San José, Costa Rica, since 1956

In Nicoya Gulf, the deadly red tide lingers

From the print edition

PAQUERA, Puntarenas – On Monday, the ferry leaving Paquera, on the east side of the Nicoya Peninsula, labored across the Gulf of Nicoya toward Puntarenas, churning through ocean waters that switched from deep aquamarine colors to scabby, ochre-red splotches.

Since early February, the gulf, and beaches and islands surrounding it, have been in the throes of one of the worst blooms of red tide in recent years. 

“You can smell it,” said Thomas Jones, a charter boat captain and kayak guide out of Paquera. “It’s putrid.”

Red tide is a naturally occurring algal bloom. It’s hardly unknown in the Gulf of Nicoya, generally blooming for several weeks in the early rainy season months of April and May. But Jones said this year’s bloom is the worst he’s seen both in terms of duration and intensity.

The algae that creates a red tide – single-celled organisms called dinoflagellates that use the sun to photosynthesize and grow – can secrete toxins which when absorbed by filter-feeding shellfish such as mussels and oysters can have deadly effects on humans who consume tainted products. Symptoms can range from vomiting and nausea to paralysis and death.

Shellfish poisoning in Costa Rica from algal blooms is rare, but the algae that secrete the toxins are present, and isolated cases of deaths on the Nicoya Peninsula have occurred. In 1972, according to the National University’s (UNA) Phytoplankton 

Laboratory,  four people died from eating tainted mollusks, and in 1989, two children died in the area from paralytic shellfish poisoning.

The Costa Rican Fisheries Institute (Incopesca) monitors red tide blooms in Costa Rica, while the Agriculture and Livestock Ministry (MAG) operates laboratories to test mollusks for toxicity. 

At the end of February, a MAG blog acknowledged that red tide blooms in the Gulf of Nicoya contain Gymnodinium catenatum, an algal species known to generate dangerous toxins, but ministry officials said there were no indications of toxins in the water. Incopesca President Luis Dobles told local news station Telenoticias on Feb. 22 the institute would continue monitoring the situation, but had not issued any restrictions on the consumption of shellfish from the area.

At press time, Incopesca did not respond to phone calls for comment on the algal bloom’s lingering presence.

According to Jones, algae in the gulf kills fish by reducing oxygen in the water and clogging fishes’ gills, causing them to suffocate.

“The fish disappear when the red [tide] moves in,” Jones said. “We don’t even bother fishing when it’s red.”

People who swim in red tide may experience rashes, skin discomfort or worse if they accidentally swallow some of the algae-infested water.

Though naturally occurring, red tide can be exacerbated by pollution in oceanic waters. Agricultural runoff and raw sewage, if present in the water, can provide algae with nutrients to thrive and grow. Fertilizers used in agriculture add phosphates and nitrates to the water that can cause algal blooms to go wild, and the upper end of the gulf, research has shown, can be particularly prone to these conditions. Add to this the unrelenting tropical sun of western Costa Rica and conditions could be right for a powerful bloom.

Residents of Paquera, besides fishing boat captains, are keenly aware of the problem of “the red.” 

From the balconies at Hotel Vista Las Islas, which overlook Isla Tortuga’s beaches – a popular day trip for tourists who want a taste of white sand, solitude and good snorkeling – guests watch the red tide circulating near the beach. Fingers and blobs of rust-colored algae twirl through the famously aquamarine waters of the gulf, moved by currents, tides and wind. In some places, the only indication of red tide are a few wisps of rusty-hued water; but in others, including the ferry route, large swaths of ocean are murky and red.

Hotel Vista Las Islas owner Thomas Kohli said the red tide struck surprisingly early this year and has lingered for nearly three months. The norm, he said, is a light bloom of up to three weeks before the noxious algae begins to decompose and disappear, leaving clear, blue waters.

Kohli said news of the red tide hasn’t affected his business much, but he is worried that if it continues, the bloom could impact tourism in the area.

A random survey of Paquera-area taxi drivers indicated that locals are attuned to the risks to their livelihood presented by red tide.

One taxista said news of the long-running red tide has kept Tico tourists, in particular, from visiting the southern Nicoya Peninsula lately. Foreign tourists, he opined, might be less aware of the local situation, or less willing to change their travel plans than domestic travelers.

Jones said he’s seen signs the red tide could be retreating. Red-tinted sea foam sitting atop the bloom is an indication the algae underneath is dying and decomposing. Days when he fishes are a sort of cat-and-mouse game with algae that can come and go from an area almost as quickly as a school of fish.

“I’ve been watching satellite images of the water temperatures and the bloom the past few weeks,” said Jones, who subscribes to an online weather service that provides surface water chlorophyll counts in different regions. Because the red tide is algae and contains chlorophyll, these counts serve as indicators of red tide concentration. “Now it’s not as bad as it was. We’re hoping it’s on the decline.”

When the tide first struck in February, Jones said he took his boat out 30 miles beyond the mouth of the gulf and found himself surrounded by rusty water.

“We didn’t bother going out any farther,” he said. “It’s pretty much game over when it’s like that.”

Oysters and Algae

Alexandra Peralta, 40, started the first oyster farm in Costa Rica four years ago in the Gulf of Nicoya at Punta Cuchillo, near Paquera. She harvests some 3,000 carefully tended Japanese oysters each week for sale to restaurants and at locations in Santa Ana and Escazú, southwest of San José. She is at the forefront of an emerging market.

Red Tide 2

Red tide, a naturally occurring algal bloom that can kill fish and release toxins that make shellfish dangerous for humans to eat, returns annually in the Gulf of Nicoya. Residents say this year’s bloom is one of the worst in recent years.

Clayton R. Norman

“Before,” she said while standing on the black gravel beach at Punta Cuchillo and looking out across her underwater farm, “there was no culture of eating oysters in Costa Rica. Now, if I had more oysters every week, I could absolutely sell them.”

She described the flavor of her Japanese oysters as “having a saltiness that you can feel and that makes you want to keep eating them.”

Besides a distributor that buys the bulk of her weekly harvest in the San José suburbs, Peralta said Europeans are her biggest customers, and they hit her product hard at Christmas.

“Europeans eat oysters at Christmas like Costa Ricans eat pork tamales,” she said. 

During the holidays demand for her crustaceans drives her to harvest 6,000 oysters – twice the demand of the rest of the year.

At 36, Peralta made the jump from working at UNA in marine resources management, where she had worked for 12 years, to being her own boss. Her previous career at the university prepared her for a new business – she worked on a team developing exactly the kind of oyster-farming system she uses now. 

“It was hard at first,” she explained while dipping her paddle into the clear waters around her farm. There is no hint of rusty algae in the immediate vicinity. “Starting my business I had a lot of support from UNA, but I couldn’t get financing to start.”

Today her father, sister and other family members work the farm with her.

Of anyone, Peralta seems at first glance to stand to lose the most from an outbreak of harmful toxins released by an algae bloom. But she was all smiles at her farm as she pulled on a pair of yellow dishwashing gloves to paddle a small canoe out to the oyster lines that run parallel to the shore, about 10 meters off the beach at low tide.

“Every 15 days I send a water sample to the National University to test for toxins,” she said.

Her water samples are tested and she gets results in approximately 24 hours. If any toxins dangerous to humans are detected she must submit water samples for the next three days – more if toxins continue to show in the samples.

At the end of each month she sends samples of her oysters to a MAG laboratory in Puntarenas to be tested.

This year she said no paralytic toxins have been found in her water or her oysters, but some water samples have turned up potentially worrisome algae.

Peralta seemed unfazed by this.

“Red tide can affect the market for my product,” she explained. “But I know I’m not going to lose all of my oysters or anything like that.”

Shellfish will naturally clear paralytic toxins from their bodies given enough time filtering food from the water in a toxin-free environment. Peralta said that if toxins are discovered in her water or oysters, she continues sending samples for testing and caring for the little bi-valves until they test free of toxins.

“I lose some money if that happens in terms of how much I earn on each oyster,” Peralta said. “That causes problems for my market because the oysters grow larger and I sell them at the same price.”

Customers then begin asking for larger oysters at a lower price. 

Standing in her paddleboat, Peralta hauled to the surface a four-tiered basket suspended in the water under a floating white buoy. She removed a green mesh bag, and from inside that she produced two handfuls of gleaming crustaceans that she held out to show, smiling broadly under the hot, Nicoya sun.

“I’m not very worried about the red tide,” she said. “The longest I’ve had to wait to sell any of my oysters because of water or meat tests has been about 22 days. 

Asked what characteristics one needs to be a successful oyster farmer, Peralta laughed again.

“Perseverance,” she said. “This work requires a lot of mano de obra [labor], a lot of work and a lot of maintenance.”

From seed to harvest, Peralta said, it takes about 10 months to grow her oysters. 

She’s been lucky, Peralta admitted, not only to get the oyster farm going in the first place, but also to have her location at Punta Cuchillo. Near the mouth of the gulf, ocean currents bring her “new water every day,” she said, and she faces fewer problems with sedimentation than she might further inside the gulf.

Peralta said she’s excited about the growing market for her product. Another oyster farm started up recently nearby, she said, which she views as a positive development.

“We don’t view it as competition,” she said. “Because this market is growing and having more oysters means more demand.”

Development along the shores of the Gulf of Nicoya is her biggest concern – besides preventing lobsters and octopuses from gobbling up her product before she can harvest it.

“When we started this, we did extensive water studies looking for heavy metals and other agricultural products,” she said. “We have great water here, but I worry about this area developing into a major tourist area.”

Construction, runoff and contamination from wastewaters from any large development projects could threaten the quality of her water, she said.

For now, though, Peralta is happy that her water tests and oyster samples are coming back clean of red tide-related toxins.

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