Adult Habitat Research Articles

Effects of the presence of litter on the composition of stream tadpoles' assemblages in an Atlantic Forest remnant of southeastern Brazil

Abstract: Many tropical anurans use forest streams to deposit their eggs, but resource use and selection by tadpoles in tropical forests are poorly known. In the present research, we hypothesized that leaf litter and water depth affect tadpole assemblages due to adult habitat selection for oviposition and/or microhabitat selection by tadpoles. Fieldwork was carried out in the Estação Biológica de Boracéia, an Atlantic Rainforest reserve in São Paulo state, southeastern Brazil. We sampled tadpoles during a year using 40 double-entry funnel-traps distributed along four streams in the forest. Only leaf litter effects are species dependent. We discussed that habitat structure significance depends on the morphological and ecological adaptation to forage and avoid competition within the tadpole community.

Ecology of the meadow spittlebug Philaenus spumarius in the Ajaccio region (Corsica) - I: spring.

The meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Aphrophoridae), is the main vector in Europe of the recently detected plant pathogen bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae). While the ecology of continental populations is well documented, nothing is known about the insular populations of P. spumarius, such as in Corsica, where the bacterium was detected in 2015. Hence, in an epidemiological context, the ecology of P. spumarius has been studied in a maquis landscape in the Ajaccio region between 2017 and 2019. Adults and nymphs were almost exclusively collected on Cistus monspeliensis L. (Cistaceae). However, very few specimens were collected in summer, suggesting a movement of the adults to sheltered habitats. Unfortunately, despite several trapping methods used, the location of adult summer habitat remains unknown for the studied population. It might be tempting to destroy the central plant host of P. spumarius populations. However, as spittlebug nymphs are highly polyphagous on low-growing plant species and as the females can lay eggs in any dead plant tissues, such practice could have limited the impact. Instead, the strong relationship between P. spumarius and C. monspeliensis could be used to monitor spittlebug populations, to limit/concentrate the means of insect control, or in an agronomic context to lure insects away from crops. Maintaining natural arboreal vegetation around agronomic systems could help decrease insect abundance - and potentially, pathogen load - on cultivated species. Such hypotheses need to be further studied by landscape experiments.

Life-stage-dependent supergene haplotype frequencies and metapopulation neutral genetic patterns of Atlantic cod, Gadus morhua, from Canada's Northern cod stock region and adjacent areas.

Among highly migratory fish species, nursery areas occupied by juveniles often differ from adult habitats. To better understand the spatial dynamics of Canada's Northern cod stock, juveniles caught off the east coast of Newfoundland and Labrador were compared to adults from the same region as well as individuals from other areas in Atlantic Canada using double-digest restriction site-associated DNA sequencing-derived single nucleotide polymorphisms. A reduced proportion of homozygotes with a chromosomal inversion located in linkage group 1 (LG1) was detected between juvenile and adult samples in the Northern cod stock region, potentially indicating age-dependent habitat use or ontogenetic selection for attributes associated with the many genes located in LG1. No selectively neutral genetic differences were found between samples from the Northern cod stock; nevertheless, significant differences were found between some of these samples and cod collected from St. Pierre Bank, Bay of Fundy, Browns Bank and the southern Scotian Shelf. Clustering analysis of variants at neutral loci provided evidence for three major genetic units: (a) the Newfoundland Atlantic Coast, (b) eastern and southern Gulf of St. Lawrence and Burgeo Bank and (c) the Bay of Fundy, Browns Bank and southern Scotian Shelf. Both adaptive and neutral population structure within the Northern cod stock should be considered by managers to promote demographic rebuilding of the stock.

Invertebrate larval distributions influenced by adult habitat distribution, larval behavior, and hydrodynamics in the retentive upwelling shadow of Monterey Bay, California, USA

Larval dispersal phases are a key determinant of population dynamics in recruitment-limited, coastal upwelling regions. Larvae were long considered to be highly susceptible to offshore transport, except in the lee of headlands where eddies form during upwelling conditions. We examined the spatial variation of benthic invertebrate larval assemblages in relation to the retentive upwelling shadow in northern Monterey Bay (California, USA) during strong upwelling (August 2013) and weak upwelling (October 2013). We characterized the spatial variation in physical characteristics of the water column, determined the cross-shore and depth distributions of invertebrate larvae in relation to the upwelling shadow, and examined how these physical and biological patterns change with upwelling strength. Larval abundances and environmental data (water temperature, salinity, chlorophyllaconcentration) were collected simultaneously using a plankton pump and profiling CTD at 3 depths: above, within, and below the chlorophyllamaximum layer. Larvae were primarily detected near the bottom. Larvae of most taxa were positively associated with a subsurface chlorophyllamaximum layer in August, but not in October when this layer was near the surface. Adult habitat distribution was related to the spatial distribution of larvae. Larvae of nearshore taxa occurred in the inner bay, while larvae of predominately offshore taxa occurred in the outer bay. Taxa with similar adult habitat (nearshore versus offshore) co-occurred in water samples. In addition, larvae of offshore taxa were commonly associated with offshore water types. Thus, the distribution of larvae within northern Monterey Bay appears to be strongly influenced by adult habitat distribution, vertical positioning of larvae in the water column, and upwelling strength.

Ontogenetic shifts in social aggregation and habitat use in a temperate reef fish

AbstractCover, both from physical structure or association with social groups, can reduce predation risk and increase foraging, leading to enhanced growth and survival, and is therefore a critical aspect of the niche for many organisms. However, the need for cover, or the need for a specific type of cover, may change as an individual grows in size, leading to niche shifts throughout development to meet these changing needs. In this study, we examine ontogenetic shifts in cover use by wild populations of a temperate reef fish, the southern hulafish, Trachinops caudimaculatus, a small, abundant planktivorous social aggregator found on temperate reefs in southern Australia. Through repeated in situ surveys, we found clear evidence of ontogenetic shifts in both microhabitat use and aggregation patterns by T. caudimaculatus juveniles in the first three months on the reef. The microhabitat associations of juvenile T. caudimaculatus became more similar to those of adult conspecifics over the study period, and over the same time frame, juveniles increasingly aggregated with adult shoals. Our findings also suggest that trade‐offs between structural and social cover are context‐dependent, with juveniles relying on structural cover longer when adult conspecific density (and thus intra‐specific competition) and/or habitat complexity (and thus the availability of shelter) is high. These findings provide rare and important observations into the complex interplay of social aggregations, habitat use, and ontogeny in wild fish populations.

Mitochondrial Haplotypes suggest Genetic Component for Habitat Preference in Blue Crabs

Atlantic blue crabs (Callinectes sapidus) are ecologically and commercially fundamental. Life stages are punctuated with migration. Adults and juveniles live in estuaries and sounds. Larval stages develop in the coastal ocean. Juvenile and adult crabs occupy habitats from high salinities to fresh water. We determined whether maturing juvenile and adult blue crab habitat use is reflected in mitochondrial cytochrome oxidase 1 haplotypes. High salinity crabs had lower haplotype diversity (0.7260 ± .03900) compared to spawning crabs (0.9841 ± .00021) and low salinity crabs (0.94154 ± .00118). Significant pairwise differences in haplotypes were found between high salinity and spawning crabs (Nm = 0.26018, p < 0.001), and between high salinity and low salinity crabs (Nm = 0.19482, p < 0.001) indicating a lack of gene flow. Crabs from high salinity had highly significant genetic differentiation compared to spawning crabs (Fst = 0.11830, p < 0.001) and low salinity crabs (Fst = 0.09689, p < 0.001). Results support the hypothesis that genetics influence habitat selection. Crab larvae mix in the coastal ocean but occupy specific habitats upon return to sounds and estuaries. These findings have implications for the management of fisheries.

Larval cross‐shore transport estimated from internal waves with a background flow: The effects of larval vertical position and depth regulation

AbstractCross‐shore velocities in the coastal ocean typically vary with depth. The direction and magnitude of transport experienced by meroplanktonic larvae will therefore be influenced by their vertical position. To quantify how swimming behavior and vertical position in internal waves influence larval cross‐shore transport in the shallow (~ 20 m), stratified coastal waters off Southern California, we deployed swarms of novel, subsurface larval mimics, the Mini‐Autonomous Underwater Explorers (M‐AUEs). The M‐AUEs were programmed to maintain a specified depth, and were deployed near a mooring. Transport of the M‐AUEs was predominantly onshore, with average velocities up to 14 cm s−1. To put the M‐AUE deployments into a broader context, we simulated > 500 individual high‐frequency internal waves observed at the mooring over a 14‐d deployment; in each internal wave, we released both depth‐keeping and passive virtual larvae every meter in the vertical. After the waves' passage, depth‐keeping virtual larvae were usually found closer to shore than passive larvae released at the same depth. Near the top of the water column (3–5‐m depth), ~ 20% of internal waves enhanced onshore transport of depth‐keeping virtual larvae by ≥ 50 m, whereas only 1% of waves gave similar enhancements to passive larvae. Our observations and simulations showed that depth‐keeping behavior in high‐frequency internal waves resulted in enhanced onshore transport at the top of the water column, and reduced offshore dispersal at the bottom, compared to being passive. Thus, even weak depth‐keeping may allow larvae to reach nearshore adult habitats more reliably than drifting passively.

Unravelling Seascape Patterns of Cryptic Life Stages: Non-Reef Habitat Use in Juvenile Parrotfishes

Juvenile fish often use alternative habitats distinct from their adult phases. Parrotfishes are an integral group of coral reef fish assemblages, are targeted in fisheries, are sensitive to reef disturbances, and have been documented as multiple-habitat users. Considering the abundance of research conducted on parrotfishes, very little is known about their juvenile ecology at the species level due to their cryptic and variable coloration patterns. We collected juvenile parrotfishes in non-reef habitats (macroalgal beds, seagrass beds, and lagoons) in the Philippines and used DNA analysis to determine species composition. The results were then compared with data on adult parrotfish abundance from underwater visual census (UVC) surveys in coral reef and non-reef habitats. Collections identified 15 species of juvenile parrotfishes in non-reef habitats, and of these, 10 were also recorded in UVCs as adults. Informed by adult surveys, 42% of the 19 parrotfish species observed as adults were classified as multi-habitat users based on their presence in coral reef and non-reef habitats. When accounting for the occurrence of species as juveniles in non-reef habitats, 93% of the species collected as juveniles would be considered multi-habitat users. Species identified as juveniles in non-reef habitats comprised 50% of the average adult parrotfish density on coral reefs and 58–94% in non-reef habitats. The species richness of juveniles in non-reef habitats was greater than that of adults occupying the same habitats, and the most common adult species observed in UVCs was not collected as juveniles in non-reef habitats. Finally, UVC suggested that 97% of juvenile parrotfish <10-cm total length was present in non-reef habitats compared to coral reefs. These results provide further evidence for ontogenetic movement across habitat boundaries for parrotfish species in a diverse and highly connected tropical seascape. This is one of the few studies to quantify links between nursery and adult habitat in parrotfishes, highlighting the importance of including non-reef habitats in ecological studies of an iconic group of coral reef fish.

Eye size and investment in frogs and toads correlate with adult habitat, activity pattern and breeding ecology.

Frogs and toads (Amphibia: Anura) display diverse ecologies and behaviours, which are often correlated with visual capacity in other vertebrates. Additionally, anurans exhibit a broad range of relative eye sizes, which have not previously been linked to ecological factors in this group. We measured relative investment in eye size and corneal size for 220 species of anurans representing all 55 currently recognized families and tested whether they were correlated with six natural history traits hypothesized to be associated with the evolution of eye size. Anuran eye size was significantly correlated with habitat, with notable decreases in eye investment among fossorial, subfossorial and aquatic species. Relative eye size was also associated with mating habitat and activity pattern. Compared to other vertebrates, anurans have relatively large eyes for their body size, indicating that vision is probably of high importance. Our study reveals the role that ecology and behaviour may have played in the evolution of anuran visual systems and highlights the usefulness of museum specimens, and importance of broad taxonomic sampling, for interpreting macroecological patterns.

MRNA profile provides novel insights into stress adaptation in mud crab megalopa, Scylla paramamosain after salinity stress

BackgroundMud crab, Scylla paramamosain, a euryhaline crustacean species, mainly inhabits the Indo-Western Pacific region. Wild mud crab spawn in high-salt condition and the salinity reduced with the growth of the hatching larvae. When the larvae grow up to megalopa, they migrate back to estuaries and coasts in virtue of the flood tide, settle and recruit adult habitats and metamorphose into the crablet stage. Adult crab can even survive in a wide salinity of 0–35 ppt. To investigate the mRNA profile after salinity stress, S. paramamosain megalopa were exposed to different salinity seawater (low, 14 ppt; control, 25 ppt; high, 39 ppt).ResultsFirstly, from the expression profiles of Na+/K+/2Cl- cotransporter, chloride channel protein 2, and ABC transporter, it turned out that the 24 h might be the most influenced duration in the short-term stress. We collected megalopa under different salinity for 24 h and then submitted to mRNA profiling. Totally, 57.87 Gb Clean Data were obtained. The comparative genomic analysis detected 342 differentially expressed genes (DEGs). The most significantly DEGs include gamma-butyrobetaine dioxygenase-like, facilitated trehalose transporter Tret1, sodium/potassium-transporting ATPase subunit alpha, rhodanese 1-like protein, etc. And the significantly enriched pathways were lysine degradation, choline metabolism in cancer, phospholipase D signaling pathway, Fc gamma R-mediated phagocytosis, and sphingolipid signaling pathway. The results indicate that in the short-term salinity stress, the megalopa might regulate some mechanism such as metabolism, immunity responses, osmoregulation to adapt to the alteration of the environment.ConclusionsThis study represents the first genome-wide transcriptome analysis of S. paramamosain megalopa for studying its stress adaption mechanisms under different salinity. The results reveal numbers of genes modified by salinity stress and some important pathways, which will provide valuable resources for discovering the molecular basis of salinity stress adaptation of S. paramamosain larvae and further boost the understanding of the potential molecular mechanisms of salinity stress adaptation for crustacean species.

Determinants of the nursery role of seagrass meadows in the sub-tropical Gulf of Mexico: inshore-offshore connectivity for snapper and grouper

Quantifying the nursery role of habitats or locations in supporting fisheries is central to understanding population-scale animal-habitat relationships, and in guiding ecosystem-based management. We assessed the nursery role of northern Gulf of Mexico seagrass meadows for gray snapper, lane snapper, and gag recruiting to Alabama’s extensive offshore reef complex. We accomplished this using broadscale juvenile trawl surveys and geochemical tags—indicative of past habitat use—stored in the otoliths of >2200 fishes. These natural tags revealed that 47-61% of snapper and gag recruits to Alabama reefs originated in Florida panhandle seagrass nurseries. Seagrass meadows in Alabama and Mississippi were also important nurseries for snappers and gag, contributing 26-46% of recruits. Despite high juvenile snapper and gag catches along the extensive Chandeleur Islands, Louisiana, relatively few of those fishes recruited to Alabama’s reefs (<13% of total recruits, across species), although they may have recruited to populations outside our sampling domain. Beyond the applied value of these data for resource management (i.e. interstate connectivity), our findings highlight broadscale drivers of the nursery role of juvenile habitats for coastal marine populations. These factors include: (1) juvenile habitat extent (i.e. extensive Florida panhandle meadows sourced the most recruits for Alabama fisheries); (2) proximity between juvenile and adult habitats (i.e. highest unit-area contribution from Alabama-Mississippi meadows); and (3) unidirectional, alongshore migration of egressing juveniles (i.e. primarily east-to-west movement, enhancing connectivity with Florida panhandle nurseries, and dampening connectivity with Chandeleur nurseries).

Citizen science and habitat modelling facilitates conservation planning for crabeater seals in the Weddell Sea

AbstractAimCreating a network of marine protected areas in the Southern Ocean requires extensive knowledge on species’ abundances, distributions and population trends especially in the Weddell Sea where year‐round pack ice makes most of the Weddell Sea inaccessible. We combine satellite images and citizen science to model habitat suitability for crabeater seals (Lobodon carcinophaga) throughout the Weddell Sea.LocationWeddell Sea, Antarctica.MethodsHigh‐resolution satellite images covering 18,219 km2 of the Weddell Sea during crabeater seal breeding season (October—November) were hosted on the crowd‐sourcing platform Tomnod (DigitalGlobe). Citizen scientists marked “maps” where seals were present/absent and these votes were compared with the votes of an experienced observer. Correction factors were used to correct votes to either a continuous probability of seal presence, or a binary seal presence/absence value. We modelled probability of seal presence using ensemble models of Random Forests (RF), Boosted Regression Trees (BRT) and Support Vector Machines (SVM), and used fitted Maxent models to model seal presence/absence data.ResultsModel predictive power was low (RF: R2 = 0.076 ± 0.002: BRT: R2 = 0.086 ± 0.0008; SVM: R2 = 0.082 ± 0.003) to average (Maxent: AUC = 0.71 ± 0.004). Distance to the ice edge and bathymetry were the most important variables that influenced crabeater seal distribution.Main conclusionsCrabeater seals were more likely to be present over abyssal water, which coincides with typical adult Antarctic krill habitat — crabeater seal preferred prey. Where ice concentrations were more variable, that is more accessible, crabeater seals were also more likely to occur. Results agreed with the known ecology of crabeaters seals and the abundance, distribution and ecology of Antarctic krill. We were able to survey the largest area ever surveyed in the Weddell Sea and provide a model to assist furthering policy around the proposed protected area.

Rusty Blackbird Habitat Selection and Survivorship during Nesting and Post-Fledging

Rusty blackbird (Euphagus carolinus) populations have declined dramatically since the 1970s and the cause of decline is still unclear. As is the case for many passerines, most research on rusty blackbirds occurs during the nesting period. Nest success is relatively high in most of the rusty blackbird’s range, but survival during the post-fledging period, when fledgling songbirds are particularly vulnerable, has not been studied. We assessed fledgling and adult survivorship and nest success in northern New Hampshire from May to August in 2010 to 2012. We also assessed fledgling and adult post-fledging habitat selection and nest-site selection. The likelihood of rusty blackbirds nesting in a given area increased with an increasing proportion of softwood/mixed-wood sapling stands and decreasing distances to first to sixth order streams. Wetlands were not selected for nest sites, but both adults and fledglings selected wetlands for post-fledging habitat. Fledglings and adults selected similar habitat post-fledging, but fledglings were much more likely to be found in habitat with an increasing proportion of softwood/mixed-wood sapling stands and were more likely to be closer to streams than adults. No habitat variables selected during nesting or post-fledging influenced daily survival rates, which were relatively low for adults over the 60-day study periods (males 0.996, females 0.998). Fledgling survival rates (0.89) were much higher than reported for species of similar size.

Scale-dependent spatial and temporal patterns of abundance and population structure of the xanthid crab Leptodius exaratus on rocky shores in Kuwait

Rocky shore habitats are common in the Arabian Gulf region, however, there is little knowledge of the patterns of spatial and temporal distribution of key intertidal organisms. The spatial and seasonal distribution of Leptodius exaratus, a keystone species rocky shores on the Kuwait coast, were investigated to better understand the ecology of the species and to gain a wider knowledge of the ecology of the rocky shore habitats in the northwest Arabian Gulf. Intensive sampling across six sites along Kuwait’s coastline over a 14 month period between November 2013 and December 2014 indicated seasonal patterns of crab abundance, increasing during the warm season and decreasing during winter and with a more large crabs observed during the summer. L. exaratus was more abundant in the mid intertidal zone on both sheltered and exposed shores. Their abundance increased towards the lower shore in sheltered sites, whereas abundance was greater towards the higher shore in exposed sites. Males and females inhabit the same habitat, with similar spatial and seasonal distributions. There was high seasonal recruitment of juveniles during summer between July and September, with some low levels of recruitment later in October and November. Moreover, juveniles follow a similar pattern of distribution as adult crabs, with abundance of juveniles being directly related to the abundance of the adult crabs and ovigerous females present on each shore. This indicates direct or indirect recruitment to the adult intertidal habitat. Significant differences in crab abundance were seen between specific sampling sites, but not at a regional level between sheltered and exposed shorelines. This suggests that abundance is influenced by localised differences between rocky shore habitat, such as habitat complexity. L. exaratus is also exploited by intertidal gleaning, which may indirectly influence patterns of crab abundance through localised differences in habitat damage.

“There and back again” − How decapod megalopae find the way home: A modelling exercise for Pachygrapsus marmoratus

Pachygrapsus marmoratus is a common coastal crab occurring in rocky shores of the northeastern Atlantic. The species presents a planktonic larval phase, constituting an interesting subject for dispersal studies, given the larval release in intertidal areas, followed by the exportation to shelf waters where larval development takes place. Onshore migration to the adult habitats is thought to be performed by the megalopa stage.Observations obtained during a summer zooplankton survey showed P. marmoratus larvae gradually farther from the coast throughout larval development, with early larval stages found in surface layers and megalopae occurring closer to the coast. The vertical migration mechanisms for larval dispersal and the return to settlement habitats were tested through physical-ecological models where the vertical distributions changed through the larval development. Ecological data, such as the ontogenetic vertical distribution of each larval stage, larval duration, and time and sites of spawning, were integrated in an oceanic model. Simulations tested different vertical distributions and periods, covering the entire larval development from intertidal areas to shelf and back to shore. The distribution of the early stages in surface layers promoted cross- and alongshore transport. Differences in the initial advection determined the positions where the more advanced stages were found later in the development. The subsurface distribution of advanced stages facilitated the transport to the inner shelf, limiting the cross-shore upwelling transport and promoting higher return to the adult habitats. Different periods of larval release resulted in contrasting dispersal patterns that could influence larval survival and recruitment to adult populations.

Mountain Plover habitat selection and nest survival in relation to weather variability and spatial attributes of black-tailed prairie dog disturbance

Abstract Habitat loss and altered disturbance regimes have led to declines in many species of grassland and sagebrush birds, including the imperiled Mountain Plover (Charadrius montanus). In certain parts of their range Mountain Plovers rely almost exclusively on black-tailed prairie dog (Cynomys ludovicianus) colonies as nesting habitat. Previous studies have examined Mountain Plover nest and brood survival on prairie dog colonies, but little is known about how colony size and shape influence these vital rates or patterns of habitat selection. We examined how (1) adult habitat utilization, (2) nest-site selection, and (3) nest success responded to a suite of local- and site-level variables on large prairie dog colony complexes in northeastern Wyoming. Abundance of adult Mountain Plovers was highest on points within older, “medium”-sized (100–500 ha) colonies with high cover of annual forbs and bare ground (5.8 birds km−2), but lower on extremely large (>2,000 ha) colonies (2.1 birds km−2). Nest sites were characterized by high proportions of annual forbs and bare ground and low cactus cover and vegetation height. Nest survival was higher for older nests, and nests with lower cactus cover, and decreased with increasing temperatures. Uncertainty was high for models of daily nest survival, potentially because of 2 competing sources of nest failure: nest depredation and nest abandonment or inviability of eggs. Drivers of these 2 sources of nest failure differed, with inclement weather and higher temperatures associated with nest abandonment or egg inviability. We highlight how prairie dogs alter vegetation structure and bare ground heterogeneously across the landscape, and how this in turn influences bird abundance and nest distribution at different temporal and spatial scales. Furthermore, our work reveals how partitioning the causes of nest failure during nest survival analyses enhances understanding of survival rate covariates.

Functional correlations of axial muscle fiber type proportions in the waterfall-climbing Hawaiian stream fish Sicyopterus stimpsoni.

Assessing the factors that contribute to successful locomotor performance can provide critical insight into how animals survive in challenging habitats. Locomotion is powered by muscles, so that differences in the relative proportions of red (slow-oxidative) vs. white (fast-glycolytic) fibers can have significant implications for locomotor performance. We compared the relative proportions of axial red muscle fibers between groups of juveniles of the amphidromous gobiid fish, Sicyopterus stimpsoni, from the Hawaiian Islands. Juveniles of this species migrate from the ocean into freshwater streams, navigating through a gauntlet of predators that require rapid escape responses, before reaching waterfalls which must be climbed (using a slow, inching behavior) to reach adult breeding habitats. We found that fish from Kaua'i have a smaller proportion of red fibers in their tail muscles than fish from Hawai'i, matching expectations based on the longer pre-waterfall stream reaches of Kaua'i that could increase exposure to predators, making reduction of red muscle and increases in white muscle advantageous. However, no difference in red muscle proportions was identified between fish that were either successful or unsuccessful in scaling model waterfalls during laboratory climbing trials, suggesting that proportions of red muscle are near a localized fitness peak among Hawaiian individuals.

Species assemblage and recruitment patterns of echinoderms on shallow rocky reefs in central New Zealand

ABSTRACT Echinoderms play important ecological roles in the benthic community, but the processes that regulate their distribution are still poorly understood. The aim of this study was to describe the community structure in the shallow rocky reefs of the Wellington region of central New Zealand. Five sites from a harbour and an open coast were surveyed for adult echinoderm density and habitat composition. Additionally, artificial collectors were deployed to assess recruitment patterns. Five taxa were responsible for the assemblage variation within sites and their abundance was highly correlated with habitat composition. Patiriella regularis was highly abundant in all sites, while Coscinasterias muricata and Evechinus chloroticus were dominant in the Harbour. Echinoderm settlement showed interannual variations, as well as differences between locations. There was a significant pulse of C. muricata settlers, while ophiuroids were present in lower numbers but constantly during the studied period. E. chloroticus settlement was sporadic and the absence of a juvenile cohort in the open coast sites suggests that recruitment might not occur for up to 4 years. The present study provides insights on the echinoderm assemblage in the shallow rocky reefs of the Wellington region and contributes to a better understanding of recruitment patterns shaping population structure.

Choosing the right home: settlement responses by larvae of six sea urchin species align with hydrodynamic traits of their contrasting adult habitats

AbstractOcean organisms as diverse as seaweeds and sea cucumbers exhibit life cycles in which dispersal occurs primarily via microscopic larvae or spores, with adults exhibiting limited or even no dispersal. In benthic animals, the larval stage concludes with irreversible settlement into the benthos. The decision of where and when to settle is thus one of substantial import. Prior work has shown that settlement in two shoreline echinoids (a sea urchin and a sand dollar) is unexpectedly sensitive to an environmental feature (intense fluid turbulence) that can be considered as a signal to larvae of their arrival in the neighbourhood of the hydrodynamically energetic habitats in which these taxa live as adults. Here, we used a comparative approach to explore the evolution of turbulence responsiveness in late-stage echinoid larvae. We examined three pairs of closely related sea urchins that differ in the energetic exposure of their adult habitats and found that larval responsiveness to turbulence was more pronounced in urchins that settle in more hydrodynamically exposed locations. These results raise the possibility that evolutionary differences in larval responsiveness to environmental indicators of appropriate adult habitat might reinforce or even provide a mechanism for vicariance in the ocean.

A novel cross‐shore transport mechanism revealed by subsurface, robotic larval mimics: Internal wave deformation of the background velocity field

AbstractCoastal physical processes are essential for the cross‐shore transport of meroplanktonic larvae to their benthic adult habitats. To investigate these processes, we released a swarm of novel, trackable, subsurface vehicles, the Mini‐Autonomous Underwater Explorers (M‐AUEs), which we programmed to mimic larval depth‐keeping behavior. The M‐AUE swarm measured a sudden net onshore transport of 30–70 m over 15–20 min, which we investigated in detail. Here, we describe a novel transport mechanism of depth‐keeping plankton revealed by these observations. In situ measurements and models showed that, as a weakly nonlinear internal wave propagated through the swarm, it deformed surface‐intensified, along‐isopycnal background velocities downward, accelerating depth‐keeping organisms onshore. These higher velocities increased both the depth‐keepers' residence time in the wave and total cross‐shore displacement, leading to wave‐induced transports twice those of fully Lagrangian organisms and four times those associated with the unperturbed background currents. Our analyses also show that integrating velocity time series from virtual larvae or mimics moving with the flow yields both larger and more accurate transport estimates than integrating velocity time series obtained at a point (Eulerian). The increased cross‐shore transport of organisms capable of vertical swimming in this wave/background‐current system is mathematically analogous to the increase in onshore transport associated with horizontal swimming in highly nonlinear internal waves. However, the mechanism described here requires much weaker swimming speeds (mm s−1 vs. cm s−1) to achieve significant onshore transports, and meroplanktonic larvae only need to orient themselves vertically, not horizontally.