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Islandinium brevispinosum
Islandinium brevispinosum Pospelova and Head, 2002, p.594-595,597-598, figs.3a-u,4a-p,5a-b,6a-c.
Holotype: Pospelova and Head, 2002, figs.3a-m.
Age: Holocene.
Original description (Pospelova and Head, 2002):
Islandinium brevispinosum Pospelova et Head sp. nov.
Diagnosis. Small proximate to proximochorate cysts with spherical to subspherical central body. Wall is brown to pale brown in color; surface smooth and covered with numerous solid spinules. Spinules more or less similar in length and shape, taper to sharp or blunt tips, and have nontabular distribution. Archeopyle saphopylic, formed by separate loss of the second, third and fourth apical plates; third apical plate approximately symmetrical about the dorsoventral midline. Accessory archeopyle sutures may also be present; otherwise no clear indication of tabulation.
Etymology: Latin brevis short, small; and spinosus thorny. With reference to the small spines that characterize this species.
Holotype: Sample NBH-324 slide 7, England Finder reference S30/3 (label to left); specimen MPK 12549; Figure 3, a–m. Modern sediment from New Bedford Harbor, Atlantic coast of Massachusetts (USA).
Description: Cysts brown to pale brown in color. Central body spherical to subspherical, with smooth surface under light microscopy and SEM, and wall thickness of about 0.3 μm or less, appearing unstratified under light microscopy. Surface bears numerous, solid, nontabulate, closely but irregularly distributed spinules with basal diameter of approximately 0.3 μm. Adjacent spinules usually separated at base by about 1.0 μm, but some basal fusion occurs in some specimens; density of spinule distribution varies somewhat between and within individual specimens. Length of spinules varies from 0.3 μm where they may appear as small bumps, up to 3.5 μm where they may be curved. Spinule length fairly constant for individual specimens; ranges from 1% to 14% of body diameter, averaging 5%. Spinules taper to fine or blunt points, as observed under both light (Figs. 3–4) and SEM (Fig. 5). Archeopyle is saphopylic, formed by separate loss of the three apical plates 2′, 3′, and 4′. Canal plate (and presumably apical pore complex) remains attached to first apical plate (1′) (Fig. 3, a–u, and possibly Fig. 4, i–m) or is lost during archeopyle formation (Fig. 4, a–h, n–p). Boundary between canal plate and 1′ is marked by a notch in archeopyle outline (Fig. 3i). Plates 3′ and 4′ are approximately the same size, whereas plate 2′ might be slightly smaller. Archeopyle, including position of third apical plate, broadly symmetrical about dorsoventral midline. Cysts show no epifluorescence.
Measurements: Holotype: central body diameter 22 μm; average length of process 1.0 μm. Range: central body diameter 18(21.5)25 μm (standard deviation 1.8 μm); average process length: 0.3(1.1)3.0 μm (standard deviation 0.6 μm). Twenty-nine specimens were measured. See also Figure 7.
Discussion: The archeopyle was seldom seen clearly in the 315 specimens scrutinized during the present study, largely due to the very thin cyst wall which readily collapses and folds. The holotype has a clearly visible archeopyle and was inflated when freshly mounted and examined in Montreal (Fig. 3, k–m). It had become slightly distorted upon its arrival in Cambridge, although all major features remain clearly discernible (Fig. 3, a–j). The archeopyle and interpreted position of adjoining plate boundaries is given in Figure 6a. These boundaries, including the presumed ortho-style first apical plate, are conjectural because accessory archeopyle sutures were seldom observed. The paucity of accessory archeopyle sutures, along with a lack of information on the number of intercalary plates, prevents full determination of the episomal tabulation. However, on the basis that I. brevispinosum probably represents the cyst of a species of the genus ProtoperidiniumBergh 1881, two possibilities are preferred. The first assumes the presence of three intercalary plates (Fig. 6b), which is a common feature of Protoperidinium species having a symmetrical episomal tabulation. The archeopyle in I. brevispinosum is relatively symmetrical about the dorsoventral midline, particularly regarding the position of the third apical plate, implying (but not proving) a symmetrical episomal tabulation. The second less likely possibility (Fig. 6c) is of four intercalary plates. Although a highly unusual configuration within the genus Protoperidinium, this possibility is due to a strong similarity between the archeopyles of Islandinium brevispinosum and of the cyst of Protoperidinium americanum (Gran and Braarud 1935) Balech 1974 (Lewis and Dodge 1987; Fig. 6g). Not only does Protoperidinium americanum have four intercalary plates (Fig. 6h), it is also the only motile-defined species within the genus Protoperidinium whose cyst is known to have an apical archeopyle. Hence, based on the above considerations, we favor three or perhaps even four intercalary plates for I. brevispinosum.
Comparison: Islandinium brevispinosum closely resembles Islandinium minutum (Harland and Reid in Harland et al. 1980 Head et al., 2001 described from modern sediments of the Beaufort Sea, Canadian Arctic. However, I. minutum is larger (central body maximum diameter 29–50 μm; average process length 3.5–7.0 μm; Head et al. 2001 and has a granulate wall surface compared to the smooth wall surface of I. brevispinosum. Statistical analysis of average process length versus central body diameter for I. brevispinosum and I. minutum demonstrates two separate clusters in the distribution (Fig. 7). The archeopyle of I. brevispinosum differs from that of I. minutum in its greater symmetry: plate 3′ is offset strongly to the left on I. minutum (Fig. 6, d–f) and implies a different configuration of intercalary plates (Fig. 6, e and f). Also, plate 2′ appears to be pentagonal in I. brevispinosum, whereas it is more or less quadrangular in I. minutum.
Islandinium cezare (de Vernal et al. 1989 ex de Vernal in Rochon et al. 1999 Head et al., 2001, described from late glacial sediments of Québec, differs from I. brevispinosum in its larger size, granulate wall surface, and in having long processes with expanded process tips.
The cyst of Protoperidinium americanum differs in its larger size (diameter 34–52 μm), prominent wall layering, and absence of processes (Lewis and Dodge 1987; Fig. 6g). Its archeopyle is relatively smaller than that of I. brevispinosum, although similar in shape.
Occurrence: Islandinium brevispinosum has been found only in modern (between <500 and <10 year) estuarine sediments of New Bedford Harbor, Clarks Cove, Apponagansett Bay, Waquoit Bay and Jehu Pond (Atlantic coast of Massachusetts, USA), Winnapaug Pond, and Narragansett Bay (Rhode Island, USA) (Fig. 2). The highest abundance (12%) is found in nutrient rich waters characterized by 23° C mean summer temperature and 30 psu mean summer salinity. Distribution is presumably more widespread than presently described. Cell contents occur in some cysts including the holotype, indicating that this is an extant species.
Thecal affinity: As with I. minutum, an affinity with the subfamily Protoperidinioideae is indicated from the epicystal tabulation and overall morphology of the cyst (Head et al. 2001). The brown cyst wall coloration and lack of epifluorescence suggest a species whose motile stage has a heterotrophic feeding strategy, which is predominant in the Protoperidiniaceae. Because the cysts are extant, the motile stage must be present in the water column. However, the only species of Protoperidinium presently reported for Buzzards Bay (New Bedford Harbor, Apponagansett Bay, and Clarks Cove) are P. bipes (Paulsen 1904) Balech 1974, P. claudicans (Paulsen 1907) Balech 1974, P. pellucidumBergh 1881, and P. steinii (Jörgensen 1900) Balech 1974 (see Pierce and Turner 1994. Of these, P. claudicans is known to produce a cyst morphologically different from I. brevispinosum (Head 1996), P. bipes has a strongly asymmetrical episomal tabulation, and P. pellucidum and P. steinii are both probably too large to produce a cyst consistently as small as I. brevispinosum. No attempt to germinate I. brevispinosum has yet been made, but this approach will ultimately establish the thecal affinity of this cyst species.
Ecological distribution:
A total of 315 complete and fragmented specimens of I. brevispinosum was observed in 54 sediment samples. All studied sites are characterized by shallow water in which depth ranges from 1 to 12 m. Embayments of Buzzards Bay were studied in most detail, with the analysis of 19 surface sediment samples (Pospelova, unpublished data) and 31 sediment samples from three cores (Pospelova et al. 2002). Figure 2a shows the spatial distribution of I. brevispinosum and its proportion in dinoflagellate cyst assemblages from Apponagansett Bay, Clarks Cove, and New Bedford Harbor. Islandinium brevispinosum was encountered in all surface samples with its abundance ranging from 1% to 12% with the highest proportion in the outer part of Apponagansett Bay. All studied sites in Buzzards Bay are characterized by mean August water temperatures ranging from 23 to 25° C and salinities from 27 to 31 psu (Howes et al. 1999). Waters in this part of Buzzards Bay are considered to be nutrient rich, with the mean August nitrate concentrations 1.8 μM and phosphate 1.7 μM. (Howes et al. 1999).
In estuaries neighboring Buzzards Bay, Waquoit Bay, and adjacent Jehu Pond, I. brevispinosum was present and comprised 4% of total dinoflagellate cyst assemblages (Fig. 2b). These waters are characterized by a mean August temperature of 24° C and salinities ranging from 28 to 29 psu (Waquoit Bay National Estuarine Research Reserve). We do not have exact measurements of nutrient concentrations for Waquoit Bay and Jehu Pond waters, although it is known that these systems are also nutrient rich (Lamontagne and Valiela 1995).
The eight back-barrier lagoons of Rhode Island (Fig. 2c) are characterized by a range of mean August water temperatures and salinities from 19 to 23° C and from 5 to 29 psu, respectively (Lee et al. 1997). Cysts of I. brevispinosum were found only in Winnapaug Pond (1.5%; Fig. 2c), where mean August water temperature is 24° C, salinity 27 psu, concentrations of nitrates 2.0 μM, and phosphates 1.4 μM (Lee et al. 1997).
The presence of I. brevispinosum in the surface sediments of Narragansett Bay is inferred through our study of sediments from experimental tanks at the Marine Environmental Research Laboratory (University of Rhode Island) that originate from the central part of Narragansett Bay (Keller et al. 1999).
Holotype: Pospelova and Head, 2002, figs.3a-m.
Age: Holocene.
Original description (Pospelova and Head, 2002):
Islandinium brevispinosum Pospelova et Head sp. nov.
Diagnosis. Small proximate to proximochorate cysts with spherical to subspherical central body. Wall is brown to pale brown in color; surface smooth and covered with numerous solid spinules. Spinules more or less similar in length and shape, taper to sharp or blunt tips, and have nontabular distribution. Archeopyle saphopylic, formed by separate loss of the second, third and fourth apical plates; third apical plate approximately symmetrical about the dorsoventral midline. Accessory archeopyle sutures may also be present; otherwise no clear indication of tabulation.
Etymology: Latin brevis short, small; and spinosus thorny. With reference to the small spines that characterize this species.
Holotype: Sample NBH-324 slide 7, England Finder reference S30/3 (label to left); specimen MPK 12549; Figure 3, a–m. Modern sediment from New Bedford Harbor, Atlantic coast of Massachusetts (USA).
Description: Cysts brown to pale brown in color. Central body spherical to subspherical, with smooth surface under light microscopy and SEM, and wall thickness of about 0.3 μm or less, appearing unstratified under light microscopy. Surface bears numerous, solid, nontabulate, closely but irregularly distributed spinules with basal diameter of approximately 0.3 μm. Adjacent spinules usually separated at base by about 1.0 μm, but some basal fusion occurs in some specimens; density of spinule distribution varies somewhat between and within individual specimens. Length of spinules varies from 0.3 μm where they may appear as small bumps, up to 3.5 μm where they may be curved. Spinule length fairly constant for individual specimens; ranges from 1% to 14% of body diameter, averaging 5%. Spinules taper to fine or blunt points, as observed under both light (Figs. 3–4) and SEM (Fig. 5). Archeopyle is saphopylic, formed by separate loss of the three apical plates 2′, 3′, and 4′. Canal plate (and presumably apical pore complex) remains attached to first apical plate (1′) (Fig. 3, a–u, and possibly Fig. 4, i–m) or is lost during archeopyle formation (Fig. 4, a–h, n–p). Boundary between canal plate and 1′ is marked by a notch in archeopyle outline (Fig. 3i). Plates 3′ and 4′ are approximately the same size, whereas plate 2′ might be slightly smaller. Archeopyle, including position of third apical plate, broadly symmetrical about dorsoventral midline. Cysts show no epifluorescence.
Measurements: Holotype: central body diameter 22 μm; average length of process 1.0 μm. Range: central body diameter 18(21.5)25 μm (standard deviation 1.8 μm); average process length: 0.3(1.1)3.0 μm (standard deviation 0.6 μm). Twenty-nine specimens were measured. See also Figure 7.
Discussion: The archeopyle was seldom seen clearly in the 315 specimens scrutinized during the present study, largely due to the very thin cyst wall which readily collapses and folds. The holotype has a clearly visible archeopyle and was inflated when freshly mounted and examined in Montreal (Fig. 3, k–m). It had become slightly distorted upon its arrival in Cambridge, although all major features remain clearly discernible (Fig. 3, a–j). The archeopyle and interpreted position of adjoining plate boundaries is given in Figure 6a. These boundaries, including the presumed ortho-style first apical plate, are conjectural because accessory archeopyle sutures were seldom observed. The paucity of accessory archeopyle sutures, along with a lack of information on the number of intercalary plates, prevents full determination of the episomal tabulation. However, on the basis that I. brevispinosum probably represents the cyst of a species of the genus ProtoperidiniumBergh 1881, two possibilities are preferred. The first assumes the presence of three intercalary plates (Fig. 6b), which is a common feature of Protoperidinium species having a symmetrical episomal tabulation. The archeopyle in I. brevispinosum is relatively symmetrical about the dorsoventral midline, particularly regarding the position of the third apical plate, implying (but not proving) a symmetrical episomal tabulation. The second less likely possibility (Fig. 6c) is of four intercalary plates. Although a highly unusual configuration within the genus Protoperidinium, this possibility is due to a strong similarity between the archeopyles of Islandinium brevispinosum and of the cyst of Protoperidinium americanum (Gran and Braarud 1935) Balech 1974 (Lewis and Dodge 1987; Fig. 6g). Not only does Protoperidinium americanum have four intercalary plates (Fig. 6h), it is also the only motile-defined species within the genus Protoperidinium whose cyst is known to have an apical archeopyle. Hence, based on the above considerations, we favor three or perhaps even four intercalary plates for I. brevispinosum.
Comparison: Islandinium brevispinosum closely resembles Islandinium minutum (Harland and Reid in Harland et al. 1980 Head et al., 2001 described from modern sediments of the Beaufort Sea, Canadian Arctic. However, I. minutum is larger (central body maximum diameter 29–50 μm; average process length 3.5–7.0 μm; Head et al. 2001 and has a granulate wall surface compared to the smooth wall surface of I. brevispinosum. Statistical analysis of average process length versus central body diameter for I. brevispinosum and I. minutum demonstrates two separate clusters in the distribution (Fig. 7). The archeopyle of I. brevispinosum differs from that of I. minutum in its greater symmetry: plate 3′ is offset strongly to the left on I. minutum (Fig. 6, d–f) and implies a different configuration of intercalary plates (Fig. 6, e and f). Also, plate 2′ appears to be pentagonal in I. brevispinosum, whereas it is more or less quadrangular in I. minutum.
Islandinium cezare (de Vernal et al. 1989 ex de Vernal in Rochon et al. 1999 Head et al., 2001, described from late glacial sediments of Québec, differs from I. brevispinosum in its larger size, granulate wall surface, and in having long processes with expanded process tips.
The cyst of Protoperidinium americanum differs in its larger size (diameter 34–52 μm), prominent wall layering, and absence of processes (Lewis and Dodge 1987; Fig. 6g). Its archeopyle is relatively smaller than that of I. brevispinosum, although similar in shape.
Occurrence: Islandinium brevispinosum has been found only in modern (between <500 and <10 year) estuarine sediments of New Bedford Harbor, Clarks Cove, Apponagansett Bay, Waquoit Bay and Jehu Pond (Atlantic coast of Massachusetts, USA), Winnapaug Pond, and Narragansett Bay (Rhode Island, USA) (Fig. 2). The highest abundance (12%) is found in nutrient rich waters characterized by 23° C mean summer temperature and 30 psu mean summer salinity. Distribution is presumably more widespread than presently described. Cell contents occur in some cysts including the holotype, indicating that this is an extant species.
Thecal affinity: As with I. minutum, an affinity with the subfamily Protoperidinioideae is indicated from the epicystal tabulation and overall morphology of the cyst (Head et al. 2001). The brown cyst wall coloration and lack of epifluorescence suggest a species whose motile stage has a heterotrophic feeding strategy, which is predominant in the Protoperidiniaceae. Because the cysts are extant, the motile stage must be present in the water column. However, the only species of Protoperidinium presently reported for Buzzards Bay (New Bedford Harbor, Apponagansett Bay, and Clarks Cove) are P. bipes (Paulsen 1904) Balech 1974, P. claudicans (Paulsen 1907) Balech 1974, P. pellucidumBergh 1881, and P. steinii (Jörgensen 1900) Balech 1974 (see Pierce and Turner 1994. Of these, P. claudicans is known to produce a cyst morphologically different from I. brevispinosum (Head 1996), P. bipes has a strongly asymmetrical episomal tabulation, and P. pellucidum and P. steinii are both probably too large to produce a cyst consistently as small as I. brevispinosum. No attempt to germinate I. brevispinosum has yet been made, but this approach will ultimately establish the thecal affinity of this cyst species.
Ecological distribution:
A total of 315 complete and fragmented specimens of I. brevispinosum was observed in 54 sediment samples. All studied sites are characterized by shallow water in which depth ranges from 1 to 12 m. Embayments of Buzzards Bay were studied in most detail, with the analysis of 19 surface sediment samples (Pospelova, unpublished data) and 31 sediment samples from three cores (Pospelova et al. 2002). Figure 2a shows the spatial distribution of I. brevispinosum and its proportion in dinoflagellate cyst assemblages from Apponagansett Bay, Clarks Cove, and New Bedford Harbor. Islandinium brevispinosum was encountered in all surface samples with its abundance ranging from 1% to 12% with the highest proportion in the outer part of Apponagansett Bay. All studied sites in Buzzards Bay are characterized by mean August water temperatures ranging from 23 to 25° C and salinities from 27 to 31 psu (Howes et al. 1999). Waters in this part of Buzzards Bay are considered to be nutrient rich, with the mean August nitrate concentrations 1.8 μM and phosphate 1.7 μM. (Howes et al. 1999).
In estuaries neighboring Buzzards Bay, Waquoit Bay, and adjacent Jehu Pond, I. brevispinosum was present and comprised 4% of total dinoflagellate cyst assemblages (Fig. 2b). These waters are characterized by a mean August temperature of 24° C and salinities ranging from 28 to 29 psu (Waquoit Bay National Estuarine Research Reserve). We do not have exact measurements of nutrient concentrations for Waquoit Bay and Jehu Pond waters, although it is known that these systems are also nutrient rich (Lamontagne and Valiela 1995).
The eight back-barrier lagoons of Rhode Island (Fig. 2c) are characterized by a range of mean August water temperatures and salinities from 19 to 23° C and from 5 to 29 psu, respectively (Lee et al. 1997). Cysts of I. brevispinosum were found only in Winnapaug Pond (1.5%; Fig. 2c), where mean August water temperature is 24° C, salinity 27 psu, concentrations of nitrates 2.0 μM, and phosphates 1.4 μM (Lee et al. 1997).
The presence of I. brevispinosum in the surface sediments of Narragansett Bay is inferred through our study of sediments from experimental tanks at the Marine Environmental Research Laboratory (University of Rhode Island) that originate from the central part of Narragansett Bay (Keller et al. 1999).