Upogebia Pugettensis Research Articles

Co-infesting symbionts on a threatened marine host: evaluating correlations between an introduced parasitic isopod and a native symbiotic clam

In marine ecosystems, increased global-scale transportation creates opportunities for rapid introduction of invasive parasitic species that, in some cases, result in dramatic shifts within the native communities. A lack of detailed knowledge regarding the ecology of invasive marine parasites hinders our ability to develop effective conservation strategies and avoid unforeseen ecological consequences. We examined co-infestation patterns of a highly pathogenic, introduced parasitic isopod (Orthione griffenis) and a native symbiotic clam (Neaeromya rugifera) on the North American native blue mud shrimp Upogebia pugettensis. Our comparisons included infestations of O. griffenis and N. rugifera among 447 U. pugettensis hosts over 3 study years and were designed to statistically assess whether the 2 symbionts exhibited significant associations with one another. Our results indicate that infestations by the 2 symbiont species are positively correlated, such that the presence of one symbiont is a strong, positive predictor for the presence of the other. For both symbionts, host size is an important factor that drives the observed correlation. Host sex is also influential for O. griffenis. Interestingly, even after accounting for these host attributes, the infestations by the 2 symbionts continue to correlate positively, particularly among older (second-year and beyond) symbionts, highlighting the likely influence of additional host and environmental factors in driving the symbiont correlation post-settlement. We consider potential mechanisms, including differential energetic reserves and longevities between infested and co-infested hosts, in detail. These results offer insights into the ecological drivers of symbiont co-infestation, which have important implications for understanding host-parasite interactions and future conservation measures.

Estimating Long-term Trends in Populations of Two Ecosystem Engineering Burrowing Shrimps in Pacific Northwest (USA) Estuaries.

Temporal variation in the density and distribution of the burrowing shrimps, Neotrypaea californiensis and Upogebia pugettensis, were compared in two estuaries along the West coast of the United States (USA) where they are recognized as important ecosystem engineers. Since these shrimp construct deep burrows in the sediment, we quantified the relationship between burrow openings and shrimp density (1.5 and 1.7 burrow openings per shrimp for N. californiensis and U. pugettensis respectively) to permit population abundance estimates to be made over broad landscape scales. Neotrypaea californiensis populations estimated from burrow counts collected using a gridded survey design across representative tide flats declined by 25% between 2008-2010 in Yaquina Bay, Oregon and by 67% in Willapa Bay, Washington from 2006-2011, but increased again in Willapa Bay by 2014. Upogebia pugettensis had mostly disappeared from Willapa Bay by 2006 and declines were observed in Yaquina Bay, but the magnitude and long-term trajectory of U. pugettensis in this estuary was less clear. These species population fluctuations mirrored those observed in density collected at discrete sampling locations over the same period, equate to large changes in secondary production, and have likely resulted in substantial changes to estuarine habitat and food webs.

Assessing the Relative Importance of Estuarine Nursery Habitats - a Dungeness Crab (Cancer magister) Case Study.

Estuaries serve as important nurseries for many recreationally and commercially harvested fisheries species. Recent conceptual approaches (i.e., seascape) for assessing the value of estuaries to fisheries have advocated for complex habitat-scale assessments that integrate multiple life-history responses (e.g., abundance, growth, reproduction) and ecological processes across heterogeneous landscapes. Although ecologically compelling, implementing seascape approaches may not be feasible for resource-limited management agencies. In such cases, we propose that resource managers can enhance the identification of fishery-important estuarine habitats by integrating attainable aspects of the seascape approach into a more traditional single response (e.g., abundance) model. Using Dungeness crab (Cancer magister) as a case study, we applied a spatially-explicit hybrid approach to assess the relative contribution of different estuarine habitats to that important fishery species within three Oregon estuaries (Tillamook, Yaquina, and Alsea bays). We measured the abundance of juvenile C. magister from low-tide trawls in estuarine channels and the mosaic of habitat characteristics within defined home-range distances for the crabs. After identifying and reducing strong intercorrelations among habitat variable data, we developed a best-fit model that associated crab abundance with the most influential habitat variables. We found that lower-estuary side channels supported the highest abundance of juvenile crabs; furthermore, crab abundance was positively associated with high salinity and burrowing shrimp (Upogebia pugettensis) density on adjacent unvegetated tidal flats. This hybrid method produced a habitat-specific model that better predicted juvenile C. magister abundance than did a model based on generalized habitat categories.

Microbiome analyses and presence of cable bacteria in the burrow sediment of Upogebia pugettensis

We utilized methods of sediment cultivation, catalyzed reporter deposition-fluorescence in situ hybridization, scanning electron microscopy, and 16s rRNA gene sequencing to investigate the presence of novel filamentous cable bacteria (CB) in estuarine sediments bioturbated by the mud shrimp Upogebia pugettensis Dana and also to test for trophic connections between the shrimp, a commensal bivalve (Neaeromya rugifera), and the sediment. Agglutinated sediments from the linings of shrimp burrows exhibited higher abundances of CB compared to surrounding suboxic and anoxic sediments. Furthermore, CB abundance and activity increased in these sediments when they were incubated under oxygenated seawater. Through core microbiome analysis, we found that the microbiomes of the shrimp and bivalve shared 181 taxa with the sediment bacterial community, and that these shared taxa represented 17.9% of all reads. Therefore, bacterial biomass in the burrow sediment lining is likely a major food source for both the shrimp and the bivalve. The biogeochemical conditions created by shrimp burrows and other irrigators may help promote the growth of CB and select for other dominant members of the bacterial community, particularly a variety of members of the Proteobacteria. These associations give new understanding to the ecology of a burrowing crustacean that is common, but in decline, throughout intertidal mudflats of Northeastern Pacific estuaries.

Recruitment Ecology of Burrowing Shrimps in US Pacific Coast Estuaries

Recruitment is a strong determinant of year class strength and adult population density especially for sessile benthic invertebrates where post-settlement mortality and competition are low or relatively stable over time. A series of surveys were undertaken to characterize recruitment and post-settlement processes for two species of burrowing shrimps, Neotrypaea californiensis and Upogebia pugettensis in order to determine how they influenced broader adult populations in US west coast estuaries. On average, U. pugettensis decapodids settled earlier (April–July), recruited almost exclusively to areas with conspecific adults, and grew more rapidly during their first summer than N. californiensis. Neotrypaea californiensis decapodids settled and recruited over a longer period (June–November) and were distributed across the tidal flat. While initially more abundant in areas with conspecific adults, they also either survived better or redistributed as small juvenile shrimp to areas where adults were absent. Linear relationships were found between abundance of newly recruited (0+ age class) shrimp and that of older 1+ shrimp a year later. Positive slopes were close to one for N. californiensis but less than one for U. pugettensis, suggesting lower survival. Annual recruitment varied dramatically but was more consistent for both species in Yaquina Bay. Patterns in strong recruitment years amongst estuaries, particularly for U. pugettensis, suggest the presence of multi-estuary metapopulations linked via larval dispersal. These results have important implications for shrimp population management including control for shellfish aquaculture, but also conservation of estuarine habitats due to the strong influence of these ecosystem engineers on the benthic community.

Identification of Burrowing Shrimp Food Sources Along an Estuarine Gradient Using Fatty Acid Analysis and Stable Isotope Ratios

Two species of burrowing shrimp occur in high densities in US West Coast estuaries, the ghost shrimp, Neotrypaea californiensis, and the blue mud shrimp, Upogebia pugettensis. Both species of shrimp are considered ecosystem engineers as they bioturbate and irrigate extensive galleries within the sediment. While their burrows comprise a dominant habitat type in west coast estuaries, little is known about these shrimps’ diet and their role in estuarine food webs. The primary goals of this study were to identify major components of burrowing shrimp diets and detect variation in these diets along an estuarine gradient using combined fatty acid (FA) and stable isotope (SI) analyses. Shrimp and potential food sources including eelgrass blades, epiphytes, Ulva, sedimentary particulate organic matter (SPOM), burrow walls, and particulate organic material (POM) were sampled at different locations within Yaquina Bay, Oregon in August 2012. Both SI and FA analyses indicated differences in food resources assimilated by shrimp along the estuarine gradient. SI values showed that diets for U. pugettensis consisted of carbon sources derived primarily from POM and SPOM, while POM and epiphytes were primary carbon sources for N. californiensis. Shrimp from lower estuarine sites had high levels of 16:1ω7 and 20:5ω3 FAs suggesting their diet is enriched with marine diatoms. Shrimp from upriver showed greater proportion of FA associated with dinoflagellates and terrestrial sources as indicated by a high percentage of C18 polyunsaturated FAs (PUFAs). This is the first study to evaluate diets of these two shrimp species using complimentary FA and SI approaches.

No evidence that the introduced parasite Orthione griffenis Markham, 2004 causes sex change or differential mortality in the native mud shrimp, Upogebia pugettensis (Dana, 1852)

Dramatic, rapid, population declines of the native North American burrowing shrimp Upogebia pugettensis (Dana, 1852) are associated with intense infestations by the introduced Asian bopyrid isopod parasite, Orthione griffenis Markham, 2004. However, expected host weight losses with increasing parasite weights do not occur, even among apparently castrated females. The prevailing assumption that energetic losses cause host castration have thus remained open to question, and the mechanism(s) resulting in castration and consequent population declines of U. pugettensis have remained unclear. Proposed alternative explanations for these declines, which have been based on a dramatically greater prevalence of O. griffenis among U. pugettensis females, include parasite induced sex change, increased male mortality, and differential tidal exposure of sexes to settling O. griffenis larvae. We examined 508 O. griffenis infestations from 2,014 shrimp collected from 26 stations in 5 Oregon estuaries to test these alternative hypotheses. We expected greater infestation frequencies among females than among males and a close association of O. griffenis infestations with intersex shrimp in the overall population if feminization occurs. We also expected covariation in sex ratio with tide exposure if O. griffenis settlement is sex linked. Instead, we found an overall 1:1.07 sex ratio, a lack of association of intersex U. pugettensis with O. griffenis infestations, and an unchanging sex ratio with tidal exposure, precluding parasite induced sex change, male mortality, or tidal immersion effects on infestations. The most likely mechanism driving U. pugettensis declines thus remains castration due to host energetic losses. This energetic interaction is likely to be resolved quantitatively through controlled experiments and increasingly detailed field surveys over time.

A rapid intertidal megafauna survey method applied to Upogebia pugettensis, and its introduced parasite, Orthione griffensis

Declines or extinctions of the native northeast Pacific intertidal blue mud shrimp, Upogebia pugettensis (Dana, 1852), over the species range are directly associated with intense infestations by the introduced Asian bopyrid isopod parasite, Orthione griffenis Markham, 2004. Single point sampling sites and anecdotal records poorly resolve how this interaction occurs within estuaries and among geographical regions. This broad scale interaction can only be resolved at the meta-population scales over which they occur but the surveys needed for this research are proceeding slowly or, in most cases, have not begun. The large efforts and major field and computational resources that grid or random point surveys employed for this work to date have proven to be major obstacles. We therefore tested a new method in Alsea Bay, Oregon, in which shrimp bed perimeters and areas are algebraically defined previous to direct sampling within predefined population areas. This new method is intuitive, reduces logistics, greatly reduces field and computational resources and produces equally useful results to previous survey methods. The Alsea Bay populations of U. pugettensis surveyed by these new methods are sufficiently abundant to remain “ecosystem engineers.” However, intense infestations of their populations by Orthione cause significant reproductive losses. The Alsea Bay population appears to be declining along with all other known U. pugettensis in Oregon estuaries.

Isolation and characterization of novel microsatellite loci in two species of burrowing shrimp, Neotrypaea californiensis and Upogebia pugettensis

Burrowing thalassinid shrimp are important ecosystem engineers in estuarine benthic communities. We characterized 31 microsatellite loci in two shrimp species, Neotrypaea californiensis and Upogebia pugettensis, which are of current management concern due to declining abundance and interactions with shellfish aquaculture. All loci were variable with three to 22 alleles per locus and observed heterozygosity of 0.22–1.00. There were only four deviations from Hardy–Weinberg expectations and no significant linkage disequilibrium. These are the first microsatellites characterized for these species and provide a useful tool for further characterization of population structure and diversity.

Brain Acetylcholinesterase Activity in Shiner Perch (Cymatogaster aggregata) and Juvenile Chinook Salmon (Oncorhynchus tshawytscha) After Application of Carbaryl to Control Burrowing Shrimp Within Willapa Bay, Washington

Carbaryl has been applied in Willapa Bay, Washington, for five decades to control burrowing shrimp (Neotrypaea californiensis and Upogebia pugettensis) on commercial oyster (Crassostrea gigas) beds. Concerns about effects on nontarget species, including fishes, have led to restrictions in use despite a lack of data on in situ exposure. We measured brain acetylcholinesterase (AChE) activity in adult Shiner perch (Cymatogaster aggregata) and juvenile Chinook salmon (Oncorhynchus tshawytscha) after operational applications. We hypothesized that exposure in Shiner perch would be greater than in juvenile Chinook salmon because of their greater site fidelity and benthic foraging. However, Shiner perch exhibited no statistically significant AChE inhibition. Enzyme activity was statistically decreased (≤14%) in juvenile Chinook salmon after a second spray event; however, inhibition was less than that associated with overt effects and was similar to controls by 48h after the spray. Diet analyses confirmed that Shiner perch were primarily feeding on benthic invertebrates and that juvenile Chinook salmon were feeding primarily within the water column. Composition of Shiner perch diets and amount of food consumed varied little among channels and time periods; however, Shiner perch on beds consumed more food 6h after application than those at other time points and locations. There were no consistent differences in the diets of juvenile Chinook salmon within channels among time periods. Results suggest (1) that carbaryl applications pose little hazard to fish in the bay having habitat and dietary preferences similar to those of Shiner perch and juvenile Chinook salmon and (2) that quantification of direct exposure in the field is essential to adequately assess risk.

Bioinfiltration: Irrigation-Driven Transport of Clay Particles Through Bioturbated Sediments

Abstract The transport of clay-size particles into the pore networks of siliciclastic sediments by the bioirrigating activities of burrowing organisms is demonstrated here for the first time. In a laboratory microcosm, evidence for the advection of kaolinite particles into pore spaces was observed at the interface between two buried sand layers. The clay transport was caused by the burrow-irrigating behavior of the mud shrimp Upogebia pugettensis. The term “bioinfiltration” is introduced herein to describe the process of particulate transport into pore-water networks. Given the abundance of bioirrigating organisms in shallow-marine environments, bioinfiltration may be a widespread phenomenon affecting the properties of large sediment volumes. The introduction of clay mineral particles into otherwise clay-free sediments through bioirrigation would affect the sediment characteristics significantly. In particular, bioinfiltrated clays would occlude pore space, could act as precursors to the production of authigenic cements, and inhibit the growth of quartz cements—all of which would reduce the permeability and porosity of hydrocarbon reservoirs and groundwater aquifers. Bioinfiltration therefore needs to be considered when assessing the origins and diagenetic effects of clay particles in bioturbated sediments, and is likely also to be of significance to sediment biogeochemistry and infaunal ecology. This is because of the potential influence of sedimentary pore occlusion on pore-water exchange, and through the introduction of particulate organic nutrients into the sediment as flocs or colloids. Such changes are likely to affect microbial productivity, which is thought to be the food source of many burrowing micro- and macro-organisms.

Ecological periodic tables for benthic macrofaunal usage of estuarine habitats: Insights from a case study in Tillamook Bay, Oregon, USA

This study validates the ecological relevance of estuarine habitat types to the benthic macrofaunal community and, together with previous similar studies, suggests they can serve as elements in ecological periodic tables of benthic macrofaunal usage in the bioregion. We compared benthic macrofaunal Bray–Curtis similarity and the means of eight benthic macrofaunal community measures across seven habitat types in Tillamook Bay, Oregon, USA: intertidal eelgrass (Zostera marina), dwarf eelgrass (Zostera japonica), oyster (Crassostrea gigas) ground culture, burrowing mud shrimp (Upogebia pugettensis), burrowing ghost shrimp (Neotrypaea californiensis), sand and subtidal. Benthic macrofaunal Bray–Curtis similarity differed among all the habitats except ghost shrimp and sand. The habitat rank order on mean benthic macrofaunal species richness, abundance and biomass was dwarf eelgrass ≈ oyster ≥ mud shrimp ≈ eelgrass > sand ≈ ghost shrimp ≈ subtidal. The benthic macrofaunal habitat usage pattern in Tillamook Bay was, with a few exceptions, similar to that in two other US Pacific Northwest estuaries. The exceptions indicate variants of eelgrass and ghost shrimp habitat that differ in benthic macrofaunal usage perhaps due to differences in the coarseness of the sand fraction of the sediments in which they live. The similarities indicate periodic benthic macrofaunal usage patterns across the other habitat types extend over a wider geographic scale and range of environmental conditions than previously known.

An introduced Asian parasite threatens northeastern Pacific estuarine ecosystems

The introduced Asian parasitic bopyrid isopod, Orthione griffenis, was first discovered on the Pacific coast of North America in Washington in 1988 and next in California in 1992. The range of Orthione presently extends from British Columbia to Baja California, where it infests at least two species of the native estuary mud shrimp, Upogebia. Intense Orthi- one infestations are associated with the apparent demise of many local populations of Upogebia pugettensis yet nonindigenous origins of Orthione in North America and thus the ecological significance of its impacts have remained in doubt. Six criteria reveal that Orthione is introduced to North America: its conspecificity with disjunct Asian populations, its earliest (1950s) collections in Asia, its late discovery among symbiotic species associated with Upogebia, its historical absence, and its appearance in North America coincident with extensive new ballast water traffic from Asia. Orthione is the first recognized bopyrid isopod invasion globally. Coexistence of U. pugettensis, which are ecosystem engineers, with its newly acquired parasite cannot be assumed. Orthione threatens eastern Pacific estuary ecosystems where Upogebia were previously abundant.

Physiological consequences of parasite infection in the burrowing mud shrimp, Upogebia pugettensis, a widespread ecosystem engineer

The burrowing mud shrimp, Upogebia pugettensis, is an important ecosystem engineer throughout bays and estuaries along the Pacific coast of North America. Populations of U. pugettensis have recently declined throughout its range. A likely reason for this decline is the arrival of an invasive bopyrid isopod parasite, Orthione griffenis, which has colonised the system and increased in prevalence. We tested the following three hypotheses regarding this host–parasite system: (1) parasite infection is correlated with the volume of water processed by the host; (2) infection negatively affects host’s energetic state; and (3) infection causes feminisation in male hosts. We used several physiological and morphological measures to quantify the effects of this parasite infection on U. pugettensis. The parasite appears to have different physiological effects on male and female hosts. Our study provides mixed support for the previous theory that predicted the mechanistic interactions between this host and its new parasite. Recent examples from other systems have demonstrated that invasive parasites can have far-reaching influences when they infect ecosystem engineers. Given the negative effects of O. griffenis on U. pugettensis, this invasive parasite may have similarly large impacts on Pacific North-west estuaries throughout its invaded range.

Ecological periodic tables for benthic macrofaunal usage of estuarine habitats in the US Pacific Northwest

This study shows that spatially and temporally recurring benthic macrofauna–habitat patterns validate the ecological relevance of habitat types to benthic macrofauna and suggest they can serve as elements in ecological periodic tables of benthic macrofaunal usage. We discovered patterns across nine habitat types (intertidal eelgrass [ Zostera marina], dwarf eelgrass [ Zostera japonica], oyster [ Crassostrea gigas] ground culture, burrowing mud shrimp [ Upogebia pugettensis], burrowing ghost shrimp [ Neotrypaea californiensis], shell, sand, mud, and subtidal) on a variety of benthic macrofaunal community state variables in Grays Harbor, Washington, USA and compared them to those in Willapa Bay, Washington, USA. There were nominal differences in benthic macrofaunal Bray–Curtis similarity between all the habitats investigated except eelgrass and oyster in both estuaries. Across-habitat patterns on mean benthic macrofaunal species richness, abundance, biomass, abundance of deposit, suspension and facultative feeders, a dominance and a diversity index for the five habitats common to both studies were the same on a rank measurement scale: eelgrass ≈ oyster > mud shrimp > ghost shrimp ≈ subtidal. The patterns for most of the habitats and benthic macrofaunal measures were the same on a ratio measurement scale.

Ecological periodic tables for nekton usage of four US Pacific Northwest estuarine habitats

We compared the species composition and abundance of the total nekton community, using the Bray–Curtis similarity coefficient, and mean total nekton, fish and crab species richness, abundance and biomass, and shrimp abundance across four intertidal habitats in a US Pacific Northwest estuary: (i) eelgrass ( Zostera marina ); (ii) burrowing mud shrimp ( Upogebia pugettensis ); (iii) burrowing ghost shrimp ( Neotrypaea californiensis ); and (iv) unvegetated sand. Field sampling was conducted during daytime high tides, and was quantitative, stratified-by-habitat, randomized, and estuary-wide. More than 10 000 nekton specimens belonging to 64 taxa were collected in 454 samples during 10 sampling periods, each approximately one-month-long (from June to November), over 3 years (1998–2000). Non-metric multidimensional scaling analyses revealed annually recurring across-habitat patterns in total nekton Bray–Curtis similarity. Two-way (habitat, year) analyses of variance revealed annually recurring across-habitat patterns on 10 indicators of nekton-habitat quality and preference. Total nekton species richness, abundance, and biomass were, respectively, on average, 8 ×, 25 ×, and 25× greater in eelgrass, 4 ×, 6 ×, and 5× greater in mud shrimp, and 2 ×, 3 ×, and 2× greater in ghost shrimp, than in sand habitat. Our findings validate the ecological relevance of our habitats to nekton, and suggest they can serve as elements in ecological periodic tables of nekton habitat usage.

Is the Collapse of Mud Shrimp (Upogebia pugettensis) Populations Along the Pacific Coast of North America Caused by Outbreaks of a Previously Unknown Bopyrid Isopod Parasite (Orthione griffenis)?

A dramatic increase in prevalence of the recently discovered bopyrid isopod parasite, Orthione griffenis, likely introduced in the 1980s from Asia to the Pacific coast of North America, coincided with the 2002 collapse of a population of its burrowing mud shrimp host, Upogebia pugettensis, in Willapa Bay, Washington that had been stable since monitoring began in 1988. An examination of whether O. griffenis infections were sufficient to cause this decline and other recently noted U. pugettensis population collapses in Pacific Coast estuaries was conducted. O. griffenis prevalence was the highest in large reproductive-sized female shrimp and caused an estimated average 68% loss of U. pugettensis reproduction in Yaquina Bay, Oregon over a 5-year period. O. griffenis prevalence fluctuated from year to year, but trends were similar in all estuaries sampled. Uninfected shrimp transplanted back into locations from which they had disappeared acquired the parasite, suggesting that O. griffenis is extremely effective at finding its host even in estuaries with very low host density. Since both U. pugettensis and O. griffenis have pelagic larval stages, their population dynamics are also influenced by coastal nearshore oceanography and estuarine recruitment success. Coastwide lack of estuarine recruitment appears to coincide with declines in density of a co-occurring thalassinid shrimp, Neotrypaea californiensis, but cannot alone explain U. pugettensis population collapses. Although patterns observed to date could be explained by the presence of either a native or introduced parasitic castrator, assumptions of a resilient co-evolved host–parasite relationship do not apply for introduced species, so continued efforts to follow the spatial extent and consequences of the O. griffenis–U. pugettensis host–parasite relationship are warranted.

VARIATION IN BURROW-WALL MICROMORPHOLOGIES OF SELECT INTERTIDAL INVERTEBRATES ALONG THE PACIFIC NORTHWEST COAST, USA: BEHAVIORAL AND DIAGENETIC IMPLICATIONS

Abstract Burrow-wall micromorphologies produced by nine different intertidal invertebrates were characterized by scanning electron microscopy. Minimally disturbed burrows and host sediment associated with Heteromastus filiformis, Saccoglossus bromophenolosus, Corophium volutator, Clymenella sp., Phoronopsis viridis, Cirriformia luxuriosa, Arenicola marina, Nereis virens, and Upogebia pugettensis were collected from various locales along the western coast of Washington and California. Scanning electron micrographs show several unique sedimentary characteristics present in the burrow lining of each invertebrate. Three traits—grain orientation and grain-size distribution, the nature of the mucus lining, and the presence of wall sculpture—appear significant in describing the microscale burrow lining. In several burrow types, the burrow structure was distinguishable from the matrix by changes in the modal grain size and sorting of the burrow-wall sediment. Variations in the type of packing—cubic versus rhomboh...

Effects of a newly invasive parasite on the burrowing mud shrimp, a widespread ecosystem engineer

The burrowing mud shrimp Upogebia pugettensis is an important ecosystem engineer in Pacific bays and estuaries from Alaska to Baja California. Recently, mud shrimp populations throughout this range have declined precipitously. This decline has followed invasion by a bopyrid isopod, Orthione griffenis, which parasitizes and removes hemolymph from the shrimp's gill cham- bers. However, a causal link between this invasive parasite and the decline of its host has yet to be demonstrated. I used observed allometric relationships between the parasite and its host, spatial pat- terns of parasite prevalence across host demographics, and simulation modeling to explore potential mechanisms leading to this causal link. Results here, considered with other work, suggest that this parasite may hamper host reproduction by increasing metabolic demands. First, shrimp are more likely to become infected with increasing exposure to parasite-laden water, which varies both with the proportion of time that tides cover individual shrimp burrows and with each shrimp's size-specific pumping rate of water through its burrow. Second, parasites impose a metabolic burden on their host that is proportional to parasite size, which itself increases with time since infection. Third, increasing metabolic costs in turn reduce reproductive capacity, potentially through feminization of male hosts. Fourth, increased metabolic costs of infection are most detrimental when feeding time is limited, which occurs in higher intertidal areas. These conclusions should be taken as testable hypotheses that, if examined, will elucidate this host-parasite interaction and clarify if this new invasive parasite is capable of reducing and eliminating this important ecosystem engineer.

Geochemical ecosystem engineering by the mud shrimp Upogebia pugettensis (Crustacea: Thalassinidae) in Yaquina Bay, Oregon: Density‐dependent effects on organic matter remineralization and nutrient cycling

We investigated the effect of the thalassinid mud shrimp Upogebia pugettensis on organic matter and nutrient cycling on Idaho Flat, an intertidal flat in the Yaquina River estuary, Oregon. Field studies were conducted to measure carbon and nitrogen remineralization rates and benthic fluxes relative to shrimp population density. Organic carbon remineralization rates estimated from incubations increased with burrow density. Similarly, benthic oxygen uptake increased linearly with burrow density. Shrimp bioirrigation enhanced carbon remineralization up to 2.9 times; its effects on nitrogen cycling were even more dramatic, enhancing ammonification rates up to 7 times, nitrification rates between 3 and 9 times, and estimated denitrification up to 4 times relative to portions of the tide flat lacking shrimp. Bioirrigation by shrimp also reduced pore‐water inventories of dissolved inorganic nitrogen (DIN), resulting in DIN fluxes that increased exponentially with burrow density up to 15‐fold relative to No‐shrimp plots. For both C and N fluxes, the strongest density‐dependent relationships occurred with burrow hole density rather than shrimp population density or biomass. Combined with population mapping of mud shrimp populations on Idaho Flat, we estimate that total areal C and DIN effluxes on the tide flat were enhanced 1.9 and 3.7 times, respectively, relative to areal fluxes expected if no shrimp were present. Mud shrimp thus perform as geochemical ecosystem engineers that strongly affect the flux and fate of C and N in Pacific estuaries.