Larval Advection Research Articles

Dispersal and seasonal movements of Pacific halibut (Hippoglossus stenolepis) in the eastern Bering Sea and Aleutian Islands, as inferred from satellite-transmitting archival tags

BackgroundUnderstanding connectivity is critical to the management of exploited fish stocks, but migratory dynamics of Pacific halibut (Hippoglossus stenolepis) in the Bering Sea and Aleutian Islands region are not well-understood. In the current study, 145 Pacific halibut ≥ 82 cm fork length were tagged with Pop-up Archival Transmitting (PAT) tags to evaluate interannual dispersal, seasonal migration, and depth-specific habitat use.ResultsEndpoint locations obtained after 1 year at liberty (n = 79), fishery recoveries after 2–3 years at liberty (n = 5), and at-liberty geopositions based on light data (n = 5313 estimates from 109 fish) indicated geographically distinct movement patterns: Pacific halibut tagged in the Western and Central Aleutian Islands remained within the island groups in which the fish had been tagged; fish in the eastern Bering Sea remained in that ocean basin, moving among International Pacific Halibut Commission (IPHC) regulatory areas and into Russian waters; those tagged south of Unimak Pass in IPHC Regulatory Area 4A displayed the greatest amount of emigration, dispersing eastward both seasonally and interannually to as far south as Washington State. Analysis of daily maximum depth and temperature data from 113 individuals demonstrated group-level variation in summer temperatures experienced by the fish and in the timing, duration, and synchrony of movement to deep-water wintering grounds.ConclusionsDepth-specific habitat use was suggestive of regionally explicit migratory contingents, while interannual dispersal patterns were consistent with the existence of multiple functional spawning units. The results may guide future research to examine cross-basin connectivity in the Northern Bering Sea and provide inputs for numerical modelling of individual movements, larval advection, and recruitment analyses.

Genomic survey of edible cockle (Cerastoderma edule) in the Northeast Atlantic: A baseline for sustainable management of its wild resources.

Knowledge on correlations between environmental factors and genome divergence between populations of marine species is crucial for sustainable management of fisheries and wild populations. The edible cockle (Cerastoderma edule) is a marine bivalve distributed along the Northeast Atlantic coast of Europe and is an important resource from both commercial and ecological perspectives. We performed a population genomics screening using 2b‐RAD genotyping on 9309 SNPs localized in the cockle's genome on a sample of 536 specimens pertaining to 14 beds in the Northeast Atlantic Ocean to analyse the genetic structure with regard to environmental variables. Larval dispersal modelling considering species behaviour and interannual/interseasonal variation in ocean conditions was carried out as an essential background to which compare genetic information. Cockle populations in the Northeast Atlantic displayed low but significant geographical differentiation between populations (F ST = 0.0240; p < 0.001), albeit not across generations. We identified 742 and 36 outlier SNPs related to divergent and balancing selection in all the geographical scenarios inspected, and sea temperature and salinity were the main environmental correlates suggested. Highly significant linkage disequilibrium was detected at specific genomic regions against the very low values observed across the whole genome. Two main genetic groups were identified, northwards and southwards of French Brittany. Larval dispersal modelling suggested a barrier for larval dispersal linked to the Ushant front that could explain these two genetic clusters. Further genetic subdivision was observed using outlier loci and considering larval advection. The northern group was divided into the Irish/Celtic Seas and the English Channel/North Sea, while the southern group was divided into three subgroups. This information represents the baseline for the management of cockles, designing conservation strategies, founding broodstock for depleted beds and producing suitable seed for aquaculture production.

Mismatch of thermal optima between performance measures, life stages and species of spiny lobster

In an ocean warming hotspot off south-east Australia, many species have expanded their ranges polewards, including the eastern rock lobster, Sagmariasus verreauxi. This species is likely extending its range via larval advection into Tasmanian coastal waters, which are occupied by the more commercially important southern rock lobster, Jasus edwardsii. Here, thermal tolerances of these lobster species at two life stages were investigated to assess how they may respond to warming ocean temperatures. We found that the pattern, optimum and magnitude of thermal responses differed between performance measures, life stages and species. Sagmariasus verreauxi had a warmer optimal temperature for aerobic scope and escape speed than J. edwardsii. However, J. edwardsii had a higher magnitude of escape speed, indicating higher capacity for escape performance. There were also differences between life stages within species, with the larval stage having higher variation in optimal temperatures between measures than juveniles. This inconsistency in performance optima and magnitude indicates that single performance measures at single life stages are unlikely to accurately predict whole animal performance in terms of life-time survival and fitness. However, combined results of this study suggest that with continued ocean warming, S. verreauxi is likely to continue to extend its distribution polewards and increase in abundance in Tasmania.

Red king crab larval advection in Bristol Bay: Implications for recruitment variability

AbstractRecruitment variability is poorly understood for Bering Sea crab stocks. The nearshore area in southwest Bristol Bay (Alaska, USA) is hypothesized as having historically (i.e., prior to ~ 1980) been the most important spawning ground for Bristol Bay red king crab (Paralithodes camtschaticus) because post‐larvae are thought to have been most likely to reach optimal settlement habitat along the Alaska Peninsula when hatched from this area as part of an endless‐belt reproductive strategy. We coupled a biophysical and oceanographic circulation model to test this hypothesis, investigate larval connectivity of more recent female spatial distributions, and evaluate the importance of climate variability on larval advection trajectories. Predicted settlement success varied through changes in larval pelagic duration and oceanographic circulation patterns: Shorter advective distance was associated with warmer conditions, causing higher rates of local retention relative to cold conditions. Contrary to earlier models, most larvae hatched in southwest Bristol Bay were advected offshore away from good habitat, whereas larvae hatched in central and nearshore Bristol Bay were retained in or advected to good habitat along the Alaska Peninsula. Our results suggest contemporary spatial distributions can supply settlement‐competent larvae to nurseries along the Alaska Peninsula and that under certain conditions, larvae may reach the Pribilof Islands when hatched from southwest Bristol Bay. Our study informs the role of environmental variability on larval transport and provides context within which to structure future investigations of recruitment mechanisms.

The Atlantic blue crab Callinectes sapidus Rathbun, 1896 expands its non-native distribution into the Ria Formosa lagoon and the Guadiana estuary (SW-Iberian Peninsula, Europe)

Author(s): Morais, Pedro; Gaspar, Miguel; Garel, Erwan; Baptista, Vania; Cruz, Joana; Cerveira, Ines; Leitao, Francisco; Teodosio, Maria Alexandra | Abstract: The Atlantic blue crab Callinectes sapidus Rathbun, 1896 is native in the western Atlantic, however it is a non-indigenous species across Europe since 1900, among other world regions. In this paper, we report the first occurrences of this species in the Ria Formosa lagoon and in the Guadiana estuary (SW-Iberian Peninsula, Europe) which occurred in 2016 and July 2017, respectively. We hypothesize that the introduction of this species into these ecosystems might be due to the expansion of the Guadalquivir estuary population through natural processes (larval advection, active movement), or due to unintended introduction events after being transported aboard fishing boats, or, less likely, through ballast water. Changes in Guadiana’s river flow after the construction of the Alqueva dam might also explain the presence of another non-indigenous species in the Guadiana estuary. The hypotheses presented, regarding the introduction of the Atlantic blue crab into these ecosystems and of its co-occurrence with other decapod species, are framed in a broader context to serve as a future research framework. The use of the Atlantic blue crab as a new fishing resource is also proposed, namely if it is to be used exclusively by local communities and if no deleterious impacts upon other fisheries and the ecosystem occur from this new fishery.

Spatial surface temperature correlates of American lobster (Homarus americanus) settlement in the Gulf of Maine and southern New England shelf

American lobster, Homarus americanus H. Milne-Edwards, 1837, populations along the east coast of North America are geographically distributed over some of the steepest latitudinal ocean temperature gradients in the world. A disconnect between spawner biomass and postlarval settlement, i.e., young-of-year (YoY) recruitment, to the sea bed at the end of the larval season highlights the role of external environmental factors. To understand the spatial dimension of sea surface temperature correlates of settlement, we compared over two decades of inter-annual variation in lobster settlement at three oceanographically contrasting areas: the Bay of Fundy, coastal Gulf of Maine, and southern New England, with satellite-derived sea surface temperature anomaly (SSTa) patterns over the coastal regions and shelf waters. Correlations were performed between the settlement time series and monthly SSTa maps at time lags relevant to larval hatching, development, transport, and settlement. Settlement was significantly and positively correlated with SSTa in southern New England, showing associations with upstream areas over Georges Bank and southern Nova Scotia during months when larvae are expected in the water column (July–August). The Gulf of Maine site was correlated with SSTa in the immediate vicinity of the settlement site, and only in the month of settlement sampling. Settlement at the Bay of Fundy site was not correlated to SSTa patterns. The observed associations are consistent with larval advection by residual oceanic flow structure in the region, and are further supported by studies on lobster larval supply and genetic connectivity reported in the literature.

Exploring the effect of sampling, protogyny, and larval advection on stock estimates subject to no-take closures in a spatially complex coral reef line fishery on the Great Barrier Reef, Australia

Simulation is used to evaluate the ability of a two-region, age-structured assessment model to provide accurate and precise estimates of stock status (i.e., the ratio of female spawning biomass to unfished female spawning biomass) for coral trout (Plectropomus leopardus) on the Great Barrier Reef (GBR), Australia. The model used to generate the simulated data used by the assessment model is a spatially complex age- and sex-structured population dynamics model that captures the protogynous nature of coral trout. Stock status is underestimated (negatively biased), with the extent of negative bias related to mis-specification of the breeding strategy of the target fish stock, the impact of the amount of larval connectivity among reefs, the number of reefs closed to fishing, as well as exploitation rates. The estimates of stock status were less negatively biased when fishery-independent index and age- and length-composition data were available from closed areas. The results will inform the development of management strategies for coral trout in the GBR and highlight the importance of basing evaluations of estimation and management performance on operating models that capture ecologically important processes such as metapopulation dynamics and protogynous life history.

Predicting spread of aquatic invasive species by lake currents

Knowledge of aquatic invasive species (AIS) dispersal is important to inform surveillance and management efforts to slow the spread of established invaders. We studied potential dispersal of invasive Eurasian ruffe Gymnocephalus cernua and golden mussel Limnoperna fortunei larvae in Lakes Michigan and Erie using a three-dimensional particle transport model. Ruffe is currently in Lake Superior and northern Lake Michigan, while Limnoperna has not yet invaded the Great Lakes. We predicted larval transport during several spawning seasons (individual years) from several major tributaries and ports that are most prone to invasion because of their significant recreational and commercial usage. Depending on release location, larvae traveled distances ranging from < 1 km to tens of kilometers (in some cases over 100–200 km, depending on species) during 2–3 weeks of drift time. Dispersal distances from nearshore locations (i.e. rivers and ports) were smaller than from offshore deballasting locations near ports. Limnoperna dispersal distances were larger than ruffe due to stronger seasonal currents and longer drift period. Settlement areas resulting from offshore releases were larger than for nearshore releases, and larger for Limnoperna than for ruffe. Model results compared favorably to observed spread of ruffe and Dreissena spp. mussels in Lake Michigan. Our modeling effort suggests that larval advection by lake currents is an important AIS dispersal mechanism in the Great Lakes. It also emphasizes the importance of effective surveillance programs that maximize early detection of new introductions before lake current dispersal obviates containment and prevention of spread and impacts.

Assemblages of micronektonic fishes and invertebrates in a gradient of regional warming along the Western Antarctic Peninsula

Micronektonic fishes and invertebrates were sampled with 32 midwater trawls at nine sites along the Western Antarctic Peninsula (WAP) in the austral fall (March–April) of 2010. Study sites were located within four hypothesized hydrographic regions: near Joinville Island in Region I, at Croker Passage, near Anvers Island, and near Renaud Island in Region II, within Marguerite Bay and the Marguerite Trough in Region III, and near Charcot Island in Region IV. A total of 62 taxa representing 12 taxonomic groups of pelagic invertebrates and 9 families of fish were captured, but assemblages were dominated by only a few species. The most numerically abundant taxa were the euphausiids, Thysanoessa macrura, Euphausia superba, and E. crystallorophias, combining to contribute nearly 79% of the total catch. Biomass dominants included E. superba, which contributed more than 44% of the total catch, the notothenioid Pleuragramma antarctica, and the salp, Salpa thompsoni. A comparison of total catches among sites revealed that the largest volumetric abundances and biomasses were captured at the Marguerite Bay site.Cluster analysis of abundance data identified distinct multispecies assemblages at Joinville Island in Region I, Croker Passage in Region II, Marguerite Bay in Region III, and Charcot Island in Region IV. A fifth distinct assemblage included samples from sites near Anvers and Renaud Island in Region II, and from the Marguerite Trough in Region III. Assemblages at Joinville Island and Croker Passage were both dominated by E. superba and S. thompsoni, but hydrographic conditions at Joinville Island favored a neritic assemblage, underscored by substantial numbers of P. antarctica. The assemblage at Croker Passage was more oceanic in nature with major inputs from the myctophid, Electrona antarctica and the hyperiid amphipod, Themisto gaudichaudii. Marguerite Bay and Charcot Island were well-mixed assemblages with strong representation by both neritic and oceanic fauna. The mid-peninsula assemblage was oceanic in character, being overwhelmingly dominated by Thysanoessa macrura and T. gaudichaudii.Pleuragramma antarctica were captured at five sites: Joinville Island, Croker Passage, Marguerite Bay, and the two sites near Charcot Island. They were completely absent at the two sites near Anvers Island, at Renaud Island, and in the Marguerite Trough. One fish was captured in Croker Passage. The majority of fish captured in Marguerite Bay were larger than 150 mm standard length (SL), with very few fish of smaller size present. If resident populations of Pleuragramma reproduce and recruit locally rather than being sustained by larval advection, those populations will be highly susceptible to local disappearance. This may be the causative factor behind the absence of Pleuragramma from the mid-peninsula region. Continued warming and subsequent sea ice reductions may not only cause Pleuragramma population collapses in the Marguerite Bay and Charcot Island regions, but may also change the character of the faunal assemblages along the WAP to those of an oceanic system.

Stock-specific advection of larval walleye (Sander vitreus) in western Lake Erie: Implications for larval growth, mixing, and stock discrimination

Physical processes can generate spatiotemporal heterogeneity in habitat quality for fish and also influence the overlap of pre-recruit individuals (e.g., larvae) with high-quality habitat through hydrodynamic advection. In turn, individuals from different stocks that are produced in different spawning locations or at different times may experience dissimilar habitat conditions, which can underlie within- and among-stock variability in larval growth and survival. While such physically-mediated variation has been shown to be important in driving intra- and inter-annual patterns in recruitment in marine ecosystems, its role in governing larval advection, growth, survival, and recruitment has received less attention in large lake ecosystems such as the Laurentian Great Lakes. Herein, we used a hydrodynamic model linked to a larval walleye (Sander vitreus) individual-based model to explore how the timing and location of larval walleye emergence from several spawning sites in western Lake Erie (Maumee, Sandusky, and Detroit rivers; Ohio reef complex) can influence advection pathways and mixing among these local spawning populations (stocks), and how spatiotemporal variation in thermal habitat can influence stock-specific larval growth. While basin-wide advection patterns were fairly similar during 2011 and 2012, smaller scale advection patterns and the degree of stock mixing varied both within and between years. Additionally, differences in larval growth were evident among stocks and among cohorts within stocks which were attributed to spatiotemporal differences in water temperature. Using these findings, we discuss the value of linked physical–biological models for understanding the recruitment process and addressing fisheries management problems in the world's Great Lakes.

Environmental factors influencing the recruitment and catch of tropical Panulirus lobsters in southern Java, Indonesia

Tropical Panulirus lobster fisheries in many parts of the world are open-access and poorly-regulated. This is in part because tropical Panulirus lobsters have an extended pelagic larval phase (up to 9 months) and their larval settlement may take place in different habitats and depths. When recruits of a fishery are believed not spawned locally, regulatory incentives are weak. We assessed the potential sources of recruits to a small, valuable fishery for six species of Panulirus lobster in southern Java, Indonesia with a larval advection model. The model predicted that between 1993 and 2007, 50–90% of the recruits were sourced locally compared to a mean of 25% from remote locations. The relative intensity of the Indonesian flow-through, the south Java current and seasonal onshore winds appear to be important in the local retention of recruits. Local fisheries records showed a strong seasonality in catch that we compared to potential environmental triggers with boosted regression trees. We found that the increased catch was associated with the rapid onset of increased rainfall (>90mm) at the start of the monsoon (November–May). Fishers believe the coastal runoff during periods of high rainfall increases turbidity and thus enhanced catchability. Catches declined dramatically during an extended monsoon in 2010–2011, but recovered in early 2012 when rainfall patterns became more seasonal. These combined results show that there may be potential benefit of implementing local fisheries management regulations to increase sustainability. However, their effectiveness may be difficult to detect due to the strong influence of climate and oceanographic variability on both recruitment and subsequent catch.

Patterns in connectivity and retention of simulated Tanner crab (Chionoecetes bairdi) larvae in the eastern Bering Sea

The eastern Bering Sea (EBS) population of Tanner crab (Chionoecetes bairdi) has exhibited high variability in recruitment to the commercially exploited stock since the late 1970s. Concurrently, apparent shifts in crab distribution have also been observed. Larval advection patterns and associated local retention offer a potential mechanism for these observations. The Regional Ocean Modeling System (ROMS) was used to simulate larval Tanner crab advection patterns over 1978–2004 based on larval hatching sites inferred from the distributions of reproductive females sampled during annual National Marine Fisheries Service trawl surveys. Connectivity among EBS subregions was examined by comparing start and end float locations after 60days of simulated drift. High levels of retention (>50% of floats) were observed in the majority of source subregions, and contributed significantly to the total number of endpoints in each region. Patterns in advection and resultant interregional connectivity were variable, with strongest sustained connectivity occurring along shelf, within individual domains. Increased settlement potential in the outer domain and southern middle domain after 1990 is consistent with an observed geographic shift in fishery productivity. Apparent reliance of Bristol Bay on local larval retention validates recent spatial fishery management to conserve this area as a subpopulation.

Clues from the recent past to assess recruitment of Mediterranean small pelagic fishes under sea warming scenarios

Knowledge of the effect of environmental variables on the early life history of fishes is essential to assess the effect of future environmental changes on the recruitment of commercial species. We investigate the effect of sea warming on two small pelagic fishes (Engraulis encrasicolus and Sardinella aurita) in the NW Mediterranean Sea based on the analysis of ichthyoplankton data collected in two surveys of contrasting conditions: the exceptionally warm summer of 2003, which may be indicative of conditions under future climate change scenarios, and the summer of 2004, with temperatures within the climatic average for the period 2000-2012. We use fine-resolution environmental variables measured locally and Generalized Additive Models to assess the influence of environment on these two summer-spawning small pelagic fishes. We show that sea surface temperature is the main environmental factor explaining abundance, but other factors (food availability and water currents) have additional roles tuning the effect of temperature. In the hot summer of 2003 we observed a decline of local egg production of anchovy and an increase of larval advection from the colder Gulf of Lions compared to 2004. Round sardinella spawning was higher in 2003 than in 2004 and extended over a wider area, but larvae viability was compromised by the lower availability of trophic resources. We hypothesize that future changes in environmental forcing on these two co-occurring summer spawning species will determine differential larval survival, with cascading effects on the upper trophic levels which feed on these species, including negative impacts on their fisheries.

Does larval advection explain latitudinal differences in recruitment across upwelling regimes?

Larval supply determines year-class strength of fisheries and complex ecological interactions among adults of benthic marine species. In upwelling regions, a latitudinal cline in the intensity and persistence of upwelling is thought to affect larval advection and recruitment, thereby regulating the intensity of interactions in adult populations and communities. We tested this hypothesis by determining the monthly cross-shelf abundances of nearshore benthic crus- tacean larvae throughout development during the peak upwelling season for 7 years in a region of intermittent upwelling and high recruitment (45°N). We tested whether larvae were found far- ther offshore during upwelling conditions, and we compared their interspecific cross-shelf distri- butions to previous results from a region of strong, persistent upwelling (38°N). We also compared larval abundances across the 2 upwelling regions for 1 year. Most species were retained near- shore, regardless of intra- and inter-annual variations in the intensity of upwelling. In both upwelling regions, larvae of each species consistently occurred at different distances from the shore. Further, there were no differences in nearshore larval abundance across upwelling regions for all but 1 larval stage of 1 species. Thus, latitudinal variations in the intensity and persistence of upwelling do not appear to affect larval survival, providing further evidence that nearshore pro- cesses may be a primary determinant of larval delivery to the rocky intertidal across these regions.

Are the Laurentian Great Lakes great enough for Hjort?

Abstract Hjort's insights on marine fish recruitment and larval fish advection are presumed not applicable to freshwater lakes because most freshwater lakes are small. The Laurentian Great Lakes (LGL), however, are large enough for certain oceanic-type hydrodynamics, such as strong currents and upwelling, to affect the distribution and survival of larval fish and thus fall under Hjort's purview. However, there are evolutionary constraints because LGL species underwent an evolutionary bottleneck during glaciation, ∼10 000 years BP. We consider three narratives pertinent to both the spatial scale and the evolutionary time-scale of the LGL. The first reviews recent evidence of offshore advection and subsequent cross-lake dispersal of larval and juvenile yellow perch, a coastal demersal species in Lake Michigan. The second narrative suggests that biotic interactions, rather than spatial scale itself, could account for the transition in the critical period of Lake Michigan yellow perch period from a juvenile to a larval critical period. In the third narrative, we consider whether the deep LGL lack a significant native pelagic larval fish predator. We propose that the LGL, in combination with the older World's Great Lakes, present an opportunity to explore evolution and adaptation of fish to oceanic type physical conditions.

Combining field observations and modeling approaches to examine Greenland halibut (Reinhardtius hippoglossoides) early life ecology in the southeastern Bering Sea

Spawning in Greenland halibut (Reinhardtius hippoglossoides) occurs along the continental slope and in submarine canyons in the eastern Bering Sea. It is assumed that these bathymetric features and their associated circulation patterns deliver eggs and larvae to suitable nursery habitats over the continental shelf. However, there have been no directed field studies examining spawning areas or transport of Greenland halibut early life stages in the Bering Sea, nor is it known how large-scale oceanographic forcing modulates specific physical mechanisms of delivery. The present study was undertaken to: better define spawning areas of Greenland halibut, examine development and distribution of larvae, and understand the influence of climate variations on interannual patterns of transport, distribution and abundance. Eggs were found in Bering and Pribilof Canyons and over the adjacent slope in February and early March, confirming that spawning occurs in these regions. Larvae were present over the slope, outer shelf and middle shelf in winter and spring, and settled juveniles were collected over the shelf in September. Oceanographic modeling approaches that simulate larval advection from spawning to nursery habitats indicate that depth-discrete variations in transport pathways from submarine canyons to the adjacent shelf contribute to interannual variability in transport trajectories. Overall, our results highlight specific physical mechanisms of delivery that are modulated by large-scale atmospheric and oceanographic forcing, potentially varying the degree of slope–shelf connectivity for Greenland halibut and other slope-spawning species.

Limited recruitment during relaxation events: Larval advection and behavior in an upwelling system

We capitalized on a long‐term record of larval recruitment and a distinctive oceanographic signature to reveal how changes in ocean conditions affect larval advection, behavior, and recruitment in a region of strong, persistent upwelling and recruitment limitation. We repeatedly sampled the vertical and horizontal distribution of a larval assemblage and ocean conditions during infrequent relaxations of prevailing upwelling winds near Bodega Bay, California. During prolonged relaxation events, a poleward, coastal, boundary current imported low‐salinity surface waters that were devoid of larvae to the study area. The resident larval assemblage was restricted to cold, saline, bottom waters and pushed offshore while diel vertical migrations were suppressed. Hence, changes in oceanographic conditions strongly affected behaviorally mediated larval distributions, revealing the reason that few species recruit during relaxation events in this region. During relaxation events in upwelling regions, poleward coastal boundary currents will force larvae offshore throughout the water column at small headlands and in seaward‐flowing bottom currents at straight coastlines, but recruitment may decrease markedly only near estuaries where few larvae will arrive in low‐salinity surface waters. Targeted profiling of larval assemblages complements widespread monitoring of recruitment from shore and is necessary to determine how changing ocean conditions affect larval distributions, recruitment dynamics, and the connectivity of populations.

Mesoscale advection of Upogebia pusilla larvae through an upwelling filament in the Canaries Coastal Transition Zone (CTZ)

Larval transport has a strong influence on marine populations and ecosystem function. Traditional hypotheses establish that larvae of coastal species are swept offshore during strong upwelling periods producing low recruitment rates; however, recent studies have demonstrated that this hypothesis is not supported by larval distribution data. The present study examines the influence of upwelling filaments on larval advection and wastage. During August 1993, the transport of Upogebia pusilla was analysed in relation to an offshore filament off Northwest Africa. This mesoscale structure was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf and extended 150 km westward into the oligotrophic open ocean waters. The horizontal distribution depicted by U. pusilla larvae was strongly influenced by the oceanographic features of the Canaries Coastal Transition Zone (CTZ). Specifically, the larvae were closely associated with upwelling front and filament position, showing that these neritic larvae can be advected 10–100s of kilometres offshore through the filament. However, the low larval densities observed in the samples suggest that many larvae might remain close to the coast, thus avoiding seaward transport. This implies that filaments probably do not significantly affect the recruitment success of intertidal invertebrates such us U. pusilla in upwelling systems.

Climate‐index response profiling indicates larval transport is driving population fluctuations in nudibranch gastropods from the northeast Pacific Ocean

We illustrate a novel method, climate‐index response profiling, for testing mechanistic hypotheses for abundance fluctuations in long‐term marine data sets. (1) Autoregressive models were fitted to time‐series data for multiple species using climate indices as external regressors. The resulting regression coefficients for each species we term a climate‐index response profile (CIRP). (2) Mechanistic hypotheses were rejected based on the summary response profile across species obtained by meta‐analysis. (3) Monte‐Carlo simulations of the CIRPs for all species at all sites were performed to generate null expectations to test the significance of nonrejected hypotheses. We applied this method to historical data of 56 nudibranch species from three intertidal sites studied independently in central California during nonoverlapping time periods between 1969 and 1995, combined with recent resurveys from these same sites. Adult populations are strongly correlated with the multivariate El Niño‐Southern Oscillation index and sea‐surface height, increasing during El Niño and decreasing during La Niña events. Our data are consistent with recruitment limitation via larval advection as the primary driver of adult abundance variation. El Niño conditions increase recruitment by cross‐shelf onshore advection of larvae from both southern and northern populations, and alongshore larval advection from southern source populations. We hypothesize that recent declines of California nudibranchs are temporary, and populations will recover as El Niño conditions return to the California current.

Three-dimensional distribution of small pelagic fish larvae (Sardinops sagax and Engraulis mordax) in a tidal-mixing front and surrounding waters (Gulf of California)

Engraulis mordax and Sardinops sagax spawn in the highly productive midriff archipelago region of the Gulf of California, where intense tidal mixing produces a sharp thermal front. We analyzed the three-dimensional larval distribution of both species around the front from data obtained in February 2007 with opening- closing nets (505 μm) in 50 m strata from the surface to 200 m depth. Engraulis mordax preflexion larvae and S. sagax preflexion and flexion larvae were on the warm side of the front in the upper 100 m of the water column, mostly in the > 16°C mixed layer. However, S. sagax preflexion and flexion larvae tended to be absent from the stations of maximum abundance of E. mordax. The geostrophic jet associated with the front functioned as a boundary by hindering larval advection to the cold side. The wide distribution of E. mordax flexion larvae throughout the area (found down to 150 m) resulted from the species spawning in several regions. The spawning areas and the optimal conditions for E. mordax larvae had a wider range than those for S. sagax. Larval three-dimensional distribution in other ecosystems might differ as function of the species spawning interaction and the evolution of the physical system.