Reproduction, growth and chemical composition of Ulva sp. in response to different light treatments

In this study, Ulva sp. collected on Helgoland were subjected to one of four light treatments consisting of different light colour and daylength: 24h blue light, 24h white light, 16h blue light and 16h white light. All algae were kept in a temperature controlled dark room on Helgoland at 15 °C. Over the course of 44 days growth rate, photosynthesis (via oxygen spot optodes) and reproductive area were measured. At the end of the experiment the antioxidant activity of extracts from the algae was measured using the ABTS radical decolourization assay. In addition chlorophyll and carotenoid concentration were analysed for all treatments. The aim was to identify conditions with minimal reproduction and maximal growth and antioxidant activity. These parameters were of interested for potential applications of Ulva in the development of alternative packaging material. White light treatments had higher growth rates than blue light (12.6 and 10.6 % d-1 vs. 4.17 and 2.69 % d-1). However this is likely due to differences in light intensity rather than colour. Similarly, reproduction only occurred in white light treatments and irrespective of daylength. Since the algae grown in white light also were biggest, this trend is also not necessarily attributable to light colour and more likely a consequence of size. Antioxidant activity was highest in algae grown under 24h-BL. While this is also at least partially a consequence of light intensity, light colour also seems to play a role. Pigment content followed a similar trend with treatments under low light intensity (blue light) containing more pigments than those under high intensity (white) light. The 24h white light treatment was an exception to this and did not differ significantly from treatments under blue light. The implication of light colour and intensity, both daily and short term, for algal physiology in general and algae in this study in particular are reviewed. Potential strategies to manipulate antioxidants in the context of commercial applications such as biodegradable, sustainable packaging are discussed

Coarse particulate organic matter in the interstitial zone of three French headwater streams

Headwater woodland streams are primarily heterotrophic: they receive substantial inputs of organic matter from the riparian vegetation, while autochthonous primary production is generally low. A substantial part of leaf litter entering running waters may be buried in the streambed because of flooding and sediment movement. Although the general significance of the hyporheic zone for stream metabolism has been reported early, organic matter storage within the sediment of streams has received less attention, with most studies only quantifying accumulations at the streambed surface and ignoring other stream compartments. In the present study, the amounts of three fractions of coarse particulate organic matter (CPOM; > 16, 4–16 and 1–4 mm) were determined in late autumn and early spring in the interstitial and benthic zones of three head- water streams of the Montagne Noire (South-Western France) differing in their substratum grain size. Our findings demonstrated that the total CPOM content in the interstitial zone can be much (up to one order of magnitude) higher than at the sediment surface. The sandy bottomed stream exhibited a higher amount of CPOM (whatever the size fraction) than the two other streams, suggesting that the sediment particle size may be a major determinant of CPOM storage. Given the large amount of organic matter stored in the interstitial zone, this compartment may play an important role for the carbon turnover and associated trophic dynamics in the stream ecosystem

Optimisation of at-sea culture and harvest conditions for cultivated Macrocystis pyrifera: yield, biofouling and biochemical composition of cultured biomass

Seaweed cultivation is gaining interest world-wide for both food and non-food applications. Global seaweed aquaculture production currently exceeds 32 Mt WW per annum but is dominated (86% of total) by Asian countries. To meet future demand for seaweed products, regions beyond Asia with aquaculture production potential are being explored. The goal of this study was to assess the suitability of the native kelp Macrocystis pyrifera (Phaeophyceae, Laminariales), for aquaculture in Tasmania, south-eastern Australia. M. pyrifera was cultivated on seeded twine on loops (1 – 5 m depth) along 100-m longlines at two sites (Okehampton Bay and Great Taylor Bay) from April-November 2020. Temporal and spatial variability in (1) yield (kg m-1, WW), (2) biofouling (% coverage), and (3) biochemical composition (including proximate composition, fatty acids, dietary minerals, heavy metal profiling, C, N, H, S concentrations and C:N ratio, antioxidants (phenolic compounds), and pigments (Chl-a, Chl-c, fucoxanthin)) was compared amongst the two cultivation sites, at two depths (1 and 5 m) from harvests between July – November 2020. Yield (kg m-1, WW) did not significantly change across harvest times, but was greater at a depth of 1 m compared to 5 m. Biofouling on the kelp blades increased significantly in early spring (September). The biochemical composition of the cultured biomass varied over time, between sites and with depth for most of the compounds analysed. Higher lipid, protein and ash content was reported for cultures cultivated at Okehampton Bay compared to Great Taylor Bay and at 5 m compared to 1 m depth, and levels of these macronutrients decreased during the harvest period. The iodine content was slightly above the tolerable content for dried seaweed products in Australia and New Zealand. The combined results of yield, biofouling, and biochemical composition suggest that, for an April deployment at the sites investigated, M. pyrifera should be harvested in July-August (mid to late winter) to optimise yield and quality of the cultured kelp biomass. These findings provide a better understanding of the variation in growth and quality of cultivated M. pyrifera biomass in the region, and inform future management and development of kelp aquaculture in south-eastern Australia and in a global context

Diel changes in stream benthos density on stones and artificial substrates

Diel changes in stream benthos density were studied by comparing faunal densities on naturally occurring stones collected at noon and at midnight and on artificial substrates (bricks) collected at 2 hr intervals for 24 hr. Over all dates and all rivers, on stones, nighttime densities were higher in 37 cases, lower in 35 cases and unchanged in three cases. The magnitude of nocturnal density increases (expressed as a proportion of daytime density) ranged between 0.03 and 1.08 and the magnitude of nocturnal density decreases ranged between 0.01 and 0.81. Diel density changes on bricks generally were variable and not synchronized with changes in light intensity, but in most cases (60%) densities were greater at night.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42906/1/10750_2004_Article_BF00018889.pd

ZUR KENNTNIS DER WASSERMILBENFAUNA DER SUEDLICHEN HOCHVOGESEN (Hydrachnellae, Acari)

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