Behavioural and metabolic adaptations of marine isopods to the rafting life style

Abstract

Rafting on floating objects is a common dispersal mechanism for many marine invertebrates. In order to identify adaptations to the rafting life style, we compared behavioural and metabolic characteristics of two isopods, the obligate rafter Idotea metallica and the facultative rafter Idotea baltica. In laboratory experiments, I. metallica showed low locomotive activity and a tight association to the substratum. Idotea baltica, in contrast, was more active with more frequent excursions in the surrounding water column. Oxygen consumption rates were similar in both species. Idotea metallica fed on zooplankton making this species widely independent of autochthonous food resources of the raft. Feeding rates and digestive enzyme activities were low in I. metallica. Reduced egestion rates may indicate slow gut passage and, thus, efficient resorption of nutrients. Efficient food utilization and the ability to accumulate high amounts of storage products, i.e. lipids, indicate a possible adaptation of I. metallica to low food availability or starvation. The feeding behaviour of I. baltica, in contrast, was more herbivorous and appeared wasteful and inefficient. Low lipid contents in I. baltica also indicate poor storage reserves. Thus, I. baltica requires a permanent access to food.

A summer heat wave decreases the immunocompetence of the mesograzer, Idotea baltica

“…I. baltica relies on permanent access to food, in its natural habitat it only rarely experiences phases of food deprivation, and is thus severely aVected when food is temporarily limited ). Temporary starvation is known to result in delayed maturity and decreased reproduction as I. baltica have only limited storage of internal compounds such as lipids (Gutow et al 2006). …”

Differential life history responses of two Idotea species (Crustacea: Isopoda) to food limitation

“…As an adaptation to low and unpredictable food levels male Idotea metallica use available food resources more economically than male I. baltica (Gutow et al 2006) and possess more extensive internal resources (i.e. lipids).…”

“…In its typical subtidal to intertidal habitat, dense canopies of benthic macroalgae such as Fucus vesiculosus provide an apparently unlimited food resource. The fact that food is always available in excess to I. baltica is reflected in the species' wasteful feeding habits with high ingestion rates and inefficient assimilation of ingested food items (Gutow et al 2006).…”

“…Consequently, as an obligate rafter, I. metallica has evolved an economic life style with low activity, efficient assimilation of ingested food items and accumulation of internal storage products (i.e. lipids; Gutow et al 2006). The more economic use of available food resources by I. metallica indicates that this species may be better adapted to life in non-equilibrium environments than I. baltica.…”

Long-distance dispersal, low connectivity and molecular evidence of a new cryptic species in the obligate rafter Caprella andreae Mayer, 1890 (Crustacea: Amphipoda: Caprellidae)

“…Passive dispersal through rafting and floating can greatly enhance natural dispersal in the marine environment and is supposed to be the main process leading to long-distance dispersal of these brooding marine invertebrates (Johannesson 1988;Locke and Corey 1989;Thiel and Gutow 2005b;Goodbody-Gringley et al 2010). Both natural (detached macroalgae, hydroids, and bryozoans) and artificial (buoys, pieces of wood or plastic, and ropes) floating substrata constitute ubiquitous dispersal agents for a wide diversity of organisms (Castilla and Guiñez 2000;Gutow et al 2006). Many marine vertebrates such as whales, manatees, and sea turtles also provide a suitable substratum for the attachment of these epibionts (Caine 1986;Pfaller et al 2008;Suárez-Morales et al 2010), with some individuals supporting abundant and diverse epibiont communities.…”