Aaron W. E. Galloway

Partitioning the Relative Importance of Phylogeny and Environmental Conditions on Phytoplankton Fatty Acids

Essential fatty acids (EFA), which are primarily generated by phytoplankton, limit growth and reproduction in diverse heterotrophs. The biochemical composition of phytoplankton is well-known to be governed both by phylogeny and environmental conditions. Nutrients, light, salinity, and temperature all affect both phytoplankton growth and fatty acid composition. However, the relative importance of taxonomy and environment on algal fatty acid content has yet to be comparatively quantified, thus inhibiting predictions of changes to phytoplankton food quality in response to global environmental change. We compiled 1145 published marine and freshwater phytoplankton fatty acid profiles, consisting of 208 species from six major taxonomic groups, cultured in a wide range of environmental conditions, and used a multivariate distance-based linear model to quantify the total variation explained by each variable. Our results show that taxonomic group accounts for 3-4 times more variation in phytoplankton fatty acids than the most important growth condition variables. The results underscore that environmental conditions clearly affect phytoplankton fatty acid profiles, but also show that conditions account for relatively low variation compared to phylogeny. This suggests that the underlying mechanism determining basal food quality in aquatic habitats is primarily phytoplankton community composition, and allows for prediction of environmental-scale EFA dynamics based on phytoplankton community data. We used the compiled dataset to calculate seasonal dynamics of long-chain EFA (LCEFA; ≥C20 ɷ-3 and ɷ-6 polyunsaturated fatty acid) concentrations and ɷ-3:ɷ-6 EFA ratios in Lake Washington using a multi-decadal phytoplankton community time series. These analyses quantify temporal dynamics of algal-derived LCEFA and food quality in a freshwater ecosystem that has undergone large community changes as a result of shifting resource management practices, highlighting diatoms, cryptophytes and dinoflagellates as key sources of LCEFA. Moreover, the analyses indicate that future shifts towards cyanobacteria-dominated communities will result in lower LCEFA content in aquatic ecosystems.

FATTY ACID SIGNATURES DIFFERENTIATE MARINE MACROPHYTES AT ORDINAL AND FAMILY RANKS 1

Primary productivity by plants and algae is the fundamental source of energy in virtually all food webs. Furthermore, photosynthetic organisms are the sole source for ω‐3 and ω‐6 essential fatty acids (EFA) to upper trophic levels. Because animals cannot synthesize EFA, these molecules may be useful as trophic markers for tracking sources of primary production through food webs if different primary producer groups have different EFA signatures. We tested the hypothesis that different marine macrophyte groups have distinct fatty acid (FA) signatures by conducting a phylogenetic survey of 40 marine macrophytes (seaweeds and seagrasses) representing 36 families, 21 orders, and four phyla in the San Juan Archipelago, WA, USA. We used multivariate statistics to show that FA composition differed significantly (P < 0.001) among phyla, orders, and families using 44 FA and a subset of seven EFA (P < 0.001). A second analysis of published EFA data of 123 additional macrophytes confirmed that this pattern was robust on a global scale (P < 0.001). This phylogenetic differentiation of macrophyte taxa shows a clear relationship between macrophyte phylogeny and FA content and strongly suggests that FA signature analyses can offer a viable approach to clarifying fundamental questions about the contribution of different basal resources to food webs. Moreover, these results imply that taxa with commercially valuable EFA signatures will likely share such characteristics with other closely related taxa that have not yet been evaluated for FA content.

A fatty acid based bayesian approach for inferring diet in aquatic consumers

We modified the stable isotope mixing model MixSIR to infer primary producer contributions to consumer diets based on their fatty acid composition. To parameterize the algorithm, we generated a ‘consumer-resource library’ of FA signatures of Daphnia fed different algal diets, using 34 feeding trials representing diverse phytoplankton lineages. This library corresponds to the resource or producer file in classic Bayesian mixing models such as MixSIR or SIAR. Because this library is based on the FA profiles of zooplankton consuming known diets, and not the FA profiles of algae directly, trophic modification of consumer lipids is directly accounted for. To test the model, we simulated hypothetical Daphnia comprised of 80% diatoms, 10% green algae, and 10% cryptophytes and compared the FA signatures of these known pseudo-mixtures to outputs generated by the mixing model. The algorithm inferred these simulated consumers were comprised of 82% (63-92%) [median (2.5th to 97.5th percentile credible interval)] diatoms, 11% (4-22%) green algae, and 6% (0-25%) cryptophytes. We used the same model with published phytoplankton stable isotope (SI) data for δ13C and δ15N to examine how a SI based approach resolved a similar scenario. With SI, the algorithm inferred that the simulated consumer assimilated 52% (4-91%) diatoms, 23% (1-78%) green algae, and 18% (1-73%) cyanobacteria. The accuracy and precision of SI based estimates was extremely sensitive to both resource and consumer uncertainty, as well as the trophic fractionation assumption. These results indicate that when using only two tracers with substantial uncertainty for the putative resources, as is often the case in this class of analyses, the underdetermined constraint in consumer-resource SI analyses may be intractable. The FA based approach alleviated the underdetermined constraint because many more FA biomarkers were utilized (n < 20), different primary producers (e.g., diatoms, green algae, and cryptophytes) have very characteristic FA compositions, and the FA profiles of many aquatic primary consumers are strongly influenced by their diets.

Terrestrial carbohydrates support freshwater zooplankton during phytoplankton deficiency

Freshwater food webs can be partly supported by terrestrial primary production, often deriving from plant litter of surrounding catchment vegetation. Although consisting mainly of poorly bioavailable lignin, with low protein and lipid content, the carbohydrates from fallen tree leaves and shoreline vegetation may be utilized by aquatic consumers. Here we show that during phytoplankton deficiency, zooplankton (Daphnia magna) can benefit from terrestrial particulate organic matter by using terrestrial-origin carbohydrates for energy and sparing essential fatty acids and amino acids for somatic growth and reproduction. Assimilated terrestrial-origin fatty acids from shoreline reed particles exceeded available diet, indicating that Daphnia may convert a part of their dietary carbohydrates to saturated fatty acids. This conversion was not observed with birch leaf diets, which had lower carbohydrate content. Subsequent analysis of 21 boreal and subarctic lakes showed that diet of herbivorous zooplankton is mainly based on high-quality phytoplankton rich in essential polyunsaturated fatty acids. The proportion of low-quality diets (bacteria and terrestrial particulate organic matter) was <28% of the assimilated carbon. Taken collectively, the incorporation of terrestrial carbon into zooplankton was not directly related to the concentration of terrestrial organic matter in experiments or lakes, but rather to the low availability of phytoplankton.

A Survey of Ungulates by Students Along Rural School Bus Routes

We tested the reliability and utility of students, Grades 1–8, to count mule deer (Odocoileus hemionus) and elk (Cervus elephus) along rural school bus routes in Kittitas County, Washington, from 2003 to 2004 as part of an investigation on wildlife response to rural development. Student and supervisor counts of deer and elk were similar (α = .05). Student involvement was sustained by the presence of the supervisor and by providing a three-tiered incentives package to encourage participation. Our results demonstrate that students provide an opportunity for cost-effective long-term monitoring of changes in ungulate distribution along public transit routes. Beside providing information needed by wildlife managers, students and the community can benefit by increasing their ecological literacy and community participation.

Trophic Transfer of Macroalgal Fatty Acids in Two Urchin Species: Digestion, Egestion, and Tissue Building

Sea urchins are ecosystem engineers of nearshore benthic communities because of their influence on the abundance and distribution of macroalgal species. Urchins are notoriously inefficient in assimilation of their macroalgal diets, so their fecal production can provide a nutritional subsidy to benthic consumers that cannot capture and handle large macroalgae. We studied the assimilation of macroalgal diets by urchins by analyzing the profiles of trophic biomarkers such as fatty acids (FAs). We tracked macroalgal diet assimilation in both Strongylocentrotus droebachiensis and S. purpuratus. Juvenile S. droebachiensis and adult S. purpuratus were maintained for 180 and 70 days, respectively, on one of three monoculture diets from three algal phyla: Nereocystis luetkeana, Pyropia sp., or Ulva sp. We then analyzed FA profiles of the macroalgal tissue fed to urchins as well as urchin gonad, gut, digesta, and egesta (feces) to directly evaluate trophic modification and compare nutritional quality of urchin food sources, urchin tissues, and fecal subsidies. In the S. purpuratus assay, there were significantly more total lipids in the digesta and egesta than in the algae consumed. The FA profiles of urchin tissues differed among urchin species, all diets, and tissue types. Despite these differences, we observed similar patterns in the relationships between the urchin and macroalgal tissues for both species. Egesta produced by urchins fed each of the three diets were depleted with respect to the concentration of important long chain polyunsaturated fatty acids (LCPUFAs), but did not differ significantly from the source alga consumed. Both urchin species were shown to synthesize and selectively retain both the precursor and resulting LCPUFAs involved in the synthesis of the LCPUFAs 20:4⍵6 and 20:5⍵3. S. droebachiensis and S. purpuratus exhibited consistent patterns in the respective depletion and retention of precursor FAs and resulting LCPUFAs of Pyropia and Ulva tissues, suggesting species level control of macroalgal digestion or differential tissue processing by gut microbiota. For both S. droebachiensis and S. purpuratus, macroalgal diet was a surprisingly strong driver of urchin tissue fatty acids; this indicates the potential of fatty acids for future quantitative trophic estimates of urchin assimilation of algal phyla in natural settings.

Range expansion of tropical pyrosomes in the northeast Pacific Ocean

Pyrosomes are colonial pelagic tunicates that have fascinated marine biologists for over a century. Their name comes from the “fiery” bioluminescence that luminous organs produce at night time. Blooms of pyrosomes, identified as Pyrosoma atlanticum (Peron, 1804), have recently appeared in the North Pacific Ocean (Fig. 1), prompting questions about environmental factors that triggered their appearance and persistence over multiple seasons as well as potential ecosystem impacts. Pelagic tunicates, which include salps, dolioloids, and pyrosomes, are Urochordates that spend their whole life cycle in the plankton and feed using fine mucus meshes. Pyrosomes are colonies of zooids that are connected in a chitinous tunic and resemble colonial benthic ascidians (Class Ascidiacea). Genetically identical blastozooids are added to the colony via asexual budding. Pyrosome colonies can reach lengths of several meters, with pyrosomes in the northeastern Pacific reaching up to 80 cm in length (Brodeur et al. 2018). Ciliary beating within the zooids achieves both suspension feeding and locomotion (Alldredge and Madin 1982). Each zooid contains luminous organs that may be used to communicate with zooids further away within the colony in response to mechanical or light stimuli (Bowlby et al. 1990). Pyrosomes remain one of the least-studied planktonic grazers, in spite of their widespread distribution and ecological significance. Like other pelagic tunicates, pyrosomes are known to form high density blooms reaching tens of individuals per cubic meter, with swarms of P. atlanticum removing >50% of phytoplankton standing stock in the 0–10 m layer (Drits et al. 1992). Most species, including P. atlanticum,

Massive crab recruitment events to the shallow subtidal zone

Highdensity and temporally pulsed propagule recruitment strategies are common in many plants (e.g., masting, Kelly 1994), and both terrestrial (e.g., cicada emergence; Williams and Simon 1995) and marine invertebrates (reviewed in Caley et al. 1996). The extent and effects of recruitment pulses on population dynamics of the species involved and their subsidy to local predator populations are broadly appreciated (Karban 1982, Byström 2006). While well documented for many sessile marine invertebrates, such as barnacles (e.g., Strathmann and Branscomb 1979), curiously, such massrecruitment events to the marine benthos have not, to our knowledge, been described for mobile consumer species like crabs. Large, episodic influxes of new settlers could have very strong, yet underappreciated, impacts on the communities in which they land, both as a source of prey and as predators on local organisms. During a SCUBA dive at Port Orford, Oregon, USA on 19 April 2016, Galloway observed a remarkably dense benthic aggregation of recently settled Cancer (Metacarcinus) magister megalopae, the final larval stage of decapod crustaceans, as well as new recruits (firstinstar settlers). Between 7 and 13 m depth (the deepest descent) and throughout the 45min dive, every surface of the rocky reef, including sessile invertebrates, algae, vertical rock walls, and cobbles, in an estimated 100m2 area, was completely covered with new recruits. The recruits were stacked upon each other, several individuals deep. Without a camera during this dive, Galloway collected a handful of crabs and photographed them on the shore to document their size (Appendix S1). Based on the carapace width of the recruits (mean = 7.1 mm, SD = 0.69, n = 12), we estimated a density of ~22,000 crabs/m2 (one layer of crabs), and densities may have been as high as ~65,000 crabs/m2 (three layers of crabs). There were no recruits observed at this site on an earlier dive on 4 April 2016. Observations by an Oregon Department of Fish and Wildlife (ODFW) biologist (J. Watson, personal communication) were consistent with ours. Two days before, Watson was sampling demersal rockfish using hook and line near Depoe Bay, Oregon (250 km to the north), and reported that an usually large proportion of rockfish caught, particularly black rockfish (Sebastes melanops), were regurgitating newly settled Dungeness crabs. On a SCUBA dive at the original dive site (Graveyard Point; 42.73837° N, 124.49938° W) 23 d later (13 May 2016), there were still dense aggregations of new recruits, with densities of ~5,000–11,000 crabs/m2 (Fig. 1a), but the recruits were now located at the interface between the rocky reef and the cobble/sandy bottom. On this same day, ODFW biologists were conducting remote operated vehicle (ROV) surveys near the Redfish Rocks Marine Reserve, ~7 km south of the Port Orford dive site, and also observed dense aggregations of new recruits (~3,000– 7,000 crabs/m2; Video S1). On nine subsequent dive surveys at rocky reefs in the Port Orford area (sites within a 20km2 area), and as late as 31 August 2016, juvenile age 0+ crabs (~6–13 mm carapace width) were observed in groups in all habitat types, including vertical walls, at densities ranging from Ecology, 0(0), 2017, pp. 1–4