Perturbations in a pelagic food web during the NE pacific large marine heatwave and persistent harmful diatom blooms.

Unprecedented warm ocean conditions, driven by the Large Marine Heatwave (LMH) and the 2015-16 El Niño in the Northeast Pacific favored pervasive toxigenic Pseudo-nitzschia spp. blooms that caused widespread ecological impacts, but little is known about the magnitude to which marine food webs were altered. Here, we assessed the trophic transfer of domoic acid (DA; a neurotoxin) and changes in trophic position from multiple key species during the peak of the LMH and El Niño in 2015 in comparison with 2018, a reference non-anomalous warm year.

Stable isotope analysis reveals differences in domoic acid accumulation and feeding strategies of key vectors in a California hotspot for outbreaks.

Given the effects of harmful algal blooms (HABs) on human and wildlife health, understanding how domoic acid (DA) is accumulated and transferred through food webs is critical for recognizing the most affected marine communities and predicting ecosystem effects. This study combines stable isotopes of carbon (δC) and nitrogen (δN) from bulk muscle tissue with DA measurements from viscera to identify the foraging strategies of important DA vectors and predators in Monterey Bay, CA. Tissue samples were collected from 27 species across three habitats in the summer of 2018 and 2019 (time periods without prominent HABs).

Cooperative feeding in common dolphins as suggested by ontogenetic patterns in δ N bulk and amino acids.

Understanding the effect of stage-specific traits on species feeding habits can reveal how natural selection shapes life strategies. Amino acid (AA) nitrogen stable isotopes (δ N) provide multiple proxies of habitat baseline values and diet that can improve our understanding of species feeding strategies relative to their animal metabolism. We evaluated the effect of body length as a proxy for life stage and sex on the feeding habits of the common dolphin Delphinus delphis delphis using δ C and δ N in bulk tissue and AAs δ N from skin samples collected for almost two decades.

Amino acid δN underestimation of cetacean trophic positions highlights limited understanding of isotopic fractionation in higher marine consumers.

Compound-specific stable isotope analysis (CSIA) of amino acids (AAs) has been rapidly incorporated in ecological studies to resolve consumer trophic position (TP). Differential N fractionation of "trophic" AAs, which undergo trophic N enrichment, and "source" AAs, which undergo minimal trophic N enrichment and serve as a proxy for primary producer δN values, allows for internal calibration of TP. Recent studies, however, have shown the difference between source and trophic AA δN values in higher marine consumers is less than predicted from empirical studies of invertebrates and fish.

Amino acid-specific δN trophic enrichment factors in fish fed with formulated diets varying in protein quantity and quality.

Compound-specific isotope analysis (CSIA) of amino acids (AAs) in consumer tissues is a developing technique with wide-ranging applications for identifying nitrogen (N) sources and estimating animal trophic level. Controlled experiments are essential for determining which dietary conditions influence variability in N stable isotopes (δN) trophic enrichment factors in bulk tissue (TEF) and AAs (TEF). To date, however, studies have not independently evaluated the effect of protein quantity and quality (digestibility) on TEFs, complicating the application of AA-δN values for estimating trophic levels.