Northeastern Naturalist Vol. 21, No. 3 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 369 2014 NORTHEASTERN NATURALIST 21(3):369–379 Records of Bryozoans in the Freshwater Reach of the Hudson River Estuary Toby M. Michelena1, Celeste Ostman1, Charles W. Boylen1, and Sandra A. Nierzwicki-Bauer1,* Abstract - We collected statoblasts of the bryozoans Pectinatella magnifica, Lophopodella carteri, and Cristatella mucedo from multiple locations within the Hudson River Estuary and at the confluence of the Mohawk and the Hudson Rivers during benthic invertebrate sampling activities October 2009–November 2011. We identified both P. magnifica and L. carteri at geographically separated locations within the estuary. Although these animals are exclusively freshwater organisms, we found P. magnifica and L. carteri statoblasts in both freshwater and brackish water environments; only P. magnifica is considered indigenous to New York. Based upon the distribution of statoblasts, it is unknown whether C. mucedo is resident in the estuary. However, our findings indicate that the estuary and the Mohawk River have established populations of L. carteri and P. magnifica. Introduction Organisms in the Phylum Ectoprocta (Bryozoa) are colonial aquatic invertebrates that have been in existence since the Lower Ordovician (Ryland 1970). There are more than 4000 extant species world-wide, most of which are marine (Pennak 1978, Ryland 1970). The Phylactolaemata is the only exclusively freshwater class of bryozoans (Ryland 1970, Wood 2010), and fewer than 100 species of Phylactolaemata are known worldwide (Wood 2002). Members of the Class Phylactolaemata are found in virtually every type of freshwater ecosystem. They are filter-feeding, sessile organisms that are frequently found in slow-moving clear water, although many species also inhabit faster -moving and/or turbid waters (Ryland 1970, Wood 2010). Other water-quality characteristics including temperature, salinity, and pH also determine the distribution of these organisms (Økland and Økland 2005, Wood 2005). Of the 3 extant classes of Bryozoa, only phylactolaemates survive periods of unfavorable environmental conditions by producing statoblasts—dormant, asexual reproductive structures. Statoblasts are resistant to severe conditions and germinate when the environment is conducive to growth (Pennak 1978). Statoblast morphology is species-specific and can be used for taxonomic identification (Ricciardi and Wood 1992, Wood 2010). Statoblasts are mobile in the environment because they are transported by currents, attach to other organisms, or can be carried in the guts of birds (Charalambidou et al. 2003, Green et al. 2008, Marsh and Wood 2002, Wood 2001). Therefore, while the presence of statoblasts may indicate a resident 1Darrin Fresh Water Institute and Department of Biology, Rensselaer Polytechnic Institute, 110 8th Street, MRC 307, Troy, NY 12180-3590. Corresponding author - nierzs@rpi.edu. Manuscript Editor: David Strayer Northeastern Naturalist 370 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 Vol. 21, No. 3 population, their existence in a specific area does not necessar ily correspond to the location of the mature animal. Bryozoans are common within both fresh and marine waters of the northeastern US, including New York (Rogick 1940, Rogick and Brown 1942). The 3 freshwater species that are the subject of this paper—Pectinatella magnifica (Leidy) (Magnificent Bryozoan), Lophopodella carteri, (Hyatt) and Cristatella mucedo (Cuvier)— have been recorded from the northeastern US, but, to our knowledge, there are no literature reports of these or any other species of bryozoan in the freshwater portion of the Hudson River Estuary. Pectinatella magnifica has been recorded in many small ponds and lakes in New York (Rogick 1940). In addition, there are unpublished reports of P. magnifica in Tivoli North Bay, a small bay on the east side of the Hudson River Estuary at River Kilometer 158 (E. Kiviat, Hudsonia, Annandale, NY, unpubl. data). This species is a common and widely distributed freshwater bryozoan, native to North America, primarily east of the Mississippi River in warmer waters (Pennak 1 978, Wood 2010). Lophopodella carteri is not native to the US, and was most likely introduced with imported aquatic plants in the 1930s (Masters 1940). It is native to Southeast Asia and has been documented in northern Africa (Bushnell 1965, Ricciardi and Reiswig 1994). Wood (2010) described this species as uncommon but locally abundant, and Pennak (1978) described it as rare. There are no known reports of this species in the Hudson River watershed. Cristatella mucedo is a Holarctic species that is typically found in slow-moving streams or lakes and uses any type of substrate for attachment (Lacourt 1968, Økland and Økland 2005). Previous to our study, there were no known reports of this organism in the Hudson River Estuary watershed. The mainstem of the Hudson River Estuary has been extensively investigated with respect to physical and chemical interactions (Levinton and Waldman 2006). Comparatively little effort has been focused on the small embayments along the estuary. These small embayments and the tributaries that feed them include habitats that may be suitable for bryozoans. We report on the geographic distribution of bryozoan statoblasts in and around these small embayments. Site Description The Hudson River Estuary is ~248 km long, extending from the Battery in New York Harbor (river kilometer [RK] 0) to the Federal Dam in Troy, NY (RK 248). The major inputs to the estuary are the upper Hudson River and the Mohawk River, which enters the upper Hudson River immediately north of the estuary boundary (Fig. 1). There are ~65 major rivers and streams that drain the watershed and feed the estuary (Penhollow et al. 2006). The drainage area of the estuary’s watershed, including the upper Hudson and Mohawk Rivers, is ~34,450 km2 (Phillips and Hanchar 1996). The study area comprised a ~190-km length of the estuary and upper Hudson River from immediately south of Indian Point (~RK 61) to immediately north of Lock #1 of the Champlain Canal (~RK 256). We sampled at 8 sites within the study Northeastern Naturalist Vol. 21, No. 3 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 371 area, primarily at the confluence of major tributaries to the estuary (Table 1); two of these locations (Upper Hudson and Mohawk River) are north of the estuary boundary. These sample areas encompassed both freshwater and brackish areas of the estuary (Table 1). Figure 1. A) Location map of Hudson River Estuary watershed including the Upper Hudson and Mohawk River watersheds (USGS 2013b). B) Sub-watersheds within the estuary watershed boundary: 1) Hannacroix, 2) Stockport, 3) Rondout, and 4) Fishkill (USGS 1980). Study-sample areas are found at the confluence of sub-watershed tributaries and the estuary. Table 1. The name, location designator, and environmental characteristics of the study sites. Conductivity Secchi-depth (m) (μS/cm) Sample area Sites mean (min, max) mean (min, max) Habitat type Upper Hudson River (AW) AW01–AW02 1.42 (0.7, 2.0) 143 (85, 237) Freshwater/ non-tidal Mohawk River (MR) MR01–MR04 1.52 (0.1, 3.4) 299 (169, 522) Freshwater/ non-tidal Normanskill Creek (NK) NK01 1.07 (0.35, 1.9) 310 (119, 509) Freshwater/tidal Hannacroix Creek (HC) HC01–HC03 0.99 (0.3, 1.5) 217 (110, 333) Freshwater/tidal Stockport Creek (SP) SP01–SP04 0.78 (0.1, 2.2) 199 (64, 282) Freshwater/tidal Rondout Creek (RO) RO01–RO04 0.70 (0.1, 1.2) 227 (133, 613) Freshwater/tidal Fishkill Creek (FK) FK01–FK04 0.62 (0.1. 1.7) 612 (180, 3690) Freshwater/ brackish/tidal Haverstraw Bay (HB) HB01–HB02 0.54 (0.1, 1.5) 2992 (151, 8560) Brackish/tidal Northeastern Naturalist 372 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 Vol. 21, No. 3 The Hudson River Estuary includes marine, brackish, and fresh water. The northern limit of the salt front is Poughkeepsie, NY (RK 124), although the salt front rarely reaches this point (Simpson et al. 2006; USGS 1988, 2013a). The remaining northern reach of the estuary is exclusively fresh wate r. Methods We collected sediment samples during ice-free months from September 2009 through November 2011. We collected all samples within the estuary at or near high tide in water that was 1–5 m deep. We accessed sample locations by boat and recorded coordinates with an onboard GPS system. All specimens, except those found at RO-02 and RO-03, were collected within 30 m of shore. Sample locations RO-02 and RO-03 were up to 100 m from shore at the edge of a large Trapa natans L. (Water-Chestnut) bed that prevented nearshore access. We collected sediment samples and analyzed them for benthic invertebrate species diversity, sediment-size distribution, and organic carbon content. We conducted sampling with a petite PONAR dredge (Scoops-008890, Wildco, Yulee, FL), placed collected sediment into 2.5-L plastic containers, and stored the samples on ice for transport to the laboratory. In the laboratory, we recorded the sediment volume and then sieved it through a 500-μm-mesh bucket sieve. We collected the material remaining in the sieve, placed it into a plastic container, and stored it in 10% buffered formalin at room temperature. We emptied the formalin-preserved samples into a white bin and visually scanned the material for invertebrates. Invertebrates were picked with forceps and placed into a container filled with 10% buffered formalin for later identification and photo-documentation. Items picked from the sieved samples were examined using a Nikon Model C-LEDS stereo-microscope. We photographed the collected invertebrates with an Idea Spot digital camera and software (Taubman et al. 2001) and identified each organism to the lowest taxon practicable; taxonomy of bryozoans is based on Wood (2010). Physical and chemical data were also collected for each sampling event. Measurements made in the field included: dissolved oxygen and temperature profiles taken at 1-m increments from the water surface to the sediment surface using a YSI Model 550A meter (YSI, Inc., Yellow Springs, OH), manual depth readings taken to the nearest 0.1 m with a line and bob, and water transparency assessed with a Secchi disk. We collected depth-integrated water samples using an electric peristaltic pump, placed in an integrated collection vessel, and subsequently transferred samples to 2-L brown plastic bottles that were stored on ice and transported to the laboratory. We made conductivity and pH measurements using an Oakton pH/Con 510 Series meter (Oakton Instruments, Vernon Hills, IL). Results We identified statoblasts of 3 bryozoan species—P. magnifica, L. carteri, and C. mucedo—from our samples (Fig. 2). These statoblasts were collected over a large Northeastern Naturalist Vol. 21, No. 3 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 373 geographic area (Figs. 1, 3). We did not find bryozoan colonies, likely because we used the petite PONAR dredge that was designed for sediment sampling but is not intended to collect fragile organisms attached to macrophytes or rocks. Statoblasts were found in 3 distinct groups relative to the mainstem of the estuary and associated tributaries (Table 2). For group 1 sites, water flow was directly influenced by the tributary and not the estuary (Fig. 3), creating a habitat that was the most likely to support statoblasts from or ganisms living in tributaries. Figure 2. Bryozoan statoblasts collected in the Hudson River Estuary: A) Pectinatella magnifica, B) Lophopodella carteri, and C) Cristatella mucedo. Northeastern Naturalist 374 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 Vol. 21, No. 3 Group 2 locations were in or near the mainstem of the estuary (Fig. 3), with the flow dominated by the estuary as opposed to a tributary. Both HC-03 and RO-04 had suitable habitat for bryozoans—rocks, tree debris, and human-made bulkheads. However, these sampling locations also had high potential to yield statoblasts that were being transported down the estuary from other locales. Group 3 collection areas were all distant from the confluence point of the tributary and were not in the mainstem of the estuary (Fig 3). More importantly, the sites were located at the edge of extensive Water-Chestnut beds. Although Water- Chestnut beds have periods of very low dissolved oxygen, and therefore may not be suitable for bryozoans (Caraco and Cole 2002), the edges of these macrophyte Table 2. Groupings of sampling sites by habitat type. Debris refers to material such as logs and rocks. # = group number. # Sites Flow Habitat type 1 MR-01, MR-02, MR-03, HC-01, Direct flow from tributaries Macrophytes and debris FK-01 2 HC-03, RO-04, MR-04, HB-02 Direct flow from estuary Debris, human-made bulkheads 3 RO-02, RO-03, FK-02, FK-03 Direct flow dampened by Macrophytes and debris macrophyte beds Figure 3. Sampling locations in the Hudson River Estuary where statoblasts were collected: A) Mohawk River, B) Hannacroix Bay, C) Rondout Bay, D) Fishkill Bay, and E) Haverstraw Bay (NYSDOP 2013). No statoblasts were found at the Upper Hudson, Normanskill, or Stockport sites. Numbers indicate collection sites. Initials indicate species present. Pm: P. magnifica, Lc: L. carteri, and Cm: C. mucedo. Northeastern Naturalist Vol. 21, No. 3 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 375 beds may still provide habitat for the animals as well as reduce the influence of the flow of both the tributaries and the estuary. The physical and chemical data we collected demonstrate differences between the sampling locations. Water clarity, as determined by Secchi-depth measurements, varied north to south with higher water clarity in the northern locations (Table 1). We also observed a north-to-south conductivity gradient; the northern reach of the study area had low average conductivity , and conductivity was higher in the southern sampling locations (Table 1). Discussion The geographic range and frequency of bryozoan statoblasts collected in the Hudson River Estuary indicate that bryozoans reside within the estuary watershed. Of the 3 species identified, only P. magnifica had previously been documented from New York and potentially in the estuary. Lophopodella carteri and Cristatella mucedo have been reported at locations within the Northeast but not in New York State (Pennak 1978, Rogick 1940, Wood 2010). Statoblasts can travel significant distances in riverine systems, carried either by birds or currents (Charalambidou et al. 2003, Green et al. 2008, Marsh and Wood 2002, Wood 2001). The statoblasts of P. magnifica and C. mucedo are buoyant and easily carried by water currents or other vectors, although they will also sink to the sediments. Statoblasts of L. carteri sink but are easily moved through the benthic environment (Wood and Marsh, 1996). Given the mobility of statoblasts and the fact that 2 of these species were not known previously from the estuary watershed, the origin of the statoblasts requires investigation. There are 3 potential sources of the statoblasts. First, they might have been produced from bryozoans that reside within the estuary and adjacent embayments near the sampling locations. Second, the statoblasts might have been washed into the estuary from tributary locations above the head-of-tide, or third, they might have been transported into the estuary by anthropogenic (i.e., boating/shipping) or animal (i.e., bird ) vectors. We found statoblasts of P. magnifica at 3 locations spread over the length of the study area, in addition to earlier reports from Tivoli North Bay. This finding indicates that P. magnifica is most likely a permanent resident of the estuary. However, the data collected to date do not provide sufficient detail to establish its population range or density in the estuary. Lophopodella carteri is a non-indigenous species that was inadvertently introduced into North America via trade in tropical and subtropical plants; both the Delaware River and the Great Lakes are likely points of introduction (Masters 1940). L. carteri was the most common statoblast found in our samples and also had the widest geographical distribution (Fig. 3), which supports the contention that this species is a permanent resident of the estuary. The point of introduction of L. carteri into the estuary is an important question. We identified statoblasts of L. carteri from the Mohawk River, whereas we found no statoblasts of any species at the upper Hudson River sampling location, even though the upper Hudson locations had the least turbid water and the lowest conductivity (salinity). The most logical route of introduction of L. carteri into Northeastern Naturalist 376 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 Vol. 21, No. 3 the estuary is through the Mohawk River and Erie Canal system, which provides a direct link to the Great Lakes where there is a known population of this species (Masters 1940). Although it is possible that commercial shipping from New York Harbor could be a source of bryozoans for the estuary, they would not be the source of statoblasts at the confluence of the Mohawk River because large transport ships cannot transit past the Federal Dam. Based upon the evidence collected during this study, we hypothesize that the Hudson River Estuary was colonized by L. carteri from the Mohawk River/Erie Canal. If the proposed invasion hypothesis is correct, populations of this species may exist throughout the Mohawk River and Erie Canal. Within the estuary, statoblasts of C. mucedo were found only at the confluence of the Hannacroix Creek (Tables 1, 2), and we collected only 2 of them during our study. This species is not native to New York, and in view of the limited number of statoblasts collected, it is not possible to be certain that there are viable populations in the estuary or even within the Hudson River Estuary watershed. Additional specimens collected at multiple sites or over multiple years will be required to confirm that these animals are established within t he estuary. Because these statoblasts were only found in the Hannacroix area, a more thorough assessment of the watershed supporting this stream might also identify the source of the C. mucedo statoblasts. We observed variation in water quality among our sites. Ryland (1970) noted that freshwater bryozoans are commonly found in clear, quiet waters, and Wood (2010) stated that most common freshwater bryozoans, except for P. magnifica, are able to tolerate turbid conditions. Secchi-disk readings at our sample areas ranged from 0.1 m to 3.4 m, declining in a north–south direction. Overall, the Secchi data indicate turbidity that is the product of an environment that carries a large particulate load. The change in turbidity as a function of location within the estuary, along with the wide distribution of L. carteri, suggests that this species tolerates to a broad array of conditions. Except for the Fishkill (FK-01, FK-02 and FK-03) and Haverstraw Bay (HB-02) locations, all our sampling areas were in fresh water. Haverstraw Bay is usually oligohaline but can periodically become a freshwater system during periods of high flow (Cooper et al. 1988, Swaney et al. 1999). Fishkill Bay (RK 97) alternates between fresh and brackish conditions based upon movement of the salt front (NYBCEP 1997). We found P. magnifica and L. carteri statoblasts at the Fishkill location, and we collected the L. carteri statoblast the Haverstraw Bay site. There is little information regarding salinity tolerance of these species. Wood (2005) reported preliminary work on salinity tolerance of 3 species including L. carteri. He observed that the species had slightly bent tentacles at 0.3 ppt salinity, and the organisms were dead at 0.7 ppt salinity. Based upon the conductivity readings, salinity at the Fishkill site ranged between 0.08 ppt and 2.0 ppt (Table 1). We were surprised to detect L. carteri at the Haverstraw Bay location. This site is usually oligohaline (Swaney et al. 1999) and had the lowest water clarity of the sampling areas included in this study (Table 1). Further, the sampling location is Northeastern Naturalist Vol. 21, No. 3 T.M. Michelena, C. Ostman, C.W. Boylen and S.A. Nierzwicki-Bauer 2014 377 in an area with strong currents, and the substrate is primarily small cobbles and gravel, with little or no suitable substrate for bryozoans to attach. Thus, the statoblasts we collected at this location may have been transported by the river or some other vector, and likely do not represent an established population in this segment of the estuary. The source of the bryozoan statoblasts at Fishkill is a question that our study did not answer, but about which we hypothesize here. Due to the periodically brackish nature of this site, one explanation for their presence is that they originated in Fishkill, above the head-of-tide. Another possibility is that the bryozoans were residents of the estuary at or near Fishkill Bay. There is a large marsh system immediately adjacent to the confluence of Fishkill with Fishkill Bay that apparently provides excellent habitat for bryozoans—extensive plants, rocks, and debris on which the animals could attach. Further, with only 2 constricted outlets to Fishkill Bay under the rail causeway, the water flow within the marsh is relatively slow. However, this marsh is clearly influenced by the estuary and is therefore brackish during portions of the year. Fishkill Bay is not brackish in the long periods during the months when the water is warm, typically June and July. Bryozoans are typically active when the water temperature is 15–28 °C (Wood 2010). Further, Rogick (1935) demonstrated that L.carteri requires less than 60 days from the germination of the statoblast to the appearance of new statoblasts, a finding that supports the idea that the periods of time that Fishkill Bay is freshwater may be sufficient for the maturation of bryozoans, and could reasonably facilitate establishment of permanent populations. Comprehensive surveys of bryozoans are necessary to further refine the status and distributions of bryozoan species in the Hudson River basin. These surveys should include areas within the estuary as well as selected tributaries. Particular emphasis is warranted for the Fishkill area to determine the origin of the statoblasts found in this brackish-water site. Additional surveys will increase our understanding of bryozoan distribution in the Hudson River Estuary and watershed. 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