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2018 Final Report Sustainable oyster restoration requires oyster reproduction: Variation in reproduction across Hudson/Raritan Estuary environments Dr. Matthew P. Hare Objective for Summer 2018 Understand how salinity affects the timing of oyster reproduction and fecundity in the Hudson River Estuary, and measure the reproductive plasticity of TZ-HB broodstock. Funding from WRI for these objectives was combined with the research stipend to Polgar Fellow Kaili Gregory (Hudson River Foundation funding; Gregory and Hare 2019) to achieve the results described here. Hypotheses Hypothesis 1: All else being equal, oyster gametogenesis is delayed in lower salinity waters relative to higher salinities. Hypothesis 2: TZ-HB oyster adults, when transplanted along the salinity gradient, show a plastic adjustment of gametogenic timing in response to average salinity. TZ-HB dredged adults (Hypothesis 2) TZ-HB oyster adults were dredged on June 15, 2018 and ~50 were transplanted to each of 5 experimental cage sites (Fig. 1). Logistical and scheduling constraints prevented earlier sampling and it was decided that too much of the gametogenic season had been spent in the TZ-HB region to have gametogenesis assays in 2018 be very meaningful about reproductive timing in the post- transplant environment. Growth and survivorship were monitored but no histology was conducted on these dredged adults. Growth rate and survivorship of dredged TZ-HB oysters was measured monthly June – August and in October. Growth of wild TZ-HB oysters was similar at all sites. At RED, there was a 44% mortality rate between August and October (Fig. 2). Survivorship was very high (> 93%) at all other sites. Fig. 2: Survivorship of 2018 TZ-HB adults at 5 sites, Site names as in Fig. 1. Fig. 1: Map of TZ-HB oyster transplant locations with October 2018 average salinity 1
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2018 Final ReportSustainable oyster restoration requires oyster reproduction:

Variation in reproduction across Hudson/Raritan Estuary environmentsDr. Matthew P. Hare

Objective for Summer 2018Understand how salinity affects the timing of oyster reproduction and fecundity in the Hudson River Estuary, and measure the reproductive plasticity of TZ-HB broodstock. Funding from WRIfor these objectives was combined with the research stipend to Polgar Fellow Kaili Gregory (Hudson River Foundation funding; Gregory and Hare 2019) to achieve the results described here.

HypothesesHypothesis 1: All else being equal, oyster gametogenesis is delayed in lower salinity watersrelative to higher salinities. Hypothesis 2: TZ-HB oyster adults, when transplanted along the salinity gradient, show a plasticadjustment of gametogenic timing in response to average salinity.

TZ-HB dredged adults (Hypothesis 2) TZ-HB oyster adults were dredged on June 15, 2018 and ~50 were transplanted to each of 5 experimental cage sites (Fig. 1). Logistical and scheduling constraints prevented earlier sampling and it was decided that too much of the gametogenic season had been spent in the TZ-HB region to have gametogenesis assays in 2018 be very meaningful about reproductive timing in the post-transplant environment. Growth and survivorship were monitored but no histology was conducted on these dredged adults. Growth rate and survivorship of dredged TZ-HB oysters was measured monthly June – August and in October. Growth of wild TZ-HB oysters was similar at all sites. At RED, there was a 44% mortality rate between August and October (Fig. 2). Survivorship was very high (> 93%) at all other sites.

Fig. 2: Survivorship of 2018 TZ-HB adults at 5 sites, Site names as in Fig. 1.

Fig. 1: Map of TZ-HB oyster transplant locations with October 2018 average salinity

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Timing of oyster reproduction (Hypothesis 1)

Temperate latitude eastern oysters require two years of growth before they become reproductive. Therefore, we studied eastern oyster cohorts out-planted as one month old juveniles in August 2016 by the Hare Lab (studies funded by the Atkinson Center for a Sustainable Future). Over the past two years, the Hare Lab has monitored survivorship and growth for three oyster strains (3 experimental cohorts with different parentage) maintained in experimental cages hung from docks. These 2016 cohorts are independent replicates of initial experiments run from 2015 to 2017 at a subset of the sites (McFarland and Hare 2018).

The three oyster strains studied here included wild TZ-HB, a hatchery-produced cohort and a selectively bred aquaculture strain. All three strains were approximately the same age (within 1 month) at the time of outplant. The wild oyster sample was obtained as August wild-set recruits on bivalve shell in the vicinity of the wild TZ-HB remnant population. The hatchery cohort was produced by strip-spawning wild Martha’s Vineyard oysters from a moderate salinity lagoon (similar to methods in McFarland and Hare, 2018). The larvae were then cultured by the Martha’s Vineyard Shellfish Group and sent to the Cornell Cooperative Extension hatchery in Southold, New York to set on shell in an upwelling system for three weeks during August 2016 before outplanting to the HRE cages. Seed oysters from a selectively bred aquaculture strain also were acquired in August 2016. Aquaculture seed and hatchery-produced oysters were kept in small-mesh bags until large enough to be contained in poly mesh netting bags within the cages.

For histology, a maximum of 20 oysters were collected from each cohort at each of 4 sites (Table 1). The number collected was limited by cohort abundance and budget. Planned sample size variation prioritized July and August samples, but poor survivorship at some sites prevented complete sampling.

Table 1: Histology sample sizes by site, strain and month. HH = Hastings, SB = Science Barge, RED = Red Hook, PGB = Paerdegat Basin, AQ = aquaculture strain. Dates were June 15-21, July 8-13 and August 8-13. Site HH SB RED PGB

Jun Jul Aug Jun Jul Aug Jun Jul Aug Jun Jul Aug

AQ 13 20 20 13 20 20 11 18 20 13 19 20

Hatchery 13 12 12 13 20 20 0 0 0 13 18 20

Wild 13 20 19 13 20 20 0 8 6 13 20 20

For each oyster, a 4mm slice from a standardized body position was dissected and preserved in Davidson’s Solution for 7 days before washing with 70% ethanol and standard histology preparation with hematoxylin and eosin staining by Cornell University Animal Health Diagnostic Center.

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Histology slides were examined at 10X and 40X magnification to score gametogenic development on a “Gonad Index” scale of 0 to 10 (Table 2). A random linear model was created based on the gonad index results to predict multiple interaction effects of sex, location, strain, and month on GI. For this model, the GI values from 6-10 were relabeled to 5-1 (6 = 5, 7 = 4, 8 = 3, 9 = 2, 10 = 1) to allow for averages that reflect the true gonad condition. For example, two

Table 2: Description of Gonad Index stages (derived from Volety 2008). Stage Description 0 Neuter or indeterminate sex despite good histology preparation; no presence of

follicle or connective tissue 1 Determinate sex indicating beginnings of gametogenesis; no mature gametes

visible 2 Females: no more than one-third mature eggs relative to developing eggs

Males: fringe follicles starting to accumulate mature gametes; low density of sperm

3 Females: no more than one-half mature eggs relative to developing eggs Males: visible connective tissue; visible sperm tails in center of some follicles

4 Females: mostly mature polygonal eggs and distended follicles with somedeveloping eggs still visibleMales: small amount of visible connective tissue; compact follicles; sperm tailsvisible in most follicles

5 Females: only mature polygonal eggs; no empty spaces from spawning gametes Males: sperm have visible tails; uniformly high sperm density in packed follicles; no visible connective tissue

6 Active spawning is occurring; follicle structure is disruptedFemales: general rounding of eggs; a few empty spaces from released eggs Males: reduction in sperm density; sperm tails less visible

7 Follicles one-half depleted of gametesMales: sperm area reduced to one-half of gonadal area

8 Follicles two-thirds depleted of mature gametes; further reduction of gonadaland connective tissue area

9 Only residual gametes remain; determinate sex; further reduction of gonadaland connective tissue area

10 Gonads devoid of most or all gametes; connective tissue is still visible but very minimal; sex not always determinateFemales: one or two visible eggs remain Males: connective tissue has a few remaining sperm to allow for sex identification

oysters with gonad indexes of 2 and 9, respectively, would have a meaningless “unfolded” average GI of 5.5. Neither of the oysters are at peak reproductive spawning, yet that is what the “unfolded” average would suggest. For the folded index with 9=2, the “folded” average in this example would be 2, reflecting the oyster’s true relation to peak reproduction (Volety 2008). A dummy variable [0,1] was assigned to the GI values before “folding”, called ‘GI trend’ to represent the pre- and post-spawning GI distributions. GI values 1-5 were assigned GI trend=0

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to represent oysters that are still actively growing gonads. GI values 6-10 were assigned GI trend=1 to represent oysters that were spawning or resorbing their gametes. GI values of 0 were ignored for the GI trend variable because it was impossible to confirm if an oyster with a GI of 0 had failed to develop gametes or had completely resorbed gametes. A one-way analysis of variance (ANOVA) was performed on the model that included the effects of sex, location, strain, month, and GI trend on GI. Results were deemed significant at P < 0.05. Predicted means and confidence intervals were generated using the random linear model and plotted for select combinations of variables. Statistical analyses were conducted using RStudio (RStudio Team, 2016).

Results and Discussion

From May until mid-July 2018 average surface temperatures increased from 18 to 25°C, with the four monitored TZ-HB outplant sites experiencing a north to south range spanning 3-4°C. Salinity ranged 4-14 psu for the two up-estuary (northern) sites HH and SB, and 18 – 26 at the two down-estuary (southern) sites RED and KCC.

The overall ANOVA model did not show a significant effect of strain (p = 0.08), sex (p = 0.22) or location (p = 0.94). Oyster strain was a marginally significant effect (p = 0.08), but there was no clear pattern of difference, for example between the low salinity wild HB-TZ strain versus the two hatchery-produced mesohaline strains. Month and GI trend were the only significant factors other than interaction effects. Month was expected to be significant because of the strong seasonality of reproduction in temperate oysters and because GI trend separates the early build up of gonad versus later post-spawning resorption. The two strongest interaction effects were Month*GI tend, explained above, and Month*Location. This latter interaction and the three-way Month*Location*GI trend was our focus for the hypothesis that reproduction would be shifted later at more northern, lower salinity sites. However, the patterns were more complicated and interesting than this, as shown by plotting GI averages separately for pre- and post-spawning oysters (i.e., unfolded GI-trend 0 and 1), and considering the counts of pre-and post-spawning oysters by location and month (Fig. 3).

Table 3: ANOVA results for effect on GI by all tested variables. Significant result (p £ 0.05) denoted by “**”. Variable P values Sex 0.2227975 Strain 0.0842607 Month 7.725e-10 ** Location 0.9357032 GI trend 3.508e-05 ** Strain*GI trend 0.9443797 Month* GI trend 5.245e-07 ** Location*GI trend 0.0464173 ** Month*Location 4.044e-09 ** Month*Location* GI trend 0.0008605 **

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Fig. 3: Means and 95% confidence intervals for unfolded gonad index plotted for each experimental site within each month. Means correspond to linear model results for the first half of the GI (GI-trend = 0, gonad maturation) and the second half (GI-trend = 1, spawning and gonad resorption). Boxed numbers provide mean values and integers on margins provide counts of oysters contributing to the corresponding mean. Site abbreviations as in Fig. 1.

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In June the majority of oysters were pre-spawn and northern sites at lower salinity had higher pre-spawn GI means (more advanced gametogenesis) than PGB in Jamaica Bay. In mid-July the majority of oysters were still pre-spawn and GI means were similar across the salinity gradient except for an exceptionally advanced pattern in the harbor at RED. By August the harbor and Jamaica Bay sites had almost all spawned whereas the two northern sites had only 50% of oysters spawned. In summary, northern low salinity sites seemed to have a reproductive phenology that was more extended June – August whereas at the harbor and Jamaica Bay sites oysters had a narrower reproductive season where they were slower to mature in June and most oysters were done spawning by mid-August. Given the lack of a significant strain effect, these phenology differences across locations are likely caused by acclimation to different environments.

The importance of these results is twofold for understanding the biology and restoration potential of TZ-HB oysters. First, TZ-HB adults seem to be tolerant of the broad range of environmental conditions in the HRE, with the possible exception of New York Harbor. This suggests that adult transplants may be a restoration strategy worth considering. This option potentially provides a rapid boost to natural reproduction and larval supply on restored habitats, two important population processes that are delayed two or more years if the only plantings are juvenile seed oysters. One of the unknowns not yet addressed (because we were not able to include the adult transplants in the histological assays) is the relative degree of gametogenesis immediately after winter or spring transplant (i.e., how long is the acclimation process for this trait). Second, our histological comparison of reproductive phenology along the salinity gradient (for two year old oysters transplanted at one month age) indicates that environment is a more important determinant than genetics. There may be heritable traits of TZ-HB oysters that have become locally adapted to their low-salinity environment, but reproductive phenology does not appear to be one of them, perhaps because phenotypic plasticity is adaptive for reproductive timing no matter where an oyster lives. An important remaining consideration bearing on the restoration efficacy of TZ-HB transplants is the relative performance of their larvae in different HRE environments. Moving broodstock to the lower estuary is a waste if they produce larvae that are genetically less well equipped to survive there. Thus, testing for local adaptation of larval environmental tolerances is an important next step for a full evaluation of the TZ-HB population and its capacity to contribute to population expansion.

Literature Cited

Gregory, M. K. and M. Hare. 2018. The effect of salinity on eastern oyster reproduction in the Hudson River Estuary. Section IV:1-35 pp. In S.H. Fernald, D.J. Yozzo and H. Andreyko (eds.), Final Reports of the Tibor T. Polgar Fellowship Program, 2018 Hudson River Foundation.

McFarland, K. & M.P. Hare. 2018. Restoring oysters to urban estuaries: the importance of habitat quality for eastern oysters near New York City.

RStudio Team (2016). RStudio: Integrated Development for R. RStudio, Inc., Boston, MA URL http://www.rstudio.com/.

Volety, A. K. 2008. Effects of salinity, heavy metals and pesticides on health and physiology of oysters in the Caloosahatchee Estuary, Florida. Ecotoxicology 17(7).

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