Out of the Blue: The Failure of the Introduced Sea Anemone Sagartia elegans (Dalyell, 1848) in Salem Harbor, Massachusetts.
The spread of introduced species has become a global ecological and conservation crisis as invasive organisms are increasingly altering terrestrial and aquatic communities worldwide (Mooney and Cleland, 2001; Gurevitch and Padilla, 2004; Simberloff et al., 2005, 2013; Bellard et al., 2016). Success or failure of biological invasions can be determined at multiple stages in the introduction continuum as organisms cross major invasion barriers (Blackburn et al., 2011). It is expected that most potential introductions do not succeed (Williamson and Fitter, 1996; Lockwood et al., 2005; Blackburn et al., 2011; Zenni and Nunez, 2013; King and Reed, 2016) and that many invasions may fail multiple times before becoming successful (Sax and Brown, 2000; Dlugosch and Parker, 2008; Simberloff, 2009). Despite this, invasion biology has focused primarily on species that have established successfully (e.g., Richardson and Pysek, 2008; Maclsaac et al., 2011; Budy et al., 2013). The few studies of failed invasions have provided many important insights into invasion biology, particularly in species distribution modeling and analyses of historical factors associated with invasions (Zenni and Nunez, 2013). More studies of failed invasion would promote a deeper understanding of the invasion process.
Even sparser than the literature on failed invasions is the documentation of the failure of an introduced species after surviving multiple years in its new environment. Common reasons for the failure of an established population include natural disasters, competition and parasitism by a subsequently introduced species, lack of propagule pressure, intentional eradication, or inadvertent anthropogenic intervention (e.g., Hillman, 1985; Simberloff, 1992; Carlton and Eldredge, 2009; Gaubert and Zenatello, 2009; Kaplan et al., 2010). Understanding the environmental factors leading to the failure of established populations would allow for better management of introduced species.
One notable case of a failed invasion, investigated here, involves the sea anemone Sagartia elegans (Dalyell, 1848) in Salem, Massachusetts. A population of S. elegans was first found in the summer of 2000 at a single marina in Salem Harbor (Hawthorne Cove Marina [HCM]), during an introduced-species survey (Pederson et al., 2005), where it was identified by Larry Harris and James Carlton by comparing external morphology of the newly found sea anemone to potential source location anemones. It matched the descriptions found in Stephenson (1935), Manuel (1988), and Wood (2013). It was particularly abundant in 2000 and, therefore, was suspected to have been introduced some years prior. Subsequent rapid assessment surveys in 2003, 2007, and 2010 also found S. elegans at HCM (Pederson et al., 2005; Wells et al., 2014). The introduced population of S. elegans in Salem Harbor was seasonally abundant; it appeared as early as June but died back completely by January. Summertime abundance of S. elegans did not have an obvious decline or increase over this time. Exhaustive surveys of public spaces in Salem Harbor, including intertidal environments and marshes, failed to find any other populations of S. elegans (B. Warren, Salem Sound Coast-watch, pers. comm.).
Sagartia elegans is native to the European coast and can be found in subtidal habitats from the Adriatic Sea to Scandinavia, to depths of 60 meters, attached to hard substrata (Manuel, 1988; Ates et al., 1998; Grebelnyi and Kovtun, 2013) and artificial substrata (Coolen et al., 2018). Within this range, S. elegans may experience temperatures ranging from 1 [degrees]C, in its northeastern range during the coldest months, to 26 [degrees]C, in the Mediterranean during the warmest months (Kennedy, 2019). In the Netherlands, S. elegans was present only after mild winters with relatively high minimum sea temperature (>5 [degrees]C), and it disappeared during especially cold winters (Braber and Borghouts, 1977; Ates et al., 1998). Typical of sea anemones, S. elegans is gonochoristic; it sexually reproduces through broadcast spawning (Stephenson, 1929), and it does not have a resting stage. The only method of asexual reproduction observed in S. elegans is pedal laceration (Stephenson, 1929; Manuel, 1988; Shaw, 1991), in which small pieces of the pedal disk and internal structures break off and regenerate into new daughter anemones. Within its native range, S. elegans is preyed upon by the nudibranch Aeolidia papulosa (Linnaeus, 1761) (Mollusca, Gastropoda); but it is not the preferential prey species, possibly because of its cnidome (i.e., cnidae complement) and the presence of acontia used in defense (Edmunds et al., 1974). Sagartia elegans has been reported outside of its native range in Salem Harbor (Pederson et al., 2005) and the northwestern Black Sea (Grebelnyi and Kovtun, 2013).
In the present study, we exhaustively surveyed for S. elegans in Salem Harbor and quantified important abiotic factors affecting growth, asexual reproduction, and survival. We use these factors to explore potential reasons for the disappearance of S. elegans from Salem Harbor. Impacts of temperature and salinity were determined in field and laboratory experiments.
Materials and Methods
On the western Atlantic, Sagartia elegans (Dalyell, 1848) has been found within Salem Harbor only at a single site (HCM, described below). Salem Harbor is an embayment on the northern coast of Massachusetts Bay. For the purpose of this study, Salem Harbor is defined as the area bound by a line drawn between Juniper Point, Salem, Massachusetts (GPS coordinates: 42.5337, -70.8644), and Fluen Point, Marblehead, Massachusetts (42.5215, -70.8522) (Fig. 1). Salem Harbor is about 24 km northeast of Boston. Surface area within the harbor is about 370 hectares, ranging in volume from 10.2 to 20.1 megaliters, with an average depth of 5.2 m at high tide (Anderson et al., 1975). Harbor surface water temperature ranged from 1 [degrees]C to 24 [degrees]C, with peak temperatures in early August and lowest temperatures in January and February (CDW, unpubl. data). Salinity ranged from 23.5 to 34.5 ppt during an environmental impact assessment (Anderson et al., 1975), although current ranges are unknown. During the time S. elegans was present at HCM, a coal- and oil-fired power plant was present; but it has since been decommissioned and replaced with a natural gas-fired power plant (Sedor, 2014).
HCM is a private marina with 110 slips, located on the northern shore of Salem Harbor (42.5214, -70.8825). Float fouling communities are dominated by ascidians and arborescent bryozoans on the vertical surfaces and by mussels and clonal anemones (Metridium senile (Linnaeus, 1761)) on the horizontal surfaces. Sides of floats are scraped annually by marina staff for maintenance purposes. Depth at HCM ranges from 1 to 4 m. HCM is known for its exceptionally high load of introduced species compared to other sites in the Gulf of Maine (Pederson et al., 2005; Wells et al., 2014).
Laboratory culture and measurement methods
Polyps of about 250 S. elegans individuals were collected from several different locations on the floating docks in HCM during October 2010 in order to create cultures for use in the following experiments. Polyps were removed from the shells of the mussel Mytilus edulis Linnaeus, 1758 by hand and were placed in shallow dish pans held at 15 [degrees]C on a 12h: 12h light: dark cycle in a temperature- and light-controlled room at the University of New Hampshire. Cultures were fed brine shrimp Artemia franciscana Kellogg, 1906 three times weekly. Anemones were allowed to asexually reproduce, and the asexual products were used in the subsequent experiments. Cultures were not maintained as clonal lines.
Wells (2013) found that the best method for accurately measuring the growth of anemones, without disturbing and removing them from their substratum, was to measure the pedal disk surface area (PDSA), assuming that the pedal disk was ellipsoid. The following equation for an ellipsoid was used to calculate pedal disk surface area for S. elegans:
PDSA = [pi] x [[D.sub.maj]/2] x [[D.sub.min]/2],
where [D.sub.maj] is the length of the major axis of the pedal disk (i.e., maximum diameter) and [D.sub.min] is the length of the minor axis (i.e., perpendicular to the maximum).
Field surveys were conducted to explore the seasonal population dynamics of S. elegans in its introduced range and to find any remnant populations. Because S. elegans was expected to maintain an annual population at HCM, surveys in 2009 and 2010 were originally conducted for other purposes; and their methods differ slightly from the more extensive 2011-2013 surveys.
On October 23, 2009, during a pilot study, the density of S. elegans was approximated by counting all polyps on haphazardly chosen vertical sides of 15 floats (about 0.40 [m.sup.2]) at HCM. In the late summer to early winter of 2010, the density of S. elegans was approximated by counting all polyps on haphazardly chosen vertical sides of 20 floats at HCM. Counts were done from August to December monthly (four surveys). From June 2011 to January 2013, every 1-4 weeks (48 surveys), the density of S. elegans was approximated by counting polyps within 0.06-[m.sup.2] (0.25 x 0.25-m) polyvinylchloride (PVC) quadrats laid haphazardly on a vertical side of 30 floats at HCM. A scuba survey was performed in November 2011 to determine whether S. elegans was on the underside of the floats. The bottoms of 54 floats were examined for S. elegans polyps. In November and December 2012, floating docks and other structures were examined for polyps of S. elegans via kayak (Table 1).
Field survival and growth study
Temperature is highly variable within Salem Harbor, and temperature is frequently indicated as the major reason for established populations failing (Zenni and Nunez, 2013). Laboratory-cultured anemones were allowed to attach to panels; and the panels were hung off HCM in two separate years to explore the relationship between temperature and S. elegans growth, asexual reproduction, and survival. In June 2011, 10 sanded but otherwise clean acrylic glass panels (0.01 [m.sup.2], 10.0 x 10.0 x 0.4 cm) with 5 polyps of S. elegans were hung. Panels were hung so that they were isolated from the floats at HCM to prevent predation. Floating structures, such as fouling panels, have reduced predation because of their isolation from habitats with predators (Dumont et al., 2011). At the start of the experiment and about every two weeks thereafter, we noted PDSA, number of pedal lacerates (i.e., asexual offspring) produced, and whether or not animals had visibly ripe gonads, until all animals had released from the panels or died, in January 2012. Animals that had released from the panels were assumed to have died because there are few suitable habitats for hard-bottom anemones such as S. elegans underneath HCM and because there is a substantial population of their predator, the nudibranch Aeolidia papillosa (Linnaeus, 1761) (Wells, 2013). Pedal lacerates were discarded so that daughter anemones would not compete for space with the original anemones and to facilitate tracking of adult survival. Temperature was measured concurrently using a HOBO Pendant temperature and light data logger 64K (Onset Computer Corporation, Bourne, MA) set to measure temperature every 20 minutes. From June 2012 to January 2013, the experiment was repeated with 10 polyps of S. elegans per panel. Measurements of PDSA were taken every one to two weeks, but pedal lacerates were not counted. Panels were removed in January 2013. Linear regressions comparing size (both years) and asexual reproduction (2011 only) to temperature were performed. Size measurements from 2011 and 2012 were pooled. Because animals died or fell off the panels and because panels fell off as a result of wave action throughout the experiment, sample size varied across time.
Laboratory temperature and salinity study
Within its native range, S. elegans is sensitive to salinity and does not survive in brackish conditions in estuaries (Ates et al., 1998). Salinity within Salem Harbor can range from 23.5 to 34.5 ppt, frequently dropping below full-strength seawater (Anderson et al., 1975); and it is, therefore, a possible reason for S. elegans' disappearance. The effect of salinity on growth, asexual reproduction, and survival was quantified through laboratory experiments. We spread 120 S. elegans polyps evenly across 12 Sterilite containers (Sterilite, Town-send, MA) (1.7 L; 10 anemones per container). Anemones were chosen haphazardly from culture tanks. Containers were filled with 1.0 L of water at 1 of 4 levels of salinity (3 replicate containers per treatment): 20, 25, 30, or 35 ppt. Ultraviolet (UV)-sterilized seawater (500-[micro]m filtered, average of 31 ppt) was decreased in salinity through the addition of deionized water or was increased in salinity by the addition of Instant Ocean sea salt (Spectrum Brands, Madison, WI) to achieve these salinities. Salinities were measured with a refractometer. The 12 containers were placed within 3 Sterilite water baths (39 L; 4 containers per bath). Water baths were filled with 13 L of freshwater and were heated with a 150-W JBJ (Inglewood, CA) True Temp Titanium Heating System to 15 [degrees]C at the beginning oftheexperiment,inordertoemulateOctobertemperatures, just before temperatures precipitously drop (CDW, unpubl, data). The heating systems have internal temperature monitors with an accuracy of [+ or -]0.3 [degrees]C. One Minijet 404 submersible pump (Spectrum Brands Pet, Blacksburg, VA) was placed in each water bath to ensure even heat distribution within the water baths. The water baths were placed in a temperature-controlled room at 4.0 [degrees]C on a 12h: 12 h light: dark cycle. Temperature was decreased by 3.0 [degrees]C on days 14 and 29, after which temperature was decreased by 1.0 [degrees]C every 2 weeks (days 41, 55, 70, 83, and 97) until ambient temperature had been reached. This drop in temperature resembled the temperature drop measured in Salem Harbor between October and January (CDW, unpubl. data). At the start of the experiment and approximately every seven days thereafter, size was measured, and pedal lacerates were counted and then discarded. Animals were fed 1.0 mL (12,000 nauplii per mL) of A. franciscana nauplii 3 times weekly. This amount of food completely satiated anemones at the time of feeding, and digestion of this amount of A. franciscana took approximately 24 hours. Water movement and aeration within the containers were provided by two air pumps connected to a gang-valve system. Water was changed with fresh seawater adjusted to the proper salinity two days prior to days when temperature was reduced. Containers that had complete mortality within the first three weeks were discarded and were not included in analyses because anemones were within temperatures and salinities found to be acceptable in initial pilot studies. Anemones that died were not replaced because there was concern that starting some containers at different temperatures would affect their growth, reproduction, or mortality. In addition, 4 containers with 10 anemones per tank were kept in a separate temperature-controlled room at 15 [degrees]C on a 12h: 12h light:dark cycle. Water changing, feeding regime, and sampling followed the same methods as the experimental treatments. Linear regressions were performed comparing growth and shrinkage rates for S. elegans.
In 2009, Sagartia elegans was present in October (average 4.2 polyps [m.sup.-2], Fig. 2). Anemones were primarily found within dead Mytilus edulis shells and attached to live M. edulis, although many sea anemones were also found attached to the floats and as epibionts on other fouling organisms. No S. elegans individuals were sexually mature, and all were of the same color.
In 2010, S. elegans was present from September to December. Densities were highest in early October (average 210 polyps [m.sup.-2]) and were dropping precipitously by December (Fig. 2). Temperature was the highest in September (21.2 [degrees]C), and it slowly decreased until December (7.4 [degrees]C) (Massachusetts Bay Buoy, Northeastern Regional Association of Coastal Ocean Observing Systems, 2019). The highest abundance of sea anemones was on primary space on the vertical surfaces of the floats within the first 10 cm below the water surface. Sea anemones were also epibiotic on M. edulis, Ciona intestinalis (Linnaeus, 1767), Steyla clava Herdman, 1881, Ostrea edulis Linnaeus, 1758, Ulva lactuca Linnaeus, 1753, Saccharina latissima (Linnaeus) C.E.Lane, C.Mayes, Druehl & G.W.Saunders, 2006, and Chondrus crispus Stackhouse, 1797. In addition, they were found attached to free-floating Ascophyilum nodosum (Linnaeus) Le Jolis, 1863, which were tangled with the floats. Most polyps were 14 mm in diameter and larger, and all polyps above 20 mm had female gonads visible through their oral disk. All S. elegans individuals were of the same color.
From June 2011 to January 2013, we failed to detect S. elegans through all methods, including the repeated surveys of the vertical sides of floats (Fig. 2), kayak surveys, and the scuba survey.
Field survival and growth study
Both the size of S. elegans (Fig. 3A, [R.sup.2] = 0.913, [F.sub.1, 24] = 250.79, P < 0.001, linear regression) and the number of pedal lacerates being produced (Fig. 3B, [R.sup.2] = 0.929, [F.sub.1, 6] = 78.82, P < 0.001, linear regression) were strongly correlated with temperature. Size and asexual reproduction decreased with temperature. Asexual reproduction stopped after temperature fell below 9.3 [degrees]C. Three of the 10 panels in 2011 were dislodged from HCM during Hurricane Irene on August 27, 2011. On panels still attached, many of the anemones were heavily damaged, with some subsequently disappearing in September. After the losses during and directly after Hurricane Irene, anemones were not lost until November. While the hurricane had a major initial impact, after the hurricane the rate of disappearance from the panels was similar between years. After temperature dropped below 11 [degrees]C, anemones disappeared at an accelerated rate; and all anemones had disappeared prior to temperatures decreasing to 6 [degrees]C.
Laboratory temperature and salinity study
Anemones in all treatments grew until temperature was decreased below 9 [degrees]C, at which point animals started to shrink (Fig. 4A). Anemones in the control group continued to grow throughout the experiment. There was no significant difference between growth rates ([F.sub.3, 6] = 2.95, P = 0.120, ANOVA) and shrinkage rates ([F.sub.3, 6] = 0.19, P = 0.901, ANOVA) in the four salinity treatments, although the sample size was very small (n = 2 - 3). The pooled mean growth rate before the temperature decreased below 9 [degrees]C was 0.21 [mm.sup.2] [day.sup.-1]; and after decreasing below 9 [degrees]C, the shrinkage rate was 0.11 [mm.sup.2] day . Beyond 9 [degrees]C, asexual reproduction stopped, except for one pedal lacerate produced at 8 [degrees]C and 6 [degrees]C (Fig. 4B). Control anemones produced a mean of 0.07 pedal lacerates per day throughout the experiment. Polyps of S. elegans in the experimental treatments started dying once temperature decreased below 7 [degrees]C (Fig. 4C). Anemones were considered dead when tissue started to visibly degrade, which was preceded by loss of color and release from the substratum. After the third week at 4 [degrees]C, all polyps in all treatments, except for 2 polyps in the 30-ppt treatment, had died. Polyps still alive at 4 [degrees]C were heavily discolored and unattached.
Sagartia elegans disappeared from Salem Harbor sometime between December 2010 and June 2011. Extensive surveys of the only location where S. elegans had been found failed to detect any individuals. Wider searches, including kayak and scuba surveys (this study) and intertidal and benthic surveys, also failed to locate any remnant populations (B. Warren, Salem Sound Coastwatch, pers. comm.). Additional surveys in 2013 and 2018 did not locate any 5. elegans individuals at HCM (Wells et al., 2014; A. Pappal, Massachusetts Coastal Zone Management, pers. comm.).
We conclude that temperature likely played the largest role in the disappearance of S. elegans. Temperatures below 6 [degrees]C were found to be detrimental to S. elegans' survival both in culture and in the field (Figs. 3A, 4C). This is higher than the minimum temperature (5 [degrees]C) found by Braber and Borghouts (1977) and Ates et al. (1998) in the field. Within the species' native range, certain populations of S. elegans may experience temperatures as low as 1 [degrees]C (Kennedy, 2019). It seems that the source population of the original colonization of 5. elegans was from its southern native range.
In the 9 years prior to the disappearance of 5. elegans, winter sea surface temperature was below 6 [degrees]C for a minimum of 76 consecutive days and, on average, for 97.3 consecutive days. In the winter of 2011, there were 112 consecutive days of below 6 [degrees]C sea surface temperature (Massachusetts Bay Buoy, Northeastern Regional Association of Coastal Ocean Observing Systems, 2019). For S. elegans to survive winter temperatures, there must have been a temperature refuge in Salem Harbor. It is highly unlikely that a new invasion was occurring every year, because the vector for sea anemone introduction is typically hull fouling (Carlton, 2003). The only plausible refuge in Salem Harbor was a coal- and oil-fired power plant located less than 100 meters from HCM (Fig. 1). This power plant used Salem Harbor water for thermoelectric cooling and discharged water back into the harbor through a discharge channel that opened toward HCM (Anderson et al., 1975). The plant was allowed to discharge water up to 15.8 [degrees]C warmer than ambient temperature, and temperatures within the discharge channel could have risen up to 9.6 [degrees]C (Anderson et al., 1975). On average, winter effluent temperatures were 12.6 [degrees]C (US Department of Energy, 1982), more than sufficiently warm for S. elegans to survive the cold winters; and the power plant had been under significantly more use since 1982 (Mooney and Kawa, 2008). Water within Salem Harbor was not significantly warmed outside of the discharge channel (Anderson et al., 1975). An increase of only several degrees during the winter would be enough to keep S. elegans alive throughout the winter months in this channel. A change in power plant procedures, such as cleaning the discharge channels during winter (i.e., directly killing fouling organisms) or a short reduction in boiler service (i.e., a reduction in discharge temperature), could have massive impacts on a refuge population already stressed by New England winter temperatures. There are no public records of the power plant changing its power plant procedures in the winter of 2010 and 2011.
Many aquatic organisms use warm-water effluent to survive in locations that would normally be too cold (e.g., Langford et al., 1972; Galloway and Kilambi, 1988; Crutchfield, 1995; Peterson et al., 2005; Simard et al., 2012; Lukas et al., 2017). Thermally influenced systems are hotspots for introduced species, providing habitat for animals outside of their normal temperature range (reviewed in Lukas et al., 2017). Growth rate and survival during winter were increased in introduced tilapia Oreochromis niloticus (Linnaeus, 1758) using the thermal effluent from an aquaculture facility (Peterson et al., 2005) and a nuclear power plant (Crutchfield, 1995). The introduced Asian clam Corbicula fluminea (O. F. Muller, 1774) survived in warm-water effluent during the cold winter months in the St. Lawrence River (Simard et al., 2012), and then it subsequently repopulated sites downstream during warmer months (Morgan et al., 2004). The widely introduced bryozoan Bugula neritina (Linnaeus, 1758) had large populations on a dock heated by power plant effluent in south Wales, and it disappeared only after the power plant was decommissioned (Ryland et al., 2011). Similarly, S. elegans was absent from HCM during the winter and spring before its failure, and it repopulated HCM from a refuge population each summer. This may have been facilitated by the ability of S. elegans to travel short distances via ballooning, where polyps fill with seawater, release from their substratum, and then reattach via use of their tentacles (Wells, 2013), a behavior also seen in congeners (Gosse, 1860; Ashworth and Annandale, 1904).
Salinity was likely not responsible for S. elegans failure in Salem Harbor. Laboratory experiments found that the introduced population of S. elegans was not sensitive to salinities ranging from 20 to 35 ppt, which completely covers the range of salinities observed in Salem Harbor (Anderson et al., 1975).
In addition to temperature stress, the introduced population of S. elegans was likely one clone. All animals were of one color morph, in contrast to the variety of color morphs in their native range; there are at least five fairly distinct color morphs (Stephenson, 1935; Manuel, 1988; Wood, 2013). Although S. elegans is gonochoristic, all sexually mature S. elegans individuals had female gonads, indicative of a clonal population. Within a sexually reproducing population of sea anemones, the sex ratio is commonly 1:1 (Gemmill, 1920; Carter and Thorpe, 1981; Jennison, 1981; Sebens, 1981; Shaw et al., 1987; Hunt and Ayre, 1989). The possibility of there being more than one female clone of the same color cannot be excluded; however, our data strongly support that there was not a sexually reproducing population reducing adaptive potential. Sagartia elegans would not have had a chance to adapt to the Gulf of Maine environment and, therefore, was likely to fail at some point. Failure of clonal populations of another introduced sea anemone, Diadumene lineata (Verrill, 1869), is apparently common (Shick et al., 1979); yet there have been no studies focusing on these ephemeral populations.
One possible method for controlling the spread of introduced species that have invaded regions beyond their thermal tolerance may be to briefly shut down or reduce the activity of industry providing a thermal refuge. This assumes that the introduced species could not live without the thermal refuge and that the cost of temporarily discontinuing industry for the required amount of time to kill the introduced species is less than the damage that the introduced species would inflict on the local ecosystem. Another possibility is modifying the temperature of effluent leaving the facility. As of June 2012, the coal- and oil-fired power plant in Salem Harbor was decommissioned; and it is being replaced by a natural gas-fired power plant (Ailworth, 2012), which will eliminate impact on local water temperatures because the natural gas boilers being built will be air cooled (Buttaro et al., 2014). It would be informative to do a comparative study of the fouling community at HCM before and after shutdown of the power plant, because HCM is a highly invaded site compared to other nearby sites (Pederson et al., 2005; Wells et al., 2014).
Increased effort in detecting introduced species immediately or shortly after invasion will be imperative to both eradication efforts and the collection of data on failed invasions. More data on failed invasions will promote a deeper understanding of the invasion process because little work has been focused on failed introduced species. Particular effort in detecting and understanding the special cases where an introduced species becomes established and then subsequently fails will be especially helpful in introduced species management because these reasons could be developed into possible management skills for the eradication of newly invaded species.
We thank J. Bryant, S. Edquist, J. Eichenlaub, S. Goodnight, S. Grabbert, J. Langevin, K. LePage, S. Marchand, J. Marovelli, V. McTague, S. Pope, and K. Pope for field and laboratory assistance; S. Edquist, S. Fritscher, J. Haney, H. Hayford, E. Heery, W. King, E. Linck, M. Litvaitis, A. Lowe, S. Marchand, J. Ruesink, and K. Sebens for reading and commenting on the manuscript; and N. Flaherty for allowing the use of the Hawthorne Cove Marina floating docks to stage this research. Partial support was provided by a US Department of Agriculture Agricultural Experiment Station Hatch Grant to LGH.
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CHRISTOPHER D. WELLS (1,*) AND LARRY G. HARRIS (2)
(1) Research Foundation, State University of New York at Buffalo, Buffalo, New York; and (2) Department of Biology, University of New Hampshire, Durham, New Hampshire
Received 29 May 2018; Accepted 14 July 2019; Published online 9 December 2019.
(*) To whom correspondence should be addressed. Email: Christopher.email@example.com.
Abbreviations: HCM, Hawthorne Cove Marina; PDSA. pedal disk surface area.
Table 1 Georeferenced sites examined for Sagartia elegans during kayak surveys in November and December 2012 Date of survey Site Type GPS coordinates November 2012 Salem Harbormaster Floating dock 42.5255, -70.8693 floating dock November 2012 Floats in Cat Cove Floating 42.5257, -70.8736 structure November and Power plant water Floating 42.5231, -70.8763 structures December 2012 discharge channel November and Salem Ferry Floating dock 42.5214, -70.8796 December 2012 floating dock December 2012 Friendship of Full-rigged ship 42.5201, -70.8865 Salem December 2012 Pickering Wharf Floating dock 42.5194, -70.8872 December 2012 Palmer Cove Floating dock 42.5137, -70.8869 Yacht Club
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|Title Annotation:||failed invasions|
|Author:||Wells, Christopher D.; Harris, Larry G.|
|Publication:||The Biological Bulletin|
|Article Type:||Technical report|
|Date:||Dec 1, 2019|
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