COMMENTARY

The dreaded sea itch strikes again!

by The Green Hornet

Tuesday,  February 28, 2006

Last week a friend of mine visiting from up north was laid low by a serious case of sea itch. He hadn’t visited us for several years, and thought that it would be safe to go snorkelling in early February. Wrong. 

I explained to him that the usual sea itch “season” we could rely on 20 years ago – March and maybe April – had now extended from March through to August but could, in fact, happen at pretty much any time during the year. He asked me why, and I didn’t have an answer until I read a recent paper in the scientific journal Trends in Ecology and Evolution. 
Like many of the ecological ills that affect us these days, it’s got to do with global warming. 

As oceans play a major role in the global carbon cycle, they directly affect the rate and nature of climate change. Surprisingly, there have been relatively few long-term series of biological measurements in marine environments. 

I recall a feature on Cuba’s reefs published in National Geographic a few years ago, written by Peter Benchley, in which he reported being surprised by a strange microscopic creature that inflicted a nasty “bite” that itched for weeks after he had been stung. The paper in Trends in Ecology and Evolution is by Graham Hays and colleagues at the University of Wales, who note that, among marine biota, plankton “are particularly good indicators of climate change in the marine environment for several reasons. 

First, unlike other marine species such as fish and many intertidal organisms few species of plankton are commercially exploited; therefore any long-term changes can be attributed to climate change.

“Second,” Prof. Hays continues, “most species are short lived and so population size is less influenced by the persistence of individuals from previous years. This leads to a tight coupling between environmental change and plankton dynamics. Third, plankton can show dramatic changes in distribution because they are free-floating and can respond easily to changes in temperature and oceanic current systems by expanding and contracting their ranges.”

Changes in plankton distribution

The authors report that, for example, there is “strong evidence for systematic changes in plankton abundance and community structure over recent decades in many areas worldwide.”

The paper goes on to point out that Antarctic krill – a tiny, shrimp-like marine crustacean that is a key component in the diet of whales and other marine mammals that filter their food from seawater – have declined in abundance by more than an order of magnitude during the past 25 years. This decline has been directly linked to reduced food availability for the krill in the form of phytoplankton (microscopic free-floating aquatic plants) blooms in summer and ice algae in winter.

Additionally, there have been numerous recorded correlations between mesozooplankton (bigger plankton, up to 22 mm in size, including “sea itch”) and large-scale climate influences, including changes in distribution concurrent with changes in water temperature. Although the search for mechanistic links between climate and plankton continues, write Hays and colleagues, “the impact of weather on the intensity of ocean mixing (and its reverse, ocean stratification) is likely to be central to the linkage.

This intensity, in turn, affects light levels, surface temperatures and the magnitude of nutrient recycling from deep layers, thereby influencing phytoplankton growth and thus driving bottom-up processes (i.e. the role of members of one trophic level as food items for higher trophic levels) throughout the pelagic food chain.”

The authors further note that, inevitably, such trophic (relating to the value of food) changes can impact fish populations and hence commercial fish catch, and cite several instances in which relatively abrupt declines or increases in fish stocks can be attributed to plankton fluctuations.

For example, Allison L. Perry, of the University of East Anglia in England, and colleagues studied the bottom-living fish assemblage in the North Sea (the waters of which have warmed by 1.05 degrees Celsius – 1.89 degrees Fahrenheit – between 1977 and 2001) and discovered that the distributions of both exploited and non-exploited North Sea fishes have responded markedly to recent increases in sea temperature, with nearly two-thirds of species shifting in mean latitude or depth or both over 25 years.

This is the conclusion of a recent paper in the journal Science, in which Perry and colleagues found that centres of distribution shifted northward for 13 of 376 species, including both exploited species such as cod and sole, and non-exploited species such as scaldfish and snakeblenny. These distribution changes can be attributed to the redistribution of the fish’s primary food source – plankton.

Okay, you say, but what’s that all got to do with sea itch? Well, sea itch is a form of plankton, = the larvae of thimble jellyfish. They make life extremely unpleasant for those who encounter them – and they can be encountered pretty much everywhere in the Caribbean Sea these days. If you have never been “stung”, consider yourself fortunate.

Itchy skin eruptions from sea itch

The common symptoms include intensely itchy skin eruptions with small blisters and elevated areas of skin. Found primarily on parts of the body covered by swimwear, these lesions may also appear on the armpits and neck and occasionally on the arms and legs. 

Many divers and swimmers call it “sea lice”. The term is a misnomer, however. Sea lice are actually fish parasites that do not affect humans and have nothing to do with “sea bather’s eruption”, which is caused by jellyfish larvae. 

The primary offenders in Florida and Caribbean waters are the larvae of the thimble jellyfish. These larvae, generally half a millimetre long, can find their way into bathing suits – even passing through the mesh of some suits – and become trapped against the skin, and sting.

The larvae are visible to the naked eye but become nearly invisible in the water. 

And the absence of adult thimble jellies in the area is no guarantee that the youngsters aren’t around. 

The best indication that the larvae are about is the appearance of the rash on swimmers or divers, though you can sometimes detect them by observing bubbles that don’t burst on the surface of the sea. 

The symptoms will appear very soon (24 hours or less) after exposure to the organism and will persist for several days. Some cases have been reported which have a three- or four-day delay in onset and a prolonged course lasting several weeks. Symptoms may include fever, chills, headaches, nausea and vomiting. Severe symptoms occur particularly in children, although adults have shown similar reactions. 

Since many of the symptoms are consistent with other illnesses, diagnosis is sometimes difficult unless the attending physician knows of the diver’s exposure to infested water. Often the symptoms are very mild, and other causes may be considered or diagnosed incorrectly at first, reports Dr. G. Yancey Mebane in the DAN Divers Alert.

Many cases of sea bather’s eruption clear up spontaneously, but others require treatment. Antihistamines and antipruritic (anti-itching) agents may be used, but the results are not good in many cases. 

Severe reactions are rare, but children and individuals with allergies or diseases affecting the immune system may be at risk. In the severe cases, some doctors prefer to use cortisone, by tablet or injection, says Dr. Mebrane. 

Sea itch prevention sometimes works Prevention for the diver means adequate protection by wetsuit or impermeable dive skin. Snorkellers wearing T-shirts and women wearing one-piece bathing suits are vulnerable because of the trapping action of the fabric. 

The following is recommended if you have been diving or swimming in an area where the jellyfish larvae are present. Remove your wetsuit, dive skin or bathing suit before showering, since the fresh water may discharge the nematocysts trapped in the fabric. There have been many reports of the condition recurring when the same bathing suit is worn again, suggesting that the larvae may remain in clothing. 

I have found that immediate application of rubbing alcohol to the affected parts of the body, repeated every ten minutes or so over a period of an hour, will usually neutralise the sting.

Sea itch won’t kill you unless you have a very severe reaction, but it is extremely unpleasant. It’s a clear sign that global warming is disrupting the oceanic food web, and you can bet there are even more serious consequences on the way. Just think about that when you leave your SUV running in Foster’s parking lot so the a/c keeps it cool while you shop – and make your own personal contribution to global warming.

Back...