Parasites can have strong impacts but are thought to contribute little biomass to ecosystems. We quantified the biomass of free-living and parasitic species in three estuaries on the Pacific coast of California and Baja California. Here we show that parasites have substantial biomass in these ecosystems. We found that parasite biomass exceeded that of top predators. The biomass of trematodes was particularly high, being comparable to that of the abundant birds, fishes, burrowing shrimps and polychaetes. Trophically transmitted parasites and parasitic castrators subsumed more biomass than did other parasitic functional groups. The extended phenotype biomass controlled by parasitic castrators sometimes exceeded that of their uninfected hosts. The annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass. This biomass and productivity of parasites implies a profound role for infectious processes in these estuaries.

Ecosystem energetic implications of parasite and free-living biomass in three estuaries

Ecology of sea lice parasitic on farmed and wild fish

Global warming can affect the world's biota and the functioning of ecosystems in many indirect ways. Recent evidence indicates that climate change can alter the geographical distribution of parasitic diseases, with potentially drastic consequences for their hosts. It is also possible that warmer conditions could promote the transmission of parasites and raise their local abundance. Here I have compiled experimental data on the effect of temperature on the emergence of infective stages (cercariae) of trematode parasites from their snail intermediate hosts. Temperature-mediated changes in cercarial output varied widely among trematode species, from small reductions to 200-fold increases in response to a 10 degrees C rise in temperature, with a geometric mean suggesting an almost 8-fold increase. Overall, the observed temperature-mediated increases in cercarial output are much more substantial than those expected from basic physiological processes, for which 2- to 3-fold increases are normally seen. Some of the most extreme increases in cercarial output may be artefacts of the methods used in the original studies; however, exclusion of these extreme values has little impact on the preceding conclusion. Across both species values and phylogenetically independent contrasts, neither the magnitude of the initial cercarial output nor the shell size of the snail host correlated with the relative increase in cercarial production mediated by rising temperature. In contrast, the latitude from which the snail-trematode association originated correlated negatively with temperature-mediated increases in cercarial production: within the 20 degrees to 55 degrees latitude range, trematodes from lower latitudes showed more pronounced temperature-driven increases in cercarial output than those from higher latitudes. These results suggest that the small increases in air and water temperature forecast by many climate models will not only influence the geographical distribution of some diseases, but may also promote the proliferation of their infective stages in many ecosystems.

/pdf/global-warming-and-temperature-mediated-increases-in-4t4ze6q208.pdf

Global warming and temperature-mediated increases in cercarial emergence in trematode parasites.

Where possible, automation has been a common response of humankind to many activities that have to be repeated numerous times. The routine identification of specimens of previously described species has many of the characteristics of other activities that have been automated, and poses a major constraint on studies in many areas of both pure and applied biology. In this paper, we consider some of the reasons why automated species identification has not become widely employed, and whether it is a realistic option, addressing the notions that it is too difficult, too threatening, too different or too costly. Although recognizing that there are some very real technical obstacles yet to be overcome, we argue that progress in the development of automated species identification is extremely encouraging that such an approach has the potential to make a valuable contribution to reducing the burden of routine identifications. Vision and enterprise are perhaps more limiting at present than practical constraints on what might possibly be achieved.

/pdf/automated-species-identification-why-not-3q3nh3ozor.pdf

Automated species identification: why not?

Causes and effects of a highly successful marine invasion: Case-study of the introduced Pacific oyster Crassostrea gigas in continental NW European estuaries

To determine how physical processes and biological behaviors influence larval dispersal on the inner shelf, time series of larval concentrations were quantified during August 1994, on the Outer Banks of North Carolina, U.S.A. Zooplankton pumps, moored in 21 m of water at 3.2, 8.7, and 12.2 m above bottom, collected larvae every 3 h for 3 weeks. Physical variables and larvae were sampled at similar time and space scales. Larval concentrations were typically 10 2 ‐10 4 m 23 for polychaetes, bivalves, and gastropods and 10‐10 2 m 23 for brachyuran crab zoeae. There were two dominant scales of variability, 3‐6 h and 2‐10 d. The high-frequency signal is partially explained by diel vertical migrations—nocturnal ascent and daytime descent. This pattern would allow larvae to feed in subthermocline waters while avoiding visual predators. Low-frequency variations tracked with water temperature. Highest concentrations of worm larvae occurred in cool (upwelled) water and of crab zoeae in warm (downwelled) water. At least two larval groups comprised the clam and snail time series, one with fairly high abundances in cool water and the other with peak concentrations in warm water. Wind-driven cross-shelf transport is the most plausible explanation for these low-frequency fluctuations. For example, dense patches of worm larvae overlying parental habitat (offshore muds) would be carried shoreward in cool, upwelling flows. In contrast, brachyuran zoeae in nearsurface waters would descend at the coast during downwelling and, together with larvae aloft nearshore sediments, be transported seaward below the thermocline. Thus advected by strong along-shore and weaker cross-shelf currents, larvae zigzag up and down the coast. Vertically traversing the water column while they feed and grow, larvae ultimately seek a suitable habitat in which to settle.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2002.47.3.0803

Larval distributions in inner‐shelf waters: The roles of wind‐driven cross‐shelf currents and diel vertical migrations

Quantification of planktonic larval distributions has been limited by processing time, given the large numbers of samples generated by extensive field surveys. Until recently, the only technique available for reliable species identification of bivalve larvae was direct microscopic observation, but even this method is restricted to larval stages and species that can be distinguished morphologically. Molecular methods (e.g. antibody and oligonucleotide markers) show considerable promise for identifying bivalve larvae to species, regardless of developmental stage, alleviating ambiguity or subjectivity of some traditional, morphology-based taxonomy. Moreover, attaching species-specific molecular probes to fluorescent reporter tags, for example, has great potential for automated, expedited sample-processing. Optical identification techniques are promising, but probably not at the species level. Current methods of distinguishing bivalve larvae-morphological, molecular (i.e. immunological and DNA-based), or optical-are reviewed here to facilitate the selection of appropriate techniques for a given research problem and to stimulate the development of creative alternative approaches for rapid and accurate species identification.

/pdf/techniques-for-the-identification-of-bivalve-larvae-18yhqha9e1.pdf

Techniques for the identification of bivalve larvae

Trematode parasites in intertidal estuaries ex- perience constantly varying conditions, with the presence or absence of water potentially limiting larval transport be- tween hosts. Given the short life spans (24 h) of cercariae, emergence timing should be optimized to enhance the prob- ability of successful transmission. In the present study, field measurements and laboratory experiments identified pro- cesses that regulate the emergence of cercariae from their first intermediate snail hosts in an intertidal marsh. Larvae emerged over species-specific temperature ranges, exclu- sively during daylight hours, and only when snails were submerged. The three factors operate over different tempo- ral scales: temperature monthly, light diurnally (24-h pe- riod), and water depth tidally (12-h period). Each stimulus creates a necessary condition for the next, forming a hier- archy of environmental cues. Emergence as the tide floods would favor transport within the estuary, and light may trigger direct (downward or upward) swimming toward host habitats. Abbreviated dispersal would retain asexually re- produced cercariae within the marsh, and local mixing would diversify the gene pool of larvae encysting on sub- sequent hosts. In contrast to the timing of cercarial release, emergence duration was under endogenous control. Dura- tion of emergence decreased from sunrise to sunset, perhaps in response to the diminishing lighted interval as the day progresses. Circadian rhythms that control cercarial emer- gence of freshwater species (including schistosomes) are often set by the activity patterns of subsequent hosts. In this estuary, however, the synchronizing agent is the tides. To-

Patterns and processes of larval emergence in an estuarine parasite system.

Marine benthic invertebrates living in dense, intraspecific aggregations are important community members because they provide structural habitat for other species. Here, we determined the mechanisms that facilitate gregarious larval settlement and promote group living. Using suspension-feeding oysters (Crassostrea gigas) residing in large assemblages (“reefs”), experiments were conducted under laboratory conditions that simulated critical aspects of natural estuarine habitats. Oyster larvae were attracted to the scent of their conspecific elders. In still-water trials, they moved downward and settled after contacting a waterborne, adult chemical cue. Yet, mortality of larvae placed in the adult pallial cavity was very high (mean of 91.3%). This seeming paradox of larval attraction to adult cannibals was resolved via laboratory flume (2 cm/s and 6 cm/s flows) experiments. Suspension-feeding activity did not significantly affect flow speeds or directions. Moreover, weak (mean of 1.65 mm/s) adult ciliary currents effectively entrained phytoplankton but rarely captured larvae. In fact, only a small percentage (≤4.6%) of settlers was cannibalized in flume trials, even when they passed within 1 mm of the inhalant opening, or “gape” (a narrow slit between two valves). Larvae cued by conspecifics potentially attach to any portion of the shell surface, but there is a low probability that they will land in or near the inhalant opening. On juvenile and adult oysters, for example, the mean ratio of gape to shell surface area was only 0.025. Furthermore, in surveys of juvenile/adult oysters at nine field sites (Hood Canal and eastern Olympic Peninsula, Washington, USA), the gape was ≤5.2% of the total plane surface area of the reef. Thus, an oyster larva settling onto a reef of suspension-feeding adults is unlikely to be cannibalized. Given this low mortality risk at settlement, future fitness payoffs (e.g., improved fertilization success) may drive the evolution of a gregarious settlement cue that promotes group living.

Mechanisms reconciling gregarious larval settlement with adult cannibalism

Planktonic cercariae (parasite larvae) of digenetic flatworms (Himasthla rhigedana) encyst up to 100% of intermediate host populations. Toward explaining such high prevalence, larval behavior and passive-transport processes were evaluated experimentally for their roles in waterborne parasite transmission. Using a new application of laser and digital video imaging technologies, we quantified cercarial movements in still water and in simulated field flows. In still water, downward swimming in response to light, irrespective of intensity or source, and gravity brought larvae to the bottom three-times faster than gravitational sinking alone. A 33% elevation in temperature (18–24°C) caused a 71% increase in swim speed. In flume flows characteristic of southern California salt marshes (u* = 0.2 cm/s, occurring >80% of the time), vertical larval distributions were highly bottom skewed. The mean downward swim speed (0.59 cm/s at 24°C) was three times faster than turbulent fluctuations (w′ = 0.23 cm/s), indicating...

https://www.jstor.org/stable/pdfplus/3450153.pdf

Cheryl Ann Zimmer

Papers

Larval distributions in inner‐shelf waters: The roles of wind‐driven cross‐shelf currents and diel vertical migrations

Techniques for the identification of bivalve larvae

Patterns and processes of larval emergence in an estuarine parasite system.

Mechanisms reconciling gregarious larval settlement with adult cannibalism

Larval swimming overpowers turbulent mixing and facilitates transmission of a marine parasite