Grantee Research Project Results
2004 Progress Report: Physiology and Ecology of Macroalgal Blooms on Coral Reefs off Southeast Florida
EPA Grant Number: R830414Title: Physiology and Ecology of Macroalgal Blooms on Coral Reefs off Southeast Florida
Investigators: Lapointe, Brian E. , Barile, Peter J. , Yentsch, Charles S.
Institution: Harbor Branch Oceanographic Institution, Inc.
Current Institution: Harbor Branch Oceanographic Institution, Inc. , Plankton Research and Instruments
EPA Project Officer: Packard, Benjamin H
Project Period: October 14, 2002 through October 13, 2004 (Extended to October 13, 2005)
Project Period Covered by this Report: October 14, 2003 through October 13, 2004
Project Amount: $279,098
RFA: Ecology and Oceanography of Harmful Algal Blooms (2002) RFA Text | Recipients Lists
Research Category: Water Quality , Aquatic Ecosystems , Water
Objective:
The objectives of this research project are to:
- use digital underwater video imagery to determine seasonal (quarterly) variation in growth of the invasive green seaweeds Codium isthmocladum, Caulerpa verticillata, and Caulerpa brachypus at two reef sites (Princess Anne [PA], North Colonel’s Ledge [NCL]) in northern Palm Beach County, Florida;
- analyze quarterly tissue samples of the invasive seaweeds at the two reef sites for their carbon:nitrogen:phosphorus contents (C:N:P ratios) and δ15N (15N/14N) contents;
- perform studies on the photophysiology (Photosynthetic Efficiency = Fv/Fm) of the target species;
- determine the relative importance of ammonium versus nitrate to the nitrogenous nutrition of the target species;
- and perform laboratory and field grazing assays to determine the potential for herbivores to control these blooms.
Progress Summary:
Objective 1
We successfully tracked the seasonal growth patterns of the invasive green macroalgae using digital video imagery with the random point count method in 2003/2004. The resulting biotic cover data demonstrate how Caulerpa brachypus var. parvifolia became the dominant organism (60–90% cover) at both reef sites in 2003/2004. This research is important because it documented the expansion of this alien species (Pacific native) on reefs in northern Palm Beach County. We also have quantified the presence of lesser abundant (< 30% cover) invasive macroalgae on these reefs, which include Codium isthmocladum, Caulerpa verticillata, Caulerpa racemosa, Caulerpa mexicana, and Caulerpa prolifera.
Objective 2
We successfully collected and analyzed the quarterly macroalgae samples from the two reef sites for C:N:P ratios and δ15N values in 2003/2004. Overall, the tissue C:N:P data revealed significant variability over the period of record for Caulerpa brachypus and Caulerpa racemosa. For example, the C:N ratio of Caulerpa brachypus increased from approximately 10:1 to greater than 20:1 between winter and spring of 2003 but remained less than 15:1 throughout the 2004 samplings. With the exception of the April 2003 sampling, there were no significant (P > 0.05) differences in C:N ratio in Caulerpa brachypus between the PA and NCL sites in 2003/2004. The C:P ratio of Caulerpa brachypus varied between approximately 400-600 at both reef sites with significant differences among sites occurring only in October 2003. Considerable variability occurred in the N:P ratio of Caulerpa brachypus, which ranged from approximately 22 to 58 in 2003/2004. In general, N:P ratios greater than 35 are indicative of P-limited growth whereas ratios less than 30 are indicative of N-limited growth. Therefore, these blooms of Caulerpa Brachypus may be limited by both N and P, depending on the time of year.
Overall, there were no significant differences in δ15N of Caulerpa brachypus, Caulerpa racemosa, Caulerpa verticillata, and Codium isthmocladum between the PA and NCL sites during the 2-year study. These values ranged from approximately +2 to +9 ‰ in Caulerpa brachypus and Caulerpa racemosa and varied significantly over the period of study (Kruskall Wallis, P < 0.0001). Relatively high values of +5 to +9 ‰ occurred from February to July of 2003 compared to low values of +2 to +4 ‰ in the fall 2003 and winter 2004 samplings. This pattern suggests a significant seasonal variation in N source to these blooms, switching from sewage (+4 to +9 ‰) in the winter, spring and summer months to other sources, such as agricultural runoff (< +4 ‰) in the fall when N loading from stormwater runoff is maximum.
Objective 3
The major goal of Objective 3 is to establish what combination of environmental and geophysical factors promoted the bloom at these particular locations. The biological/optical approach used was measurement of fluorescence yield that is an established index of the efficiency of light harvesting by photo systems of the harmful algal bloom (HAB) species involved. Using this approach, we established that the high efficiency of Caulerpa brachypus and other Caulerpa spp., which dominated the biotic cover of the reef provided a light harvesting advantage over the local primary producers. The bloom, therefore, constituted invasive phenomena. The environmental features favoring this and promoting invasiveness are ample sunlight, relatively high water clarity, and a close proximity to replete nutrient concentrations from local sediments and offshore water masses. This provided a reef environment some 30 meters below the surface where the invasive HABs competed successfully with native reef biota. The geophysical features of the region, such as proximity to longshore current flow, upwelling, and highly conductive geological substrata, are believed to provide an excellent habitat for the growth of these rhizoidal attached algae.
Objective 4
Progress towards this objective included the successful completion of controlled, laboratory 15N uptake experiments with Codium isthmocladum, Caulerpa brachypus, and Caulerpa racemosa in summer 2004. These factorial experiments were conducted in Lunaire incubators and examined the main effects and interactions of irradiance (low = 50 μmol photons m-2s-1; high = 200 μmol photons m-2s-1 ), temperature (18, 23, and 28˚C), and N source (ammonium vs. nitrate) using 15N-labeled substrate. Although the bulk of these tissue samples is still being analyzed, preliminary data indicate that both Codium isthmocladum and Caulerpa brachypus have a strong kinetic preference (up to a 5-fold increase in uptake rate) for ammonium compared to nitrate. This would explain why blooms of these HAB species have not historically developed in response to episodic, nitrate-rich upwelling during summer months and supports the hypothesis that these blooms are being driven by low-level buildup of ammonium from land-based sources of nutrient pollution.
Objective 5
In Year 2 of the project, herbivory of Caulerpa brachypus by a specialist mesoherbivore, an Elysiid nudibranch, was evaluated in laboratory trials to meet Objective 5. Elysia subornata, a native to the nearby Indian River Lagoon, was assessed previously for potential biocontrol of the Mediterranean strain of Caulerpa taxifolia, as this slug is seasonally abundant and relies strictly on a diet of coenocytic Caulerpa species. Although E. subornata is efficient at consumption of the native congener Caulerpa prolifera and the invasive Caulerpa taxifolia, these mesoherbivores did not consume Caulerpa brachypus in exhaustive laboratory trials. We suspect that this may be the result of the thin, “sheet-like” morphology of this alga, as the slugs did not appear to be able to remove the “cell-sap” through radular piercing as is readily achieved in the congeners Caulerpa prolifera and Caulerpa taxifolia.
In comparative organic extraction analyses, Caulerpa brachypus also appears to have a significantly lower concentration of the anti-predator compound Caulerpenyne as compared to native Caulerpa congeners. This may explain why this alga can be consumed by herbivorous icthyofauna, in contrast to congeners that are not generally consumed by this trophic guild. These results are not supported by the current theory of herbivory on coral reefs that suggests palatability by any specific trophic group equates to categoric and complete consumption in field conditions. Rather, these results support the hypothesis that invasive species subvert pressure from established trophic pyramids and persist in previously unexploited habitats.
Future Activities:
With support from the State of Florida and in collaboration with the Florida Fish and Wildlife Research Institute, we expanded our monitoring of HABs off southeast Florida in late August 2004 to survey reefs between Miami-Dade County and St. Lucie County. These reef surveys were temporarily delayed because of hurricanes Frances and Jeanne in September 2004. The work resumed in mid-October and will continue through the spring and summer of 2005.
Journal Articles on this Report : 8 Displayed | Download in RIS Format
Other project views: | All 33 publications | 11 publications in selected types | All 11 journal articles |
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Type | Citation | ||
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Barile PJ. Evidence of anthropogenic nitrogen enrichment of the littoral waters of east central Florida. Journal of Coastal Research 2004;20(4):1237-1245 |
R830414 (2004) |
not available |
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Barile PJ, Lapointe BE. Atmospheric nitrogen deposition from a remote source enriches macroalgae in a coral reef ecosystem at Green Turtle Cay, Abacos, Bahamas. Marine Pollution Bulletin 2005;50(11):1262-1272. |
R830414 (2004) |
not available |
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Lapointe BE, Barile PJ, Matzie WR. Anthropogenic nutrient enrichment of seagrass and coral reef communities in the Lower Florida Keys: discrimination of local versus regional nitrogen sources. Journal of Experimental Marine Biology and Ecology 2004;308(1):23-58. |
R830414 (2004) |
not available |
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Lapointe BE, Barile PJ, Wynne MJ, Yentsch CS. Invasion of the green alga Caulerpa ollivieri in the Bahamas linked to anthropogenic nitrogen enrichment. Science (submitted, 2004). |
R830414 (2004) |
not available |
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Lapointe BE. Phosphorus-rich waters at Glovers Reef, Belize? Marine Pollution Bulletin 2004;48(1-2):193-195. |
R830414 (2004) |
not available |
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Lapointe BE, Barile PJ. Seagrass die-off in Florida Bay: an alternative interpretation. Estuaries 2004;27(1):157-164. |
R830414 (2003) R830414 (2004) |
not available |
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Lapointe BE, Barile PJ, Littler MM, Littler DS, Bedford BJ, Gasque C. Macroalgal blooms on southeast Florida coral reefs I. Nutrient stoichiometry of the invasive green alga Codium isthmocladum in the wider Caribbean indicates nutrient enrichment. Harmful Algae 2005;4(6):1092-1105 |
R830414 (2004) |
not available |
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Yentsch CS, Yentsch CM, Phinney DA, Lapointe BE, Yentsch SFW. The odyssey of new production. Journal of Experimental Marine Biology and Ecology 2004;300(1-2):15-30. |
R830414 (2003) R830414 (2004) |
not available |
Supplemental Keywords:
carbon, nitrogen, phosphorus, macroalgae, photosynthesis, fluorescence, herbivory, target species, laboratory grazing, field grazing, invasive green seaweeds., RFA, Scientific Discipline, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Oceanography, Aquatic Ecosystem, Environmental Microbiology, Aquatic Ecosystems, algal blooms, Ecological Risk Assessment, Ecology and Ecosystems, marine ecosystem, nutrient dynamics, macroalgal blooms, ocean outfalls, bloom dynamics, coral reefs, nutrient enrichment, nutrient kinetics, coral-algal symbiosis, algal bloom detection, benthic algae, macroalgal populations, sewage outflows, coral reef communities, benthic study, groundwaterRelevant Websites:
Progress 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.