The stoplight parrotfish, Sparisoma viride, is a visually striking marine fish commonly found in the coral reef ecosystems of the tropical western Atlantic Ocean. Its range extends from southern Florida, Bermuda, and the Caribbean Sea to Brazil. These fish are notable for their distinct color phases, which vary with age and sex, with adult males displaying vivid blue and green hues accented by yellow markings, while juveniles typically appear brown and red. Growing up to 22 inches (55 cm) in length and weighing around 3.5 pounds (1.6 kg), the stoplight parrotfish inhabits shallow coral reef waters.
Primary Food Sources
The stoplight parrotfish is primarily herbivorous, with its diet consisting almost entirely of algae found on dead coral substrates. These fish employ a scraping and excavating grazing method to consume various types of algae, including filamentous and turf algae. They particularly favor large, sparse algal turfs that grow on carbonate surfaces and are often inhabited by endolithic algae, which bore into the substrate. This preference is due to the high protein content and energetic value these specific algal types offer.
Beyond algae, the stoplight parrotfish also consumes detritus and material from dead corals. Although primarily herbivorous, adult stoplight parrotfish can be facultative corallivores, occasionally feeding on living corals like Montastrea annularis and Porites porites. When consuming coral, they do not derive nutrients from the hard coral skeleton itself, but rather from the coral polyps and the symbiotic algae, known as zooxanthellae. Notably, the stoplight parrotfish consumes significantly more coral compared to many other parrotfish species.
Specialized Feeding Structures
The stoplight parrotfish has unique anatomical adaptations for its specialized feeding habits. Its common name is derived from its beak-like mouth, which is formed by fused teeth. In the Sparisoma genus, the upper teeth are structured to fit precisely inside the lower teeth, allowing for efficient scraping. These fused teeth and powerful jaw muscles are used to effectively scrape and excavate algae from hard coral and rock surfaces.
Further aiding their digestion, stoplight parrotfish have a set of plate-like pharyngeal teeth located in the back of their throat, collectively known as the pharyngeal mill. This specialized grinding apparatus crushes the ingested coral skeletal material. The material is then processed through their digestive system.
Ecological Impact of Their Diet
The feeding activities of the stoplight parrotfish have a substantial ecological impact on coral reef ecosystems. They play a significant role as bioeroders, contributing to the health and maintenance of reef habitats by removing algae that can overgrow corals. Their grazing helps prevent algal dominance, allowing corals to thrive and facilitating reef growth.
A notable consequence of their diet is their contribution to sand production. As they graze, they ingest indigestible calcium carbonate from the coral substrate, which is then crushed by their pharyngeal teeth and expelled as fine white sand, a process known as bioerosion. A single large adult stoplight parrotfish can produce up to 1,000 pounds (450 kg) of sand annually. These fish often return to specific areas to excrete, which can lead to the formation of distinct “hills” of white sand on the reef floor. The highest rates of bioerosion by these fish occur on shallow reef sections, particularly on substrates with lower skeletal density that are infested with endolithic algae.