Deep water vegetations of Lobophora variegata (Phaeophyceae) in the coral reef of Curaçao:population dynamics in relation to mass mortality of the sea urchin Diadema antillarum

Cover, blade size, growth rate, longevity and reproduction of the foliose brown macroalga Lobophora variegata (Lamouroux) Womersley were recorded in 2 deep-water populations (25 to 35 m) in the coral reef of Curaqao (Netherlands Antilles) for over a year. No seasonal effects were observed. Although mean cover was relatively constant, turnover rates were very high with half-life of blades being, on average, only ca 20d. During ths study the herbivorous sea urchin Diadema antillam Philippi suffered mass mortality. The effect of the disappearance of this grazer was evident at one of the 2 locations, where D. antillam densities had been highest, L. vanegata cover lowest and blade sizes smallest. At this station, following D. antillarum mortality, cover and blade size increased significantly and reached a new equilibrium after ca 6 mo

Transplant experiments with two morphological growth forms of Lobophora variegata (Phaeophyceae)

At Curaçao (Netherlands Antilles), 2 spatially separated populations of the brown alga Lobophora variegata (Lamouroux) Womersley occur. Deep-water populations consist of golden-brown, erect blades, ca 86 km thick, attached to the substratum only by their crustose basal parts. Intertidal populations consist of dark-brown crusts composed of compact blades, ca 136 pm thick, which strongly adhere to the substratum. The persistence of both growth forms was tested in experiments, in which intertidal and deep-water plants were transplanted to depths of 1 m, 12 m and 30 m for 3 or 6.5mo. Although differences between growth forms decreased after transplantation, significant Mferences persisted, suggesting the existence of 2 distinct populations, kept separate

The Natural Variation of a Neural Code

The way information is represented by sequences of action potentials of spiking neurons is determined by the input each neuron receives, but also by its biophysics, and the specifics of the circuit in which it is embedded. Even the “code” of identified neurons can vary considerably from individual to individual. Here we compared the neural codes of the identified H1 neuron in the visual systems of two families of flies, blow flies and flesh flies, and explored the effect of the sensory environment that the flies were exposed to during development on the H1 code. We found that the two families differed considerably in the temporal structure of the code, its content and energetic efficiency, as well as the temporal delay of neural response. The differences in the environmental conditions during the flies' development had no significant effect. Our results may thus reflect an instance of a family-specific design of the neural code. They may also suggest that individual variability in information processing by this specific neuron, in terms of both form and content, is regulated genetically

Effect of sampling effort and sampling frequency on the composition of the planktonic crustacean assemblage: a case study of the river Danube

Although numerous studies have focused on the seasonal dynamics of riverine zooplankton, little is known about its short-term variation. In order to examine the effects of sampling frequency and sampling effort, microcrustacean samples were collected at daily intervals between 13 June and 21 July of 2007 in a parapotamal side arm of the river Danube, Hungary. Samples were also taken at biweekly intervals from November 2006 to May 2008. After presenting the community dynamics, the effect of sampling effort was evaluated with two different methods; the minimal sample size was also estimated. We introduced a single index (potential dynamic information loss; to determine the potential loss of information when sampling frequency is reduced. The formula was calculated for the total abundance, densities of the dominant taxa, adult/larva ratios of copepods and for two different diversity measures. Results suggest that abundances may experience notable fluctuations even within 1 week, as do diversities and adult/larva ratios

Information Transmission in Cercal Giant Interneurons Is Unaffected by Axonal Conduction Noise

What are the fundamental constraints on the precision and accuracy with which nervous systems can process information? One constraint must reflect the intrinsic “noisiness” of the mechanisms that transmit information between nerve cells. Most neurons transmit information through the probabilistic generation and propagation of spikes along axons, and recent modeling studies suggest that noise from spike propagation might pose a significant constraint on the rate at which information could be transmitted between neurons. However, the magnitude and functional significance of this noise source in actual cells remains poorly understood. We measured variability in conduction time along the axons of identified neurons in the cercal sensory system of the cricket Acheta domesticus, and used information theory to calculate the effects of this variability on sensory coding. We found that the variability in spike propagation speed is not large enough to constrain the accuracy of neural encoding in this system

Ecosystem knowledge for the policy concerning chemical substances: Literature survey and proposal for a research programme

Dit rapport komt voort uit de vaststelling dat de huidige beoordelingssystemen voor stoffen te weinig rekening houden met de samenstelling en het functioneren van de te beschermen ecosystemen en heeft tot doel a) een overzicht te geven van ecosysteemkenmerken die gebruikt kunnen worden voor het vaststellen van de effecten van stoffen op ecosystemen en b) te komen tot een voorstel voor een onderzoeksprogramma dat gericht is enerzijds op het beschikbaar maken van systeem-ecologische kennis voor de ontwikkeling van criteria ten behoeve van het stoffenbeleid en anderzijds op het op korte termijn kwantificeren van het ecologisch rendement van het stoffenbeleid. Als eerste stap hiertoe is er een literatuurverkenning uitgevoerd door RIVM en RIN en is er aanzet gegeven voor een onderzoeksprogramma (Deel I) Literatuurstudie en onderzoeksvoorstel zijn vervolgens ter discussie gesteld tijdens een studiedag onder voorzitterschap van de RMNO. Het verslag van deze bijeenkomst is bijgevoegd (Deel II). Op grond van de resultaten van deze workshop is een voorstel geformuleerd voor een programma van onderzoek waarin de nadruk wordt gelegd op een koppeling tussen enerzijds het stoffenbeleid ten aanzien van ecosystemen en anderzijds stofgerichte analyses van ecosystemen (Deel III). Dit voorstel, tenslotte, is besproken door vertegenwoordigers van BEON, NMF, NRLO, RIN, RIVM, Rijkswaterstaat/DGW, VROM/SR en VU, onder voorzitterschap van de RMNO. Het verslag van dit overleg is bijgevoegd (Deel IV). Het rapport is aangeboden aan de RMNO met het verzoek over het voorgestelde onderzoeksprogramma te adviseren. Een advies wordt in het eerste kwartaal van 1990 verwacht.Abstract not availableDGM/SR Hekstra G

Population dynamics of a tropical intertidal and deep-water population of Sargassum polyceratium (Phaeophyceae)

Plant numbers, plant size, number and length of primary laterals, reproduction, growth rates and turnover rates were recorded for an intertidal and a deep-water (30 m depth) population of Sargassum polyceratium Montagne at Curaçao, Netherlands Antilles, for 1.5 years. Both populations showed distinct seasonal variations in biomass and growth rates, with maxima in late summer-early autumn and minima in winter. The observed fluctuations were probably amplified by a severe autumn storm that significantly reduced biomass in both populations at the end of the first year. The main differences between the populations were a more compact growth form and higher growth rates and turnover rates of primary laterals in the intertidal population

Deep water populations of Lobophora variegata (Phaeophyceae) on the coral reef of Curacao: influence of grazing and dispersal on distribution patterns

On the coral reef of Curaçao (Netherlands Antilles) the foliose brown macroalga Lobophora variegata (Lamouroux) Womersley displays a discontinuous depth distribution, with distinct belts in the deep algal community (below 30 m) and in the eulittoral community. This distribution pattern is attributed to high grazing pressure in the areas devoid of L. variegata, where the alga will sumve and grow year-long if protected from sea urchins and herbivorous fish. There was a distinct gradient in grazing pressure decreasing with depth. After the occurrence of mass mortality in the sea urchin Diadema antillarum Philippi, which took place in the course of this study, overall grazing pressure on the alga was reduced. However, this 'natural experiment' did not result in a very marked increase of the depth range of L. variegata, probably because the dispersal range of propagules is very limited. Recruitment only occurred within meters of the nearest L. variegata stand

The development of plankton communities in the River Rhine: a comparison of two sampling strategies

Abstract niet beschikbaarSince 1987 a fortnightly sampling programme has been carried out at Lobith and Maassluis to record seasonal development of plankton communities in the lower river Rhine. Furthermore, the development of phyto- and zooplankton was recorded in a water parcel during its transport from Bad Honnef, Germany, to the sedimentation areas Ketelmeer, Nieuwe Waterweg and Hollands Diep in the Netherlands. This "Fliessende Welle" - inventory was carried out five times in 1988 (April-August) to discriminate phases of development of plankton communities along the longitudinal axis of the river Rhine. This report composes the results obtained with both sampling strategies and evaluates the representativeness of the stations Lobith and Maassluis for long-term monitoring of planktoncommunities in the lower river Rhine. A summary (Stations, sampling methods, parameters and results) of the "Fliessende Welle" - inventory is included under cover.RIV