DOI: 10.5061/dryad.fh505
title: Data from: Bay-scale patterns in the distribution, aggregation and spatial variability of larvae of benthic invertebrates

description: This study aimed to investigate mechanisms of pattern formation in the
 larval distributions of benthic invertebrates by relating the spatial and
 temporal variability in the larval distributions to that in physical and
 biological variables, such as temperature, salinity, fluorescence and
 current velocity. Larvae were sampled at 11 sites on 7-8, and 11-12 Aug
 2008 and at 16 sites on Aug 2-4, 2009, with a 200-μm plankton ring net
 (0.75-m diameter) towed for 5 min at 3 m and 12 m depth (in and below the
 mixed layer, respectively) in St. George’s Bay, Nova Scotia, Canada. In
 2009, density, temperature, salinity, and fluorescence were measured with
 a CTD cast at each station, and currents were quantified with an ADCP
 moored at 5 locations throughout the bay. In 2008, we only measured
 temperature. 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 findings suggest that taxonomic
 groups that have functionally (i.e. swimming ability) similar larvae (e.g.
 bivalves and gastropods) also show similar dispersion properties
 (distribution and spatial variability), while the opposite is true for
 groups with functionally dissimilar larvae (e.g. bivalves and decapods).
 We also found that larval distributions of all taxa were significantly
 aggregated, although the degree of aggregation varied among taxa. Using an
 aggregation-diffusion model, we demonstrated that horizontal swimming was
 not an effective means of forming aggregations even at modest levels of
 diffusion. We hypothesize that patterns in observed horizontal
 distribution at this scale (&lt; 40 km) are determined during the
 larval phase, and that the primary mechanism for pattern formation is
 larval interaction with physical oceanographic structures (e.g.
 stratification and tidal currents).
description: Spatial distribution of
 Meroplanktonic larvae. A Canadian Healthy Oceans Network Population
 Connectivity project, PC-06Larval abundance (count
 m-3) was sampled at 11 sites on 7-8, and 11-12 Aug 2008 and at 16 sites on
 Aug 2-4, 2009 (Table 1), with a 200-μm plankton ring net (0.75-m diameter)
 towed for 5 min at each of 3 m and 12 m depth. These depths were designed
 to sample: 1) the surface mixed layer and 2) within the pycnocline, at or
 near the fluorescence maximum. The net was towed at ~1.7 m s-1 and the
 volume of filtered water was quantified using a General Oceanics flow
 meter. Using a net of this mesh size may under-estimate abundance of small
 larvae (&lt; 200 μm). However, it is a necessary compromise in this
 multi-species study to allow capture of a wide range of larval types at
 sufficient numbers (e.g. very abundant but small gastropods to larger but
 rare decapods). All plankton samples were preserved in 95% ethanol and
 larvae were identified and enumerated under a Nikon SMZ 1500, as described
 in Lloyd et al. (2012). Samples were split into subsamples using a Folsom
 plankton splitter. For n = 8, samples were split to 1/64 of the original
 volume and all subsamples were processed. Based on those samples, we
 determined that at least 20 individuals of each species were required to
 obtain an estimate of abundance that was within 5% of the true sample
 abundance. The remainder of the samples were split to between 1/128 and 1
 to ensure that ≥20 individuals of the most abundant species (Margarites
 spp., Astyris lunata, Mytilus spp., Electra pilosa. and Cancer irroratus)
 were enumerated. In addition to these 5 species that met the above
 criteria, we used some less abundant species in some data analyses (see
 below); however, the validity of the results should not be affected
 because there was no bias in the estimated abundances and there is often
 spatial and/or temporal replication.larval
 abundance.csvVemco temperature-depth
 recorder data. A Canadian Healthy Oceans Network Population Connectivity
 project, PC-06No CTD data are
 available for 2008 because of instrument failure. However, a Vemco Minilog
 Temperature-Depth Recorder (TDR) was attached to the net during plankton
 tows on 7-8 Aug 2008 providing some data, and TDR casts to 30 m depth were
 completed on 11-12 Aug 2008.VEMCO_TDR.csvTemperature, Salinity, Density and relative fluorescence. A Canadian Healthy Oceans Network Population Connectivity project, PC-06In 2009, temperature, conductivity, pressure and fluorescence were measured with a conductivity-temperature-density (CTD) profiler immediately before (A) and after (B) larval sampling at each station.CTD.csv