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# Diatom from Majerda river and Tunis lagoon, Northern Tunisia

Leila Ben Khelifa, Sahima Hamlaoui

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## To cite this version:

Leila Ben Khelifa, Sahima Hamlaoui. Diatom from Majerda river and Tunis lagoon, Northern Tunisia. 12th Central European Diatom Meeting, Mar 2019, Belvaux, Luxembourg. hal-03947972

HAL Id: hal-03947972

https://hal.science/hal-03947972

Submitted on 19 Jan 2023

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# DIATOM FROM MAJERDA RIVER AND TUNIS LAGOON, NORTHERN TUNISIA

## CENTRAL EUROPEAN DIATOM MEETING

### L. BEN KHELIFA¹ & S. HAMLAOUI¹

¹UMR 7245 CNRS/MNHN - Équipe Cyanobactéries, Cyanotoxines et Environnement
12 rue Buffon, CP39
75231 PARIS Cedex 05

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## AREA OF STUDY

<figure><img src="image_5.png" /><figcaption>Alevin of Mullet</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Sampling Epipelic diatom</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Sampling Diatom from Running waters</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Polluted area</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Pumping-Station</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Kalaât El andalous, a construction area</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Bay of Tunis</figcaption></figure>

## AIM OF THE STUDY

1. Using Diatom, Cyanophyceae and other micro flora and fauna to contribute to explain the diminution of the stock of Alevins of *Mugil Cephalus*, *Liza Ramada* and Carp (Mili S. et al., 2016) in the aquaculture Basin of the Majerda River.

2. To distinguish taxa linking with eutrophic polluted area by anthropic effect, and thus to contribute to water management of Majerda River which provides the drinking water for all the big cities of Tunisia; Tunis, Cap-Bon, Sahel et Sfax and the water for the principal agricultural area as Grombalia, Soliman, Cap-Bon, Mornag, Ras Jebel, Ousja and Kalaat El Andalous.

3. To contribute in the study of recent sedimentation in the Gulf of Tunis to prevent urbanisation effect and to understand the paleoenvironmental and paleoclimatical change during the quaternary alternance of glacial-interglacial input from the Majerda river.

4. A modern analogue for the *Cyclotella* spp. earlier referred as *Cyclotella caspia* in fossil african assemblages 'yet it is absent from the modern flora of this region (in Carvallo, L.R. et al., 1995)', is observed. A MEB identification on the frequent small specimens of *Cyclotella sp.ocellata* Pant. would give a taxonomic answer.

5. Two rare *Nitzschia* specie, one marine and one continental are of interest, if similitude in between, we might have an information about eustatic event in that area which would have affected the whole region of the SW Mediterranean Sea.

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(T.El Melki, 2008)

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LIMITE paléogéographique de la Transgression Pliocène en Tunisie Septentrionale (A. Foutane, octobre 1983)

Pliocene Marine deposit in the Majerda in Tébourba Region

<figure><img src="image_14.png" /><figcaption>Tunis lagoon with marine modern diatom</figcaption></figure>

In quaternary wet land of Tunisia this enigmatic form is often observed and some holocene layers are really rich (Tunis Lagoon, sebkha Kelbia, Gabes Gulf, etc., here in Kalaât El Andalous (Site1 Pont Mobile), **in subaerian sample** near the edge of the river, a modern analogue, for me, is obvious and so we have an indication of quaternary paleoenvironment when Diatom are absent

Modern Analogue?

## METHODOLOGY AND PRELIMINARY RESULTS

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1. *Cyanobacteria* (trichome) and microalgae were isolated using a tapered pipette and observed with a ZEISS LM (S.Hamlaoui). In Majerda River we have observed *Phormidium* sp. and *Planktothrix* sp. (Cyanophyceae), *Vaucheria* sp. (Xanthophyceae), *Ceratium hirundinella* (O.F.Müller) Dujardin (Dinophyceae), *Closterium aciculare* T. West (Zygnematophyceae). Some species of *Phormidium* and *Planktothrix* might be toxic (Hamlaoui, perso.com). Toxicity tests must be conducted to affirm that the decrease in the stock of Alevins of *Mugil Cephalus*, *Liza Ramada* and Carp (Mili S. et al., 2016), in the aquaculture Basin of the Majerda River, is due to the proliferation of these cyanobacteria. Thirteen years ago, in Majerda River, Diatom assemblage was rich with *Cyclotella* sp. *ocellata* Pant, probably corresponding to *Cyclotella choctawatcheeana* Prasad, (in Carvalho et al., 1995), in all the major ten sites of the river. In 2019, it is less distributed and often replaced by *Nitzschia acicularis* (Kütz.) W.Smith) which suggest an eutrophic freshwater habitat cf. L.Bertalot et al., 2017. In particular, in the four sites of Kalaât El Andalous, it is absent where eutrophic taxa, in particular *Thalassiosira aff. Weisslogii*, *Gyrosigma* and *Halamphora* are abundant in several sites and mostly near the Kalaât El Andalous 'station de Pompage' and the bay of Tunis.

2. In Tunis Lake 36°49'03"N, 10°14'33"E, around 40 marine species are observed (Ben Khelifa, L., 1989) and more than ten species from the Majerda River are observed with in particular, *Gyrosigma*, *Cocconeis placentula* and *Halamphora* species. Subsurface sediment of two cores (in North lake), show a rapid diagenese of diatom frustules because of the high eutrophication, however other micro-organismes are observed. Some Desmidiaes type *Pleurotaenium* Nägeli (Hamlaoui, perso.com.), suggest hot humid period in the Holocene recent whereas, one enigmatic specie observed may be nowadays near the edge of the Majerda River, suggest an aridification events and /or eustatic change within the quaternary section.

<figure><img src="image_16.png" /><figcaption>*Closterium aciculare* T. West, 1860 (Zygnematophyceae)

*Vaucheria litorea* C.Agardh Xanthophyceae</figcaption></figure>

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## MICROALGAE FROM MAJERDA RIVER

<figure><img src="image_18.png" /><figcaption>**DIATOM FROM MAJERDA RIVER, pH = 8 to 8,5 (Ben Khelifa, 1989)**</figcaption></figure>

Nowdays, IN SIDI SALEM, 36°35'26"N, 9°23'44"E, salinity vary from 0,89 and 2,41g/l Mili et al., 2016, Diatom Assemblage is rich with *Nitzschia cf.acicularis*, *Entomoeneis*, *Cyclotella cf.ocellata*, *Navicula spicula* and *Brachysira aponina*

Eutrophic microalga and microfauna are observed either in Kalaât El Andalous sites near the bay and in Tunis lagoon

**Nitzschia spp. :**
In Majerda River, this specie occur in different shape and size but has always same fibulae and a translucid body

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<figure><img src="image_20.png" /><figcaption>MARINE MODERN DIATOM FROM TUNIS LAKE</figcaption></figure>

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2

*Nitzschia sp* (around L=280µ,B=8 to40µ in Majerda River has a similitude with the marine specie *Nitzschia aff.longissima* (Bréb.) Grun., observed in modern Tunis Lake but has lost its elongate apices

## Cyclotella spp. cf. ocellata Pant

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In 1984 and 1986, in all sites of the Majerda River, *Cyclotella* sp. *ocellata* Pant. was often abundant and in diverse size and spread in different part of the river but never rich the Tunis lagoon. Today, **in 2019**, this specie is less abundant, and seems more homogene in size and is observed frequently only in Sidi Salem site. In sites from Kalaât el Andalous, this taxa is absent.

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Nowdays, in all the other sites of Kalaât El Andalous, near the bay, Eutrophication is important and **Cyclotella sp ocellata** is replaced by *Thalassiosira* and *Gyrosigma*, *Entomoeneis* and *Navicula*. They are observed even in the Tunis lagoon. *Nitzschia* species are present but not the *Nitzschia acicularis* observed in Sidi Salem

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