Grantee Research Project Results
1999 Progress Report: Chemical Ecology of Cyanobacterial Blooms on the Tropical Reefs of Guam
EPA Grant Number: R826220Title: Chemical Ecology of Cyanobacterial Blooms on the Tropical Reefs of Guam
Investigators: Paul, Valerie J.
Institution: University of Guam
EPA Project Officer: Packard, Benjamin H
Project Period: December 15, 1997 through December 14, 2000 (Extended to December 14, 2001)
Project Period Covered by this Report: December 15, 1998 through December 14, 1999
Project Amount: $325,000
RFA: Harmful Algal Blooms (1997) RFA Text | Recipients Lists
Research Category: Water Quality , Water , Aquatic Ecosystems
Objective:
Harmful algal blooms (HABs) of many types have increased in abundance and severity in the United States and worldwide in recent years. Of particular concern in coral reef habitats are the frequent and persistent seaweed blooms that increasingly have been documented. These blooms of macroalgae and other benthic primary producers such as cyanobacteria (blue-green algae) are thought to result from nutrient enrichment associated with coastal eutrophication in combination with decreased grazing by herbivorous fishes due to overfishing. The blooms can have many negative impacts including directly overgrowing and smothering corals, negatively affecting seagrass communities, and washing up on beaches and creating an unsightly mess in areas where tourism is economically essential. An additional concern for cyanobacterial blooms are the toxins associated with these common inhabitants of tropical reef communities and their impacts on other reef organisms and humans.
A large number of toxic as well as several biomedically important secondary metabolites have been isolated from marine cyanobacteria. Some of these compounds can act as feeding deterrents to a variety of herbivores. The production of deterrent secondary metabolites by benthic cyanobacteria probably facilitates the formation of cyanobacterial blooms on coral reefs because most generalist grazers avoid this potential food source. Almost nothing is known about the temporal and spatial patterns of bloom formation in reef habitats or about environmental factors affecting bloom formation and persistence. Additionally, secondary metabolite types and concentrations can vary considerably among different collections of cyanobacteria, even among collections of the same species (e.g., Lyngbya majuscula). Factors influencing this chemical variation are not at all understood.
This research will focus on documenting the temporal and spatial patterns of cyanobacterial blooms on Guam. Secondary metabolites associated with these blooms will be isolated and characterized. Effects of these compounds on feeding by herbivores such as fishes and mesograzers will be examined. Compounds released by the cyanobacteria into seawater will be characterized and examined for their effects on competitors and other microorganisms. Finally, in an attempt to understand the chemical variability observed for these blooms, effects of grazing, light, and nutrients (nitrogen, phosphorus, and iron) on secondary metabolite production will be examined in a combination of field and laboratory experiments.
This study will examine the chemical ecology of cyanobacterial blooms on Guam. To do this, we will need to determine the temporal and spatial patterns of bloom formation and persistence, the types and concentrations of natural products produced by bloom algae, the effects of these compounds on potential consumers, and the environmental factors regulating the production of toxic and deterrent compounds by the harmful cyanobacterial blooms (HCBs). These research questions coincide with the ECOHAB program objectives, which are to "understand the fundamental processes underlying the population dynamics of HABs and the impacts they precipitate."
The objectives of this research are to:
(1) document the temporal and
spatial patterns of cyanobacterial bloom formation in reef and seagrass habitats
around the island of Guam;
(2) characterize and quantify the natural
products chemistry of these cyanobacterial blooms;
(3) determine the effects
of the natural products (secondary metabolites) isolated from cyanobacterial
blooms on potential consumers, including herbivorous reef fishes and specialist
mesograzers such as sea hares; (4) examine the types and amounts of compounds
released by cyanobacteria and their effects on consumers, competitors, and other
microorganisms; and (5) manipulate light and nutrients (nitrogen, phosphorus,
and iron) in field and laboratory experiments to determine their effects on
secondary metabolite production by cyanobacteria under natural conditions.
Progress Summary:
Our goals for the 2 years have focused on Objectives 1, 2, 3, and 5 of the grant proposal and included: (1) monitoring permanent transects for cyanobacterial abundance and diversity; (2) making collections of cyanobacterial blooms; (3) extracting these collections; (4) examining the natural products chemistry of these extracts for known and novel metabolites; (5) examining the capability of these extracts to deter feeding by parrotfish, urchins, and sea hares; and (6) conducting a field experiment that manipulated herbivore abundance and nutrient availability, and assessing the effects on cyanobacterial and macroalgal abundance.
Objective 1: To document the temporal and spatial patterns of cyanobacterial bloom formation in reef and seagrass habitats around the island of Guam. We have established permanent transects at nine locations around Guam: Tanguisson, Pago Bay, Togcha, Cocos Lagoon, Fingers Reef, Piti Bombholes, and three transects in Tumon Bay (Ypao, Pia Marine, and Sails). Our initial plan for biweekly surveys was changed to once every 3 weeks, because most sites have not changed quickly and due to personnel limitations. At the Togcha site, we are surveying a persistent strain of Oscillatoria margaritifera weekly. We have taken water samples for nitrate concentration, phosphate concentration, salinity, and temperature at 5-6 week intervals. We also have installed temperature data loggers at each site. These loggers record the ambient tempera- ture every 30 minutes. Average wave height for eastern and western shores, rainfall, minutes of sunshine, and wind speed also were monitored.
The abundance of cyanobacteria at our field sites has ranged from 0 to 70 percent cover. Some field sites are dominated by one or a few abundant cyanobacteria, while others have low numbers of cyanobacteria, but high diversity. Stepwise regression was used to determine which variable or combination of variables best explained variation in cyanobacterial abundance. Although nutrient availability was not significantly associated with cyanobacterial abundance, a positive association with macroalgal abundance explained 11.5 percent of the observed variation in total cyanobacterial abundance. At one site, negative relationships with macroalgal abundance and wave height explained 79.4 percent of the observed variation in abundance of the cyanobacterium Oscillatoria margaritifera. Physical disturbance may be a more important influence on cyanobacterial abundance and distribution than either nutrient availability or interactions with macroalgae.
More than 25 abundant strains of cyanobacteria have been recorded from our 9 field sites. Some of these strains occur at more than one location. Additional research on morphological and molecular taxonomic methods is needed to confirm our strain identifications and to place our data on secondary metabolites and feeding deterrence within a phylogenetic framework. Recently, we developed molecular techniques in our laboratory to obtain 16s rDNA sequences from these strains and characterize their genetic variation.
Objective 2: To characterize and quantify the natural products chemistry of these cyanobacterial blooms. Twenty-five of the most common strains in our study sites have been extracted, yielding from 0.5 to 10 percent crude organic extract per dry mass. Most of these have been extracted in bulk, providing enough extract for chemical studies and bioassays with herbivores. Compounds have been isolated including dolastatin 11, symplostatins 1 and 2, malyngamides A and B, and majusculamides A and B. A red strain of Lyngbya majuscula that occurs at several sites around Guam has yielded a variety of known and new lipopeptides. A graduate student with Professor Richard Moore's laboratory at the University of Hawaii currently is characterizing the natural products from this cyanobacterium.
Objective 3: To determine the effects of the natural products (secondary metabolites) isolated from cyanobacterial blooms on potential consumers, including herbivorous reef fishes and specialist mesograzers such as sea hares. We have tested the feeding deterrence of 17 of the extracted strains of cyanobacteria with parrotfish (Scarus schlegeli), urchins (Echinometra mathaei), and sea hares (Stylocheilus longicauda). We have used two types of assays: (1) comparing consumption of freeze-dried, powdered cyanobacteria with consumption of freeze-dried powdered Enteromorpha clathrata (a palatable green algae), and (2) comparing consumption of crude organic extracts of cyanobacteria coated onto powdered Enteromorpha with consumption of uncoated Enteromorpha. All of the powdered cyanobacteria that we have tested have significantly reduced feeding by all three consumers. Of the assays with crude extracts, 11 deterred feeding by parrotfish, while 6 had no significant effect. Urchins were deterred by 8 extracts, while 6 had no significant effect. Sea hares were deterred by only 3 extracts, while 2 had no significant effect, and 12 stimulated feeding. S. longicauda has been considered a specialist on Lyngbya majuscula, but it clearly can consume other cyanobacteria, including Tolypothrix, Oscillatoria, and Hormothamnion. Sea hare consumption of cyanobacteria was not significantly correlated with crude extract yields or percent nitrogen content of the cyanobacteria.
Objective 5: To manipulate light and nutrients (nitrogen, phosphorus, and iron) in field and laboratory experiments to determine their effects on secondary metabolite production by cyanobacteria under natural conditions. In Year 1, we examined the role of herbivory in controlling the abundance of cyanobacteria by placing fish-exclusion cages over 0.5 m x 0.5 m quadrats on the reef flat for 3 months. Highly palatable macroalgae, including Acanthophora spicifera and Caulerpa racemosa, showed dramatic increases in abundance in the exclusion cages. A bloom of the cyanobacterium Hormothamnion enteromorphoides occurred in uncaged quadrats, partial cages, and full cages. Less H. enteromorphoides were observed in the fully and partially caged quadrats than in the uncaged quadrats, indicating that alterations in light or water flow due to the cages could have reduced cyanobacterial growth. Direct removal of macroalgae by herbivorous fishes did not stimulate bloom formation.
In Year 2, we examined the impacts of both herbivory (again using uncaged, partially caged, and fully caged quadrats) and nutrient enrichment (using a commercial fertilizer, Osmocoat Extended Time Release Fertilizer, containing nitrogen and phosphorus) on cyanobacterial and macroalgal community structure. We conducted the experiment on a reef flat that was initially dominated by the cyanobacteria Oscillatoria spp. and Tolypothrix sp. In the absence of cages, surface cover of the cyanobacterium Tolypothrix sp. declined, while cover of the cyanobacteria Oscillatoria spp. increased over the 4-month duration of the study. Lower cyanobacterial cover and biomass in the partial and full cages were correlated with higher macroalgal cover and biomass. The macroalga Dictyota bartayresii dominated the partial cages, while the macroalgae Padina tenuis and Tolypiocladia glomerulata recruited into the full cages. Palatability assays demonstrated that herbivore-exclusion shifted macroalgal species composition from unpalatable to palatable species. Nutrient enrichment increased cover of D. bartayresii in the uncaged and fully caged plots, but had no other significant effects. These results stress the critical role of herbivory in determining coral reef community structure and suggest that herbivores may buffer the effects of nutrient enrichment when the dominant algae are palatable. When the dominant algae are unpalatable, herbivores may be unable to compensate for increased levels of productivity due to nutrient enrichment. The lack of an effect of nutrient enrichment on cyanobacterial abundance agrees with the lack of a correlation between nutrient availability and cyanobacterial abundance in our monitoring data.
Future Activities:
During Year 3, we will continue our work on Objectives 1,2, 3, and 5. Now that our monitoring sites have been established, three people are conducting the field monitoring routinely. By April 2000, we will have completed 2 full years of monitoring. We are now starting to analyze these data to look for seasonal patterns in cyanobacterial abundance and diversity. We already have observed that certain species appear on the reefs at certain times of the year and then disappear for the duration of the year. We also will continue our studies of the taxonomy of these cyanobacteria by morphological and molecular methods. We are continuing to study the natural products chemistry of these blooms. We collect and extract the cyanobacterial strains that occur in large amounts at various sites around the island. We also will determine whether different cyanobacteria are releasing metabolites into seawater. Now that we have completed the feeding bioassays with many common cyanobacteria from Guam and have identified those with feeding deterrent activities, we will test pure compounds individually and in combination to assess their feeding deterrent effects.
We will address Objective 4 from the original proposal this next year by examining overgrowth of corals by cyanobacteria and the effects of cyanobacteria and their released compounds on settlement of coral larval. We also will examine the effects of extracts and purified compounds from the cyanobacteria on marine fungi.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 30 publications | 6 publications in selected types | All 6 journal articles |
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Type | Citation | ||
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Thacker RW, Ginsburg DW, Paul VJ. Effects of herbivore exclusion and nutrient enrichment on coral reef macroalgae and cyanobacteria. Coral Reefs 2001;19(4):318-329. |
R826220 (1999) R826220 (2000) R826220 (Final) |
not available |
Supplemental Keywords:
marine, benthic cyanobacteria, harmful algal blooms, monitoring, Pacific Islands, Guam, herbivory, chemical defenses, secondary metabolism, ECOHAB., RFA, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, Ecological Effects - Environmental Exposure & Risk, algal blooms, Ecological Indicators, ecological exposure, chemical ecology, ecological effects, spectroscopic methods, bloom dynamics, marine biotoxins, coral reefs, harmful algal blooms, cyanobacterial blooms, tropical reefs, bioassay, benthic algae, natural toxins, cyanobacteriaProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.