Saxitoxin and the Ochre Sea Star: Molecule of Keystone Significance and a Classic Keystone Species

Abstract

Saxitoxins (STXs) are paralytic alkaloids produced by marine dinoflagellates in response to biotic and abiotic stressors yielding harmful algal blooms. Because STX impacts coastal, near-shore communities to a greater extent than would be predicted by its relative abundance, it has been referred to as a "molecule of keystone significance" in reference to Robert Paine's Keystone Species Concept. Pisaster ochraceus, the predator upon which Paine's concept was founded, inhabits waters regularly plagued by harmful algal blooms, but the effects of STX on Pisaster have not yet been investigated. Here, we used laboratory and field experiments to examine the potential consequences of exposure to STX on sea stars' feeding, attachment to the substrate, and success in fertilization. Pisaster exhibited similar feeding behaviors when offered non-toxic prey, STX-containing prey, or a combination of the two. Although feeding behavior is unaffected, consumption of STX poses a physiological tradeoff. Sea stars in the laboratory and field had significantly lower thresholds of the force needed to detach them from their substrates after either being exposed to, or consuming, STX. High pressure (or high performance) liquid chromatography analysis indicated an accumulation of STX (and structural analogues) in sea stars' viscera, likely due to trophic transfer from toxic prey. Incidence of fertilization tended to decrease when gametes were exposed to high, yet ecologically relevant, STX concentrations of STX. These findings suggest that the molecule of keystone significance, STX, produced during harmful algal blooms extends its impacts to rocky intertidal communities by way of the keystone predator P. ochraceus.

Multiple New Paralytic Shellfish Toxin Vectors in Offshore North Sea Benthos, a Deep Secret Exposed

“…The mechanisms for sunstar toxin presence have yet to be elucidated, with further work involving live organisms required to generate supportive data. The organisms could feasibly accumulate PSTs from a dietary source, which has been used to explain echinoderm toxicity before [ 38 , 53 ]. In those cases, starfish toxicity was linked to starfish predation on a highly toxic bivalve food source.…”

“…While, the risk to humans from PSTs is wellunderstood [ 27 ], and management systems are in place to limit the risk of intoxications from shellfish consumption, PSTs can also impact animal health with negative effects on a wide range of marine organisms [ 28 ], including fish [ 29 , 30 , 31 ], whales and seals [ 32 , 33 ], otters [ 34 ], sea birds [ 35 , 36 ], sea urchins [ 37 ], starfish [ 38 ], gastropods [ 39 ], as well as bivalve molluscs [ 40 , 41 ]. Furthermore, there have been instances of PSTs affecting terrestrial animals.…”

Can single molecules bind together entire ecosystems?

“…Ferrer and his students tracked saxitoxin during and after algal blooms, recorded the force needed to remove a starfish from rocks, and found the weakest forces were needed when saxitoxin levels were at their highest during a bloom. In laboratory experiments, the toxin also altered starfish reproductive success, but didn't appear to affect which mussels became starfish food (6).…”

Marine Neurotoxins: a Double-edged Sword in Food Industry and Brain Research

“…Saxitoxin (STX) is a neurotoxin naturally produced by certain species of marine dinoflagellates and freshwater cyanobacteria [33] . STX is associated with paralytic shellfish poisoning (PSP), together with its derivatives they are often referred to as "PSP toxins" [34] .…”