Abstract
This study quantified the fine- scale (0.5 km) of variability in the horizontal distributions of benthic invertebrate larvae and related this variability to that in physical and biological variables, such as density, temperature, salinity, fluorescence and current velocity. Larvae were sampled in contiguous 500-m transects along two perpendicular 10-km transects with a 200-µm plankton ring net (0.75-m diameter) in St. George’s Bay, Nova Scotia, Canada, in Aug 2009. Temperature, conductivity, pressure and fluorescence were measured with a CTD cast at each station, and currents were measured with an Acoustic Doppler Current Profiler moored at the intersection of the 2 transects. Gastropod, bivalve and, to a lesser extent, bryozoan larvae had very similar spatial distributions, but the distribution of decapod larvae had a different pattern. These findings suggest that taxonomic groups with functionally similar larvae have similar dispersive properties such as distribution and spatial variability, while the opposite is true for groups with functionally dissimilar larvae. The spatial variability in larval distributions was anisotropic and matched the temporal/spatial variability in the current velocity. We postulate that in a system with no strong oceanographic features, the scale of spatially coherent physical forcing (e.g. tidal periodicity) can regulate the formation or maintenance of larval patches; however, swimming ability may modulate it.
Highlights
The dynamics and persistence of populations of marine benthic invertebrates are affected by connectivity, which is in turn regulated by dispersal during the planktonic larval phase [1,2]
At bay-wide scales, gastropod, bivalve and, to a lesser extent, bryozoan larvae had very similar spatial distributions, but the distribution of decapod larvae followed a different pattern. These results suggested that taxonomic groups that have functionally similar larvae show similar dispersion properties, while the opposite is true for groups with functionally dissimilar larvae
Larval distributions Collected larvae were categorized as bryozoans, bivalves, gastropods or decapods (Tab. 1)
Summary
The dynamics and persistence of populations of marine benthic invertebrates are affected by connectivity, which is in turn regulated by dispersal during the planktonic larval phase [1,2]. Spatial and temporal variability in larval supply and settlement influences the patterns of recruitment of new individuals to adult populations [3,4]. Variability in larval abundance can result from the variation in water properties at regional scales [7] to small scale features of the water column that may aggregate and transport invertebrate larvae, such as up- or downwelling [8,9], internal tidal bores [10], or frontal systems and Langmuir cells [11]. Many different physical processes can influence the spatial or temporal pattern of larval dispersal and connectivity. Patchiness or spatial heterogeneity generated by variability in larval abundance, affects the perceived patterns in the distribution of planktonic larvae, and may contribute to the detection of erroneous patterns through spatial aliasing or masking of the true pattern by high sampling variability [11]
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