Microorganisms on macrophyte debris : biodegradation and its implication in the food web

In a Mediterranean seagrass ecosystem (Posidonia oceanica ) around Ischia (Gulf of Naples) an attempt was made to study the fate of Posidonia derived particulate matter in wrack beds around and within the seagrass stands, on the shore and in the water column. Changes in total soluble carbohydrate concentrations from green and brown parts within one leaf vary from 70.7 to 25.7 mg.g-1 dry weight. Minimum values of 0.2 mg.g-1 dry weight consisting mainly of saccharose are detected for brown wrack particles. All other components found in green leaf parts, e.g. fructose, glucose and myo-inositol probably leach rapidly into the water or are transported into the rhizome prior to the loss of the brown leaf region. Only in the rhizome the trisaccharide raffinose was detected in addition to the components found in the leaves. The importance of the brown leaf fraction as a substrate for microheterotrophs is indicated by bacterial densities up to 4 x 104 cells.mm-2. This is correlated with nitrogen and carbon values, showing a decreasing C/N ratio with decreasing particle size, but increasing O2 uptake with maximum values of 10 mg.g-1.h-1 for the particle size fraction of 0.1 - 1 mm. The role of the brown dead Posidonia derived leaf tractions as energy source for consumers is discussed and attempts are made to redefine the terms "debris" and „detritus"

Grazing by mesozooplankton from Kiel Bight, Baltic Sea, on different sized algae and natural seston size fractions

Grazing experiments were conducted with natural mesozooplankton from Kiel Bight, Germany, using radioactive labelled phytoplankton cultures and seston size fractions. The results of experiments using phytoplankton cultures indicated that bivalve veligers performed highest clearance of particles within a size range of 4.7 to 6.3 µm, whereas optimum particle size for copepods was 15 µm. The results of experiments using labelled natural seston size fractions identified bivalve veligers and appendicularians as those responsible for the removal of particles within the smallest size class (<2 µm). Seston size fractions larger than 5 µm were mainly cleared by copepods and nauplii. As particle size increased, the contribution of copepod clearance to total zooplankton clearance within size classes increased from 57% (<5 µm size class) to more than 81% (30 to 100 µm size class). When the nauplii clearance rates were included, the total copepod clearance accounted for 90 to 97.6% of the total volume cleared of particles bigger than 10 µm. Despite low abundances of bivalve veligers and appendicularians in Kiel Bight at the time of the experiment, we calculated that approximately 10 and 8.5%, respectively, of the carbon ingested by total mesozooplankton was due to veliger and appendicularian grazing. The importance of bivalve veligers might be seen in their grazing on seston particles that escape predation by copepods and on the amount of energy that is therefore directed from the water column to the benthos when larvae settle

Can agricultural cultivation methods influence the healthfulness of crops for foods

The aim of the current study was to investigate if there are any health effects of long-term consumption of organically grown crops using a rat model. Crops were retrieved over two years from along-term field trial at three different locations in Denmark, using three different cultivation systems(OA, organic based on livestock manure; OB, organic based on green manure; and C, conventional with mineral fertilizers and pesticides)with two field replicates. The cultivation system had an impact on the nutritional quality, affecting γ-tocopherol, some amino acids, and fatty acid composition. Additionally, the nutritional quality was affected by harvest year and location. However, harvest year and location rather than cultivation system affected the measured health biomarkers. In conclusion, the differences in dietary treatments composed of ingredients from different cultivation systems did not lead to significant differences in the measured health biomarkers, except for a significant difference in plasma IgGl evels

The Contribution of Occult Precipitation to Nutrient Deposition on the West Coast of South Africa

The Strandveld mediterranean-ecosystem of the west coast of South Africa supports floristically diverse vegetation growing on mostly nutrient-poor aeolian sands and extending from the Atlantic Ocean tens of kilometers inland. The cold Benguela current upwelling interacts with warm onshore southerly winds in summer causing coastal fogs in this region. We hypothesized that fog and other forms of occult precipitation contribute moisture and nutrients to the vegetation. We measured occult precipitation over one year along a transect running inland in the direction of the prevailing wind and compared the nutrient concentrations with those in rainwater. Occult deposition rates of P, N, K, Mg, Ca, Na, Al and Fe all decreased with distance from the ocean. Furthermore, ratios of cations to Na were similar to those of seawater, suggesting a marine origin for these. In contrast, N and P ratios in occult precipitation were higher than in seawater. We speculate that this is due to marine foam contributing to occult precipitation. Nutrient loss in leaf litter from dominant shrub species was measured to indicate nutrient demand. We estimated that occult precipitation could meet the demand of the dominant shrubby species for annual N, P, K and Ca. Of these species, those with small leaves intercepted more moisture and nutrients than those with larger leaves and could take up foliar deposits of glycine, NO3-, NH4 + and Li (as tracer for K) through leaf surfaces. We conclude that occult deposition together with rainfall deposition are potentially important nutrient and moisture sources for the Strandveld vegetation that contribute to this vegetation being floristically distinct from neighbouring nutrient-poor Fynbos vegetation

Descriptors of Posidonia oceanica meadows: Use and application

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. (c) 2005 Elsevier Ltd. All rights reserved.Peer reviewe

Succession in a kelp bed ecosystem; clearing of primary substrate by wave-induced kelp sweeping

Observing that wave induced sweeping of the fronds of plants at the edges of kelp patches results in a relatively barren interface between kelp plants and the surrounding animal patches led to the assumption that: a) kelp sweeping could provide protection for macrophytes from grazers; and b) that it could be a mechanism allowing kelp patch expansion. The validity of the hypothesis was supported by quantitative observations on the sweeping capabilities of individual kelp plants and by characteristic species/biomass distributions within the kelp sweeping zone, the kelp patches and the adjacent animal patches. In addition, experimental clearing of the primary substrate within the various areas showed that free space will be completely occupied within 50 days unless kelp sweeping stops the faunal progression. A model describing the mechanisms that bring about successional changes at the edge of a kelp patch and leading to its expansion is proposed