The first question you might have is “what do corals eat?”. Coral polyps are living creatures that produce 95% of their food from algae. In exchange for their food, algae provide carbon dioxide, phosphorus, nitrogen, and a safe place to live. Coral polyps and algae can share nutrients in a complex way, through a system called the Coenosarc, which connects the stomachs of the algae and coral polyps.
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Seagrass
Most fish use seagrass as a nursery or sanctuary. They feed on tiny creatures found within its blades. However, many types of seagrass are also used by other species as a primary food source. For example, sea urchins and crabs often feed on seagrass leaves. Invertebrates such as snails and small fish also feed on seagrass. It is a vital habitat for many marine species, including corals.
In addition to being a food source for fish, seagrass is a habitat for many marine animals. Manatees, a type of large aquatic mammal, is directly linked to seagrass beds. These mammals are capable of consuming up to 15 percent of their body weight in seagrass. Manatees weigh from 1,000 to 3,000 pounds and can eat up to 150 pounds of seagrass daily. Corals eat seagrass, too, although they are not known to eat it directly.
Nematocysts
We may not understand how a coral colony uses its nematocysts to survive, but there are several possibilities. In the absence of a predator, nematocysts are most likely used for prey capture, defense against predators, and territorial competition. The first hypothesis suggests that the density of nematocysts in a coral colony may be related to a coral’s defensive and offensive capabilities.
The bioactive arsenal of cnidarians includes many proteins, peptides, and short neurotoxins. Many anthozoans also have hemolysins and phospholipases, which are classified as secondary metabolites. This study provides an example of how this system is involved in coral metabolism. The cnidarians themselves are a key player in this system.
Interestingly, nematocysts are arranged in a spiral pattern along a coral’s tentacles. The spiral configuration can help a coral to subdue its prey. Among these creatures are cubozoans, which include the most venomous cnidarians. The nematocysts are also a major source of calcium carbonate for corals.
Dissolved organic matter
In this study, the researchers measured the DOM and POM concentrations of both algae and corals. They then determined the ratio of DOM to POM and the accumulation rate of these two compounds. They also examined the release rates of newly synthesized organic matter by symbiotic algae. These findings support previous observations that algae and corals consume a substantial amount of dissolved organic matter.
The amount of DOM that corals and algae consume was investigated by incubating sponges in different combinations. In contrast, the amount of DON that corals and algae consume was significantly higher in HMA sponges than in LMA algae. Furthermore, DOM was assimilated at a rate of three to eight times greater than that of coral and diatom-DON. This finding has implications for understanding the composition of the coral reef.
Zooplankton
Zooplankton is a natural food source for many types of marine organisms, including corals. During the day, zooplankton is the most abundant type of organism, while at night, it is mostly made up of crustaceans. Crab megalopae and zoea are the most abundant at night, making up anywhere from 31-71% of all organisms.
The vertical distribution of zooplankton over coral reefs is complex and varies greatly depending on the types of reefs and environmental factors. Since zooplankton are the main component of coral reef food webs, knowledge of their behaviors and habitats is crucial to fully understanding their ecology and community dynamics. Here are a few examples of zooplankton and their roles on reef ecosystems:
Researchers have quantified the amount of plankton that corals capture using histological methods. Using fixed coral polyps and dissection, researchers can score them for how many prey items they consume. Although this method provides an accurate estimate of plankton grazing by corals, it is not a perfect model because some prey items degrade rapidly before they can be fixed. Another way to assess the volume of prey that corals consume is to use video analysis.
