Cartographie et état de la limite inferieure de l’herbier de Posidonia oceanica dans les Alpes-maritimes (France) – Campagne Poseïdon 1976 —

Meinesz, A.; Laurent, R.

doi:10.1515/botm.1978.21.8.513

Cited by 46 publications

(31 citation statements)

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“…Most of the heavy development has occurred in the neighborhood of poorly treated wastewater discharges, often upon decaying beds of P. oceanica (Chisholm et al 1997). P. oceanica has regressed in the northern Mediterranean for the last several decades, ostensibly as a result of pollution and coastal development (e.g., Pérès and Picard 1975;Meinesz and Laurent 1978;Falconetti and Meinesz 1989).…”

Section: Discussionmentioning

confidence: 99%

Stimulation of nitrogen fixation in refractory organic sediments by Caulerpa taxifolia(Chlorophyta)

Chisholm

Moulin

2003

Limnology & Oceanography

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Estimates of N 2 fixation by substrata associated with the rhizophytic alga Caulerpa taxifolia were obtained using the acetylene reduction method. On average, growth of C. taxifolia enhanced rates of acetylene reduction in underlying dead sea grass sediments by a factor of 28, although the degree of enhancement was variable. The average rate of ethylene production was 3.96 nmol cm Ϫ3 h Ϫ1 (range ϭ 2.5-6.2 nmol cm Ϫ3 h Ϫ1 ). There was no apparent stimulation of N 2 fixation in substrata collected close to a wastewater outlet. C. taxifolia appears to enhance N 2 fixation by releasing photosynthetic product into the rhizosphere, mimicking the behavior of saltwater vascular plants. The excreted organic C activates the fermenting bacterial community, which in turn makes substrates available to the sulfate reducers. The associated microbial reactions create strong reducing conditions that favor N 2 fixation, of which many sulfate reducers are capable. Nitrogen fixation can serve to reduce the N deficit that inhibits bacterial decomposition of refractory sea grass waste, thereby enhancing organic matter turnover and nutrient supply to the alga's rhizoids. This process likely assists C. taxifolia to proliferate upon refractory organic sediments in low-nutrient seawater.The green alga Caulerpa produces a pseudo-root system that functions to anchor the plant, as well as to take up nutrients (Williams 1984; Chisholm et al. 1996). Nutrient uptake from the substratum potentially enables the alga to proliferate in oligotrophic seawater on eutrophicated substrata (Chisholm et al. 1996). Biogeochemical studies in the northwest Mediterranean have indicated a link between the proliferation of Caulerpa taxifolia Vahl. C. (Agardh) and the availability of nutrients discharged in urban wastewater or resulting from the decay of sea grass vegetation (Chisholm et al. 1997). Association with wastewater pollution is not surprising because algal production has often been shown to increase with nutrient discharge. Association with decomposition of sea grass vegetation is less straightforward because sea grass tissues generally have low N content relative to C, which limits bacterial nutrient turnover (Goldman et al. 1987;Paerl 1990).Field and laboratory observations demonstrate that sediments containing dead sea grass matter frequently turn black in color after penetration by the rhizoids of C. taxifolia (Fig. 1). The black coloration is due to bacterial reduction of sulfate to sulfide, indicating strong reducing conditions that favor N 2 fixation. Nitrogen fixation could alleviate barriers to organic decomposition (Paerl 1990;Tibbles et al. 1994), thus enhancing nutrient supply to the alga's rhizoids. C. taxifolia 1 To whom correspondence should be addressed. Present address: 149 Eyre Street, North Ward, Queensland 4810, Australia (j.chisholm@libertysurf.fr). AcknowledgmentsWe thank D. Lerudulier for use of the gas chromatograph at the University of Nice-Sophia Antipolis and J.-C. Trinchant for help with the analytical measurement...

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Section: Discussionmentioning

confidence: 99%

Stimulation of nitrogen fixation in refractory organic sediments by Caulerpa taxifolia(Chlorophyta)

Chisholm

Moulin

2003

Limnology & Oceanography

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“…The precision of the geographical localization of the limit varies according to the method used (from 1 to about 10 m). It is noticeable that 73% of the laboratories take into account the type of lower depth limit found, as defined by Meinesz and Laurent (1978) and Boudouresque and Meinesz (1982). Fifty-five percent of the laboratories complement their observations by taking measurements of the meadow, and 86% by measurements of the sediment ahead of this limit.…”

Section: Resultsmentioning

confidence: 99%

“…The scales used are those defined by Pergent et al (1995) (57%) and Meinesz and Laurent (1978) (29%).…”

Section: Discussionmentioning

confidence: 99%

“…Concerning the position of the lower depth limit, only the scale of Pergent et al (1995) correlates the mean depth to the clarity of water. The other scales used concern the type of limits (Meinesz and Laurent, 1978;Boudouresque and Meinesz, 1982). These two types of scales should be used in tandem because they provide information about different environmental conditions.…”

Section: Discussionmentioning

confidence: 99%

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Descriptors of Posidonia oceanica meadows: Use and application

Pergent-Martinì

Leoni

Pasqualini

et al. 2005

Ecological Indicators

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161

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The conservation of the coastal marine environment requires the possession of information that enables the global quality of the environment to be evaluated reliably and relatively quickly. The use of biological indicators is often an appropriate method. Seagrasses in general, and Posidonia oceanica meadows in particular, are considered to be appropriate for biomonitoring because of their wide distribution, reasonable size, sedentary habit, easy collection and abundance and sensitivity to modifications of littoral zone. Reasoned management, on the scale of the whole Mediterranean basin, requires standardized methods of study, to be applied by both researchers and administrators, enabling comparable results to be obtained. This paper synthesises the existing methods applied to monitor P. oceanica meadows, identifies the most suitable techniques and suggests future research directions. From the results of a questionnaire, distributed to all the identified laboratories working on this topic, a list of the most commonly used descriptors was drawn up, together with the related research techniques (e.g. standardization, interest and limits, valuation of the results). It seems that the techniques used to study meadows are rather similar, but rarely identical, even though the various teams often refer to previously published works. This paper shows the interest of a practical guide that describes, in a standardized way, the most useful techniques enabling P. oceanica meadows to be used as an environmental descriptor. Indeed, it constitutes the first stage in the process.

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“…Declining seagrass coverage was first monitored at the beginning of the 20th century, when the 'wasting disease' devastated seagrass populations in the NW Atlantic (Short et al 1988). Other marked changes in seagrass coverage have been reported worldwide (Meinesz & Laurent 1978, Kemp et al 1983, Orth & Moore 1983, Cambridge & McComb 1984, Short et al 1987, Sanchez Lizaso et al 1990, Pulich & White 1991 with the implications of habitat loss discussed widely therein.…”

Section: Introductionmentioning

confidence: 91%

Predicting population decline:seagrass demographics and the reconstructive technique

Jensen¹,

Robbins²,

Bell³

1996

Mar. Ecol. Prog. Ser.

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ABSTRACT. Seagrasses constitute an important component in the nearshore coastal ecosystem, and the declining seagrass habitat is well documented in some areas. A reconstructive technique developed to discern seagrass population demographics with a single sampling event previously predicted the decline of Thalassia testudinurn populations in Florida Bay. Florida, USA. The results of that model were tested by comparing predicted and actual populations in 1994. A predicted shoot density decline of 49% was not recorded in field populations; instead the population had increased by 51%. We explored 2 potential reasons for the inaccuracy: sampling design, to account for spatial and temporal variability; and data collection procedures that create a demographic bias in the model input. We found that both factors alter the demographic statistics, which modify the model's outcome. Limitations of the model are discussed with respect to its assumptions and interpretation of results.

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Cartographie et état de la limite inferieure de l’herbier de Posidonia oceanica dans les Alpes-maritimes (France) – Campagne Poseïdon 1976 —

Cited by 46 publications

References 1 publication

Stimulation of nitrogen fixation in refractory organic sediments by Caulerpa taxifolia(Chlorophyta)

Stimulation of nitrogen fixation in refractory organic sediments by Caulerpa taxifolia(Chlorophyta)

Descriptors of Posidonia oceanica meadows: Use and application

Predicting population decline:seagrass demographics and the reconstructive technique

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