The Life and Times of Parrotfishes (Family Scaridae)
Parrotfish are an interesting and important part in the ecology of coral reefs. Their hermaphroditic lifestyle adds a twist to the way we think about fish biology. The different sexual stages add an array of different colors to the already dazzling display of contrasting shades of colors that occur on the reef (this can also add to identification problems). Parrotfish are one of the many herbivorous creatures that control algal populations on dead coral substrates which keeps algae from growing on living corals that make up the reef. This activity helps prevent algal blooms that cause coral bleaching, an event in which the symbiotic algae that live within the coral skeleton leave and the coral die as a result. Their diverse and distinctive foraging, social, sexual, and defense behaviors play a crucial role in maintaining the health of living coral reefs.
The food of choice for most parrotfish consists of algae. Preferred food types include large and sparse turfs of endolithic algae that grow on carbonate substrates. Foraging preferences were found in one study to be based upon nutritional quality of different food types. Endolithic algae constitute a major source of protein and energy for parrotfish that use a scraping technique to acquire food (Bruggemann et. al. 1994). Interestingly, defense mechanisms to avert herbivorous behavior have developed in several different species of algae. These defenses include calcification. Some of the species that produce calcium carbonate as a defense mechanism possess secondary metabolites that inhibit the ability of the herbivore to alter the deterrent compound (Hay et. al. 1994). In one study it was concluded that calcite alone does not deter the feeding behavior of parrotfish, but with the addition of a known secondary metabolite (rhinocephalin) feeding by parrotfish decreased almost to zero (Hay et. al. 1994).
Foraging usually occurs by day and many species spend up to 90% of their time foraging, with the foraging area ranging in size from 250 to 800 square meters (Bruggemann et. al. 1994). The major finding of the Bruggemann pilot study was that Sparisoma viride and Scarus vetula feed almost completely on algae that accumulates on dead coral heads, with only occasional observations being made of bites being taken on living corals. It was also noted that the feeding behavior by these two species on macro algae was very selective, with some species being totally excluded from the diet while the feeding patterns observed on most endolithic algal species seemed to be non-selective (Bruggemann et. al. 1994). This study found that, out of the several different species of macro algae that were eaten by this parrotfish species, brown algal species tended to have higher nutritional value than red algal species. However, blue-green algae or cyanobacteria, which is considered an endolithic alga, was found to have a higher nutritional value than either type of macro algae, and therefore seemed to be the preferred food type for the parrotfish species studied (Bruggemann et. al. 1994).
Bruggemann also further studied the difference in the foraging behavior of the juveniles and adults of the two species S. vetula and S. viride. The adult and juvenile forms of Scarus vetula did not leave any grazing scars behind. The adult form of Sparisoma viride left behind large grazing scars, but the juvenile of this species did not. Competition between the two species for food sources, endolithic and macro algae, is relatively low because each species utilizes these food resources differently and grazes on these types of algae in very different places. S. vetula seemed to prefer grazing on flat surfaces while S. viridae seemed to prefer grazing on concave surfaces (Bruggemann et. al. 1994). In areas where the species overlap, S. vetula was found to take much smaller bites and were usually only able to harvest the macro algae which left the majority of crustose and endolithic algae behind for S. viridae (Bruggemann et. al. 1994).
Parrotfish have a diverse social and sexual behavior that includes territorial and non-territorial groups. Territorial groups consist of one supermale or terminal male and one to three females. Non-territorial groups have been noted to have numbers reaching 54 or higher and the sex ratio and behavior is extremely variable consisting of females and juvenile or transitional males (Girolamo et. al. 1999). Parrotfish are hermaphroditic and usually begin life as females. As the fish grow larger and territory becomes available, some will mature into super-males. Supermales or terminal males are much larger and more colorful than the juvenile/ transitional males and the females, and will defend a territory. Transitional males that do not defend a territory show secondary sexual characteristics in the form of secondary testes. These indicate that the fish have ovaries as juveniles that later develop into functional testes (Girolamo et. al. 1999).
These functional groups can be further diversified among species and range from a monochromatic society that is strictly a monandric species in which males, predominantly supermales, are permanently territorial, to a dichromatic society which is diandric and in which males only hold a territory for a short period of time. These distinctions have even been seen between different populations of the same species. This behavior suggests flexibility in the social and sexual roles within the family Scaridae (Girolamo et. al. 1999). Diandric and monandric species were examined for differences in sizes between the sexes. In diandric species the juvenile, transitional, or initial-phase males as well as the females are relatively the same. The terminal males or super-males however are much larger than the females or initial-phase males. Monandric species tended to have secondary males that were larger than the females. These differences became more pronounced in species that had long life spans (Choat et. al. 1996).
The life span of parrotfish species varies from five years up to twenty years. Growth patterns between species and sexes tend to be very different. The age of a fish is estimated by alternating light and dark bands in different parts of the skeleton. The simplest method for estimating the age of a fish is to count the number of rings (otoliths) that accumulate on the sagittae (Choat et. al. 1996). Size at a certain age seems to vary tremendously between species. In one study the results showed that the largest and smallest species (4 total) examined tended to grow continuously through their life cycles. Three other species involved in the study showed a definite shift to a deterministic growth pattern that established a certain size limit early in life in the study. The first group aged only about five to six years. The group in which a defined size limit was set early tended to live longer, up to twenty years (Choat et. al. 1996). The life span of a species of parrotfish can have an effect on the amount of bioerosion that can occur on the reef over the lifetime of the fish. Obviously a fish living twenty years will have a greater amount of bioerosion attributed to it than to a fish living only five years.
Bioerosion has been linked to parrotfishes and the majority of research produced an overall estimate of sediment production (Bellwood 1995). This is an important step in understanding reef ecology but, variations in spatial patterns of the defecation of different species are also important to understanding the role that parrotfish play in the ecology of the reef. Two species were studied (Chlorus sordidus, Chlorus gibbus) and each showed very different defecation behaviors. C. sordidus tended to defecate in feeding zones or between grazing areas, while C. gibbus rarely defecated in grazing areas. C. gibbus was noted to swim for up to twenty meters away from a feeding site to defecate with some individuals showing a preference for a specific site (Bellwood 1995). The behavior of C. sordidus can be explained by the presence of a species of surgeon fish (Acanthurus lineatus), which tend to be very territorial, and attacks C. sordidus when it enters its territory. To avoid the attacks of the surgeon fish C. sordidus stays in one place for feeding and defecating. Acanthurus lineatus seems to accept the presence of C. gibbus in its territory and therefore this species of parrotfish is allowed to graze in area where A. lineatus holds territory and are allowed to pass through the surgeon fish's territory in order to defecate away from grazing sites. The differences between the two species of parrotfish have an effect on the rate of sedimentation that occurs on a reef. C. sordidus has more of an effect because this species defecates in grazing zones, while C. gibbus has less of an effect because this species has the opportunity to defecate far off the reef and away from grazing zones.
The Bruggemann study found that higher densities of endolithic algae occurred within the territories of the super-male or terminal males. These areas occurred at a depth of approximately 3.5 meters (this portion of the reef was considered to be the lower part of the reef) where the skeletal density of limestone substrates had decreased. High-density limestone substrates occurred in shallower regions of the reef and were found to be less productive for turf algae (Bruggemann et. al. 1994). This observation coincided with the theory that territories were defended as spawning sites in order to attract females to superior food sources (Bruggemann et. al. 1994). The abundance of the adult stages of many parrotfish species does not seem to be related to the use of microhabitats (Tolimieri 1998). Unlike damselfish, which needs suitable substrata for nesting sites, shelter, and algal gardens, parrotfish are pelagic spawners and most do not use the substratum in this way so it is not a necessity for many of the different species of parrotfish.
Spawning in most species occurs just before dusk. In many species spawning occurs repeatedly during a constant breeding season. Spawning takes place between a pair consisting of a supermale and a female. Group spawning has never been observed, however the behavior known as streaking has been observed in smaller males that do not hold a territory. Streaking occurs when the transitional male, which has female coloration in order to get into the supermales territory, joins the pair and releases his sperm as the female is releasing her eggs. This behavior was more commonly seen in areas where supermales took the majority of territories and the density of maturing males was high (Girolamo et. al. 1999). Supermales tend to lead a solitary lifestyle, while defending these territories for spawning and this can lead to increased risk of predation as well as parasitism.
Parasitism by marginellid snails on parrotfish that do not form mucous cocoons at night was recently discovered on a species in the Indian Ocean (Bouchet 1996). The parasitism occurred at night when the fish were sleeping. Each snail was observed with their proboscises extended to the fish. When samples of the snails were taken and stomach contents examined it was found that the majority of food ingested by the snails consisted of blood (Bouchet 1996). An Indo-Pacific marginellid species that is much larger than the one seen in the Indian Ocean was also observed to parasitize sleeping parrotfish species without the protection of a mucous cocoon. However this species of snail inserted it's lengthy proboscis into the mouth of the fish and it is suspected that the proboscis extended back to the gills that are rich in blood. No observations of parasitism on parrotfish species that form sleeping mucous cocoons were made in this study. It was concluded that species that form mucous cocoons have a lower risk of night parasitism (Bouchet 1996).
Parrotfish and their behaviors are just one essential part of keeping a reef healthy and productive in an enormously diverse ecosystem that has become threatened and in all reality could disappear if it is not protected and understood. Parrotfish perform an essential role by regulating the amount of algae present on a reef and therefore protect the living corals. This species should be respected and preserved because of the essential role it plays in the ecology of the reef. It has an enormous impact on the health of the corals now that different populations of Diadema antillarum, the long spined sea urchin, which was a formidable algal predator, has been drastically reduced (Davidson 1998). Parrotfish are one family of fishes that have filled that void and if they become extinct because of over fishing then the coral reefs will lose one more important strand in The Enchanted Braid (Davidson 1998) that keeps the reef thriving.
Bellwood, David R. 1995. Carbonate Transport and Within-Reef Patterns of Bioerosion and Sediment Release by Parrotfishes (Family Scaridae) on the Great Barrier Reef. Marine Ecology Progress Series 117: 127-136.
Bouchet, Phillepe, and Doug Perrine. 1996. More Gastropods Feeding at Night on Parrotfishes. Bulletin of Marine Science 59, no. 1: 224-229.
Bruggemann, J. Henrich, Madeliene J.H. van Oppen, and Anneke M. Breeman. 1994. Foraging by the Stoplight Parrotfish Sparisoma viride. I. Food Selection in Different, Socially Determined Habitats. Marine Ecology progress Series 106: 41-55.
Bruggemann, J. Henrich, Maarten W.M. Kuyper, and Anneke M. Breeman. 1994. Comparative Analysis of Foraging and Habitat Use by the Sympatric Caribbean Parrotfish Scarus Vetula and Sparisoma viride (Scaridae). Marine Ecology Progress Series 112: 51-66.
Choat, J.H., L.M. Axe, and D.C. Lou. 1996. Growth and Longevity in Fishes of the Family Scaridae. Marine Ecology Progress Series 145: 33-41.
Davidson, Osha Gray. 1998. The Enchanted Braid". John Wiley and Sons, Inc. 64, 180-182.
Girolamo, de M., M. Scaggiante, and M.B. Rasotto. 1999. Social Organization and Sexual Pattern in the Mediterranean Parrotfish Sparisoma cretense (Teleostei: Scaridae). Marine Biology 135: 353-360.
Hay, m. e., V.J. Paul, S.M. Lewis, K. Gustafson, J. Tucker, and R. N. Trindell. 1994. Synergisms in plant Defenses. Ecology 75, no. 6: 1714-1725.
Tolimieri, Nick. 1998. Contrasting Effects of Microhabitat Use on Large-Scale Adult Abundance in Two Families of Caribbean Reef Fishes. Marine Ecology Progress Series 167: 227-239.
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