By: Brittany Hook

Collaborative paper documents extreme water conditions that led to fish die-offs

In the spring of 2020, a historic red tide event occurred in waters off Southern California. Driven by a bloom of the dinoflagellate Lingulodinium polyedra, this event brought nighttime displays of bioluminescence to beaches along the coast, from Baja California to Santa Barbara. While the bloom gained international attention for its stunning visual displays, it also had significant negative impacts, including mass mortality among fish and other marine organisms.

Marine scientists from UC San Diego’s Scripps Institution of Oceanography, the National Oceanic and Atmospheric Administration (NOAA), and other organizations seized the opportunity to study the unprecedented event and its impacts on marine life, both in the wild and in aquariums. In a recent study, this multi-institutional team of 34 researchers identified deteriorating water quality — notably prolonged low oxygen conditions — as a significant factor in the mass mortality event. Their findings were published in the journal Elementa, and featured in a special issue focused on the 2020 red tide.

“Red tides are notoriously difficult to predict and study, so the 2020 event presented a unique opportunity for the marine science community to collaborate and use existing infrastructure to figure out what was causing these die-offs,” said lead author Zachary Skelton, a marine biologist under contract at NOAA’s Southwest Fisheries Science Center (SWFSC) and recent graduate of Scripps Oceanography. “Our paper provides valuable insights into how low- or no-oxygen conditions can harm certain marine species, particularly those inhabiting estuaries and shallow coastal areas.”

The study was informed by data from existing long-term observation programs, alongside reports from community members, field surveys, and case studies from local aquariums that use local seawater to sustain their systems. The researchers found a correlation between extreme changes in water conditions, notably dissolved oxygen and pH levels, and the dynamics of the red tide bloom. 

Sensor data along the coastline revealed extreme hypoxic (low oxygen) and hyperoxic (excess oxygen) conditions, especially in estuaries and near-shore coastal environments. These conditions impacted the health of numerous marine species, leading to the documented deaths of thousands of fishes and invertebrates, as well as several seabirds. Case studies from four local aquariums — including Birch Aquarium at Scripps, as well as two experimental aquariums at Scripps Oceanography and one at NOAA SWFSC — indicated that factors beyond large changes in oxygen and pH levels might have contributed to the observed mortality. 

Since the red tide coincided with the early stages of the COVID-19 pandemic, the team had to obtain special permission from UC San Diego and other local institutions and authorities to conduct fieldwork. Once these permissions were secured, Skelton, along with Ben Frable, collection manager of marine vertebrates at Scripps Oceanography, visited multiple beaches and estuaries around San Diego to count, photograph, and measure the dead fish and invertebrates.

Their observations and community reports — shared via social media, email, and the citizen science platform iNaturalist — revealed mass die-offs of fish and invertebrates between late April and mid-May 2020, following sharp drops in oxygen levels. Fish die-offs were disproportionately reported in the La Jolla area (including La Jolla Cove, La Jolla Shores Beach, and Scripps Beach), the Encinitas area, and Agua Hedionda Lagoon in Carlsbad. Many of these locations are enclosed or geographically sheltered areas, which limits mixing and makes it easier for blooms to concentrate.

The red tide harmed many different species, but nearshore and bottom-dwelling species fared the worst. “Many of the species that live on or near the seafloor tend to be less mobile,” said Skelton. “These creatures often stick to their preferred habitats, even while experiencing stressful conditions.”

For instance, the spotted sand bass, usually found in shallow, sandy environments, suffered the highest reported mortality among fish species, with hundreds washing up on Encinitas beaches and at Agua Hedionda Lagoon. Similarly, hundreds of California bubble snails were among the most affected invertebrates. Divers also reported deaths of species like topsmelt, round stingray, sarcastic fringehead, sanddabs, rockfish, and thornback guitarfish, which were observed underwater but did not wash ashore. The authors noted that this red tide event did not seem to harm marine mammals or cause more reported strandings than usual.

Once it was established that a mass mortality event was underway, the team wanted to find out which aspect of the red tide bloom had the biggest impact on marine organisms. Red tides occur when there is a rapid increase or “bloom” in populations of marine algae, typically dinoflagellates or other species of phytoplankton. During the daytime, these organisms photosynthesize by taking up carbon dioxide and producing oxygen. At night, the collective bloom and community respiration draw up the surrounding oxygen while producing carbon dioxide, ultimately causing changes in seawater chemistry across the day/night cycles. At peak bloom, conditions are often hyperoxic for longer periods due to the increased amount of oxygen in the water. As the bloom starts to decline — either due to the natural lifecycle of these organisms or depletion of nearby nutrients — oxygen levels are reduced, often resulting in prolonged hypoxic conditions.

Study co-author and biological oceanographer Lillian McCormick analyzed data from 11 oceanographic sensor packages deployed on moorings off the coast of San Diego. These sensors were deployed at various depths, ranging from 1.5 meters (5 feet) to approximately 100 meters (328 feet), collecting data across estuaries, shallow nearshore environments, and farther offshore.

Shallower waters, particularly within estuaries and lagoons, bore the brunt of the red tide impacts, experiencing prolonged periods of hypoxia. Agua Hedionda Lagoon and Los Peñasquitos Lagoon were the hardest hit, enduring episodes of extreme hypoxia and even anoxia, where there was no oxygen. Construction near Los Peñasquitos Lagoon during the peak bloom led to the complete closure of the lagoon to the open ocean, which likely exacerbated the situation. 

“The bloom was heavily concentrated within those estuaries, and likely worsened at one location by its complete closure for a number of weeks,” said McCormick, a postdoctoral researcher at California Sea Grant and Scripps Oceanography. “These enclosed spaces don’t see as much flushing or movement of the water as we typically see in deeper, open ocean waters.”

The authors were surprised to find that the Scripps Pier sensor, located at a depth of 4 meters (13 feet), recorded intermittent hypoxia between April 30 and May 16, 2020, for a total of 82 hours. “You often see fish die-offs happening in estuaries, or in warm water areas like Florida,” said Skelton. “But open-ocean mortality associated with these hypoxic events is pretty rare in California, so the Scripps sensor provided some unique insight into that event.” 

In addition to field observations, the authors analyzed water quality and mortality rates at four local aquarium facilities, each with different levels of filtration and supplemental oxygenation. As part of this research, members of the Tresguerres Lab at Scripps Oceanography examined the morphological changes in the gills of captive-held Pacific sardines in response to the red tide. Led by marine physiologists Garfield Kwan and Martín Tresguerres, the team employed microscopy and biochemistry techniques to examine the ionocyte, a specialized cell responsible for ion-transport akin to kidneys in mammals. Their findings revealed that sardines increased ion-transport to maintain nominal conditions during red tide exposure.

“This finding is notable because red tide events are difficult to predict and cannot be timed, so experimental data such as ours are very rare,” said Kwan, who is now a postdoctoral fellow at UC Davis. “We were fortunate to have a pre-exposure comparison of sardines due to the long-term sampling nature of the original experiment.”

McCormick and Skelton praised the collaborative efforts of all the authors, emphasizing the significant role each played in making the study possible. “It was a large community effort, with everyone contributing their existing data and working together to deepen our understanding of the issue,” said McCormick, “even when we were limited by the pandemic.”

View the published study to access the full list of 34 co-authors and their affiliated funding sources.

---

[xyz-ihs snippet=”Prepared-by-PK”]

Just like in Mexico, Lanzarote also boasts magical villages that tell the story of a mythical island where human beings live in a friendly coexistence with the elements: sea, wind, land, volcano…

These are unique places that have preserved their original architecture, traditions, history and culture. Would you like to get to know the origins of the sustainable miracle that is on this island? If so, come with us on this immersive visit to four fascinating and unknown places that embody the unique and special essence of Lanzarote.

Femés Visual Magic

Our first destination is Femés (Yaiza), where Arozarena placed his character Mararía, and a village to which Pedro Guerra dedicated a song: “En el silencio, solo los ladridos de los perros” (In the silence, only the barking of the dogs). 

Femés is a historical treasure, home to the first cathedral in the Canary Islands, destroyed by corsairs in 1543 and then rebuilt two centuries later in its current building, the chapel of San Marcial, patron saint of the island. Let your mind travel back to Lanzarote’s not-so-distant past in this walk through the village of Femés, with its rural architecture and its artisan cheese dairies, still maintained by the local farmers.

When you reach the viewpoint, you’ll discover the magic: volcanic views of Timanfaya, the beaches in the south of Lanzarote and the island of Maxorata, sharply visible on clear days.

Savour the scenery. Make the most of your stay in Femés to try some of the local specialities (kid or goat’s meat) in the village restaurants, which themselves have viewpoints overlooking the breathtaking scenery.

Punta Mujeres Coastal life

The name of this village in the municipality of Haría is enough to arouse the curiosity of the visitor. It is said to be due to a group of women who were abandoned here in 1700 by the pirates who had kidnapped them. The resemblance of the surrounding mountains to female silhouettes is also mentioned as a possibility.

Why not visit and draw your conclusions? Come and explore this beautiful northern corner whose proximity to Arrieta gives it a lively holiday atmosphere from Easter to summer. Don’t forget your swimsuit because you’re not going to want to miss out on a dip in the natural pools where there is always a presence of lively groups of families and friends.

The promenade, dotted with coves and terraces, leads to the beach of La Garita, in Arrieta, where you can eat in one of its picturesque restaurants facing the sea. This is the place to try the local produce: limpets, vieja, antoñito (a variety of porgy)…. Fresh seafood and fish never taste better than when you can hear the waves crashing on the very wall on which your table sits.

Land of cactus. The traditional crop of cochineal meanders through the northern landscape in the immense plantations of tuneras (prickly pear cactus), visible from the road through Mala or Guatiza.

Agave is abundant on Lanzarote due to its special climate. The island also produces a healing variety of aloe vera, which is used as a base for cosmetic products. If you are interested in this fascinating desert flora, don’t miss the Cactus Garden, which houses some 4,500 specimens from all five continents.

Mancha Blanca. The miracle that stopped the lava

Legend has it that in 1736 the inhabitants of the island, desperate after years of eruptions that were burying villages and crops, chanted a prayer to the Virgin for help and, at that precise moment, the eruption ceased, saving a plot of land in the middle of the rivers of lava.

The place was named Mancha Blanca, and there the hermitage of Los Dolores was built, which is visited by thousands of pilgrims every 15th of September. It’s worth setting aside a Saturday morning to explore this symbolic location in the municipality of Tinajo.

On the esplanade of the chapel there is a farmers’ market where there is no shortage of local parranda groups playing, and on sale are the organic crops grown in the mineral soil of Lanzarote: grains such as lentils, chickpeas and peas, crops grown on jable such as sweet potatoes, typical local pastries and other produce. You won’t find a better gift to take home to your friends.

Volcanic experience. This is the area that was the origin of the natural wonder that is Lanzarote today and, therefore, you mustn’t miss a visit to the Timanfaya National Park. And to better understand the importance of the historical eruptions, visit the Mancha Blanca Interpretation Centre, where admission is free.

Mozaga. Magic wines

Mozaga is located in the geographical centre of the island, between the municipalities of Teguise and San Bartolomé. This small village of 400 inhabitants, in the heart of the protected landscape of La Geria, is the symbol of the preservation of a wine-producing method that is unique in the world. Its history dates back to 1737, when the farmhouse of Captain Gaspar de Samarines, dedicated to vine growing, was built.

Once again, the volcano determined the life of the island’s inhabitants, who devised a system of cultivation under the same ashes that had destroyed the previous crops. Since then, the region has seen a proliferation of ash-mulched fields and small wineries, whose work is governed by the same rules that nature imposed on their predecessors.

Homage to Manrique. In his desire to pay tribute to this exceptional example of agriculture, the universal artist César Manrique created the Casa Museo del Campesino, a centre where you can explore everything from traditional crafts to local gastronomy. We recommend taking the wine route to visit, stopping off at one of the wineries along the way.

---

[xyz-ihs snippet=”Prepared-by-PK”]

A blanket of organogenous sand makes its way through the wide valley between the Risco de Famara and the villages of Soo and Muñique, creating an unusual landscape with a life of its own.

El Jable is an ecosystem of marine sands that is four kilometres wide, home to endemic flora and fauna and crops like no other in the world. Discover another of our natural treasures through hiking, gastronomy and ethnography.

A bird’s eye view of El Jable

A walk along the line of volcanoes in Soo, in the Chinijo Archipelago Nature Park, is the best way to appreciate the breathtaking beauty of El Jable. First of all, stop for a hearty breakfast at the village teleclub. In Soo, it is still possible to find examples of endemic flora such as the jable star onion (Androcymbium psammophilum) or the common iceplant(Mesembryanthemum crystallinum), from which soaps and dyes are obtained. 

The experience is enriched if you are accompanied by a local guide on the ascent to Pico Colorado. The views allow you to appreciate the Caldera Trasera and, as you wind up the slopes, ancient cisterns, a symbol of Lanzarote’s water culture and traditional architecture.

From the west face of the Montaña de Soo, you can see the path to the summit and a panoramic view of El Jable and the ocean. Let the trade winds gently sway you as they move the jable towards La Tiñosa. The mountain descent is no less spectacular and, on the Peña Juan de Hierro, another discovery awaits you: check out the rock engravings featuring a Lybian-Berber script.

Sweet potato, the jewel in the crown

By now, you probably know why Lanzarote’s rugged, human-tamed land offers such high-quality agricultural production. It’s no coincidence.

We have been making sustainable development a reality on the island for centuries, and this is especially evident in the cultivated land. Under heroic conditions, the farmer produces the liquid fruit of La Geria and, in El Jable, the delicacy of dry land: the sweet potato.

This local version of the sweet potato family is so sublime that it has become a symbol of traditional Canary Island cuisine, and for us, it is as unthinkable to have a sancocho stew without sweet potato as a Christmas without truchas (sweet pasties). If you are a lover of everything gourmet, you are in luck because the sweet potato plays a starring role in nouvelle cuisine. It is worth trying the sweet potato chips or the sweet potato yolk dessert created by chef Luis León.

And why do we claim it as a unique product? Because it can only be cultivated in one traditional way, in the organogenic sand that is the jable, which naturally conserves the humidity of the little rain that falls in Lanzarote.

El Jable’s wonderful harvest doesn’t end here. Visit one of the traditional Canarian restaurants and order one of the dishes based on the pumpkin, papas crías (considered the truffles of the desert), onion, or even watermelon or melon and you will understand why El Jable is one of the island’s best-kept treasures.

Endemic birds

Pipit, houbara bustard and stone curlew are the three winged residents of El Jable’s Special Protection Area for birds (SPA). If you are an ornithology enthusiast, pack your binoculars because in this semi-desert steppe ecosystem you’ll be able to observe these species, the first two of which are endemic.

The houbara bears the name of bustard, but the fact is, it’s not a bustard at all, but the species Chlamydotis undulata. You’ll have to pay close attention to spot it because, despite its large size, the Canarian houbara bustard flits about the territory in the open field and its rare appearances are a here again, gone again experience.

Berthelot’s pipit (Anthus berthelotii) is a relative of the common pipit, although as distant a relative as two and a half million years of solitary evolution will allow.

A visit to the Batateros

And, in the heart of the island, the welcoming village of San Bartolomé stands proudly, embodying the philosophy of the quiet life of the interior of Lanzarote. Its inhabitants are affectionately known as Batateros, guardians of the jable crops. A visit to the Tanit Ethnographic Museum is a must if you want to soak up the ancestral culture that is still alive on the island.

If you’re someone who likes to know a little more about the places you visit, San Bartolomé offers an almost inexhaustible supply of historical testimonies: José María Gil’s gofio mill, the Casa Ajei or the Casa Mayor Guerra, which was the governor’s house during Lanzarote’s se˚ñorial past. One last suggestion: before leaving the village, enjoy an enyesque (snack) under the flame tree on the terrace of the Plaza de la Iglesia, and take the opportunity to take a look at the billboard of the municipal theatre. The Batateros love the stage.

Eco-friendly souvenirs

After so many emotions, you’ll want to take a little piece of El Jable home with you in your backpack. It’s hard to leave the love you’ve only just met. The good news is that the farmers bring their organic produce to the island’s markets.

In Lanzarote, we reserve Sundays for Teguise, which hosts the most important street market in the Canary Islands. Tinajo also holds a farmers’ market in Mancha Blanca, in front of the Los Dolores hermitage. On Saturdays, the craft market in Haría is a good excuse to get to know this beautiful village where César Manrique spent his last years.

In Arrecife, the Church of San Ginés serves as the setting for the Saturday morning farmers’ market, where we like to hang out with the locals in one of the small terraces and taverns in the seaside area. Naturally, San Bartolomé also holds a craft market on the first Sunday of the month.

Warning: you’ll be tempted to pick up wine, jams, sea salt, onions, Lanzarote lentils, aloe vera and more… But it would be better to go home without too much luggage and just come back to the island soon. We’ll be waiting for you HERE!

---

[xyz-ihs snippet=”Prepared-by-PK”]