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THE EFFECTS OF SALINITY, LIGHT AND
TEMPERATURE ON GYROSIGMA SPP
G Reid
To cite this version:
G Reid. THE EFFECTS OF SALINITY, LIGHT AND TEMPERATURE ON GYROSIGMA SPP. Vie et Milieu / Life & Environment, Observatoire Océanologique - Laboratoire Arago, 1995, pp.215-218. �hal-03051997�
THE EFFECTS OF SALINITY, LIGHT AND TEMPERATURE
ON GYROSIGMA SPR
G. REID
Department of Botany, The Natural History Muséum, Cromwell Road, London, England
ABSTRACT - The edaphic Gyrosigma populations of two sait marshes on the Isle of Sheppey, Kent, England, are being investigated. Stations along transects (one per marsh) are being sampled on a quaterly basis of quantitative estimâtes of the Gyrosigma populations. Concurrent field measurements of salinity, tempéra-ture and pH are taken at each station. Floristic changes along transects and between the two marshes will be described, in relation to changes in the physico-chemical environment. Preliminary results of culture work on Gyrosigma fasciola will be presented.
RÉSUMÉ - Deux populations édaphiques de Gyrosigma sont étudiées dans les marais salants de l'Ile de Sheppey, Kent, U.K. Des stations réparties le long de transects (un par marécage) sont échantillonnées tous les trois mois pour obtenir une estimation quantitative des populations de Gyrosigma. La salinité, la tempé-rature et le pH sont mesurés simultanément à chaque station. Les changements floristiques le long de chaque transect et pour les deux marécages sont décrits en relation avec les changements physico-chimiques de l'environnement. Les résultats préliminaires concernant des expériences de mise en culture de G. fasciola sont présentés. GYROSIGMA TEMPERATURE SALINITY CULTURE GYROSIGMA TEMPÉRATURE SALINITÉ CULTURE INTRODUCTION
Sait marshes are subject to periodic flooding by the sea and as such the dominant feature in any sait marsh is the fluctuating salinity and tem-pérature régime. The diatoms in the marsh are submerged by the tide, but on retreat of the tide are exposed to increasing salinity due to evapo-ration from the surface of the pans, or to decrea-sing salinity due to freshwater inputs from rainwater and land run-off. Diatoms are also ex-posed to wide thermal fluctuations as the tempe-rature in shallow pans and on exposed sédiments may rise by several degrees centigrade on a warm day.
An investigation into the ecological tolérances and morphological variability of sait marsh Gy-rosigmataceae, was initiated. The taxonomy of the sigmoid naviculaceae (Gyrosigma and Pleurosig-mà) is in a state of flux with the spécifie limits of the gênera being in dispute and the stability of the various diagnostic features of the valve being disputed (Stidolph 1988, Cardinal 1989, Sterren-burg 1990). Culturing taxa under différent salini-ties, température and light régimes allows growth rates and valve morphology to be monitored under known controlled conditions. An understanding of
the plasticity and/or stability of morphological features of the cells is essential to good taxonomy. This has already been illustraded by Syvertsen's (1979) study which showed that Thalassiosira gravida Cleve and T. rotula Meunier were tempe-rature-speçific expressions of the same species. Culture work also permits the détermination of size-dependent shape variation, using different-si-zed cells of the same species (Cox 1983).
MATERIALS & METHODS
Ail samples were taken from two sait marshes on the Isle of Sheppey, Kent (Diagram 1). The marshes are situated on the south bank of the mouth of the River Thames and both are south facing. The two expérimen-tal marshes vary quite markedly in their topographie features. Marsh A is a very young sait marsh System with shallow pans and not very notable channels. The marsh is composed of a very soft fine sédiment from station 3 to 8. Marsh B is a much firmer under foot and resembles station 1 of marsh A in its topographie features in that throughout the marsh it consists of well formed pans and deep channels. Samples from exposed and submerged stations (Table I) were collected by pressing a plastic drain pipe (3 cm in diameter), 1 cm
G. REID
216
into the marsh sédiment. If water depth was too great to permit this, samples were taken by drawing a plastic tube across the surface of the sédiment so that a mixture of sédiment and water from the same surface area as that collected from the core (Round 1953) was obtained. Three replicates were taken at each site. Température, salinity, pH and mv were measured at each site using a Jenway 3070 pH meter.
Table I. - Position of the stations in the two sites and spécifie descriptions with respect to physical and che-mical environment.
Marsh A : The Swale TR030662 Station Description
1 Top of marsh. Large sait pan
2 Interface between sait marsh proper and upper marsh.
3 Middle marsh pan.
4 Middle marsh surface mud from within végétation.
5 Bottom of marsh, pan.
6 Bottom of marsh, channel at interface of mud flats and sait marsh
7 Channel, in mud flats. 8 Surface mud, low tide. Marsh B : Harty Ferry Inn TR015665 Station Description
9 Top of marsh, large pan. 10 Middle of marsh, deep channel. 11 Middle of marsh, small pan. 12 Bottom of marsh, small pan. 13 Bottom of marsh, deep channel. 14 Interface of mud flats and sait marsh. 15 Surface mud, low tide.
A small proportion of the sédiment was weighed fresh and then dried in an oven overnight and reweighed to obtain the water content of the site.
The sédiment samples were placed in Pétri dishes and the living diatoms separated from the sédiments using the lens tissue technique (Eaton & Moss 1966), fixed in Lugol's iodine, to count "live" cells. Only cells with well preserved chloroplasts were counted. Thèse were presumed to represent the actively growing popu-lation at the moment of sampling.
Rough cultures were established in Pétri dishes in GezS média (Reid & Cox submitted). Unialgal cultures of Gyrosigma were established from the rough cultures using a fine capillary tube. The cultures were subjected to différent salinities and light/temperature régimes (i.e. multifactoral design : salinity x light x température. Sa-linity 0, 7, 14, 21, 28, 35, 42 ppt., Température 5-25°C, light intensity 8-45 uEm~2sec .
RESULTS
Field Results
The température profiles over the two marsh Systems show seasonal variation (Fig. 1). Tempe-rature variation along marsh System A shows the widest fluctuation in température, whereas the fluctuation along marsh B is relatively small.
The salinity profile for the two marshes does not show such a clear seasonality (Fig. 1). There is wider fluctuation in salinity along the marsh A profile. At both marshes the greatest fluctuation occurs in the middle of the marsh, stations 2-4 and 10-12. Water content is a significantly varia-ble factor with wide fluctuation occurring between the replicates at each station and throughout the marshes (Fig. 1).
There is a significant différence in species composition between and within the stations along the marshes (F > 0.05). Gyrosigma fasciola has maximum cell densities at salinities of 22 parts per thousand and 10°C. It is mainly restricted to the winter months although it does occur in low numbers throughout the year, distribution range : middle to bottom of marsh, both Systems.
Gyrosigma spenceri has maximum cell densi-ties at 32 ppt showing a normal distribution within the salinity range 20-56 ppt. It occurs throughout the year with maximum numbers in the middle of the marsh (marsh A, station 4).
Gyrosigma balticum occurs mainly during the summer period with températures of 20°C and sa-linity 32 ppt, restricted mainly to the bottom of the marsh (marsh A, station 7).
Gyrosigma litorale occurs ail the year round and is restricted to the middle/bottom of marsh zone, occurring in maximum numbers at station
13, 1.12.1993, 30 ppt and 6°C.
Culture work on G. fasciola
Gyrosigma fasciola has died at salinities above 35 ppt; its maximum growth occurred at 21 ppt (Fig. 2). At lower salinities slight distortion in valve outline was observed.
DISCUSSION
The distribution of the edaphic diatoms is very sporadic, showing both inter-and intra-site varia-tion in species composivaria-tion and density. G. balti-cum shows an interesting seasonal pattern ; it persists as isolated individuals throughout the year (Carter 1932), but with a maximum under
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25 \ 20 | 15 \ 10 -= 5^ 1 2 3 4 5 6 7 8 Station 9 10 11 12 13 14 15 StationFig. 1. Graph showing variation in températures, salinity and water content between sites in the two sait marsh
Systems on différent occasions; A - C marsh A; D - F marsh B.
218 G. REID 30 25 20 CD ° 15 10 H 5 H , ,21 ppt -i 1 1 1 1 1 r 0 1 2 3 4 5 6 7 9 10 11 12 Time (days)
Fig. 2. Cell numbers of Gyrosigma fasciola growing un-der différent salinities. Diagram 1. Sketch map of the Isle of Sheppey, Kent, U.K.
cular conditions : salinity 32-36 ppt, 17-22°C, and water content 35-38 %. The combination of factors is critical : blooms are possible when ail thèse conditions are satisfied.
G. fasciola shows a marked seasonality which agrées well with Round 1960 and Carter 1932, oc-curring in the winter months. However it is quite an abundant species, occurring from the middle of the marsh to the mud flats. This is a wider dis-tribution range than that reported by Round and Carter. The combination of environmental condi-tions is again the key to the distribution of G. fas-ciola ; salinity 22 ppt, 8°C and a water content of 34-35 %. This agrées well with culture experi-ments where optimum growth was achieved at 21 ppt. and 10°C. Variation in the shape of the valve under culture will be dealt with in another paper.
The distribution of G. spencerii contrasts with that found by Round (1960) and Carter (1932). Although it occurs throughout the marsh maxi-mum numbers are found in the middle of the marsh. Again this can be related to the interaction of environmental conditions. Further work is nee-ded here to elucidate the key components. Water content shows most significant inter- and intra-station fluctuation and may be a key feature af-fecting the uneven distribution of the diatoms.
In the past salinity has been regarded as a key influence on the distribution of edaphic diatoms (Kolbe 1927). Culture experiments using a wide range of salinities have shown that species can grow over a wider salinity range than observed in nature (pers. obs. and Cox 1994). The
interac-tion of several environmental factors is the key to understanding the spatial distribution of eda-phic diatoms.
ACKNOWLEDGEMENTS - I wish to thank the Natural History Muséum for their financial support during this work and Eileen Cox for her continued support and comments.
REFERENCES
CARDINAL A., M. POULIN & L. BERARD-THER-RIAULT, 1989. A new criteria for species characte-rization in the gênera Donkinia, Gyrosigma and
Pleurosigma (Naviculaceae, Bacillariophyceae).
Phycologia. 28 : 15-27.
CARTER N., 1932-33. Comparative study of the alga flora of two sait marshes. Part II. /. Ecol. 21 : 128-208.
COX E.J., 1983. Observations on the diatom genus
Donkinia Ralfs in Pritchard. II. Frustular studies and
intraspecific variation. Botanica Marina. 26 : 553-566.
COX E.J., 1994. Ecological tolérances and optima- real or imaginary ? In Press.
EATON I.W. & B. MOSS, 1966. The estimation of numbers and pigment content in epipelic algal po-pulations. Limnol. Oceanogr. 11 : 584-595.
KOLBE R.W., 1927. Zur Okologie, morphologie und systematik der brackwasser - Diatomeen.
Pflanzen-forsch. 7 : 1-145.
REID G. & E.J. COX, 1995. A modified sea water mé-dium for the culture of large benthic diatoms. Sub-mitted.
ROUND F.E., 1953. An investigation of two benthic algal communities in Malham Tarn, Yorkshire. Arch.
Hydrobiol. 50 : 529-547.
ROUND F.E., 1960. The diatom flora of a sait marsh on the River Dee. New Phytol. 59 : 332-348. STERRENBURG F.A.S., 1991. Studies on the gênera
Gyrosigma and Pleurosigma (Bacillariophyceae). A
new phenomenon : co-existence of dissimilar raphe structure in populations of several species. In : Rickard M. & Coste M. (eds). Ouvrage dédié à la Mémoire du Professeur Henry Germain
(1903-1989) : 235-242.
STIDOLPH S.R., 1988. Observations and remarks on the morphology an taxonomy of the diatom gênera
Gyrosigma Hassall and Pleurosigma W. Smith. Nova Hedwigia. 47 : 377-388.
SYVERTSEN E.E., 1976. Thalassiosira rotula and T.
gravida ecology and morphology. Beihefte Nova Hedwigia. 54 : 99-112.
Reçu le 3 novembre 1994; received November 3, 1994 Accepté le 12 décembre 1994; accepted December 12, 1994
