Coral reefs & algae have a symbiotic relationship, where single-celled algae (called zoozanthellae) living inside corals provide energy to build the intricate calcium-carbonate structures that host an entire underwater ecosystem (for more on reef-building corals check out this Creature Feature). However, as with most things in life, too much of a good thing can turn bad; too much algae can actually kill off coral cells (known as “coral bleaching”).
Coral reefs use help from herbivores (i.e. plant-eaters), such as fish and invertebrates to keep algae levels in check. Macroherbivores, like green turtles (Chelonia mydas), are the aquatic lawn mowers of the coral reef and are able to munch on copious amounts of marine plant matter, making them an important landscaper in the coral reef ecosystem.
Sketch and fact contributed by Karli Chudeau
Sources: Goatley, C.H.R., Hoey, A.S., & Bellwood, D.R. (2012). The role of turtles as coral reef macroherbivores. PLoS ONE, 7(6), e39979. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0039979