Herbivory

Abstract

Coral reefsare experiencing large scale degradation. Motivated by the need for regular data monitoring and forquantification of the state and change of benthic and pelagic organisms,the Global Coral Reef Monitoring Networkprotocolwas executed on 18 dive sites in fished and unfished areasaround the island of Saba in the Saba National Marine Park (SNMP) in the Dutch Caribbean from March to May 2019. Pictures of the benthos were taken andanalysed with the Coral Point Count Excel extension software and fish biomass was calculated through the Bayesian length-weight-relationship. Although considerablybelow the Caribbean-wide average, coral cover around the island seems to be slowlyrecoveringfrom past diseasesand hurricane events. Coral species richnesspositively correlates with reef fish density and Serranidae species richness. As in other parts of the Caribbean, macroalgae in the SNMP arerapidly spreadingand increasingly competefor space with habitat-providing gorgonians, sponges and other benthic organisms. Incontrast toexpectations, fish density and biomass continue to increase, evenin zones where fishing is allowed. This mightbe explained by the higher availability of macroalgae that serve as food for variousherbivorous fish species, which in turn are, amongst others, the prey of predatory fish and thosehigher up in the trophic cascade. However, with the exception ofthe commercially important fish family Lutjanidae all key fish species have declinedin average size in recent years. Another findingis the increase of coral diseases. The results indicate the need for further species-specific research in order to identify the factorsthat arecausing the degradation ofthe reefs in the SNMP. A better understandingofthe interactions, ecological roles and functions of benthic and fish communities is therefore essential for the protection of reefs, that are of high value to Saba. The results of this study contribute to the adaptive management of the Saba Conservation Foundation that manages the SNMP.

Keywords: GCRMN, Reef Health Index, marine protected area, fish-benthos interaction, macroalgae, herbivory, trophic cascade, fishing, coral disease, Caribbean

Herbivory grazing patterns by parrotfish, family Scaridae, and surgeonfish, family Acanthuridae, were investigated on the leeward side of Bonaire, Netherlands Antilles. Due to overfishing, coral disease, declining water quality and global climate changes, coral reefs worldwide are in danger of undergoing phase shifts from coraldominated to algal-dominated ecosystems (Hughes 2007; Nybakken 2001). When nutrient levels are high, algal communities are highly productive and may outcompete corals (Breeman et al 1994). In healthy coral systems herbivores suppress algal growth and are a key component in preventing phase shifts, thus managing reef resilience (Hughes 2007; Folk and Nystrom 2001). This study measured herbivory rates and bite sizes of several species of coral reef fishes on the island of Bonaire, Netherlands Antilles. These measurements and species density data (Steneck 2005) were used to rank species according to their level of herbivory. The five selected herbivore species were the terminal and initial phase Sparisoma viride (Stoplight Parrotfish), terminal and initial phase Scarus vetula (Queen Parrotfish), terminal phase Scarus taeniopterus (Princess Parrotfish), Acanthurus coeruleus (Blue Tang), and Acanthurus bahanus (Ocean Surgeon). Although Scarus vetula has the highest grazing rate (# bites/min) and largest bite size (cm2 ), this study calculates that Scarus taeniopterus, due to large densities, are the primary consumers of algae in the waters of Bonaire (cm2 /minute/species/100m2 ), followed by Scarus vetula terminal phase and Scarus vetula initial phase. As coral reefs are becoming more algal dominated due to nutrient enrichment, knowledge of herbivore ecology and management of herbivore populations is critical to understanding and protecting these threatened ecosystems.

This student research was retrieved from Physis: Journal of Marine Science III (Spring 2008)19: 49-54 from CIEE Bonaire.

The purpose of this research was to determine the level of defensive aggression of the threespot damselfish, Stagastes planifrons, when exposed to intruders of different species using models. Adult S. planifrons were exposed to models of a conspecific, an herbivorous fish, Sparisoma viride, and a predator, Aulostomus maculatus. Attack rates and retreat rates of S. planifrons were determined by observations during exposure to models. It was expected that aggression levels would be highest towards the conspecific model and lowest towards the predator model and that evasive behavior would be highest in the presence of the predator model and lowest with the conspecific. It was found that there is a significant difference in the level of aggression when encountering a predator versus a conspecific, showing more aggression towards the conspecific and more evasion towards the predator. No significant difference was found in the aggression levels shown between the predator and the herbivore. Exposure to the predator elicited the highest number of retreats, also showing a significant difference in the level of evasion when comparing all three models. The results suggest that S. planifrons are able to differentiate between intruder species and react depending on the level of threat posed and perhaps on what is most energy efficient.

This student research was retrieved from Physis: Journal of Marine Science III (Spring 2008)19: 13-18 from CIEE Bonaire.

Artificial reefs are commonly used to increase habitat space for reef-dwelling organisms. Coral reefs in Bonaire, Dutch Caribbean, are degrading due to factors such as disease, bleaching events, and heavy storms, reducing habitat space for reef fish. Two different artificial reefs were deployed on the leeward side of Bonaire in 2011: one block and one branching structure. Studies found that both reefs supported fish communities but utilization of the reefs by fish was not studied. The current study examines utilization of branching and block-style artificial reefs for foraging and feeding activities by herbivores and predators to assess which reef structure provides more resources for fish. Herbivore grazing and predator stalking rates were calculated as well as herbivory and predation pressure at increasing distances away from the artificial reef. The branching artificial reef supported more herbivore and predator activity compared to the block reef, suggesting structural complexity increases important sheltering and feeding areas for reef fish. Predation and herbivory pressures showed no trend with increasing distance from the artificial reef while predation pressure decreased with increasing distances from the natural reef. This suggests that the artificial reef may act as a shelter between the reef crest and the surrounding sand and rubble area, thereby increasing foraging distances of fish coming from the reef crest. Not only resident, but transient individuals, were found to use the artificial reefs for feeding and sheltering, suggesting that artificial reefs do not need to create permanent habitats in order to be important habitat for reef fish.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 46-57 from CIEE Bonaire.

Herbivores are important structuring agents for ecosystems worldwide. While effects of grazing by herbivorous fish are well studied, their roles in organismal dispersal have only recently become a topic of interest. Location preference and range of defecation may indicate the importance of their contribution to organism spreading. This study therefore examined the distribution and frequency of defecation of the princess parrotfish (Scarus taeniopterus) and queen parrotfish (Scarus vetula) between coral reef and sand flat habitats. Observations were performed using SCUBA in Bonaire, Dutch Caribbean. Target species were observed for 20-minute trials in each habitat. Defecation frequency, bite frequency, maximum distance between defecations, and location of defecation were recorded and averaged for each species in each habitat, and compared between species and habitats through two-way analysis of variance (ANOVA). Additionally, unique food sources observed during trials were sampled and examined in the lab. S. taeniopterus individuals were found to defecate significantly less and have smaller maximum distance between defecations within the reef habitat than the sand habitat, while S. vetula did not show significant behavioral changes for any of the variables between the two habitats. Lab results also suggest that S. taeniopterus may be opportunistic omnivores. This study offers insight to behavioral plasticity and specificity to habitat type, and provides a broader understanding of dietary plasticity and ecological roles for S. taeniopterus and S. vetula.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 1-13 from CIEE Bonaire.

Abstract: 

The mechanisms by which algae disperse across space on coral reefs are poorly known. We inves- tigated the ability of four common Caribbean herbivorous fish species to disperse viable algal fragments through consumption of macroalgae and subsequent defecation. Fragments of all major algal taxa (Phaeophyta, Rhodophyta, and Chlorophyta) were found in 98.7 % of the fecal droppings of all fish species; however, the ability to survive gut passage and reattach to a substrate differed between algal taxa. While survival and reattachment approached zero for Phaeophyta and Chlorophyta, 76.4 % of the fragments belonging to the group Rhodophyta (mostly species in the order Gelidiaceae) survived gut passage, and were able to grow and reattach to the substrate by forming new rhizoids. Our results thus show that Gelidid algal species are dispersed by swimming herbivores. While the relative contribution of this mechanism to overall algal dispersal and recruitment in a wider ecological context remains unknown, our findings illustrate a previously undescribed mechanism of algal dispersal on coral reefs which is analogous to the dispersal of terrestrial plants, plant fragments, and seeds via herbivore ingestion and defecation.