Pagès JF et al. (2013), The Mediterranean benthic herbivores show diver...

ECB-ART-42876

PLoS One 2013 Jan 01;85:e62719. doi: 10.1371/journal.pone.0062719.

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The Mediterranean benthic herbivores show diverse responses to extreme storm disturbances.

Pagès JF , Gera A , Romero J , Farina S , Garcia-Rubies A , Hereu B , Alcoverro T .

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Catastrophic storms have been observed to be one of the major elements in shaping the standing structure of marine benthic ecosystems. Yet, little is known about the effect of catastrophic storms on ecosystem processes. Specifically, herbivory is the main control mechanism of macrophyte communities in the Mediterranean, with two main key herbivores: the sea urchin Paracentrotus lividus and the fish Sarpa salpa. Consequently, the effects of extreme storm events on these two herbivores (at the population level and on their behaviour) may be critical for the functioning of the ecosystem. With the aim of filling this gap, we took advantage of two parallel studies that were conducted before, during and after an unexpected catastrophic storm event. Specifically, fish and sea urchin abundance were assessed before and after the storm in monitored fixed areas (one site for sea urchin assessment and 3 sites for fish visual transects). Additionally, we investigated the behavioural response to the disturbance of S. salpa fishes that had been tagged with acoustic transmitters. Given their low mobility, sea urchins were severely affected by the storm (ca. 50% losses) with higher losses in those patches with a higher density of sea urchins. This may be due to a limited availability of refuges within each patch. In contrast, fish abundance was not affected, as fish were able to move to protected areas (i.e. deeper) as a result of the high mobility of this species. Our results highlight that catastrophic storms differentially affect the two dominant macroherbivores of rocky macroalgal and seagrass systems due to differences in mobility and escaping strategies. This study emphasises that under catastrophic disturbances, the presence of different responses among the key herbivores of the system may be critical for the maintenance of the herbivory function.

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Genes referenced: LOC100887844 LOC100888042 LOC100893907

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	Figure 1. Location of the two monitoring programs conducted before and after the severe Easterly storm.Circled areas are zoomed in the next panel. The grey arrow in panel b) points out the direction of the storm (east). Panel c) shows the passive acoustic monitoring array deployed to track S. salpa individuals. Each receiver is numbered. This figure is composed of a topographic base map 1∶50 000 property of the Institut Cartogràfic de Catalunya (accessible from www.icc.cat) and a bionomic map property of the Universitat de Barcelona [60], [61].
	Figure 2. Effects of the storm on P. lividus population.a) Effect of the factor time (before the storm [2008] and after the storm [2009]) to the mean sea urchin abundance per patch. Different lower case letters indicate statistically significant differences (see Table 1). The arrow symbolizes the storm event. b) Effect of the factor size and time on mean sea urchin abundance per patch. Note that sea urchins of 5–6 cm were the most abundant; the asterisks show this was significant (Table 1). c) Effect of seagrass patch area after the storm on the abundance of sea urchins per patch after the storm. d) Effect of sea urchin density before the storm on the number of sea urchins lost per patch. Model fits are plotted as solid lines ± the standard error (see model coefficients in Table 1).
	Figure 3. Effects of the storm on S. salpa population.Mean S. salpa abundance per transect (number of S. salpa individuals per 250 m2) as a function of the factor year. The same lower case letters indicate that differences were not statistically significant (see Table 2). The arrow indicates the storm event (December 2008).
	Figure 4. Time series of the daily maximum wave height (Hmax) and S.salpa daily mean depth.Each panel corresponds to an individual fish. Vertical dotted lines indicate the date of storms with Hmax >2 m, and the thicker dashed line with an arrow indicates the date of the December 2008 catastrophic storm event. Note that fishes responded to most storms by moving to deeper areas. Note the disappearance of some fishes for several days following the studied storm.
	Figure 5. Time series of the daily maximum wave height (Hmax) and S. salpa travelled distanced per day.Each panel corresponds to an individual fish. Vertical dotted lines indicate the date of storms with Hmax >2 m, and the thicker dashed line with an arrow indicates the date of the December 2008 catastrophic storm event. Note that in general the distances travelled per day were higher in stormy days.

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