The title is a question posed by my colleague, Dave Caron, at University of Southern California when sea lions started stranding from domoic acid poisoning in Orange County a couple weeks ago. We were definitely caught off guard by this one. After the monstrous Pseudo-nitzschia bloom of 2015 that covered such a large swath of coastline from Santa Barbara to Alaska and a patchy year of blooms in 2016 that affected Sonoma and Humboldt County crabbing, it was not expected that domoic acid would appear with such a vengeance in the Southern California Bight. The last time we saw really large numbers of sea lions dying in this region was 2007. Now there is a very concerning loss of seabird life in the Santa Barbara Channel and sick, pregnant sea lions littering the coast from Santa Barbara down to San Diego. Other marine mammals such as elephant seals, dolphins, and even the endangered Guadalupe Fur Seal are stranding in unusually high numbers. There had certainly been a lull in this kind of stranding related to harmful algal bloom activity in the south. This was partly explained (perhaps) by waters associated with the Pacific Warm Anomaly being too warm for Pseudo-nitzschia to thrive, i.e. outside of the “Goldilocks zone” occurring further north. It doesn’t mean we don’t routinely see this potentially toxic diatom in moderate to high numbers, it just means that in areas where we monitor, like Santa Monica, Newport, and Scripps Piers, there had not been much in the way of toxins to report in recent years and certainly no animal strandings. This year, we are still not seeing the kind of domoic acid levels at the piers that might cause a large alert, but animals are appearing at the beach disoriented and seizing. The California Harmful Algae Risk Mapping System (C-HARM) system predicts fairly high levels of domoic acid offshore in the region, which may signal that sea lions and birds are acquiring the toxin outside the very nearshore coastal zone. Experience tells us, however, that these blooms are very patchy and also occur below the surface where animals are foraging. Satellites that supply key observations for the toxin model cannot detect subsurface blooms.
One thing reported fairly often in the media is that the bloom is being “fed” by pollution or fertilizers from land, or that this event is associated with all the rain we have had this winter. It is best to exercise caution here since the timing is not consistent with the run-off hypothesis. Pseudo-nitzschia began to appear more in relation to the “spring transition” than it did in the direct aftermath of the rain events. Once river plumes reach the ocean, there is an awful lot of dilution that takes place, particularly after a week or two. During spring, however, nutrients start to change as a result of upwelling and will encourage the growth of this diatom. The satellite perspective indicates that this bloom may have started offshore, away from land influence. The reasons for the sudden explosion of DA production will take time to tease out.
Another confounding factor is that at Scripps Pier and other monitoring sites, there is an increase in “red tides” formed by certain (non-toxic) dinoflagellates. This is happening alongside the Pseudo-nitzschia bloom and may also explain things like seabird deaths. The animals are not starving and don’t appear hypothermic, but the possibility that biosurfactants (hydrophobic substances produced by the dinoflagellates that stick to bird feathers) are impeding their ability to forage is something that should not be overlooked. Melissa Carter at Scripps has warned that we may be ignoring this dual-bloom situation because of the many sick sea lions overwhelming the marine mammal rescue centers. Most are pregnant females, and many are reportedly doing much better after aborting their fetuses. Because pregnant females forage longer and further out to sustain their fetal pups, they are at higher risk of acquiring lethal doses of the neurotoxin. One sad reality is that even if they survive and are released back into the wild, their brains may be damaged enough to leave them stranded again during the next big toxic event or even from chronic exposure to background levels of domoic acid in the ecosystem.