The mysterious disappearance of great white sharks in South Africa’s fake bay has triggered a ripple effect on the entire marine ecosystem, according to a groundbreaking 20-year study published this week in the field of marine science.
Researchers at the University of Miami have documented how these apex predators’ deficiencies disrupt the delicate balance of marine organisms, while the effects of the effects are pending through multiple food networks to confirm long-term ecological theories about predator relations.
“This loss of iconic apex predators has resulted in an increase in sightings of cape seals and septa sharks, which in turn coincides with the decline of species they rely on for food,” said Dr. Neil Hammerschlag.
The study began in 2000 and tracked a sharp decline in white shark populations since 2015, eventually reaching a complete disappearance from the region by mid-2018. Although the researchers cannot point out the exact reason, they noted that sharks have caught sharks in conservation nets for years, and the latest predation of orcas may have caused their disappearance.
What happened next was how the response of marine ecosystems disappeared when it was rarely seen. After the white shark disappears, the cape seal (the shark’s shaped prey) appears sharply. Reports of seal sightings in the region increased by 520%, and SEALs began to be far ahead of the previous ones within the bay.
Seals break through their hunting activities, so sharks don’t have to worry, resulting in horned mackerels being a key prey for SEALs. The team recorded 44% of the summer population of these fish.
Meanwhile, seven g of sharks (avoided the area due to the predation of white sharks) to fill the ecological gap. Before the white sharks refused to become a common sight, their presence was completely absent from the ship-base investigation.
This influx of the seven-g shark created its own cascade effect. Smaller shark species used as prey, including pajama Catsharks and Smooth Hund sharks, fell by 72% and 42%, respectively.
“Using underwater video surveys for more than a decade has provided us with snapshots of food webs before and after the Fake Bay disappears,” explains co-author and former graduate student Yakira Herskowitz. “The number of individuals of a given species recorded in the video will not only inform us of their numerical abundance, but also their behavior, as species that increase in predation risk often become more elusive and therefore have less chance of detection on our cameras.”
The study is strikingly, it provides real-world evidence supporting the “nutrition cascade” theory, an idea that changes at the top of the food web can trigger the ripple effect through lower levels. Previous research on this cascade in marine environments has been limited, mainly due to the challenges of studying vast marine ecosystems.
The team used a variety of methods to document these changes, including standardized ship-based surveys around Seal Island, citizen science observations, and an underwater video station located in the Fake Bay.
The magnitude of these ecological changes varies in a pattern consistent with the theory of trophic cascade. The biggest changes occur in species directly affected by white sharks (seals and septagos), with smaller effects gradually observed in species below the food chain.
Although the study focuses on a bay in South Africa, its implications extend globally. Shark populations face pressures from fishing, habitat loss and climate change around the world. If the wrong bay scenario plays a role in other marine ecosystems, the consequences can be far-reaching.
“Without these apex predators to regulate the population, the measurable changes we see may have long-term effects on ocean health,” Hammerschlag noted.
These findings highlight the key role Apex predators play in maintaining marine biodiversity and highlight the need to increase efforts to protect these important species before more ecosystems suffer similar damage, a sober reminder that in essence everything is connected.
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