Hotter seas lead to coral bleaching along Colombia’s coast, 2023 expeditions find

Coral bleaching is on the rise along Colombia’s Caribbean coast, according to the results of several expeditions made by Corales de Paz, an NGO that works to conserve and restore the South American country’s coral reefs. The NGO surveyed coastal coral reefs July 27-31, 2023, off the towns of Rincón del Mar, Pico de Náufrago and Canto del Mero.

The NGO found that 25% of the hard coral colonies showed some degree of bleaching. In impacted colonies, the percentage of bleached tissue was around 52%, indicating a moderate-to-high level of damage.

Coral bleaching is caused by hotter ocean temperatures due to climate change, which, combined with pollution and ocean acidification, severely impacts the corals. Coral reefs are key to the survival of around a million species that contribute to the food security of numerous coastal communities.

Bleaching occurs when corals become stressed and expel the tiny algae that live inside them, which provide up to 80% of their nutrition.

“When [the algae] are expelled, the corals no longer have anything to eat. If high temperature conditions persist for a long time, the corals can die of hunger,” explains Laura Cotrino, scientific director of Corales de Paz.

Losing hard coral reefs has a domino effect, resulting in a massive loss of biodiversity. It also impacts the economy due to a loss of profits from tourism and fisheries.

Alert in Colombia’s Caribbean coast

The July expedition to Rincón del Mar found that high temperatures in the Gulf of Morrosquillo had led to bleaching events. During the monitoring, the temperature was around 31° Celsius (87.8° Fahrenheit), which was consistent with satellite information on the sea surface temperature provided by the organization Aqualink. A type 1 alert was issued in the Gulf of Morrosquillo as a result of the weeks-long high temperature. The type 1 alert means probable coral bleaching. In September, the alert was upgraded to type 2, meaning significant coral bleaching and loss may occur.

Corales de Paz shared the information from its first expedition with environmental authorities and asked to expand monitoring efforts to nearby areas so that stakeholders could make informed decisions and take corrective actions to counter the bleaching events.

Given that the expedition marked the first sampling carried out in the area, Corales de Paz had no previous data against which to compare their findings. It was therefore not possible for the organization to confirm how the situation compared with the past, according to Cotrino. What they are concerned about is the existence of coral bleaching and, she says, that’s something to pay attention to.

Corales de Paz has also carried out monitoring in other areas along Colombia’s Caribbean coast, such as offshore from the cities of Santa Marta and Varadero as well as the island of Providencia

Providencia showed the least damage, with just 7% of the corals sampled showing signs of bleaching.

“The reef sampled in Providencia was found in a very healthy state overall — the results show good coral cover and a good diversity of fish,” says Juliana Rodríguez, manager of the Corales de Paz’s Energy Reef Project.

For Rodríguez, this is a positive finding and shows that the reef is highly resilient and has recovered from the impact of Hurricane Iota, in November 2020, which dumped large amount of sediments.

“We think that, after the hurricane and all the sediments it brought, the reef has recovered quite well and has a high degree of resilience,” says Rodríguez.

According to Cotrino, healthy reefs can reduce the force of waves on coastal communities up to 97%, reducing the potential destruction of climate-related storms. Losing coral ecosystems means losing important ecosystem services, among others, such as food security and tourism.

In Santa Marta, investigators found a more complicated situation. Sampling in 2023 at Punta Venado found that 28.5% of the corals were bleached, with the average area of bleached corals per colony reaching 30.8%.

The group has monitored the Varadero area in Cartagena Bay for four years. Although the resilience of its reef continues to surprise investigators, they say the increasing sea temperature is beginning to seriously affect the reefs.

Varadero’s coral reefs are located in the mouth of the Canal del Dique (an artificial fork of the Magdalena River), an area where coral reefs are unexpected due to the lack of light penetrating the water because of excess nutrients, sediments and pollution. “You wouldn’t expect to find them but they are there,” Cotrino says.

In Corales de Paz’s last expedition, carried out between Aug. 24 and 25, divers found coral coverage of 41% at Varadero, a significant percentage when compared with other areas such as Santa Marta and Providencia. While a surprising find, there is no question that hotter water is impacting the coral reefs.

In total, the investigators found that 40.4% of colonies in the 1,600 square meters (17,222 square feet) sampled showed signs of bleaching, with most of the colonies about 66.8% bleached.

As in the case of Rincón del Mar, the results in Varadero led the NGO to issue an early warning of coral bleaching as well as a recommendation to expand monitoring efforts to nearby areas. They also temporarily suspended coral restoration projects to avoid further losses and allow the ecosystems to recover.

Temporarily pausing restoration

Along Colombia’s Caribbean coast, different restoration projects are being implemented with an aim to increase coral cover. However, when the sea temperature is above normal levels, such efforts are wasted. According to Cotrino, it is important that environmental authorities distribute this information to those involved in carrying out such projects, so that they can temporarily pause activities.

Cotrino said that restoration involves growing coral fragments in nurseries — a process known as microfragmentation — until the corals mature and are ready to be moved back to restoration sites. The transplanting process stresses the corals, adding to the stress caused by the increase in sea temperature. She adds that environmental authorities should monitor coral reefs to identify which coral reefs are most resilient against warming temperatures and which coral species are most successful in restoration.

According to Cotrino, although coral bleaching is occurring, many colonies remain healthy. These healthy colonies should be monitored so that if the sea temperature returns to normal, researchers can gain a better understanding of how some colonies survive heat and adapt.

According to Rodríguez, the regional environmental authorities have responded positively to the monitoring data, enabling Corales de Paz to take early measures. The group shared all results with the relevant environmental authorities, whom the organization relies on for assistance with their expeditions. The authorities are now being trained on Reef Check protocols, which are used by teams of citizen scientists in more than 40 countries worldwide through a network of divers (known as EcoDivers), conducting more than 600 studies annually to monitor the coral reef health.

There is ongoing concern about the increase in coral bleaching, with the warmest day ever recorded globally in the ocean taking place on July 31, 2023. The scientific community announced that the global surface water had reached 20.96°C (69.73°F), an increase of 0.5°C (0.9°F) compared with its average temperature.

According to climatologist Martín Jacques-Coper, an academic in the Department of Geophysics at the University of Concepción, a warming of 0.5°C can quickly displace some species. Although species are accustomed to some temperature variation, they cannot survive in their natural habitat if changes are too much.

Cotrino says they would like more people to report on corals and become involved with coral monitoring activities. She says that more eyes on the water would shed light on what is really happening to Colombia’s coral reefs.

 
Banner image: In Varadero, 40.4% of coral colonies show signs of bleaching, most of which are 66.8% bleached. Photo courtesy of Corales de Paz.

This story was reported by Mongabay’s Latam team and first published here on our Latam site on Sept. 29, 2023.