Pelagic Stage Research Articles

Marine connectivity dynamics: clarifying cosmopolitan distributions of marine interstitial invertebrates and the meiofauna paradox

Many interstitial species were first described as widely distributed, often cosmopolitan or amphi-oceanic, contrasting with descriptions of a sedentary life style and the general absence of pelagic dispersal stages. These inconsistencies became known as the “meiofauna paradox”. In this review, we present a literature review investigating these inconsistencies and address the assumptions of the meiofauna paradox. We break the paradox down to two aspects including species distribution and dispersal. Focusing on distribution, we demonstrate that wide distributions are seldom given and false records likely stem from biological phenomena like stasis or recent speciation. These phenomena account for morphological similarity, ultimately represented by the pronounced occurrence of cryptic species with restricted distribution ranges. Additionally, taxonomic artefacts such as the erroneous application of taxonomic keys contribute to the report of widely distributed species. Considering dispersal, we point out the mismatch between traditional assumptions of meiofaunal sedentarism and growing experimental and empirical evidences suggesting higher dispersal potential. These evidences include not only indications for dispersal by pelagic stages, but further consider ecological and life-history traits in shaping distribution ranges. We conclude that the meiofauna paradox sensu stricto most likely does not exist and provide a roadmap for future research, suggesting a focus on morphological similarity and marine connectivity. Meiofaunal research should concentrate on evolutionary factors resulting in morphological similarity, improving the taxonomic resolution of species complexes and conducting more sophisticated experimental experiments to meiofaunal dispersal. In all cases, meiofaunal research will benefit from high-throughput sequencing such as genome scanning approaches, metagenomics or metatranscriptomics.

Earliest ontogeny of early Cambrian acrotretoid brachiopods \u2014 first evidence for metamorphosis and its implications

BackgroundOur understanding of the ontogeny of Palaeozoic brachiopods has changed significantly during the last two decades. However, the micromorphic acrotretoids have received relatively little attention, resulting in a poor knowledge of their ontogeny, origin and earliest evolution. The uniquely well preserved early Cambrian fossil records in South China provide a great new opportunity to investigate the phylogenetically important ontogeny of the earliest acrotretoid brachiopods, and give new details of the dramatic changes in anatomy of acrotretoid brachiopods during the transition from planktotrophic larvae to filter feeding sedentary juveniles.ResultsWell preserved specimens of the earliest Cambrian acrotretoid brachiopods Eohadrotreta zhenbaensis and Eohadrotreta? zhujiahensis (Cambrian Series 2, Shuijingtuo Formation, Three Gorges area, South China) provide new insights into early acrotretoid ontogeny, and have significance for elucidating the poorly understood early phylogeny of the linguliform brachiopods. A more comprehensive understanding of the applied terminology based on new observation, especially in definition of the major growth stages (embryo, planktotrophic larva, post-metamorphically sessile juvenile and adult), is established. The so-called acrotretoid “larval shell” of both valves of Eohadrotreta demonstrates evidence for metamorphosis (shedding of the larval setae and transitions of shell secretion), during the planktotrophic stage. Therefore, it is here termed the metamorphic shell. The inferred early acrotretoid larval body plan included a bivalved protegulum, secreted at the beginning of the pelagic stage, which later developed two pairs of larval dorsal setal sacs and anterior–posterior alignment of the gut during metamorphosis.ConclusionThe primary larval body plan of acrotretoid Eohadrotreta is now known to have been shared with most early linguliforms and their relatives (including paterinates, siphonotretoids, early linguloids, the problematic mickwitziids, as well as many early rhynchonelliforms). It is suggested that this type of earliest ontogeny can be considered as plesiomorphic for the Brachiopoda and probably first evolved in stem group brachiopods with subsequent heterochronic changes.

Ontogenetic variation in photosensitivity of developing echinoderm propagules

Swimming behaviours and sensory abilities of early pelagic stages play a prominent role in the life history and ecology of sessile/sedentary benthic species, with implications for settlement, recruitment and dispersal. Light is a particularly important driver of navigational behaviour in the ocean, as a signal of key habitat characteristics (e.g., depth, shelter). Work to date on phototaxis has largely focused on planktotrophic larvae that feed during development, and much less on the larger lecithotrophic larvae that rely on maternal provisions (yolk). It remains unclear how responses to light might differ among ciliated propagules of different sizes and nutritional modes. The present study explored if/how phototactic responses are modulated by ontogeny (from embryo to larva), nutritional mode and light colour (wavelength) in ciliated propagules using four co-occurring species of echinoderms: the sea stars Asterias rubens and Crossaster papposus, the sea urchin Strongylocentrotus droebachiensis and the sea cucumber Cucumaria frondosa. Two types of behavioural responses to stimuli (white, red, and blue light) were examined: 1) taxis when the light stimulus was placed at one end of the chamber (net movement towards or away from the light stimulus) and 2) activity level, using a suite of swimming metrics, under uniform illumination. All four species consistently displayed some level of photosensitivity to white light and responses varied intra- and interspecifically. When the stimulus was red or blue light, planktotrophs modified their phototactic responses in a species- and stage-specific manner, while lecithotrophs generally displayed responses without a clear net direction. Swimming speeds displayed stage and species-specific variation under constant red or blue light, but swimming trajectories were consistently straighter under red light, resulting in greater displacement. Taken together, the results suggest that propagules of species with different life-history strategies respond to light stimuli in distinctive stage-wise manners. Interestingly, ontogenetic patterns were not conserved within nutritional modes or taxa. Further investigations of species-specific responses to light might help clarify its roles, in combination with factors such as buoyancy and gravity, in the ecology of propagules of benthic invertebrates.

Larval description and habitat utilization of an amphidromous goby, Redigobius bikolanus (Gobiidae)

AbstractRedigobius bikolanus(Gobiidae), which is distributed widely in the tropical regions of the West Pacific, is categorized as an amphidromous fish. Such fish reproduce in fresh water and newly hatched larvae immediately drift downstream to the estuary and sea where they spend a pelagic stage before returning upstream as juveniles. The morphology of larvalR. bikolanushas been reported mainly from Japan, whereas little is known about the early stages of this species on the Asian continent. To understand larval growth of this goby, monthly and bimonthly collections with ichthyoplankton nets were made in the Tien Yen estuary in northern Vietnam, from October 2014 to September 2015. A total of 282 larvae (preflexion to postflexion stages, 2.3-5.4 mm body length) ofR. bikolanuswere collected from the center of the current in May, but none were captured in the waters near the banks. The larvae were similar in general morphology to those of common gobies, but could be distinguished from other gobiid genera by two very large stellate melanophores on the ventral surface of the trunk and tail. Descriptions ofR. bikolanuslarvae based on a series of wild specimens are provided. The fishes occurred in low salinities (0.2-2.3 PSU) within 1 m from the surface layer. Together with the wide range of size and developmental stages, this suggests that larvae ofR. bikolanusutilize the center of the current of the Tien Yen estuary as their nursery area. This habitat has not been recorded in Japan.

Assessing impacts of simulated oil spills on the Northeast Arctic cod fishery

We simulate oil spills of 1500 and 4500m3/day lasting 14, 45, and 90days in the spawning grounds of the commercial fish species, Northeast Arctic cod. Modeling the life history of individual fish eggs and larvae, we predict deviations from the historical pattern of recruitment to the adult population due to toxic oil exposures. Reductions in survival for pelagic stages of cod were 0–10%, up to a maximum of 43%. These reductions resulted in a decrease in adult cod biomass of <3% for most scenarios, up to a maximum of 12%. In all simulations, the adult population remained at full reproductive potential with a sufficient number of juveniles surviving to replenish the population. The diverse age distribution helps protect the adult cod population from reductions in a single year's recruitment after a major oil spill. These results provide insights to assist in managing oil spill impacts on fisheries.

Vertical distribution of snow crab (Chionoecetes opilio) pelagic stages in the Gulf of St. Lawrence (Canada) and effect of temperature on development and survival

AbstractKnowledge of the vertical distribution, thermal habitat, and growth of the larvae of the cold stenothermic snow crab (Chionoecetes opilio) is incomplete and inconsistent. This study explored aspects of the vertical distribution and development rate of larvae from eastern Canada. In the Gulf of St. Lawrence (GSL), during 2002, the mean vertical positions of the snow crab zoeae I and II larvae were recorded within and above the permanent thermocline and in close association with the depth of strong density discontinuities in the stratified water column. No statistically significant differences were detected between nighttime and daytime vertical positions. The water temperatures at the centre of the larvae distributions were 2–3 °C in late May in the colder northern GSL and 7–8 °C in June in the warmer southern GSL. Data from the literature and from a rearing experiment in 2014 were used to develop functions linking development and survival to water temperature. Assuming the snow crab larvae remain in the upper mixed layer until final metamorphosis, development may last 2.2–4 months depending on hatch time and location. Development would be prolonged by several weeks if premolt megalopae move into and reside in the deeper, colder waters as appears to be the case. A relative survival index suggests that optimum temperature for development is around 10.8 °C, 9.5 °C, and 8.7 °C for snow crab zoea I, zoea II, and megalopa, respectively. These results should contribute to modelling efforts that aim to evaluate the extent of larval drift and location of potential settlement areas, as well as the potential impact of climate change on snow crab in the North Atlantic.

Distribution, reproduction, and feeding of West African shrimp Plesionika carinata Holthuis, 1951 (Decapoda, Pandalidae)

Plesionika carinata is endemic in the West African tropical biogeographical realm and is distributed from the western Sahara coast (23°35′ N) to southern Namibia (29° S). A total of 263 individuals with a total carapace length of 31 to 71 mm have been studied. P. carinata juveniles are pelagic and occur over depths from 340 to 2000 m or more, mainly over the lower part of the continental slope in summer and over the upper part of the continental slope in autumn. Adults are mainly benthic and occur on the edge of the shelf and the upper part of the continental slope (at depths of 300 to 880 m). Ovigerous females have 750 to 3330 eggs 0.45–0.5 × 0.5–0.65 mm in size on pleopods. Plesionika carinata feeds on abundant micronectonic and macroplanktonic crustaceans (euphausiids and pelagic shrimps) at earlier pelagic stages; it is detritophagous/necrophagous and predatory near the bottom when adult.

Biological report of a giant deep-sea squid Onykia robusta collected from the Sanriku Coast, Japan: implications for low genetic diversity

Despite their appeal to both researchers and the general public, the biology of giant deep-sea squids remains enigmatic. The robust clubhook squid Onykia robusta (Verrill, 1876) is one of the largest living deep-sea squids. It is distributed across the northern Pacific Ocean between Japan and California, including the Bering Sea. Although this species has been frequently caught by fishermen, its biology remains largely unknown. In this paper, I report biological data from one specimen, which was collected from the Sanriku Coast of northeastern Japan. The individual was a sexually mature female (total length: 246 cm, mantle length: 125 cm, wet body weight: 26 kg) and with oocytes that may have been large enough to begin yolk accumulation. Low genetic diversity within this species was implied by comparative analysis of the mitochondrial DNA (mtDNA) cytochrome oxidase I (COI) gene (n = 5; additional four sequences sourced from GenBank). The low nucleotide diversity (π = 0.0044) was similar to that of the deep-sea giant squid Architeuthis dux, which is known from mtDNA analysis to lack discernible population structure, showing no genetic differentiation among samples from different regions of the Pacific. Architeuthis dux has been hypothesized to be highly migratory, probably through a pelagic paralarval stage. My data suggest the presence of a common dispersal strategy among the deep-sea giant squids.

A model for simulating the active dispersal of juvenile sea turtles with a case study on western Pacific leatherback turtles.

Oceanic currents are known to broadly shape the dispersal of juvenile sea turtles during their pelagic stage. Accordingly, simple passive drift models are widely used to investigate the distribution at sea of various juvenile sea turtle populations. However, evidence is growing that juveniles do not drift purely passively but also display some swimming activity likely directed towards favorable habitats. We therefore present here a novel Sea Turtle Active Movement Model (STAMM) in which juvenile sea turtles actively disperse under the combined effects of oceanic currents and habitat-driven movements. This model applies to all sea turtle species but is calibrated here for leatherback turtles (Dermochelys coriacea). It is first tested in a simulation of the active dispersal of juveniles originating from Jamursba-Medi, a main nesting beach of the western Pacific leatherback population. Dispersal into the North Pacific Ocean is specifically investigated. Simulation results demonstrate that, while oceanic currents broadly shape the dispersal area, modeled habitat-driven movements strongly structure the spatial and temporal distribution of juveniles within this area. In particular, these movements lead juveniles to gather in the North Pacific Transition Zone (NPTZ) and to undertake seasonal north-south migrations. More surprisingly, juveniles in the NPTZ are simulated to swim mostly towards west which considerably slows down their progression towards the American west coast. This increases their residence time, and hence the risk of interactions with fisheries, in the central and eastern part of the North Pacific basin. Simulated habitat-driven movements also strongly reduce the risk of cold-induced mortality. This risk appears to be larger among the juveniles that rapidly circulate into the Kuroshio than among those that first drift into the North Equatorial Counter Current (NECC). This mechanism might induce marked interannual variability in juvenile survival as the strength and position of the NECC are directly linked to El Niño activity.

Early life history of the small yellow croaker (Larimichthys polyactis) in sandy ridges of the South Yellow Sea

ABSTRACTThe early life history of the small yellow croaker Larimichthys polyactis was studied using the otolith microchemistry of juvenile fish and a recruitment survey in the sandy ridges of the South Yellow Sea. The otolith Sr/Ca ratio regime shifted markedly at the age of 5–7 days (early April) and 37–41 days (around early May). Subsequently, the Sr/Ca ratio was almost constant until late June, indicating an aggregation of L. polyactis juveniles in the relatively stable habitat of the sandy ridges, which was supported by a recruitment survey that showed a rapid increase in the number of juveniles in the same area between early May and the end of June. Variations in the Sr/Ca ratio between early April and early May might reflect a habitat adaptive strategy of L. polyactis in the pelagic stage to hydrodynamic processes of the sandy ridges. Based on the aforementioned habitat shifts and recruitment phenology, it was hypothesised that L. polyactis juveniles disperse between early April and early May, inhabit sandy ridges to feed, and migrate offshore in late June.

Larval development and post‐larval growth of Branchiomma bairdi (Annelida: Sabellidae) from a Mediterranean population

AbstractBranchiomma bairdi is a Caribbean fan worm introduced in several localities worldwide, including the Mediterranean Sea, where the species’ range has rapidly expanded. Reproduction in B. bairdi was previously investigated in both extra‐Mediterranean and Mediterranean areas, but no information is available on larval development and post‐larval growth. In the present article, we examined these features for a population from the Mar Grande of Taranto (Ionian Sea). The species is hermaphrodite, and fertilization occurs in situ. Mucus seems to play an important role in fertilization, and also in preserving eggs before fertilization. The trochophore stage develops within the mucus and after hatching, larvae swim for about 3 d before settlement. The trochophore showed a distinct prototroch and two red dorsolateral larval eyes. The pelagic stage takes only 96 h even though prototroch is maintained after settlement, disappearing at 5 d, when larvae showed three chaetigers and branchial crown consisted of four radioles. Some interesting observations concerning changes in the morphology of chaetae and in the number of uncini during growth are also reported, together with discussion of the development of stylodes, an important diagnostic feature in Branchiomma species identification.

Life history differences and latitudinal variation in recruitment in two species of arctic-boreal perciform fishes, the fish doctor Gymnelus viridis and the Arctic shanny Stichaeus punctatus

Growth and recruitment were examined in two arctic-boreal, shallow water marine perciform species: the fish doctor Gymnelus viridis (Zoarcidae) and the Arctic shanny Stichaeus punctatus (Stichaeidae). G. viridis ranges in the Canadian Arctic from northern Hudson Bay to northern Ellesmere Island, whereas S. punctatus has a more southerly range from Nova Scotia coastal waters to northern Hudson Bay. At Nuvuk Islands in northeastern Hudson Bay, where the two species are sympatric in shallow water, they had comparable juvenile growth rates but temporal variation in 0+ recruitment was substantially greater in S. punctatus. This difference may stem from their contrasting early life histories. S. punctatus spawns large numbers of small demersal eggs that hatch into pelagic larvae, whereas G. viridis spawns small numbers of large demersal eggs that hatch directly into demersal juveniles with no pelagic stage, suggesting that recruitment in G. viridis should be less sensitive to yearly variation in the onset of the ice-free period in Hudson Bay and the subsequent pulse of pelagic invertebrate production. Relative to Nuvuk, recruitment variation in G. viridis was found to be greater at Resolute, Cornwallis Island, close to its northern range limit, whereas recruitment variation in S. punctatus was not evident in Newfoundland, closer to its southern range limit.

Fecundity of the Far-Eastern flatfishes Pleuronectiformes. 2. Comparative taxonomic analysis: fecundity, abundance and distribution of the species

Comparative analysis is made for absolute, species-specific and total fecundity of 31 flatfish species in the North Pacific from North America to the Japan Sea. Normally the individuals of larger size have higher fecundity. Similarity between the species by fecundity dynamics in dependence on body length and age is evaluated. Significance of the absolute fecundity for abundance or distribution of the species is discussed. Generally, the species with medium or high fecundity are more abundant than those with low number of eggs. The widest distribution is intrinsic for flatfish species with medium length of the early pelagic stage of their life.

Impact of the fishery for late-larval European sardine (Sardina pilchardus) on the adult stock in the Adriatic Sea

Bianchetto [“white” late-larval and juvenile stages (‘fry’) mainly of sardine (Sardina pilchardus)] was fished traditionally along most of the Italian coast. The Gulf of Manfredonia (southwest Adriatic Sea) hosts a sardine nursery which was historically exploited by the bianchetto fishery using trawlnets; the fishery was banned in 2010. Here, we model this larval fishery under different assumptions of catch and natural mortality to assess its impact on the adult sardine stocks in the Adriatic Sea. The results show that the impact of the fishery is heavily dependent on the choice of early-stage natural mortality. The model proposed by Pepin (1991). Effect of temperature and size on development, mortality, and survival rates of the pelagic early life history stages of marine fish. Canadian Journal of Fisheries and Aquatic Sciences, 48: 503–518. was selected as the most plausible. Under this assumption, the direct effect of the bianchetto fishery in the Gulf of Manfredonia on the Adriatic adult sardine stock appears to be low, but not negligible, with impacts estimated as a 0.1–2% increase in the numbers of sardine at age 1 in the absence of a bianchetto fishery. Projections show that a 5% impact on age 1 sardine may be sufficient to bring the adult stock below safe levels. Therefore, given the uncertainties surrounding the impact assessment and the current status of the stock, if this fishery were to be resumed, catches should be kept at the lowest possible level until the underlying processes are better understood.

Ocean Productivity May Predict Recruitment of the Rainbow Wrasse (Coris julis).

Predicting recruitment fluctuations of fish populations remains the Holy Grail of fisheries science. While previous work has linked recruitment of reef fish to environmental variables including temperature, the demonstration of a robust relationship with productivity remains elusive. Despite decades of research, empirical evidence to support this critical link remains limited. Here we identify a consistent and strong relationship between recruitment of a temperate wrasse Coris julis, from temperate reefs in the mid-Atlantic region, with Chlorophyll, over contrasting scales, across multiple years. Additionally, we find that the correlation between Chlorophyll and recruitment is not simply masking a temperature-recruitment relationship. Understanding the potential mechanisms underlying recruitment variability, particularly as it relates to changing climate and ocean regimes, is a critical first step towards characterizing species’ vulnerability to mismatches between pulsed planktonic production and early pelagic life stages.

Effects of dietary lipid profile on larval performance and lipid management in Senegalese sole

The aim of this study was to evaluate the short- and long-term effects of diets consisting in rotifers enriched with different oil emulsions (differing mainly in triacylglycerols levels) and provided during the first week of life. Survival, growth, metamorphosis progress, lipid profile and molecular regulatory pathways were evaluated. For comparison purposes, a diet used routinely in the aquaculture industry based on microalgae was also carried out. The present study shows that dietary triacylglycerols (TAG) levels and fatty acid composition modulate larval survival and growth when supplied during larval pelagic stages. Histological observation and gene expression pattern showed that early larvae regulated intestinal lipid transport, showing a coordinate activation of apolipoproteins transcripts. Multivariate analyses identified the major contribution of apoEa to discriminate samples by dietary treatments, pointing out the importance of this apolipoprotein as key molecular marker for intestinal lipid mobilization. However, our data indicate that transport capacity is limited in early larvae, increasing in anterior intestine as intestine maturates with larval development, while the increase of fat deposits in the posterior intestine in older larvae supports the limited capacity of this gut section for lipid transport. The accumulation of TAG, phosphocholine (PC) and oleic acid (OA) along pre- and early metamorphosis indicates that these lipids influences positively daily mortality rate, eye-migration progress and growth. Moreover, larval TAG amounts correlate highly with apoA-IVBa3 mRNA levels, indicating an active role of this apolipoprotein in endogenous lipid mobilization during development. These data provide new evidence that TAG, PC and OA dietary levels are important for larval development and complement the available information about energy management in sole larvae reinforcing the rotifer feeding period as critical to produce high-quality larvae. Statement of relevanceThis paper provides new clues about the mechanisms involved in lipid management in larvae and their consequences during their life-cycle to produce high-quality fry and optimize husbandry procedures.

Oceanic currents drove population genetic connectivity of the brown alga Sargassum thunbergii in the north‐west Pacific

AbstractAimOceanic currents are among the most pervasive hydrodynamic features in shaping community dynamics, population connectivity and phylogeographical structure of intertidal species. Here, we test whether population structure and biogeographical gradients of genetic diversity in the brown alga Sargassum thunbergii are correlated with oceanic currents in the north‐west Pacific (NWP).LocationNorth‐west Pacific (25.07°N–43.36°N).MethodsNuclear internal transcribed spacer‐2 and mitochondrial cox3 sequences were obtained from 835 and 810 individuals of S. thunbergii respectively. Parsimony networks and phylogenetic trees (maximum parsimony and Bayesian inference) were constructed to evaluate phylogeographical structure. Pairwise FST estimates and analyses of molecular variance (AMOVA) at various hierarchical levels (latitude, longitude, marine provinces, biogeographical basins and zoogeographical zones) were conducted to elucidate population genetic differentiation. migrate software was used to estimate the number of migrants between adjacent populations.ResultsSeveral lines of evidence indicate that S. thunbergii is characterized by shallow population structure. Geographical distances do not correlate with population pairwise genetic differentiations. The corridor/stepping‐stone model‐based coalescent analyses reveal high levels of asymmetric gene flow among S. thunbergii populations, with the numbers of migrants largely corresponding to the directions of oceanic current systems in the NWP. Genetic signatures also indicate that Jeju Island, Korea might act as a transition zone for dispersal of S. thunbergii in the NWP driven by the Kuroshio Current, thus facilitating subsequent transportation northward into the Sea of Japan and the Yellow‐Bohai Sea.Main conclusionsPopulation genetic homogeneity in S. thunbergii was mainly structured by oceanic currents rather than palaeoclimatic events. Our study illustrates an important phylogeographical case of how coastal hydrodynamic factors contributed to population connectivity and geographical shifts of genetic diversity for marine organisms without a pelagic stage.

Four new records of stranded Kemp’s ridley turtle Lepidochelys kempii in the NW Iberian Peninsula

The critically endangered Kemp’s ridley turtle (Lepidochelys kempii) has a reduced distribution range concentrated in the Gulf of Mexico and only a few pelagic stage juveniles occasionally strand on European coasts. In the study area only three individuals have been recorded previously, most recently in 2001. Four new records of Kemp’s ridley turtle are reported from the northwestern Iberian Peninsula in 2014. All of them were juvenile with a maximum straight carapace length of 26.8 cm. Two of them were found alive, but died on the first two days at the rehabilitation centres. The largest individual stranded in November presented signs of incidental capture in fishing gears. The four records in just one year are a significant increase compared to previous data for the species in this area, and the data obtained contribute to the local knowledge on species phenology, size, distribution and threats.

Do some deep-sea, sediment-dwelling species of harpacticoid copepods have 1000-km-scale range sizes?

The range sizes of sediment-dwelling deep-sea species are largely unknown. Such knowledge is important because a deep sea composed in large part of species with 100-km-scale ranges would be very different from one composed predominantly of species with 1000-km-scale ranges. For example, the total species richness would be much greater in the first case than in the second. As a step towards the determination of the distribution of species' range sizes in the deep sea, we asked whether harpacticoid copepods (Crustacea) on the continental rise in the northeastern Pacific had 1000-km-scale range sizes. We chose harpacticoids because they occur widely in deep-sea sediments and thus are a typical deep-sea taxon. In addition, they have no pelagic stage in their life history, so they allow a conservative test of hypotheses about species' range sizes. We used morphology and gene-sequence data to assign individuals to species. At least 13.3% of the species we studied had 1000-km-scale ranges, raising the question of how these species maintain genetic continuity.

Active dispersal in loggerhead sea turtles ( Caretta caretta ) during the ‘lost years’

Highly migratory marine species can travel long distances and across entire ocean basins to reach foraging and breeding grounds, yet gaps persist in our knowledge of oceanic dispersal and habitat use. This is especially true for sea turtles, whose complex life history and lengthy pelagic stage present unique conservation challenges. Few studies have explored how these young at-sea turtles navigate their environment, but advancements in satellite technology and numerical models have shown that active and passive movements are used in relation to open ocean features. Here, we provide the first study, to the best of our knowledge, to simultaneously combine a high-resolution physical forcing ocean circulation model with long-term multi-year tracking data of young, trans-oceanic North Pacific loggerhead sea turtles during their 'lost years' at sea. From 2010 to 2014, we compare simulated trajectories of passive transport with empirical data of 1-3 year old turtles released off Japan (29.7-37.5 straight carapace length cm). After several years, the at-sea distribution of simulated current-driven trajectories significantly differed from that of the observed turtle tracks. These results underscore current theories on active dispersal by young oceanic-stage sea turtles and give further weight to hypotheses of juvenile foraging strategies for this species. Such information can also provide critical geographical information for spatially explicit conservation approaches to this endangered population.