Physical disturbance by recovering sea otter populations increases eelgrass genetic diversity

Abstract

The importance of disturbance Work in sea otters over the last few decades has transformed our understanding of the importance of specific species, or keystones, as drivers of community structure and stability. Foster et al . took the next step and tested whether otter foraging might influence genetic diversity in an eelgrass ecosystem (see the Perspective by Roman). The authors found that eelgrass genetic diversity was significantly higher where otters were present and that the impact was related to time: Longer otter presence was associated with higher genetic diversity. These results illustrate how the actions of a predator can affect the diversity of a producer in a tropic system. —SNV

Disturbance decreases genotypic diversity by reducing colonization: Implications for disturbance–diversity feedbacks

“…The observation of enhanced colonization in the absence of disturbance was also surprising, especially given that disturbance facilitating colonization is the cornerstone of multiple hypotheses predicting the relationship between disturbance and diversity (Connell, 1978; Goodsell & Connell, 2005; Sousa, 1979). This result also contrasts with previous studies suggesting that physical disturbance increases eelgrass genotypic diversity by facilitating seedling recruitment (Foster et al, 2021; Reusch, 2006; Zipperle et al, 2010). The reductions in flowering effort we observed in clipped treatments (see also Shaughnessy et al [2021]) might partially explain reductions in colonization if the colonizing genets are new seedlings, especially given that contributions to the seed bank come from both local and distant sources (Furman et al, 2015; Harwell & Orth, 2002; Ruckelshaus, 1998; Zipperle et al, 2010).…”

“…The shape of the relationship between disturbance and genotypic diversity also varies considerably among systems. For example, correlative studies show that sites with intensive disturbance histories can have higher (Hunter 1993, McMahon et al 2017, Foster et al 2021, lower (Hangelbroek et al 2002, Rusterholz et al 2009 or indistinguishable (Diaz-Almela et al 2007) genotypic richness values relative to undisturbed sites. Manipulative experiments also show mixed results in that while some studies demonstrate that variation in the strength of selection drives diversity differences between disturbed and undisturbed plots (Herrera andBazaga 2011, Whitney et al 2019), other studies show no effect (Reusch 2006, Larkin et al 2010, Hidding et al 2014 or increased richness under moderately disturbed regimes (Peng et al 2015).…”

“…The shape of the relationship between disturbance and genotypic diversity also varies considerably among systems. For example, correlative studies show that sites with intensive disturbance histories can have higher (Foster et al, 2021; Hunter, 1993; McMahon et al, 2017), lower (Hangelbroek et al, 2002; Rusterholz et al, 2009), or indistinguishable (Diaz‐Almela et al, 2007) genotypic richness values relative to undisturbed sites. Manipulative experiments also show mixed results.…”

Strategies for managing marine disease

“…Ultimately, reduced urchin population size decreases density-dependent transmission of bacterial pathogens among urchins (Table 1, Lafferty 2004). Further, conservation of predators (sea otters) promotes natural ecosystem filter resilience (eelgrass), which could increase filtering of pathogenic bacteria (Foster et al 2021, Lamb et al . 2017.…”

“…Ultimately, reduced urchin population size decreases density‐dependent transmission of bacterial pathogens among urchins (Table 1 , Lafferty, 2004 ). Furthermore, conservation of predators (sea otters) promotes natural ecosystem filter resilience (eelgrass), which could increase filtering of pathogenic bacteria (Foster et al, 2021 ; Lamb, van de Water, Bourne, Altier, Hein, et al, 2017 ). In contrast, reducing lethal take and conserving habitats may cause overcrowding of a taxon, ultimately increasing disease transmission (Davies et al, 2015 ; Lebarbenchon et al, 2007 ; McCallum et al, 2005 ; Wood et al, 2010 ; Wootton et al, 2012 ).…”