The present study was carried out in 2011 with the aims of (1) evaluating the changes in sedimentary distribution that occurred in Nador lagoon seabed (Morocco) after the implementation of the lagoon management plan in 2009; and (2) characterizing its new sedimentary status in 2011. Due to the lack of a baseline, we used the 1992 sedimentary status for comparison. The seabed surface sediment distribution showed a great change between 1992 and 2011. We found the same four sediment facies, which were present in 1992, namely: mud, sandy mud, muddy sand, and fine sand. However, in 2011, mud covered more than 54% of the lagoon seabed surface, mostly located in the middle part of the seabed, whereas in 1992, more than 80% of the lagoon seabed was covered by sandy mud. The sediments' characteristics showed moderately to poorly sorted facies (S0), ranging between platykurtic and leptokurtic (SK) and with various symmetry indices (SG). The organic matter content in sediment has strongly decreased, from values higher than 20% in most areas in 1992 to a mean value of 3.9% in 2011, ranging from 0.2% to 10.4%, thus confirming that the management actions implemented in 2009 were likely effective in reducing the organic pollution.
The objective of the present study undertaken in 2011is to evaluate the status of the benthic macroflora of the Nador lagoon after the management works carried out in 2009 to improve the lagoon environmental quality. Relying on a previous study carried out in 1987, the results of analysis in 2011 showed that the lagoon seabed macroflora recorded a marked decline and an overall change in its distribution and specific composition. The marine Phanerogams, represented by Cymodocea and Zostera, in association with Caulerpa, which were the main vegetationin 1987, were replaced by a macroflora highly dominated by macroalgae (64.3% of the total area), essentially represented by Rhodophyceae (58% of total area).In 2011, the genus Alsidiumwas the main representative in the macroflora(55% of total area),while the genus Caulerpa, and Phanerogamssaw their area of occurrence regress to 25.6% and 18% respectively.
In terms of the nutritional needs, the choice of the appropriate phytoplankton strain is the main criterion during bivalves breeding improvement in captivity. Seven nutritional diets based on tree microalgae species (Chaetoceros calcitrans, Tetraselmis suecica and Pavlova lutheri), and seven feeding rations (0%, 1%, 2%, 3%, 4%, 5% and 6%) were used to assess the nutritional pattern of Ruditapes decussatus during conditioning practices. All regimes have shown the highest ingestion rate at low food availability (1% to 3%) with a leaning to diets based on C. Calcitrans followed by T. suecica and P. lutheri respectively.A significant influence of diets quality on absorption efficiency of phytoplankton was observed for both monospecific and bispecific diets (F = 21.78, p =3.2 10-7 *** and F = 250.09, p= 2.2 10-16 ***respectively). Whereas, low influence of food availability on absorption efficiency among all used rations has been revealed by clams reared under mono, bi and trispecific diets respectively (F = 11,19, p= 1.9 10-7 ***; F = 16,63, p= 1.03 10-9 *** and F = 2.78, p=0.0534ns). Consequently, this study could be handled as a standard protocol for conditioning process in furtherance of yield maximizing and cost minimizing during spat production of bivalves in hatcheries.
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