Effect of low salinity on the activity,feeding, growth and absorption efficiency of Luidia clathrata (Echinodermata: Asteroidea)

Exposure of Luidia clathrata (Say) to low salinity (17 S) results in a decrease in activity and rate of feeding, but has little effect on the absorption efficiency. Growth, as indicated by changes in body size and energy content of the body wall and pyloric caeca, is reduced in low salinity due to a decrease in feeding rate (energy consumption) and to a decrease in efficiency of utilization of material and energy absorbed. The low efficiency indicates that either additional energy is required for maintenance or energy is used inefficiently in low salinity. Thus, L. clathrata is limited energetically in low salinities, although it lives and reproduces there.     

Numbers,biomass, and caloric content of the echinoderm fauna of the rocky shores of Barbados

The high-energy windward coasts with narrow rocky intertidal regions (Oistens, River Bay) at Barbados, West Indies, had abundant macroscopic algae (mainly Sargassum sp.) and populations of Holothuria glaberrima Selenka and Echinometra lucunter (Linnaeus), while protected ones with a wide rocky intertidal had sparse macroscopic algae and populations of E. lucunter only. The low-energy leeward coasts with wide rocky intertidal regions (Six Men's Bay, Payne's Bay) had no macroscopic algae in the surf zone and populations of E. lucunter only. Numerical densities of E. lucunter were high in all localities; the highest level of 144 m^-2 was found at Six Men's Bay; numerical densities of H. glaberrima were high at both Oistens and River Bay, the highest level of 36 m^-2 being recorded at River Bay. The caloric density of H. glaberrima at River Bay was 412 kcal m^-2. The highest combined density of H. glaberrima and E. lucunter was at Oistens (632 kcal m^-2, with 254 kcal m^-2 being due to E. lucunter). The highest caloric density of E. lucunter at Six Men's Bay was 482 kcal m^-2. Dependence on suspended food probably restricts H. glaberrima to high-energy environments while E. lucunter has an additional food source through its ability to scrape the rock substratum. E. lucunter may be more efficient in catching drift food. Mortality is suggested to be the basis of the failure of E. lucunter to displace H. glaberrima from the high-energy location.     

Multi-year, seasonal genotypic surveys of coral-algal symbioses reveal prevalent stability or post-bleaching reversion

This report documents the extent to which coral colonies show fluctuations in their associations with different endosymbiotic dinoflagellates. The genetic identity of Symbiodinium from six coral species [Acropora palmata (Lamarck), A. cervicornis (Lamarck), Siderastrea siderea (Ellis and Solander), Montastrea faveolata (Ellis and Solander), M. annularis (Ellis and Solander), and M. franksi (Gregory)] was examined seasonally over five years (1998 and 2000–2004) in the Bahamas and Florida Keys at shallow (1 to 4 m) fore-reef/patch reef sites and at deeper fore-reef (12–15 m) locations. Symbionts were identified genetically using denaturing gradient gel electrophoresis (DGGE) fingerprinting of the internal transcribed spacer region 2 (ITS2) of ribosomal RNA gene loci. Repetitive sampling from most labeled colonies from the Bahamas and the Florida Keys showed little to no change in their dominant symbiont. In contrast, certain colonies of M. annularis and M. franksi from the Florida Keys exhibited shifts in their associations attributed to recovery from the stresses of the 1997–1998 El Niño southern oscillation (ENSO) event. Over several years, a putatively stress-tolerant clade D type of Symbiodinium was progressively replaced in these colonies by symbionts typically found in M. annularis and M. franksi in Florida and at other Caribbean locations. Greater environmental fluctuations in Florida may explain the observed changes among some of the symbioses. Furthermore, symbiotic associations were more heterogeneous at shallow sites, relative to deep sites. The exposure to greater environmental variability near the surface may explain the higher symbiont diversity found within and between host colonies.     

Tiger shark (Galeocerdo cuvier) abundance and growth in a subtropical embayment: evidence from 7 years of standardized fishing effort

The tiger shark (Galeocerdo cuvier Peron and Lesueur 1822) is a widely distributed predator with a broad diet and the potential to affect marine community structure, yet information on local patterns of abundance for this species is lacking. Tiger shark catch data were gathered over 7 years of tag and release research fishing (1991–2000, 2002–2004) in Shark Bay, Western Australia (25°45′S, 113°44′E). Sharks were caught using drumlines deployed in six permanent zones (~3 km² in area). Fishing effort was standardized across days and months, and catch rates on hooks were expressed as the number of sharks caught h⁻¹. A total of 449 individual tiger sharks was captured; 29 were recaptured. Tiger shark catch rate showed seasonal periodicity, being higher during the warm season (Sep–May) than during the cold season (Jun–Aug), and was marked by inter-annual variability. The most striking feature of the catch data was a consistent pattern of slow, continuous variation within each year from a peak during the height of the warm season (February) to a trough in the cold season (July). Annual growth rates of recaptured individuals were generally consistent with estimates from other regions, but exceeded those for populations elsewhere for sharks >275 cm fork length (FL), perhaps because mature sharks in the study area rely heavily on large prey. The data suggest that (1) the threat of predation faced by animals consumed by tiger sharks fluctuates dramatically within and between years, and (2) efforts to monitor large shark abundance should be extensive enough to detect inter-annual variation and sufficiently intensive to account for intra-annual trends.     

Phenotypic differentiation in female preference related to geographic variation in male predation risk in the Trinidad guppy (Poecilia reticulata)

Summary Populations of the Trinidad guppy range from areas with high levels of predation by other species of fish to areas with little or no piscine predation. Previous studies have shown that variation among populations in male coloration can be explained by a balance between female preference for brighter males and natural selection against bright males. High levels of male courtship activity may also increase both predation risk and mating success. Therefore, in high-predation areas, females that mate with males that court frequently as well as those that choose bright males would presumably produce male offspring with low survivorship. Consistent with this variation in natural selection, we observed that females from high-predation populations were less likely to choose bright and frequently courting males than females from low-predation populations. This result supports the hypothesis that female preference is evolving as a character genetically correlated with the preferred male character, in which case higher levels of natural selection acting against the male character should be related to lower levels of female preference.     

Environmental and genetic influences on mating strategies along a replicated food availability gradient in guppies (Poecilia reticulata)

Food availability is expected to influence the relative cost of different mating tactics, but little attention has been paid to this potential source of adaptive geographic variation in behavior. Associations between the frequency of different mating tactics and resource availability could arise because tactic use responds directly to food intake (phenotypic plasticity), because populations exposed to different average levels of food availability have diverged genetically in tactic use, or both. Different populations of guppies (Poecilia reticulata) in Trinidad experience different average levels of food availability. We combined field observations with laboratory “common garden” and diet experiments to examine how this environmental gradient has influenced the evolution of male mating tactics. Three independent components of variation in male behavior were found in the field: courtship versus foraging, dominance interactions, and interference competition versus searching for mates. Compared with low-food-availability sites, males at high-food-availability sites devoted more effort to interference competition. This difference disappeared in the common garden experiment, which suggests that it was caused by phenotypic plasticity and not genetic divergence. In the diet experiment, interference competition was more frequent and intense among males raised on the greater of two food levels, but this was only true for fish descended from sites with low food availability. Thus, the association between interference competition and food availability in the field can be attributed to a genetically variable norm of reaction. Genetically variable norms of reaction with respect to food intake were found for the other two behavioral components as well and are discussed in relation to the patterns observed in the field. Our results indicate that food availability gradients are an important, albeit complex, source of geographic variation in male mating strategies.