Valuable fisheries and aquaculture industries for the geoduck Panopea generosa in North America, have stimulated interest in developing similar activities for geoduck species in New Zealand. The potential for establishing commercial enterprises for P. zelandica in New Zealand is reviewed. Although small fisheries for this species have existed since the late 1980s, the total annual landings have never exceeded 31.4 t. In 2006, P. zelandica was placed onto the New Zealand Quota Management System, with a total allowable catch of 40.5 t. Despite low capture rates, P. zelandica has several traits—similar to those for Panopea generosa—that may make it amenable for fisheries and aquaculture development. In terms of fisheries, it is typically found in benign coastal embayments and harbors, and it appears most dense in shallow subtidal waters (<15 m). Developing a sustainable fishery, however, will be contingent on a full understanding of the reproductive biology and ecology of P. zelandica; its unusual reproductive strategy (functional protandry) may result in a fishery that specifically targets females, which dominate the larger/older size classes in wild populations. With respect to aquaculture, adults can be readily spawned and larvae grown through to settlement. The largest impediment to fisheries development is a lack of information on the location of actual populations, and the low densities and natural mortality rates of known populations. The development of aquaculture will be hindered primarily by the ability to cultivate postsettlement individuals. Under current legislation, cultured marine organisms must be grown on structures, as a result of seabed ownership issues, although pond culture may be an alternative method for cultivating hatchery-reared stock. Despite these issues, P. zelandica shows potential for commercial exploitation, and it is a primary species identified to meet the New Zealand aquaculture sector's ambitious target of NZ$1 billion by 2025.

Geoducks (Panopea spp.) are recognized as one of the longest-lived and largest burrowing bivalves. Five extant species support commercial fisheries in different countries, yet their phylogenetic relationships are unclear. Phylogenetic analyses using cytochrome oxidase c subunit I, 28S, and 18S partial sequences on five Panopea spp. were performed to understand existing biogeography and to unravel taxonomic uncertainties in the genus. The cytochrome oxidase c subunit I sequences revealed two major clades. The first clade included Panopea zelandica as a sister taxon of Panopea globosa; the second clade included Panopea abbreviata, Panopea generosa, andPanopea japonica.Contrary to expectations, geographically proximate species (P. generosa and P. globosa) belong to different lineages, and geographically distant species (P. generosa and P. japonica) showed lower genetic distance at nuclear loci, suggesting that P. generosa could be related to the common ancestor of P. japonica. Divergence values for mitochondrial DNA, however, indicated that P. japonica might be regarded as a distinct species. Analyses using both nuclear genes suggest that the ancestral species of P. globosa may have been broadly distributed through the Pacific coast to South America.

Age validation is commonly based on the marginal increment ratio (MIR). This procedure has been used to validate the annual periodicity of growth band deposition. In this study, MIR data from geoducks Panopea globosa and Panopea generosa were analyzed using a new method for age validation based on a sinusoidal model. The model used four parameters, including the amplitude |δ|, defined as half the distance between the highest and the lowest values of the function; ρ, which is the cycle from 0–2π; τ, which is the horizontal shift; and λ, which is the vertical shift, or displacement. When the parameters in the sinusoidal function were estimated, the period could be computed as . The parameters were estimated using a maximum likelihood estimator. In addition, temperature and chlorophyll a were analyzed relative to the individual growth in shells. Based on parametric and nonparametric tests of the MIR data, the analysis identified a monthly progression of growth increment formation over an annual period. The data indicated that the shell growth of the outermost band is synchronized in both species; however, analysis of variance and the Kruskal—Wallis test applied to P. generosa and P. globosa, respectively, could not describe the individual growth as an annual sinusoidal cycle. Similar results were found with the environmental variables, which suggested seasonal changes in environmental variables are associated with measurements of the MIR. The sinusoidal model proposed in this study confirmed the annual cycle of growth lines for P. generosa (Ω = 12.16 mo; CI, 11.91–12.53 mo; P<0.05) and P. globosa (Ω = 11.82 mo; CI, 11.52–12.16 mo; P<0.05). The model provides reasonable fits to the data and can be used for age validation in both species.

Among the challenges facing aquaculture of native species are potential negative effects of gene flow from cultured to wild populations. Estimates of gene flow are based in large part on the capacity for gamete exchange between individuals, and make estimates of reproductive output and timing of gametogenesis in adjacent cultured and wild populations important to assess. Farmed geoducks of known age from each of five year classes and from nearby wild populations were sampled for reproductive development and other morphometric parameters in March, April, and May 2007 from three Puget Sound, Washington, locations. Results indicate that, at all three locations, cultured geoducks began to mature during year 2 and were fully mature by year 3, with males maturing earlier and at a smaller size than females. It was estimated that 50% maturation occurs at 64 mm in shell length. The gender ratio in 2–5-y-old geoducks was male biased relative to the 1:1 sex ratio observed in wild populations (P << 0.05), providing evidence for facultative protandric dioecy. Rates of maturation in cultured populations were synchronous with nearby wild populations. Overall, mean relative fecundity of cultured 3-, 4-, and 5-y-old clams was approximately 25% that of mean wild relative fecundity. These results suggest that reproductive interactions between cultured and wild geoducks can potentially occur through two mechanisms. First, when farmed geoducks are in proximity to wild geoduck aggregations, spawning may be synchronized, with subsequent gametic interaction occurring. Second, planktonic larvae produced from cultured populations may subsequently settle and mature to propagate with wild conspecifics. Interactions between cultured and wild conspecifics are important to assess especially in cases when domestication selection is proceeding via hatchery-based breeding and other approaches.

This research examined the individual effects of temperature and ration on growth and survival of juveniles of the Pacific geoduck Panopea generosa Gould, 1850, in two separate experiments. Growth parameters measured included shell length, daily shell increment, individual total body wet weight, specific growth rate, individual total body dry weight, and total body ash-free dry weight (AFDW). Larvae in all treatments were fed a binary microalgal diet of Chaetoceros muelleri and Tisochrysis lutea mixed at a 1:1 ratio by AFDW. The temperature experiment examined the effect of four temperatures (7°C, 11°C, 15°C, and 19°C) using two geoduck cohorts. One cohort was comprised of larger juveniles (mean initial shell length ± SE, 3.22 ± 0.05 mm) and the other included smaller individuals (0.54 ± 0.01 mm) which were cultured for 28 days and 21 days, respectively. Using a separate cohort, the foodration experiment examined the effect of nine rations (0.0, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, and 128.0 × 10⁶ equivalent T. lutea cells per individual per day) on four size classes of geoduck juveniles obtained from the same spawning batch (mean initial shell length ± SE, size class 1,2.34 ± 0.04 mm; size class 2, 3.32 ± 0.04 mm; size class 3,4.13 ± 0.04 mm; and size class 4, 4.98 ± 0.04 mm) for 7 days. On the final sampling day, there were significant differences among all four temperatures for all growth parameters except AFDW, with each parameter increasing significantly for each increase in temperature. For AFDW, there were no significant differences between 7°C and 19°C, nor between 11°C and 15°C, with the first set of two temperatures producing juveniles with significantly less AFDW than the latter set. In general, optimal ration levels increased with increasing geoduck size. To optimize growth in shell length, individual total body wet weight, and/or individual total body dry weight, the following rations are recommended for size classes 1, 2, 3, and 4, respectively: 4.0 or 8.0, 8.0, 16.0 or 32.0, and 32.0 or 64.0 × 10⁶ equivalent T. lutea cells per individual per day. Refinement of an understanding of optimum juvenile geoduck culture conditions contributes to the general knowledge of the species’ physiology and helps maximize the commercial hatchery production of geoduck seed.

Developmental larval stages of the geoduck Panopea globosa (Dall, 1898) are described for the first time. Growth rate, survival, and the length—size relationship were also assessed at 22°C in five independently reared cohorts. Clearance rates (CR), ingestion rates (IR), dry weight, and organic weight of select larval stages were quantified in two additional runs. Clearance rates and IR were evaluated as a function of cell concentration (50, 100, 200 and 300 cells/µL) of the chrysophyte Isochrysis sp. (clone T-ISO) using static systems. Conspicuous larval stages appeared after 20 h (trochophore), 24 h (straight hinge or “D”), 5–6 day (early umboned), 9–10 days (intermediate umboned), 11–12 days (late umboned), and 12–14 days (pediveliger). The larval period for P. globosa lasted between 12 days and 14 days, and the shell length recorded at settlement ranged from 332–356 µm (mean, 343 ± 4.2 µm). The overall average gross growth rate of the five larval cohorts was ∼20 µm/day. The relationship between larval shell length (in micrometers) and organic weight (in micrograms) followed a power function with an exponent value of 2.43, whereas the relationship between dry weight and organic weight was linear. Survival rate was approximately 50% in three larval cohorts and 20% in two cohorts. Clearance rates were inversely related to microalgal concentration regardless of larval size, and ranged from 0.3–1.5 µL/h (D larvae) to 15–59 µL/h (pediveliger, 330µm). On the other hand, IR increased with increasing algal concentration, and reached maximum values at 200 cells/µL, except in D-hinge larvae, which exhibited a maximum IR at all concentrations tested. At the highest concentration (300 cells/µL), premetamorphic larvae inhibited their IR. Overall, IR increased from 57–85 cells/h (D-hinge larvae) to 40- or 50-fold when larvae reached the premetamorphic stage. The current study revealed that P. globosa has a short larval period and high survival rate, and withstands a wide range of food concentrations without inhibiting its IR. Therefore, this species appears to be an excellent candidate for hatchery production.

The burrowing behavior, growth, and size-dependent burrowing rates of two geoduck species—Panopea globosa and Panopea generosa—from the Mexican coast were assessed during early juvenile development (6–7 mo) using 30-L aquariums with a muddy or sandy sediment substrate. Preburial response time, digging rates, and growth were recorded monthly for organisms with an initial shell length of 5 mm (P. globosa) or 10mm (P. generosa), and continued for 6 or 7 mo. Organisms were fed Isochrysis sp. (clone T-ISO) at libitum on a daily basis during the experimental period. Digging behaviors included the inflation of the geoduck siphon, followed by expulsion of a water jet through the pedal orifice, in conjunction with coordinated muscular contractions of the foot. Both species exhibited a lag in their burial response time that was related linearly to shell length, with rates of 4.5 min/mm (P. globosa) and 3.4 min/mm (P. generosa). Burrowing rates were independent of shell length and were similar in both species (∼0.9–1.4 mm/min) for a size range of 7–36 mm, but were slower in 5-mm seed (0.4 mm/min). Shell growth rate increased linearly with time and was faster in P. globosa (162 µm/day) than P. generosa (61 µm/day). These results suggest that short-term temporary enclosures may be useful for restocking natural populations of geoducks with laboratory-produced seed, at a size as small as 7 mm.

Thirty adult organisms of Panopea globosa, an endemic geoduck species from Baja California, Mexico, were collected monthly during a maturation cycle (October through January). Histological and semiquantitative histochemical changes (total lipids and carbohydrates) were assessed in gonad tissue during the maturation process. Biochemical quantification of proteins, lipids, carbohydrates, vitellogenin, and vitellin was performed on hemolymph and gonad tissues of all specimens. The theoretical diameter of oocytes was also estimated from their surface area, measured in histological sections of gonads. Five distinct gonadal stages were identified in both male and female geoducks, with previtellogenic (PVt)/early spermatogenic (ES) gonads being observed in October. Spawning took place in December/January when the temperature reached a plateau of ∼18.5°C. Oocyte diameter varied between 25.5 µm(PVt stage) and 74.8 µm during the late vitellogenic stage (LVt). The percent of lipids and carbohydrates evaluated histochemically in females closely mirrored the gonadal stages, as well as the diameter. Quantitative changes in proteins, lipids, and carbohydrates in the hemolymph did not show a clear temporal pattern, yet the level of vitellogenin increased from 16.4 (PVt stage)—47.8 µg/mL (LVt stage) and correlated with the oocyte diameter. The weightspecific content of proteins, lipids, and carbohydrates in the gonads was significantly greater during PVt and ES than the other gonadal stages, and remained relatively constant thereafter. Vitellin content mirrored the evolution of each maturation stage and correlated significantly with oocyte diameter. Vitellogenin or vitellin can be used as a reliable quantitative index of gender and degree of gonadic maturity in females. Hemolymph can be obtained readily from the pericardial cavity without affecting the performance of the organism significantly, which further makes vitellogenin a valuable, nonlethal marker for this genus.

Lucrative commercial cultivation of Pacific geoduck (Panopea generosa) has developed in the United States within the past 20 y, making it one of the most economically important commercial shellfish species harvested for export. Aquaculture of the species exists in close proximity to native populations, but very little is known about the health of native populations. Baseline information on endosymbiont identification, prevalence, intensity, and geographic distribution are necessary to facilitate management and/or mitigation of potential disease interactions between cultured and natural shellfish stocks. A survey of Pacific geoduck (P. generosa) parasites from three natural populations in Washington state (Totten Inlet, Thorndyke Bay, Freshwater Bay) was conducted in 2008 to 2010. Histopathology of 634 animals was used to explore trends of parasite presence and to identify potential environmental factors (site distribution, collection depth, and season) that influence parasite assemblages. Endosymbionts observed on histological examination included Rickettsia-like organisms (RLOs) in the ctenidia (n = 246); an unidentified metazoan parasite in the siphon epithelium (n = 220); and microsporidia-like species in the intestine (n = 103), siphonmuscle (n = 28), and ova (a Steinhausia-like parasite; n = 99). This study reveals the presence of three microsporidia-like organisms (including Steinhausia-like parasites) not previously described in geoducks. Assemblages of most parasites showed strong seasonal variations and site-specific distributions throughout the year. The presence of Rickettsia-like organisms may be driven by seasonal elevated temperatures, and was extremely common at Freshwater Bay. Metazoans and microsporidia were common in South Puget Sound and exhibited high infection intensity year-round. Spawning season drove Steinhausia-like parasite presence with no spatial driver. Baseline information on natural parasite levels, distribution, and infection loads complements ongoing monitoring of natural geoduck population dynamics, and provides crucial information to evaluate future disease events should they occur.

The Pacific geoduck Panopea generosa is distributed throughout the North Pacific temperate zone from Alaska to Baja California and is described as a species that reaches large sizes, has prolonged longevity, and exhibits slow growth. This study assessed the individual growth and population structure of the P. generosa population located at its southernmost geographic distribution limit. Shell length and total weight data were obtained from a commercial fishery established on Punta Canoas, Baja California. Individual age was determined by counting growth lines for 243 organisms. The results revealed the following averages: shell length (SL), 113.5 mm; total weight, 511.8 g; age, 12.5 y. The relationship of SL to total weight showed negative allometric growth (b = 2.16). Size-at-age data were adjusted to von Bertalanffy, Gompertz, logistic, Johnson, and Schnute growth models according to the multimodel inference (MMI) approach. The best candidate growth model was selected based on the Akaike information criterion (AIC) and the Schwartz—Bayesian criterion (SBC). The AIC indicated that the Schnute growth model was the best candidate growth model, whereas the SBC showed the Johnson growth model was best. These growth models indicate that between 7 y and 8 y of age, organisms reach 75% of their estimated asymptotic length (SL, ∼103 mm), and although the growth rate decreases subsequently, growth continues up to 25 y (maximum age observed). The MMI approach applied to the analysis of growth in Panopea species identified particular population attributes that are not observable via the von Bertalanffy model. The population of P. generosa from Punta Canoas exhibited smaller mean SL, lower mean weight, an age structure with fewer age classes, and slower growth when compared with northern populations in Washington state and British Columbia, Canada.

Studies about individual growth for geoducks are relevant because they allow an understanding of biomass production and its maintenance in the population. This study presents the first growth curves for Panopea globosa from the southwestern Baja California Peninsula. Geoduck samples were collected from November 2006 to October 2007 in Bahía Magdalena (n = 392). The morphological data for live individuals were obtained and their ages were estimated from the right shell by counting band growth from a thin section cut from the hinge plate region. The length-at-age data were fitted to six growth models—Gompertz, Johnson, von Bertalanffy growth model (VBGM), generalized VBGM, Richards, and Schnute—using a negative log-likelihood function. The models were analyzed using multimodel inference to select the best candidate growth model based on the Akaike information criterion. The results indicate the size structure from Bahía Magdalena has a unimodal shape and shows negative allometric growth in the relationship between shell length and total weight (b = 2.4). Shell lengths varied from 93–206 mm and total weight ranged from 332–2824 g. Age validation was based on the marginal increment ratio, and suggested the growth line and band were deposited annually. Growth line formation occurred annually between January and April, and the growth band was deposited from June to December. A dominance of older year classes, from 13–22 y, was noted along with an estimated maximum age of 47 y. Based on multimodel inference, the Gompertz growth model was the best candidate for estimating growth for P. globosa. The estimated parameters included an asymptotic size of 167.51 mm, the rate at which the asymptotic size was reached was 0.218, and the age at size 0 was 0.003. These growth parameters for P. globosa from the southwestern of the Baja California Peninsula show the length at age in this region is greater than in the central Gulf of California, suggesting that management rules must be based regionally.

Natural mortality estimates are commonly computed from empirical methods or catch curve analysis, and their values are assumed constant for age or size in a population; however, estimates of natural mortality usually vary spatially, temporally, or by size and age. Several factors affect natural mortality rates, such as predation, disease, senescence, cannibalism, starvation, or environmental factors. Seven gnomonic time divisions (GTD) were used to estimate the natural mortality of Panopea globosa for specific portions of its life history: 1, egg to trochophore larvae (24 h); 2, early larvae (6.5 days); 3, late larvae (11 days); 4, early juvenile (35 days); 5, juvenile (3–9 mo); 6, late juvenile (1–2 y); and 7, preadult to adult (47 y). The statistical procedure based on gnomonic time divisions assumes units of time increase as a constant proportion of time elapsed from the end of the previous biological stage; in this manner, the method estimates a vector of natural mortality values by dividing the life cycle into specific time-based subunits. The results provided the following values of naturalmortality atGTD: 1 = 537.42/y; 2 = 230.32/y; 3 = 134.35/y; 4 = 33.58/y; 5 = 2.55/y; 6 = 2.21/y; and 7 = 0.046/y. The consistency of the estimates derived were compared with previous reports of mortality rates and yielded similar values. The gnomonic time method proved to be particularly effective in estimating natural mortality based on the specific life history and life span of the geoduck.

In the upper Gulf of California, a lucrative fishery of the Cortes geoduck Panopea globosa (Dall 1898) is developing rapidly. Both exploited and unexploited areas for this fishery still exist in this area. The effect of the data source of the length-atage data on growth models fitted to Panopea globosa was evaluated. Five growth models were tested: von Bertalanffy, logistic, Gompertz, Schnute, and Schnute-Richards. The parameters of each model and their confidence intervals (CIs) were computed using the maximum likelihood method. Multimodel inference was used to average the asymptotic length for each area. The bestfitting model was selected using Akaike's information criterion (AIC). According to this criterion, the logistic growth model best described the growth of P. globosa in unexploited beds, and the Schnute models performed best in exploited beds. The asymptotic length values obtained frommultimodel inferencewere 161.88 mm (95% CI, 161.83–161.93 mm) in unexploited beds and 205.20 mm (95% CI, 197.60–212.96 mm) in exploited beds. The latter value is the largest asymptotic length obtained for any Panopea species worldwide. In conclusion, the data source of the length-at-age data clearly affects the performance of growth models.

Geoduck (Panopea globosa and Panopea generosa) fisheries regulations in the Gulf of California and Baja California Peninsula, Mexico, are based on a minimum legal size (shell length, 130 mm), limited bed harvests with densities greater than 0.4 geoduck/m², maximum allowable catch, and restrictions on fishing activity on identified beds. Data on age structure and growth rate for geoducks could greatly improve fisheries management in the region; however, variability in size-at-age data for geoducks has made it difficult to develop a sound management strategy, and the presence of outliers in the data have influenced parameter estimates significantly. Different probability density functions can be applied as fat-tail distributions in mixture probability distributions. In the current study, outlier effects on candidate growth models in P. globosa were analyzed, as well as model performance when parameters were estimated using a two-component mixture probability distribution function. The best candidate growth model was selected based on the Akaike information criterion (AIC) and the Bayesian information criterion (BIC). Results suggest that growth models analyzed yielded an estimated asymptotic length larger than 160 mm in shell length. The logistic growth model was selected following the AIC, whereas the von Bertalanffy growth model was based on the BIC. A lack of congruence between the two statistics indicated insufficient evidence in P. globosa size-at-age data to support a best candidate growth model. It is suggested that growth compensation (when cohort size-at-age variability decreases with time or age) was operating in the population evaluated. Consequently, the size-at-age data were more scattered for younger individuals compared with older ones.

Marine bivalves are important ecosystem constituents and frequently support valuable fisheries. In many nearshore areas, human disturbance—including declining habitat and water quality—can affect the distribution and abundance of bivalve populations, and complicate ecosystem and fishery management assessments. Infaunal bivalves, in particular, are frequently cryptic and difficult to detect; thus, assessing potential impacts on their populations requires suitable, scalable methods for estimating abundance and distribution. In this study, population size of a common benthic bivalve (the geoduck Panopea generosa) is estimated with a Bayesian habitat-based model fit to scuba and tethered camera data in Hood Canal, a fjord basin in Washington state. Densities declined more than two orders of magnitude along a north—south gradient, concomitant with patterns of deepwater dissolved oxygen, and intensity and duration of seasonal hypoxia. Across the basin, geoducks were most abundant in loose, unconsolidated, sand substrate. The current study demonstrates the utility of using scuba, tethered video, and habitat models to estimate the abundance and distribution of a large infaunal bivalve at a regional (385-km²) scale.

In this study, Kimura's likelihood ratio test was used to compare growth curves for Panopea generosa, Panopea globosa, Panopea zelandica, and Panopea abbreviata. The curves were generated from previous studies using the von Bertalanffy growth model (VBGM). Geoducks P. generosa and P. globosa are distributed throughout the northern hemisphere; the other two species are found in the southern hemisphere. Individual parameters were used from the VBGM for each species from previously published resources to calculate the average length-at-age (Lt_i) data for intervals of 1–20 y. In this study, any Lt_i estimated for any of the species was considered as data to fit a global model and to compute error estimation. The average asymptotic lengths were 147.5 mm, 142.7 mm, 111.1 mm, and 102.5 mm, respectively, for each species listed earlier. These findings provided good evidence that the northern hemisphere species, P. generosa and P. globosa, are the largest and had no significant differences in length between them. The species from the southern hemisphere (P. zelandica and P. abbreviata) were the shortest, with a significant difference in length between them. Three of the four species analyzed inhabit the Pacific Ocean, with only P. abbreviata, the smallest of the four geoducks studied, being endemic to the southwestern Atlantic.

The geoduck Panopea globosa is found on the Pacific coast of Baja California south of Bahia Magdalena Bay and throughout the Gulf of California, and sustains a vibrant and growing fishery. Despite morphometric analyses that suggest populations from the Pacific are distinct from those inside the Gulf of California, it is unclear whether populations are connected via larval dispersal and gene flow throughout its range. Thirteen microsatellite loci were used to estimate levels of genetic diversity and to evaluate genetic connectivity patterns among four exploited populations, including clams from the Pacific (Bahia Magdalena) and the Gulf of California (San Felipe, Puerto Peñasco, and Guaymas). Geoducks from Bahia Magdalena showed significant genetic differentiation from populations inside the Gulf of California, particularly when compared with San Felipe and Puerto Peñasco. Gene flow and inferred larval dispersal were found to be predominantly unidirectional, and followed the typical anticyclonic (clockwise) circulation of the northern Gulf of California during late fall and winter when geoducks spawn. San Felipe is located upstream relative to the oceanographic flow and has the largest effective population size. This population also showed evidence of local retention of larvae and may serve as the main source of larvae to downstream populations that show a gradient of reduced diversity and population size along the direction of the prevailing flow. The asymmetry found in connectivity patterns has implications for distributing the fishery effort and no-take zones in the Gulf of California to increase sustainability.

Aquaculture for the Pacific geoduck (Panopea generosa) is a small but expanding industry in Washington state, where geoducks are native and genetic interactions between wild and cultured geoducks are likely. To examine the potential genetic implications of geoduck aquaculture, genetic diversity, and effective number of breeders (N_b), five contiguous year-classes of cultured geoducks were compared with a wild population. The results from five microsatellite loci indicate the cultured year-classes exhibited reduced allelic richness and N_b as well as increased mean pairwise genetic relatedness. However, examination of relationships within year-classes using sibship assignment revealed that many parents contributed progeny to each year-class. The geoducks in each year-class were comprised of 9 to 25 full-sib groups as well as a large number of individuals unrelated to others at the full-sib level. No clear pattern emerged regarding changes in genetic diversity during the 5-y time span of this study. To decrease the genetic risk to wild geoducks, the results suggest that hatcheries should increase the genetic diversity of cultured geoducks by adopting a partial factorial mating scheme, or they should minimize gene flow from cultured to wild populations by culturing sterile triploid geoducks.

Intertidal aquaculture for geoducks (Panopea generosa Gould, 1850) is expanding in southern Puget Sound, Washington, where gently sloping sandy beaches are used for field culture. Geoduck aquaculture contributes significantly to the regional economy, but has become controversial because of a range of unresolved questions involving potential biological impacts on marine ecosystems. From 2008 through 2012, the authors used a “before-after-control-impact” experimental design, emphasizing spatial scales comparable with those used by geoduck culturists to evaluate the effects of harvesting market-ready geoducks on associated benthic infaunal communities. Infauna were sampled at three different study locations in southern Puget Sound at monthly intervals before, during, and after harvests of clams, and along extralimital transects extending away from the edges of cultured plots to assess the effects of harvest activities in adjacent uncultured habitat. Using multivariate statistical approaches, strong seasonal and spatial signals in patterns of abundance were found, but there was scant evidence of effects on the community structure associated with geoduck harvest disturbances within cultured plots. Likewise, no indications of significant “spillover” effects of harvest on uncultured habitat adjacent to cultured plots were noted. Complementary univariate approaches revealed little evidence of harvest effects on infaunal biodiversity and indications of modest effects on populations of individual infaunal taxa. Of 10 common taxa analyzed, only three showed evidence of reduced densities, although minor, after harvests whereas the remaining seven taxa indicated either neutral responses to harvest disturbances or increased abundance either during or in the months after harvest events. It is suggested that a relatively active natural disturbance regime, including both small-scale and large-scale events that occur with comparable intensity but more frequently than geoduck harvest events in cultured plots, has facilitated assemblage-level infaunal resistance and resilience to harvest disturbances.

In Washington state, commercial culture of geoducks (Panopea generosa) involves large-scale out-planting of juveniles to intertidal habitats, and installation of PVC tubes and netting to exclude predators and increase early survival. Structures associated with this nascent aquaculture method are examined to determine whether they affect patterns of use by resident and transient macrofauna. Results are summarized from regular surveys of aquaculture operations and reference beaches in 2009 to 2011 at three sites during three phases of culture: (1) pregear (-geoducks, -structure), (2) gear present ( geoducks, structures), and (3) postgear ( geoducks, -structures). Resident macroinvertebrates (infauna and epifauna) were sampled monthly (in most cases) using coring methods at low tide during all three phases. Differences in community composition between culture plots and reference areas were examined with permutational analysis of variance and homogeneity of multivariate dispersion tests. Scuba and shoreline transect surveys were used to examine habitat use by transient fish and macroinvertebrates. Analysis of similarity and complementary nonmetric multidimensional scaling were used to compare differences between species functional groups and habitat type during different aquaculture phases. Results suggest that resident and transient macrofauna respond differently to structures associated with geoduck aquaculture. No consistent differences in the community of resident macrofauna were observed at culture plots or reference areas at the three sites during any year. Conversely, total abundance of transient fish and macroinvertebrates were more than two times greater at culture plots than reference areas when aquaculture structures were in place. Community composition differed (analysis of similarity) between culture and reference plots during the gear-present phase, but did not persist to the next farming stage (postgear). Habitat complexity associated with shellfish aquaculture may attract some structure-associated transient species observed infrequently on reference beaches, and may displace other species that typically occur in areas lacking epibenthic structure. This study provides a first look at the effects of multiple phases of geoduck farming on macrofauna, and has important implications for the management of a rapidly expanding sector of the aquaculture industry.