There is a marked threshold in changes in out-of-burrow activity in the polychaete <i>Hediste</i><i>diversicolor</i> in response to increasingly flounder (Platichthys flesus) conditioned seawater.

<p>For up to four predatory juvenile <i>P</i>. <i>flesus</i> in a water tank supplying the polychaete tank, monitored out of burrow behaviour was not significantly different from that found in control animals. For five or more predators in the supplying water tank, polychaete behaviour changed markedly (H. <i>diversicolor</i> were less active). a) mean number of emergences per night. Adding five or more significantly reduced the number of emergence events (from 31.5 ± 7.71 to 2.15 ± 0.48 b) mean duration of emergences was reduced (from 5.45 ± 0.2 seconds to 1.41 ± 0.15 seconds) when water was conditioned with five or more <i>P</i>. <i>flesus</i>; c) mean maximum distance of emergences changed markedly (from 2.55 ± 0.13 cm to 2.04 ± 0.07 cm) when there were five or more <i>P</i>. <i>flesus</i> in the supplying water tank. Recordings were made over 5 consecutive nights (dark phase 10 h). N=16 per treatment with means ± standard deviation.</p

Most aspects of out-of-burrow activity in the polychaete <i>Hediste</i><i>diversicolor</i> decrease in response to seawater spiked with increasing concentrations of mucous from flounder (Platichthys flesus), herring (Clupea harengus) and plaice (Pleuronestes platessa): a) mean number of emergences decreases with no significant difference between fish species; b) mean duration of emergences decreases.

<p>There are no significant differences between fish species; c) mean maximum distance of emergences decreases for all fish species used. However, the reduction in emergence distance in animals receiving water spiked with mucous from pelagic herring is significantly less marked. Recordings were made over 3 consecutive nights (dark phase 10 h). N=16 per treatment with means ± standard deviation. </p

Out-of-burrow activity in the polychaete <i>Hediste</i><i>diversicolor</i> decreases more gradually in response to increasing levels of mucous from flounder (Platichthys flesus) spiked sea water.

<p>We added mucous taken from <i>P</i>. <i>flesus</i> directly to the polychaete tank. Final mucous concentrations ranged from 0.1 to 1.2 µg per ml seawater. Behavioural changes in monitored traits in <i>H</i>. <i>diversicolor</i> occurred from a concentration of 0.4 µg/ml onwards and were generally more gradual than for the life predator experiments. a) Mean number of emergences for control and mucous concentrations below 0.4 µg/ml (40.33 ± 2.52) were reduced to 1.3 ± 0.18 for the highest amounts of mucous; b) mean duration of emergences was at its lowest for the two highest concentrations tested (1.38 ± 0.03 seconds); c) mean maximum distance of emergences: For mucous concentrations higher than or equal to 1 µg/ml, there was a significant reduction of foraging distance (average 1.55 ± 0.01 cm). Recordings were made over 3 consecutive nights (dark phase 10 h). N=16 per treatment with means ± standard deviation.</p

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

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>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

Experimental Sediment Total Oxygen Uptake (TOU) rates.

<p>Oxygen flux rates during closed incubations for experimental sediments under varying organic matter treatments (0, 0.1 and 1%) at <b>A</b> ambient (15°C) and <b>B</b> summer maximum temperatures (20°C). Error bars represent standard error.</p