Temperate rocky subtidal reef community reveals human impacts across the entire food web
Food webs as representations of who eats whom are at the core of community ecology. Incorporation of tools from network theory enables assessment of how complex systems respond to natural and human-induced stressors, revealing how harvesting may degrade the properties and resilience of food webs. We present a comprehensive, coastal marine food web that includes 147 taxa cooccurring on shallow subtidal reefs along the highly productive and exploited Humboldt Current System of central Chile. This food web has connectance of 0.06, link density of 1204 and mean chain length of 4.3. The fractions of intermediate (76%), omnivorous (49%) and cannibalistic (8%) nodes are slightly lower than those observed in other marine food webs. Of the 147 nodes, 34 are harvested. Links to harvested nodes represented 50 to 100% of all trophic links of non-harvested nodes, illustrating the great impact that fishery pressure can have on the food web. The food web was compartmentalized into 5 sub-webs with high representation of harvested taxa. This structure changes if the fishery node is removed. Similarity analyses identified groups of harvested species with non-harvested nodes, suggesting that these tropho-equivalents could be sentinel species for the community-wide impacts of coastal fisheries. We conclude that fishing effects can be transmitted throughout the food web, with no compartments completely unaffected by harvesting. It is urgent to establish monitoring programs for community-wide effects of fisheries and assess whether resilience of these highly productive subtidal food webs has already been compromised, thereby identifying essential nodes that require stronger fisheries regulation.
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