their massive presence: higher water temperatures, favorable currents, and abundant food . This combination results in swarms of jellyfish that, almost without "choosing" to do so, are carried to the coastline.
Lifeguards at various beaches agree that every summer there's a period when jellyfish appear in large numbers . What's changing now is the frequency: the warm sea episodes are recurring, and with them, the number of encounters between tourists and jellyfish is increasing.
From an ecological perspective, the increased presence of these animals is also an indicator of changes in the South Atlantic , linked to ocean warming and altered predator-prey relationships. It is not an isolated phenomenon: it is part of a global context of climate variations.
Why do jellyfish sting and what does it feel like?
The discomfort reported by many swimmers is due to the function of stinging cells, called cnidocytes , present in the tentacles. Each of these cells contains a kind of tiny harpoon loaded with toxin that is discharged when something touches the surface of the tentacle.
Upon contact with human skin, this defensive mechanism generates intense burning, a stinging sensation, redness, and itching in the affected area. The severity of the reaction depends on the species, the duration of contact, and the individual's sensitivity; children and those with highly reactive skin tend to experience the most severe reactions.
In the vast majority of cases, insect bites are not serious and only cause local irritation that subsides within hours or days, especially if treated promptly. However, the sensation can be very bothersome and cause concern, particularly when the appropriate treatment is unknown.
The lifeguards of Mar del Plata, who have already attended to numerous tourists stung by jellyfish this summer, insist that there is no "attack" typical of the animal: the contact is accidental, and the defense mechanism is triggered in the same way as it would be against a small fish.
Only in rare cases may more severe symptoms appear , such as difficulty breathing, dizziness, extensive swelling, or general malaise. In these situations, it is essential to go to a health center as soon as possible to rule out a serious allergic reaction or other complication.
First aid: what to do if you get stung by a jellyfish in Mar del Plata
If you come into contact with jellyfish tentacles, the first thing to do is get out of the water immediately . Staying in the water increases the chances of further contact with tentacle fragments that may still be floating and not visible to the naked eye.
Lifeguards recommend not rubbing the affected area with your hands, sand, towels, or any other material. This action, which is often done instinctively, activates more stinging cells that haven't yet released toxins, worsening the skin reaction.
Another key point is to avoid washing with fresh water . The sudden change in salinity can stimulate the release of cnidocytes that remain attached to the skin. Instead, it is advisable to rinse gently with seawater , which helps to remove tentacle fragments without releasing more toxins.
When available, vinegar is often a useful ally in inactivating the stinging cells of several of the species present in the region. After its application, applying local cold (for example, ice wrapped in a cloth or a cold pack) helps to relieve pain and reduce inflammation in the affected area.
If the burning sensation persists, many healthcare professionals may prescribe mild corticosteroid creams or topical antihistamines , always under medical supervision. Any sudden worsening of the condition or generalized symptoms requires immediate evaluation in an emergency department.
When to see a doctor and what signs to watch for
Although jellyfish stings can usually be treated with basic first aid on the beach, certain signs warrant seeking help as soon as possible. These include difficulty breathing, chest tightness, or wheezing.
Other warning signs include extensive swelling that extends beyond the contact area , widespread hives, intense dizziness, nausea, fainting, or any manifestation that suggests a severe allergic reaction.
In such cases, specialists recommend not delaying consultation and going to a health center or beach care post , where specific medications can be administered and clinical evolution monitored during the first few hours.
Children, the elderly, and those with a history of significant allergies are groups in which extra caution is advised. If a child reports severe pain, cries inconsolably, or shows general malaise, it is wise to have them evaluated by a professional.
At the same time, lifeguards remind people not to try unproven home remedies (such as applying urine, alcohol, lemon, or irritating substances), as these can worsen skin injuries or delay the application of appropriate treatments.
How to prevent stings: tips for swimmers
Completely avoiding contact with jellyfish in the open sea is difficult, but there are some simple guidelines you can follow to significantly reduce the risk . The first is to pay attention to the flags, signs, and announcements from lifeguards, who continuously monitor sea conditions.
When an increase in jellyfish is detected on a section of beach , some kind of warning is usually issued. In these circumstances, the wisest course of action is to limit swimming, find another part of the coast with fewer jellyfish, or simply stay on the sand.
It is also important not to handle specimens washed ashore , whether out of curiosity or to take photos. Even if the body appears lifeless, the tentacles can remain active for some time and cause a sting with the slightest touch, to both adults and children playing in the sand.
Wearing protective clothing such as UV shirts or thin wetsuits acts as a physical barrier between the skin and the tentacles, especially in areas where jellyfish are known to appear every summer. These garments are common among surfers, bodyboarders, and other water sports enthusiasts, but they can also be useful for regular swimmers.
Finally, it's advisable to enter the water with caution on days with very calm seas and high temperatures , as these are the conditions in which jellyfish tend to congregate near the surf. Observing the water's surface and the wet sand before entering the water can prevent more than one unpleasant surprise.
The increased presence of jellyfish in Mar del Plata this summer is part of a broader trend of warmer seas and climate change , also being observed in other parts of the Atlantic. Far from being a rarity, it has become a recurring phenomenon that requires adapting beach habits: staying informed, following lifeguard instructions, and knowing basic first aid measures allow you to continue enjoying the sea, even knowing that jellyfish can appear at any time during the season.
