The effects of predator abundance and habitat structural complexity on survival of juvenile sea urchins

We studied the effect of the abundance of predatory fishes and structural complexity of algal assemblages on the survival of juveniles of the sea urchin Paracentrotus lividus on Mediterranean infralittoral rocky bottoms. Post-settlement juveniles (2–10 mm) were placed on four distinct natural substrates with increasing structural complexity (coralline barren, algal turf, erect fleshy algal assemblages and small crevices) inside and outside the Medes Islands Marine Reserve. Predation on these sea urchins increased at greater abundance of predatory fishes, and decreased with greater structural complexity. The refuge provided by structural complexity, however, decreased with increasing size of sea urchin recruits. Predation on the smallest post-settlers was carried out almost exclusively by small fishes (<20 cm), mainly the labrid Coris julis, while the dominant predator of larger juveniles was the sparid Diplodus sargus. Our results demonstrate the cascading effects caused by the prohibition of fishing in marine reserves, and highlight the potential role of small predatory fishes in the control of sea urchin populations.Communicated by O. Kinne, Oldendorf/Luhe     

Parasites and headless chaetognaths in the Indian Ocean

Typhloscolecid polychaetes, assigned to the genera Typhloscolex (Typhloscolex muelleri) and Travisiopsis (Travisiopsis dubia), feeding on chaetognaths are reported for the first time from the Indian Ocean. These parasitic/predatory polychaetes cause decapitation in the chaetognath Flacisagitta enflata, either by eating the head or by causing injuries to the neck or body. Data from eastern Africa to western India showed a peak of polychaete infestation and decapitation of F. enflata in the Seychelles. A 5% peak occurrence (turnover rate is unknown) of decapitated individuals indicates that this parasitism/predation may have an important impact on local F. enflata populations. The harpacticoid copepod Microsetella norwegica was found feeding on the head and the reproductive organs of F. enflata. Therefore, this copepod may cause both decapitation and castration. Flatworm parasites are reported from the body cavity of F. enflata. Digeneans probably belonging to the genera Aphanurus, Parahemiurus, Accacladocoelium and Opechona, along with the accacoeliid Cercaria owreae and didymozoid metacercariae, were found. Cestode larvae were also recovered. No nematodes were found inside chaetognaths in this study.Communicated by O. Kinne, Oldendorf/Luhe     

A mark-recapture study of male<Emphasis Type="Italic"> Colletes cunicularius</Emphasis> bees: implications for pollination by sexual deception

An unusual pollination strategy is pollination by sexual deception in which orchids sexually attract male insects as pollinators. One gap in knowledge concerns the pattern and extent of pollinator movement among these sexually deceptive flowers and how this translates to pollen and gene flow. Our aim was to use mark and recapture techniques to investigate the behavior and movement of male Colletes cunicularius, an important bee pollinator of Ophrys. Our study site was located in northern Switzerland where a large population of the bees was nesting. Within two plots, (10×40 m), we marked bees with different colors and numbered tags. Seventeen percent of the 577 marked bees were recaptured over a period of 1 to a maximum of 11 days. However, the number of recaptures dropped dramatically after 3–5 days, suggesting an average lifetime of less than 10 days. Mark-recapture distances varied from 0 to 50 m, with a mean of 5 m. Our findings show that individual male bees patrol a specific and restricted region of the nesting area in search of mates. This mark-recapture study provides the first clues about the potential movement of pollen within populations of Ophrys orchids. We predict that orchid-pollen movements mediated by bees will be similar to the mark-recapture distances in this study. Parallel studies within orchid populations, including direct studies of pollen movement, are now required to better understand how pollinator mate-searching behavior translates to pollination success and pollen movement within sexually deceptive orchid populations.Communicated by R.F.A. Moritz     

Two different proteases produced by a deep-sea psychrotrophic bacterial strain,<Emphasis Type="Italic"> Pseudoaltermonas</Emphasis> sp. SM9913

A psychrotrophic bacterial strain, Pseudoaltermonas sp. SM9913, was isolated from deep-sea sediment collected at 1,855 m depth. Two proteases produced by Pseudoaltermonas sp. SM9913 were purified, MPC-01 and MCP-02. MCP-01 is a serine protease with a molecular weight of 60.7 kDa. It is cold-adapted with an optimum temperature of 30–35°C. Its K_m and E_a for the hydrolysis of casein were 0.18% and 39.1 kJ mol^–1, respectively. It had low thermostability, and its activity was reduced by 73% after incubation at 40°C for 10 min. MCP-02 is a mesophilic metalloprotease with a molecular weight of 36 kDa. Its optimum temperature for the hydrolysis of casein was 50–55°C. The K_m and E_a of MCP-02 for the hydrolysis of casein were 0.36% and 59.3 kJ mol^–1, respectively. MCP-02 had high thermostability, and its activity was reduced by only 30.5% after incubation at 60°C for 10 min. At low temperatures, Pseudoaltermonas sp. SM9913 mainly produced the psychrophilic protease MCP-01.Communicated by O. Kinne, Oldendorf/Luhe     

Feeding ecology of the three juvenile phases of the spiny lobster<Emphasis Type="Italic"> Panulirus argus</Emphasis> in a tropical reef lagoon

The three juvenile phases of the spiny lobster Panulirus argus (algal phase: 5-15 mm carapace length, CL; postalgal phase: 15-45 mm CL, and subadults: 45-80 mm CL) occur in the reef lagoon at Puerto Morelos, Mexico. The algal phase abounds in this lagoon, which is covered by extensive seagrass-algal meadows, but the density of postalgal and subadult juveniles is low, owing to the scarcity of crevice-type shelters suitable for these phases. The feeding ecology of the three juvenile phases was investigated to examine whether spatial or temporal differences in food intake, diet composition, or nutritional condition occurred among phases and could partially account for the low abundance of the larger juveniles. Juveniles were collected by divers at night, from January to November 1995, throughout the mid-lagoon and back-reef zones. Percent stomach fullness, relative weight of the digestive gland (RWDG, an index of nutritional condition), percent frequency of occurrence and percent volume of food categories in the diet were compared between sexes, juvenile phases, molt stages (postmolt, intermolt, premolt), seasons, and sampling zones (mid-lagoon and back-reef zones). Significant differences in stomach fullness occurred only among molt stages, mainly because postmolt individuals had emptier stomachs. The main food categories in all juvenile phases were crustaceans (mostly hermit crabs and brachyurans) and gastropods, but the food spectrum was wide, including many other animal taxa as well as plant matter. In June 1995, the epibenthic macrofauna was sampled in five sites in the lagoon that differed in their amount of vegetation. The most abundant taxa in all sites were decapods and gastropods, but density and diversity measures showed that the distribution of these potential prey taxa for juvenile P. argus was rather patchy. Diet overlap in juvenile lobsters was high between sexes, juvenile phases, sampling zones, seasons, and molting stages, indicating that all juveniles fed on the same general food categories throughout time. The only factor that affected the RWDG was the juvenile phase. RWDG was significantly lower in subadults than in algal and postalgal phases, suggesting a poorer nutritional condition in the largest juveniles. This may be related to the scarcity of suitable shelters for large juveniles throughout the lagoon, which may preclude subadults from exploiting food resources in areas of the lagoon where shelter is limited.     

Costs and benefits of communal rearing to female prairie voles (<Emphasis Type="Italic">Microtus ochrogaster</Emphasis>)

Communal rearing of offspring may help mothers maximize their investment in offspring at a reduced cost to their own bodily condition, thus maximizing their potential for reproductive success. The objective of this study was to quantify the costs and benefits of communal rearing to prairie vole (Microtus ochrogaster) pups and mothers. Mothers were assigned to one of three social units: solitary mothers, singularly breeding groups (i.e. one mother and one non-reproductive sister) and plurally breeding groups (i.e. two lactating sisters). For each type of social unit, some replicates were provided with food ad libitum, while others were provided with limited food. The body mass of focal mothers (i.e. the first mother to produce a litter) was a significant predictor of pup growth. Regardless of food availability, litters of focal mothers in plurally breeding groups gained more weight than litters reared by solitary mothers. Pups reared in singularly breeding groups were intermediate in weight gain, but did not gain significantly more weight than solitary offspring. There was no difference in the body mass of focal mothers from each type of social unit, regardless of food availability. Within plurally breeding groups, the weight gain of the two litters and body mass of focal and second mothers did not differ. However, focal mothers from plurally breeding groups nursed fewer pups than solitary mothers and also fewer pups than their nestmates when food was limited. Our results suggest that plural breeding results in greater fitness to mothers than solitary and singular breeding.Communicated by E. Korpimäki     

Fluctuating asymmetry and nutritional condition of Baltic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) larvae

The level of fluctuating asymmetry (FA), defined as random deviations from perfect bilateral symmetry, is assumed to reflect the developmental instability (DI) of an organism. Because environmental and genetic stress may increase DI, FA has been used to assess the level of stress experienced by, for example, fish. In this study, left–right asymmetry of lapillar otoliths was related to nutritional condition as estimated from RNA/DNA ratios, in order to investigate the utility of FA to detect feeding-related stress in Baltic cod, Gadus morhua L., larvae. Cod larvae in intermediate and good nutritional condition showed similar values of FA, and these were more symmetric than for larvae in poor condition. As increased levels of FA were restricted to larvae in a condition comparable to that of larvae experiencing at least 3 days of starvation in laboratory experiments, it is suggested that FA is an insensitive indicator of short-term feeding success of larval cod. However, FA can be used to reveal severely starved larva populations and probably also populations that have been subjected to prolonged sub-optimal feeding conditions.     

Local changes in the composition and community structure of suprabenthic peracarid crustaceans on the bathyal Mediterranean: influence of environmental factors

Deep-water assemblages of suprabenthic peracarids were analyzed in the SW Balearic Islands (Algerian Basin, southwestern Mediterranean) between 249 and 1,622 m depth; the patterns of species composition, possible zonation, and trophic structure found in this area were compared with those exhibited by peracarids in the mainland side of the Catalan Sea slope (northwestern Mediterranean). One hundred and four peracarid species (plus one leptostracan) were identified on the Balearic Islands slope, amphipods being the most diversified taxon (45 species). On the Balearic slope, two distinct depth assemblages were distinguished: one at the upper slope (US), between 249 and 402 m depth and the second at the deep slope, between 543 and 1,620 m depth. A remarkable species substitution occurred at depths between 402 and 638 m. In the Catalan Sea, in addition to the US assemblage occupying depths between 208 and 408 m, a second boundary of faunal change was found around 1,250 m. Suprabenthos biomass increased from 242 to approximately 500 m. Suprabenthos attained the highest biomass values (100 g wet weight/10,000 m²) at intermediate depths between 504 and 1,211 m, as also occurred with the associated zooplankton collected with suprabenthos (peak biomass between 502 m and 898 m). Suprabenthos biomass did not show any significant correlation with any environmental water-column variable. In contrast, zooplankton (especially small fish and decapod crustaceans) showed a significant positive correlation with fluorometry and turbidity at different levels of the water column. The feeding guilds of species showed important differences between the two areas only on the US, with a higher abundance of deposit feeders in the Catalan Sea (20.4%) than in the Balearic Islands (4.2%). The low contribution of deposit feeders in the SW Balearic Islands may ultimately be a consequence of the lack of river discharges in this area.Communicated by S.A. Poulet, Roscoff     

Sexual dimorphism and male mating success in the tentacled blenny, <Emphasis Type="Italic">Parablennius tentacularis</Emphasis> (Teleostei: Blenniidae)

Although external sexually dimorphic traits are commonly found in males of combtooth blenny species, little is known about the benefit they can convey to male mating success. Indeed, while female preferences for large males have been demonstrated in some species, the possible role played by dimorphic ornaments has been neglected. We now report on the tentacled blenny, Parablennius tentacularis, a species where males are characterized by bulb glands on the anal fin and both sexes exhibit a dark spot on the dorsal fin and orbital tentacles. Males are territorial, make nests in empty bivalve shells, and provide solitary parental care for the eggs. Using morphometric analysis and field collected data on male and female external features, nest characteristics and number of eggs in the nests, we have assessed the development of dimorphic traits in both sexes and male mating success. The results reveal that orbital tentacles of males are more developed and more variable in size than those of females. Larger males exhibit longer orbital tentacles and larger anal glands but do not necessarily occupy larger nests. Male mating success is significantly correlated with the inner nest surface area and with orbital tentacle size but not with body size. These results provide support for a primary role of male ornaments in enhancing blenny male mating success and are discussed in the context of mate choice for direct and indirect benefits.