Disturbance intensity, disturbance extent and ocean climate modulate kelp forest understory communities

Abstract

Disturbances often control community structure by removing large dominant species, allowing new species to colonize. Disturbances vary in intensity and extent, and their effects on resident communities can depend on local environmental conditions. We tested the effects of disturbance intensity and extent on different functional groups of understory species in kelp forests at 4 locations along an ocean climate gradient in Western Australia. We hypothesized that, compared to intact canopies, increasing disturbance intensities (50 and 100% of kelp removal) and extents (2, 4 and 8 m diameter) would promote light-dependent competitors (turf, foliose, articulated coralline and fucoid seaweeds) at the expense of less light-dependent functional groups (invertebrates and encrusting seaweeds). We also hypothesized that these effects would be most pronounced at warmer relative to cooler locations, where metabolic and ecological rates are faster. The first hypothesis was supported; light-dependent understory groups (turfs, in particular) increased, while less light-dependent groups (crusts in particular) decreased with increasing disturbance regimes. However, the second hypothesis was not supported; even though understory communities differed between locations and turf covers were highest at the warmest location, we found no significant interactions between locations and disturbance regimes. Importantly, our results revealed that even small-scale partial canopy loss can have significant effects on kelp-associated communities. The implied community-wide, density-dependent effects have implications for the management and conservation of kelp forests, because restoration of ecological functions must also consider the density of kelp forests, not simply their presence or absence.

Persistence of seaweed forests in the anthropocene will depend on warming and marine heatwave profiles

“…Similar effects were observed during a clearing experiment in Western Australia where removal of Ecklonia with subsequent higher light levels, low abrasion levels, and release of space competition benefitted turfs as well as fucoids like Sargassum (Wernberg et al. 2020).…”

Phenotypic plasticity is not a cline: Thermal physiology of an intertidal barnacle over 20° of latitude

“…Under less predictable environmental scenarios, the energetic costs associated with plasticity—such as a lower reproductive output—might outweigh its benefits, making plastic populations more vulnerable to the increased environmental stochasticity predicted for marine environments in the future (Holbrook et al., 2019). Given that upwelling might become intensified under a warmer climate (Sydeman et al., 2014) and that these changes seem to already be taking place along the transitional zone (Wernberg et al., 2020), the elevated costs incurred through strong plasticity imply that local population extinction probability in these regions will be high (see Reed et al., 2011). Previous studies on J. cirratus showed that despite the slight population structure in this species—roughly associated with the 30°S biogeographic transition zone—suggests some degree of local adaptation, there is no support for complete isolation by distance in this species.…”

Rapid recovery of native habitat-builders following physical disturbance on pier pilings offsets colonization of cryptogenic and non-indigenous species in a Chilean port

“…2). Opportunism can involve a greater diversity of traits (e.g., reproductive output), but it generally implies a low rank in the competitive hierarchy (i.e., along an inter-specific competition-colonization trade-off, Greene and Schoener 1982;Chesson 2000;Valdivia et al 2005;Wernberg et al 2020). For instance, although barnacle larvae may disperse over kilometers in several weeks (Shanks 2009;Pappalardo et al 2016), small species such as Balanus laevis (see Fig.…”