Peak Recruitment Research Articles

Population dynamics of the green-lipped mussel, Perna canaliculus, at various spatial and temporal scales in northern New Zealand

Ecological processes that differentiate and maintain intertidal populations of mussels, Perna canaliculus, were studied within three sites at Ninety Mile Beach, northern New Zealand. At these three sites (Scott Point, The Bluff and Tonatona Beach), the dynamics of larval availability, primary and secondary settlement, recruitment and mortality rates were investigated at various spatial and temporal scales. (1) Mussel concentrations in seawater were variable with respect to study site and time of year, with highest abundances at the northernmost population (Scott Point) and lowest concentrations at the middle population (The Bluff). In seawater at all three sites, small mussels (< 0.25 mm in shell length) were more abundant in August 2000, while larger mussels (> 0.5 mm in shell length) were more abundant in March 2001. (2) Primary and secondary settlement patterns were investigated during short-term (daily) and long-term (monthly) settlement experiments, within quadrats that were cleared of all mussels in both the mussel bed and in adjacent algal band habitats. At all sites, primary settlement (< 0.5 mm in shell length) was high within the algal band habitat in August 1999, 2000 and 2001. Conversely, secondary settlement (> 2.0 mm in shell length) was high within cleared areas in the mussel beds in November–March 1999–2000 and 2000–2001. Abundance of mussels settling on artificial substrates placed in the intertidal did not differ greatly from comparable areas of natural substrates (bare rock or algae within cleared quadrats). (3) Recruitment and mortality rates were recorded during monthly surveys of the adult populations. Within three mussel size classes (< 24, 25–74 and > 75 mm in shell length), peak recruitment coincided with high mortality in August of the 2 years studied. However, the most dramatic turnover of the population was observed at Scott Point in both years, following a spawning event. In adjacent waters at Scott Point, large accumulations of drift algae covered (up to 100% cover) with juvenile mussels may deplete food supplies usually delivered to intertidal adult mussels, causing their demise. Mats of adult mussels were observed “peeling-off” from the rocky shore at this time of the year, making space available to the new recruits. Where nearshore algal accumulations were moderate to low, only moderate to low mussel turnovers were observed (e.g. Tonatona Beach and The Bluff).

Biology and fishery of the whelk Buccinanops globulosum (Kiener, 1834) in northern coastal waters of the San Matías Gulf (Patagonia, Argentina)

The whelk Buccinanops globulosum, a very common prosobranch mollusk in northern Patagonian, is the target of a new fishery in San Matías Gulf. Given certain biological characteristics making this species susceptible to overfishing, a study started in 2000 in order to collect data on demography and growth at age of this species, with the aim to design and to implement a provisional management plan. Mean density was estimated at 111 individuals m −2 (S.D. = 16.77). Females outnumbered males in most of the months ( P < 0.05) and appeared laying egg capsules from November to January. The smallest female carrying egg capsules was 45.2 mm total conch length ( n = 36). Recruitment peak was identified in January 2002 and January–February 2003. Early crawling juveniles had a mean size of 4.2 mm conch length (S.D. = 0.51, n = 60). A total of 450 individuals (263 females and 187 males) were examined for growth at age. Significant differences were found in the growth parameters between sexes (maximum likelihood method; χ = 92.34; gl = 3; P < 0.001). Growth of males was lower than growth of females. Commercial capture of whelks is done by diving using a bait of fish discarded or open living purple clams. Only adults up 4 cm are retained during the fishing operations in a net bag. During 2000–2004 the annual catch varied from 20 to 9200 kg. Fluctuations in landings have more often reflected market prices rather than changes in the abundance of the resource. If effort for this whelk increases it should be necessary to consider a period of no fishery at all in the reproductive/recruitment period in order to ensure the sustainability of the stock.

Population and seasonal distribution of Procamallanus daccai in Eutropiichthys vacha in Kaptai Lake, Chittagong, Bangladesh

The population and seasonal distribution of Procamallanus daccai (Nematoda: Procamallanidae) in Eutropiichthys vacha (Siluridae) from the Kaptai Lake were studied for a period of 20 months during 1986-1987. A total of 208 fish were necropsied and 5652 worms were recovered, of which 2392 were from 87 infected male fish and 3260 were from 89 infected female fish. Prevalence values varied from 50% to 95%. The intensity and abundance of nematodes fluctuated over the study period and are statistically significant (F=14.87, P<0.0001), and showed a seasonal preference for the summer period (F=33.39, P<0.05). The mean intensity was the highest in the smallest size group at 66.3+/-12.7 which gradually decreased to 4+/-1.89 in the largest size group. No significant differences were found between parasites from male and female hosts, except in the summer. Male parasites were less abundant in the population. Female worms were grouped into immature, maturing and gravid and all these stages were present throughout the year. The highest occurrence of both immature and gravid P. daccai was found during the months of February to April each year. Peak recruitment seems to occur during this period due to the presence of high quantities of immature worms.

POPULATION DYNAMICS OF PHILURETER TRIGONIOPSIS (MONOGENEA: ANCYROCEPHALINAE) FROM URINARY ORGANS OF GALAXIAS MACULATUS (OSMERIFORMES: GALAXIIDAE) IN A COLD TEMPERATE ANDEAN PATAGONIAN LAKE (ARGENTINA)

Philureter trigoniopsis parasitizes the ureters and urinary bladder of Galaxias maculatus in Patagonian Andean lakes. To investigate factors associated with variation in the prevalence and intensity of this monogenean, fish were sampled periodically over 2 yr in Lake Gutiérrez. Prevalence and mean intensity are higher in smaller fishes than in larger ones. A seasonal pattern was observed, with peak recruitment and peak mean intensity occurring in early spring (September), followed by lows in late summer (January-February). Galaxias maculatus length classes are spatially segregated due to seasonal migrations, so the annual infection cycle is characterized by higher prevalence and intensity from late winter to early summer in the smaller fish from the deep zone of the lake.

Estrutura populacional de Hepatus pudibundus (Herbst) (Crustacea, Decapoda) na Armação do Itapocoroy, Penha, Santa Catarina, Brasil

Caranguejos são geralmente capturados como fauna acompanhante na pesca de arrasto do camarão sete-barbas, que opera intensivamente no litoral da Armação do Itapocoroy (26º42'36"S-26º46'20"S, 48º35'02"W-48º37'06"W). O objetivo deste estudo é fornecer informações sobre a estrutura da população de H. pudibundus capturados como fauna acompanhante do camarão sete-barbas. De agosto/1998 a julho/1999 foram capturados 1.319 exemplares, dos quais 473 eram machos (35,86%) e 846 fêmeas (64,14%). As freqüências relativas entre os sexos foram diferentes do esperado para a população (1:1). As fêmeas ovígeras ocorreram nos meses de dezembro a maio e em julho, sendo mais abundantes em março e se distribuíram nas classes de 3,0 a 7,0 cm. Os jovens foram registrados ao longo do ano, mas com maior abundância nos meses de inverno onde acontece provavelmente o pico de recrutamento. O tamanho de primeira maturação foi estimado em 3,6 cm de largura total da carapaça para as fêmeas e 3,5 cm para os machos. Os machos apresentaram uma associação maior entre a largura da carapaça e o peso fresco que as fêmeas, porém, em ambos o crescimento alométrico entre estas variáveis foi negativo.

Early life histories in the bryozoan Schizobrachiella sanguinea: a case study

Mediterranean populations of Schizobrachiella sanguinea seem to span a wide range of contrasting benthic habitats. We have studied adult, larval, and recruit populations of S. sanguinea from sublittoral (approximately 10 m depth) communities at Blanes (Spain, NW Mediterranean). At the study site, the species colonises semi-obscure caves and, to a lesser extent, communities of sciaphilic algae. Our first goal was to show the periods of brooding, larval release, and recruitment. Plankton was collected about twice a week between July 1998 and June 2000 over an artificial reef. A total of 303 larvae were collected in 23 of the 102 days of sampling. At the study site the species shows a single, annual larval release period, which occurs from late March to June–July every year. Recruits were found from late May to late August 1999 and in late May 2000. A recruitment peak was observed in July 1999 and again in late May 2000. The presence of brooding adults corresponded to the periods of larval supply and recruitment. Our second goal was to investigate the causes of the variable distribution of the species along several communities in the north-west Mediterranean Sea. We describe adult distribution and the dynamics of larval supply, recruitment of early (≤15 days from settlement) and late (≤4 months from settlement) recruits. Patterns of larval presence and early recruit distribution along the communities on the reef did not reflect the adult distributions, whereas this was closely matched by the distribution of late recruits. Post-recruitment mortality strongly affected recruits of the PA (photophilic algae) and SA (sciaphilic algae) communities, whereas it was very low in the communities of SOC (semi-obscure caves). Mortality of recruits was density independent and colony survivorship in the SA communities, where recruitment was the highest, appeared strongly affected by competition with brown algae. Like the majority of cheilostomate bryozoans, S. sanguinea releases a coronate larva capable of active swimming and positive reaction to light. Such swimming abilities may allow larvae to actively select the substrate on which to settle and to avoid unsuitable substrates. It seems that larval behaviour does not explain the preference of S. sanguinea for sciaphilic habitats. High post-recruitment mortality due to various factors, especially competition with fast-growing algae, seems particularly relevant in determining the adult distributions observed.

Coupling between Clathrin-Coated-Pit Invagination, Cortactin Recruitment, and Membrane Scission Observed in Live Cells

During clathrin-mediated endocytosis, membrane scission marks the isolation of a cargo-laden clathrin-coated pit (CCP) from the cell exterior. Here we used live-cell imaging of a pH-sensitive cargo to visualize the formation of clathrin-coated vesicles (CCVs) at single CCPs with a time resolution of seconds. We show that CCPs are highly dynamic and can produce multiple vesicles in succession. Using alternating evanescent field and epifluorescence illumination, we show that CCP invagination and scission are tightly coupled, with scission coinciding with maximal displacement of CCPs from the plasma membrane and with peak recruitment of cortactin-DsRed, a dynamin and F-actin binding protein. Finally, perturbing actin polymerization with latrunculin-B drastically reduces the efficiency of membrane scission and affects many aspects of CCP dynamics. We propose that CCP invagination, actin polymerization, and CCV formation are highly coordinated for efficient endocytosis.

Life history and production of Agapetus quadratus (Trichoptera: Glossosomatidae) in a temporary, spring‐fed stream

Summary1. The life history and trophic basis of production of the caddisfly grazer Agapetus quadratus were studied in the torrent Gorg Blau, a spring‐fed stream on the island of Majorca that dries annually during summer.2. Quantitative random samples were taken every 2–3 weeks during an annual surficial flow period, from November 2000 to mid‐July 2001. Instars of field‐collected larvae were determined by measurements of head width and pronotum length, and the sex of all pupae was determined to study sexual dimorphism and sex ratio.3. Stage‐frequency histograms suggested a trivoltine population, with an average cohort time of 4 months. Larval development was asynchronous, with continuous growth and overlapping generations. Recruitment peaks were identified in mid‐November, early March and late June, indicative of winter, spring and summer generations. On average, females were larger than males and the mean sex ratio was 2 : 3 (females : males). Population densities and biomasses derived from the field data were used to calculate production and turnover rate.4. Annual production of A. quadratus in the torrent Gorg Blau (4.80 g dry mass m−2 year−1) was the highest ever reported for the genus, being comparable with that estimated for some insects with rapid development and multiple cohorts.5. Estimates of production of A. quadratus were combined with foregut content analysis to estimate the fraction of total production derived from the principal food sources: algae and organic detritus. Algae supported a major proportion of the production of this grazer.6. The low density of predators characteristic of many temporary streams, and the small amplitudes in discharge and temperature during most of the wet period that characterise the spring habitats might allow high levels of grazer production in this particular Mediterranean stream.

Meso-scale spatial variation in settlement and recruitment of intertidal barnacles along the coast of central Chile

Spatial and temporal variation in recruitment can be the leading determinant of popu- lation fluctuations in species with pelagic larval stages. Characterizing and identifying the causes of such variation is, therefore, necessary to understand population dynamics, and to develop conserva- tion and management strategies. We examined spatial patterns in settlement and recruitment of the intertidal barnacles Jehlius cirratus, Notochthamalus scabrosus and Notobalanus flosculus, and their relationships with environmental variables operating at meso- (sea surface temperature, SST) and small (local topography) scales. Settlement and recruitment were studied over 6 mo at biweekly intervals at 16 sites along 120 km of coastline in central Chile. All species showed similar temporal patterns, with a peak in settlement and recruitment during austral spring. We decomposed the spa- tial patterns into their corresponding meso-scale trend (from a few to 10s of kilometers) and into their small-scale (site) residual variation. Recruitment of chthamaloid species was highly and positively correlated at meso- and small-scales, and the among-site rankings showed consistency of the spatial structure throughout the recruitment season. SST explained a significant fraction of the variance in recruitment of the chthamaloids at the meso-scale, and spatial analysis showed coincident decorrela- tion scales of about 35 km for SST and recruitment. In contrast, recruitment of balanoid species did not show a clear spatial structure, was not associated with meso-scale variation in SST, and local topography seemed to play a significant role in their settlement. Topographically modified upwelling dynamics over scales of 10s of kilometers is the most plausible factor shaping meso-scale variation in recruitment of chthamaloid barnacles, whereas settlement and recruitment of balanoid species seem more strongly influenced by processes acting at local scales. The spatial scale and structure of recruitment provide guidelines for the placement and spacing of protected areas in the region.

Spike-triggered average torque and muscle fiber conduction velocity of low-threshold motor units following submaximal endurance contractions

The motor unit twitch torque is modified by sustained contraction, but the association to changes in muscle fiber electrophysiological properties is not fully known. Thus twitch torque, muscle fiber conduction velocity, and action potential properties of single motor units were assessed in 11 subjects following an isometric submaximal contraction of the tibialis anterior muscle until endurance. The volunteers activated a target motor unit at the minimum discharge rate in eight 3-min-long contractions, three before and five after an isometric contraction at 40% of the maximal torque, sustained until endurance. Multichannel surface electromyogram signals and joint torque were averaged with the target motor unit potential as trigger. Discharge rate (mean +/- SE, 6.6 +/- 0.2 pulses/s) and interpulse interval variability (33.3 +/- 7.0%) were not different in the eight contractions. Peak twitch torque and recruitment threshold increased significantly (93 +/- 29 and 12 +/- 5%, P <0.05) in the contraction immediately after the endurance task with respect to the preendurance values (0.94 +/- 0.26 mN.m and 3.7 +/- 0.5% of the maximal torque), whereas time to peak of the twitch torque did not change (74.4 +/- 10.1 ms). Muscle fiber conduction velocity decreased and action potential duration increased in the contraction after the endurance (6.3 +/- 1.8 and 9.8 +/- 1.8%, respectively, P <0.05; preendurance values, 3.9 +/- 0.2 m/s and 11.1 +/- 0.8 ms), whereas the surface potential peak-to-peak amplitude did not change (27.1 +/- 3.1 microV). There was no significant correlation between the relative changes in muscle fiber conduction velocity or surface potential duration and in peak twitch torque (R2= 0.04 and 0.10, respectively). In conclusion, modifications in peak twitch torque of low-threshold motor units with sustained contraction are mainly determined by mechanisms not related to changes in action potential shape and in its propagation velocity.

Recruitment of Picea mariana, Pinus banksiana, and Populus tremuloides across a burn severity gradient following wildfire in the southern boreal forest of Quebec

Most studies of postfire tree recruitment have occurred in severely burned portions, despite the fact that partial burning is common. In this study we examined regeneration following a 1997 fire in the boreal forest of Quebec. A model of postfire recruitment was elaborated using parameters such as the proportion of trees killed (severity), the proportions of postfire seedbed types and their associated juvenile survivorship, the available seed supply, the available bud supply (for Populus tremuloides Michx.), and the granivory rate. All three species had peak recruitment in the first or second summer, and the recruitment episode was essentially finished after the third year. Mineral soil and surviving Sphagnum were the best seedbeds for both conifer species. Seedbed frequency was essentially independent of crown fire severity except for surviving Sphagnum, which was concentrated primarily where severity was light. Conifer fecundity was much lower in the lightly burned stands, a result we attribute to a higher granivory rate. The fecundity (seedlings/basal area for the conifers or suckers/basal area for Populus) in the severe sites was typical of the few other North American studies of postfire recruitment, where the published data permit us to make the comparison.

Population parameters and exploitation rate of demersal fishes in Brunei Darussalam (1989–1990)

Abstract Growth parameters ( L ∞ and K ) and mortality coefficients ( Z , M and F ) were estimated for 25 fish species caught in Brunei Darussalam. The number of recruitment peaks, growth performance index ( φ ′) and exploitation ratio ( E = F / Z ) was also assessed for each species. Routines in the FAO-ICLARM Stock Assessment Tools (FiSAT) software were used to estimate the parameters from length distribution data collected during a trawl survey in the coastal waters (10–100 m depth) of Brunei Darussalam from July 1989 to June 1990. The key parameters were used in yield- (Y/R) and biomass-per-recruit (B/R) analyses to derive reference points and evaluate the exploitation status of the 25 species. The E estimates for the 25 species were compared with those from other studies conducted in South and Southeast Asia to assess the relative exploitation status of demersal fish stocks in Brunei Darussalam. The other parameters obtained were also compared with available estimates to evaluate consistency of the results with current knowledge about the species in the region. The 25 species studied represented 70% of demersal abundance off Brunei Darussalam during the 1989–1990 survey. Relatively high K (and low L ∞ ) values, typical of short-lived tropical fishes, were obtained for most (22) of the species. Combined with the high Z (0.85–3.40) and M (0.73–3.10) estimates, these results imply low annual survival and high turnover rates. All 25 species exhibited year-round recruitment, with 20 species having two recruitment peaks annually and five species having a single annual recruitment peak. The φ ′ (2.05–3.32) and M parameters obtained were consistent with those available in the literature for the 25 species. The values of F (0.03–0.72) and E (0.02–0.27), however, were low compared to other assessments conducted in South and Southeast Asia. Estimates of E for the 25 species were also low compared to the E 0.1 (0.31–0.42) reference points obtained from the Y/R and B/R analyses. Low length-at-first capture was evident for 6 of the 25 species, although this is technologically difficult to avoid in multispecies fisheries. Overall, the results indicate that the 25 fish species were lightly fished in 1989–1990. The results provide baseline information (as well as reference points) that can be incorporated into wider reference systems relevant to current fisheries assessment and management in Brunei Darussalam, and are relevant to further (multispecies or ecosystem) studies of fisheries in the country and the region.

Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui Southward and Chthamalus stellatus (Poli) (Crustacea: Cirripedia) over an European scale

Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui and Chthamalus stellatus was examined over an European scale. The study was carried out using standardised protocols at a series of locations. The five locations chosen (SW Ireland, NW Spain, SW Portugal and NW and NE Italy) span a large part of the range of these species in Europe. The spatial scales were location (hundreds of kilometres) and shore (thousands of metres). Estimates of total cumulative recruitment (cyprids and metamorphs) summed over the year (April 1997 to March 1998) showed substantial variation between locations which was dependent on the species. Recruitment was highest in SW Portugal for C. montagui and in SW Ireland and NW Spain for C. stellatus. Overall recruitment of C. montagui was higher than that of C. stellatus at all locations except SW Ireland, where recruitment of the two species was not significantly different. There were significant differences among shores in each location. The recruitment period of both species varied with location, with recruitment beginning earlier further south. In general, recruitment of C. montagui and C. stellatus was recorded in 8 months in NW Spain and NE Italy, while only in 7 months in SW Ireland. Recruitment of C. montagui occurred in 10 months in SW Portugal, but no recruits of C. stellatus were found. In all locations there was at least one distinct peak of recruitment. In SW Ireland both species showed only one peak of recruitment, a month after initiation. At the more southerly Atlantic locations, as well as in the Mediterranean, two unequal peaks of recruitment were generally seen. During recruit census, the number of cyprids, in comparison to metamorphs, found at any location was very low. In SW Ireland and NW Spain cyprids of both species were found, while in SW Portugal and in the Mediterranean, only cyprids of C. montagui were found.

Leukocyte Recruitment to Peritoneal Cavity of Rats Following Formalin Injection: Role of Tachykinin Receptors

The aim of this work was to verify whether formalin would induce leukocyte recruitment following intraperitoneal (i.p.) injection in rats. Formalin (1.25 – 2.5%) induced cell recruitment, which was concentration- and time-dependent (0 – 24 h). Two peaks of leukocyte recruitment were observed. The first peak (from 2 to 4 h) was characterized by a mixed polymorphonuclear and lymphocyte cell population (representing an increase of 100 – 220% and 55 – 60%, respectively), whereas the second peak was characterized by a marked increase in lymphocytes at 24 h (representing an increase of 230%). Pretreatment of animals with specific antagonists for neurokinin NK1, NK2, and NK3 receptors (SR140333, SR48968, and SR142801 compounds, respectively) reduced the early leukocyte increase (representing a significant reduction of 65%, 51%, and 46%, respectively), whereas only the treatment with NK2-specific antagonist reduced the late cell increase induced by formalin injection (amounting to a significant reduction of 48%). These results suggested that substance P, neurokinin A, and neurokinin B release accounted for formalin-induced cell migratory activity. The anti-inflammatory drug dexamethasone also reduced cell recruitment, which was mainly related to a reduction in 79% of the neutrophils at 4 h following 1.25% formalin injection, suggesting also a release of lipid mediators (eicosanoids and/or platelet-activating factor) and/or cytokines/chemokines by the formalin injection.

Population dynamics, infestation and host selection of Vexilla vexillum, an ectoparasitic muricid of echinoids, in Madagascar

The symbiotic interaction, population and infestation dynamics of the muricid Vexilla vexillum (Gmelin, 1791) on 2 echinoid species, Tripneustes gratilla (Linnaeus, 1785) and Echinometra mathaei (Blainville, 1825), was investigated on the barrier reef off Toliara (Madagascar). V. vexillum is an ectoparasitic muricid which was exclusively found in association with sea urchins, on which it moves freely and browses over the integument. Host recovery from damage caused by muricid grazing was dependent on lesion size. Small lesions regenerated while larger ones were subjected to secondary infections, which led to host death. A 27 mo survey (2000 to 2003) of the muricid's population dynamics revealed annual recruitment episodes during the mid-summer season (December to January). Patterns of recruitment peaks were apparently linked to its reproductive cycle. Demographic parameters including growth and mortality rates of the muricid were estimated from analysis of size-frequency distributions. Growth was described by the von Bertalanffy function. The model predicts that V. vexillum is a fast-growing species in which asymptotic shell length (L infinity = 1.024 cm) is reached 6 to 7 mo after recruitment. The growth rate constant K, and shell length at settlement L0, were estimated from the model. Estimated mortality rate was 55% yr(-1); V. vexillum has a short lifespan. The observed high growth rate together with the high mortality rate suggest that V. vexillum is a semelparous species. A field survey of the infestation dynamics of V. vexillum was performed during 3 consecutive years, with seasonal variation in parasite prevalence on both echinoid host species. Although both T. gratilla and E. mathaei were infested, a preference towards T. gratilla was noted. This was attributed to T. gratilla's test morphology (which allows better accessibility for grazing), to the muricid's higher recognition capacity of T. gratilla (as determined by olfactory experiments) and to the high recruitment predictability of that particular host. This study provides novel information on the biology of V. vexillum, an echinoid epidermal grazer, and its relationship with 2 ecologically and economically important echinoid species.

Recruitment indices of European hake, Merluccius merluccius (Linnaeus 1758), in the Northwest Mediterranean based on landings from bottom-trawl multispecies fisheries

Abstract Temporal and spatial variation in Merluccius merluccius recruitment in the Northwest Mediterranean is examined, and recruitment indices are derived from monthly M. merluccius catch rates of four bottom-trawl fleets operating in Spanish and Italian waters during the period 1991–1999. Where M. merluccius catches were not recorded by size category, multivariate techniques were applied to species proportions in order to identify catch records most representative of recruit abundance. Selected catch rates were analysed by generalized linear models (GLMs) to estimate recruitment indices. The GLMs explain large proportions of the variation in recruit abundance (50–84%) and indicate significant annual and seasonal variation in recruitment strength. Vessel was by far the most important factor affecting catch rates of recruits, stressing the need to account for vessel characteristics when analysing commercial catch data for stock assessment. Seasonal patterns of recruitment reveal similarities among the study areas and interannual variations within areas. One major recruitment peak was identified in each area during either spring/summer or late summer/winter. In most areas, recruitment between 1991 and 1999 seemed to decline, but this could not be confirmed owing to high interannual variability. The coherence of annual fluctuations in recruitment indices with those of MEDITS surveys supports the present results.

A temperature-dependent reproductive model for spotted seatrout (Cynoscion nebulosus) explaining spatio-temporal variations in reproduction and young-of-the-year recruitment in Florida estuaries

Abstract Spotted seatrout (Cynoscion nebulosus) exhibit various seasonal patterns of reproduction and juvenile recruitment in estuaries across their range. To explain this variability, data on the reproductive state of 1674 individual females from the Indian River Lagoon were used to develop a generalized additive model (GAM) describing the relationship between reproduction and local environmental conditions. The model predicted that optimum spawning conditions exist at a water temperature of 29°C, indicating that if this temperature was exceeded during the spawning season, spawning activity would be temporarily curtailed, which would lead to a bimodal recruitment curve. In contrast, daily mean water temperatures below the optimum condition would result in a single recruitment peak. The reproductive model was largely consistent with historical information on spotted seatrout spawning seasonality along the gulf and Atlantic coasts of the US. Factors other than temperature (i.e., hours after sunset, lunar period and size and condition factor of females) were also found to regulate reproductive activity. Model predictions of the number of recruits based on local temperature regimes during the spawning season were compared to actual catches of juvenile spotted seatrout in three Florida estuaries. The reproductive model was able to predict the timing and modality of recruitment, but the relative amplitude of the fluctuations in abundance was dampened considerably compared to the observed variation.

Seasonal dynamics of Zostera caulescens: relative importance of flowering shoots to net production

Zostera caulescens occurs only in limited localities around Japan and Korea, and is listed as a threatened plant species in Japan. We present the first quantitative data on seasonal dynamics of Z. caulescens based on a 13-month field study of a subtidal seagrass bed (4–6 m deep) in Funakoshi Bay, northeastern Japan. We investigated the relative importance of flowering shoots on total net production: these flowering shoots form a canopy structure several meters above the sea bottom. Flowering shoots were observed throughout the year but showed large seasonal variation in density, with a maximum in spring to summer (>30 shoots m −2) and a minimum in winter (3 shoots m −2). The density of vegetative shoots fluctuated between 120 and 238 shoots m −2, but did not show a significant seasonal variation. Age distribution of both flowering and vegetative shoots showed marked seasonal variation, with the peak in recruitment observed during winter to early spring. Leaf plastochrone intervals were 2- to 3-fold shorter in summer than in winter, with an annual average of 15.3 and 18.1 days for flowering and vegetative shoots, respectively. On the basis of these data, the absolute age of the oldest flowering shoot was estimated at 13 months. Biomass and net production of Z. caulescens were highest in summer and lowest in winter. During spring to autumn, flowering shoots constituted more than 70% of both biomass and production, while the contribution of vegetative shoots dominated during winter, when the density of flowering shoots was low. Annual net production was estimated to be 292 and 134 g DW m −2 per year for the aboveground parts of flowering and vegetative shoots, respectively, and 47 g DW m −2 per year for the belowground parts, giving a total of 473 g DW m −2 per year. These findings demonstrated that the flowering shoots of Z. caulescens are important not only for seed production, but also as major photosynthetic parts of the population, helping to achieve high primary production despite their distribution at the deeper parts of the multispecific seagrass bed.

Seasonal trends in the recruitment of skipjack tuna ( Katsuwonus pelamis) to the fishing ground in the southwest Atlantic

We studied the recruitment of skipjack tuna ( Katsuwonus pelamis) in the southeast of South America. Scientific literature about skipjack tuna spawning behavior in the Atlantic Ocean is not conclusive. Some authors suggest erratic spawning throughout the year in eastern equatorial Atlantic waters while others suggest aggregation of eggs and larvae off the eastern tropical coast of South America in spring and summer. Time series analysis of length frequency was used to study the dynamics of skipjack recruitment. We found peaks of recruitment to the fishery ground, with periods of 12 months. The peaks for a 12-month period, defined by an increase in contribution of young fish in early summer and a sequential decrease until spring, were not strong. Therefore, the existence of seasonal signals embedded in an erratic continuous recruitment across the year is the most creditable hypothesis for the southwestern Atlantic. Differences in the recruitment pattern on the main fishing grounds should be considered in assessment models for skipjack stocks in the Atlantic Ocean.

Stand history and its consequences for the present and future dynamic in two silver fir (Abies alba Mill.) stands in the high Pesio Valley (Piedmont, Italy)

Two silver fir (Abies alba Mill.) forest stands have been identified on unmanaged parts of previously managed forests in the Alta Valle Pesio e Tanaro Regional Park (Piedmont, Italy) in order to study their origin, past forest dynamic and disturbance history. The historical development and the successional history of these stands were investigated in two plots of 2000 m$^2$ by means of the following techniques: size and age structure analysis, abrupt growth changes analysis, establishment of pioneer species and of early-seral shade-intolerant species, historical data of logging. The stands investigated are relatively young; in the past 70 years some periods of heavy logging have been identified. Intense cutting has caused the establishment of an abundant regeneration of shade intolerant early-seral broadleaves species. The peak recruitment period of the broadleaves occurred around 1940 in plot 1 and around 1975 in plot 2. The current structures and composition of the forest are therefore the result of anthropogenic activity, indeed, the presence of pure silver fir stands in the past were the result of human intervention. The silver fir will share future dominance with several broadleaves species such as the beech (Fagus sylvatica L.) and the sycamore (Acer pseudoplatanus L.) although the exact successional status of these stands is unresolved.