Novel crab predator causes marine ecosystem regime shift

Abstract

The escalating spread of invasive species increases the risk of disrupting the pathways of energy flow through native ecosystems, modify the relative importance of resource (‘bottom-up’) and consumer (‘top-down’) control in food webs and thereby govern biomass production at different trophic levels. The current lack of understanding of interaction cascades triggered by non-indigenous species underscores the need for more basic exploratory research to assess the degree to which novel species regulate bottom-up and/or top down control. Novel predators are expected to produce the strongest effects by decimating consumers, and leading to the blooms of primary producers. Here we show how the arrival of the invasive crab Rhithropanopeus harrisii into the Baltic Sea – a bottom-up controlled ecosystem where no equivalent predators ever existed – appeared to trigger not only strong top-down control resulting in a decline in richness and biomass of benthic invertebrates, but also an increase in pelagic nutrients and phytoplankton biomass. Thus, the addition of a novel interaction – crab predation – to an ecosystem has a potential to reduce the relative importance of bottom-up regulation, relax benthic-pelagic coupling and reallocate large amounts of nutrients from benthic to pelagic processes, resulting in a regime shift to a degraded ecosystem state.

Fitness and community feedbacks: the two axes that drive long-term invasion impacts

“…Sharp spatial boundaries (ecotones) can arise between alternate communities in a homogeneous or smooth environment (Liautaud et al 2019), and a perturbation can push a community from one state to the other. From our work, it follows that those phenomena ought to be deeply entangled with the communities' longterm response to invasions (Gaertner et al 2014, Kotta et al 2018). This connection is strongest when there is at most one equilibrium per species composition.…”

“…But knowing that an invasion can occur, can we predict its long-term consequences (Levine et al 2003), such as whether it drives other species to extinction, or even causes an ecosystem regime shift (Scheffer et al 2001, Gaertner et al 2014, Kotta et al 2018? These long-term consequences are not only tied to characteristics of the invader and its immediate interaction partners (predators, prey, competitors...).…”

Global Systematic Review of Methodological Approaches to Analyze Coastal Shelf Food Webs

“…Along with these analytical methods, certain other approaches may also be used to provide qualitative supplementary information on food preferences in certain cases. For example, the structure of organs involved in the capture and consumption of prey items (e.g., Platt and Warwick, 1980), observations of feeding habits through direct observations (e.g., Paine, 1980;Kvitek and Bretz, 2005), field enclosure/exclusion experiments, and mesocosm experiments (e.g., O'Connor and Bruno, 2009;Kotta et al, 2018) may provide direct evidence on the trophic preferences of a species. However, such approaches can only be useful in a small number of studies dealing with the feeding habits of specific conspicuous marine consumers within spatiotemporally restricted environments, and thus have limited application in contemporary food web science.…”

Prey size selection in invasive (Hemigrapsus sanguineus and H. takanoi) compared with native (Carcinus maenas) marine crabs

“…In marine ecosystems, decapod crabs are among the most prominent invasive predators, often causing strong effects on recipient communities (Brockerhoff & McLay, 2011; Kotta et al ., 2018; Swart et al ., 2018). Arguably best studied in this respect is the invasion of European shore crabs ( Carcinus maenas ) along North American shores, where experimental work over the last decades has identified an overlap of the prey species spectrum and prey size preferences with native and other invasive crabs, with subsequent diverse effects on the invaded marine communities (see review by Klassen & Locke, 2007).…”