The whitespotted eagle ray (Aetobatus narinari) possesses powerful jaws and plate-like teeth that allow it to eat a wide range of items. In Florida's Indian River Lagoon, hard clam farmers have viewed this species as a threat to their production and profits. However, there is limited information available on their life history, including their diet, despite being protected in Florida and globally designated as “endangered.” Previous observations have shown their diet varies depending on their location, with different types of clams and marine snails being consumed.
Understanding the diet of marine predators is typically achieved through visual observations, but it's challenging for shell-crushing predators like the whitespotted eagle ray because they consume the soft tissues of their mollusk prey, leaving behind a mix of mushy materials in their gut. Decoding their recent meals is a formidable task.
Florida Atlantic University's Harbor Branch Oceanographic Institute and Mote Marine Laboratory & Aquarium conducted a new study, providing the first quantitative description of the whitespotted eagle ray's diet in U.S. coastal waters.
Through a combination of visual-based gut content analysis and DNA barcoding, a technique that identifies species using specific regions of the genome, researchers have discovered detailed feeding patterns of the whitespotted eagle ray. Their findings, published in the journal Fishes, have significant implications for shellfish enhancement efforts and species management.
The study reveals that the whitespotted eagle ray has a much broader diet than previously known, and it varies across different regions in Florida. Interestingly, they did not find commercially or recreationally important bivalves like hard clams, oysters, or scallops in their diet. Instead, they predominantly consumed cockles and wedge shells, which are not majorly significant in Florida's shellfish industry.
However, the rays also preyed on predatory conchs, known to harm important bivalve populations, showcasing their multi-faceted role in the food chain. They both feed directly on bivalves and control the predators of these valuable resources.
Matt Ajemian, Ph.D., the senior author and director of the Fisheries Ecology and Conservation Lab at FAU Harbor Branch, stated that the dietary data from their study fills knowledge gaps about whitespotted eagle rays and sheds light on their interactions with shellfish enhancement activities in Florida's coastal waters. The findings suggest that the rays can play a beneficial role in reducing predation threats from predatory snails on bivalve shellfish operations. However, this interaction might be complex, depending on the rays' size, as they consume more bivalves when young and more conchs and whelks as they grow.
The study observed 33 different prey items in the gut contents of 50 whitespotted eagle rays collected from four locations in Florida. This includes hermit crabs, but it's unclear if their consumption was intentional or incidental.
Understanding the dietary preferences of whitespotted eagle rays is valuable in studying toxin pathways, especially in ecosystems like the Indian River Lagoon during harmful algal blooms. The rays are likely exposed to toxins from blooms, as toxins transfer through both the bivalve and gastropod prey identified in the study.
Source: Florida Atlantic University