Algorithm for algal rhythms

January 31, 2021

An atlas of harmful algal blooms across the Red Sea reveals their link with industrial aquaculture and how these blooms have changed in recent decades.

Warming oceans and anthropogenic pollution have led to more frequent and extensive harmful algal blooms (HABs) worldwide. These rapid surges in productivity occur when algae suddenly experience advantageous conditions, usually an influx of nutrients, and take over their environment, suffocating other marine life and spreading toxins through the food chain. These blooms harm wild and farmed fish and reduce marine biodiversity.

"HABs are a global problem," says Elamurugu Alias Gokul, a Ph.D. student at KAUST, "and are often associated with socio-economic and environmental issues that affect public health, fisheries and aquaculture."

The Red Sea supports the countries situated along its shores through its thriving coral reefs, excellent biodiversity and growing aquaculture industry. "Aquaculture is essential for the economic prosperity of the Kingdom of Saudi Arabia," says Gokul, "but it is also a major source of marine pollution." Despite growing concerns that HABs are exacerbated by climate change and aquaculture, there is a lack of studies dedicated to understanding their seasonal and interannual variability across the region.

Gokul and his colleagues analyzed high-resolution satellite data to map HABs across the Red Sea between 2003 and 2017. They studied changes in ocean color to determine the presence or absence of HABs and used remotely sensed concentrations of chlorophyll-a -- a photosynthetic pigment in aquatic algae -- as a proxy for phytoplankton abundance. As the researchers expected, most events occurred during warm summer months in the southern Red Sea, where they were also longer lasting (up to 32 days) and more widespread (up to 5000 square kilometers), possibly due to the monsoon winds that drive nutrient-rich waters from the Indian Ocean.

The researchers then focused on the area around NAQUA, the largest fish farm in the Red Sea, and compared variations in HABs with aquaculture production. Between 2002 and 2010, annual aquaculture output increased from around 4000 tonnes to 22,370 tonnes, and the average size of HABs near the site grew from 65 square kilometers to 392 square kilometers. "The high chlorophyll concentrations in the vicinity of the facility's discharge point suggest that elevated nutrients from aquaculture waste have contributed to the spread of HABs," says Gokul.

The team is already developing an algorithm that can distinguish between individual phytoplankton species. "This information is vital for understanding which species were responsible for past HAB outbreaks across the Red Sea," adds Ibrahim Hoteit, who oversaw the research. "But we also intend to develop an automated remote-sensing system that can detect and report HABs in real time."

These remote-sensing tools could help identify and monitor areas at higher risk from harmful algal blooms, particularly around aquaculture facilities, helping the development of a sustainable waste management plan that protects the marine environment and the future of fisheries in the Red Sea.

King Abdullah University of Science & Technology (KAUST)

Related Fisheries Articles from Brightsurf:

Assessing El Niño's impact on fisheries and aquaculture around the world
New report presents the main regional consequences caused by the five types of the climate pattern.

Dissolved oxygen and pH policy leave fisheries at risk
In a Policy Forum, ''Dissolved oxygen and pH criteria leave fisheries at risk'' published in the April 24 issue of the journal Science, Stony Brook University's Dr.

Fisheries management is actually working, global analysis shows
Nearly half of the fish caught worldwide are from stocks that are scientifically monitored and, on average, are increasing in abundance.

Meeting the challenges facing fisheries climate risk insurance
Insurance schemes with the potential to improve the resilience of global fisheries face a host of future challenges, researchers say.

Healthy mangroves help coral reef fisheries under climate stress
Healthy mangroves can help fight the consequences of climate change on coral reef fisheries, according to a University of Queensland-led study.

Study champions inland fisheries as rural nutrition hero
Researchers from MSU and the FAO synthesize new data and assessment methods to show how freshwater fish feed poor rural populations in many areas of the world.

For global fisheries, it's a small world after all
Even though many nations manage their fish stocks as if they were local resources, marine fisheries and fish populations are a single, highly interconnected and globally shared resource, a new study emphasizes.

New study maps how ocean currents connect the world's fisheries
It's a small world after all -- especially when it comes to marine fisheries, with a new study revealing they form a single network, with over $10 billion worth of fish each year being caught in a country other than the one in which it spawned.

Federal subsidies for US commercial fisheries should be rejected
A pending rule change proposed by the US National Marine Fisheries Service would allow the use of public funds to underwrite low-interest loans for the construction of new commercial fishing vessels.

Sustainable fisheries and conservation policy
There are roughly five times as many recreational fishers as commercial fishers throughout the world.

Read More: Fisheries News and Fisheries Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to