Observational constraints on the physical nature of submillimetre source multiplicity : chance projections are common

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Interferometric observations have demonstrated that a significant fraction of single-dish submillimetre (submm) sources are blends of multiple submm galaxies (SMGs), but the nature of this multiplicity, i.e. whether the galaxies are physically associated or chance projections, has not been determined.We performed spectroscopy of 11 SMGs in six multicomponent submm sources, obtaining spectroscopic redshifts for nine of them. For an additional two component SMGs, we detected continuum emission but no obvious features.We supplement our observed sources with four single-dish submm sources from the literature. This sample allows us to statistically constrain the physical nature of single-dish submm source multiplicity for the first time. In three (3/7, or 43 -33 +39 per cent at 95 per cent confidence) of the single-dish sources for which the nature of the blending is unambiguous, the components for which spectroscopic redshifts are available are physically associated, whereas 4/7 (57 -39 +33 per cent) have at least one unassociated component. When components whose spectra exhibit continuum but no features and for which the photometric redshift is significantly different from the spectroscopic redshift of the other component are also considered, 6/9 (67 -37 +26 per cent) of the single-dish sources are comprised of at least one unassociated component SMG. The nature of the multiplicity of one single-dish source is ambiguous. We conclude that physically associated systems and chance projections both contribute to the multicomponent single-dish submm source population. This result contradicts the conventional wisdom that bright submm sources are solely a result of merger-induced starbursts, as blending of unassociated galaxies is also important.Peer reviewe

Acid (H₂S0₄) production, persistence, and functional importance of the annual, brown seaweed Desmarestia viridis in Newfoundland, Canada

Current models of shallow rocky community organization and stability in the northwestern Atlantic (NWA) emphasize kelps and their vulnerability to grazers and other mortality agents. This paradigm may overshadow the possible contribution of other groups of less studied seaweeds with overlapping distribution to ecosystem resilience. The annual, brown seaweed Desmarestia viridis is one of only a few species of fleshy seaweeds commonly found in urchin barrens in the NW A. The exceptional ability of D. viridis sporophytes to produce and store sulfuric acid (H₂S0₄) in intracellular vacuoles makes the species a compelling model for studies of controls and importance of acid production in seaweeds at the individual, population, and community levels. This research used laboratory experiments and surveys of individuals and populations throughout an entire growth season (February to October 2011) at two subtidal sites on the southeastern tip of Newfoundland (Canada) to determine controls of acid production in, as well as the functional importance and persistence of, D. viridis sporophytes. Results showed that light, grazing, and epibionts have no perceptible effects on intracellular acidity, whereas temperature and wave action exert strong, synergistic effects. Mortality rates and sea temperature from March to late June were relatively low, whereas the onset of increasing mortality in mid-August coincided with marked increases in sea temperature. The quick development of "Desmarestia beds" in urchin barrens created biological structure for major recruitment pulses in characteristic invertebrate and fish assemblages. These findings provide novel insights into the ecological and evolutionary causes and consequences of acid production in Desmarestiales, while elevating the importance of D. viridis as a foundation species in urchin barrens in the NWA

Monitoring data of key benthic reef species, in Cape Rodney- Okakari Point Marine Reserve and adjacent fished sites: 1999-2019

The Cape Rodney- Okakari Point Marine Reserve is New Zealand's oldest no-take marine reserve situated along the Leigh coast (est. 1978; the 'Leigh Marine Reserve' hereafter). Historic information on rocky reef communities in the Leigh Marine Reserve is available from baseline surveys in 1978 (Ayling 1978) and repeated in the 1990s (Babcock et al. 1999). While these provide valuable information on long-term changes in the reserve, they did not include fished reefs outside the reserve that provide a control for the effect of protection. The monitoring program presented here was established in 1999 and includes four sites inside and four sites outside the Leigh Marine Reserve (Shears and Babcock 2003). At these sites, the reefs are gradually sloping from the intertidal to the reef edge, occurring at ~8–15 m depth. From 1999–2000 the reefs were surveyed in four depth ranges (10 m), but subsequent sampling has focussed on the 4-6 m depth range as this is representative of the depth range where sea urchins (Evechinus chloroticus) are most abundant and can form barren habitat (Shears & Babcock 2003; Shears et al. 2008). This depth range has been sampled sporadically (every 1–3 yr at these sites since 2001; note that only fished sites were surveyed in 2003). The surveys were conducted on SCUBA, and at each site, five 1-m2 quadrats were haphazardly sampled within the 4–6 m depth range. Within each quadrat, the density (the number of individuals per metre square) of sea urchins and all large brown macroalgae were recorded (e.g. Ecklonia radiate, Carpophyllum spp., Cystophora spp. and Sargassum sinclairii). For sea urchins, behaviour was recorded as 'cryptic' (sea urchins found in holes, cracks or crevices) or 'exposed' (sea urchins are out in the open and have a strong impact on macroalgal communities; Spyksma et al. 2017). For all large macroalgae the length of all fronds was measured to the nearest 5 cm using a measuring tape. For E. radiata, measurements were taken for both stipe and total length (i.e. from the top of the holdfast to the meristem and the distal end of the lamina, respectively). The percent cover of crustose coralline algae, bare rock, turfing algae (e.g. articulated coralline, red foliose), filamentous algae and sediment was assessed visually in each quadrat. In cases where filamentous algae were recorded as overlaying turf and encrusting algae, such that total cover exceeds 100%, the cover data was standardised to add up to 100%

Non-metric multidimensional scaling (nMDS) plots of Bray-Curtis similarities of <i>Desmarestia viridis</i>, <i>Desmarestia aculeata</i>, and <i>Agarum clathratum</i> based on associated epifauna (4^th-root transformed density, individuals g⁻¹ of seaweed) from 18 February to 9 October, 2011 at Keys Point.

<p>(A) Each data point is the average of samples for a given month [n = 7 to 10, except 3 for <i>A. clathratum</i> in February, for a total n = 221]. The trajectory of change for each seaweed is shown by solid lines connecting consecutive months. Numbers next to symbols indicate sampling month: February (2), March (3), April (4), May (5), June (6), July (7), August (8), September (9), and October (10). (B, C, D) Each data point is one sample within a given month (n =  80 [<i>D. viridis</i>], 77 [<i>D. aculeata</i>], and 64 [<i>A. clathratum</i>]). Group 1 and Group 2 designate clusters of months used in ANOSIM and SIMPER analyses (see Results).</p

Summary of two-way ANOVAs (applied to raw data) examining the effect of Seaweed (<i>Desmarestia viridis</i>, <i>Desmarestia aculeata</i>, and <i>Agarum clathratum</i>) and Month (each of nine sampling months: February to October, 2011) on the density of individuals in the six numerically dominant invertebrate taxa, and gastropod (<i>Lacuna vincta</i>) and fish (unknown species) egg masses at Keys Point (see caption of Fig. 5 for species in each taxa).

<p>Summary of two-way ANOVAs (applied to raw data) examining the effect of Seaweed (<i>Desmarestia viridis</i>, <i>Desmarestia aculeata</i>, and <i>Agarum clathratum</i>) and Month (each of nine sampling months: February to October, 2011) on the density of individuals in the six numerically dominant invertebrate taxa, and gastropod (<i>Lacuna vincta</i>) and fish (unknown species) egg masses at Keys Point (see caption of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098204#pone-0098204-g005" target="_blank">Fig. 5</a> for species in each taxa).</p

Relationships between <i>Desmarestia viridis</i> cover and urchin (<i>Strongylocentrotus droebachiensis</i>) density at 2, 3, 4, and 8 m depths at Bread and Cheese Cove (BCC) and Keys Point (KP) from 8 April to 23 September, 2011.

<p>Each data point is the mean cover and corresponding mean density calculated from the 10 frames of each pair of transects for a given site, depth, and date. Solid lines are the linear regression fits to data for each site (p<0.05; n = 12) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098204#pone-0098204-t002" target="_blank">Table 2</a> for the details of the regressions).</p

Summary of three-way ANOVA (applied to raw data) examining the effect of Site (BCC and KP), Depth (2, 3, 4, and 8 m), and sampling Date (12 dates) on the cover of <i>Desmarestia viridis</i> on the seabed from 8 April to 23 September, 2011 (see “Materials and methods” for the details of the two error terms).

<p>Summary of three-way ANOVA (applied to raw data) examining the effect of Site (BCC and KP), Depth (2, 3, 4, and 8 m), and sampling Date (12 dates) on the cover of <i>Desmarestia viridis</i> on the seabed from 8 April to 23 September, 2011 (see “Materials and methods” for the details of the two error terms).</p

Mean (±SE) density (note the change in scale) of individuals in the six numerically dominant invertebrate taxa and gastropod (<i>Lacuna vincta</i>) and fish (unknown species) egg masses associated with <i>Desmarestia viridis</i>, <i>Desmarestia aculeata</i>, and <i>Agarum clathratum</i> from 18 February to 9 October, 2011 at Keys Point (n = 7 to 10 for each data point, except for <i>A</i>. <i>clathratum</i> in February where n = 3).

<p>Bivalvia: <i>Hiatella arctica, Modiolus modiolus,</i> and <i>Mytilus</i> sp.; Gastropoda: <i>Dendronotus frondosus, Lacuna vincta,</i> and <i>Margarites helicinus</i>; Copepoda: unidentified species in the Order Harpacticoida; Amphipoda: <i>Ampithoe rubricata, Calliopius laeviusculus, Caprella linearis, Caprella septentrionalis, Gammarellus angulosus, Gammarus oceanicus, Gammarus setosus, Ischyrocerus anguipes, Leptocheirus pinguis, Pontogeneia inermis,</i> and <i>Stenothoe brevicornis</i>; Polychaeta: <i>Alitta virens, Autolytinae</i> sp., <i>Bylgides sarsi, Lepidonotus squamatus, Nereis pelagica, Phyllodoce mucosa,</i> and <i>Spirorbis borealis</i>; Isopoda: <i>Idotea baltica</i> and <i>Munna</i> sp.</p

Empirical model of ecological interactions in sporophytes of the annual, acidic (H₂SO₄), brown seaweed <i>Desmarestia viridis</i> in urchin (<i>Strongylocentrotus droebachiensis</i>) barrens in eastern Canada throughout an entire growth season (March to October).

<p>The dominant environmental controls (temperature and urchin grazing) are shown as open rectangles and dashed lines, <i>D. viridis</i> traits (cover/sweeping, specific growth rate [SGR], pH, and mortality) as gray ellipses and solid lines, and epifauna (fish eggs, bivalves [B], herbivorous gastropods [G], and predatory polychaetes [P] and isopods [I]) as solid rectangles and dotted lines. Numbers above rectangles and ellipses are the sources of information for temporal variation: 1 [present study]; 2 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098204#pone.0098204-Gagnon2" target="_blank">[28]</a>; 3 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098204#pone.0098204-Scheibling1" target="_blank">[30]</a>; 4 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098204#pone.0098204-Blain1" target="_blank">[35]</a>; 5 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098204#pone.0098204-Adey1" target="_blank">[57]</a>; 6 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098204#pone.0098204-Gagnon4" target="_blank">[36]</a> (see “Discussion” for a detailed description of the model).</p

Loss in mean (+SE) wet weight as a percentage of initial wet weight of tissues (Experiment 1) and agar-embedded extracts (Experiment 2) of <i>Desmarestia viridis</i>, <i>Desmarestia aculeata, Agarum clathratum</i>, and <i>Alaria esculenta</i> sporophytes exposed 48 h to grazing by 10 green sea urchins, <i>Strongylocentrotus droebachiensis</i>.

<p>Bars not sharing the same letter are different (LS means tests, p<0.05; n = 15 [Experiment 1] and 20 [Experiment 2]) (see “Materials and methods” for a description of each experiment and nature of the procedural control in Experiment 2).</p