STUDIES ON THE FLORA LIVING ON TESTUDINUM KONIG IN BISCAYNE BAY, FLORIDA!

GREGORIO REYES·VASQUEZ2 University oj Miami, Rosenstiel School oj Marine and Atmospheric Sciences

ABSTRACT A study of the diatom flora living on Thalassia testudinum Konig in Biscayne Bay was carried out from November 1964 to July 1965. This paper records 42 of pennate , representing 20 genera. One new species has been described. The ranges of salinity and temperature within which the studied species thrive are established. Salinity and temperature do not appear to have a direct effect on the distribution and succession of the diatoms living on T halassia. The characteristics of the sediments and/ or the presence of substances produced by other organisms appear to have more influence on the occurrence of the diatoms living on Thalassia than do salinity and temperature.

INTRODUCTION AND ACKNOWLEDGMENTS Thalassia testudinum Konig, the turtle grass, is the dominant in shallow waters in the western tropical Atlantic. Its occurrence has been established from the southern United States to southern Brazil (Moore, 1963; Phillips, 1960; Voss & Voss, 1955). Thalassia beds provide food, surface for settling, and shelter for a great number of organisms, among them different kinds of which find a suitable substratum for attachment on the leaves of this . Moore & Work (unpublished manuscript) have estimated the surface provided by Thalassia leaves at Bear Cut (Key Biscayne), and they have found an average value of 7.42 m2 of leaf area per m2 of bottom. Depending on conditions, this value is variable, but it gives an indication of the increase of surface area available to organisms in localities where this plant is present. Few organisms feed on the turtle grass itself; however, many small and gastropods, as well as fish, feed on the attached algae and the bacterial film, as has been pointed out by Darnell (1958), Randall (1964 ), and Wood (1964). These herbivores constitute the second step in a food chain, and they can be eaten in turn by forms higher in the chain (carnivores).

1 Contribution No. 1151 from the University of Miami, Rosenstiel School of Marine and Atmospheric Sciences. This investigation was supported by a fellowship from Instituto Venezolano de Investi- gaciones Cientificas, Caracas, Venezuela, and the manuscript was submitted to the Faculty of the Graduate School of the University of Miami in partial fulfillment of the requirements for the degree of Master of Science. 2 Present address: Instituto Venezo]ano de Investigaciones Cientificas, Apartado 1827, Caracas, Venezuela. 106 Bulletin of Marine Science [20(1) Although the epiphytes living on Thalassia were studied by Humm (1964), no attention was paid to the diatoms present. The purpose of this paper is to record the occurrence of diatoms living on Thalassia leaves and, by parallel examinations of some physical factors, to deduce some ecological considerations. The author expresses appreciation to Professor E. J. Ferguson Wood for his advice in the preparation of this paper. I am also grateful to Mr. Mulford Martin of the New York Botanical Garden, for his valuable assist- ance during my visit to New York. Very special thanks are due to Dr. Liselotte Vareschi of Universidad Central de Venezuela for her assistance in the Latin diagnosis of Cocconeis woodii, n. spec.

STATIONS Five stations were selected for sampling the Thalassia beds in Biscayne Bay. Studies on the turtle grass had been carried out in some of those stations before. Station No.1, Matheson Hammock.-The station was located at the wad- ing beach, where the bottom consists of a thin layer of quartz sand over a thick bed of mangrove peat. This zone does not appear to be influenced by tidal currents. Collections were made weekly, during the period from November 1964 to July 1965. Station No.2, Bear Cut.-This station was located on the northeast part of Key Biscayne, on the Atlantic side. It was bordered by coral reef forma- tions. The bottom was sand containing decayed organic matter and broken shells of molluscs. It was visited each week from November 1964 to July 1965. Station No.3, Southwest Point (Key Biscayne).-This was located south of Hurricane Harbor (Fig. 1). The bottom was sandy mud with a high content of decaying organic matter. This station was affected by tidal currents. It was visited during November-December 1964 and February- March 1965. Station No.4, Soldier Key.-The station was located at the south end of the island. It corresponded to area "B" in the studies carried out by Voss & Voss (1955). The bottom consisted of sandy mud with fragments of Porites, calcareous algae, Foraminifera, broken shells of molluscs, echinoderm spicules, and decaying vegetable matter. It was visited during November-December 1964 and February-March 1965. Station No.5, Ragged Keys.-The Ragged Keys are located south of Soldier Key. This station was just in front of the tower at the southern part of the third key south of Soldier Key (see Fig. 1). The bottom at this 1970] Reyes-Vasquez: Diatom Flora of Thalassia 107

M I AMI

()

l> -< z

Soldier Key

o• 8to. 4

l> -<

Q DRagged

il ,.\ Keys O ·V

FIGURE 1. Map of Biscayne Bay area, showing locations of stations. station resembled that at Soldier Key, except that it was softer and the amount of decaying matter appeared to be greater. Silting was also great. This zone was affected by strong tidal currents. It was visited during November-December 1964 and February-March 1965.

MATERIALS AND METHODS Samples of the leaves of Thalassia were collected in the field, using the technique suggested by Siadeckova (1962). A small jar was filled with 108 Bulletin of Marine Science [20(1 ) sea water and placed over the plant; the leaves were then cut off with a pair of scissors. The jar was covered, and the sample taken to the labora- tory for analysis. About ten leaves were taken from different in each sampling visit. In the laboratory the leaves were carefully removed from the jar and cut into pieces, from which the periphyton was gently scraped with a scalpel. The periphyton was suspended in 10 ml of 3 per cent hydrochloric acid solution, and the areas of the pieces of leaves were measured by determining the lengths and widths with calipers, or by placing the pieces on a sheet of graph paper ruled in mm. The counts were made following the method suggested by Sladeckova (1962). After mixing thoroughly, one ml of the periphyton sample was taken with a microbiological pipette and placed in a Sedgwick-Rafter counting cell; in this way the filling error, pointed out by Gilbert (1942), was avoided. The sample was examined under a compound microscope, with low magnification (Ph A 10/0.25, 160/-Reichert objective and lOx eyepiece), and with the aid of a Whipple-Hausser ocular micrometer previ- ously calibrated, 50 fields were counted at random. The counts made by using the Sedgwick-Rafter counting cell were com- pared with the results obtained by using an American Optical Bright-Line Hematocytometer and they were found to be in agreement. The results are expressed as 10glOof the number of individuals per cm2 of leaf (Fig. 2). The water in which the leaves were brought to the laboratory was cen- trifuged, and the organisms present were identified. For purposes of identification of the diatoms, other samples were taken and treated with 3 per cent hydrochloric acid, as suggested by Conger (1950). The acid dissolves the carbonates that are present and also acts as a preservative. By treating the sample in this way, the cleaning procedure is shortened because the step of washing out the preservative (usually formaldehyde) is eliminated. The samples were boiled in concentrated hydrochloric acid, and then drops of concentrated nitric acid were added, in accordance with the technique described by Crosby & Wood (1959). After several washings and centrifugations to eliminate the acids and concentrate the samples, permanent slides were made by mounting the specimens in Canada balsam. In some cases when rapid identifications were necessary, samples of periphyton suspended in distilled water were calcined and mounted in Canada balsam. The slides prepared in this way are not as good as those made after cleaning the frustules with acids, but they permit fast identifications. Temperatures of the water were determined with a mercury bulb ther- mometer calibrated in tenths of a degree, centigrade. Salinities were determined by conductivity in a salinity bridge at the 1970] Reyes-Vasquez: Diatom Flora of Thalassia 109 Rosenstiel School of Marine and Atmospheric Sciences, University of Miami. Determination of wet and dry weights of the periphyton was suggested, but since the diatoms do not constitute the only organisms present in the periphyton, these experiments were not attempted. Aleem (1949) developed a method for estimating the periodicity of epiphytic diatoms on the basis of the amount of silica present. This method, however, cannot be applied in the present study because a single species is never present, but rather a group of different species, and the amount of silica in their frustules is variable; on the other hand, the presence of empty frustules or the loss of cells during handling will affect the results.

IDENTIFICATION OF THE DIATOMS The identification of the diatoms is based on the shape, sculpture, mark- ings, and other features exhibited by the frustules. These characteristics appear to be constant; however, some anomalies have been reported. Crosby & Wood (1958) found chains of Chaetoceros with the characters of one species at one end of the chain and those of another species at the other end. Wood (1959, 1963) found frustules bearing the characters of one genus in the upper valve and those of another in the lower valve; this suggests that the shape and structure of the siliceous frustule may not be a valid specific character for this group of organisms. Hendey (1959), studying the frustules of diatoms belonging to different families, found similar structure. He stated that these similarities may be accounted for more by the possibility of a common chemical constitution in the protoplasm providing a similar molecular matrix for the silicon molecules, than by any close phylogenetic relationship between the species. The studies of the valves under the electron microscope have permitted the establishment of certain varieties as separate species; such is the case of Cocconeis stauroneiformis Okuno, once considered to be a variety of Cocconeis scutellum Ehr. (C. scutellum var. stauroneiformis Cleve). Another of the limitations is that, under certain circumstances, some diatoms lose their siliceous frustules and continue living as naked bodies (Hendey 1945, 1946). Hendey (1954) also studied Nitzschia closterium (Ehr.) W. Smith, forma minutissima Allen & Nelson, and stated that the organism is really Phaeodactylum tricornutum. Further electron microscopic studies carried out by Lewin (1957) revealed that it is a diatom with only one valve. On the other hand, many species have been erected on the basis of simple varieties. In spite of all these limitations, the identification and systematics of diatoms are still based on the characters exhibited by the frustules, because no other acceptable basis has yet been found. 110 Bulletin at Marine Science [20(1 )

TABLE 1 TEMPERATURE AND SALINITY LIMITS WITHIN WHICH DIATOM SPECIES OCCURRED IN THE EpONTIC COMMUNITY ON Thalassia IN BISCAYNE BAY FROM Nov. 1964 TO JULY 1965

Temperature (OC) Salinity (%0)

mill. max. mill. max. Synedra lulgens 18.6 32.4 32.850 37.900 Synedra ulna 18.0 32.4 30.150 38.850 Synedra undulata 18.0 32.4 31.750 37.250 Grammatophora marina 18.6 32.4 31.850 38.900 Grammatophora serpentina 22.8 32.4 32.650 37.800 Rhabdonema adriaticum 19.0 32.4 30.150 38.950 Licmophora ahbreviata 18.6 32.4 30.050 38.500 Licmophora flabellata 18.6 25.0 32.600 37.300 Licmophora grandis 21.7 32.4 31.800 36.750 Licmophora remulus 19.6 32.4 31.800 34.500 Climacosphenia moniligera 19.0 30.0 30.150 37.900 Striatella interrupta 18.0 32.4 30.150 37.250 Striatella unipunctata 18.6 30.0 30.150 38.600 Achnanthes longipes 21.5 26.0 30.150 37.250 Cocconeis placentula 18.0 32.4 30.150 38.650 Cocconeis scutellum 18.0 30.0 30.400 38.800 Cocconeis woodii 19.6 32.4 30.400 37.600 Trachyneis aspera 21.7 28.0 30.150 35.600 Diploneis crahro 18.0 30.0 32.650 37.250 Pleurosigma angulatum 18.6 32.4 30.400 38.500 Pleurosigma jormosum 18.6 26.0 30.150 35.500 Pleurosigma naviculaceum 18.6 26.0 30.150 35.500 Gyrosigma balticum 18.6 26.1 31.800 36.600 Mastogloia angulata 18.0 32.4 30.050 37.600 M astogloia binotata 18.0 32.4 31.250 37.600 Mastogloia crib rosa 18.0 30.0 31.850 38.950 Mastogloia crucicula 18.0 28.0 31.850 37.250 Mastogloia erythraea 18.0 26.0 32.500 37.250 Mastogloia fimbriata 18.0 25.0 33.100 37.250 M astogloia ovala 21.7 25.0 33.100 37.250 Mastogloia pumila 18.0 25.0 32.600 37.250 Mastogloia splendida 18.6 28.0 30.400 37.250 Amphiprora alata 18.0 28.0 32.950 36.550 Tropidoneis lepidoptera 18.6 25.5 30.750 37.250 Amphora proteus 18.0 32.4 31.800 37.600 Amphora robusta 18.6 31.3 32.200 37.250 R hopalodia gibberula 18.6 32.4 31.800 37.250 Cylindrotheca closterium 18.0 32.4 30.150 38.900 Bacillaria paxillifer 18.6 26.5 30.150 37.250 Surirella fastuosa 18.6 28.0 31.800 37.250 SW'irella gemma 18.0 28.0 30.150 35.500 1970] Reyes-Vasquez: Diatom Flora of Thalassia 111 In the identification of the diatoms living on Thalassia testudinum Konig, the following reports have been used: Boyer (1926, 1927), Castracane (1886), Cleve (1894, 1895), Cleve-Euler (1951, 1952, 1953a, 1953b, 1955), Crosby & Wood (1959), Cupp (1943), Filho & Kutner (1962), Gregory (1857), Grunow (1877), Hendey (1951, 1964), Hustedt (1930, 1931,1932, 1933a, 1933b, 1937), Ktitzing (1833, 1844), Lebour (1930), Lewis (1861), Schmidt (1893, 1894), van Heurck (1880, 1881, 1882, 1896), and Wood (1963).

EFFECTS OF SALINITY AND TEMPERATURE Salinity appears to have no direct limiting effect upon the majority of the species studied; almost all of them exhibit a wide salinity range (euryhalines). However, field observations of the occurrence of Licmo- phora remulus indicated a narrow range of salinity for this species. Since it was found primarily in salinities ranging from 31.8%0 to 34.5%0, its occurrence can be determined by this factor. Another species with a narrow range of salinity is Trachyneis aspera, which was found associated with the diatom flora living on Thalassia. The salinity ranges of the studied species are shown in Table 1. The temperature in the bay ranges from 18.0°C to 32.4°C. Of the 42 observed species, the following exhibit a narrow range of temperature: Achnanthes longipes from 21.5° to 26.0°C, and Mastogloia ovala from 21.7° to 25.0°C. This physical factor does not appear to have a direct effect either, but undoubtedly its effect on the growth of the bacterial population is important. Table 1 shows the temperature ranges for the different species. Wood (1964) studied the temperature and salinity ranges within which different species grow in the Australian estuaries. When his results were compared with those obtained at Biscayne Bay it was found that, except for Gyrosigma balticum, the species occurring in both areas can stand higher salinities in Biscayne Bay. As far as temperature was concerned, the maximum temperatures for the species present in both areas were observed to be higher in Biscayne Bay (only Licmophora {iabellata showed almost the same value). (See Table 2.) These high tolerances to salinity and temperature seem to be due to physiological adaptations, since the Australian estuaries do not have high salinities and temperatures (Wood, personal communication).

SEASONAL DISTRIBUTION It is difficult to make a detailed correlation of diatom maxima with hydrological conditions, because species involved in these maxima may vary from season to season, as pointed out by Crosby & Wood (1959). 112 Bulletin of Marine Science [20(1 )

TABLE 2

COMPARISON OF THE VALUES FOR MAXIMUM TEMPERATURE AND SALINITY FOR SPECIES PRESENT IN AUSTRALIA AND BISCAYNE BAY (Values for Australian diatoms after Wood, 1964)

Temperature (OC) Salinity (%0) Australia Biscayne Bay Australia Biscayne Bay Achnanthes longipes 19.2 26.0 38.296 37.250 Amphiprora alata 28.0 37.600 Bacillaria paxillifer 26.2 26.5 35.588 37.250 Climacosphenia moniligera 24.2 30.0 35.950 37.900 Striatella interrupta 25.18 32.4 35.769 37.250 Striatella unipunctata 26.2 30.0 35.588 38.600 Grammatophora marina 26.2 32.4 35.588 38.900 Licmophora abbreviata 26.2 32.4 35.949 38.500 Licmophora !label/ala 26.3 25.0 35.769 37.300 Cylindrotheca closterium 25.9 32.4 35.408 38.900 Pleurosigma angulatum 25.8 32.4 35.227 38.500 Gyrosigma balticum 22.8 26.1 35.769 36.600 Pleurosigma formosum 21.0 26.0 34.145 35.500 Synedra ulna 21.2 32.4 35.769 38.500 Tropidoneis lepidoptera 21.2 25.5 35.047 37.250

The differences between the occurrences of the diatoms at stations 1 and 2 (Fig. 2) suggest that the diatom flora on Thalassia is not subjected to the limiting factors which control the planktonic flora or other organisms present in the periphyton on the turtle grass, such as the blue-green algae. The diatoms present in the sediments are found throughout the year, and many species are also present in the periphyton at the same time. The presence of a very rich bacterial flora in the sediments makes possible a constant replenishment of nutrients in the water, so that nitrogen and phosphorus compounds cannot be considered as limiting factors. Hendey (1951) pointed out that the bacterial flora is constantly building up reserves of nutrients which can be released when turbulence is sufficient enough to disturb the sediments. In our observations, it was found that species of three genera were dominant at different times in the diatom flora found on Thalassia testu- dinum in Biscayne Bay, from November 1964 to July 1965. Licmophora abbreviata was the dominant form at Bear Cut during the period from November 1964 to January 1965; at the Matheson Hammock station and at Southwest Point this species was present as a dominant during November, but in the middle of December it was replaced by Licmophora remulus at both stations. The dominant form at Soldier Key and the Ragged Keys was Licmophora grandis. 1970] Reyes- Vasquez: Diatom Flora of Thalassia 113

4.4

4.3

4.2 @ N E 4.1 u .•... ~ 4.0 o ~ 3.9 a 03.8

'"Q 3.7 ...J

3.6

3.5

NOV DEC JAN FEB MAR APR MAY JUN JUL J 9 6 4 I 9 65

FIGURE 2. Seasonal distribution of diatoms found on Thalassia testudinum Konig in Biscayne Bay, between November 1964 and July 1965. A = Station No.1 (Matheson Hammock); B = Station No.2 (Bear Cut).

During the month of January, due to the weather conditions and diffi- culties in getting transportation, the stations at Soldier Key and the Ragged Keys were not visited. The population of Licmophora remulus started to decline during the second half of January, and Mastogloia crucicula became the dominant form, persisting to the middle of March. At Bear Cut, Mastogloia angulata was found dominant, and the species Mastogloia binotata was the dominant form at Soldier Key and the Ragged Keys during February and March 1965. When the Mastogloia species started to decline, Cocconeis scutellum and Licmophora abbreviata became dominant, the first at the Matheson Hammock station and the second at Bear Cut. At the latter station, Cocconeis scutellum and C. placentula were found to be subdominants. In the middle of June, when the species of the genus Cocconeis and Licmophora abbreviata were still abundant at Bear Cut, Licmophora remulus occurred as a dominant species at the Matheson Hammock station, and Striatella interrupta and S. unipunctata were the subdominant species. 114 Bulletin of Marine Science [20(1 )

Suborder ARAPHIDINEAE Family Fragilariaceae Genus Thalassionema Hustedt, 1932 Thalassionema nitzschioides (Grun.) Hustedt, 1932 Thalassionema nitzschioides Hustedt, 1932: 244, fig. 725. Synedra nitzschioides Grunow, 1862: 403, pI. 5, fig. 18. Thalassiothrix nitzschioides Grunow, 1881: pI. 43, figs.7-10.-Lebour, 1930: 198, fig. 160.-Cleve-Euler, 1953a: 75, fig. 400.-Crosby & Wood, 1959: 3, pI. 1, fig. 2. Thalassiothrix curvata Castracane, 1886: 55, pl. 24, fig. 6. Description.-Cells rectangular, elongate and slightly bent in girdle view; linear or slightly lanceolate in valvar view. Both ends similar. The cells are held together by mucous cushions produced in one end, forming star- shaped or zigzag colonies. Length 15}.t-86}.t. Distribution.-This species has been found associated with the periphyton on Thalassia at all the stations; it was abundant in plankton samples at the same time.

Genus Synedra Ehr., 1830 Synedra fulgens (Grev.) W. Smith, 1853 Synedra fulgens W. Smith, 1853: 74, pI. 12, fig. 103.-Boyer, 1926: 208.- Hustedt, 1932: 228, fig. 717.-Hendey, 1951: 36, pI. 12, figs. 4-5.- Crosby & Wood, 1959: 6, pl. 2, fig. 10. Exil/aria fulgens Greville, 1827: pl. 291. Description.-Cells solitary, usual1y attached to the substrate by means of a mucous pad. Sometimes forming irregular fan-shaped colonies. Valves linear-Ianceolate; pseudoraphe indistinct, lying in a median position. Cen- tral area slightly inflated. Valve surface finely striate; striae 15 in 10 }.t. Distribution.-Present in plankton samples and in the periphyton on Thalassia at stations 1, 4, and 5 from March to July 1965.

Synedra ulna (Nitzsch) Ehr., 1838 Synedra ulna Ehrenberg, 1838: 211.-Boyer, 1926: 198.-Cleve-Euler, 1953a: 60, fig. 382a, b, c.-Crosby & Wood, 1959: 6, pI. 2, figs. 11a, b. Bacillaria ulna Nitzsch, 1817: 99. Descriptiol1.-Cel1s more or less elongate, linear in girdle view. Valves linear or linear-Ianceolate, with rostrate ends. Valve surface furnished with transverse striae, 9-10 in 10}.t. Central area, if present, quadrangular. Pseudoraphe distinct, linear and narrow. Length 100}.t-230}.t. Distribution.-It was found associated with the periphyton on Thalassia, and in the sediments at al1 the stations, from November 1964 to January 1965, in March 1965, and from May to July 1965. 1970] Reyes-Vasquez: Diatom Flora of Thalassia 115 Synedra undulata (Bail.) Greg., 1857 Synedra undulata Gregory, 1857: 531, pI. 6, fig. 107.-Hustedt, 1932: 224, fig. 714.-Cupp, 1943: 181, fig. 132.-Crosby & Wood, 1959: 6, pI. 2, fig. 9. Toxarium undulatum Bailey, 1854: 15, figs. 24-25. Description.-Cells usually solitary, frustule long and narrow. Valves linear with undulate margins. Valve surface furnished with transverse striae, irregular in the central part, but more or less regular near the ends. Pseudoraphe indistinct. Length up to 400 fL. Distribution.-Present at all the stations in the periphyton on Thalassia, as well as in the sediments, from November 1964 to July 1965.

Genus Grammatophora Ehr., 1839 Grammatophora marina (Lyngb.) Klitz., 1844 Grammatophora marina Ki.itzing, 1844: 128, pI. 17, fig. 24.-Boyer, 1926: 156.-Hustedt, 1931: 43, fig. 569.-Hendey, 1951: 38.-Crosby & Wood, 1959: 7, pI. 2, fig. 16. Diatoma marinum Lyngbye, 1819: 180. Description.-Cells quadrangular in girdle view, with straight internal septa, curved in the free end. Frequently forming zigzag chains. Valves linear. Valve surface with 15-20 striae in 10 fL. Length 15fL-60fL. Distribution.-This species was found in plankton samples and in the periphyton on Thalassia at stations 1, 2, 4, and 5 in November 1964, in January 1965, and in March to July 1965.

Grammatophora serpentina Ehr., 1844 Grammatophora serpentina Ehrenberg, 1844b: 203.-Hustedt, 1931: 49, fig. 577.-Hendey, 1951: 38.-Crosby & Wood, 1959: 7, pI. 2, fig. 17. Description.-Cells short, united by opposite and alternate ends to form zigzag chains. Sometimes solitary. Frustule in girdle view shows septa with two or more undulations, each septum ending in a hook. Valves linear elliptic, with transverse striae not clearly visible. Pseudoraphe narrow. Length 25fL-50fL. Distribution.-Present in the periphyton on Thalassia at stations 1 and 5, from March to July 1965.

Genus Rhabdonema Klitz., 1844 Rhabdonema adriaticum Klitz., 1844 Rhabdonema adriaticum Ki.itzing, 1844: 126, pI. 18, fig. 7.-Boyer, 1926: 150.-Hustedt, 1931: 23, :fig.552.-Hendey, 1951: 39.-Crosby & Wood, 1959: 8, pI. 1, figs. 20a, b, c. 116 Bulletin of Marine Science [20(1 ) Description.-Cells forming ribbonlike chains, usually lying in girdle view. The frustules are quadrangular with rounded hyaline corners, multiseptate; the septa decreasing in length toward the center. Valves linear elliptic; valve surface furnished with transverse striae. Length 40,u-70,u. Distribution.-Present in the periphyton on Thalassia at all the stations. Genus Licmophora Ag., 1827 Licmophora abbreviata Ag., 1831 Licmophora abbreviata Agardh, 1831: 42.-Hustedt, 1931: 66, fig. 590.- Cleve-Euler, 1953a: 17, fig. 318.-Crosby & Wood, 1959: 9, pI. 2, fig. 24. Podosphenia lyngbyei Ki.itzing,1844: 121. Licmophora lyngbyei (Ki.itz.) Grunow, 1881: 47, figs. 14-21; pI. 48, fig. 1.- Boyer, 1926: 169.-Lebour, 1930: 203, fig. 165.-Hendey, 1951: 40. Description.-Cells colonial, united by short mucous stipes. Frustules clavate in valve view, with round ends; pseudoraphe narrow but distinct. Valve surface furnished with transverse striae, 12-14 in 10,u. Frustules cuneate in girdle view. Numerous internal septa visible as lines. Length 50,u-80,u. Distribution.-This species was found mainly on Thalassia, and occasion- ally in plankton samples at stations 1, 2, 4, and 5 from November to December 1964, and March to July 1965. Licmophora flabellata (Grev.) Ag., 1831 Licmophora flabellata Agardh, 1831: 41.-Boyer, 1926: 165.-Hustedt, 1931: 58, fig. 581.-Hendey, 1951: 39, pI. 16, figs. 1-2, 12.-Crosby & Wood, 1959: 9, pI. 2, figs. 23a, b. Exillaria flabellata Greville, 1827: pI. 289. Description.-Cells elongate, narrow and cuneate in girdle view, with numerous distinct septa; clavate to cuneate lanceolate in valvar view. Valve surface faintly striated. The cells are joined valve to valve, to form fan-shaped colonies, supported on irregular branching mucous stipes. Length 60ft-ll Oft. Distribution.-In the periphyton on Thalassia at stations 4 and 5 during December 1964. Licmophora grandis (Klitz.) Grun., 1881 Licmophora grandis Grunow, 1881: pI. 48, figs. 2-3.-Hustedt, 1931: 79, fig. 608.-Crosby & Wood, 1959: 10, pI. 3, fig. 25. Rhipidophora grandis Ki.itzing, 1844: 122, pI. 11, fig. 1. Description.-Cells cuneate in girdle view, with rounded corners; deep septa visible. Valve view narrowly clavate, surface furnished with transverse striae, 20 in 10,u. Pseudoraphe distinct. Length 95,u-170ft. 1970] Reyes-Vasquez: Diatom Flora of Thalassia 117 Distribution.-Present at all the stations, in the periphyton on Thalassia, from November 1964 to February 1965, and in April 1965. It was also found occasionally in plankton samples at stations 2 and 4. Licmophora remulus Grun., 1877 Licmophora remulus Grunow, 1877: 165, pI. 193, figs. la, b.-Hustedt, 1931: 57, fig. 580. Description.-Cells stipitate, clavate in girdle view with acute round cor- ners. Septa very short. Valves spatulate in the upper part, then constricted in a very thin, linear lower part. The basis slightly inflated. Pseudoraphe very narrow, indistinct in the lower part. Valve surface furnished with transverse striae, 36-40 in 10 fI-. Length 120fl--230fl-. Distribution.- This species was found only in the periphyton on Thalassia at stations 1 and 3 from December 1964 to January 1965, and from June to July 1965. Genus Climacosphenia Ehr., 1841 Climacosphenia moniligera Ehr., 1841 Climacosphenia moniligera Ehrenberg, 1841: 411, pI. 2, fig. VI.-Hustedt, 1931: 89, fig. 635.-Crosby & Wood, 1959: 10, pI. 3, figs. 27a-d. Description.-Cells cuneate in girdle view, with straight sides. Two septa with numerous foramina; those from the upper part are round to square, becoming elliptic toward the basis. In valve view clavate. Transverse striae finely punctate, and the number in 10 p. is variable. Length 120p.-500fl-. Distribution.-Present in the sediments and in the periphytic community on Thalassia. Found at all the stations from November to December 1964 and from March to July 1965.

Genus Striatella Ag., 1832 Striatella interrupta (Ehr.) Heiberg, 1863 Striatella interrupta Heiberg, 1863: 73, pI. 5, fig. 15.-Hustedt, 1931: 34, fig. 562.-Cleve-Euler, 1953a: 8, fig. 297.-Crosby & Wood, 1959: 11, pI. 3, fig. 29. Tessella interrupta Ehrenberg, 1838: 202. Description.-Cells forming ribbonlike colonies. Frustules tabular in girdle view, with corners slightly round. Septa numerous, 6-8 in 10 fI-, straight or slightly undulated, apparently interrupted in pervalvar axis. Frustules linear elliptic in valve view; pseudoraphe very narrow but distinct. Valve surface furnished with fine transverse striae. Length 15p.-60p.. At the station at Matheson Hammock, a variety of this species was abundant in July 1965. It differs in the shape of the internal septa, which are strongly undulated. 118 Bulletin of Marine Science [20( 1 ) Distribution.-Present in the periphyton on Thalassia and in plankton samples at stations 1 and 3 during November 1964, and from January to July 1965. It was also present but not abundant at the other stations. Striatella unipunctata (Lyngb.) Ag., 1832 Striatella unipunctata Agardh, 1832: 61.-Lebour, 1930: 200, fig. 162.- Hustedt, 1931: 32, fig. 560.-Crosby & Wood, 1959: 10, pI. 3, fig. 28.- Hendey, 1964: 161, pi. 26, figs. 17-18. Fragilaria unipunctata Lyngbye, 1819: 62. Description.-Cells forming zigzag chains. Frustules in girdle view tabular with slightly round corners, showing numerous straight septa (6-10 in 10 p.) not interrupted in pervalvar axis. Valve view linear to elliptic lanceolate. Valve surface furnished with delicate puncta; pseudoraphe very narrow but distinct. Chromatophores radially arranged around the nucleus in the cen- ter of the cell. Length 60p.-130p.. Distribution.-This species was found in the periphyton on Thalassia and also in the sediments and plankton samples at all the stations during November 1964, and from March to July 1965. Suborder MONORAPHIDINEAE Family Achnanthaceae Genus Achnanthes Bory, 1822 Achnanthes longipes Ag., 1824 Achnanthes longipes Agardh, 1824: l.-Ki.itzing, 1833: 575.-van Heurck, 1880: pI. 26, figs. 13-16.-Boyer, 1927: 231.-Hustedt, 1933a: 427, fig. 878.-Hendey, 1951: 42, pi. 1, figs. 1-9; pi. 2, figs. 1-12; pI. 3, figs. 1-12; pi. 16, figs. 6-7; pI. 18, figs. 2-5.-Crosby & Wood, 1959: 12, pI. 3, figs. 36a, b. Description.-Cells solitary or in ribbon-colonies, attached to the substrate by a mucous stipe. Frustules in valve view linear elliptic, often constricted in the middle. Valve surface strongly punctate; puncta arranged in double rows alternating with strong costae. Upper valve with a narrow pseu- doraphe; lower valve with strong raphe. Frustule in girdle view strongly genuflexed, furnished with parallel striae. Length 36p.-85p.. Distribution.- This species is not very common in the periphyton on Thalassia. It was found at all the stations during November 1964, in Feb- ruary 1965, and April to May 1965. Genus Cocconeis Ehr., 1838, em. Grun., 1868 Cocconeis placentula Ehr., 1838 Cocconeis placentula Ehrenberg, 1838: 194.--van Heurck, 1880: pi. 30, figs. 26-27.-Cleve, 1895: 169.-Boyer, 1927: 244.-Hustedt, 1933a: 347, fig. 802.-Wood, 1963: 251, pI. 4, fig. 72. 1970] Reyes- Vasquez: Diatom Flora of Thalassia 119 Description.-Cells flat or slightly arched; valves elliptical; the upper valve with narrow linear pseudoraphe, surface furnished with radial transverse striae distinctly punctate; puncta arranged in compact, undulate, Jongitu- dinallines; lower valve with distinct straight raphe not reaching the ends; axial area very narrow, central area round and very small. Length 11p.-70p.. Distribution.-It was found in the sediments and in the periphyton on Thalassia at stations 1, 2, and 3 during November-December 1964, February-April 1965, and June-July 1965. Cocconeis scutellum Ehr., 1838 Cocconeis scutellum Ehrenberg, 1838: 194.-Schmidt, 1894: pI. 190, figs. 17-20.-van Heurck, 1880: pI. 29, figs. 1-3.-Cleve, 1895: 170.-Boyer, 1927: 245.-Hustedt, 1933a: 337, fig. 790.-Hendey, 1951: 44, pI. 10, fig. 9.-Crosby & Wood, 1959: 13, pI. 3, figs. 39a, b. Description.-Frustules with dissimilar valves. Broadly elliptical in valve view. Upper valve with pseudoraphe and coarse puncta arranged in trans- verse striae usually ending at the margin in a finely punctate space. Lower valve with a straight raphe and a marginal loculiferous rim. Length 30p.-60p..

Distribution.-Present in the periphytic community on Thalassia and III the sediments at all the stations from November 1964 to July 1965. Cocconeis wood ii, nov. spec. Fig. 3 Cocconeis sp. Wood, 1963: 252, pI. 4, fig. 74. Descriptioll.-Valves elliptical; upper valve with a narrow, sigmoid, excen- tric pseudoraphe, valve surface furnished with coarse, punctate, radial striae. Lower valve with a marginalloculiferous rim and a sigmoid raphe, axial areas very narrow, central area small and circular; valve surface finely punctate. Striae 9-10 in 10 p.. Length 18p.-50p., breadth 9p.-24p.. Valvae ellipticae, 18p.-SOp. longae, 9p.-24p. latae. Areovalva cum area media angusto-sigmoidea, excentrica; striis crassis radiantibus circiter 9-10 in 10 p., distincte punctatis. Rhaphovalva cum margine loculifero et raphe sigmoidea, area axiali angustissima; area centrali parva orbicularique, tenere puncticulate. Type-locality.-Biscayne Bay, Miami, Florida. Type-slide.-Deposited in the herbarium of the Academy of Natural Sci- ences, Philadelphia. Museum number A.G.c. 48281. Etymology.-Dedicated to Professor E. J. Ferguson Wood, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami. 120 Bulletin of Marine Science [20(1 )

FIGURE 3. Cocconeis woodii, nov. spec.

Distribution.- This species was found by Wood (1963) in the sediments of Texas bays. In Biscayne Bay it has been found in the periphyton on Thalassia at station 1, from November 1964 to January 1965 and from March to July 1965.

Suborder BIRAPHIDINEAE Family Naviculaceae Genus Trachyneis Cleve, 1894 Trachyneis aspera (Ehr.) Cleve, 1894 Trachyneis aspera Cleve, 1894: 191.-Boyer, 1927: 428.-Hendey, 1951: 55.-Crosby & Wood, 1959: 22, pI. 5, fig. 63. Pinnularia aspera Ehrenberg, 1840: 213. Navicula aspera Ehrenberg, 1854: 35. Description.-Cells solitary. Frustules rectangular in girdle view, with round corners; constricted in pervalvar axis. Valves elliptic to linear lanceolate with round ends. Central area forming a transverse stauros widened outwards; axial area narrow or linear and unilateral. Alveoli arranged in radiate transverse striae. 1970] Reyes- Vasquez: Diatom Flora of Thalassia 121

Distribution.-It was found in the sediments and associated with the periphyton on Thalassia at all the stations, during November-December 1964 and March-April 1965.

Genus Diploneis Ehr., 1844 Diploneis crabro Bhr., 1844 Diploneis crabro Ehrenberg, 1844a: 85.~Cleve, 1894: 100.-Hustedt, 1937: 616, fig. 1028.-Hendey, 1951: 59, pI. 16, fig. B.-Cleve-Euler, 1953b: 86, fig. 660c.-Crosby & Wood, 1959: 24, pI. 5, fig. 71a. Navicula pandura Brebisson, 1854: 253, fig. 4. Description.-Cells solitary. Valves panduriform. Central nodule sub- circular to quadrate. Horns narrow and parallel, bordered by a row of large puncta. Costa very strong, alternating with double rows of small areolae. Lunule broad, usually linear. Length 50p.-120p.. Distribution.-Present in plankton samples of high salinity; frequent in sediments and occasionally on Thalassia at stations 4 and 5.

Genus Gyrosigma Hassall, 1845 Gyrosigma balticum (Bhr.) Cleve, 1845 Gyrosigma balticum (Ehr.) Cleve, 1894: 118.-Boyer, 1927: 456.-Hendey, 1951: 61, pI. 11, fig. 9.-Cleve-Euler, 1952: 10, fig. 1331. Navicula baltica Ehrenberg, 1838: 180, pI. B, fig. 10. Pleurosigma balticum (Ehr.) W. Smith, 1852: 8, pI. 1, figs. 1-3.-van Heurck, 1896: 256, pI. 7, fig. 272.-Crosby & Wood, 1959: 26, pI. 6, figs. 80a, b. Description.-Cells solitary, valves linear, sigmoid toward the ends; apices obtuse. Axial area very narrow. Raphe sigmoid with the same curvature as the valve margin, particularly toward the ends, flexuose close to the central nodule; central area small; valve surface with striae arranged in equidistant transverse and longitudinal rows, 10-12 in 10 ,.,.. Length 90p.-190p.. Distribution.-Found in sediments; usually associated with the ,periphyton on Thalassia. Present at stations 1, 3,4, and 5 during November-December 1964, in February 1965, and April-May 1965.

Genus Pleurosigma W. Smith, 1852 Pleurosigma angulatum (Quekett) W. Smith, 1852 Pleurosigma angulatum (Quekett) W. Smith, 1852: 7, pI. 1, figs. 7-9.- van Heurck, 1896: 251, pI. 6, fig. 257.-Boyer, 1927: 271.-Hendey, 1951: 61, pI. 11, fig. 8.-Cleve-Euler, 1952: 23, fig. 1372.-Crosby & Wood, 1959: 26, pI. 6, fig. 79a, b. Navicula angulata Quekett, 1848: 438, pI. 7, figs.4-7. 122 Bulletin of Marine Science [20 (1) Description.-Cells solitary. Valves rhomboid-sigmoid. Raphe sigmoid; central and axial areas absent or very narrow. Central nodule small. Valve striated in oblique equidistant rows becoming transverse near the apices, (18-20 in 10 fJ-). Length 90,u.-160fJ-. Distribution.-Present in sediments from muddy shores, in plankton sam- ples, and in the periphyton on Thalassia at aU the stations, from November 1964 to July 1965. Pleurosigma formosum W. Smith, 1852 Pleurosigma formosum W. Smith, 1852: 5, pI. 1, fig. l.-van Heurck, 1896: 254, pI. 35, figs. 914-915.-Boyer, 1927: 467.-Crosby & Wood, 1959: 27, pI. 6, figs. 82a, b.-Hendey, 1964: 242. Description.-Cells solitary; valves elongate and narrow, slightly sigmoid. Raphe sigmoid and excentric, becoming very close to the margin of the valve. Striae in transverse and oblique rows. Length 140,u.-200,u.. Distribution.-Present in sediments and periphyton on Thalassia at all the stations from November 1964 to April 1965. Pleurosigma naviculaceum Breb., 1854 Pleurosigma naviculaceum Brebisson, 1854: 255, fig. 7.-van Heurck, 1896: 252, pI. 6, fig. 266.-Crosby & Wood, 1959: 26, pI. 6, fig. 78.-Hendey, 1964: 243. Description.-Valves broadly lanceolate, slightly sigmoid toward the apices. Raphe sigmoid. Valve surface with transverse and oblique striae (trans- verse, 18-20 in 10,u.; oblique, 16-18 in 10 ,u.). Length 80,u.-90p.. Distribution.-Associated with the periphyton on Thalassia and in the sediments at all the stations during November-December 1964 and April- May 1965.

Genus Mastogloia Thwaites in W. Smith, 1856 Mastogloia angulata Lewis, 1861 Mastogloia angulata Lewis, 1861: 65, pi. 2, fig. 4.-Schmidt, 1893: pI. 187, figs. 4-11.-Boyer, 1927: 334.-Hustedt, 1933b: 465, fig. 885.-Wood, 1963: 264, pI. 7, fig. 139. Description.-Valves elliptic to elliptic lanceolate with slightly produced round ends; raphe straight; axial area very narrow; central area, when present, is very small. Valve surface areolate. Numerous loculi forming bands which do not reach the ends; usually two or three large loculi in the middle. Length 35"..-90"... Distribution.-Present in the periphyton on Thalassia at all the stations during November 1964 and from January to April 1965. 1970J Reyes-Vasquez: Diatom Flora of Thalassia 123 Mastogloia bil10tata (Grun.) Cleve, 1895 Maslogloia binolata (Grun.) Cleve, 1895: 148.-Hustedt, 1933b: 470, fig. 889.-Wood, 1963: 264, pI. 7, fig. 143.-Hendey, 1964: 238, pI. 37, fig. 11. Cocconeis binotata Grunow, 1863: 141, pI. 4, fig. 13. Orthoneis binolala (Grun.) van Heurck, 1896: 284. Descriptiol1.- Valves broadly elliptical; raphe straight. Axial area very narrow; central area transversely dilated. Valve surface areolate, in radial rows. One large median loculus on each margin occupying about 10 of the valve length. Free margin of the loculi straight. Length 20ft-40ft. Distributiol1.-Found in sediments as well as in the periphyton on Thalassia at all the stations during December 1964 and from February to April 1965. Mastogloia cribrosa Grun., 1860 Maslogloia cribrosa Grunow, 1860: 577, pI. 7, fig. lOc.-Hustedt, 1933b: 468, fig. 887.-Crosby & Wood, 1959: 29, pI. 6, fig. 87. Orthoneis crib rosa (Grun.) Cleve, 1895: 149. Descriptiol1.-Cells often enclosed in a mucous sheath. Valves broadly elliptic with straight raphe; central and axial areas very narrow; central nodule small. Valve surface areolated or coarsely punctate. Loculi forming bands reaching the apices, usually 12 on each side; free margin of the loculi straight. Length 30ft-50ft. Distributiol1.-Present in the sediments and in the periphyton on Thalassia at all the stations, during December 1964 and February-March 1965. Mastogloia crucicula (Grun.) Cleve, 1895 Mastogloia crucicula (Gron.) Cleve, 1895: 148.-Hustedt, 1933b: 475, fig. 894.-Wood, 1963: 265, pI. 8, figs. 148a, b. Orthoneis crucicula Grunow, 1877: 177, pI. 195, figs. 8a, b. Description.-Valve elliptic; raphe straight; central area as a narrow trans- verse band reaching the margin of the valve; axial area very narrow. Valve surface areolate, areolae arranged in radial rows; loculi do not reach the ends; two loculi on each side, located between the middle and the end. Length 14ft-22ft. Distributiol1.-Present in the periphyton on Thalassia at all the stations from January to March 1965. Mastogloia erythraea Grun., 1860 Mastogloia erythraea Grunow, 1860: 577, pI. 7, fig. 4; 1877: 174, pI. 94, fig. 15.-Schmidt, 1893: pI. 186, fig. 36.-Cleve, 1895: 154.-Hustedt, 1933b: 524, fig. 959.-Wood, 1963: 265, pI. 8, fig. 149. Maslogloia interrupta Hantzsch, 1863: 20, pI. 6A, fig. 5a, b. 124 Bulletin of Marine Science [20(1) Description.-Valves lanceolate to rhombic lanceolate, the ends more or less produced; raphe strongly undulate from the central nodule, straight to the ends. Areas narrow, valve surface transversely striate, longitudinal lines present. Loculi bands do not reach the ends and are separated from the margin of the cell. The large loculi are between the middle and the ends; the number of large loculi is variable, in the variety biocellata they are located in the middle. Frustules with large loculi diagonally arranged, or present in only one half of the cell, have been found at the Ragged Keys station. Length 23p.-80p.. Distribution.-This species was found in the periphyton on Thalassia as well as in sediments at stations 4 and 5 during November-December 1964 and February-March 1965.

Mastogloia fimbriata (Brightw.) Cleve, 1895 Mastogloia fimbriata Cleve, 1895: 148.- Hustedt, 1933b: 464, fig. 884. Cocconeis fimbriata Brightwell, 1859: 179, pI. 9. fig. 3. Description.-Valves eJliptic; raphe straight or slightly bent; axial area very narrow; central area slightly linear to elliptic. Valve surface with double rows of small areolae in the margin; the areolae in the inner part are loose. Loculi forming a rim along the margin, cuneate with the narrow end toward the margin of the valve; the free margins of the loculi convex or straight. Distribution.-It was found in the periphytic community on Thalassia at stations 3, 4, and 5 from February to March 1965. Mastogloia ovata Grun., 1860 Mastogloia ovata Grunow, 1860: 578, pI. 7, fig. 12.-Schmidt, 1893: pI. 188, fig. 42.-Hustedt, 1933b: 476, fig. 895. Description.-Valves broadly elliptic; raphe straight or slightly undulate; central area very small and circular, or absent. Axial area very narrow. Valve surface punctate, puncta arranged in radial transverse and longi- tudinal rows. Loculi forming a rim along the margin, all of the same size with the free margin straight. Length 15p.-30p.. Distribution.-It has been found in sediments and periphyton on Thalassia at stations 3, 4, and 5 during November-December 1964 and February- March 1965. Mastogloia pumila (Grun.) Cleve, 1895 Mastogloia pumila (Grun.) Cleve, 1895: 157.-Hustedt, 1933b: 553, fig. 983.-Wood, 1963: 266, pI. 8, figs. 15a, b, c. Mastogloia braunii var. pumila Grunow, 1880: pI. 4, fig. 23. Description.-Valves linear elliptic, with weakly produced ends; raphe straight; axial area narrow; central area rectangular, with lateral extensions 1970] Reyes-Vasquez: Diatom Flora of Thalassia 125 forming an H. Loculi 6 to 8 on each side, not reaching the ends, those located in the middle being the largest. Valve surface striate, striae slightly radial. Length 20ft-25ft. Distribution.-Present in sediments as well as in periphyton on Thalassia at stations 2, 3, 4, and 5 from January to March 1965.

Mastogloia splendida (Greg.) Cleve, 1895 Mastogloia splendida (Greg.) Cleve, 1895: 148.-Boyer, 1927: 329.- Hustedt, 1933b: 463, fig. 883.-Hendey, 1964: 237. Cocconeis splendida Gregory, 1857: 493, pI. 9, fig. 29. Orthoneis splendida (Greg.) Grunow, 1880: pI. 28, figs. 1-2. Description.-Valves elliptic to circular; raphe strongly bent toward the same side at the ends; axial area narrow, central area small and circular. Valve surface furnished with areolae arranged in rows which become double in the margin. Loculi rectangular, forming a rim along the margin of the valve, 2-6 loculi in 10ft. Length 30ft-50ft. Distribution.-This species was found in the periphyton on Thalassia at stations 1, 3, 4, and 5 during November~December 1964 and February- March 1965. Genus Tropidoneis Cleve, 1894 Tropidoneis lepidoptera (Greg.) Cleve, 1894 Tropidoneis lepidoptera (Greg.) Cleve, 1894: 25.-Hendey, 1951: 66.- Crosby & Wood, 1959: 31, pI. 7, fig. 92. Amphiprora lepidoptera Gregory, 1857: 505, pI. 4, fig. 59. Orthotropis lepidoptera van Heurck, 1896: 263. Description.-Cells solitary, frustules linear with acute and apiculate ends in valve view. Wings distinct, projecting above and below the central nodule. Raphe straight; central area indistinct, small. Length 240ft-260ft. Distribution.-Associated with the periphyton on Thalassia at stations 1, 3, 4, and 5 during November-December 1964.

Genus Amphiprora Ehr., 1841 Amphiprora alata (Ehr.) Klitz., 1844 Amphiprora alata (Ehr.) Kiitzing, 1844: 107, pI. 3, fig. 63.-Cleve, 1894: 15.-van Heurck, 1896: 262, fig. 52.-Boyer, 1927: 483.-Hendey, 1951: 66, pI. 15, figs. 1-3.-Wood, 1963: 242, pI. 1, figs. 16a, b. Navicula alata Ehrenberg, 1840: 212. Description.-Cells solitary or forming short ribbons. Frustules in girdle view constricted and twisted in the middle. Valves linear with acute apices; raphe enclosed in a sigmoid keel coarsely punctate, formed by the raised axial area. Valve surface striate, striae 16-17 in 10 ft. Length 90ft-100ft. 126 Bulletin of Marine Science [20(1 ) Distribution.-Present in the periphytic community on Thalassia at stations 2 and 4, from November 1964 to July 1965. It was also found in sediments and occasionally in plankton samples.

Family Cymbellaceae Genus Amphora Ehr., 1840 Amphora proteus Greg., 1857 Amphora proteus Gregory, 1857: 518, pi. 13, fig. 81.-Cleve-Euler, 1953b: 92, fig. 673.-Crosby & Wood, 1959: 32, pi. 7, fig. 94. Description.-Cells solitary. Frustules elliptic to oblong, barrel-shaped, in girdle view. Valves lunate, sometimes arcuate with an almost straight ventral margin. Central area absent. Raphe biarcuate. Valve surface striate. Length 400-600. Distribution.-Present in the periphyton on Thalassia and in sediments at all the stations during December 1964 and from March to July 1965.

Amphora robusta Greg., 1857 Amphora robusta Gregory, 1857: 516, pI. 13, fig. 79.-Cleve-Euler, 1953b: 92, fig. 672.-Wood, 1963: 245, pi. 3, fig. 37. Description.-Cells solitary. Frustules broadly elliptical to oblong, with weakly truncate ends in girdle view. Valves lunate with straight or concave ventral margin. Raphe biarcuate. Central and axial areas indistinct. Valve surface striate. Length 350-500. Distribution.- This species was found in sediments and in the periphytic community on Thalassia at stations 1, 2, 4, and 5 during November and December 1964.

Genus Rhopalodia O. MUlier, 1895 Rhopalodia gibberula (Ehr.) O. MUller, 1895 Rhopalodia gibberula (Ehr.) O. Muller, 1895: 58.-Boyer, 1927, 450.- Cleve-Euler, 1952: 42, fig. 1415.-Wood, 1963: 279, pI. 12, figs. 230a-d. Eunotia gibberula Ehrenberg, 1841: 414. Description.-Frustules elliptical to elliptic lanceolate. Valves lunate with straight to slightly concave ventral margin; dorsal margin strongly arcuate; ends sometimes produced or bent ventrally and slightly expanded. Costae distant, 3-6 in 10 0, with intermediate rows of fine puncta, 14-17 in 10 p.. Length 40p.-50p.. Distribution.-Associated with the periphyton on Thalassia at all the stations during November 1964, February-March and May-July 1965. It was also found in sediments at the same stations. 1970] Reyes- Vasquez: Diatom Flora of Thalassia 127 Family Bacillariaceae Genus Cylindrotheca Rabenh. em. Reimann & Lewin, 1964 Cylindrotheca closterium (Ehr.) Reimann & Lewin, 1964 Cylindrotheca closterium (Ehr.) Reimann & Lewin, 1964: 289, pI. 124, figs. 1-6; pI. 125, figs. 1-8. Nitzschia closterium (Ehr.) W. Smith, 1853: 42, pI. 15, fig. 120.-Boyer, 1927: 526.-Lebour, 1930: 212, fig. 176.-Cupp, 1943: 200, fig. 153.- Crosby & Wood, 1959: 38, pI. 1, fig. 17. Ceratoneis closterium Ehrenberg, 1839: 144. Description.-Cells solitary, fusiform in valve view with ends prolonged to form long awns, straight or bent to the same or opposite sides. Valve sur- face traversed by more or less transapical silicified thickenings. Raphe traversed by a series of fibulae joined directly to the valve surface. Chro- matophores two, in the middle of the cell. Length 50""-80",,. Distribution.-Present in plankton samples, sediments and periphyton on Thalassia at all the stations from November 1964 to July 1965.

Genus Bacillaria Gmelin, 1788 Bacillaria paxillifer (0. F. MUlier) Nitzsch, 1817 Bacillaria paxillifer (0. F. MUlier) Nitzsch, 1817: 75.-Hendey, 1951: 74.- Crosby & Wood, 1959: 40, pI. 8, fig. 119. Vibrio paxillifer O. F. MUlier, 1786: 54. Bacillaria paradoxa Gmelin, 1788: 3903. Description.-Cells in colonies arranged in palisade formation, able to slide laterally with respect to each other to form an elongated chain. Valves linear to linear lanceolate with produced ends; keel central with strong puncta. Valve surface transversely striated. Length 70""-100",,. Distribution.-This species was found in plankton samples, sediments and periphyton on Thalassia at all the stations during November 1964, January 1965, and March-May 1965. Suborder SURIRELLINEAE Family Surirellaceae Genus SW'irella Turpin, 1828 Surirella fastuosa (Ehr.) Klitz., 1844 Surirella fastuosa (Ehr.) KUtzing, 1844: 62, pI. 28, fig. 19.-Lebour, 1930: 125, fig. 18a.-Hendey, 1951: 75, pI. 9, fig. 40.-Crosby & Wood, 1959: 41, pI. 8, fig. 121a.-Filho & Kutner, 1962: 19, pI. 6, fig. 40. Navicula fastuosa Ehrenberg, 1840: 214. Description.-Cells solitary, ovate or broadly elliptic in valve view; costae few, 1-2 in 10 "",dilated toward the margin. Central area broadly lanceolate and hyaline or faintly striated. Length 60,u.-120,u.. 128 Bulletin of Marine Science [20(1) Distribution.-Present in sediments as well as in the periphyton on Tha- lassia at stations 1, 3, 4, and 5 from February to July 1965.

Surirella gemma (Ehr.) Klitz., 1844 Surirella gemma (Ehr.) KUtzing, 1844: 62, pI. 7, fig. n.-Boyer, 1927: 450.-Hendey, 1951: 76, pI. 14, figs. 1-3.-Crosby & Wood, 1959: 41, pI. 8, fig. 122.-Filho & Kutner, 1962: 20, pI. 2, fig. 7. Navicula gemma Ehrenberg, 1839: 156, pI. 4, fig. 5. Description.-Cells solitary, narrow cuneate in girdle view; oval to elliptic in valve view. Alae reduced; axial area narrow. Costae narrow and alternated at irregular intervals. Valve surface finely striated. Length 72p.-80p.. Distribution.-Present in sediments as well as in the periphyton on Tha- lassia at all the stations from February to July 1965.

DISCUSSION AND CONCLUSIONS The diatom flora living on the turtle grass (Thalassia testudinum Konig) seems to be influenced more by the ecological conditions of the sediments, than by those ecological factors which determine the occurrence of plank- tonic diatoms, this being in agreement with the suggestion formulated by Baas-Becking & Wood (1955) that the sediments dominate the milieu in estuaries. No direct effects of salinity and temperature were observed on most of the species, although, as it has been pointed out before, Licmophora remulus seems to be affected by salinities greater than 34.5%0 and lower than 31.8%0. This species was dominant from December to January, and from June to July at the Matheson Hammock station. It was found also from December to January at the Southwest Point station. These two stations have in common a muddy sediment rich in decaying organic matter. During low tides the temperature of the water and exposed sediments rises considerably, and this seems to favor the growth of that attack organic compounds and release substances such as iron compounds, vita- mins, etc., which can be utilized by other organisms, among them diatoms. Hulburt & Rodman (1963) found neritic species in the phytoplankton near Bermuda; they pointed out that those species appear to be favored by the availability of iron, silicate, and vitamin B12• Probably the occurrence of diatom species on Thalassia is determ'ined by the presence of substances that promote or inhibit their growth, those substances being produced by organisms associated with the epontic and benthic communities. Another important factor controlling populations of diatoms is grazing; it is known that the grazing rate of herbivores is variable with temperature. The analysis of the samples taken from the stations show that at least 1970] Reyes-Vasquez: Diatom Flora of Thalassia 129 some species exhibit seasonal occurrence; such is the case for species of the genus Mastogloia (M. angulata, M. binotata and M. crucicula), which became dominants from February to March, and species of the genera Licmophora and Cocconeis, which were dominants at the stations from November to December and from March to July. The observations carried out on the diatom flora on Thalassia indicate that these organisms constitute a very important part of the periphyton in this area. However, Pomeroy (1960) reported that leaves of turtle grass stripped of "aufwuchs" show the same photosynthetic rate as the unmodi- fied leaves. This statement as a general conclusion is difficult to accept and may be due to the conditions of his experiment. Humm (1964), suggested that the organisms present on those leaves examined by Pomeroy may have been diatoms and that that could be the explanation for similar values for the photosynthetic rates. We have found that in different places in the Bay, and at the same time, the epontic flora is variable in number and compo- sition of species of diatoms, and that diatoms are quite abundant in certain places, such as Matheson Hammock. Studies on the productivity of the periphyton at this station will be rewarding. The species of diatoms found on Thalassia testudinum have been reported before from the periphyton on some other sea grasses, and they also occur in sediments (Wood, 1959, 1963).

SUMARIO

ESTUDIOS SOBRE LA FLORA DIATOMOL6GICA QUE VIVE SOBRE Thalassia testudinum KONIG EN BISCAYNE BAY, FLORIDA Las diatomeas que crecen sobre las hojas de Thalassia testudinum Konig, se colectaron de cinco estaciones en Biscayne Bay, durante el perfodo de Noviembre 1964 a Julio 1965. Se describen los metodos empleados en el presente estudio. Se discute la validez de los caracteres empleados en la identificaci6n de las especies de diatomeas. Se discute brevemente el efecto de la salinidad y la temperatura sobre el desarrollo de las diatomeas encontradas y se compar an los !imites de tolerancia a estos factores encontrados en Biscayne Bay, con los observados por Wood (1964) en estuarios de Australia. Las diferencias se atribuyen a adaptaciones fisiol6gicas. Se discuten brevemente las variaciones estacionales de algunas especies. Se describen cuarenta y dos especies de diatomeas, una de ellas, Coc- coneis woodU, es nueva para la ciencia. Las observaciones llevadas a cabo indican que la flora diatomol6gica constituye una parte importante del perifiton sobre Thalassia, en el area estudiada. 130 Bulletin of Marine Science [20(1 ) LITERATURE CITED AGARDH,C. A. 1824. Systema algarum. Lundae, 312 pp. 1830a. Conspectus criticus Diatomacearum. Part 1. Lundae, pp. 1-16. 1830b. Conspectus criticus Diatomacearum. Part 2. Lundae, pp. 17-38. 1831. Conspectus criticus Diatomacearum. Part 3. Lundae, pp. 39-48. 1832. Conspectus criticus Diatomacearum. Part 4. Lundae, pp. 49-66. ALEEM, A. A. ] 949. A quantitative method for estimating the periodicity of diatoms. J. mar. bio!. Ass. U.K., 28: 713-717. BAAS-BECKING,L. G. M. ANDE. J. F. WOOD 1955. Biological processes in the estuarine environment. Parts I and II. Proc. K. ned. Akad. Wet., 58: 160-181. BAILEY,J. W. 1854. Notes on new species and localities of microscopical organisms. Smithson. Contr. Knowl., 7: 1-16. BOYER,C. S. ]926. Synopsis of the North American Diatomaceae. Part I. Proc. Acad. nat. Sci. Philad., Suppl., 78: 1-228. 1927. Synopsis of the North American Diatomaceae. Part II. Proc. Acad. nat. Sci. Philad., Suppl., 79: 229-583. BREBISSON,A. DE 1854. Notes sur quelques diatomees marines nouvelles ou rares du littoral de Cherbourg. Mem. Soc. nat. Sci. Cherbourg, 2: 24] -258. BRIGHTWELL,T. ]859. On some of the rare or undescribed species of Diatomaceae. Quart. 11microsc. Sci., 7: ]79-]81. CASTRACANE,A. F. 1886. Report on the Diatomaceae collected by H.M.S. CHALLENGERduring the years ]873-76. Rep. Challenger Exp., Botany, 2: 1-178, pis. I-XXX. CLEVE, P. T. ]894. Synopsis of the naviculoid diatoms. Part I. Bih. K. svenska. VetensAkad. Hand!., 26(2): ]-194. 1895. Synopsis of the naviculoid diatoms. Part II. Bih. K. svenska. VetensAkad. Hand!., 27(3): 1-219. CLEVE-EuLER,A. ]951. Die Diatomeen von Schweden und Finland. Part I. K. svenska. VetensAkad. HandI., Fjarde Ser., 2(1): 1-163, figs. 1-294, 6 pis. 1952. Die Diatomeen von Schweden und Finland. Part V. K. svenska. VetensAkad. HandI., Fjiirde Ser., 3(3): 1-153, figs. 1318-1583, 1 pI. 1953a. Die Diatomeen von Schweden und Finland. Part II. K. svenska. VetensAkad. HandI., Fjiirde Ser., 4(1): 1-158, figs. 292-483. 1953b. Die Diatomeen von Schweden und Finland. Part III. K. svenska. VetensAkad. Hand!., Fjiirde Ser., 4(5): 1-255, figs. 484-970. 1955. Die Diatomeen von Schweden und Finland. Part IV. K. svenska. VetensAkad. Hand!., Fjiirde Ser., 5(4): 1-232, figs. 971-1317. CONGER,P. S. 1950. A new method for the preservation of diatoms and other orgamc siliceous structures. Trans. Am. microsc. Soc., 69( 1): 66-68. 1970] Reyes-Vasquez: Diatom Flora of Thalassia 131

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