Scientists tie Florida phytoplankton flowers to starving dolphins

In 2013, 8% of Bottle North Dolphins in Florida’s Indian River Lagoon passed away. Currently, it is being investigated that dolphins may have been starved as important habitats for nutritious prey have been destroyed by phytoplankton flowers.

This bloom was driven by the accumulation of fertilizer lagoons, drainage from septic tanks, and other by-products of human activity rich in nutrients such as nitrogen and phosphorus.

“We have linked mortality and malnutrition to energy reduction following dolphin diet changes,” said Dr. Charles Jacoby of Florida’s Flood Hub for applied research and innovation in response to the authors of a marine science frontier article.

“We linked dietary changes to changes in prey availability, and prey changes to abundance of sea grasses and a reduction in the entire system of drifting macroalgae. These reductions were driven by intense, extensive, long-term, long-term shading from phytoplankton.”

Signs of trouble

In 2013, scientists monitoring the Indian River Lagoon noticed that dolphin populations were struggling. Of the 337 dolphins they observed, 64% lost weight, 5% weakened, and 77 died.

“The extraordinary death event is an unexpected and outstanding event with significant deaths of any marine mammal,” explained Megan the Stolen from the Blue World Research Institute, the first author of the article. “The 2013 event was characterized by significant increases in mortality and extensive evidence of malnutrition.”

Bottlenor dolphins are large, long-lived animals that eat relatively large amounts of prey of many different species. In other words, disruption to local ecosystems can affect them. In this case, researchers suspected that phytoplankton blooms in 2011, fueled by nutrient-rich byproducts of human activity that flow into the lagoon and accumulates, caused significant changes.

Bloom shades the bottom-dwelling sea grasses and macroalgae that are found in most of the lagoon, killing these important habitats for dolphin prey, potentially impairing the dolphin’s hunting capabilities. However, it is difficult to prove what dolphins are eating. Observing dolphins feeding on the surface of water does not give birth to a complete diet.

Instead, the researchers focused on isotopic analysis of muscle biopsies collected from chain-covered dolphins between 1993 and 2013.

The stable isotope ratio of carbon to nitrogen in dolphin muscles represents a mix of similar proportions of prey, so using prey reference values, scientists can track dietary changes over time and compare them with modern fisheries and large presences.

Ripple effect

Scientists have discovered changes in the diet of dolphins. From 2011 to 2013, they ate more sea bre and less rare fish.

This was consistent with fisheries surveillance, which documented changes in availability of the two species. That is, fewer Mares and Sea Bream. It also coincided with the abundance of seagrass and macroalgae habitats over the same period. The transition from rare fish to sea bream meant that dolphins needed to eat about 15% more prey to acquire the same amount of energy.

“The widespread presence of dietary changes and malnutrition suggests that dolphins struggled to catch all types of adequate prey,” said co-author Wendy Noke Darden of the Hubs Seaworld Research Institute.

“The loss of major structural habitat may have reduced overall foraging success by causing changes in prey richness and distribution.”

Data were also tallied with causes of death recorded due to stuck dolphins. Between 2000 and 2020, malnutrition caused 17% of all recorded deaths, but in 2013 this figure rose to 61%.

“Every study has its limits,” warned Dr. Graham, a co-author worthy of the University of Central Florida.

“We did not have data on the proportion of stable isotopes in all prey that dolphins ate between 1993 and 1999. As such, we were unable to fully explain the dietary changes observed from that early period to 2000 to 2010. Furthermore, the link between malnutrition and dietary changes was enhanced by stable isotope data from the muscles of surviving dolphins.”

“Phytoplankton flowers are part of a productive ecosystem,” Jacoby said.

“Feeling flowers that are abnormally intense, extensive, or long-term nutrients that enter the system produces harmful effects, and in most cases people’s activities promote these overloads.