In our first blog post, we shared details about the reef surveys conducted in Hawaii by the Seattle Aquarium every winter since 2009. In 2017, our ninth consecutive year in Hawaii, we added a water quality component to our marine fish/coral surveys as part of a NOAA coral reef health grant we received to support this work.
Coral reefs and their associated fish assemblages are threatened and disappearing worldwide. Monitoring reef fish and coral health stability, growth or decline is important for the management of these fragile ecosystems. In addition, measuring the presence or persistence of toxic chemicals in these areas will shed light into how such chemicals may be producing negative effects on the reefs.
Twenty-one samples were taken, at depths ranging between 15 and 45 feet, in four different areas of the Big Island, over a span of five days. Because 2017 was our first year conducting water quality tests gathered at depth in these reef systems, our sample size is limited: one sample taken at one point in time. It’s important to put these values in context with data from other agencies with larger sample sizes and long-term datasets.
What did we measure and what were the results?
Enterococcus: A fecal indicator bacteria that occurs normally in the gut of vertebrates. If contained, there is no disease risk, but it may cause infections if introduced to other parts of the body. Results ranged from zero to 50 colony-forming units per 100 ml of water. All values were under the maximum sample value used to close Hawaii beaches.
Microplastics: Found in four out of seven sites.
PBDE (Polybrominated diphenyl ethers): Flame-retardant chemicals used in a wide variety of products. Hawaii banned the use of some forms of PBDE in 2004. Two samples had values just above the minimum detection limit of the assay (>0.04 ppb).
Pyrethroid: A common insecticide (the natural form is extracted from chrysanthemum), it’s chemically synthesized for large-scale use. Aquatic invertebrates and fish have been found to be sensitive to these chemicals. Five samples had values above the minimum detection limit (>1.085 ppb).
DDT (Dichloro-diphenyl-trichloroethane): An organochlorine insecticide that was shown to be highly toxic and was banned in the U.S. in 1972. Twelve samples had values of >2.637 ppb. Because the DDT values are much higher than expected, we believe that matrix interference is occurring, and this assay cannot be accurately used for saltwater samples.
Glyphosate: The active ingredient in the herbicide Roundup™. The manufacturer claims that Roundup is harmless to animals and humans because the mechanism of action it uses (which allows it to kill weeds), called the shikimate pathway, is absent in all animals. However, the shikimate pathway is present in bacteria and targets beneficial as well as harmful bacteria, and thus may negatively affect fish, invertebrates or mammals. Results: Measured in all samples tested, over the minimum detection limit (>0.24 ppb).
Nitrates (as N): Nutrients found in human and animal waste, as well as the breakdown of plants. At high levels, nitrates encourage algal blooms, which can cause low oxygen levels in the water and lead to the death of oxygen-dependent marine organisms. Values ranged from 1.38 to 10.68 µmol/L.
Orthophosphate (as P): The reactive form of phosphate, produced by natural processes of decaying plants and animals and man-made sources such as partially treated/untreated sewage, runoff from agricultural sites, and application of some lawn fertilizers. Similarly to nitrates, it can cause algal blooms at high levels. Values ranged from 0.04 to 0.25 µmol/L.
Silica (as Si): Compounds present in all living organisms. Silicon and phosphorous or silicon and nitrogen ratio are thought to contribute to the type of algae that will dominate: diatoms versus cyanobacteria. Results ranged from 2.54 to 81 µmol/L.
Ammonium (as N): One of several forms of nitrogen that, at high levels, cause direct toxic effects on aquatic life. Results: below minimum detection limit of <0.36 µmol/L for all sites.
Some substances were found at higher rates in some sites than others—for instance, enterococcus and PBDE were highest at Site 1 (in Puako) and Site 4 (in Old Kona), suggesting influx of water likely from septic systems carrying these contaminants. Pyrethroids, glyphosate, nitrates, orthophoshates, glyphosate, DDT and ammonium were found in approximately equal amounts among all sites—meaning that these chemicals were used equally at each site.
Overall, the water quality in these areas was relatively good at depth. Because the samples were taken at the reef level (not in surface waters, and not along the shoreline), it’s expected for them to be lower than what other research groups may have reported in surface and shoreline waters. These levels are baseline and should be repeated to determine significant trends.