Abstract
Larval dispersal data are increasingly sought after in ecology and marine conservation, the latter often requiring information under time limited circumstances. Basic estimates of dispersal (based on average current speeds and planktonic larval duration (PLD)) are often used in these situations, usually acknowledging their oversimplified nature, but rarely with an understanding of how oversimplified those assumptions are. Larval dispersal models (LDMs) are becoming more accessible and may produce “better” dispersal predictions than estimates, but the uncertainty introduced by choosing one underlying hydrodynamic model over another is rarely discussed. This case study uses theoretical and simplified deep-sea LDMs to compare the passive predictions of dispersal as driven by two different hydrodynamic models (HYCOM and POLCOMS) and a range of informed basic estimates (based on average current speeds of 0.05, 0.1, and 0.2 m/s). The aim is to provide generalisable insight into the predictive variability introduced by a) choosing a model over an estimate, and b) one hydrodynamic over another. LDMs were found to be up to an order of magnitude more conservative in dispersal distance predictions than even the slowest tested estimate (0.05 m/s). The difference increased with PLD which may result in a bigger disparity for deep-sea species predictions. Although the LDMs were more spatially targeted than the estimates, the two LDM predictions were also significantly different from each other. This means that choosing one hydrodynamic model over another could result in contrasting ecological interpretations or advice for marine conservation. These results show a greater potential for hydrodynamic model variability than previously appreciated by larval dispersal ecologists and strongly advocates groundtruthing predictions before use in management. Advice is offered for improved model selection and interpretation of predictions.
Highlights
Larval dispersal is an important ecological process
An effective self-sustaining network needs each Marine Protected Areas (MPAs) to Comparing Deep-Sea Larval Dispersal Models supply larvae to both itself and another for protected populations to persist (Roberts et al, 2003) – something that will only be achieved by chance without dispersal data to base informed decisions upon
The most basic way to fulfill this need is to estimate larval dispersal using a distance /speed /time calculation based on average current speeds and planktonic larval durations (PLDs)
Summary
Larval dispersal is an important ecological process. Many benthic animals rely upon this phase as their only means to colonize a new area, making the process pivotal in individual survival as well as in population dynamics and persistence.Existing global efforts to establish networks of Marine Protected Areas (MPAs) are hampered without knowledge of larval dispersal. An effective self-sustaining network needs each MPA to Comparing Deep-Sea Larval Dispersal Models supply larvae to both itself and another for protected populations to persist (Roberts et al, 2003) – something that will only be achieved by chance without dispersal data to base informed decisions upon. The most basic way to fulfill this need is to estimate larval dispersal using a distance /speed /time calculation based on average current speeds and planktonic larval durations (PLDs). This technique, hereafter termed “an estimate,” while highly simplistic, takes very little time, money, effort, or expertise to produce. It is hard to quantify just how oversimplified these estimates may be
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