Predation constrains host choice for a marine mesograzer

Abstract

For small sedentary herbivores that inhabit seaweeds, choosing a host that provides adequate nutrition and refuge should be favored by natural selection. Yet, the relative importance of seaweed nutritional value versus habitat quality in driving mesograzer host choice remains poorly understood for most herbivores. Previous work in coastal North Carolina, USA, and 2 tropical locations suggests that amphipods often utilize host seaweeds that offer superior refuge from both omnivorous and carnivorous consumers. Our study was conducted in New Zealand, where carnivores alone are the major consumers of seaweed-dwelling amphipods. We show that the herbivorous amphipod Aora typica preferentially utilizes the dictyotalean seaweed Dictyota kunthii over a dominant canopy-forming kelp, Ecklonia radiata, and that this preferred seaweed host provides a superior refuge from predators in both laboratory and field experiments. There was no difference in A. typica feeding preference between D. kunthii and E. radiata, but A. typica grew faster when reared on E. radiata. These results suggest that seaweed refuge quality, not nutritional quality, drives A. typica host preference and distribution in this system. KEY WORDS: Amphipod · Enemy-free space · Fitness · Plant−herbivore interaction · New Zealand · SeaweedResale or republication not permitted without written consent of the publisher

Microhabitat partitioning in seagrass mesograzers is driven by consistent species choices across multiple predator and competitor contexts

“…Unpublished data shows that gammarid amphipods tethered in the field in Bodega Bay without access to preferred microhabitat are rapidly consumed (50-100% consumed within 24 h; J. Stachowicz unpubl.). This is consistent with data for other epifauna from similar systems, which can shift their microhabitat use in the presence of predators to a substrate with higher value as shelter (Zamzow et al 2010, Beermann andBoos 2015), or suffer increased mortality from predation in the absence of their preferred host plant (Holmlund et al 1990, Duffy and Hay 1991, Moran et al 2010, Lasley-Rasher et al 2011. However, we found that the presence of two fish predators did not influence mesograzers in their microhabitat use even though the predators were very active and attempted to feed on the grazers behind the mesh barrier.…”

“…One of the reasons that microhabitat choice is thought to be important in plant–arthropod systems such as this one has to do with the need for ‘enemy‐free‐space’ (Duffy and Hay , Berdegue et al ). In particular, if predation susceptibility is determined by the match between grazer and plant morphology, using a microhabitat that poses a less optimal fit might result in increased exposure to predators (Duffy and Hay , Boström and Mattila , Lasley‐Rasher et al ). Unpublished data shows that gammarid amphipods tethered in the field in Bodega Bay without access to preferred microhabitat are rapidly consumed (50–100% consumed within 24 h; J. Stachowicz unpubl.).…”

“…Seagrass-associated epifauna are frequently exposed to high predation pressure (Duffy 2006), and "enemy-free space" (Berdegue et al 1996) has been observed to be a principal determinant of grazer microhabitat use (Duffy and Hay 1991, Boström and Mattila 1999, Lasley-Rasher et al 2011. The value of a microhabitat as shelter from predation is often defined by plant morphology (Martin-Smith 1993, Kley et al 2009), and grazer traits like size, shape and color that can determine successful microhabitat utilization.…”

Invasive seaweeds transform habitat structure and increase biodiversity of associated species

“…Meso-invertebrates inhabiting the host species exhibit tradeoffs in their host plant choice between nutritional value of the seaweed, the value of the seaweed as a shelter from intense predation, and the availability of palatable seaweed in the environment (Duffy & Hay 1991;Lasley-Rasher et al 2011). They are important members of seaweed assemblages as they can affect ecological processes such as recruitment potential, biofouling, and fish behaviour (Enge, Nylund & Pavia 2013; Wright et al 2014).…”

Benthic cyanobacterial mats serve as a refuge and food for the amphipod Gammarus fasciatus

“…A habitat architecture that provides hiding from predators is crucial (Zamzow et al, 2010) and often valued more than food (Norderhaug, 2004) by marine amphipods. Indeed, amphipods were more abundant on marine macroalgae providing refuge from predation than on vegetation they preferentially fed on, both in laboratory and in situ (Duffy & Hay, 1991;Lasley-Rasher et al, 2011).…”