Longer Pelagic Larval Duration Research Articles

Shared and distinct patterns of genetic structure in two sympatric large decapods

AbstractAimComparing genetic structure in species with shared spatial ranges and ecological niches can help identify how dissimilar aspects of biology can shape differences in population connectivity. Similarly, where species are widely distributed across heterogeneous environments and major topographic barriers, knowledge of the structuring of populations can help reveal the impacts of factors which limit dispersal and/or drive divergence, aiding conservation management.LocationEuropean seas of the northeast Atlantic and Mediterranean.TaxaEuropean clawed lobster (Homarus gammarus) and European crawfish (Palinurus elephas), two sympatric, heavily fished decapods with extensive dispersal potential.MethodsBy RAD‐sequencing 214 H. gammarus from 32 locations and 349 P. elephas from 15 locations, we isolated 6340 and 7681 SNP loci, respectively. Using these data to characterise contemporary population structuring, we investigate potential spatial and environmental drivers of genomic heterogeneity.ResultsWe found higher levels of differentiation among clawed lobsters than crawfish, both globally and within basins, and demonstrate where known hydrographic and topographic barriers generate shared patterns of divergence, such as a genetic break between the Atlantic and Mediterranean basins. Genetic structure not common to both species is principally apparent in the Atlantic portions of their range, where clawed lobster exhibits a genetic cline and increased differentiation towards range margins, while crawfish appear effectively panmictic throughout this region.Main ConclusionsWe attribute the comparative lack of crawfish population structuring to their greater dispersal tendencies via a longer pelagic larval duration and sporadic adult movements. In contrast, genetic connectivity in clawed lobster is relatively restricted, with the correlation of site of origin and temperature to geographical heterogeneity at many divergent loci indicative of both neutral and adaptive processes. Our results help inform how contemporary management can account for likely demographic connectivity and marry the conservation of genomic variation with sustainable fisheries in these ecologically and economically important crustaceans.

A novel integrative approach elucidates fine-scale dispersal patchiness in marine populations

Dispersal is one of the main determining factors of population structure. In the marine habitat, well-connected populations with large numbers of reproducing individuals are common but even so population structure can exist on a small-scale. Variation in dispersal patterns between populations or over time is often associated to geographic distance or changing oceanographic barriers. Consequently, detecting structure and variation in dispersal on a fine-scale within marine populations still remains a challenge. Here we propose and use a novel approach of combining a clustering model, early-life history trait information from fish otoliths, spatial coordinates and genetic markers to detect very fine-scale dispersal patterns. We collected 1573 individuals (946 adults and 627 juveniles) of the black-faced blenny across a small-scale (2 km) coastline as well as at a larger-scale area (<50 kms). A total of 178 single nucleotide polymorphism markers were used to evaluate relatedness patterns within this well-connected population. In our clustering models we categorized SHORT-range dispersers to be potential local recruits based on their high relatedness within and low relatedness towards other spatial clusters. Local retention and/or dispersal of this potential local recruitment varied across the 2 km coastline with higher frequency of SHORT-range dispersers towards the southwest of the area for adults. An inverse pattern was found for juveniles, showing an increase of SHORT-range dispersers towards the northeast. As we rule out selective movement and mortality from one year to the next, this pattern reveals a complex but not full genetic mixing, and variability in coastal circulation is most likely the main driver of this fine-scale chaotic genetic patchiness within this otherwise homogeneous population. When focusing on the patterns within one recruitment season, we found large differences in temperatures (from approx. 17 °C to 25 °C) as well as pelagic larval duration (PLD) for juveniles from the beginning of the season and the end of the season. We were able to detect fine-scale differences in LONG-range juvenile dispersers, representing distant migrants, depending on whether they were born at the beginning of the season with a longer PLD, or at the end of the reproductive season. The ability to detect such fine-scale dispersal patchiness will aid in our understanding of the underlying mechanisms of population structuring and chaotic patchiness in a wide range of species even with high potential dispersal abilities.

Pelagic larval duration, growth rate, and population genetic structure of the tidepool snake moray Uropterygius micropterus around the southern Ryukyu Islands, Taiwan, and the central Philippines.

The relationships between pelagic larval duration (PLD) and geographic distribution patterns or population genetic structures of fishes remain obscure and highly variable among species. To further understand the early life history of the tidepool snake moray Uropterygius micropterus and the potential relationship between PLD and population genetic structure of this species, otolith microstructure and population genetics based on concatenated mtDNA sequence (cytochrome b and cytochrome oxidase subunit I, 1,336 bp) were analyzed for 195 specimens collected from eight locations around the southern Ryukyu Islands, Taiwan, and the central Philippines. Eels with longer PLD and lower otolith growth rates were observed at relatively higher latitudes with lower water temperatures (54.6 ± 7.7 days and 1.28 ± 0.16 µm day−1 on Ishigaki Island, Japan, vs. 43.9 ± 4.9 days and 1.60 ± 0.19 µm day−1 on Badian, the Philippines), suggesting that leptocephali grew faster and had shortened pelagic periods in warmer waters. Meanwhile, the eels along the southwest coast of Taiwan had relatively longer PLD (57.9 ± 10.5 days), which might be associated with the more complex ocean current systems compared to their counterparts collected along the east coast of Taiwan (52.6 ± 8.0 days). However, the southwestern and eastern Taiwan groups had similar otolith growth rates (1.33 ± 0.19 µm day−1 vs. 1.36 ± 0.16 µm day−1). Despite the intergroup variation in PLD, genetic analysis revealed fluent gene flow among the tidepool snake morays in the study regions, implying that intraspecies PLD variation had a weak effect on genetic structure. The leptocephalus stage might have ensured the widespread gene flow among the study areas and leptocephalus growth was likely influenced by regional water temperature.

Larval dispersal in three coral reef decapod species: Influence of larval duration on the metapopulation structure.

Most coral-associated decapod species have non-migratory adult populations and depend on their planktonic larvae for dispersal. This study examined the metapopulation structure of three decapod species with different pelagic larval duration (PLD) from twelve coral reef complexes of the Gulf of Mexico. The dispersion of larvae was analyzed through the use of a realistic numerical simulation of the Gulf of Mexico with the Hybrid Coordinate Ocean Model. To study the transport and dispersion of particles in near-surface waters, a particle-tracking subroutine was run using as input the currents from the model. The simulation consisted of the launch of 100 passive particles (virtual larvae) every 24 hours from each reef throughout five years, and tracked for as long as 210 days. Results indicated that species with a short PLD, Mithraculus sculptus (PLD 8‒13 days), had a weak connection among the reefs, but higher self-recruitment, especially on the narrow western shelf. The species with a longer PLD, Dromia erythropus (28‒30 days), had a stronger connection among neighboring reefs (< 300 km). Finally, the species with an even longer PLD, Stenopus hispidus (123‒210 days), had a wider potential distribution than the other species. Circulation on synoptic, seasonal and interannual scales had differential effects on the larval dispersal of each species. The metapopulation structure of M. sculptus and D. erythropus seemed to combine features of the non-equilibrium and the patchy models, whereas that of S. hispidus presumably fit to a patchy model. These findings support previous observations that indicate that species with longer PLD tend to occupy larger areas than species with short PLD, although recruitment of juveniles to the adult populations will also depend on other factors, such as the availability of suitable habitats and the ability to colonize them.

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

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

Bio-physical connectivity patterns of benthic marine species used in the designation of Scottish nature conservation marine protected areas

Abstract Connectivity is a key consideration in the development of networks of marine protected areas (MPAs). However, little is known about the early life history of many of the epi-benthic animals that these spatial measures try to conserve. Here, a pragmatic approach to consider connectivity in such organisms is adopted, as part of the Scottish nature conservation MPA designation process. The primary tool for the study was a basic bio-physical model, forced by a circulation climatology. In the general absence of comprehensive ecological information, the model accounted for the main biological characteristics of the benthic organisms under consideration of relevance to connectivity, namely, presence, spawning season and pelagic larval duration (PLD). The results showed that some degree of connectivity between MPAs is possible even for species with short PLD although those organisms are more likely to be vulnerable to local pressures, particularly in the case of less widely distributed species and those inhabiting less dispersive inshore locations. For MPAs further offshore and species with longer PLD, our simulations suggested large-scale advection patterns crossing large-scale environmental management boundaries. Although the study was an appropriate contribution to the MPA designation process, further refinements encompassing better basic ecological information, enhanced oceanographic resolution, more realistic representation of biological processes (e.g. spawning, larval behaviour) in the model, species presence within and outside MPAs and substrate suitability maps would provide future useful confidence boundaries around the general patterns derived from our study.

Interannual variation in the larval development of a coral reef fish in response to temperature and associated environmental factors

Climate change is predicted to increase ocean temperatures and influence weather patterns. Here, we examine the influence of temperature and other environmental variables on key early life traits of the coral reef damselfish, Pomacentrus moluccensis, based on ten cohorts of newly settled fish collected over 13 years from around Lizard Island (Great Barrier Reef, Australia). Pelagic larval duration (PLD), larval growth and size at settlement were estimated through otolith microstructure analysis. Multiple regression techniques were used to measure the strength of the associations between these traits and developmental temperature, rain, wind speed and solar radiation. Temperature accounted for 18.4, 26.7 and 25.0 % of the variability in PLD, growth rates and settlement size, respectively. PLDs generally declined and growth rates generally increased with increasing temperatures to ~28 °C, above which PLDs tended to increase and growth rates tended to decrease. Size at settlement did not differ between ~25 and ~28 °C, but tended to decrease with increasing temperature above ~28 °C. Together rain, wind speed and solar radiation explained 6.3, 26.3 and 33.7 % of the remaining variability in PLD, growth rates and size at settlement, respectively. Higher wind speeds were generally associated with longer PLDs. Increasing wind, high rainfall and increasing solar radiation were associated with slower growth rates and smaller sizes at settlement. Overall, results suggest that ~28 °C is likely to be a thermal optimum for larval development for this species and other environmental factors associated with climate change including rainfall, wind speed and solar radiation should be considered in predictions of effects on larval fish.

Pelagic larval duration of two diadromous species of Kuhliidae (Teleostei: Percoidei) from Indo-Pacific insular systems

Diadromous fish species in the family Kuhliidae are able to colonise freshwater systems in Indo-Pacific islands, but their life cycle and the mechanisms involved in the colonisation of such ecosystems are poorly documented. After validating the daily rate of increment deposition in otoliths of Kuhlia rupestris, we estimated the pelagic larval duration (PLD) of K. rupestris, widely distributed in the Indo-Pacific area, and K. sauvagii, endemic to the Indian Ocean. Median PLD of K. rupestris was significantly longer than that of K. sauvagii (40.6 ± 6.9 and 32.3 ± 3.4 days (± s.d.), respectively), implying that the PLD is probably one factor controlling the extent of distribution range in Kuhlia. Within K. rupestris, individuals from New Caledonia had longer PLDs than those from Réunion Island (44.3 ± 6.7 and 37.3 ± 4.7 days (± s.d.) respectively). Further research on larval migration is needed to determine whether this was due to different environmental conditions or is population-specific. Interestingly, the PLD of these Kuhlia species is shorter than the PLD of other tropical diadromous fishes. These results improve our understanding of the dispersal strategies of freshwater fauna, to colonise and persist in tropical islands.

Pelagic larval duration is similar across 23° of latitude for two species of butterflyfish (Chaetodontidae) in eastern Australia

Duration of the pelagic phase of benthic marine fishes has been related to dispersal distance, with longer pelagic larval duration (PLD) expected to result in greater dispersal potential. Here, we examine PLDs of 2 species of coral-reef butterflyfish (Chaetodon auriga and C. flavirostris) across latitudes (14°S–37°S) along the Great Barrier Reef into south-eastern Australia; we predict that PLD will be higher for fish collected below the breeding latitudes of 24°S. For C. auriga, apart from significantly longer PLDs at Lord Howe Island and Jervis Bay (means of 54 and 52 days, respectively), all locations had similar PLDs (mean 41 days). For C. flavirostris, there was no significant location effect on PLD (mean 41.5 days); however, PLD at Lord Howe Island was 58 days with high variance precluding significance. Also, there was no significant variation in PLD among years for either species despite considerable variation in East Australian Current strength.

Weak genetic structure indicates strong dispersal limits: a tale of two coral reef fish

The extent of dispersal by pelagic larvae in marine environments, including coral reefs, is central for understanding local population dynamics and designing sustainable marine reserves. We present here the first example of a clear stepping-stone genetic structure throughout the Caribbean basin for a common coral reef species, the French grunt (Haemulon flavolineatum). Analysis of microsatellite DNA markers indicated that French grunt population structure may be characterized by overlapping populations throughout the Caribbean, influenced by independent population dynamics but with no fixed geographical boundaries. In addition, different spatial genetic patterns were found in different oceanographic regions. A second species, the bluehead wrasse (Thalassoma bifasciatum), has a much longer pelagic larval duration than French grunts and showed no explicit spatial pattern of genetic variation. This finding is concordant with the hypothesis of a positive relationship between larval dispersal and duration in the plankton. While the magnitude of the genetic signal of population structure in French grunts was very low (F(ST) approximately 0.003), the pattern of isolation-by-distance throughout the Caribbean indicated considerable population structure with important ecological and conservation significance.

Temperature influences swimming speed, growth and larval duration in coral reef fish larvae

The effects of temperature on growth, pelagic larval duration (PLD) and maximum swimming speed were compared in the tropical fish marine species Amphiprion melanopus, to determine how temperature change affects these three factors critical to survival in larvae. The effects of rearing temperature (25 and 28 °C) on the length of the larval period and growth were examined in conjunction with the effects of swimming temperature (reared at 25 °C, swum at 25 and 28 °C, reared at 28 °C, swum at 25 and 28 °C) on critical swimming speed (U-crit). Larvae reared at 25 °C had a 25% longer pelagic larval duration (PLD) than larvae reared at 28 °C, 12.3 (±0.3) days compared with 9 (±0.6) days at 25 °C. To offset this effect of reduced developmental rate, growth and U-crit were measured in larvae reared at 28 and 25 °C at the same absolute age (7 days after hatching (dah)) and same developmental age (7 dah at 28 °C cf. 11 dah at 25 °C), corresponding to the day before metamorphosis. Larvae reared at 25 °C were smaller than larvae reared at 28 °C at the same absolute age (7 dah at 25 °C cf. 7 dah at 28 °C), yet larger at similar developmental age (11 dah at 25 °C cf. 7 dah at 28 °C) when weight and standard length were compared. This stage-specific size increase did not result in better performance in larvae at the same developmental age, as there was no difference in U-crit in premetamorphic larvae reared at either temperature (7 dah at 28 °C c.f 11 dah at 25 °C). However, U-crit was considerably slower in 7-day-old larvae reared at 25 °C than larvae of the same absolute age (7 dah) reared at 28 °C. Swimming temperature controls demonstrated that a change in temperature immediately prior to swimming tests did not effect swimming performance for larvae reared at either temperature. A decreased in rearing temperature resulted in longer larval durations, reduced growth rates and slower swimming development in larvae. However, the magnitude of the response of each of these traits varied considerably. As such, larvae reared at the lower temperature were a larger size at metamorphosis but had poorer relative swimming capabilities. This study highlights the importance of measuring a range of ecologically relevant traits in developing larvae to properly characterise their relative condition and performance in response to environmental change.