The effects of prolonged emersion and submersion by tidal manipulation on marine macrobenthos

Effects of tidal manipulation, resulting in prolonged periods of emersion and submersion or in protracted tidal cycles, on estuarine benthic animals are reviewed.Prolonged submersion periods did not show effects on mortality of most benthic animals tested, with the exception of the crumb-of-bread sponge Halichondrea panicea, which, at low water-flow rates, was covered with a layer of bacteria and subsequently died.Protracted low-water periods of 18 hours during several weeks hardly caused any mortality. However, protracted low-water periods of 30 hours during some weeks or emersion during several days caused a strong increase in mortality, depending on: the duration of emersion, temperature, condition of the animals, species and age. At temperatures below –1 °C and above 24 °C mortality was generally high. Animals with a low glycogen content were more sensitive to emersion than those with a high content. Species with a shell and those that are relatively big were less sensitive than those without a shell or of small size.The reproductive cycle of benthic animals could be delayed or accelerated by both emersion and submersion.     

Levels of genetic variability in sculpins (Gottidae: Teleostei) of the North American Pacific coast and an assessment of potential correlates

We examined levels of allozymic variation in intertidal sculpins of the genera Oligocottus, Clinocottus and Artedius. Variability in these species, as assessed by the proportion of loci polymorphic and average heterozygosity per locus, was generally low but within the range of values observed for other fish groups. In reviewing the ecological and life-history attributes of these sculpins, we found only one outstanding correlate of allozyme variability–larger-bodied species tended to have lower levels of variation. Also, the level of heterozygosity was not related in any obvious way to historical/ evolutionary aspects such as position in phylogenetic trees or the inferred relative ages of species. Our study of a relatively well-defined lineage of fishes that co-occur in the same geographical region and in the same, or broadly similar, habitats, underscores the difficulty of detecting correlations between genetic variability and seemingly relevant ecological features of species.     

A new approach for testing contaminated marine sediments: fertilization success of lugworms following parental exposure

A sediment bioassay is being developed using several marine benthic invertebrates to assess the effects of parental transfer of contaminants to the gametes. In this preliminary study, the emphasis was placed on developing methods for the in vitro fertilization of lugworm, Arenicola marina, oocytes.Lugworms exposed to contaminated sediments in outdoor mesocosms were brought to the laboratory, just before the beginning of the spawning period. The reliability of an in vitro fertilization procedure was tested by varying several parts of the method. Main results are that eggs and embryos may be physically damaged by cleaning over a sieve. However, as no negative effects were observed when leaving eggs and sperm together for 24 h, the sperm need not be washed off until the embryos are preserved for further examination later on.A first, incomplete screening of the effects of contaminated harbour dredged sediments indicated some effect on the reproductive success.     

DISTRIBUTION AND SYSTEMATICS OF FRESHWATER CERAMIALES (RHODOPHYTA) IN NORTH AMERICA1

Twenty-five freshwater populations of Ceramiales were collected in North America, 24 of which were from the tropical rainforest region of Central America and the Caribbean. The streams tended to be moderate in mean current velocity (X?= 23.3 cm·S^?1) and maximum width (X?= 6.3 m) but high in temperature (X?= 23.1°C), pH (X?= 7.9), and specific conductance (X?= 320 μS·cm^?1). Three Bostrychia species were restricted to the Caribbean islands: B. moritziana (Sonder ex Kütz.) J. Ag. (syn. B. cornigera Mont. and B. radicans f. moliforme Post), with ecorticate indeterminate axes, monosiphonous ultimate branches, and cladohaptera; B. radicans (Mont.) Mont. (syn. B. leprieurii Mont and B. rivularis Harv.), with ecorticate and polysiphonous axes throughout and cladophaptera; and B. tenella (Lamour.) J. Ag., with corticate indeterminate axes, monosiphonous ultimate branches, and peripherohaptera. Ballia prieurii Kütz. was found in Belize and Costa Rica and was characterized by rebranched determinate laterals, opposite branching, and long apical cells (X?= 61 μm) and axial cells (X?= 43 μm). Caloglossa leprieurii (Mont.) J. Ag. was localized in Puerto Rico while. C. ogasawaerensis Okam. was collected only in Costa Rica. The two species were separated by site of branching (midrib vs. margin) and blade width (X?= 384 vs. 861 μm). Polysiphonia subtilissima Mont. from Florida and Jamaica had four pericentral cells, no cortication, rhizoids arising from pericentral cells, and branches initiated at trichoblast scars.     

Transfer of a marine DNA virus fromEctocarpus toFeldmannia (Ectocarpales,Phaeophyceae): aberrant symptoms and restitution of the host

Summary The marine brown algaEctocarpus siliculosus is invaded by a polyhedric virus, whose genome consists of circular, double-stranded DNA. In laboratory experiments this virus can infect a different host species,Feldmannia simplex. InfectedFeldmannia plants show severe somatic malformations. However, no functional virus particles are formed. SuchFeldmannia plants recover to resume a normal, symptom-free appearance. This result raises the possibility of intergeneric gene transfer in the natural habitat.     

Rip stop in marine algae: Minimizing the consequences of herbivore damage

Summary Structural features of marine macrophytes are generally believed to act as defences against herbivores by reducing the ability of herbivores to consume the plants. Thallus form and calcification in particular have been considered structural defences that act by reducing the probability of consumption of tissue by herbivores. Studies directly measuring the mechanical resistance of a variety of marine algae (tropical and temperate) to herbivores of two important feeding types, rasping herbivores (docoglossan limpets) and a biting herbivore (an herbivorous crab), do not support this hypothesis. I suggest that thallus form and calcification may play a more important role in minimizing the impact of herbivores by reducing the probability of subsequent tissue loss due to herbivore-induced damage. For some algal species, tissue lost subsequent to herbivore damage may greatly exceed loss due to direct consumption by herbivores. I suggest that calcification and thallus properties resulting in preferential tear directions reduce the probability of tissue loss subsequent to herbivore damage rather than prevent herbivores from removing tissue as has been suggested in the past.     

Nutritional properties of four marine microalgae for albino rats

The nutritive value of the marine microalgaeTetraselmis suecica, Isochrysis galbana, Dunaliella tertiolecta andChlorella stigmatophora was studied in diets given to rats. Biological assays were carried out in order to determine the Protein Efficiency Ratio (PER) and the Food Conversion Efficiency (FCE). Each dried microalga was fed to weaning Wistar albino rats as the sole protein source at a protein level of 12%. Control rats were given diets containing 12 % casein. Food consumption was similar in all groups. PER values obtained were 1.14 withT. suecica diet, 1.13 withI. galbana diet, 2.07 withD. tertiolecta diet and 1.13 withC. stigmatophora diet (casein, 2.50). FCE values followed a similar pattern. The data showed that the marine microalgaD. tertiolecta is a source of protein of good quality. Its PER is quite high, compared to vegetable and cereal proteins, and compares favourably with other microbial protein sources, such as yeasts or different freshwater microalgae. Haematological tests showed no significant differences among the groups in haemoglobin levels, red and white blood cell counts, differential count and mean corpuscular volume. Different blood parameters were also determined and a significant decrease in triglycerides levels appeared with all the microalgal diets, whereas a significant decrease in cholesterol appeared inD. tertiolecta andC. stigmatophora diets.     

Tris not only controls the pH in microalgal cultures,but also feeds bacteria

Tris (Tris(hydroxymethyl)amino methane), a compound often used as a buffer in microalgal culture media, sustains active bacterial growth in non-axenic microalgal cultures when sodium phosphate is present. The low pH levels caused by bacterial growth and probably the depletion of phosphorus in the medium caused the collapse ofPhaeodactylum tricornutum cultures resulting in a reduction of microalgal growth from 32 x 10⁶ to 1.1 x 10⁶ cells ml^–1. This emphasizes the need for care when interpreting the results of non-axenic microalgae cultures in which Tris or other organic buffer is added.     

Diversity of Siphonaria Sowerby I, 1823 (Gastropoda,Siphonariidae) in the Seychelles Bank and beyond

Molecular phylogenetic studies have shown that the characters of the reduced shell of the false limpets of the genus Siphonaria Sowerby I, 1823 are highly variable and often insufficient for species delimitation. The taxonomy and distribution of Siphonaria in the Indian Ocean are poorly known. We sampled Siphonaria in the Seychelles Bank to check the occurrence of recorded species using DNA sequences and to study the paths through which Siphonaria species have colonised the Seychelles Bank by reconstructing their phylogenetic relationships. Analyses of a dataset comprising 16 S rRNA gene sequences of 33 specimens from the Seychelles Bank and 300 additional Siphonaria sequences from other regions from GenBank with various methods for species delimitation resulted in 19–102 primary species hypotheses. Assemble Species by Automatic Partitioning provided a conservative estimate of the species number (42) in which several indisputable species were lumped. The results of Automatic Barcode Gap Discovery depended strongly on the assumed prior maximum intraspecific divergence, whereas the tree-based methods Generalised Mixed Yule Coalescent and Poisson Tree Processes resulted in high overestimates. The specimens from the Seychelles Bank represent three clades, belonging to the Siphonaria ‘atra’ group, the Siphonaria ‘normalis’ group and a possibly undescribed species recorded previously only from Hainan. At least two of the three species recorded from the Seychelles Bank came from the east, i.e., from the Coral Triangle in the Indo-Australian Archipelago, the region with the highest marine biodiversity worldwide. A major transport mechanism across the Indian Ocean was probably the South Equatorial Current.