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Ecosystem Overview: Structure & Function

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Ecosystem Overview: Structure & Function

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Coral reefs are complex, biodiverse marine ecosystems built by coral polyps that secrete calcium carbonate to form reef structures. These reefs support thousands of species by providing shelter, food, and breeding grounds. They are found in warm, shallow waters, especially in the Indo-Pacific and Caribbean regions (Kaiser, Attrill & Jennings, 2020).

These ecological oases have high biodiversity and productivity despite the low nutrient availability in surrounding waters (Moberg & Folke, 1999). Interestingly, despite their high productivity, most of the production is recycled within the reef, and not much coral production is consumed directly (Kaiser, Attrill & Jennings, 2020).

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Zooxanthellae are photosynthetic algae that live inside coral tissues. Through photosynthesis, they convert sunlight into energy rich compounds that the coral needs. In return, the coral provides nutrients and a safe sunny environment for the zooxanthellae.

The role of the Zooxanthellae is to support coral growth and reef-building. They contribute up to 90% of the coral’s energy needs! Sunlight is vital to for the zooxanthellae to photosynthesize, which means coral reefs are rarely found at depths below 30 meters (Kaiser, Attrill & Jennings, 2020).

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At the heart of coral reef ecosystems lies a powerful mutualistic relationship between reef building corals and zooxanthellae. These microscopic algae perform photosynthesis, converting sunlight into sugars that provide up to 90% of the coral’s energy needs. In return, corals provide the algae with carbon dioxide, nitrogen waste, and shelter in the corals soft tissues, where sunlight is abundant. The Zooxanthellae allow coral reefs to thrive in environments that are otherwise nutrient poor (Muscatine & Porter, 1977).

When corals are stressed, they have a stress response called coral bleaching. This is when the coral ejects the zooxanthellae and the white skeleton of the coral is visible. This decreased the growth and reproductive output of the coral reef. Prolonged coral bleaching leads to the death of the coral, which then leads to ecosystem collapse (Baker, 2003).

Coral reefs are hotspots of mutualistic relationships, making them a unique ecosystem. These partnerships help maintain the reefs structure and function. Cleaner wrasses remove parasites from larger fish, getting a meal while improving the health of the reef community (Jojoa, 2024). Clownfish receive prey to eat and protection among the anemones stinging tentacles, while they defend the anemone from predators like butterfly fish and get rid of harmful parasites (Marine Sanctuary Foundation, 2023).

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Agricultural runoff, which carries excess nutrients like nitrogen and phosphorus from fertilizers into the ocean, is a significant human-induced threat to coral reef ecosystems. These nutrients fuel the overgrowth of algae on the reef surface, which can outcompete and smother corals by blocking sunlight and disrupting the delicate coral zooxanthellae balance (Fabricius, 2005).

The excess nutrients can trigger harmful algal blooms and increase the frequency of coral diseases. Coral are a foundation species, building the foundation on which the rest of the ecosystem depends. This disruption in nutrient flow and energy relationships can lead to reef degradation, reduced biodiversity, and the collapse of the entire ecosystem if left unmanaged