Ultraviolet radiation effects on the behavior and recruitment of larvae from the reef coral Porites astreoides

We tested the rarely considered hypothesis that the ultraviolet portion (UVR, 280–400 nm) of the light spectrum affects patterns of recruitment in reef-building corals. The premise for this hypothesis rests in the fact that biologically relevant intensities of UVR penetrate to considerable depths (>24 m) in the clear waters surrounding many coral reefs, and that reef organisms allocate substantial resources to prevent and repair UVR damage. The ability of larvae spawned by the brown morph of the Caribbean coral, Porites astreoides, to detect and avoid UVR was assessed in petri dishes where one-half of the dish was shielded from UVR and the other exposed. Observations made every 30 min between 10:30 and 13:30 h showed significantly higher densities of larvae swimming in regions shielded from UVR. To determine how this behavior affects settlement patterns, larvae collected from P. astreoides adults at 18 m depth were released into chambers deployed at 17 m depth where they were given a choice of three different light regions in which to settle: PAR (PAR=400–700 nm), PAR+UVAR (UVAR=320–400 nm), and PAR+UVAR+UVBR (UVBR=280–320 nm). At the end of the experiment, greater numbers of P. astreoides larvae had settled in the region of the tube where UVR was reduced than would be expected if dispersion were random. To our knowledge, this is the first demonstration in any reef-building coral species that planula larvae can detect UVR and that it affects their choice of a settlement site. These results indicate that the capacity to detect and avoid habitats with biologically damaging levels of UVR may be one factor contributing to the successful recruitment of coral larvae.     

Subacute chlorpyrifos-induced alterations in serum lipids and some oxidative stress biomarkers in male Wistar rats: beneficial effect of acetyl-L-carnitine

The present study evaluated the beneficial effect of acetyl-L-carnitine (ALC) on subacute chlorpyrifos (CPF)-induced alterations in serum lipid profiles and some biomarkers of oxidative stress in Wistar rats. Twenty-eight adult male rats divided into four groups of seven animals each (group I–IV) were used: I (S/oil) received soya oil (2 ml kg^?1), II (ALC) received ALC (300 mg kg^?1); III (CPF) received CPF (8.5 mg kg^?1 ～ 1/10th LD₅₀); IV (ALC+CPF) was pretreated with ALC (300 mg kg^?1) and then exposed to CPF (8.5 mg kg^?1), 30 min later. The treatment was orally for 28 days duration. Sera obtained from blood samples were evaluated for the levels of triglyceride (TG), total cholesterol (TC), high density lipoprotein-cholesterol (HDL-c), malondialdehyde (MDA), and the activities of superoxide dismutase (SOD) and catalase (CAT). The levels of low density lipoprotein-cholesterol (LDL-c), very low density lipoprotein-cholesterol (VLDL-c), and atherogenic index (AI) were calculated. The result showed that elevated levels of TG, TC, LDL-c, VLDL-c, AI, and MDA, and the decreased levels of HDL-c, CAT, and SOD induced by CPF were modulated by ALC. It was concluded that ALC ameliorated the alterations in serum lipid and oxidative stress induced by CPF exposure in the rats, partly through its antioxidant properties.     

Physiological benefits of feeding in the spring by Lymantria dispar caterpillars on red oak and sugar maple leaves: nutrition versus oxidative stress

The rapid growth of insects that feed on tree leaves in the spring is believed to be due to high nutritional quality. This study tested the hypothesis that both high nutritional quality and low levels of oxidative stress (i.e., toxicological effects) benefit caterpillars that feed in the spring. Fourth-instar larvae of Lymantria dispar (Lepidoptera: Lymantriidae) were used to bioassay the leaves of two contrasting host plants in the spring and summer: red oak (Quercus rubra), a high-quality host, and sugar maple (Acer saccharum), a low-quality host. On spring foliage, the combined effects of rapid consumption rate, efficient nutrient assimilation, and high nutritional quality allowed larvae to grow rapidly and attain larger body mass. Ellagitannins, a major source of oxidative stress in the midgut, were at higher concentrations in the spring than in the summer in maple leaves, but were at negligible levels throughout the growing season in oak. Thus, the impact of phenolic defenses (measured as semiquinone free radicals and oxidized glutathione in the midgut) was not decreased in spring-feeding larvae. Instead, oxidative stress in larvae on maple remained at elevated levels in the spring and summer. By contrast, larvae that fed on oak had consistently low levels of oxidative stress. We conclude that oak and maple were better host plants in the spring because of their higher nutritional quality, and not because of a lower effectiveness of their chemical defenses. This work emphasizes the need to measure not only foliar nutritional and phenolic chemistry but also specific physiological responses in the herbivore, such as oxidative stress. These physiological mechanisms add to our understanding of why spring-feeding life-history strategies have evolved in some insect herbivores.     

Interspecific variation in thermal denaturation of proteins in the congeneric musselsMytilus trossulus andM. galloprovincialis: evidence from the heat-shock response and protein ubiquitination

The genetic population structure of the precominant zooplankter, the copepod Calanus finmarchicus (Gunnerus), was examined to determine whether genetically distinct populations exist in the Gulf of Maine. C. finmarchicus was sampled in three regions of the Gulf of Maine (Great South Channel, spring 1989; northern Gulf of Maine, winter 1990; Great South Channel and Georges Bank, spring 1990). Copepods from seven locations in the Great South Channel, five in the northern Gulf of Maine and four on or near Georges Bank were assayed for allozyme variation and mitochondrial DNA variation of amplified 16S rRNA and cytochrome b genes. Restriction fragment length polymorphism (RFLP) analyses of both mitochondrial DNA genes revealed no variation among any of the individuals assayed. Analysis of five polymorphic allozyme loci revealed that genetic variation among the three geographic regions was low, and genetic identities were high between all locations (I>0.97). Most of the genetic variation was among locations regardless of region. Chi-square tests were used to examine genetic similarity between specific pairs of locations within and between regions. In the northern Gulf of Maine, genetic homogeneity occurred over larger spatial scales (hundreds of km) than in either the Great South Channel or Georges Bank (tens of km). Only copepods from the Bay of Fundy and Nova Scotian Shelf locations were genetically distinct from Wilkinson Basin copepods at two loci. Copepod populations from the northern locations may have been partially isolated or they may represent immigrant populations (e.g., from the Gulf of St. Lawrence). Several pairs of locations were genetically distinct at one or more loci in the two southern regions. Differences between locations in these regions may represent distinct populations advected into the areas at different times or from different sources (e.g., genetic variation may represent a mixture of genetically distinct northern and southern copepod populations). These results suggest extensive gene flow among populations of C. finmarchicus in the Gulf of Maine with some evidence of genetic population subdivision near the Gulf's northeastern and southern boundaries.     

Photobiology of endolithic microorganisms in living coral skeletons: 1. Pigmentation, spectral reflectance and variable chlorophyll fluorescence analysis of endoliths in the massive corals Cyphastrea serailia, Porites lutea and Goniastrea australensis

We used microscopy, reflectance spectroscopy, pigment analysis, and photosynthesis-irradiance curves measured with variable fluorescence techniques to characterise the endolithic communities of phototrophic microorganisms in the skeleton of three massive corals from a shallow reef flat. Microscopic observations and reflectance spectra showed the presence of up to four distinct bands of photosynthetic microorganisms at different depths within the coral skeleton. Endolithic communities closer to the coral surface exhibited higher photosynthetic electron transport rates and a green zone dominated by Ostreobium quekettii nearest the surface had the greatest chlorophyll pigment concentration. However, Ostreobium was also present and photosynthetically active in the colourless band between the coral tissue and the green band. The spectral properties and pigment density of the endolithic bands were also found to closely correlate to photosynthetic rates as assessed by fluorometry. All endolithic communities were extremely shade-adapted, and photosynthesis was saturated at irradiances <7 μmol photons m⁻²s⁻¹.     

Sabaki River sediment load and coral stress: correlation between sediments and condition of the Malindi-Watamu reefs in Kenya (Indian Ocean)

Sediment discharges from rivers have a negative impact on coral reef ecosystems. Indicators of coral decline measured in the present study were: (1) injury to living stony corals; (2) soft coral cover; and (3) bare rocky substrate suitable for colonization by corals. The relationship between these indicators and the distribution of terrigenous sediment was studied for the Malindi-Watamu fringing reef complex along the Kenyan coast off East Africa during 1982 and 1983. Decline of this reef had been repeatedly noted during the preceding decade. The influence of terrigenous sediment from the Sabaki River appears to be strongest in the Watamu area in the south and in the northern-most part of the Malindi reef area. Correlations, between each of the above three coral stress response indicators, on the one hand, and quantitative indicators of sediment loading, on the other hand, were not clear. However, a combined coral stress indicator involving all three factors was shown to have a clear relationship with terrigenous sediment loading and provided a rapid means of field evaluation of the effects of sediment stress on stony corals. Values for the combined coral stress indicator were found to increase in proportion to increasing values of terrigenous sediment loads in both study areas. A higher coral stress indicator value means a high proportion of injured or algae infested corals, and/or a high soft coral cover, and/or a high proportion of rocky substrate suitable for, but unoccupied by, living corals.     

Providing a common diet to different marine decapods does not standardize the fatty acid profiles of their larvae: a warning sign for experimentation using invertebrate larvae produced in captivity

Larval decapods are commonly produced in captivity and employed in experiments to evaluate interspecific physiological and biochemical differences. Currently, it is still unknown if different decapod species provided a common diet and exposed to identical abiotic conditions produce newly hatched larvae (NHL) with similar fatty acid (FA) profiles. This study analyzed the FA composition of NHL from five marine shrimp species (Lysmata amboinensis, L. boggessi, L. debelius, L. seticaudata and Rhynchocinetes durbanensis) fed a common diet and stocked at constant temperature. FA profiles of NHL differed significantly within and among genera. NHL from species unable to molt from zoea I to zoea II in the absence of food (L. amboinensis, L. debelius and R. durbanensis) displayed the lowest FA contents. Researchers must be aware that providing a common diet to different species, even if closely related, may not standardize the FA profile of NHL produced in captivity.     

Differential effect of ultraviolet exposure (UVR) in the stress response of the Dinophycea Gymnodinium sp. and the Chlorophyta Dunaliella tertiolecta: mortality versus survival

Dunaliella tertiolecta (Chlorophyta) and Gymnodinium sp. (Dinophyceae) cells were exposed to ultraviolet radiation (UVR) (PAR, UVA and UVB: PAB) for 6 days either continuously or during a photoperiod. Both UVR treatments were harmful to Gymnodinium but exposure to continuous PAB had the most dramatic effects. Although a number of lesions/damage could have happened during the first few hours of exposure to UVR, in less than 24 h, Gymnodinium lost its ability to detoxify ROS efficiently, photoinhibition occurred, thymine dimers formed in the DNA, caspase-like enzymatic activities DEVDase sharply increased and cells died as determined by SYTOX-green staining. Superoxide dismutase activity did not significantly change with time, and although the catalase activity augmented in both treatments, cells still suffered from the UVR stress. Clearly, UVR was fatal to the dinoflagellate. For the chlorophyte, however, cell numbers increased regardless of the UVR treatment and mortality remained low (<20 %). F _v/F _m showed an initial decrease but then remained constant for both light treatments. After 6 days of continuous PAB exposure, however, signs of stress (thymine dimers, oxidative stress) paralleled a drop in catalase activity. Results obtained here demonstrate that the dinoflagellate Gymnodinium was much more sensitive and was harmed more rapidly by UVR exposure than the chlorophyte D. tertiolecta. The increased tolerance to UVR exposure of the chlorophyte may provide advantages over other more sensitive phytoplankton species within the photic zone. We provide strong support in the present study for repair being an important component of UV resistance in this species.