Settlement Season Research Articles

Ocean conditions influence the quality of recruiting benthic marine invertebrate larvae—Insights from fatty acids

AbstractMany marine benthic invertebrates have a pelagic life stage, during which larvae need to accumulate enough reserves to complete metamorphosis to a settled benthic juvenile. Currently, very little is known about how ocean conditions affect quality of the larvae. We studied this for three settlement seasons (2017–2019) by collecting returning Dungeness crab (Metacarcinus magister) megalopae at the Oregon coast and analyzing them for fatty acid biomarkers. We found that the larvae are omnivorous and have versatile diets. The daily larval abundance was positively correlated with larval quality. Despite the relatively high day‐to‐day variation, we found pronounced seasonal and inter‐annual differences in the body condition (size and total fatty acid content) and biomarker composition of megalopae. Especially, the early season recruits of 2017 had lower content of lipids and polyunsaturated fatty acids known to be beneficial to crustaceans. This is likely related to lingering effects of the eastern Pacific marine heat wave (2014–2016) on pelagic communities. The larvae were rich in docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) with lower levels in benthic juveniles, indicating an ontogenetic diet shift and likely lower availability of DHA and EPA in the benthic environment. The pulsed megalopa recruitment may provide substantial carbon and lipid inputs to the nearshore ecosystem as a form of pelagic subsidy. Our results reveal that ocean conditions may have an effect on the quality of returning larvae, which likely influence their recruitment performance and early juvenile success, and thus potentially also the population size and commercial catch 4 yr later.

Timing of deployment does not affect the biodiversity outcomes of ecological enhancement of coastal flood defences in northern Europe

Timing of installation is an important factor when planning the deployment of ecological enhancements to intertidal coastal and marine infrastructure. Such nature-based solutions (NbS) are increasingly used worldwide, so understanding whether the timing of deployment affects colonisation success is crucial to enhance their success and identify any ecological sensitivities that must be taken into consideration during construction. To date, none of the previous marine eco-engineering studies globally have looked specifically at timing. An unexpected COVID19 interruption in retrofitting Ecotiles designed to improve urban marine biodiversity provided a unique window of opportunity to address this research gap. We examined if time of deployment affects the early colonisation (within 18 months) success of eco-engineering enhancements. Thirty concrete tiles (Ecotiles) cast with a novel multi-scale, multi-species textured formliner were deployed on rock armour in three sites along the coast in Edinburgh, Scotland, at two different time periods (early March and late May 2020). After two settlement seasons, the colonisation success of 85% of the studied species did not vary between the times of deployment. Early colonisation success of intertidal species equalised within two settlement seasons of deployment, along with an overall increase in species richness. Crucially, these results also show that summer construction periods designed to reduce impacts on overwintering birds, do not adversely impact intertidal species during their peak (spring-summer) recruitment period in northern Europe. This novel result provides further support for widespread use of eco-engineering to enhance large coastal infrastructure projects and achieve ecological goals in northern Europe. More widely, this work contributes to the understanding of the impact of deployment timing on the success of similar NbS worldwide.

The BioGeo Ecotile: Improving biodiversity on coastal defences using a multiscale, multispecies eco-engineering design

Hard coastal defences support lower biodiversity than natural rocky shores. Ecological enhancement on coastal structures can improve biodiversity by increasing habitat heterogeneity. Most studies have investigated the effect of only one type of texture on intertidal biodiversity. There is a lack of eco-engineering designs that mimic the complexity of natural rocky shores and are scalable for real world applications and commercial manufacturing. To address these gaps, we developed a novel, multiscale (mm-cm), multispecies design called BioGeo Ecotile that is scalable and readily manufacturable. The hybrid design combines previously tested eco-engineering features (pits, holes, grooves and crevices), providing habitats for a range of intertidal organisms. To test the success of the design, Ecotiles and smooth tiles were deployed on rock armour and flood walls along Edinburgh's coast, Scotland. Post-deployment, data on species presence and abundance were collected at the start and end of the second settlement season. Textured Ecotiles supported higher species richness (F3,55 = 21.18, p < 0.001) and colonisation than smooth tiles and adjacent rock armour. Ecotiles supported more mobile species, some of which (crabs) were not recorded on the other treatments. Material type (concrete vs rock) significantly affected community composition, where concrete was dominated by fucoids and rock by barnacles. In this temperate setting, the Ecotiles have enhanced biodiversity of rock armour achieving practical conservation goals. This is the first known retrofit of tiles onto rock armour in the UK. The tiles can be scaled up to whole walls or rock armour units. We demonstrate that a science-design approach can achieve ecological and engineering goals simultaneously, which can accelerate widespread implementation of eco-engineering in large-scale projects.

Settlement and recruitment of fish in mussel farms

. Fish are thought to settle and recruit to shellfish and seaweed farms; however, there is little published evidence to support this assumption. Shellfish and seaweed farms increase structural complexity and epibiota productivity, which may attract settling fish larvae. In this study, fish settlement and recruitment patterns into 2 aquaculture habitats, mussel-kelp co-culture and mussel farm monoculture, were compared to 2 adjacent natural habitats, soft-sediment seafloor and rocky reef, within a settlement season. Standard monitoring units for the recruitment of fish (SMURFs) were used, as they are a common and reliable method for measuring temporal and spatial variability in fish settlement and recruitment among habitat types. The communities of fish species settling and recruiting to both sets of aquaculture and natural habitats were equivalent. This was most likely due to the artificial 3D structure of the mussel farm habitats functioning in a similar manner to the structural complexity of a rocky reef habitat. Further, there was indication that for at least the most abundant fish species, Fosterygion lapillum, the 2 aquaculture habitats were of sufficient quality to support growth from settlement to juvenile size classes (i.e. in mussel monoculture habitat 65% were newly settled in December, and 86% were of juvenile size class by February). Overall, these findings provide foundational quantitative evidence of the interactions that fish have with mussel farms and increases the understanding of restorative opportunities for aquaculture operations.

Assisted Natural Recovery: A Novel Approach to Enhance Diadema antillarum Recruitment

The massive die-off of the sea urchin Diadema antillarum in 1983–1984 is one the main reasons for low coral recruitment and little coral recovery in the Caribbean. As the natural recovery of D. antillarum is slow to non-existent, multiple restoration studies have been attempted. There are currently three different approaches to obtain individuals for restocking: the translocation of wild-collected juveniles or adults, lab-reared juveniles cultured from wild-collected settlers, or lab-reared juveniles cultured from gametes. All three methods are costly and can only be applied on a relatively small scale. We here propose a fourth, new, approach, which we term assisted natural recovery (ANR) of D. antillarum populations. ANR, a concept already applied in terrestrial restoration to restore forests and grasslands, can accelerate succession by removing barriers to natural recovery. In this study, performed on the Dutch Caribbean island of Saba, suitable settlement substrate was provided in the form of bio ball streamers that were attached to the reef shortly before the settlement season. At the end of the experiment, reefs with streamers had significantly higher D. antillarum recruit densities than control reefs without additional settlement substrate, indicating that the lack of settlement substrate is an important factor constraining natural recovery. However, D. antillarum recruit abundance was low compared to the measured settlement rates, possibly due to low post-settlement survival. The size distribution of recruits showed that recruits almost never became larger than 20 mm, which is likely due to predation. We conclude that, next to low settlement availability, low post-settlement survival and high predation on recruits also constrain the natural recovery of D. antillarum populations on Saba. To improve the survival of settlers till adults, we propose to 1) reduce predation on settlers by using bio balls or other substrates that can provide shelter to larger individuals and 2) optimize the reef habitat by removing macroalgae, either manually or by facilitating other herbivores. To improve the survival of recruits, we suggest to 1) choose sites with a known lower predation density or 2) protect recruits with a corral around the reef underneath the streamers. The combination of these measures could improve prospects for ANR, and we expect this new approach can contribute to the recovery of D. antillarum populations in the future.

High peak settlement of Diadema antillarum on different artificial collectors in the Eastern Caribbean

The massive die-off of the herbivorous sea urchin Diadema antillarum in 1983 and 1984 resulted in phase shifts on Caribbean coral reefs, where macroalgae replaced coral as the most dominant benthic group. Since then, D. antillarum recovery has been slow to non-existent on most reefs. Studying settlement rates can provide insight into the mechanisms constraining the recovery of D. antillarum, while efficient settlement collectors can be used to identify locations with high settlement rates and to collect settlers for restoration practices. The aim of this study was to compare pre and post die-off settlement rates and to determine possible settlement peaks in the Eastern Caribbean island of St. Eustatius. Additionally, we aimed to determine the effectiveness and reproducibility of five different settlement collectors for D. antillarum. D. antillarum settlement around St. Eustatius was highest in May, June and August and low during the rest of the study. Before the die-off, settlement recorded for Curaçao was high throughout the year and was characterized by multiple settlement peaks. Even though peak settlement rates in this study were in the same order of magnitude as in Curaçao before the die-off, overall yearly settlement rates around St. Eustatius were still lower. As no juvenile or adult D. antillarum were observed on the reefs around the settlement collectors, it is likely that other factors are hindering the recovery of the island's D. antillarum populations. Of all five materials tested, bio ball collectors were the most effective and reproducible method to monitor D. antillarum settlement. Panels yielded the least numbers of settlers, which can partly be explained by their position close to the seabed. Settler collection was higher in mid-water layers compared to close to the bottom and maximized when strings of bio balls were used instead of clumps. We recommend research into the feasibility of aiding D. antillarum recovery by providing suitable settlement substrate during the peak of the settlement season and adequate shelter to increase post-settlement survival of settlers. The bio ball collectors could serve as a suitable settlement substrate for this new approach of assisted natural recovery.

Revisiting cross-shelf transport of Dungeness crab (Metacarcinus magister) megalopae by the internal tide using 16 years of daily abundance data

Many marine organisms have a biphasic life beginning with a planktonic larva that undergoes development on the continental shelf. These larvae ultimately need to return to the nearshore environment to settle. One proposed mechanism of transport to the nearshore is the internal tide. The Dungeness crab, Metacarcinus (Cancer) magister, is one species that is hypothesized to be transported by the internal tide. In addition to daily cycles in catch of megalopae being correlated with the internal tide, the annual catch of megalopae is correlated with the Pacific Decadal Oscillation. However, intial studies occurred during a positive phase Pacific Decadal Oscillation. In this study, we analyze an additional 12 years of data (16 years total) to determine if the internal tide continues to be correlated with the transport of Dungeness crab megalopae. We used wavelet analyses and cross-Fourier analysis to relate the catch of megalopae to the daily maximum tidal range, wind speed, and sea surface temperature. We found that over 16 years, the correlation with the daily maximum tidal range continues to be the strongest correlate with the daily catch of megalopae. These results continue to suggest megalopae are transported across the continental shelf by the internal tide. Our use of wavelets allowed us to examine the annual trends in periodicity of returning megalopae. We found that the periodicities at tidal frequencies did not persist throughout the settlement season. We hypothesize this indicates cross-shelf transport is primarily regulated by the internal tide but additional, unknown factors, interact with the internal tide affecting the number of returning larvae. We conclude by discussing why high-frequency sampling is an important component of ecological time series.

Toward an Integrated Model for Soft-Mobility

A key urban design challenge is to create built environments that encourage outdoor activity all year round. This study explores a new model for soft-mobility that places the interaction between the urban form, the seasonal climate and climate change, and the individual at the center of people’s soft-mobility choices, or in more general, their modal choice. The research methods used were comparative studies of documents, surveys, mental mapping, and photo elicitation. These studies were undertaken to research people’s outdoor activity in the built environment during the winter season of a cold climate settlement. The results were analyzed against the three-dimensions of the model. In the discussion it is argued that in places with significant climate variation, the interaction between the urban form, the season, and the individual together influence soft-mobility choices. In turn, these interactions influence people’s level of outdoor activity and the individual health benefits such activity can afford. In conclusion, it is highlighted that all three dimensions of the model are in a constant state of change and evolution, especially in relation to planning and development processes and climate change.

Wave-modulation of mussel daily settlement at contrasting rocky shores in central Chile: topographic regulation of transport mechanisms in the surf zone

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 606:39-53 (2018) - DOI: https://doi.org/10.3354/meps12782 Wave-modulation of mussel daily settlement at contrasting rocky shores in central Chile: topographic regulation of transport mechanisms in the surf zone Nicolas Weidberg1,3,*, Bryan Bularz1, Sebastián López-Rodríguez1, Sergio Andrés Navarrete1,2 1Estación Costera de Investigaciones Marinas (ECIM), Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, 6513677 Santiago, Chile 2LINCGlobal CSIC-UC and Center for Applied Ecology and Sustainability (CAPES), Pontifica Universidad Católica de Chile, 6513677 Santiago, Chile 3Present address: Department of Arctic and Marine Biology, University of Tromsø, 9019 Tromsø, Norway *Corresponding author: j_weidberg@hotmail.com ABSTRACT: Settlement is a complex biological process that, for most species, marks the end of pelagic larval life and the beginning of benthic life, and is therefore critical for the replenishment and persistence of marine benthic populations. Increasing evidence points to the surf zone as an important last hurdle modulating successful onshore larval settlement in intertidal and shallow subtidal habitats. Wave hydrodynamics cause the development of near-bottom flows, which have been suggested as a mechanism of cross-surf zone transport of heavy sinking competent larvae of mussels. Here, we tested the generality of this model with new data, contrasting 2 distant (100 km) sites with different surf zone configurations and slopes. Daily mussel settlement rates were measured for 3 periods of 10 d over 3 different settlement seasons between 2015 and 2017, and were related to potential cross-shore transport mechanisms. When corrected for differences in surf zone slope between sites and de-seasoned, near-bed bottom flows explained 87% of the variance in daily settlement at both sites, with the exception of the steep surf zone site in 2016, when settlement increased even faster with the flow. When flow direction is considered, site-specific alongshore and cross-shore transport patterns emerge at the reflective and dissipative shores, respectively. These patterns suggest that wave-induced transport through the surf zone can be a general mechanism favoring onshore mussel settlement, and highlight the importance of local topography in modulating such transport mechanisms. KEY WORDS: Larval supply · Orbital velocities · Coastal orientation · Upwelling Full text in pdf format Supplementary material PreviousNextCite this article as: Weidberg N, Bularz B, López-Rodríguez S, Navarrete SA (2018) Wave-modulation of mussel daily settlement at contrasting rocky shores in central Chile: topographic regulation of transport mechanisms in the surf zone. Mar Ecol Prog Ser 606:39-53. https://doi.org/10.3354/meps12782 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 606. Online publication date: November 15, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Industrial Seawater Cooling Systems under Threat from the Invasive Green Mussel Perna viridis

The green mussel Perna viridis, native to the Asia-Pacific region, has been introduced to other regions such as the Caribbean, Japan and North and South America. It is a large, commercially important species, widely cultivated and harvested in Southeast Asia, but is also considered an invasive species elsewhere, capable of replacing native species. As a fouling organism in intake systems of coastal power plants, it causes flow blockage and loss of cooling efficiency. Mussel colonization during peak settlement season can exceed 35,000 individuals/m2 and biomass can exceed 100 kg/m2. They can withstand wide fluctuations in temperature and salinity. Previous work has shown that a conventional biofouling control measure such as chlorination is not very effective against these bivalves, unless applied continuously for extended periods of time. We require more efficient, environmentally compatible methods of biofouling control. The paper discusses these issues in the context of the perceived invasion potential of P. viridis.

Settlement and post-settlement survival rates of the white seabream (Diplodus sargus) in the western Mediterranean Sea.

Survival during the settlement window is a limiting variable for recruitment. The survival is believed to be strongly determined by biological interactions and sea conditions, however it has been poorly investigated. We examined the settlement patterns related to relevant biotic and abiotic factors (i.e. Density-dependence, wind stress, wave height and coastal current velocity) potentially determining post-settler survival rates of a coastal necto-benthic fish of wide distribution in the Mediterranean and eastern Atlantic, the white seabream (Diplodus sargus). An observational study of the demography of juveniles of this species was carried out at six coves in Menorca Island (Balearic Islands, western Mediterranean). Three of the coves were located in the northern and wind exposed coast, at the Northeast (NE) side; while the other three were found along the southern and sheltered coast, at the Southwest (SW) side of the island. The settlement period extended from early May to late June and maximum juvenile densities at the sampling sites varied between 5 and 11 ind. m-1 with maximum values observed in late May simultaneously occurring in the two coasts. Our analysis of juvenile survival, based on the interpretation of the observed patters using an individual based model (IBM), revealed two stages in the size-mortality relationships. An initial density-dependent stage was observed for juveniles up to 20 mm TL, followed by a density independent stage when other factors dominated the survival at sizes > 20 mm TL. No significant environmental effects were observed for the small size class (<20mm TL). Different significant environmental effects affecting NE and SW coves were observed for the medium (20-30mm TL) and large (>30mm TL) size class. In the NE, the wind stress consistently affected the density of fish of 20–30 mm and >30 mm TL with a dome-shape effect with higher densities at intermediate values of wind stress and negative effect at the extremes. The best models applied in the SW coves showed a significant non-linear negative effect on fish density that was also consistent for both groups 20–30 mm and >30 mm TL. Higher densities were observed at low values of wave height in the two groups. Because of these variations, the number of juveniles present at the end of the period was unrelated to their initial density and average survival varied among locations. In consequence, recruitment was (1) primarily limited by denso-dependient procedures at settlement stage, and (2) by sea conditions at post-settlement, where extreme wave conditions depleted juveniles. Accordingly, regional hydrodynamic conditions during the settlement season produced significant impacts on the juvenile densities depending on their size and with contrasted effects in respectto cove orientation. The similar strength in larval supply between coves, in addition to the similar mean phenology for settlers in the north and south of the Island, suggests that all fish may come from the same parental reproductive pool. These factors should be taken into account when assessing relationships between settlers, recruits and adults of white seabream.

Testing for Sediment Acidification Effects on Within-Season Variability in Juvenile Soft-Shell Clam (Mya arenaria) Abundance on the Northern Shore of the Bay of Fundy

Soft-shell clams (Mya arenaria) can serve important ecological roles in intertidal mudflats and are an important economic and recreational resource in the northwestern Atlantic. However, environmental factors affecting newly-settled and juvenile clam abundances within a given settlement season remain uncertain. We conducted a field study assessing relationships between juvenile soft-shell clam abundance and spatial, temporal, and environmental variables in coastal mudflats of the northern shore of the Bay of Fundy. Sediment pH and low-tide water temperature (tide pools) were monitored in situ on a biweekly–monthly basis over the course of the M. arenaria settlement season in 2012 at four study sites to quantify diel variation in sediment pH and temperature. Core samples were also collected to quantify M. arenaria (<6 mm) abundance. Sea-surface and air temperature, and in situ sediment pH and water temperature were then used to predict clam abundance. Sediment pH was spatially and temporally variable, while in situ temperature was stable and declined over the sampling season. Akaike’s information criterion model selection indicated that models incorporating site, date, and air temperature best predicted 2012 recruitment patterns in linear models when all variables were included. When only environmental variables were included, the best linear model included minimum air temperature and sediment pH. When data were averaged across dates for each site to remove potential temporal effects, mean clam abundance displayed a significant positive relationship with sediment pH and sediment grain size, but not minimum air temperature. The results of this study suggest that sediment pH and/or sediment grain size may influence within-season juvenile soft-shell clam abundances across mudflats in the Bay of Fundy. Field experiments at the same (or similar) sites are now needed to confirm the mechanism driving the observed relationships.

Comparative Studies on the Biological Glue of Some Opportunistic Adult Marine Macro-Fouling After Dislodgement and Construction of Temporary Faunal Conglomerations

Comparative Studies on the Biological Glue of Some Opportunistic Adult Marine Macro-Fouling After Dislodgement and Construction of Temporary Faunal Conglomerations This study aimed to elucidate the composition of the biological glue of the sea anemone Metridium senile, the tubeworm Serpula vermicularis, the acorn barnacle Balanus amphitrite, the gastropod limpet Patella aspera and the sea squirt Styela plicata and to analyze these biological glue in the different seasons of the year. Furthermore, to propose antifouling strategies that can be developed from the present results. The sessile macro-fouling have the capability to dislodge and crawl searching for new suitable substrata for attachment. A total of 30 taxa representing five phyla were sampled every season across Northern Khobar estuarine beach of the Arabian Gulf. The proximate compositions of protein, lipid and carbohydrate in the basal discs or attachment integuments were measured using the Folin-Ciocalteu Phenol method of 66 Lowry et al., the chloroform-methanol method according to Folch et al. and the phenol-sulfuric acid method of Dubois et al. respectively. The total fat, protein, carbohydrate, and moisture contents ranged from 1 ± 0.57% -2 ± 0.98%, 23 ± 1.60 -23 ± 0.80, 0,2 ± 0,10 -1,98 ± 0,20 and 71 ± 0.61% -72 ± 2.07% by weight, respectively. The indispensable and conditional amino acids predominated in tissues were estimated. A high-pressure chromatographic separation was applied for amino acid analysis of biological glue. The most predominant amino acids were Aspartic acid (Asp D), Glutamine (Gln Q), Glycine (Gly G), Methionine (Met M), Phenylalanine (Phe F), Serine (Ser S) and Valine (Val V). Proteins in biological glue of the five species were resolved by SDS-PAGE and digested with trypsin. The majority of the resolved protein spots were within the molecular size ranging from 250 kDa to less than 30-kDa. The total lipid was estimated by chloroform-methanol method according to Folch et al. Capillary gas chromatography was applied to measure the fatty acid profiles of the biological glue. The lipid content of the biological glue of the five species studied were roughly similar but in different quantities. It was found that lipids of biological glue were predominant by C18:1 V-5, C18:2 V-6, C19:1 v- 8, C20:1 V-9, C24:1 V-6, C19:2 V-6. The estimation of total carbohydrate content of tissue in the basal discs or attachment integuments of the five macro-benthos ranged from 2.5 to 8.7 mg carbohydrates g-1 wet weight. The carbohydrate content of the biological glue was apparently dependent partly on species and partly on the season of settlement. All data obtained were statistically analyzed using One-way analysis of variance (ANOVA) of means with significance at P 0.05; Tukey's Multiple Comparison Test Mean Difference at P>0.05, P 0.05.

Does settlement and season of birth influence body size? A cross-sectional study of school children and adolescents in Republic of Niger

Background: The objective of the present study was to examine the effect of season of birth and settlement on body dimensions of children and adolescents from Niger Republic. The study group comprises 1547 boys and 1660 girls from Niger Republic. Materials and Methods: The study was conducted in rural, urban, and semi-urban regions in the Southeast Region of Niger Republic. Data were collected with structured questionnaire followed by anthropometric measurements of stature and weight. Others are head, hip, waist, leg, and mid-upper arm circumference (MUAC). Biceps, triceps, subscapular, and supra-iliac skinfolds were also measured. Statistical analyses included Student's t- test, one-way analysis of variance. Results: Birth weight, weight, stature, and body mass index showed little sexual dimorphism across various age groups. There were significant differences in all anthropometric variables based on settlements (P 0.05). Individuals residing in semi-urban area have significantly higher body dimensions than those from the other two settlements except for stature, weight, and MUAC. Individuals born in dry season have higher body dimensions than their counterparts born in wet season. Marked significant differences in body dimensions based on the season of birth were observed among boys than girls. Conclusion: The present study reveals difference in body sizes based on settlements while the magnitude of the impact of season of birth is more among boys than girls.

Spatio-temporal patterns of coral recruitment at Vamizi Island, Quirimbas Archipelago, Mozambique

Spatial and temporal patterns of recruitment of reef corals were assessed for the first time in Mozambique by deploying settlement plates at various spatio-temporal scales between October 2012 and October 2013. The abundance of juvenile corals (5−50 mm in diameter) was assessed along transects. Settlement of acroporids was highly seasonal, with 97% of spat settling between July and October 2013. Pocilloporids settled throughout the year, peaking slightly between October 2012 and January 2013. The annual mean larval settlement of up to 1 135 spat m−2 was comparable to that on other East African reefs, but was dominated by acroporids, which constituted over 80% of all spat, whereas pocilloporids settle in higher densities in Kenya and South Africa. The peak settlement season also differed from other African locations. A greater proportion of variance in settlement rates occurred at the spatial scale of kilometres (between sites) and centimetres (between settlement plates) than at the scale of metres (between subsites), implying that most patchiness occurs at those scales. The peak in acroporid settlement coincided with the period of multispecific spawning, with settlement occurring as early as nine days after a spawning event. As no similar spawning events have been reported for other reefs in the area, our results suggest that these spawning events strongly influence overall annual settlement rates and promote high levels of self-seeding at Vamizi. There was no relationship between settlement of larvae to settlement plates and juvenile density on adjacent reefs, suggesting either variable levels of early post-settlement mortality or high interannual variability in settlement.

Fine root production, turnover, and decomposition in a fast-growth Eucalyptus urophylla plantation in southern China

A rapid increase of Eucalyptus plantation area in southern China has raised widespread attention in the field of ecology and forestry. It might be argued that fast-growth Eucalyptus would increase the consumption of resources and thus cause soil degradation. Fine root dynamics could provide insight into nutrient uptake or return. This study therefore focused on fine root production, turnover, and decomposition in a subtropical Eucalyptus urophylla plantation. Sequential coring method was used to estimate fine root production and turnover rate. Root decomposition rate and root nitrogen (N) and phosphorus (P) dynamics were determined using the litterbag method. In this study, roots were divided into three diameter classes: <1, 1–2, and 2–3 mm. We settled litterbags with all three different root diameter classes under the forest floor (0–10 cm) in winter, spring, and summer. The total production of fine roots at diameter <2 mm was 45.4 g m−2 year−1, and its turnover rate was 0.58 year−1. The roots at diameter <1 mm showed much greater production or turnover rate than those at diameter 1–2 mm. The root mass loss from litterbag across the three diameter classes (<1, 1–2, and 2–3 mm) was similar at the beginning period of 180 days, but significantly different later. The decomposition constant (k value) of roots estimated by exponential decay model decreased with increasing diameter class. In addition, the season of litterbag settlement also had effects on root mass loss. In root nutrient dynamics, the fractions of initial N immobilized increased with increasing diameter class. Root P at the three diameter classes showed a similar mineralization pattern. Our studies on fine root production, turnover, and decomposition give some important insights into nutrient cycling between plant and soil in Eucalyptus plantations. Our results which show that fine roots had relatively low production and turnover rate partly explain the potential soil degradation under the short rotation systems. The variation of root dynamics among different diameter classes suggests that to accurately assess fine root roles, one should consider the effects of root diameter size.

Atmospheric forcing drives recruitment variation in the Dungeness crab (Cancer magister), revisited

AbstractFor 12 yr (1997–2001, 2006–2012) daily abundance of Cancer magister megalopae was measured in Coos Bay, Oregon. Before 2007 from 2000 to 80 000 megalopae were caught annually. In 2007, catch jumped and has since varied from 164 000 to 2.3 million. The step change in catch size appears related to a shift to negative Pacific Decadal Oscillation (PDO) values. Late season catches, which cannot be due to local spawning, are negatively correlated to the PDO, suggesting that these megalopae derive from north of the California Current. During periods of lower and higher catches, annual returns of megalopae were significantly negatively correlated to the day of the year of the spring transition and positively correlated to the amount of upwelling during the settlement season. The size of the Oregon commercial catch lagged 4 yr to allow for growth of recruits into the fishery is set by the number of returning megalopae; the relationship is parabolic. At lower returns, the population is recruitment limited, but at higher returns, density‐dependent effects predominate and set the commercial catch. Lagged commercial catches in Washington and Northern and Central California were also related to the number of megalopae returning to Coos Bay, suggesting that the forces causing variation in larval success are coast wide. If high return rates are due to a PDO regime shift, then for years to decades the commercial catch may be set by density‐dependent effects following settlement and the huge numbers of returning megalopae may impact benthic community structure.

Effects of physical disturbance on a sub-Antarctic middle intertidal bivalve assemblage

We present for the first time the vulnerability to disturbance of a bivalve assemblage situated in the middle intertidal zone of the Atlantic coast of the Southern South America (53°36′S, 67°58′W). This intertidal zone is characterized by a high level of sand movement preventing any establishment of sessile organisms on the vertical sides of rock outcrops. The coast is prone to potential spills from nearby hydrocarbon marine platforms, but this benthic assemblage has been poorly studied. In February 2001, we exposed the assemblage to two different experimental conditions: a complete removal of bivalves and a physical disturbance and tracked its recovery during the following 4 years. The disturbance lowered the diversity of associated fauna and made the sediment layer trapped among bivalves disappear, which was not restored. Mytilus chilensis was recruited into crevices or between byssi in the following settlement season, i.e. summer 2002. The recuperation of mussel coverage to predisturbance levels took 3 years after the total removal. In April 2004 the size frequency distributions, density and biomass/number ratio of M. chilensis were similar to those at the start of the experiment. Perumytilus purpuratus recovered more slowly than M. chilensis, probably due to its slower growth rate compared to M. chilensis and dependence on an adequate byssus matrix for settlement. The main apparent stressor was the irruption of sand, covering the bivalve assemblage for variable periods of time. This bivalve assemblage is characterized by low predatory pressure and therefore we hypothesize that it is predominantly controlled by competition for space.

Being young in a changing world: how temperature and salinity changes interactively modify the performance of larval stages of the barnacle Amphibalanus improvisus

The fate of key species, such as the barnacle Amphibalanus improvisus, in the course of global change is of particular interest since any change in their abundance and/or performance may entail community-wide effects. In the fluctuating Western Baltic, species typically experience a broad range of environmental conditions, which may preselect them to better cope with climate change. In this study, we examined the sensitivity of two crucial ontogenetic phases (naupliar, cypris) of the barnacle toward a range of temperature (12, 20, and 28°C) and salinity (5, 15, and 30 psu) combinations. Under all salinity treatments, nauplii developed faster at intermediate and high temperatures. Cyprid metamorphosis success, in contrast, was interactively impacted by temperature and salinity. Survival of nauplii decreased with increasing salinity under all temperature treatments. Highest settlement rates occurred at the intermediate temperature and salinity combination, i.e., 20°C and 15 psu. Settlement success of “naive” cyprids, i.e., when nauplii were raised in the absence of stress (20°C/15 psu), was less impacted by stressful temperature/salinity combinations than that of cyprids with a stress history. Here, settlement success was highest at 30 psu particularly at low and high temperatures. Surprisingly, larval survival was not highest under the conditions typical for the Kiel Fjord at the season of peak settlement (20°C/15 psu). The proportion of nauplii that ultimately transformed to attached juveniles was, however, highest under these “home” conditions. Overall, only particularly stressful combinations of temperature and salinity substantially reduced larval performance and development. Given more time for adaptation, the relatively smooth climate shifts predicted will probably not dramatically affect this species.

Diet and feeding niches of juvenile Gadus morhua, Melanogrammus aeglefinus and Merlangius merlangus during the settlement transition in the northern North Sea

A study on the feeding ecology of juvenile cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus during the pelagic to demersal transition was carried out on fishes sampled throughout their settlement season at a local nursery ground in the north-western North Sea, off the Scottish east coast. A comprehensive quantitative taxonomic analysis of the diets, as described in the paper, showed the emergence of distinctive feeding niches, minimizing the potential for competition between species and size categories. The diet of the juveniles changed with fish size, water depth, time of year and distance offshore. Small G. morhua were present in the study area earlier in the season, settled further inshore and ate a higher proportion of pelagic prey (copepods) and as size increased they moved into deeper waters and targeted larger, more benthic prey. As M. aeglefinus grew larger and moved into deeper waters, a diet of largely copepods, amphipods, pelagic Ammodytes spp., cyprids and pelagic gastropods evolved to one dominated predominantly by fishes and benthic invertebrates. In the case of M. merlangus, widespread ages and sizes throughout the sampling season, a consequence of their more protracted spawning season, resulted in dietary changes which were more likely to be influenced by seasonal changes in the prey field, in addition to developmental (size) changes, than the diets of the other two species.