Natural inducers for coral larval metamorphosis

 Coral gametes from Acropora millepora (Ehrenberg, 1834) and from multi-species spawning slicks provided larvae for use in metamorphosis assays with a selection of naturally occurring inducer chemicals. Four species of crustose coralline algae, one non-coralline crustose alga and two branching coralline algae induced larval metamorphosis. However, one additional species of branching coralline algae did not produce a larval response. Metamorphosis was also observed when larvae were exposed to skeleton from the massive coral Goniastrea retiformis (Lamarck, 1816) and to calcified reef rubble, demonstrating metamorphosis is possible in the absence of encrusting algae. Chemical extracts from these algae and the coral skeleton, obtained using either decalcification or simple methanol extraction procedures, also contained active inducers. These results extend the number of crustose algal species known to induce coral metamorphosis, suggest that some inducers may not necessarily be strongly associated with the calcified algal cell walls, and indicate that inducer sources in reef habitats may be more diverse than previously reported. Accepted: 21 May 1999     

Differential survival among life stages contributes to co‐dominance of Abies mariesii and Abies veitchii in a sub‐alpine old‐growth forest

Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade‐tolerant dominant trees in a sub‐alpine old‐growth forest? Do such differences in demography contribute to the coexistence and co‐dominance of the two species? Location: Sub‐alpine, old‐growth forest on Mt. Ontake, central Honshu, Japan. Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44‐ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm). Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and sub‐canopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow‐pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow‐pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life‐stages determines relative dominance of the two species in the canopy. Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co‐dominance at the canopy stage.     

Responses of the estuarine copepod Pseudodiaptomus annandalei to diatom polyunsaturated aldehydes: Reproduction,survival and postembryonic development

The euryhaline calanoid copepod Pseudodiaptomus annandalei perennially occurs in tropical and subtropical brackish water ecosystems and harbors supporting harmful algal blooms. In the present paper we provide a quantitative assessment of the influence of the diatom-derived poly-unsaturated aldehyde (PUA), 2-trans-4-trans-decadienal on demographic traits of P. annandalei. The survival and reproduction of P. annandalei were recorded in life table experiments, using a cohort of adult males and females exposed to a range of concentrations (0.75, 1.5, 3 and 4.5 μM) of decadienal. Higher mortality of female cohorts and lower reproduction were recorded with increasing concentrations of decadienal (3 and 4.5 μM). The estimated survival time for cohort females (control: 9.7 days; 4.5 μM decadienal: 4.7 days) and developmental stages of copepods (control: 10.5 days; 4.5 μM decadienal: 1.0 days) in decadienal applied medium (Isochrysis galbana + decadienal) was significantly lower than those in control (only I. galbana). Detrimental effects further eroded recruitment by increasing naupliar mortality and impairing copepodite development to adulthood. Since P. annandalei is widely used in the aquaculture industry in Asia, the present results call for a limited use of PUA producing diatoms as algal food to avoid impairing copepod reproduction and development.     

Recruitment prediction for Pacific herring (Clupea pallasi) on the west coast of Vancouver Island, Canada

The accurate prediction of recruitment to the fishery is a very important tool within the management structure of any fish stock being exploited. In the case of the Pacific herring, Clupea pallasi, fishery in Canada, a forecast of the abundance of each herring stock is particularly important for formulating an annual catch quota. The sustainable management of the fishery and the resource is based in part on accurate recruitment forecasting because Pacific herring are short-lived and so the recruitment contributes a significant part of the total spawning run targeted by the fishery each year. Several factors are believed be important in determining the success of recruitment besides spawners biomass. Since herrings are “r” strategists, conditions related to the egg, the planktonic, or even the juvenile stage might determine the future level of recruitment. Recently a formula that defines conditions for a semi-quantitative level of recruitment forecast was elaborated using genetic algorithms and current study attempts to improve on this model. Using salinity in two quarterly periods during the planktonic and pre-recruit stages, temperature and spawning biomass for the west coast of Vancouver Island stock, classification rules that define recruitment in 3 different levels (low, medium and high) were developed with a genetic algorithm, setting low and high boundaries for each condition. A 75% success in classifying recruitment was obtained. The model was shown to be particularly effective at predicting when the recruitment would be low, which could be important from the perspective of the Precautionary Approach and the sustainable management of this stock.     

Coexistence in a sea urchin guild and its implications to coral reef diversity and degradation

Summary Coexistence between the coral reef inhabiting sea urchins Echinometra mathaei, Diadema savignyi and D. setosum was studied by comparing differences in body morphology, distribution, diet, susceptibility to predators, intra- and interspecific competition and settlement. The three species share similar diets and broad within-habitat distributions but differ in their microspatial preferences. E. mathaei is the smallest species, has the highest settlement rates and lives territorially within small burrows or crevices. D. savignyi is intermediate in size and lives frequently in intermediate size crevices or occassionally in social groups. D. setosum is the largest species and occassionally lives in large crevices or more frequently in social groups. Both Diadema have similarily low settlement rates. Competition experiments showed that E. mathaei was consistently the top competitor for crevice space. Diadema species shared larger crevices but competition occured within smaller crevices and was frequently won by the largest individual, regardless of species. D. savignyi may be the top competitor for crevice space between the Diadema species due to a reduced spine length/test size ratio which gives it a larger test for the same crevice size requirement. Predation rates were high for E. mathaei and low for both Diadema species. Coexistence is mediated by predation on the competitive-dominant while predation coupled with different body morphologies and behavior allows spatial resource partitioning of the reef's variable topography. Consequently, the three variables of predation, topographic complexity and differing body shapes create the observed species diversity. A reduction in predators due to stochastic fluctuations or from fishing pressure can lead to E. mathaei population increases and competitive exclusion of Diadema.     

Forensic biological pursuits of exotic fish origins: piranha in Hawaii

Synopsis The otoliths of an adult red-bellied piranha, Pygocentrus nattereri, captured from a reservoir in Hawaii were scrutinized to determine the fish's origin and growth history. Sagittal otoliths of the piranha, P. nattereri, contained internal microincrements visible by Scanning Electron Microscopy. The medial cross sectional plane of the sagitta was resolved to provide counts for the most visible micro-increments. An opportune spawning of confiscated adults provided samples for verification of daily increment formation. Daily formation of microincrements was verified from hatched individuals, and confirmed the suitability of otoliths for revealing daily patterns in the age and growth of piranhas. The central area of the sagitta was diffuse in regards to otolith microstructure and indicated the fish was held in an unchanging environment (aquarium). Therefore, otoliths provide important life history or forensic information incorporated within their structural components. The visualization of daily microincrements in the otolith of a juvenile allowed the determination of age at and since release. Fish grew rapidly after being released into the wild. From otolith increments the date of release for an individual fish can be calculated with acceptable accuracy. As presented, otolith structural information can provide age and growth data which are essential to the management of introduced species.     

Variation in abundance and survival of fish larvae in shallow eutrophic lake Tjeukemeer

Synopsis Variations in abundance and survival of larvae of the major fish species, bream, roach, pikeperch, perch and smelt were studied in shallow eutrophic lake Tjeukemeer (1986–1988). Except for smelt, the size of the spawning stock and the abundance of larvae were not related. Both the timing of appearance of larvae and their growth rate were determined by water temperature as was shown by a growth model developed earlier for Tjeukemeer fishes. In cyprinids and percids the survival of the larvae was hypothesized to be negatively related to the duration of the earliest stages. Except in cyprinids, the abundance of 0+ juvenile fish could be explained by the number of larvae. In cyprinids 0+ juvenile abundance at the end of the year was not related to the number of larvae in May and June. The cyprinid juvenile survival rates are hypothesized to be related to the size of the main cyprinid predator, 0+ pikeperch.     

Comparative survivorship and life history of painted greenling (Oxylebius pictus) in Puget Sound,Washington and Monterey Bay,California

Synopsis The painted greenling, Oxylebius pictus, a hexagrammid fish of shallow, northeastern Pacific rocky habitats was observed and collected near the center of its range at Monterey Bay, California, and near the northern limit of its distribution at Puget Sound. Life history characteristics were compared for breeding stocks from the two areas. Mean and maximum adult body sizes (lengths and wet weights) and longevities of both sexes are greater at Puget Sound. Also, both males and females reach sexual maturity at a smaller body length at Monterey. Age group 0 and I juveniles are twice as abundant as adults at Monterey but rare at Puget Sound. Monterey females have greater relative fecundities. Egg development rates are similar at equivalent temperatures; eggs are smaller, however, at Monterey, and thus embryos are smaller at hatching. Length increase is faster for Puget Sound juveniles; adult fish in the two areas grow in length at comparable rates, although weight per body length is consistently greater for Monterey fish. These findings reflect a poorer survivorship at Monterey, where natural predation on fertilized eggs and the mortality rates of adult males are greater.     

Comparative recruitment patterns of two non-pioneer canopy tree species in French Guiana

Summary A comparative study was conducted on the recruitment patterns of two non-pioneer tree species, one dispersed by arboreal mammals and birds (Virola michelii, Myristicaceae) and the other by rodents (Moronobea coccinea, Clusiaceae). These species differ in fruiting phenology, seed size, dispersal distance, germination time and seed nutrient exhaustion. In both species, establishment patterns were consistent with the escape hypothesis and the Janzen-Connell model. Virola seeds need not be buried to survive and germinate, and may produce a seedling carpet beneath the parent. Moronobea seedlings only establish from seeds buried by scatterhoarding rodents in the surrounding understory. One-year survival of Virola seedlings was 47.8% and was greater >10 m than < 10 m from the largest parent tree. In contrast, survival of Moronobea seedlings was 56% 3 years after seed dispersal. Survival of juveniles was greater in gaps than in the understory for Virola but not for Moronobea. Moronobea survival was greater than Virola survival in both microhabitats. Both species establish in the understory, yet both grew faster in gaps. Virola appeared to be more gap-dependent than Moronobea which may persist several years in the understory until a gap occurs. Virola and Moronobea illustrate two intermediate recruitment patterns along an hypothetical continuum of nonpioneer species replacement (Bazzaz and Pickett 1980; Swaine and Whitmore 1988).     

Population ecology of Acacia tortilis in the semi-arid region of the Sudan

Abstract. The population ecology of Acacia tortilis, one of the important woody species in the arid and semi-arid regions of northern Africa, was studied in the Sudan: Ten sample plots were established and all individuals in the plots were mapped and their basal diameter, stem height, crown height and cover measured annually for three years. Individuals were grouped into different height-classes, ‘life-forms’: trees >1.65 m, shrubs > 0.65 m and < 1.65 m, saplings < 0.65 m and seedlings (saplings less than one year old). The population density was 510 ind./ ha in 1985, 432 ind. / ha in 1986 and 218 ind. / ha in 1987. The life-form distribution of the population showed clear differences between plots and years. Mortality in Acacia tortilis, expressed as loss in individuals per year, amounted to 167 ind. / ha / yr. Drought and lethal cutting were found to be the main mortality factors. The population declined by 15.3 % from 1985 to 1986 and by 49.5 % from 1986 to 1987. Natality (recruitment), expressed as number of newly established saplings, was 13 ind. / ha / yr. Recruitment is apparently discontinuous and bound to years with a relatively high precipitation.