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Revue de micropaléontologie 49 (2006) 45–53

Original article

* CorrE-ma

0035-15doi:10.1

Distribution and new ecological data of Pseudothurammina limnetis

espondingil address

98/$ - see016/j.revm

(Scott and Medioli) on the brackish tidal marshes

of Minho/Coura estuary, Northern Portugal

Répartition et nouvelles données écologiques

de Pseudothurammina limnetis (Scott et Medioli) dans les marécages

saumâtres de l’estuaire du Minho/Coura, Nord du Portugal

João Moreno a, Francisco Fatela b,*, César Andrade b, Teresa Drago c

a Centro de Geologia, Faculdade de Ciências da Universidade de Lisboa, Edifício C6, Campo Grande, 1749-016 Lisboa, Portugalb Centro e Departamento de Geologia, Faculdade de Ciências da Universidade de Lisboa, Edifício C6, Campo Grande, 1749-016 Lisboa, Portugal

c IPIMAR/CRIPSUL, Av. 5 de Outubro, 8700-305 Olhão, Portugal

Abstract

Pseudothurammina limnetis (Scott and Medioli) revealed an important contribution to the characterization of IB and IA2 subzones of highmarsh from present brackish environments of Minho/Coura tidal marsh. Its occurrence can represent up to 68% of living assemblage probablyunder optimum salinity values between 8‰ and 14‰, strongly contrasting with published data where P. limnetis tends to be associated to highersalinity values and always with low proportions. This unusual dominance under such environmental conditions can be seen as a new ecologicaldata of P. limnetis. Its dominance at the Minho/Coura high marsh must also be stressed because no previous record of P. limnetis was found in theEuropean coastal environments. The record and abundance of living P. limnetis in marsh sediments can be markedly influenced by the labprocessing of the sediment marsh samples, considering its way of occurrence, frequently attached to plant debris, and test fragility. The completeanalysis of residue larger than 63 μm, including a careful observation of plant debris under wet conditions, is strongly suggested.© 2006 Elsevier SAS. All rights reserved.

Résumé

La répartition de Pseudothurammina limnetis (Scott et Medioli) dans les marécages saumâtres de l’estuaire du Minho/Coura apporte unecontribution importante pour la caractérisation des subzones IB et IA2 du haut marais, où leur présence peut atteindre 68 % de l’assemblagedes foraminifères benthiques vivants. La dominance de P. limnetis semble aussi liée à la salinité des eaux interstitielles des sédiments, notammentà une gamme de valeurs comprise entre 8 ‰ et 14 ‰. Ces observations peuvent être envisagées comme des données écologiques nouvelles. Eneffet elles s’opposent aux résultats publiés jusqu’ici, qui enregistrent toujours une abondance relative de P. limnetis faible, souvent associée à desvaleurs de salinité plus élevées. Leur dominance dans le haut marais du Minho/Coura est aussi importante, car aucune référence de P. limnetis n’aété signalée dans les environnements côtiers de l’Europe. La présence et l’abondance des formes vivantes de P. limnetis dans les sedimentsmarécageux peut être assez influencées par le traitement des échantillons, quand on considère la fragilité de son test et son mode de vie, souventattachée aux débris végétaux. On suggère, par la suite, d’analyser complètement l’ensemble du résidu de lavage supérieur à 63 μm et d’observerminutieusement les débris végétaux en milieu humide.© 2006 Elsevier SAS. All rights reserved.

Keywords: Living Pseudothurammina limnetis; Brackish tidal marsh; Portugal

Mots clés : Pseudothurammina limnetis vivante ; Marécage saumâtre ; Portugal

author.: ffatela@fc.ul.pt (F. Fatela).

front matter © 2006 Elsevier SAS. All rights reserved.ic.2005.11.002

J. Moreno et al. / Revue de micropaléontologie 49 (2006) 45–5346

1. Introduction

Tidal marsh represents a fundamental environment to under-stand the distribution of coastal foraminifera. The knowledgeof their ecology has a main importance to paleoecological in-terpretation. A basic pattern of main living species distributionhave been found around the world (e.g. Murray, 1971, 1991;Pujos, 1971, 1976; Carbonel and Pujos, 1974; Scott and Med-ioli, 1980; Debenay et al., 1987; Cearreta, 1988; Scott andLeckie, 1990; Hayward and Hollis, 1994; De Rijk, 1995; Alejoet al., 1999; Hayward et al., 1999; Diz et al., 2000; Murray etal., 2000; Debenay et al., 2000, 2002; Cearreta et al., 2002a;Sen Gupta, 2002).

Pseudothurammina limnetis has been reported with low oc-currence in New Zealand, Australia, both the coasts of NorthAmerica and Brazil (e.g. Hayward et al., 1999), and to the bestof our knowledge has not been previously referred in coastalenvironments of Europe (e.g. Pujos, 1971; Debenay, 1978;Pascual, 1990; Murray, 1991; Cearreta et al., 2002b; Diz,2004; Alday, 2004).

This study of the present-day assemblages of benthic fora-minifera from the Minho/Coura estuary and tidal marshes re-vealed an important contribution of P. limnetis (Scott and Med-ioli) to the foraminiferal marsh zonation of this region (Morenoet al., 2005).

2. Study area

The Minho river is located in the North of Portugal (Fig. 1),where it defines the political border with Spain (Galicia). Itsbasin is settled in a region dominated by carbonate depletedrocks of igneous and metamorphic nature.

The Minho estuary trends NNE–SSW and presents a high-mesotidal regime: the maximum amplitude of the astronomicalspring tide reaches 4 m and may be amplified by storm surge(Taborda and Dias, 1991). It provides a small accommodationvolume for the tidal prism and the large sand shoal that occu-pies most of the estuarine mouth constricts the seawater input,which is more effective during flood tides spring. In addition,the Minho basin drains the rainiest region of Portugal, with anaverage annual precipitation of 1300 mm (Alves, 1996). Alltogether these characteristics prevent extensive penetration ofa salt wedge into the estuary. During low spring tide the sea-water is completely flushed out (Moreno et al., 2005).

The widest expansions of intertidal environments in the leftmargin of the Minho (around 2.5 km2) occurs at its confluencewith the Coura river, providing an adequate site to investigatethe present-day distribution of foraminiferal assemblages in re-lation with the vertical zonation of the tidal marsh (Moreno etal., 2005).

3. Material and methods

Fifty two surface sediment samples were collected in Apriland October 2002 (under Spring and Autumn conditions, re-spectively) along the cross shore profiles of Pedras Ruivas(PR), railway bridge (CP) and Pinelas (PIC), which extend

across the salt marsh, tidal flat and channel environments ofMinho/Coura (Fig. 1).

Each sample consists of 10 cm3 of the topmost 1 cm layer ofsurface sediment that was stored immersed in alcohol and RoseBengal solution (1 g/l) (Lutze, 1964). Sediment has been washedthrough a 63 μm sieve, followed by separation using a micropip-ette and a wet picking procedure. This way the specimens on theplant debris were retrieved. When possible, at least 100 stainedforaminifera were counted (Fatela and Taborda, 2002) in eachsample, which we assume as representative of the living assem-blage at the time of collection. Identification of P. limnetis wasmade under a stereoscopic binocular microscope after Scott andMedioli (1980), and systematic description follows Loeblich andTappan (1988). Photographs of P. limnetis were taken using aconventional and a scanning electron microscope.

Temperature, salinity and pH were measured along the pro-files, in sediment interstitial water during low water. This waterseeped and accumulated inside perforated PVC tubes pre-viously inserted into the sediment to a depth of 40 cm belowsurface following De Rijk (1995). The temperature and salinityof estuarine water has also been controlled close to the bottom,in high and low water during spring tide. Water parameterswere measured with a multiparameter probe Horiba U-22 anda WTW conduktometer LF 191.

Altimetric data of the profiles have been obtained using aZeiss Elta R55 total station and were further connected to thenational hydrographic datum (Hydrographic Zero—HZ—which lies 2 m below mean sea level) using differential GPS(vertical resolution better than 1 cm). These data were com-bined with tabulated astronomical tide prevision (Instituto Hi-drográfico, http://www.hidrografico.pt //dadosonline/mares/) tocalculate relative time of submersion of the sampling locations.Data on elevation and time of successive slack waters during2002 were interpolated to calculate a series of water heights ateach 10 min, using a simple sinusoidal fit, adequate to describemonochromatic astronomical-driven semidiurnal tides. Thisseries was further processed to compute annual absolute andrelative frequencies of residence of the water level at each10 cm elevation interval above datum that were added to yieldsubmersion times as a function of ground elevation.

4. Systematic description

P. limnetis was identified for the first time as Thuramminalimnetis in the surface sediments of Wallace Basin salt marsh(Nova Scotia, Canada) by Scott and Medioli (1980).

Order FORAMINIFERIDA Eichwald, 1830.Suborder TEXTULARIINA Delage and Hérouard, 1896.Superfamily ASTRORHIZACEA Brady, 1881.Family PSAMMOSPHAERIDAE Haeckel, 1894.Subfamily THURAMMININAE Miklukho-Maklay, 1963.Genus Pseudothurammina Scott, Medioli and Williamson,

1981.P. limnetis (Scott and Medioli, 1980).Plate 1, Figs. 1–6.1980. Thurammina? limnetis - Scott and Medioli, pp. 43, Pl.

2, Figs. 1–3.1981. P. limnetis - Scott et al., pp. 126.

Fig. 1. A. Location of study area in Portugal. B. Minho estuary and Coura tributary. Dark gray and dashed areas indicate tidal marsh. Sampling profiles: PR – PedrasRuivas, CP – railway bridge and PIC – Pinelas.Fig. 1. A. Plan de situation. B. Localisation des zones marécageuses dans l’estuaire du Minho et de l’afluent Coura. Zones grises et tiretées. Localisation des profilsd’échantillonnage PR – Pedras Ruivas, CP – pont des chemins de fer et PIC – Pinelas.

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Description: Test free or attached, corresponding to a singlesubglobular chamber, with a variable number of irregular shorttubular protuberances; apertures at the end of this protuber-ances are circular in shape; wall agglutinated, flexible and thin,showing a surface moderately rough, usually white; the attach-ment area is free of grains, where the inner organic layer can beseen in living specimens, but that rapidly disintegrates afterdeath.

Remarks: Our specimens are very similar to those figuredby Scott and Medioli (1980) except that they never presentmore than two tubular protuberances and are mostly attachedto vegetation or plant debris.

5. Results

5.1. Environmental parameters

Synoptic measurements of salinity, temperature and pH ob-tained during low waters along the three profiles are presentedin Table 1.

The salinity of the Pedras Ruivas transect (PR), yielded0.3‰ in the infratidal domain (PR1), contrasting with 15.8‰(PR5) to 7.7‰ (PR10) in interstitial water of the marsh; thetemperature presented a low range of variability: 11.8 °C

(PR1), 12.1 °C (PR8) to 10.3 °C (PR6); the pH yielded 5.81at the infratidal (PR1) and ranged between 6.10 (PR5) and 4.03(PR8).

The salinity of CP transect, yielded 4.36‰ at the infratidal(CP1) against 15.4‰ (CP2) to 7.2‰ (CP7); the temperaturealso presented a low range of variability: 11.4 °C (CP1) against12.9 °C (CP4) to 10.9 °C (CP7); the pH yielded 6.35 at theinfratidal (CP1) and ranged between 7.95 (CP5) and 4.50(CP2).

The salinity of Pinelas transect (PIC), yielded 0.1‰ at theinfratidal (PIC1) against 2.9‰ (PIC4) to 1.6‰ (PIC5); thetemperature presented once more a low range of variability:11.9 °C (CP1) against 12.3 °C (PIC5) to 11.2 °C (CP7); thepH yielded 4.33 at the infratidal (PIC1) and ranged between5.65 (PIC5) and 3.65 (PIC4).

5.2. P. limnetis (Scott and Medioli) occurrence

At the Minho/Coura brackish tidal marsh P. limnetis is es-sentially present in well vegetated areas of the IB high marshzone, associated with M. fusca (Brady) and Psammosphaerasp., between 3.00 and 3.50 m above the HZ, where yearly re-lative submersion frequency (submersion time) is less than14% (Fig. 2).

Plate 1. Selected P. limnetis (Scott and Medioli) from Pedras Ruivas (PR) tidal marsh profile. Fig. 1. Apertural view; Figs. 2–6. Most representative ways ofoccurrence. Bar scale = 100 μm.Planche 1. Exemplaires de P. limnetis (Scott et Medioli) sélectionnés sur le profil de Pedras Ruivas (PR). Fig. 1. Vue orale ; Figs. 2–6. Modes d’occurrence les plussignificatifs. Échelle = 100 μm.

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Fig. 2. Zonation of tidal marsh living foraminifera assemblages (Moreno et al., 2005).Fig. 2. Répartition des assemblages de foraminifères vivants sur le marécage (Moreno et al., 2005).

Table 1Salinity, temperature and pH of interstitial water and elevation of sites, relative to the HZSalinité, température et pH de l’eau interstitielle ; altimétrie des points d’échantillonnage par rapport au Zéro Hydrographique (HZ)

J. Moreno et al. / Revue de micropaléontologie 49 (2006) 45–53 49

However P. limnetis became dominant in IA2 highest highmarsh zone, 3.50 m above the HZ – (submersion time less than1%), being followed by H. manilaensis Andersen and Haplo-phragmoides sp. (Fig. 2). These occurrences are very consis-tent at Pedras Ruivas (PR) and railway bridge (CP) transects(Figs. 3A and 3B); nevertheless P. limnetis, shows a residualpresence at Pinelas (PIC), the inner Coura tidal marsh transect(Fig. 3C).

In dead assemblages, P. limnetis shows a general tendencyof a lower proportion and all the values tend to be close to eachother along high marsh zone IA; for instance, at PR8 its pre-sence is reduced from 46.8% (living) to 12.5% (dead) and atCP7 reduces from 43.7% (living) to 27.7% (dead) (Appendices1 and 2).

In our samples P. limnetis occurs mostly attached to vegeta-tion or plant debris, including inside leaves and small branches.

Fig. 3A. Living percentages of P. limnetis across Pedras Ruivas (PR) tidal marsh transect, in April and October (Moreno et al., 2005).Fig. 3A. Pourcentages des formes vivantes de P. limnetis sur le profil de Pedras Ruivas (PR), au mois d’Avril et d’Octobre (Moreno et al., 2005).

Fig. 3B. Living percentages of P. limnetis across railway bridge (CP) tidal marsh transect, in April and October (Moreno et al., 2005).Fig. 3B. Pourcentages des formes vivantes de P. limnetis sur le profil du pont des chemins de fer (CP), au mois d’Avril et d’Octobre (Moreno et al., 2005).

Fig. 3C. Living percentages of P. limnetis across Pinelas (PIC) tidal marsh transect, in April and October (Moreno et al., 2005).Fig. 3C. Pourcentages des formes vivantes de P. limnetis sur le profil de Pinelas (PIC), au mois d’Avril et d’Octobre (Moreno et al., 2005).

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Often each one of this small fragments presents several speci-mens of attached living P. limnetis (Plate 1).

6. Discussion

In the Minho/Coura tidal marsh P. limnetis presents severaldifferences comparing with its referred distribution. This speciesis usually recorded in low marsh (Scott and Leckie, 1990); in thetransition from low to high marsh (Scott and Medioli, 1980;Scott and Leckie, 1990; De Rijk, 1995) or in the lower highmarsh subzone IB (Debenay et al., 2000). In our studyP. limnetis occurs above high marsh subzone IB and becamedominant at high marsh subzone IA2, between mean high waterspring tide and highest high water levels from ~3.50 to 3.94 mabove HZ. The closer distribution to our zonation is shown byGehrels (1994) at Wells Little River Marsh (Coast of Maine,USA) but in his case Jadammina macrescens (Brady) is thedominant species showing a few living P. limnetis.

The occurrence of P. limnetis is mostly referred in saltmarshes where salinity ranges between 10‰ and 30‰ (Scottand Leckie, 1990; De Rijk, 1995; Debenay et al., 2000; Hay-ward and Hollis, 1994; Sen Gupta, 2002), with an optimum forits presence between 20‰ and 30‰ suggested by Scott andMedioli (1980). Otherwise De Rijk (1995) refers a little corre-lation between this species and salinity. In the present study ofbrackish tidal marsh of Minho/Coura estuary P. limnetis is veryabundant, even dominant, under salinity values of interstitialwater between 8‰ and 14‰ at PR and CP transects (Table 1).At Pinelas transect, where salinity values are much lower, ran-ging between 2‰ and 7‰, P. limnetis as a low contribution tothe assemblage.

Some different ecological preferences, like submersion timelower than 14% and low salinity of pore-water sediment, seemsto be pointed out by the dominance of P. limnetis in the Minho/Coura high marsh zone.

Another remarkable difference in our study concerns theabundance of living P. limnetis which often reaches around45%, or more (68.8% at PR8), of the assemblage at high marshsubzone IA2, contrasting with the low abundances reported bythe authors cited above. Considering that P. limnetis mostlyoccurs attached to vegetation or plant debris, including insideleaves and small branches and that each one of this structurescan support several living specimens, the use of a 500 μm sieveto eliminate the coarser fraction of sediment can be responsiblefor the lost of the most part of the individuals from this species.Drying the residue can also affect the preservation of this spe-cies, attending to the fragility of P. limnetis and of its marshplants support.

7. Conclusions

P. limnetis has an important contribution to the characteriza-tion of tidal marshes, namely IB and IA2 subzones of highmarsh from brackish environments between 3 m above theHZ and the upper limit of tidal marsh. When a good preserva-tion of tests is achieved in the Holocene sediments, this distri-bution of P. limnetis can also give an important contribution tothe studies of sea-level changes in this region.

The presence of P. limnetis probably has an optimum undersalinity values of interstitial waters ranging between 8‰ and14‰.

Its unusual dominance in this environment, under a lowtime of submersion (high marsh) and low salinity, seems toreveal new ecological data of P. limnetis.

The attaching to marsh vegetation and plant debris is anessential way of occurrence of P. limnetis.

The low abundance or absence of this species from coastalzones around the world may be probably associated with en-vironmental factors, or with the processing of sediment sam-ples that do not consider the specificity of P. limnetis way ofoccurrence, found in Minho/Coura tidal marsh. In fact the re-cord of P. limnetis can be markedly influenced by the kind oftreatment of the marsh samples. The complete analysis of resi-due above 63 μm, including a careful observation of vegetationfragments and plant debris (without elimination ofthe > 500 μm fraction), always under wet conditions, isstrongly suggested.

The dominance of P. limnetis in the Minho/Coura highmarsh zone seems to be the first European occurrence nowbeing recorded. Its distribution in Minho estuary can alsosuggest that species can not be universally used as indicatorof vertical elevation (Debenay and Guillou, 2002) becausecomposition, elevation and vertical range of assemblagezones are variable within and between sites (Edwards et al.,2004).

Acknowledgements

This paper is a contribution of Envichanges project, fundedby FCT (PDCTM/PP/MAR/15251/99). The authors are grate-ful to Dr. João Cascalho (MNHN-UL) and to Celso Pinto forassistance during field work.

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Appendix A

Living P. limnetis (Scott and Medioli) absolute frequency along the three transects.Abondances absolues des individus vivants de Pseudothurammina limnetis (Scott et Medioli) sur les trois profils.

Appendix B

Dead P. limnetis (Scott and Medioli) absolute frequency along the three transects.Abondances absolues des individus morts de Pseudothurammina limnetis (Scott et Medioli) sur les trois profils.

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