Simulations Of Larval Dispersal Research Articles

Integration of population genetics with oceanographic models reveals strong connectivity among coral reefs across Seychelles

Many countries with tropical reef systems face hard choices preserving coral reefs in the face of climate change on limited budgets. One approach to maximising regional reef resilience is targeting management efforts and resources at reefs that export large numbers of larvae to other reefs. However, this requires reef connectivity to be quantified. To map coral connectivity in the Seychelles reef system we carried out a population genomic study of the Porites lutea species complex using 241 sequenced colonies from multiple islands. To identify oceanographic drivers of this connectivity and quantify variability, we further used a 2 km resolution regional ocean simulation coupled with a larval dispersal model to predict the flow of coral larvae between reef sites. Patterns of admixture and gene flow are broadly supported by model predictions, but the realised connectivity is greater than that predicted from model simulations. Both methods detected a biogeographic dispersal barrier between the Inner and Outer Islands of Seychelles. However, this barrier is permeable and substantial larval transport is possible across Seychelles, particularly for one of two putative species found in our genomic study. The broad agreement between predicted connectivity and observed genetic patterns supports the use of such larval dispersal simulations in reef system management in Seychelles and the wider region.

Genetic population structure of the precious coral Corallium japonicum in the Northwest Pacific

Population sizes of the Japanese red coral Corallium japonicum have been severely affected by poaching and overfishing. Although genetic structure and connectivity patterns are considered important parameters for conservation strategies, there are few studies focusing on the population genetics of C. japonicum in the Northwest Pacific. We examined the genetic population structure of C. japonicum, in the Northwest Pacific. We used restriction-site-associated DNA sequencing (RAD-seq), which can be used to identify genome-wide single-nucleotide polymorphism (SNPs), to reveal detailed within-species genetic variations. Using the variable SNP loci identified from this analysis, we successfully evaluated the population-level genetic diversity and patterns of gene flow among multiple populations of C. japonicum around Japan. The results of genetic analysis basically showed that gene flow is widely maintained in the geographic range examined in this study, but the analysis in combination with larval dispersal simulations revealed several populations that were genetically distinct from the other populations, suggesting geographically limited gene flows. The information obtained from this study will be useful for the design of effective management schemes for C. japonicum, which is under threat from overfishing.

Larval dispersal simulations and connectivity predictions for Mediterranean gorgonian species: sensitivity to flow representation and biological traits

Abstract Larval dispersal enables demographic and genetic connectivity among marine populations. For many sessile species, it is the only natural mechanism for resilience after major population disturbances, as those that have been affecting Mediterranean gorgonian species inside and outside Marine Protected Areas (MPAs). Larval dispersal simulation is a powerful tool to anticipate connectivity among populations which might be altered by modelling choices. We assessed how flow representation (resolution and vertical turbulence) and larval traits (pelagic larval duration, release timing and duration, larval vertical behaviour) influenced populations connectivity among five coastal rocky locations in the northwestern Mediterranean, four of them being designated as MPAs. We used a finer (0.3 km) and coarser (1.5 km) flow resolution in two years to assess, using a hierarchical simulation approach, the sensitivity of connectivity patterns to the above parameters. Larval traits corresponded to two gorgonian species, the neutrally buoyant Eunicella singularis and the passive sinker Paramuricea clavata. Ocean model resolution was the most influential factor on resulting connectivity patterns. When using the finer flow model resolution, connectivity patterns were equally influenced by all larval traits while vertical turbulence could be neglected. Hence, advising the design of coastal MPAs with regional connectivity estimates requires adequate flow simulation resolution.

Seascape Genomics Reveals Metapopulation Connectivity Network of Paramuricea biscaya in the Northern Gulf of Mexico

The degree of connectivity among populations influences their ability to respond to natural and anthropogenic stressors. In marine systems, determining the scale, rate, and directionality of larval dispersal is therefore, central to understanding how coral metapopulations are interconnected and the degree of resiliency in the event of a localized disturbance. Understanding these source-sink dynamics is essential to guide restoration efforts and for the study of ecology and evolution in the ocean. The patterns and mechanisms of connectivity in the deep-sea (>200 m deep) are largely understudied. In this study, we investigated the spatial diversity patterns and metapopulation connectivity of the octocoral Paramuricea biscaya throughout the northern Gulf of Mexico (GoM). Paramuricea biscaya is one of the most abundant corals on the lower continental slope (between 1,200 and 2,500 m) in the GoM. The 2010 Deepwater Horizon oil spill (DWH) directly impacted populations of this species and thus are considered primary targets for restoration. We used a combination of seascape genomic analyses, high-resolution ocean circulation modeling, and larval dispersal simulations to quantify the degree of population structuring and connectivity among P. biscaya populations. Evidence supports the hypotheses that the genetic diversity of P. biscaya is structured by depth, and that larval dispersal among connected populations is asymmetric due to dominant ocean circulation patterns. Our results suggest that there are intermediate unsampled populations in the central GoM that serve as stepping stones for dispersal. The data suggest that the DeSoto Canyon area, and possibly the West Florida Escarpment, critically act as sources of larvae for areas impacted by the DWH oil spill in the Mississippi Canyon. This work illustrates that the management of deep-sea marine protected areas should incorporate knowledge of connectivity networks and depth-dependent processes throughout the water column.

Metapopulation dynamics of oysters: sources, sinks, and implications for conservation and restoration

AbstractMetapopulation and source–sink dynamics are increasingly considered within spatially explicit management of wildlife populations, yet the application of these concepts has generally been limited to comparisons of the performance (e.g., demographic rates or dispersal) inside vs. outside protected areas, and at spatial scales that do not encompass an entire metapopulation. In the present study, a spatially explicit, size‐structured matrix model was applied to simulate the dynamics of an Eastern oyster (Crassostrea virginica) metapopulation in the second largest estuary in the United States—the Albemarle‐Pamlico Estuarine System in North Carolina. The model integrated larval dispersal simulations with empirical measures of oyster demographic rates to simulate the dynamics of the entire oyster metapopulation consisting of 646 reefs and five reef types: (1) restored subtidal reefs closed to harvest (i.e., sanctuaries or protected areas; n = 14), (2) restored subtidal reefs open to harvest (n = 53), (3) natural subtidal reefs open to harvest (n = 301), (4) natural intertidal reefs open to harvest (n = 129), and (5) oyster reefs on manmade, hard structures such as seawalls (n = 149). Key findings included (1) an overall stable, yet slightly declining oyster metapopulation, (2) variable reef type‐specific population trajectories, largely dependent on spatiotemporal variation in larval recruitment, (3) a greater relative importance of inter‐reef larval connectivity on metapopulation dynamics than local larval retention processes, and (4) spatiotemporal variation in the source–sink status of reef subpopulations wherein subtidal sanctuaries and reefs located in the northeastern portion of the estuary were frequent sources. From a management perspective, continued protection of oyster sanctuaries is warranted. Sanctuaries represented only 6.2% of the total reef area, however, they harbored 19% (± 2%) of all oysters and produced 25% (± 6%) of all larvae settling within the metapopulation. Additional management priorities should focus on restoration or conservation of subpopulations that serve as frequent source subpopulations (including those with poor demographic rates, but high connectivity potential), and management of harvest from sink subpopulations. The application of a source–sink framework and similar integrated modeling approach could inform management of oysters in other systems, as well as other species that exhibit similar metapopulation characteristics.

Potential impact of climate change on northern shrimp habitats and connectivity on the Newfoundland and Labrador continental shelves

AbstractThe effect of climate change on ocean circulation and environmental conditions will likely impact important fisheries species which have a limited habitat range and a prolonged larval dispersal phase. Based on projections from a regional scale ice‐ocean model (RCP 8.5 scenario), we investigated the spatial distribution variability of the bentho‐pelagic northern shrimp (Pandalus borealis) preferred depth and thermal habitat and larval settlement patterns in the Newfoundland and Labrador waters for the next 70 years. Our projections of ocean temperature revealed the persistence of major shelf‐scale temperature features, but a gradual increase of bottom water temperatures by more than 4°C by 2090. Such warming led to an expansion of the potentially suitable habitat for northern shrimp from 2010 to 2050 prior to a decline and shift towards more coastal and southern areas from 2060 to 2090. The modification of the northern shrimp suitable habitat distribution, associated with changes in the ocean circulation features, affected the settlement patterns from larval dispersal simulations and the temperatures encountered by larvae. During the projection period, historically important areas were mostly negatively impacted in terms of suitable habitat and settlement potential, whereas areas that had been less important in the past (e.g., the north and the shallow area to the south) were projected to receive more settlers in comparison with the historical period. Our study demonstrated the important role of shelf‐scale processes in determining larval connectivity and suggests that regional scale ocean models are needed to assess potential impacts of climate change on fisheries and ecosystems.

New insights on the population genetic structure of the great scallop (Pecten maximus) in the English Channel, coupling microsatellite data and demogenetic simulations

Abstract The great scallop (Pecten maximus) is a commercially important bivalve in Europe, particularly in the English Channel, where fisheries are managed at regional and local scales through the regulation of fishing effort. In the long term, knowledge about larval dispersal and gene flow between populations is essential to ensure proper stock management. Yet, previous population genetic studies have reported contradictory results. In this study, scallop samples collected across the main fishing grounds along the French and English coasts of the English Channel (20 samples with temporal replicates for three sites, n = 1059 individuals), and the population genetic structure was analysed using 13 microsatellite loci. Coupling empirical genetic data with demogenetic modelling based on a biophysical model simulating larval exchanges among scallop beds revealed a subtle genetic differentiation between south‐west English populations and the rest of the English Channel, which was consistent with larval dispersal simulations. The present study provides a step forward in the understanding of great scallop population biology in the English Channel, underlining the fact that even in a context of potentially high gene flow and recent divergence times since the end of the last glacial maximum, weak but significant spatial genetic structure can be identified at a regional scale.

Modeled buoyancy of eggs and larvae of the deep-sea shrimp Aristeus antennatus (Crustacea: Decapoda) in the northwestern Mediterranean Sea.

Information on the buoyancy of eggs and larvae from deep-sea species is rare but necessary for explaining the position of non-swimming larvae in the water column. Due to embryonic morphology and ecology diversities, egg buoyancy has important variations within one species and among other ones. Nevertheless, it has hardly been explored if this buoyancy variability can be a strategy for deep-sea larvae to optimize their transport beyond their spawning areas. In the northwestern Mediterranean Sea, protozoea and mysis larvae of the commercial deep-sea shrimp Aristeus antennatus were recently found in upper layers, but to present, earlier stages like eggs and nauplii have not been collected. Using a Lagrangian transport model and larval characteristics, we evaluate the buoyancy and hydrodynamic effects on the transport of A. antennatus' larvae in the northwestern Mediterranean Sea. The transport models suggested that 75% of buoyant eggs released between 500 and 800 m depth (i.e., known spawning area), reached the upper water layers (0-75 m depth). Then, according to the modeled larval drifts, three spawning regions were defined in the studied area: 1) the northern part, along a continental margin crossed by large submarine canyons; 2) the central part, with two circular circulation structures (i.e., eddies); and 3) the southern part, with currents flowing through a channel. The number of larvae in the most upper layer (0-5 m depth) was higher if the larval transport model accounted for the ascent of eggs and nauplii (81%) instead of eggs reaching the surface before hatching (50%). The larvae reaching the most water upper layer (0-5 m depth) had higher rates of dispersal than the ones transported below the surface layer (deeper than 5 m depth). The results of larval dispersal simulations have implications for the understanding of A. antennatus larval ecology and for management decisions related to the shrimp fisheries in the northwestern Mediterranean Sea.

Weak genetic structure despite strong genomic signal in lesser sandeel in the North Sea.

Sandeels are an ecologically important group of fishes; they are a key part of the food chain serving as food for marine mammals, seabirds and fish. Sandeels are further targeted by a large industrial fishery, which has led to concern about ecosystem effects. In the North Sea, the lesser sandeel Ammodytes marinus is by far the most prevalent species of sandeel in the fishery. Management of sandeel in the North Sea plus the Kattegat is currently divided into seven geographical areas, based on subtle differences in demography, population dynamics and results from simulations of larval dispersal. However, little is known about the underlying genetic population structure. In this study, we used 2,522 SNPs derived from restriction site‐associated DNA sequencing (RADseq) typed in 429 fish representing four main sandeel management areas. Our main results showed (a) a lack of a clear spatially defined genetic structure across the majority of genetic markers and (b) the existence of a group of at least 13 SNPs under strong linkage disequilibrium which together separate North Sea sandeel into three haplotype clusters, suggestive of one or more structural variants in the genome. Analyses of the spatial distribution of these putative structural variants suggest at least partial reproductive isolation of sandeel in the western management area along the Scottish coast, supporting a separate management. Our results highlight the importance of the application of a large number of markers to be able to detect weak patterns of differentiation. This study contributes to increasing the genetic knowledge of this important exploited species, and results can be used to improve our understanding of population dynamics and stock structure.

Limited fine-scale larval dispersal of the threatened brooding corals Heliopora spp. as evidenced by population genetics and numerical simulation

Coral reefs are declining worldwide due to regional and global anthropogenic stress. Sekisei Lagoon and areas in its vicinity are impacted by the same stresses. Sekisei Lagoon is the largest coral reef area in Japan covering an area of almost 15 km × 20 km. Being situated upstream of Kuroshio Current, coral reefs in this area could supply larvae to downstream such as the Ryukyu Archipelago, facilitating high biodiversity. To conserve corals in such an area, estimation of larval dispersal among populations is essential because connectivity via larval dispersal is associated with the time for replenishment after disturbance. Isolated coral populations have a higher risk of local extinction. The purpose of this study is to reveal genetically isolated populations of brooding corals with short larval durations in and around Sekisei Lagoon. For this purpose, we utilized both population genetic analysis and larval dispersal simulations. Based on genotyping of 929 colonies of blue coral, Heliopora spp., collected from 22 sites around Sekisei Lagoon, genetic analysis suggested self-recruitment with connectivity in the southeastern sites and northwestern sites. Particle-tracking larval dispersal simulations also revealed similar patterns, corroborating the genetic results. These results suggest that lagoonal scale connectivity among populations of Heliopora spp. in Sekisei Lagoon is limited, as expected based on its short larval duration. Our results highlight the fact that most of the Heliopora spp. populations are genetically isolated, even inside Sekisei Lagoon, implying that the likelihood of being replenished by larval supply from surrounding populations after a disturbance is low and have a higher risk of local extinction than other coral species with high larval dispersal potential.

The relative effect of behaviour in larval dispersal in a low energy embayment

This study examined the relative importance of tidal phase, larval behaviour, release site, depth layer, and vertical swimming velocity on mean in-sea dispersal distance, retention, distance from shore, and population connectivity. Using a biophysical model, we simulated larval dispersal of marine benthic invertebrates for 6 taxonomic groups representing different combinations of swimming speed, and depth preference in St. George’s Bay, NS, Canada, a shallow bay with low energy (e.g. lack of estuarine circulation). The biophysical model was run over a period of 3months, from Jul to Sep, representing the period when larvae of the targeted species were present, and at each of 3years. Overall, release site had the strongest effect of all factors on the dispersal metrics. Although less important than release site in our system, vertical distribution and swim speed had a significant effect which would likely be more pronounced in high (i.e. with features such as estuarine circulation or internal waves) than low energy environments. Retention and distance from shore were more responsive to our manipulations than dispersal distance, both in terms of the number of ecologically significant effects and the magnitudes of their effect size. These findings allow for the prioritization of biophysical model parameters and improved simulations of larval dispersal.

Connectivity and Dispersal Patterns of Protected Biogenic Reefs: Implications for the Conservation of Modiolus modiolus (L.) in the Irish Sea.

Biogenic reefs created by Modiolus modiolus (Linnaeus, 1758) (horse mussel reefs) are marine habitats which support high levels of species biodiversity and provide valuable ecosystem services. Currently, M. modiolus reefs are listed as a threatened and/or declining species and habitat in all OSPAR regions and thus are highlighted as a conservation priority under the EU Marine Strategy Framework Directive (MSFD). Determining patterns of larval dispersal and genetic connectivity of remaining horse mussel populations can inform management efforts and is a critical component of effective marine spatial planning (MSP). Larval dispersal patterns and genetic structure were determined for several M. modiolus bed populations in the Irish Sea including those in Wales (North Pen Llŷn), Isle of Man (Point of Ayre) and Northern Ireland (Ards Peninsula and Strangford Lough). Simulations of larval dispersal suggested extant connectivity between populations within the Irish Sea. Results from the genetic analysis carried out using newly developed microsatellite DNA markers were consistent with those of the biophysical model. Results indicated moderately significant differentiation between the Northern Ireland populations and those in the Isle of Man and Wales. Simulations of larval dispersal over a 30 day pelagic larval duration (PLD) suggest that connectivity over a spatial scale of 150km is possible between some source and sink populations. However, it appears unlikely that larvae from Northern Ireland will connect directly with sites on the Llŷn or Isle of Man. It also appears unlikely that larvae from the Llŷn connect directly to any of the other sites. Taken together the data establishes a baseline for underpinning management and conservation of these important and threatened marine habitats in the southern part of the known range.

How much do marine connectivity fluctuations matter?

There is growing awareness that fluctuations in larval flux (connectivity) depress the long-run growth of marine metapopulations, but by how much is unclear. Here, we explore how reproductive schedule and larval behavior affect how much connectivity fluctuations depress growth. We combine larval dispersal simulations from the Florida Keys with theoretical results to calculate the effect of fluctuations on bicolor damselfish (Stegastes partitus). We find that fluctuations depress growth only slightly (∼2%), but the effect would be much stronger for an organism that spawned only part of the year. Larval behavior can also matter, as vertical migration allows larvae to become entrained in eddies. Eddies synchronize connectivity fluctuations, further decreasing growth. However, here, they also divide the Keys into largely independently fluctuating regions, mitigating the effects of local synchrony. Therefore, in situations where connectivity fluctuations matter, the presence of independently fluctuating regions due to larval behavior may be important.

Using larval dispersal simulations for marine protected area design: Application to the Gulf of Lions (northwest Mediterranean)

The design (location and size) of sustaining, no‐take reserves was investigated by combining realistic numerical simulations of larval dispersal from a sedentary marine species with a population dynamics model. The method explored, a priori: (1) the planktonic larval duration (PLD) of self‐persistent populations within no‐take reserves with radii from 1 to 20 km, (2) the size of a no‐take reserve reaching self‐persistent recruitment of the reserve population, and (3) offspring spillover to adjacent fisheries for PLDs from 1 to 6 weeks. In the Gulf of Lions (northwest Mediterranean), as the radius of a no‐take reserve increased to 20 km, the median PLD of a self‐persistent species within the reserve increased from 2 to 6.5 d. No unique relation between PLD and sustaining no‐take reserve size could be established because of large spatial and temporal variabilities, thus precluding any general guidelines for marine protected area sizes. For species with mass spawning lasting < 3 d, variability due to spawning timing yielded twice the spatial variability, reflecting strong wind variability. In contrast, when spawning lasted more than 10 d, the spawning location became more important. Thus, a biological process (spawning duration) can trigger deterministic and stochastic effects of environmental variability. Finally, some unprotected areas (Narbonne to Agde and the Camargue) clearly appeared to be better locations than the existing no‐take reserves for maximizing biodiversity persistence within a reasonable no‐take reserve size (10 to 20 km) and for producing offspring spillover important for regional fisheries (80%).

Behavior constrains the dispersal of long-lived spiny lobster larvae

Behavior such as ontogenetic vertical migration (OVM) limits the transport of marine larvae with short pelagic larval durations (PLDs), but its effect on the supposed long-distance disper- sal of larvae with long PLDs is unknown. We conducted laboratory tests of ontogenetic change in lar- val phototaxis and examined size-specific patterns of larval distribution in the plankton to character- ize OVM in the Caribbean spiny lobster Panulirus argus during its long (6 mo) PLD. We then used a coupled biophysical model to explore the consequences of OVM and hydrodynamics on larval P. argus dispersal in the Caribbean Sea. Larvae reared in the laboratory were positively phototatic for the first 2 mo and then avoided light thereafter, similar that seen in the planktonic distribution of same-sized larvae. Simulations of larval dispersal from 13 spawning sites in the Caribbean Sea pre- dicted that twice as many larvae would recruit to nurseries if they displayed OVM compared with passive dispersers. Larvae with OVM typically settled 1000 km away. OVM also produced an asymmetrical bimodal pattern of dispersal dominated by larvae that settled near their origin (~60%), but showed a second peak of larvae that dispersed over long distances (~20%). Hydrodynamics created subregional differ- ences in the potential for self-recruitment. Our findings suggest that (1) larval behavior constrains the dispersal of even long-lived larvae, particularly in tandem with retentive oceanographic environ- ments, and (2) larval sources of P. argus in the Caribbean Sea cannot be estimated from passive trans- port and surface circulation.

Genetic Analyses and Simulations of Larval Dispersal Reveal Distinct Populations and Directional Connectivity across the Range of the Hawaiian Grouper (Epinephelus quernus)

Integration of ecological and genetic data to study patterns of biological connectivity can aid in ecosystem-based management. Here we investigated connectivity of the Hawaiian grouperEpinephelus quernus, a species of management concern within the Main Hawaiian Islands (MHI), by comparing genetic analyses with simulated larval dispersal patterns across the species range in the Hawaiian Archipelago and Johnston Atoll. Larval simulations revealed higher dispersal from the MHI to the Northwestern Hawaiian Islands (NWHI) than in the opposite direction and evidence for a dispersal corridor between Johnston and the middle of the Hawaiian Archipelago. Genetic analyses using mitochondrial DNA (mtDNA) control region sequences and microsatellites revealed relatively high connectivity across the Hawaiian Archipelago, with the exception of genetically distinct populations and higher mtDNA diversity in the mid-Archipelago. These analyses support the preservation of the mid-archipelago as a source of genetic diversity and a region of connectivity with locations outside the Hawaiian Archipelago. Additionally, our evidence for directional dispersal away from the MHI lends caution to any management decisions that would rely on the NWHI replenishing depleted MHI stocks.

Simulating larval dispersal processes for abalone using a coupled particle-tracking and hydrodynamic model: implications for refugium design

A coupled particle-tracking and hydrodynamic model, into which observed current data were assimilated, was used to simulate larval dispersal of large abalone (Haliotis discus discus, H. gigan- tea, and H. madaka) in Sagami Bay, Japan. The aims of this study were to (1) clarify larval dispersal pro- cesses and settlement sites, and (2) evaluate the existing harvest refugium and estimate the suitability of other areas for larval sources, using this model. In the larval dispersal simulations, particles were re- leased at the time of hatching, which was calculated from the estimated time of fertilization/potential spawning and based upon the water temperature. The results of larval dispersal simulations indicate 2 different dispersal patterns: (1) transport toward the coast after dispersal offshore, and (2) gradual dis- persal offshore. The refugium was compared with 3 hypothetical reproductive sources located 1 km north, west, and south of the refugium. During settlement competency, transport success (transport to the area at the depth of adult habitat: ≤ 30 m) of particles released at the refugium was highest (27 to 75%), and suggested that the location of this refugium was more suitable for a larval source than those of the hypothetical reproductive sources. Multiple potential larval settlement sites were identified. These results have important implications for refugium design at the study site. The method and model devel- oped in the present study could be used for evaluating harvest refugia and for identifying effective lo- cations for reproductive sources and potential settlement sites.

Effects of small‐scale features and local wind forcing on tracer dispersion and estimates of population connectivity in a regional scale circulation model

A small‐scale model of the Southern California–Northern Baja California coastline has been developed to explore dispersion over the continental shelf, with specific attention to physical parameters pertinent to simulations of larval dispersal and population connectivity. The ROMS simulation employs a nested grid system, with an inner domain resolution of 600 m and an outer domain resolution of 1.5 km. Realistic bathymetry and forcing were employed to investigate the effects of passive transport of tracers introduced at locations with known communities of mytilid mussels along the coastline. The effects of topographic resolution, boundary conditions, and choice of meteorological forcing products on dispersion rates, tracer trajectories, and the subsequent measures of population connectivity were examined. In particular, the choice of wind forcing product resulted in different circulation patterns and tracer trajectories and had especially important consequences on measures of larval connectivity such as self‐seeding, potential for larval settlement (import), and contribution to the pool of available larvae (export). While some forcing products performed better when model data were compared to field measurements, no product was clearly superior. The uncertainty in results, which may appear minor in larger‐scale temperature or surface velocity fields, is significant when examining a sensitive passive tracer. This modeling uncertainty needs to be addressed when interpreting connectivity results.

Dispersal of barnacle larvae along the central California coast: A modeling study

To investigate the biological and physical mechanisms affecting larval dispersal, we embedded a model of Balanus glandula larval development and behavior into physical circulation fields of waters along the central California coast. Physical circulation fields were generated by a three‐dimensional ocean circulation model with a horizontal resolution of 1.5 km and 20 topography‐following layers in the vertical. The ocean circulation model was forced by air—sea fluxes derived from a mesoscale atmospheric model and assimilated temperature and salinity data from the Autonomous Ocean Sampling Network II experiment. An ecosystem model that calculated chlorophyll a (a proxy for larval food concentration) was also coupled to the ocean circulation model. The coupled model of larval development, larval behavior, food concentration, and physical circulation was used to run simulations of larval dispersal. Simulation results predicted a greater return of larvae to the nearshore waters with relaxation circulation patterns than with upwelling. More larvae were supplied to the coast north of Monterey Bay than to the south, and larvae that successfully returned to the nearshore waters generally had limited dispersal distances. These modeling results agree with previous observations of B. glandula population dynamics in central California.

Larval dispersal simulations: correlation with the crown-of-thorns starfish outbreaks database

The work reported in this paper is a further development of results from a research programme whose principal objective is to achieve an understanding of the large-scale population dynamics of Acanthaster planci. The research is based on the development and use of numerical models of hydrodynamics and resulting larval dispersal throughout a large portion of the Great Barrier Reef. It is chiefly concerned with the large-scale statistical patterns of larval dispersal, the central hypothesis being that passive hydrodynamic dispersal plays an important role in the recruitment process. The present aim is to examine more closely than has been done before the consistencies between the modelling results and the database of recorded observations of crown-of-thorns starfish outbreaks. Reefs in the Cairns and Central Sections of the Great Barrier Reef Marine Park that were recorded as carrying active outbreaks during the period 1979-89 were used as sources in a programme of intensive simulations of Acanthaster larval dispersal under forcing by the wind, tidal action and the East Australian Current. The resulting broad-scale patterns of larval dispersal were found to be in strong qualitative agreement with the observed spatial and temporal distribution of adult Acanthaster populations. Statistical analysis of the results revealed a strong positive correlation between potential recruitment on surveyed reefs, as estimated by the dispersal simulations, and the observed presence of outbreak populations on those reefs. The correlation was particularly strong when different cross-shelf zones were considered separately.