Contrasting effects of ocean warming on different components of plant-herbivore interactions

Abstract

There is increasing uncertainty of how marine ecosystems will respond to rising temperatures. While studies have focused on the impacts of warming on individual species, knowledge of how species interactions are likely to respond is scant. The strength of even simple two-species interactions is influenced by several interacting mechanisms, each potentially changing with temperature. We used controlled experiments to assess how plant-herbivore interactions respond to temperature for three structural dominant macrophytes in the Mediterranean and their principal sea urchin herbivore. Increasing temperature differentially influenced plant-specific growth, sea urchin growth and metabolism, consumption rates and herbivore preferences, but not movement behaviour. Evaluating these empirical observations against conceptual models of plant-herbivore performance, it appears likely that while the strength of herbivory may increase for the tested macroalga, for the two dominant seagrasses, the interaction strength may remain relatively unchanged or even weaken as temperatures rise. These results show a clear set of winners and losers in the warming Mediterranean as the complex factors driving species interactions change.

Ocean warming and tropical invaders erode the performance of a key herbivore

“…It is considered to be a key herbivore, due to its major role in structuring and controlling macroalgal assemblages that are themselves an important habitat for many species . Western Mediterranean populations were also reported to die at temperatures above 29°C, and to decline in performance in values just below it (Pag es et al 2017). In a previous study, we reported a thermal threshold of~30.5°C, above which sea urchin mortality increases dramatically, indicating that the recent rapid warming along the Israeli coast may play a role in its population collapse on the southeastern Mediterranean reefs (Yeruham et al 2015).…”

“…In a bioinvasion context, effective invasive consumers might compete for resources with native consumers and thereby reduce their survivability and reproduction potential (Simberloff 2005). However, this combined scenario has rarely been experimentally tested (Pag es et al 2017). However, this combined scenario has rarely been experimentally tested (Pag es et al 2017).…”

Consumptive and non‐consumptive effects of predators vary with the ontogeny of their prey

“…We used P. oceanica as a food resource since it is easy to control and measure in consumption experiments (Pagès et al. ), and the objective of this experiment was merely to confirm if predator non‐consumptive effects on prey feeding behavior existed. Leaves were removed after 7 d, and the total area consumed was estimated using a ruler.…”

“…In both trials, experimental sea urchins were provided four 5 9 1 cm pieces of the seagrass Posidonia oceanica (a common food for this species) that had been cleaned of epibionts. We used P. oceanica as a food resource since it is easy to control and measure in consumption experiments (Pag es et al 2017), and the objective of this experiment was merely to confirm if predator nonconsumptive effects on prey feeding behavior existed. Leaves were removed after 7 d, and the total area consumed was estimated using a ruler.…”

“…The formation and persistence of barren areas has traditionally been linked to changes in sea urchin abundance, either as a result of the loss of their predators by overharvesting (Estes and Duggins 1995, Sala et al 1998, Shears and Babcock 2003, enhanced urchin recruitment (Cardona et al 2013) or both (Ling et al 2009). The presence of predators however also induces a host of non-consumptive effects on sea urchins, including habitat shifts, reductions in grazing activity and movement patterns (Nelson and Vance 1979, Cowen 1983, Scheibling and Hamm 1991, Freeman 2006, Pag es 2013. For example, sea urchins increase refuge (e.g., crevice) occupancy, move less and have shorter home range sizes in areas where predators abound (Hereu 2005, Spyksma et al 2017.…”