a-c. Multispecies assessment of emergence (%) in response to sediment burial.

<p>Factors assessed: a) Duration (days); b) Sediment fraction (C = course, M = medium, F = fine) and; c) Depth of burial (cm) above organism.</p

Sediment Burial Intolerance of Marine Macroinvertebrates

<div><p>The marine environment contains suspended particulate matter which originates from natural and anthropogenic sources. Settlement of this material can leave benthic organisms susceptible to smothering, especially if burial is sudden i.e. following storms or activities such as dredging. Their survival will depend on their tolerance to, and their ability to escape from burial. Here we present data from a multi-factorial experiment measuring burial responses incorporating duration, sediment fraction and depth. Six macroinvertebrates commonly found in sediment rich environments were selected for their commercial and/or conservation importance. Assessments revealed that the brittle star (<i>Ophiura ophiura</i>), the queen scallop (<i>Aequipecten opercularis</i>) and the sea squirt (<i>Ciona intestinalis</i>) were all highly intolerant to burial whilst the green urchin (<i>Psammichinus miliaris</i>) and the anemone (<i>Sagartiogeton laceratus</i>), showed intermediate and low intolerance respectively, to burial. The least intolerant, with very high survival was the Ross worm (<i>Sabellaria spinulosa</i>). With the exception of <i>C</i>. <i>intestinalis</i>, increasing duration and depth of burial with finer sediment fractions resulted in increased mortality for all species assessed. For <i>C</i>. <i>intestinalis</i> depth of burial and sediment fraction were found to be inconsequential since there was complete mortality of all specimens buried for more than one day. When burial emergence was assessed <i>O</i>. <i>ophiura</i> emerged most frequently, followed by <i>P</i>. <i>miliaris</i>. The former emerged most frequently from the medium and fine sediments whereas <i>P</i>. <i>miliaris</i> emerged more frequently from coarse sediment. Both <i>A</i>. <i>opercularis</i> and <i>S</i>. <i>laceratus</i> showed similar emergence responses over time, with <i>A</i>. <i>opercularis</i> emerging more frequently under coarse sediments. The frequency of emergence of <i>S</i>. <i>laceratus</i> increased with progressively finer sediment and <i>C</i>. <i>intestinalis</i> did not emerge from burial irrespective of sediment fraction or depth. Finally, and perhaps unsurprisingly, the greatest ability to emerge from burial in all other species was from shallow (2 cm) burial. Although survival was consistently highly dependent on duration and depth of burial as expected, emergence behaviour was not as easily predictable thereby confounding predictions. We conclude that responses to burial are highly species specific and therefore tolerance generalisations are likely to be oversimplifications. These data may be used to inform environmental impact models that allow forecasting of the cumulative impacts of seabed disturbance and may provide mitigation measures for the sustainable use of the seabed.</p></div

Burial tolerance data for marine macroinvertebrates

Indexed spreadshee

<i>Sabellaria spinulosa</i> clump with ‘emergence tubes’.

<p>‘Emergence tubes’ constructed during burial by 2 cm fine (0.1–0.25 mm) sand for 16 days. The inset (top left) shows an isolated emergence tube which breaks off the main parent colony easily, and through which an individual animal is clearly visible. The inset (bottom left) shows three tubes emerging from the sediment following burial (Image source: Kim Last).</p

Indicators of mortality used to assess organisms following burial treatments.

<p>Indicators of mortality used to assess organisms following burial treatments.</p

a-c. Multispecies assessment of mortality (%) in response to sediment burial.

<p>Factors tested: a) Duration (days); b) Sediment fraction (C = course, M = medium, F = fine) and; c) Depth of burial (cm) above organism.</p

<i>M</i>. <i>edulis</i> byssus production on different surfaces and before/after burial (Exp. 3b).

<p>Counts of where the byssus threads were laid (A) indicated that there was higher activity on sediment particles (Buried sediment, x = 0.21, se = 0.09, emerged sediment x = 5.19, se = 1.44) and vertical surfaces (Buried vertical, x = 0.45, se = 0.24, emerged vertical x = 10.56, se = 1.28) in mussels which emerged than those that remained buried (remained buried n = 33, emerged n = 57). Byssus production in mussels prior to burial, measured after three days, was found to be similar (Buried, postburial x = 6.48, se = 0.87, Emerged, postburial x = 20.72, se = 1.51), but was higher for those that emerged, determined post burial (Buried, preburial x = 9.06, se = 1.25, Emerged, preburial, x = 8.44, se = 1.36)(B).</p

Hutchison et al Mussel Burial Data

Indexed data where: VORT = experimental tank number; duration = burial time in days; depth = burial depth in cm; sediment = c coarse, m medium, f fine; length = length of mussel in mm; width = width of mussel in mm; died = 0 no 1 yes; treatment = t treatment c control; temp = cold 8 degrees, ambient 14.5 degree, warm 20 degrees; depth = control free, control in chamber, shallow 2cm, medium 5cm, deep 7cm; duration = in days post start; position = position in VORT, inside or outside; pre- post- burial = number of byssus plaques laid before or after sediment burial; petri = pertidish; pot = burial chamber; sed = sediment; CI-grav = gravitational condition index; CI-shell = shell condition index

Schematic of multi-factorial nested experimental design.

<p>Each trial contained two control mussels (one free and one in a chamber) and three treatment mussels each burial to depths of 2, 5 and 7cm (n = 5, Control n (C_n) = 2, Treatment n (T_n) = 3). These five mussels were repeated for three sediment fractions; coarse, medium-fine and fine (n = 15, C_n = 6, T_n = 9) and for five burial durations (n = 75, C_n = 30, T_n = 45). Each set was replicated three times (n = 225, C_n = 90, T_n = 135), per species.”</p

<i>M</i>. <i>edulis</i> emergence from burial.

<p>Still images from video footage (filmed under infra-red light) showing the emergence of <i>M</i>. <i>edulis</i> from sediment burial over the course of several hours at night. The foot was laying byssus threads on the sediment and on the vertical (glass) surface.</p