Larval Dispersal Models Research Articles

Maximum sustainable swimming speeds of late-stage larvae of nine species of reef fishes

We examined the maximum sustainable swimming speed of late-stage larvae of nine species of tropical reef fishes from around Lizard Island, Great Barrier Reef, Australia. Larvae were captured in light traps and were swum in flumes at different experimental swimming speeds (of 5 cm s −1 intervals) continuously for 24 h. Logistic regression was used to determine the speed at which 90% of larvae were able to maintain swimming, and this was used to indicate the maximum sustainable swimming speed for each species. Maximum sustainable swimming speeds varied among the species examined, with the lethrinid maintaining the fastest sustainable swimming speed (24 cm s −1), followed by the Pomacentridae (10–20 cm s −1) and the Apogonidae (8–12 cm s −1). U-crit (maximum speed) explained 64% of the variation in sustainable speed among species, whereas total length only explained 33% of the variation in sustained swimming. A regression fitted across species suggests that 50% U-crit is a good approximation of the speed able to be maintained by these larvae for 24 h. A model based on a cubic relationship between sustained swimming time and speed was found to be more successful than either length or U-crit as a method of estimating sustainable swimming speed for most of the species examined. Overall, we found that swimming speed is an important factor when considering the potential for active swimming behaviour to influence dispersal patterns, recruitment success and levels of self-recruitment in reef fish larvae and needs to be carefully considered in models of larval dispersal.

Does behaviour explain the larval dispersal of coral reef fishes better than oceanography?– An individual based model simulation approach

Until recently, oceanographic models have been used, with limited success, to predict the larval dispersal of coral reef fishes. Settlement‐stage larvae have been shown to be capable swimmers and have highly developed sensory organs. We built two simulation individual based models (IBMs) of larval dispersal in the Dampier Archipelago, Western Australia. One followed an oceanographic model, while the other was driven by behavioural constraints. We compare predictions of these models with an extensive dataset from a light‐trapping programme in an attempt to elucidate the overriding mechanism of larval coral reef fish dispersal.

Hydrodynamic modelling of snapper Pagrus auratus egg and larval dispersal in Shark Bay, Western Australia: reproductive isolation at a fine spatial scale

Ichthyoplankton data collected between 1997 and 2000 were combined with the results of numerical modelling to investigate the dispersal of snapper Pagrus auratus eggs and larvae in Shark Bay, Western Australia. A 3-dimensional hydrodynamic model was coupled with a 2-dimensional Lagrangian particle-tracking program to simulate passive transport of these plank- tonic particles. Modelling analysed the separate and combined effects of the region's principal hydrodynamic forces of tide, wind and the Leeuwin Current. Model runs simulated a 30 d period to recreate residual transport on time scales encompassing early snapper development prior to settlement. Hydrodynamic conditions during winter were tidally dominated and exhibited minimal residual flows. Eggs and larvae were retained within residual eddies that were coincident with the 4 main spawning areas. No connectivity between these areas was observed. The results provided further evidence of the existence of a number of proximate but geographically discrete spawning populations of snapper in Shark Bay waters. Hydrodynamic retention provides a mechanism that partly explains existing data indicating that snapper stock-structure in the region is complex. Such information is fundamental to determining the most appropriate geographic scale at which local snapper populations should be managed.

Genetic analysis of sexual reproduction in the dendrophylliid coral Balanophyllia elegans

The ahermatypic scleractinian Balanophyllia elegans has served as a model of limited larval dispersal in an aclonal species. However, other species from the same family (Dendrophylliidae) produce larvae asexually, and closely connected polyps of B. elegans, potentially the result of asexual reproduction, are commonly observed in the field. Here, we use a combination of laboratory experiments, controlled crosses, and genetic surveys of field-collected individuals to demonstrate (1) marker allozymes are inherited in accordance with Mendel's laws, (2) polyps that are connected in the field are not genetically identical, and (3) laboratory manipulation of a single polyp can produce a second polyp on the aboral side of the original, but not adjacent to the original. In combination, these results suggest that the larvae of B. elegans result from mictic sexual reproduction, and that connected polyps result not from asexual budding but rather from the fusion of genetically distinct individuals.

A review of the population biology and host-parasite interactions of the sea louse Lepeophtheirus salmonis (Copepoda: Caligidae).

Lepeophtheirus salmonis is a specific parasite of salmonids that occurs in the Atlantic and Pacific Oceans. When infestations are heavy fish mortality can occur although the factors that are responsible for causing epizootics, especially in wild salmonid populations are still largely unknown. Over the past 20 years this parasite has caused significant economic losses in farmed salmon production and possibly in wild salmonid populations locally. Understanding the connectivity between populations is crucial to an understanding of the epidemiology of infections and for management of infections in aquaculture. Data from genetics, pesticide resistance, larval dispersal models and spatial and temporal patterns of infestation in wild and farmed hosts suggests a spatially highly structured metapopulation the components of which have different levels of connectivity, probabilities of extinction and influence on the development of local infestations. The population structure is defined mainly by the dispersal dynamics of the planktonic stages and the behaviour of the host. Until recently virtually nothing was known about the relationship between the parasite and the host, or how the host may influence lice at local or population level. Typically, impacts on the host have usually been reported in terms of pathological lesions caused by attachment and feeding of the adult stages, as well as localised mild epithelial responses to juvenile attachment. However many studies report pathology associated with severe infestation. Recent new studies on the host-parasite interactions of L. salmonis have shown that this parasite induces stress-related responses systemically in the host skin and gills and that the stress response and immune systems are modulated. In the second part of this review, these new studies are presented, together with results from other host-parasite model systems where data for caligid sea lice are missing. One of the most revealing methods reported recently is the application of a net confinement stressor to examine modulation of the stress response and immune system of the host fish. This approach has shown that although until now, infective stages of L. salmonis were not thought to affect the host, they do induce systematic effects in the host that result in a stress response and modulated immune system. Host-parasite interactions affecting these stress responses and the immune system may be key factors in facilitating epizootics by reducing the host's ability to reject the parasites, as well as reducing disease resistance under some environmental conditions. The host-parasite interaction therefore needs to be incorporated into any model of population structure and dynamics.

ARTIGO RETRATADO] Diffusion Model Applied to Postfeeding Larval Dispersal in Blowflies (Diptera: Calliphoridae)

This paper presents a diffusion model of larval dispersal specifically designed to account for particular aspects of postfeeding larval dispersal from the food source in organisms such as blowflies. In these organisms the dispersal of immatures includes two groups of individuals, those that are actively migrating and those that have initiated the pupation process. The classical diffusion equation in one dimension was modified to incorporate a function which describes the burying of larvae to become pupae. The analytical solution of this equation predicts oscillatory and monotonic dispersal behaviors, which are observed in experimental populations of blowfly species.

Theoretical approaches to forensic entomology: I. Mathematical model of postfeeding larval dispersal

Abstract: An overall theoretical approach to model phenomena of interest for forensic entomology is advanced. Efforts are concentrated in identifying biological attributes at the individual, population and community of the arthropod fauna associated with decomposing human corpses and then incorporating these attributes into mathematical models. In particular in this paper a diffusion model of dispersal of postfeeding larvae is described for blowflies, which are the most common insects associated with corpses.

Comparative persistence of marine fish larvae from pelagic versus demersal eggs off southwestern Nova Scotia, Canada

Two groupings of larval fish were repeatedly identified by principal component analyses of larval densities from four broad-scale surveys during the spring and summer of 1985–1987 off southwestern Nova Scotia, Canada. Larvae originating from pelagic eggs (four species within Gadidae and Pleuronectidae) constituted one group, which were uniformly distributed over the sampling area with densities not correlated with bathymetry, although nearly all spawning occurs on the shallow western cap of Browns Bank, 100 km offshore. Larvae from demersal eggs (five species within Pholidae, Stichaeidae, Cottidae, Agonidae) constituted the second group, which dominated the shallow-water environments both inshore and on Browns Bank. Lower patchiness indices were evident amongst larvae from pelagic eggs in small and large sampling-gear collections (average 3.4 and 3.1, respectively) compared to fish hatching from demersal eggs (average 5.1 and 4.6). Fine-scale nearshore surveys over a 5 wk period in 1987 also showed that larvae of demersal eggs had a less variable distribution along an inshoreoffshore transect. Larvae from demersal eggs appear spatially persistent through the release of well-developed larvae from non-drifting eggs. These conclusions are consistent with other studies over a range of spatial scales in temperate and tropical environments, demonstrating that single-species models of larval dispersal are inadequate to account for the distributional patterns of larval fish in general.

The Consequences of Short‐Distance Larval Dispersal in a Sessile Marine Invertebrate

The colonial ascidian—algal symbiosis Didemnum molle Herdman occurs in large numbers (densities of >100 colonies/m2) on shallow patch reefs in the lagoon at Lizard Island, Australia. Shallow—water currents in the lagoon are driven unidirectionally by the southeast trade winds most of the year. The patch reefs are several hundred metres apart and are separated by sand flats. The largest populations of D. molle occur on the upstream ends of the patch reefs. D. molle larvae, followed underwater, dispersed invariably downstream in the direction of the water current at °1—2 m/min. Although larvae were capable of swimming for up to 2 h, they generally settled in 10—15 min when given a suitable substratum such as a dark surface. Larvae experimentally denied a suitable substratum for 40 min settled rapidly when provided with a dark surface, suggesting that when larvae encounter a reef after drifting over sand flats, they probably settle immediately. A qualitative model of larval dispersal was developed to predict the settlement pattern of D. molle in the lagoon at Lizard Island. Three predictions of the model were tested by measuring larval recruitment upstream and downstream of an experimental patch reef for 1 wk before, then 1 wk after denuding the reef of all reproductive D. molle colonies. The results agree with the model, indicating that larval recruitment of D. molle in the lizard Island lagoon is a highly predictable process. The settlement pattern that results from the dispersal model describes the upstream distribution of adult D. molle colonies on patch reefs in the Lizard Island lagoon.

Larval Mortality from Offshore Mixing as a Link between Precompetent and Competent Periods of Development

A model of larval dispersal of coastal benthic invertebrates is proposed: Eddy mixing spreads larvae in the onshore-offshore direction during the period before competence to settle and continues to take larvae both onshore and offshore after they are competent to settle; predators kill larvae during both precompetent and competent periods. Distribution of larval stages of several species are consistent with the model. The model correctly predicts (1) increased competent period with increased precompetent period in comparisons among species, and (2) a competent period greater than or equal to the precompetent period. The model predicts a decrease in the ratio of competent to precompetent period as precompetent period increases, which is not apparent in available data. Also, some observed competent periods are longer than those predicted by the model. Reasons for these departures from predictions are suggested. The model differs from previous optimization or maximization models for planktonic larvae by including onshore-offshore mixing and thereby linking selection on the precompetent and competent periods.