Perception and Choice of Substratum by Epifaunal Amphipods Associated with Seagrasses

Abstract

Laboratory experiments showed that the three epifaunal amphipods Cymadusa cornpta, Grandidierella bonnieroides, and Melita elongata, normally associated with seagrasses, are capable of detecting small differences in the density of seagrass and actively select areas of high blade density. When different seagrass species -Thalassia testudinurn, Syringodiurn filiforme, and Halodule wrightii -were offered with equal blade biomass, H, wrightii was selected due to its high ratio surface area: biomass. When offered equal surface area all three amphipod species were randomly distributed among the seagrass species, confirming the hypothesis that surface area is the habitat characteristic chosen. It was concluded that blade surface area of macrophytes provides the best estimate of habitat complexity in seagrass meadows. The surface area relationship also held for C. compta when the highly branched red alga Gracilaria foliifera was used as a substratum. Degree of habitat selectivity by the three species of amphipods was related to known differences in vulnerability to predation by Lagodon rhornboides. It is concluded that habitat preference and biological interactions must both be examined to fully understand distributional patterns in seagrass epifauna.

Patterns and Processes of Chasmagnathus granulata and Cyrtograpsus angulatus (Brachyura: Grapsidae) Recruitment in Mar Chiquita Coastal Lagoon, Argentina

“…Historically, the hypothesis of differential mortality due to predation has been first proposed as the cause of the correlation between macrofauna abundance and habitat complexity (Heck & Orth, 1980;Stoner, 1980). Density-dependent mortality has been reported as the most important post-settlement factor affecting recruitment in decapods (Olmi et al, 1990;Wahle & Steneck, 1991;Eggleston & Armstrong, 1995;Palmer et al, 1996;Moksnes et al, 1997;Moksnes, 1999).…”

Pipefish foraging: effects of fish size, prey size and altered habitat complexity

“…Here I examine pipefishamphipod interactions (2 fish sizes and 3 amphipod sizes) at 2 levels of habitat (artificial seagrass) complexity. Various investigators have used different measures of complexity in vegetated habitats: biomass (Orth 1977, Stoner 1980, shooWblade density (Homziak et al 1982), surface area (Stoner & Lewis 1985), and surfaceto-volume ratio (Coull & Wells 1983). I have observed gammarid amphipods to preferentially occupy the spaces between the basal portions of artificial seagrass blades, apparently reducing their conspicuousness and vulnerability to pipefish.…”

Penicillus capitatus: an algal island for macrocrustaceans

“…Nocturnal locomotory activity is well-known in seagrass-associated peracarids (Robertson & Howard 1978, Stoner 1980 and any differential dispersal characteristics could greatly influence the pattern of recruitment on Penicillus capitatus. Second, Nagle (1968) suggested that competitive interactions among peracarid species result in displacement of certain species from macroalgae.…”

“…Penicillus capitatus has 634 cm2 g-' ash-free dry wt (Lewis unpubl. ), (or 199 cm2 g-' dry wt) and Halodule wrightii has 715 cm2 g p l dry wt (Stoner 1980). Despite considerable variation in the abundance of fauna in samples of P. capitatus and H. Penicillus capitatus differed distinctively from Halodule wrightii in species composition and relative abundances (Table 4).…”