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Edge effects reverse facilitation by a widespread foundation species

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ABSTRACT

Dense aggregations of foundation species often mitigate environmental stresses for organisms living among them. Considerable work documents such benefits by comparing conditions inside versus outside these biogenic habitats. However, environmental gradients commonly arise across the extent of even single patches of habitat-forming species, including cases where stresses diverge between habitat interiors and edges. We ask here whether such edge effects could alter how habitat-forming species influence residents, potentially changing the strength or direction of interactions (i.e., from stress amelioration to exacerbation). We take as a model system the classic marine foundation species, Mytilus californianus, the California mussel. Results demonstrate that mussel beds both increase and decrease thermal stresses. Over a distance of 6 to 10 cm from the bed interior to its upper surface, peak temperatures climb from as much as 20 °C below to 5 °C above those of adjacent bedrock. This directional shift in temperature modification affects interactions with juvenile mussels, such that thermal stresses and associated mortality risk are higher at the bed surface, but substantially reduced deeper within the adult matrix. These findings provide a case example of how stress gradients generated across biogenic habitats can markedly alter ecological interactions even within a single habitat patch.

No MeSH data available.


Related in: MedlinePlus

Vertical temperature gradient across mussel beds.Boxplots of temperature measurements by depth within mussel beds (N = 4) at Bodega Marine Reserve, California, USA. Data are from measurements taken within 30 minutes on a single day (18 April 2013; ambient air temperature: 11 °C) at the same shore elevation (2.1 m above MLLW).
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f2: Vertical temperature gradient across mussel beds.Boxplots of temperature measurements by depth within mussel beds (N = 4) at Bodega Marine Reserve, California, USA. Data are from measurements taken within 30 minutes on a single day (18 April 2013; ambient air temperature: 11 °C) at the same shore elevation (2.1 m above MLLW).

Mentions: Our data indicate that peak temperatures at low tide can differ substantially between interiors and upper surfaces of mussel aggregations (Fig. 1), and that these locations mark the end points of a strong, within-habitat gradient in thermal maxima (Fig. 2). Relative to adjacent bedrock, mussel bed microhabitats simultaneously elevated and reduced peak temperatures, depending on location. Interior mussel bed microhabitats remained below 25 °C even on the hottest days (Fig. 1), and peak values were reduced by an average of 10 to 15 °C compared to adjacent bedrock. In contrast, and particularly in months of high solar radiation between late spring and fall, monthly thermal maxima on mussel bed surfaces exceeded bedrock maxima by 2 to 5 °C (Fig. 1), occasionally reaching temperatures above 40 °C. Thermal maxima inside mussel beds were consistently lower, and less variable, than at mussel bed surfaces 6 to 10 cm away, or in adjacent rock clearings (see also Supplementary Information online, Fig. S1, for a sample time series). Temperatures recorded within and on the surface of mussel beds differed by up to 19.3 °C over the course of a month and 20.7 °C over a single day.


Edge effects reverse facilitation by a widespread foundation species
Vertical temperature gradient across mussel beds.Boxplots of temperature measurements by depth within mussel beds (N = 4) at Bodega Marine Reserve, California, USA. Data are from measurements taken within 30 minutes on a single day (18 April 2013; ambient air temperature: 11 °C) at the same shore elevation (2.1 m above MLLW).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120328&req=5

f2: Vertical temperature gradient across mussel beds.Boxplots of temperature measurements by depth within mussel beds (N = 4) at Bodega Marine Reserve, California, USA. Data are from measurements taken within 30 minutes on a single day (18 April 2013; ambient air temperature: 11 °C) at the same shore elevation (2.1 m above MLLW).
Mentions: Our data indicate that peak temperatures at low tide can differ substantially between interiors and upper surfaces of mussel aggregations (Fig. 1), and that these locations mark the end points of a strong, within-habitat gradient in thermal maxima (Fig. 2). Relative to adjacent bedrock, mussel bed microhabitats simultaneously elevated and reduced peak temperatures, depending on location. Interior mussel bed microhabitats remained below 25 °C even on the hottest days (Fig. 1), and peak values were reduced by an average of 10 to 15 °C compared to adjacent bedrock. In contrast, and particularly in months of high solar radiation between late spring and fall, monthly thermal maxima on mussel bed surfaces exceeded bedrock maxima by 2 to 5 °C (Fig. 1), occasionally reaching temperatures above 40 °C. Thermal maxima inside mussel beds were consistently lower, and less variable, than at mussel bed surfaces 6 to 10 cm away, or in adjacent rock clearings (see also Supplementary Information online, Fig. S1, for a sample time series). Temperatures recorded within and on the surface of mussel beds differed by up to 19.3 °C over the course of a month and 20.7 °C over a single day.

View Article: PubMed Central - PubMed

ABSTRACT

Dense aggregations of foundation species often mitigate environmental stresses for organisms living among them. Considerable work documents such benefits by comparing conditions inside versus outside these biogenic habitats. However, environmental gradients commonly arise across the extent of even single patches of habitat-forming species, including cases where stresses diverge between habitat interiors and edges. We ask here whether such edge effects could alter how habitat-forming species influence residents, potentially changing the strength or direction of interactions (i.e., from stress amelioration to exacerbation). We take as a model system the classic marine foundation species, Mytilus californianus, the California mussel. Results demonstrate that mussel beds both increase and decrease thermal stresses. Over a distance of 6 to 10 cm from the bed interior to its upper surface, peak temperatures climb from as much as 20 °C below to 5 °C above those of adjacent bedrock. This directional shift in temperature modification affects interactions with juvenile mussels, such that thermal stresses and associated mortality risk are higher at the bed surface, but substantially reduced deeper within the adult matrix. These findings provide a case example of how stress gradients generated across biogenic habitats can markedly alter ecological interactions even within a single habitat patch.

No MeSH data available.


Related in: MedlinePlus