Grazing

Feces consumption by nominally herbivorous fishes in the Caribbean: an underappreciated source of nutrients?

Abstract

Parrotfishes and surgeonfishes are major Caribbean herbivores that primarily graze reef algae and thereby play an important functional role in indirectly promoting coral recruitment and growth. Yet, an emerging body of research suggests that these nominal herbivores graze on a diverse array of other food sources and researchers have questioned whether they may target more nutrient-dense foods growing within or upon algae, such as cyanobacteria. In this study, we investigated the speciesspecific foraging rates of parrotfishes and surgeonfishes on Brown Chromis (Chromis multilineata) fecal pellets compared to other major dietary items. We found that almost 85% of observed fecal pellets were ingested by fishes and that over 90% of ingested fecal pellets were consumed by parrotfishes and surgeonfishes alone. While there were species-specific differences in the levels of feces consumption (coprophagy), we found that all three surgeonfishes (Acanthurus chirurgus, A. coeruleus, and A. tractus) and six of the nine of parrotfish species surveyed (Scarus coeruleus, S. iseri, S. taeniopterus, S. vetula, Sparisoma aurofrenatum, and S. viride) consumed C. multilineata feces. To better understand the nutritional value of this behavior, we analyzed the composition of proteins, lipids, carbohydrates, total calories, and micronutrients in C. multilineata fecal pellets and compared these to published values for other food sources targeted by these fishes. Our findings suggest that these fecal pellets may have higher values of proteins, carbohydrates, total calories, and important micronutrients, such as phosphorus, compared to various macroalgae and the epilithic algae matrix, though comparable or lower values compared to cyanobacteria. To our knowledge, this is the first study to document coprophagy by tropical herbivorous fishes in the Caribbean region. This research advances our understanding of the foraging ecology of nominally herbivorous fishes and highlights the importance of fish feces as a nutritional resource on coral reefs.

Date
2022
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Bonaire

Examining the effect of different grazers on algal biomass

Herbivory drives ecosystem dynamics in both terrestrial and marine habitats, controlling type and biomass of vegetation. In tropical coral reefs, herbivorous fishes and invertebrates feed on benthic macroalgae, resulting in decreased algal biomass and increased hard substratum available for coral growth and recruitment, providing for increased levels of biodiversity. In 1983, the long-spined sea urchin, Diadema antillarum, suffered mass mortality in the Caribbean, resulting in dramatic changes to ecosystem dynamics such as decreased coral cover and increased macroalgal cover. This study aimed to examine the impact of various grazers on algal biomass in areas with and without D. antillarum in Bonaire, Dutch Caribbean, from late February to early April, 2012, using herbivore exclusion cages with varying levels of exclusion. Grazer categories were established based on cage type and proximity to D. antillarum. It was hypothesized that algal biomass would decrease with increased herbivore access. At locations with D. antillarum, there was a general increase in algal biomass with increased exclusion, whereas at locations without D. antillarum, the opposite trend was observed. Algal biomass generally decreased with increased grazer access; however, differences were not statistically significant. Herbivorous fishes removed the highest amount of algae, followed by D. antillarum, and large invertebrates. This study shows the importance of multiple herbivores in maintaining low algal biomass in Bonaire.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 1-8 from CIEE Bonaire.

Date
2012
Data type
Other resources
Theme
Research and monitoring
Tags
Geographic location
Bonaire
Author

Parrotfish abundance and corallivory at the Yellow Sub dive site in Bonaire, Dutch Caribbean

Parrotfish are some of the most widely recognized reef fish in the world. They occupy almost every tropical reef on the planet, and through their eating behavior, dramatically transform ecosystems. Parrotfish mainly consume macroalgae, but have been known to consume coral and therefore have a potentially negative impact on coral fitness. Although parrotfish corallivory is a well-known behavior, little is known about why it occurs, and how severe the effects are on marine ecosystems. The purpose of this experiment was to quantify the amount of coral colonies that parrotfish feed on at the Yellow Sub dive site in Bonaire Dutch Caribbean. By collecting data on the extent of parrotfish corallivory, there will be a larger body of knowledge from which questions about parrotfish grazing can be answered. To carry out this experiment, 30 meter transect tapes placed at depths of nine and 15 meters were used to first catalogue all of the coral by species, size, and if it had been bitten by parrotfish. Next three transect swims were used to categorize all parrotfish by size, species, and any special behavior (i.e. coral consumption). Results showed a higher abundance of parrotfish in transects at nine meters than at 15 meters. Parrotfish preferred the coral species Montastraea annularis, but there was no relationship between the presence of parrotfish and the percentage of coral bitten.

This student research was retrieved from Physis: Journal of Marine Science XII (Fall 2012)19: 16-21 from CIEE Bonaire.

Date
2012
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire

How much time can herbivore protection buy for coral reefs under realistic regimes of hurricanes and coral bleaching?

Abstract:

Coral reefs have been more severely impacted by recent climate instability than any other ecosystem on Earth. Corals tolerate a narrow range of physical environmental stress, and increases in sea temperature of just 1 1C over several weeks can result in mass coral mortality, often exceeding 95% of individuals over hundreds of square kilometres. Even conservative climate models predict that mass coral bleaching events could occur annually by 2050. Unfortunately, managers of coral-reef resources have few options available to meet this challenge. Here, we investigate the role that fisheries conservation tools, including the designation of marine reserves, can play in altering future trajectories of Caribbean coral reefs. We use an individual-based model of the ecological dynamics to test the influence of spatially realistic regimes of disturbance on coral populations. Two major sources of disturbance, hurricanes and coral bleaching, are simulated in contrasting regions of the Caribbean: Belize, Bonaire, and the Bahamas. Simulations are extended to 2099 using the HadGEM1 climate model. We find that coral populations can maintain themselves under all levels of hurricane disturbance providing that grazing levels are high. Regional differences in hurricane frequency are found to cause strikingly different spatial patterns of reef health with greater patchiness occurring in Belize, which has less frequent disturbance, than the Bahamas. The addition of coral bleaching led to a much more homogenous reef state over the seascape. Moreover, in the presence of bleaching, all reefs exhibited a decline in health over time, though with substantial variation among regions. Although the protection of herbivores does not prevent reef degradation it does delay rates of coral loss even under the most severe thermal and hurricane regimes. Thus, we can estimate the degree to which local conservation can help buy time for reefs with values ranging between 18 years in the Bahamas and over 50 years in Bonaire, compared with heavily fished systems. Ultimately, we demonstrate that local conservation measures can benefit reef ecosystem services but that their impact will vary spatially and temporally. Recognizing where such management interventions will either help or fail is an important step towards both achieving sustainable use of coral-reef resources and maximizing resource management investments. 

Date
2011
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire