“Toxicity” of the fish-killing alga, Heterosigma akashiwo, to larval herring and sea urchins
Tanner Yess, Northern Kentucky University, Highland Heights, KY
yesst1[at]gmail.com
Title - Abstract - Introduction - Bioassays - Results - Conclusions - References - Acknowledgements
Abstract
Harmful algal blooms are becoming more frequent worldwide partially due to anthropogenic pollution. Heterosigma akashiwo, a raphidophyte, has been linked to fish kills in many Pacific Rim countries, including the United States, and may be toxic to a wide range of marine species. The goal of this project was to evaluate the toxicity of H. akashiwo to early life stages of two important fishery resources in the Puget Sound region. Pacific herring (Clupea pallasi) is a valuable forage fish, fed on by many commercially important species while the green sea urchin (Strongylocentrotus droebachiensis) is an ecologically important species, which also sustains a valuable commercial fishery. This study used bioassay protocols developed at Shannon Point Marine Center to test the toxicity of H. akashiwo to early larval stages of Pacific herring. Test endpoints for herring larvae were survival, growth, and feeding success. To test the toxicity of H. akashiwo to green sea urchins, I followed an ASTM standard protocol. Test endpoints for the sea urchin test were survival and normal development to the pluteus larval stage. Test results have shown no evidence of toxicity to herring or urchin larvae. Each species has displayed survival greater than 70% while exposed to the highest concentrations of Heterosigma. H. akashiwo’s mode of “toxicity” may not affect larval fish or invertebrates.
Title - Abstract - Introduction - Bioassays - Results - Conclusions - References - Acknowledgements
Introduction
Heterosigma akashiwo, a raphidophyte linked to fish kills in many Pacific Rim countries may be toxic to a wide range of marine species. In Puget Sound, blooms of H. akashiwo are prominent from May-June, when water temperatures begin to warm. The densities of blooms are typically 1,000 – 10,000 cells/mL (Fairbanks 1992). Despite knowledge of H. akashiwo’s ecology and physiology, few studies have attempted to determine directly its mode of ichthyotoxicity (i.e., Reactive Oxygen Species (H2O2), neurotoxin, gill damage or asphyxiation).
Bioassay protocols were used to evaluate the toxicity of H. akashiwo to early life stages of two important fishery resources in Puget Sound. A non-toxic alga (Isochrysis galbana) was tested to evaluate potential physical effects of high algal densities.
Title - Abstract - Introduction - Bioassays - Results - Conclusions - References - Acknowledgements
Bioassays
Larval Herring Bioassay:
Testing was conducted following the protocol of Dinnel et al. (2008).
Test conditions: 12ºC, 30 ‰ salinity, 16:8 h light:dark photoperiod, 7-day exposures, 10 fish/beaker, test volume 200 ml, replication 4x per test concentration.
Parameters tested: survival, feeding success, and growth in terms of final dry weight.
Null Hypothesis: Toxins from H. akashiwo will have no effect on herring survival, feeding, or growth.
Feeding (yellow) and non-feeding:
Sea Urchin Embryo Bioassay:
Testing was conducted following the ASTM (2005) protocol.
Test conditions: 15ºC, 30 ‰ salinity, 16:8 h light:dark photoperiod, 96-h exposures, 3,000 embryos/beaker, replication 4x per test concentration.
Parameter tested: survival to normal pluteus stage.
Null Hypothesis: H. akashwio and I. galbana will have no effect on sea urchin embryo survival to a normal pluteus.
| Normal Pluteus: | Abnormal Pluteus: |
 |  |
Title - Abstract - Introduction - Bioassays - Results - Conclusions - References - Acknowledgements
Results
Herring:
Figure 1. Mean survival and dry weights of larval herring following 7-day exposures to densities of H. akashiwo ranging from 1,000 to 16,000 cells/ml. Standard errors shown.
Figure 2. Mean daily feeding success for larval herring exposed to H. akashiwo densities of 1,000 to 16,000 cells/ml (colored number x 1,000) for 7 days.
Urchins:
Figure 3. Mean normal survival of sea urchin embryos exposed to 2,500 to 40,000 cells/ml of H. akashiwo for 96 hours. Standard errors are shown.
Figure 4. Mean normal survival of sea urchin embryos exposed to 125,000 to 1,000,000 cells/ml of I. galbana for 96 hours. Standard errors are shown.
Title - Abstract - Introduction - Bioassays - Results - Conclusions - References - Acknowledgements
Conclusions
Neither H. akashiwo nor I. galbana limit herring survival, feeding, or growth at the cell densities tested.
H. akashiwo does not affect sea urchin survival and development to the pluteus stage for the densities tested. Only the highest concentration of I. galbana affected sea urchin development.
H. akashiwo’s mode of “toxicity” may not affect larval fish or invertebrates.
References
- ASTM (American Society for Testing and Materials). 2005. Standard guide for conducting static acute toxicity tests with echinoid embryos. Standard Guide E 1563 (Pp. 960-975) in: Annual Book of ASTM Standards, 2005. Vol 11.05. Biological Effects and Environmental Fate; Biotechnology. ASTM International, Conshohocken, PA.
- Dinnel, P.A. 2008b. Pacific herring, Clupea pallasi, embryo and larval bioassay protocols. Summary Report for Washington Department of Ecology. 18 pp.
- Fairbanks, C. 1992. Growth of th red time alga Heterosigma akashiwo. Accepted in Partial Completion of the Requirements for th Degree Masters of Science, WWU.
Title - Abstract - Introduction - Experimental Setup - Results - Conclusions - References - Acknowledgements
Acknowledgements
I would like to thank Paul Dinnel, for his guidance and expertise. Brian Bingham, Steve Sulkin and all of SPMC.