Lipid and fatty acid composition of diatoms revisited: rapid wound-activated change of food quality parameters influences herbivorous copepod reproductive success.

Lipid and fatty acid composition are considered to be key parameters that determine the nutritive quality of phytoplankton diets for zooplanktonic herbivores. The fitness, reproduction and physiology of the grazers are influenced by these factors. The trophic transfer of lipids and fatty acids from algal cells has been typically studied by using simple extraction and quantification approaches, which, as we argue here, do not reflect the actual situation in the plankton.

Survey of the chemical defence potential of diatoms: screening of fifty one species for alpha,beta,gamma,delta-unsaturated aldehydes.

In recent years a negative influence of diatom-derived alpha,beta,gamma,delta-unsaturated aldehydes (PUA) on the reproductive success of copepods and invertebrates has been suggested. Since adverse chemical properties of diatoms would question the traditional view of the marine food web, this defense mechanism has been investigated in detail, but the PUA-release by test organisms has only been determined in a few cases. The observed effects were nevertheless frequently discussed from a general point of view often leading to contradictory conclusions.

Determination and quantification of alpha,beta,gamma,delta-unsaturated aldehydes as pentafluorobenzyl-oxime derivates in diatom cultures and natural phytoplankton populations: application in marine field studies.

Reactive alpha,beta,gamma,delta-unsaturated aldehydes and oxo-acids produced by marine diatoms upon cell damage interfere negatively with the reproduction success of their grazers. A simple, sensitive and specific method based on gas-chromatography coupled to mass spectrometry (EI or CI/EC) was developed for the quantification of these deleterious substances in laboratory diatom cultures and in natural phytoplankton populations. For aldehyde quantification, diatom containing samples are damaged in the presence of O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride (PFBHA.

Cytotoxicity of diatom-derived oxylipins in organisms belonging to different phyla.

The cytotoxicity of several saturated and unsaturated marine diatom-derived aldehydes and an oxo-acid have been screened in vitro and in vivo against different organisms, such as bacteria, algae, fungi, echinoderms, molluscs and crustaceans. Conjugated unsaturated aldehydes like 2E,4E-decadienal, 2E,4E-octadienal, 5E,7E-9-oxo-nonadienoic acid and 2E-decenal were active against bacteria and fungi and showed weak algicidal activity. By contrast, the saturated aldehyde decanal and the non-conjugated aldehyde 4Z-decenal had either low or no significant biological activity.

Aldehyde suppression of copepod recruitment in blooms of a ubiquitous planktonic diatom.

The growth cycle in nutrient-rich, aquatic environments starts with a diatom bloom that ends in mass sinking of ungrazed cells and phytodetritus. The low grazing pressure on these blooms has been attributed to the inability of overwintering copepod populations to track them temporally. We tested an alternative explanation: that dominant diatom species impair the reproductive success of their grazers.

Evidence for a direct link between stress and immunity in the mollusc Haliotis tuberculata.

Stress is thought to cause increased disease outbreaks and mortality in a number of invertebrates but currently very little information is available on mechanisms linking physiological states of stress and reduced disease resistance in these organisms. In the present study, we examined the possibility that stress alters immune functions, the principal line of defense against pathogens, in a molluscan model, the abalone Haliotis turbeculata. Immune parameters were investigated in abalones subjected to a 15 min mechanical disturbance which, as indicated by noradrenaline and dopamine hemolymphatic levels, resulted in a transient state of physiological stress.

P35-sensitive caspases, MAP kinases and Rho modulate beta-adrenergic induction of apoptosis in mollusc immune cells.

Apoptosis is an important mechanism for the preservation of a healthy and balanced immune system in vertebrates. Little is known, however, about how apoptotic processes regulate invertebrate immune defenses. In the present study, we show that noradrenaline, a catecholamine produced by the neuroendocrine system and by immune cells in molluscs, is able to induce apoptosis of oyster Crassostrea gigas hemocytes.

Stress-induced immune changes in the oyster Crassostrea gigas.

Information concerning the effect of stress on invertebrate immune functions are scarce. The present study investigated the consequences of a 15-min mechanical disturbance on immune parameters in oysters Crassostrea gigas. As indicated by noradrenaline and dopamine measurements, the mechanical disturbance caused a transient state of stress in oysters.