Leaf dynamics and standing stocks of intertidal Zostera noltii Hornem. and Cymodocea nodosa (Ucria) Ascherson on the Banc d'Arguin (Mauritania)

Abstract

Leaf dynamics and standing stocks of intertidal seagrasses were studied in the Baie d'Aouatif (Parc National du Banc d'Arguin, Mauritania) in April and September 1988 . Standing stocks of Zostera noltii Hornem . suggest a unimodal seasonal curve similar to what is found for populations at higher latitudes . Also, leaf growth rates (0 .03 cm2 cm -2 day -1 on average) were similar to those found at higher latitudes in these months . Variation in leaf loss over tidal depth, time and different locations in the Baie d'Aouatif was larger and more often significant than variation in leaf growth . In general, Z . noltii beds in the Baie d'Aouatif had comparable leaf growth rates and standing stocks . In both months losses were almost always higher than or equal to growth . Variation in leaf loss over time was much higher in the plots that were situated high in the intertidal than in lower plots. This is explained by differences in susceptibility to sloughing, which is presumably higher in periods with low tide around noon for shallow depths .In an experiment using artificial shading nets, in situ leaf growth was affected negatively from 94% shading onwards . This shading was observed to reduce the light intensity reaching the seagrass bed to a level below the reported range of light compensation points for Z . noltii .Cymodocea nodosa (Ucria) Ascherson on average had higher leaf area and relative growth rates than Z. noltii and much lower loss rates, resulting in a positive net increase in September . Standing stocks were also higher than for Z . noltii . A mixed seagrass bed containing the above two species and Halodule wrightii Ascherson had the highest observed total biomass : 335 g M-2 ash-free dry weight . 157

Benthic metabolism in shallow coastal ecosystems of the Banc d’Arguin, Mauritania

“…We measured CR both at night and during the day in opaque enclosures, and our estimates should be close to the daily averages. During our study, seagrass biomasses were similar to those previously reported for the Banc d'Arguin (van Lent et al 1991, Vermaat et al 1993, Honkoop et al 2008, Folmer et al 2012, with similar values in November and January.…”

“…This significant winter production may be related to the dense periphyton cover observed in January, when damaged C. nodosa leaves were observed, which can compensate for less leaf photosynthesis in the winter (Enríquez et al 2004). The high CR in the subtidal areas may be due to the mineralization of organic matter produced locally (Holmer et al 2004) or imported from the intertidal zone, since Z. noltii leaf loss is greater than C. nodosa leaf loss in our study area (Vermaat et al 1993). This leaf loss led to hypoxia at the end of the night in the C. nodosa bed in November and probably during periods when the temperature was relatively high (August -October).…”

“…Therefore, benthic communities are likely the major contributors to organic carbon fluxes (Wolff et al 1993b). The production of benthic communities has already been investigated in this area (De Jong et al 1991, van Lent et al 1991, Vermaat et al 1993, and Hemminga & Nieuwenhuize (1991) estimated that the export of organic material from intertidal seagrass beds is low, since most of senescent leaves are trapped in seagrass beds. Based largely on these data, a first comprehensive overview of the functioning of the Banc d'Arguin ecosystem was established by Wolff et al (1993b).…”

Are epiphytes a significant component of intertidal Zostera noltii beds?

“…Z. noltii is frequently found in intertidal areas where it can be exposed to long periods of emersion and to strong tidal currents. Many studies have been conducted to measure the biomass, the growth and the production of Z. noltii in intertidal areas (Vermaat et al, 1987(Vermaat et al, , 1993Pérez-Lloréns and Niell, 1993;Philippart, 1995a;Auby and Labourg, 1996;Marbà et al, 1996;Vermaat and Verhagen, 1996;Brun et al, 2003). But few authors have attempted to compare Z. noltii biomass with the other components of the seagrass ecosystem (Asmus and Asmus, 1985;2000).…”

Αποκρίσεις των θαλάσσιων αγγειόσπερμων Halophila stipulacea και Cymodocea nodosa στην έκθεση σε νανοσωματίδια αργύρου και διοξειδίου του τιτανίου

“…Το C. nodosa συναντάται επίσης σε ακτές του Ατλαντικού Ωκεανού, από την Πορτογαλία έως τη Σενεγάλη, ενώ είναι κοινό στα Κανάρια Νησιά (den Hartog, 1970, Short et al 2010. Κατανέμεται από τη μεσοπαραλιακή ζώνη μέχρι βάθους 33-35 m (Vermaat et al 1993, Reyes et al 1995, Canals & Ballesteros 1997, Short et al 2010) και μπορεί να βρεθεί σε ποικιλία κινητών υποστρωμάτων, από αδρή άμμο έως λασπώδη υποστρώματα (Peduzzi & Vukonič 1990, Pavón-Salas et al 2000. Αυτό το είδος μπορεί να αποικίσει διαφορετικούς περιβαλλοντικούς τύπους, όπως ανοικτά παράκτια ύδατα, εκβολές και λιμνοθάλασσες και σχηματίζει μονοειδικούς και, μερικές φορές, μικτούς λειμώνες με το Z. noltii (Terrados & Ros 1992, Cancemi et al 2002.…”