Why the shores of the Red Sea turn pink every year

Eilat is the southernmost city of Israel, located on the Gulf of Aqaba in the Red Sea. It is known for its warm climate, coral reefs, and vibrant tourism industry.

Each year in March and April, visitors to Eilat can witness a stunning spectacle. The shores turn pink due to millions of tiny crustaceans with large eyes. These organisms, identified as amphipods, belong to the order Amphipoda.

A recent study provides new insight into this unusual phenomenon. The research was led by Professor Tamar Guy-Haim from Israel Oceanographic and Limnological Research (IOLR), in collaboration with Dr. Bracha Farstey from the Interuniversity Institute for Marine Sciences in Eilat.

Pink shores on the Red Sea

The pink color of amphipods comes from carotenoid pigments that they obtain through their diet.

The researchers used an integrative taxonomy approach, combining genetic analysis with morphological identification, to classify these creatures.

The team also examined environmental factors contributing to their mass mortality, which happens yearly during the same months.

“Like in a detective mystery, we tested several hypotheses,” explained Professor Guy-Haim. “Many amphipods exhibit a unique reproductive strategy known as semelparity, where reproduction occurs only once in their lifetime, after which the females die, often simultaneously.”

“However, our analyses showed an almost equal ratio of males to females, along with individuals of different sizes, allowing us to rule out semelparity as the root cause.”

Environmental stressors and amphipod mortality

Climate change and marine heat waves have caused mass die-offs in the past. In the summer of 2017, sea temperatures in Eilat rose by over 4°C in just two and a half days, leading to mass coral reef fish deaths.

However, the researchers found no unusual temperature spikes during the amphipod mortality events.

“Sometimes, environmental stressors increase susceptibility to parasites and pathogens,” noted Professor Guy-Haim. “This has been observed in reef fish and the long-spined sea urchin in Eilat. However, we found no supporting evidence for this hypothesis either.”

A possible natural cycle

To dig deeper, the researchers reviewed scientific literature and discovered a similar event from March 1977. Back then, amphipods covered the shores of Aqaba in large numbers, suggesting this phenomenon might be part of a natural cycle.

Previous studies in the Gulf of Aqaba have documented ocean currents known as eddies. These circular currents can either bring deep, nutrient-rich waters to the surface (upwelling) or push surface water downward (downwelling).

Amphipods in strong ocean currents

In the Northern Hemisphere, cyclonic eddies rotate counterclockwise, pulling deep waters to the surface. In the northern Gulf of Aqaba, these currents strengthen between November and April, becoming up to ten times faster than normal surface currents.

“We hypothesize that the amphipods were trapped in a cyclonic eddy in the northern Gulf and transported by the currents toward the shore,” explained Professor Guy-Haim.

“In Hawaii, a mass mortality event of the same amphipod species was documented following the formation of a cyclonic eddy.”

“This is currently our leading hypothesis, but further research is needed to better understand the relationship between current dynamics and such phenomena in the Gulf of Aqaba and other marine systems worldwide.”

Amphipods’ role in marine ecosystems

Amphipods hold an essential place in marine food webs. They serve as a food source for fish, seabirds, and even whales. Understanding their life cycle and movement patterns helps researchers study larger ecological processes in marine environments.

This ongoing research could reveal more about the natural forces shaping marine life. Future studies may offer deeper insight into how ocean currents influence marine species worldwide.

Potential impacts on marine biodiversity

When large numbers of amphipods die, it can affect the ocean ecosystem in different ways.

If too many amphipods disappear, animals that eat them – like fish and seabirds – might struggle to find enough food. This could change how these animals feed and survive.

Scientists are studying whether these deaths harm local marine life or if animals have adapted to this cycle over time. If this happens regularly, some species might rely on these seasonal die-offs as a food source.

Further research on amphipods

Understanding amphipod population dynamics in the Red Sea can help scientists monitor broader ecological trends.

Researchers plan to continue tracking amphipod movements and mortality patterns in the Gulf of Aqaba. They aim to determine whether these events are purely natural or if human activities and climate shifts play a role.

Future studies could focus on how amphipods respond to environmental stress and whether their deaths influence marine food webs. With better data, scientists can predict changes in marine ecosystems and protect species affected by shifting ocean conditions.

The study is published in the journal Ecology and Evolution.

Image Credit: Omri Amosi, Israel Nature and Parks Authority

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