Exposure assessment of the biotoxin domoic acid in California sea lions: application of a bioenergetic model

Abstract

The biotoxin domoic acid (DA), produced by diatoms of the genus Pseudo-nitzschia, has caused massive California sea lion Zalophus californianus mortalities and live strandings along the California coast. Since quantifying the field DA dose that causes toxic effects in sea lions is logistically difficult, a bioenergetic model that uses age/sex-specific energy requirements was developed to estimate DA doses, assuming ingestion of 2 important vector species: anchovies Engraulis mordax and sardines Sardinops sagax. In this model, uncertainty and variability were incorporated by assigning sampling distributions to each model variable. Variables included: (1) vector energy density and assimilation efficiency of gross fish energy; (2) sea lion weight and energy requirements adjusted for energy expenditures associated with foraging, growth and reproduction; and (3) DA concentration in the vector species. Model outputs were analyzed relative to thresholds that cause adverse effects in other mammal species (1 and 2.71 mg DA kg -1 body weight). Based on DA concentrations measured in fish during a previous Pseudo-nitzschia bloom, consumption of anchovies versus sardines as 20% of the sea lions' daily intake would result in a 4-fold increase in risk of non-lethal toxic effects. Across age classes, the median DA dose in pups (7 to 12 mo old) was twice that estimated for juveniles and was between 2 and 4 times greater than for adults. In DA dose estimates most of the variability resulted from the uncertainty associated with the energy density of the vector species and DA concentration in sardines rather than from the uncertainty associated with sea lions. Finally, we highlight the most relevant areas of research needed for determining a definitive risk of sea lion exposure to DA. KEY WORDS: Domoic acid · Exposure assessment · California sea lion · Probabilistic modelResale or republication not permitted without written consent of the publisher

In Utero Domoic Acid Toxicity: A Fetal Basis to Adult Disease in the California Sea Lion (Zalophus californianus)

“…Yet at exposure levels of milligrams per kilograms, as is realistic for a California sea lion [22], domoic acid is a damaging neurotoxin. At the level of the receptor in the brain domoic acid binds to kainate subtypes of ionotropic glutamate receptors to induce excitotoxicity by release of glutamate and activation of NMDA ionotropic glutamate receptors [23].…”

Energy and prey requirements of California sea lions under variable environmental conditions

“…Bioenergetic models provide quantitative estimates of energy requirements by summing the costs associated with different physiological processes and animal behaviors. They have been developed for a number of marine mammal species to address both physiological and ecological questions, such as energy demands and prey requirements (Olesiuk 1993, Winship et al 2002, Noren 2011, Rechsteiner et al 2013, N oren et al 2014, trophic impacts and inter actions with commercial fisheries (Cornick et al 2006, Trzcinski et al 2006, Weise & Harvey 2008, Morissette & Brodie 2014, the risk of disease and toxin exposure (Bejarano et al 2007), and the role of energy balance in population dynamics (N ew et al 2013, 2014). Linking changes in energy budgets with reproductive success is a goal in developing bioenergetic models (Williams et al 2006, Villegas-Amtmann et al 2015 and an important component in understanding how responses to prey availability and anthropogenic disturbance ultimately affect population dynamics (Costa 2012).…”

Domoic acid disrupts the activity and connectivity of neuronal networks in organotypic brain slice cultures

“…This bloom severely poisoned hundreds of sea lions and led to the closing of several important fisheries in California, Oregon, and Washington. California sea lions regularly ingest domoic acid at concentrations reaching mg/kg levels during harmful algal blooms (Bejarano et al, 2007). Multiple marine species will likely face increasing exposure risk in the future as ocean temperatures continue to rise.…”