All four test species have adult life stages that reside near or on the seabed well out of harms way from the effects of a surface oil spill or possible presence of chemical herders. However, these species also have early life stages (gametes, embryos and larvae) that develop in the water column where they are more likely to be impacted by an oil spill and ongoing mitigation operations when seasonally present. The four species also cover several animal groups and trophic levels with the early life stages being present across all seasons of the year.

Green sea urchins reside on the ocean floor and are harvested in Atlantic Canada with commercial landings typically valued at more than $5 million annually. Sea urchin gametes are expressed into the water column where fertilization occurs when the seawater temperature is optimally about 8-12 ºC. A sea urchin fertilization test was used in this study to assess fertilization success in the presence of both herders at varying concentrations. 
 
American lobster forms the basis of a very important fishery throughout Atlantic Canada with landings expected to be over $2 billion each year. Female lobsters carry fertilized eggs on their abdomen for about a year with hatching in the Bay of Fundy region occurring during late-summer to mid-fall when seawater temperature is near its peak. “Huntsman Marine has developed numerous repeatable exposures involving all lobster life stages, with a frequently performed test focused on the newly hatched Stage I larvae that live in the upper water column where interaction with a surface oil spill is possible during those 3-4 months when larval lobsters are present,” explained Asnicar. 
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Testing with Atlantic cod and lumpfish larvae is another Huntsman Marine specialty that is not readily performed by other toxicology labs globally. Both of these tests require maintenance of in house adults that become mature to spawn and provide access to gametes or fertilized eggs for incubation and hatching. The commercial value of Atlantic cod landings is presently a shadow of what it once was but still surpasses $20 million annually. Spawning occurs during winter and this requires exposure temperatures to be maintained at 3-7 ºC to provide realistic results. The lumpfish fishery is considerably lower in value but the species is receiving more recent attention due to its threatened status and consideration for listing under the Species at Risk Act in Canada. Lumpfish spawn in the April-May period and testing occurred at 12±2 ºC. 

The herder Siltech was found to be between 4 and 78 times more toxic than ThickSlick regardless of the test species or endpoint measured. The sea urchin fertilization test produced the most sensitive endpoint in the study with an effective concentration to cause an impact in 50% (EC50) of the fertilization success of 1.0 mg/L following a 20-minute exposure to Siltech. The least sensitive test to Siltech was from the lumpfish exposure for 3 hr with the lethal concentration to cause mortality in 50% (LC50) of the exposed larvae to be 13.4 mg/L. Siltech caused significantly higher mortality in Stage I lobsters than ThickSlick, however, all larvae that survived were able to molt from Stage I to Stage II lobsters during the exposure trials. 

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Exposures to the herder ThickSlick using the same early life stages provided very different sensitivity results. The hatching success of 20-day-old cod embryos was the least sensitive to ThickSlick with an EC50 of 476.6 mg/L. The most sensitive endpoints were the survival of 24-hr-old cod embryos, with an LC50 of 8.6 mg/L at 48 hr and 7.6 mg/L at 72 hr, and the sea urchin fertilization 20-min EC50 of 8.8 mg/L. 

The choice of whether and which herder to use in the event of an oil spill will be based on what is approved by regulators, the type of oil spilled, and net environmental benefit analysis for the specific environmental sensitivity. “We are pleased to contribute necessary hazard data that regulators may use when choosing the best path forward to address a possible oil spill while providing the highest level of protection to the environment,” concluded Asnicar. 

The research publication was co-authored by researchers at Aarhus University (Roskilde, Denmark) and Fisheries & Ocean Canada. The study was funded by Fisheries & Ocean Canada through Canada’s Ocean Protection Plan, New Brunswick Innovation Foundation and The Huntsman Marine Science Centre.