Spatial Variation In Recruitment Research Articles

Coral larval recruitment in north-western Australia predicted by regional and local conditions

Understanding ecological processes that shape contemporary and future communities facilitates knowledge-based environmental management. In marine ecosystems, one of the most important processes is the supply of new recruits into a population. Here, we investigated spatiotemporal variability in coral recruitment at 15 reefs throughout the Dampier Archipelago, north-western Australia between 2015 and 2017 and identified the best environmental predictors for coral recruitment patterns over this period. Large differences in recruitment were observed among years with the average density of recruits increasing by 375% from 0.017 recruits cm−2 in 2015 to 0.059 recruits cm−2 in 2017. Despite differences in recruitment among years, the rank order of coral recruit density among reefs remained similar among years, suggesting that spatial variation in recruitment within the Dampier Archipelago is partly deterministic and predictable. The density of coral recruits was best explained by percent cover of live corals at both local (within 5 m) and meso-scales (within 15 km), water turbidity and an oceanographic model that predicted larval dispersal. The highest density of coral recruits (~0.13 recruits cm−2 or 37 recruits per tile) occurred on reefs within sub-regions (15 km) with greater than 35% coral cover, low to moderate turbidity (KD490 < 0.2) and moderate to high modelled predictions of larval dispersal. Our results demonstrate that broad-scale larval dispersal models, when combined with local metrics of percent hard coral cover and water turbidity, can reliably predict the relative abundance of coral recruits over large geographical areas and thus can identify hotspots of recruit abundance and potential recovery following environmental disturbances; information that is essential for effective management of coral reefs.

Spatial and temporal genetic variation in an exploited reef fish: The effects of exploitation on cohort genetic structure.

Many coral reef fishes are fished, often resulting in detrimental genetic effects; however, reef fishes often show unpredictable patterns of genetic variation, which potentially mask the effects of fishing. Our goals were to characterize spatial and temporal genetic variation and determine the effects of fishing on an exploited reef fish, Plectropomus leopardus, Lacepède (the common coral trout). To determine population structure, we genotyped 417 Great Barrier Reef coral trout from four populations sampled in 2 years (1996 and 2004) at nine microsatellite loci. To test for exploitation effects, we additionally genotyped 869 individuals from a single cohort (ages 3–5) across eight different reefs, including fished and control populations. Genetic structure differed substantially in the two sampled years, with only 1 year exhibiting isolation by distance. Thus, genetic drift likely plays a role in shaping population genetic structure in this species. Although we found no loss of genetic diversity associated with exploitation, our relatedness patterns show that pulse fishing likely affects population genetics. Additionally, genetic structure in the cohort samples likely reflected spatial variation in recruitment contributing to genetic structure at the population level. Overall, we show that fishing does impact coral reef fishes, highlighting the importance of repeated widespread sampling to accurately characterize the genetic structure of reef fishes, as well as the power of analysing cohorts to avoid the impacts of recruitment‐related genetic swamping. The high temporal and spatial variability in genetic structure, combined with possible selection effects, will make conservation/management of reef fish species complex.

Seedling recruitment correlates with seed input across seed sizes: implications for coexistence.

Understanding controls on recruitment is critical to predicting community assembly, diversity, and coexistence. Theory posits that at mean fecundity, recruitment of highly fecund small-seeded plants should be primarily microsite limited, which is indicated by a saturating recruitment function. In contrast, species that produce fewer large seeds are more likely to be seed-limited, which is characterized by a linear recruitment function. If these patterns hold in nature, seed predation that disproportionately affects larger-seeded species can limit their establishment. We tested these predictions by comparing recruitment functions among 16 co-occurring perennial forb species that vary by over two orders of magnitude in seed size. We also assessed how postdispersal seed predation by mice influenced recruitment. We added seeds at densities from zero to three times natural fecundity of each species to undisturbed plots and examined spatial variation in recruitment by conducting experiments across 10 grassland sites that varied in productivity and resource availability. Consistent across two replicated years, most species had linear recruitment functions across the range of added seed densities, indicative of seed-limited recruitment. Depending on year, the recruitment functions of only 19-37% of target species saturated near their average fecundity, and this was not associated with seed size. Recruitment was strongly inhibited by rodent seed predation for large-seeded species but not for smaller-seeded species. Proportional recruitment was more sensitive to spatial variation in recruitment conditions across sites for some small-seeded species than for large-seeded species. These results contradict the common belief that highly fecund small-seeded species suffer from microsite-limited recruitment. Rather, they imply that, at least episodically, recruitment can be strongly correlated to plant fecundity. However, proportional recruitment of small-seeded species was inhibited at productive sites to a greater extent than large-seeded species. Results also show that in a system where the dominant granivore prefers larger seeds, low-fecundity large-seeded species can suffer from even greater seed-limited recruitment than would occur in the absence of predators.

Spatial Variability in Recruitment of an Infaunal Bivalve: Experimental Effects of Predator Exclusion on the Softshell Clam (Mya arenariaL.) along Three Tidal Estuaries in Southern Maine, USA

The infaunal, suspension-feeding softshell clam (Mya arenaria L.) is a conspicuous member of the intertidal macrofauna in numerous northern temperate and boreal soft-bottom communities. Recruitment variability can affect the magnitude and scope of various ecosystem services provided by M. arenaria, including its role as a source of food and energy for organisms at higher trophic levels. Manipulative field experiments were conducted in the intertidal zone in 2014 and 2015 at three tidal estuaries in southern Maine, to investigate the importance of post-settlement processes in determining the strength of the annual 0-y class cohort across predator-exclusion treatments within and between tidal heights. Four short-term (4–5 mo), small-scale studies over both years in the Webhannet River (Wells, ME) and Fore River (Portland, ME), the two southernmost estuaries, demonstrated that clam recruits were up to 118× more abundant when predators were deterred versus controls. In a 7-mo study conducted in the Harraseeket River (HR; Freeport, ME) during 2014, recruits of Mya attained densities 899× greater in large-scale plots designed to exclude large (>6 mm) predators than in ambient, adjacent sediments where predators were undeterred. A novel, epibenthic settlement trap (0.15 m2), initially containing no sediments and designed to deter both infaunal and epibenthic predators larger than 1.9 mm, was used to examine spatial variability in clam recruitment over a 6-mo period in 2015 in the HR. Traps showed a 60-fold difference in mean number of clam recruits between sides of the river only 600 m apart. Collectively, results suggest that post-settlement mortality rates of 0-y class individuals of Mya exceed 99% at these locations, severely limiting ecosystem services they would otherwise provide, and that these early losses are primarily responsible for explaining distribution and abundance patterns of ≥1-y class individuals.

Spatial variability in recruitment of benthos near drilling sites in the Iheya North hydrothermal field in the Okinawa Trough

Due to increasing anthropogenic impacts on deep-sea hydrothermal vent ecosystems, it is essential to understand population structure and maintenance through larval recruitment and recovery of vent faunas after disturbances. In this study, we quantified vent animal recruitment in the Okinawa Trough, in the western Pacific Ocean. This is the first study to investigate recruitment patterns at a man-made hydrothermal vent. Colonization plates were deployed at three sites. Site 1 manifested new hydrothermal shimmering with small chimneys, white bacterial mats, and some alvinocaridid shrimp that arrived after drilling. Site 2 showed no evidence of newly arrived foundation species after drilling, and Site 3 had pre-existing animal communities in the vicinity of the new vent. Twenty-two months after deployment, colonization plates were retrieved and recruited animals were inventoried. Species composition and abundance differed among sites, but relatively high similarity in species composition was observed at Sites 1 and 3, though not at Site 2. Newly established communities on the plates at Sites 1 and 2 (no pre-existing fauna) showed lower species richness and abundance than at Site 3. Differences in abundance and size-frequency distributions of major recruits on the plates (i.e. Lepetodrilus nux, Bathymodiolus spp.) suggest the importance of reproductive and early life-history characteristics in spatial variability of recruitment. Lepetodrilus nux populations established on the plates at Site 1 showed high genetic connectivity. These results illustrate the importance of localized recruitment, which may have a significant impact on sustainability of vent faunal populations, despite the existence of regional metapopulations.

How Life History Characteristics and Environmental Forcing Shape Settlement Success of Coral Reef Fishes

Larval settlement is shaped by the interaction of biological processes (e.g., life history strategies, behavior etc.) and the environment (e.g., temperature, currents etc.). This is particularly true for many reef fishes where larval stages disperse offshore, often spending weeks to months in the pelagic realm before settling to shallow-water reefs. Our ability to predict reef fish settlement and subsequent recruitment and population dynamics depends on our ability to characterize how biological processes interact with the dynamic physical environment. Here we develop and apply an individual-based model that combines biological processes with high-resolution physical forcing to predict larval fish dispersal and settlement over time and space. Our model tracks individual larval fish from spawning to settlement and allows for the inclusion of biologically relevant stochasticity (individual variability) in modeled processes. Our model is also trait-based, which allows individuals to vary in life history characteristics, making it possible to mechanistically link the resulting variability in settlement probabilities to underlying traits such as spawning date and location, pelagic larval duration (PLD), body morphology, etc. We employ our biophysical model to examine how biology interacts with the physical environment to shape settlement predictions for reef fish off western and southern Hawai‘i Island. Linked to prevailing surface currents, we find increased probabilities of settling associated with shorter PLDs and fish spawned in southern and southwestern locations. Superimposed on this, eddies, common to leeward Hawai‘i Island, offer a second pathway to successful settlement for individuals with longer PLDs, particularly for fish spawning in summer months. Finally, we illustrate how lunar-timed spawning as well as morphological features (e.g., fin and head spines) may impact settlement success by altering the mortality landscape experienced by larvae. This work identifies life history characteristics that predict the self-recruitment pathways necessary for population persistence for the relatively isolated Hawai‘i Island. Our results can be used to develop future hypotheses regarding temporal and spatial variation in recruitment for reef fishes on Hawai‘i Island and beyond.

Large wood recruitment processes and transported volumes in Swiss mountain streams during the extreme flood of August 2005

The extreme flood event that occurred in August 2005 was the most costly (documented) natural hazard event in the history of Switzerland. The flood was accompanied by the mobilization of >69,000m3 of large wood (LW) throughout the affected area. As recognized afterward, wood played an important role in exacerbating the damages, mainly because of log jams at bridges and weirs. The present study aimed at assessing the risk posed by wood in various catchments by investigating the amount and spatial variability of recruited and transported LW. Data regarding LW quantities were obtained by field surveys, remote sensing techniques (LiDAR), and GIS analysis and was subsequently translated into a conceptual model of wood transport mass balance. Detailed wood budgets and transport diagrams were established for four study catchments of Swiss mountain streams, showing the spatial variability of LW recruitment and deposition. Despite some uncertainties with regard to parameter assumptions, the sum of reconstructed wood input and observed deposition volumes agree reasonably well. Mass wasting such as landslides and debris flows were the dominant recruitment processes in headwater streams. In contrast, LW recruitment from lateral bank erosion became significant in the lower part of mountain streams where the catchment reached a size of about 100km2. According to our analysis, ~88% of the reconstructed total wood input was fresh, i.e., coming from living trees that were recruited from adjacent areas during the event. This implies an average deadwood contribution of 12%, most of which was estimated to have been in-channel deadwood entrained during the flood event.

Spatial variability in recruitment of acroporid corals and predatory starfish along the Onna coast, Okinawa, Japan

We compared spatial variability in re- cruitment patterns between acroporid corals and the predatory crown-of-thorns starfish Acanthaster planci along the Onna village coast of Okinawa Island, Japan. Our objective was to understand population dynamics of both predator and prey. To quantify re- cruitment, we established artificial recruitment plates for acroporid corals and conducted quadrat surveys for juvenile A. planci at 7 sites. We also examined dis- tributional patterns of adult populations of both spe- cies and observed surface currents during larval dis- persal periods using GPS-equipped surface drifters. Acroporid recruits typically arrived in greater num- bers at more northern sites. Despite high variability, A. planci recruits displayed similar spatial patterns. Drifter trajectories suggest that these spatial recruit- ment patterns are probably driven by near-shore currents in the summer. Moreover, current data imply a complicated metapopulation relationship in this region, especially for A. planci, new recruits of which may mainly originate outside of the Onna area. Meta - population dynamics within the study area and among surrounding regions must be explained by the com- plex surface current circulation, because simpler ex- planations involving only the Kuroshio Current do not adequately describe the relationship between these populations.

Influence of habitat and population density on recruitment and spatial dynamics of the sea urchin Paracentrotus lividus: implications for harvest refugia

Abstract We studied the spatial variation in recruitment and the population dynamics of the sea urchin Paracentrotus lividus, analysing the effect of depth and presence of sea urchin aggregations on population structure. Over 90% of the observed recruits (individuals under 1 year of age) were concentrated in aggregations found in shallow waters. In these areas, a positive linear relationship was found between adult and recruit density, possibly due to higher survival rates of juveniles taking refuge among the spines of adults. The scarcity of recruits and the presence of adult sea urchins at depths of 8 and 12 m suggest the migration of part of the population towards deep areas when individuals reach a size of ∼40 mm. In light of these results, the implementation of harvest refugia for sea urchins in shallow areas could constitute an effective fishery management tool for this species. High population densities could enhance recruitment, given the inverse density dependence of this process, while their migratory pattern would guarantee biomass exportation towards deeper fishing grounds.

Effects of flooding on recruitment and abundance of Golden Perch (Macquaria ambigua ambigua) in the lower River Murray

SummaryFlooding is often considered a stimulus for production of fish in floodplain rivers. In the southern Murray–Darling Basin (MDB), Australia, however, few native fish species have been shown to use the floodplain for spawning, and recruitment has been positively and negatively associated with flooding. In 2010/11, extensive flooding in the lower River Murray provided an opportunity to investigate the recruitment response of Golden Perch (Macquaria ambigua ambigua) following 10 years of drought and floodplain isolation. Annual variation in Golden Perch abundance and recruitment were investigated in anabranch and main channel habitats at Chowilla in the floodplain geomorphic region of the lower River Murray over a 7‐year period incorporating the flood and 6 years of in‐channel flow. Spatial variation in recruitment in the lower River Murray was also investigated by comparing the age structure of Golden Perch in the swamplands/lakes, gorge and floodplain geomorphic regions. Golden Perch abundance in the Chowilla region increased significantly postflooding compared with drought years. Age structures indicated that increased abundance was due predominantly to fish spawned during the flood (2010/11) and the previous year (2009/10), which was characterised by in‐channel flows. Age structure was similar in the nearby Katarapko Anabranch system indicating a uniform postflood recruitment response in the floodplain geomorphic region. Juvenile Golden Perch from the 2010/11 and 2009/10 cohorts were less apparent in the gorge and swamplands/lakes regions. Golden Perch have flexible life histories and will spawn and recruit in association with in‐channel rises in flow and overbank flows, but significant increases in abundance in the lower River Murray may result from overbank flooding. Contemporary approaches to flow restoration in the MDB emphasise overbank flows and floodplain processes. We suggest, however, that environmental flow management that incorporates floodplain and in‐channel processes, at appropriate spatio‐temporal scales, will result in more robust populations of Golden Perch.

Using hierarchical sampling to understand scales of spatial variation in early coral recruitment

Ecological patterns are created by processes acting over multiple spatial and temporal scales. By com- bining spatially explicit sampling with variance compo- nents models, the relative importance of spatial scale to overall variability can be determined. We used a spatially structured experimental design in the Mombasa Marine National Park in Kenya to quantify variation in coral recruitment across four spatial scales (*1-1,000 m) and to generate hypotheses about processes affecting recruitment and potential sources of post-settlement mortality during early life history. For the dominant recruiting corals (Pocillopora spp.), variation in recruitment on surfaces protected from fish grazing was greatest at the largest spatial scale examined (1,000 m). We hypothesize that recruitment on protected surfaces varies mainly with larval delivery due to different lagoonal circulation and water flow between sites. Conversely, variation on surfaces exposed to fishes was greatest at the smallest spatial scale (1 m). We hypothesize that recruitment on exposed sur- faces mainly reflects local differences in the scale and intensity of fish grazing, which may obscure larval delivery patterns. Spatial variation in recruitment can affect many ecological processes and factors, including growth, sur- vival to maturity, the distribution of habitat, and variation in species interaction strengths. This study demonstrates how spatially explicit sampling, followed by variance components modeling to partition variance across scales, can help to identify potential drivers of patterns at each relevant scale.

Recruitment dynamics of two low-density neotropical multiple-use tree species

In the present study, we describe the temporal and spatial variability in recruitment, growth, and mortality rates of seedlings and saplings of two low-density neotropical tree species, Dipteryx odorata and Copaifera reticulata in Eastern Amazonia, Brazil. As both species have important timber and non-timber uses, for each species we compare regeneration parameters among different management scenarios (sites used for timber logging, non-timber product extraction, and undisturbed forests). Results suggest that both species share similar natural regeneration characteristics. These include temporally and spatially asynchronous germination, existence of individuals that have more abundant and frequent fruit production than the average of the population and a positive influence of the mother tree crown on seedling and sapling density. The management activities analyzed did not influence the regeneration parameters of both species, which suggests that timber logging the way it was performed and current rates of D. odorata seed gathering and C. reticulata tapping at the study site are not sufficiently intense to threaten species population. However, some species characteristics, such as their reproductive strategies, light-demanding syndromes, low-dispersal ranges, and high-mortality rates of seedlings make both species vulnerable to exploitation.

Pre- and post-settlement factors controlling spatial variation in recruitment across a cold-seep mussel bed

The size structure of a population of the mussel 'Bathymodiolus' childressi shifts dra- matically across the mussel bed encircling the Brine Pool NR 1 cold seep in the Gulf of Mexico. While the fringes of the bed are inhabited by large mussels, small juveniles are abundant only at the edge of the pool, leading to the inference that larvae settle preferentially near the source of methane. We used in situ experiments to test whether this shift in size distribution is structured by differences in larval supply, settlement, substratum selection by settling larvae, juvenile mortality, growth, or predation across the mussel bed. We investigated the variation of these factors adjacent to the pool, at the fringes of the mussel bed, and also 2 m away from the bed. Neither the supply of larvae nor the density of settlers (<0.5 mm long) collected on settlement plates differed among the 3 zones. Juve- niles (mean length: 9 mm) survived and grew equally well in all 3 zones. Survival was higher in caged than in uncaged juveniles (5 to 15 mm long), but mortality of uncaged juveniles was similar at all distances from the pool, suggesting that predation alone does not cause the observed differences in size structure. We reject the prevailing hypothesis that the distribution pattern can be attributed to settlement preferences of larvae alone. We hypothesize that very early post-settlement mortality, secondary settlement, and/or later migration of juveniles play a role in establishing and maintaining the persistent pattern of size structure across this mussel bed.

Early post-settlement mortality and the structure of coral assemblages

Events occurring early in life history can have profound effects on the structure of populations and communities. In particular, susceptibility to predation is often highest early in life, and can greatly influence community structure. To better understand these events in reef-forming coral communities, we investigated how spatial variation in recruitment and early post-settlement predation influenced the spatial structure of a coral assemblage. Over a 5 yr period, we compared recruitment of corals and abundance of juveniles and adults at a combination of 3 locations and 3 depths in French Polynesia. We then measured mortality of recruits (<3 mo old) and juveniles (about 1 to 4 yr old), and abundance of potential predators. Results demonstrate the crucial role of events occurring in the first weeks of the benthic stage. The abundance of scraping herbivorous parrotfishes explained substantial spatial variation in the mortality of recruits, but not juveniles, revealing a likely effect of incidental removal by grazing. Conversely, abundance of coral-feeding butterflyfishes explained substantial spatial variation in the mortality of juveniles. These findings underscore the importance of incidental mortality from grazing and specialized corallivory on coral populations. Moreover, these processes can play a key role in determining spatial patterns in coral assemblage structure.

Life history and matrix heterogeneity interact to shape metapopulation connectivity in spatially structured environments

Metapopulation models have historically treated a landscape as a collection of habitat patches separated by a matrix of uniformly unsuitable habitat. This perspective is still apparent in many studies of marine metapopulations, in which recruitment variation is generally assumed to be primarily the result of variability in ocean currents and interactions with disperser behavior, with little consideration of spatial structure that can affect disperser viability. We use a simple model of dispersal of marine larvae to demonstrate how heterogeneity in dispersal habitat (i.e., the matrix) can generate substantial spatial variation in recruitment. Furthermore, we show how this heterogeneity can interact with larval life-history variation to create alternative patterns of source-sink dynamics. Finally, we place our results in the context of spatially structured matrix population models, and we propose the damping ratio of the connectivity matrix as a general and novel measure of landscape connectivity that may provide conceptual unification to the fields of metapopulation biology and landscape ecology.

Local adaptation along a continuous coastline: Prey recruitment drives differentiation in a predatory snail

Recent work demonstrates that nearshore oceanography can generate strong variation in the delivery of resources (nutrients and larvae) to benthic marine communities over spatial scales of tens to hundreds of kilometers. Moreover, variation in the strength of these bottom-up inputs is often spatially consistent, linked to regional centers of upwelling, coastal topography, and other stable features of the coastline. Whereas the ecological effects of these oceanographic links are increasingly clear, the possibility that these same bottom-up forces might impose spatially varying selection on consumers has not been addressed. Here, we test the hypothesis that a carnivorous snail (Nucella canaliculata) with direct development is locally adapted to persistent differences in prey recruitment within two adjacent oceanographic regions (northern California and Oregon, USA). Previous laboratory studies demonstrated that snails from Oregon rarely drilled the thick-shelled mussel Mytilus californianus, whereas snails from California readily drilled this prey. To test whether these differences reflect local adaptation, snails from two populations in each region were raised through two laboratory generations to minimize the potential influence of nongenetic effects. We then reciprocally outplanted these F2 generation snails to field enclosures at each of the four sites and monitored their growth for 11 months. Recruitment and availability of preferred prey (the acorn barnacle Balanus glandula and blue mussel Mytilus trossulus) at the experimental sites were 1-3 orders of magnitude lower in California than in Oregon. At the California sites, snails that originated from Oregon sources failed to drill larger M. californianus, encountered few alternative prey, and showed almost no growth. In contrast, snails from California drilled M. californianus and showed substantial growth. These results strongly suggest that the capacity of California snails to drill M. californianus allows these snails to succeed in an oceanographic region where the recruitment of alternative, preferred prey is low. More broadly, our results suggest that persistent spatial variation in recruitment and other oceanographically mediated processes may lead to adaptive differentiation among populations of consumers in adjacent coastal regions.

Cross-front variations in adult abundance and recruitment of Patagonian scallop (Zygochlamys patagonica) at the SW Atlantic Shelf Break Front

Abstract Mauna, A. C., Franco, B. C., Baldoni, A., Acha, E. M., Lasta, M. L., and Iribarne, O. O. 2008. Cross-front variations in adult abundance and recruitment of Patagonian scallop (Zygochlamys patagonica) at the SW Atlantic Shelf Break Front. – ICES Journal of Marine Science, 65: 1184–1190. We studied cross-front variations in adult abundance and recruitment of Patagonian scallop (Zygochlamys patagonica) and their relationship with the Shelf Break Front and satellite-derived chlorophyll a in the Southwest Atlantic between 38°S and 39°30′S. Integrated data from commercial fleets (CF, 1996–2005), research cruises (RC, 1998–2005), sea surface temperature (SST; 1985–1997), and satellite-derived chlorophyll a (CSAT; 1998–2004) were included in the analysis. One-way ANOVA was used to assess differences in recruitment and scallop abundance in a cross-front direction. The abundance of scallops was greatest (RC &gt; 200 kg h−1) closer to the onshore side of the front or beneath it, and the East–West extension of scallop beds (∼40 km) matched the seasonal zonal displacement of the front (∼37 km). The highest CSAT gradients were west of or matched the position of the front. The annual mean position of the front correlated with the spatial variability in recruitment within areas where the species recruited successfully (RC &gt; 2000 h−1). The spatial variability in adult abundance and recruitment of scallops is strongly related to the spatial variability in the position of the front and with the high CSAT concentrations associated with it.

SPATIAL ENVIRONMENTAL CORRELATES OF INTERTIDAL RECRUITMENT: A TEST USING BARNACLES IN NORTHERN CHILE

Nearshore circulation processes and local geomorphological patterns are thought to be important correlates of spatial variation in larval recruitment of benthic organisms. However, few studies have attempted to quantitatively separate their relative influences upon recruitment dynamics. Here we use 12 study sites spanning 250 km of the northern Chile upwelling ecosystem and the intertidal barnacles Jehlius cirratus and Notochthamalus scabrosus to examine the extent to which spatial variation in larval recruitment is related to environmental variability and how these relationships depend on spatial autocorrelation. We find that upwelling intensity and wind velocity are negatively related to larval recruitment while surface slicks showed a positive correlation. However, the pure effect of each environmental variable was lower than its combined effects. Taking spatial autocorrelation into account, we find that the spatially structured variation of upwelling dynamics, distance to upwelling fronts, wind velocity, and slick occurrence explained most of the variation in barnacle recruitment. Spatial variation in recruitment rates of barnacles showed a characteristic length scale of 60–70 km, similar to the scale estimated for the spatially structured variables (upwelling, wind velocity, and surface slicks). We find that conditions for the occurrence of surface slicks (as surrogates of internal waves activity) seem to operate across several sites, suggesting a meso‐ instead local‐scale influence over spatial variation in barnacle recruitment. Our results suggest that spatial variation in barnacle recruitment is modulated by the combined influence of several spatially structured nearshore processes operating at scales of 60–70 km and that spatial autocorrelation must be taken into account in the study of the recruitment–environment relationship. However, the influence of local and small‐scale factors on recruitment dynamics of benthic invertebrates should be interpreted cautiously.

Impacts of contrasting land-use history on composition, soils, and development of mixed-oak, coastal plain forests on Shelter Island, New York

The Mashomack Preserve on Shelter Island, New York contains one of the premier oak-dominated coastal plain forests in the northeastern U.S. It represents a unique opportunity to study woody species in juxtaposed forests that differ primarily in past land-use (logging versus agriculture). We researched how contrasting land-use history affected: 1) tree species composition, size, and age structure; 2) soil chemistry and morphology; 3) the dominance of Smilax, a native invasive shrub; and 4) the historical ecology and successional pathways. Randomly located plots were sampled for vegetation and soils in the unplowed interior forest versus the maritime forest that was cleared and/or plowed for agriculture and grazing in the 18th and 19th centuries and then abandoned after 1870. The upper soil profile was examined for soil nutrients and pH, the presence/absence of a plow layer (Ap) and for soil charcoal. Tree cores (N = 130) were taken across both forest types to include the full range of species and diameter size classes to assess temporal and spatial variation in recruitment. Maritime forests are closer to the ocean shore and are dominated by Quercus velutina, Sassafras albidum, Carya glabra, and Q. alba, whereas the interior forests are dominated by Q. velutina, Acer rubrum, C. glabra, and Q. prinus. The interior forest plots appear to have continually supported forests, have soils that are somewhat doughtier and less fertile, and lack a plowed horizon, but have frequent soil charcoal as compared with the maritime forest. Formerly plowed and grazed maritime soils are more fertile and Q. alba has greater importance, while Q. velutina has lower importance. Following agricultural abandonment, the maritime forest understory became dominated by thickets of Smilax and presently has lower tree diversity than interior forests. Tree regeneration is sparse in both forest types due, at least in part, to intense browsing by white-tailed deer (Odocoileus virginianus). The interior forest exhibits a predictable successional pathway from mixed-oak to A. rubrum and Fagus grandifolia, which is not apparent in the maritime black oak forests. We believe that differences in overstory and understory composition, species diversity, and successional pathways between the two forest types can be mainly attributed to contrasting land-use history. Smilax is a super-dominant species that has profoundly influenced many ecological processes on the preserve and if left unchecked will continue to do so long into the future.

Spatial patterns of recruitment in a demersal fish as revealed by seabird diet

Understanding recruitment in demersal fish requires determination of larval survival and delivery to appropriate settling habitats. Sanddabs Citharichthys sp. are an abundant neritic fish of Central California, an area of persistent upwelling. 'Upwelling shadows' develop in the lee of coastal promontories, retain surface waters, and may promote spatial variation in fish settlement. To test this hypothesis, we studied the diet and foraging dimensions of a seabird (Cepphus columba) specializing in sanddab consumption at windward and leeward sites over a 6 yr period. We inte- grated the bird's take of sanddab with information on upwelling intensity and variability and sanddab larval abundance based on net sampling. Seabird diet at both sub-colonies was variable, but dominated by Age 1 sanddabs. Sanddabs were more prevalent in the diet of guillemots at the lee- ward site, and diet was more variable at the windward site. Persistent upwelling led to regional increases in sanddab larval abundance which, in turn, resulted in enhanced recruitment to leeward waters, as reflected in seabird diet. Pulsed upwelling was related to apparent increased recruitment in windward waters. This study is one of the first to suggest that seabird diet can be used as an indicator of spatial variability in recruitment and settlement of demersal forage fish.