Parrotfish on the Great Barrier Reef
Parrotfish are a highly abundant subfamily of wrasses that are found on reefs across the world. Named after their beak and colours, parrotfish are an important ecological piece in the GBR due to their feeding habits. Parrotfish are largely herbivores that feed mostly on surface algae but will also eat and digest coral polyps and zooxanthellae as a by-product of algal grazing. Parrotfish are categorized into three different functional feeding groups, which are excavators, (gouge out the substrate) scrapers, (scratch the substrate) and browsers (feed on seagrasses and things living on seagrass). Whilst the excavators, and to a lesser extent, the scrapers, do damage to the coral and the reef that they feed on, it is a minute factor in coral mortality on the reef, and is far outweighed by the benefits they provide. Whilst parrotfish were though of as corallivores for a long time, they were really feeding on the algae growth on the substrate and coral. This means they are a very important algal control factor, as well as reef builder, due to the quantity of rock that is digested, cleaned, and excreted as fresh sand.
Parrotfish social structures are quite varied between species with complicated life cycles. Majority of parrotfish species are sequential hermaphrodites, beginning life as females, then changing to males later in life. However, in some species the males change immediately from females, and others have dedicated breeding females that never change sex. When parrotfish undergo a sex change, they also undergo colour changes which have been proven to be linked to the hormonal changes that occur during this transition. Most species will have one dominant male defending and fertilising a harem of females, until the females grow big enough, change sex, and challenge the male for authority.
Parrotfish also rely heavily on mucus to protect themselves. At night, they will encase themselves in a mucus bubble that presumably prevents their scent from being detected by predators. Even during the day though, their scales are coated with another mucus, which is rich in antioxidants, and believed to assist in repairing external body damage.