Imprudent fishing harvests and consequent trophic cascades on the West Florida shelf over the last half century: A harbinger of increased human deaths from paralytic shellfish poisoning along the southeastern United States, in response to oligotrophicatio

Within the context of ubiquitous overfishing of piscivores, recent consequent increments of jellyfish and clupeids have occurred at the zooplanktivore trophic level in the eastern Gulf of Mexico (GOM), after overfishing of one of their predators, i.e. red snapper. Initiation of a local trophic cascade thence led to declines of herbivore stocks, documented here on the West Florida shelf. These exacerbating world-wide trophic cascades have resulted in larger harmful algal blooms (HABs), already present at the base of most coastal food webs. Impacts on human health have thus far been minimal within nutrient-rich coastal regions. To provide a setting for past morbidities, consideration is given to chronologies of other trophic cascades within eutrophic, cold water marine ecosystems of the Scotian Sea, in the Gulf of Alaska, off Southwest Africa, within the Barents, White, and Black Seas, in the Gulf of Maine, and finally in the North Sea. Next, comparison is now made here of recent ten-fold increments within Florida waters of both relatively benign and saxitoxic HABs, some of which are fatal to humans. These events are placed in a perspective of other warm shelf systems of the South China and Caribbean Seas to assess prior and possible future poison toxicities of oligotrophic coastal habitats. Past wide-spread kills of fishes and sea urchins over the Caribbean Sea and the downstream GOM are examined in relation to the potential transmission of dinoflagellate saxitoxin and other epizootic poison vectors by western boundary currents over larger “commons” than local embayments. Furthermore, since some HABs produce more potent saxitoxins upon nutrient depletion, recent decisions to ban seasonal fertilizer applications to Florida lawns may have unintended consequences. In the future, human-killing phytoplankton, rather than relatively benign fish-killing HABs of the past, may be dispersed along the southeastern United States seaboard.

Research highlights
► Recent trophic cascades of coastal seas may have exacerbated the toxic impacts of seasonal normally occurring, nutrient-starved harmful algal blooms (HABs) over the last 50 years within a total of at least 15 shelf ecosystems.
► Trophic cascades down marine food webs of these shelves were initiated from overfishing of top predators, i.e. fish-eating piscivores such as cod, mackerel, pollock, snapper, and grouper, resulting in greater accumulation of the algal prey of zooplankton herbivores, upon additional relaxation of grazing stress.
► Among the plant prey items were saxitoxic dinoflagellate HABs, whose saxitoxin poisons can at times be much more toxic to humans than synthetic nerve gases, i.e. sarin, during Paralytic Shellfish Poisoning (PSP) events, killing >100 humans around the South China Sea over the last few decades.
► Like the nitrogen- and phosphorus-limited laboratory cultures of these saxitoxic dinoflagellates, these results suggest that nutrient-depletion of coastal waters can also lead to more toxic forms of field populations of these HABs, such that the potential now exists for increased public health impacts of a greater number and wider extent of future PSP events, as a consequence of legislated reductions of nutrient loadings to Florida coastal waters.