The role of overgrazing and anthropogenic disturbance in shaping spatial patterns of distribution of an invasive seaweed

Abstract

Summary1. Natural and human-generated disturbances are widely acknowledged as key drivers of biological invasions. Understanding the role of spatial patterns of compounded disturbances in determining invader establishment and spread can enhance the effectiveness of control strategies. 2. Using the framework of 1/f noise models and by means of a field experiment, we evaluated how the simultaneous exposure of Posidonia oceanica meadows to disturbances (namely overgrazing and rhizome uprooting from vessel anchoring) differing in spatial extent and degree of autocorrelation influenced the establishment and spread of the invasive seaweed, Caulerpa racemosa. Effects on invader establishment and spread were evaluated by means of mixed-effect models relating spatial patterns of disturbance and presence or abundance of C. racemosa, quantified through spectral coefficients. 3. The spatial distribution of C. racemosa mimicked that of overgrazing, both variables showing positive autocorrelation. Yet, C. racemosa was unable to disperse from disturbed patches into adjacent intact areas. The uprooting of rhizomes did not promote the establishment of C. racemosa, but magnified (≃18 times) the proliferation of the exotic seaweed when coupled with overgrazing. 4. Synthesis and applications. Fish overgrazing of Posidonia oceanica lessens the resistance of seagrass beds to invasion by Caulerpa racemosa. Thus, conservation strategies (e.g. marine protected areas) aiming to restore over-exploited fish populations may indirectly enhance the susceptibility of P. oceanica meadows to invasion by C. racemosa. Uprooting of P. oceanica rhizomes, such as that caused by boat anchoring, exacerbates the effects of overgrazing. The anchoring of recreational vessels should be, therefore, strictly regulated in areas characterized by intense grazing of P. oceanica leaves. More generally, our study shows that native herbivores may indirectly facilitate invasion by reducing the resistance of resident plant communities and suggests that sounded strategies for controlling the establishment and spread of invasive species require taking into account the interactive effects of natural and anthropogenic disturbances.

Photoacclimation of Caulerpa cylindracea: Light as a limiting factor in the invasion of native Mediterranean seagrass meadows

“…the CLIPPING treatment) allowed C. cylindracea to achieve a carbon balance three times higher than those recorded in the IN and the SHADED treatments, as well as Hk daily periods longer than 5 h. These results reinforce the hypothesis supported by the other results obtained in this study that light availability inside the seagrass canopy limits the photosynthetic performance of the algae, and are consistent with recent experimental studies demonstrating that the removal of P. oceanica leaves promotes the establishment and spread of the invasive seaweed (Tamburello et al, 2014). However, despite the efficient use of light demonstrated by the alga, stolons transplanted to the CLIPPING plots presented apical growth rates and biomass losses similar to that recorded in IN and SHADED treatments.…”

Effect of grazing on distribution and recovery of harvested stands of Lessonia berteroana kelp in northern Chile

“…Marine ecosystems worldwide are intensely exploited and their spatial distribution is altered in space and time (Steneck et al 2013, Tamburello et al 2014. Thus, determining the key ecological mechanisms at play in exploited natural communities is relevant to understand their vulnerability and resilience potential (e.g.…”

“…Herbivory influences both intra-and interspecific relationships in local communities and modifies the landscape structure (Duffy 2002, Poore et al 2012. In this way, the role of herbivores is especially relevant in human-disturbed communities where impacts on the spatial distribution and composition of primary producers can be either compensated or intensified by herbivory (Tegner & Dayton 2000, Steneck et al 2002, 2013, Graham 2004, Tamburello et al 2014.…”

Linking disturbance and resistance to invasion via changes in biodiversity: a conceptual model and an experimental test on rocky reefs

“…; Tamburello et al. ). This suggests that dominance by species characterized by marked differences in competitive ability (Ceccherelli et al.…”