Sediment rafting: a novel mechanism for the small-scale dispersal of intertidal estuarine meiofauna

Abstract

ABSTRACT. Epontic diatoms from intertidal sandy sediments produce considerable quantities of extracellular mucopolysaccharides that are used for locomotion, adhesion to sediment particles and as antidesiccants. These mucoid exopolymers dry out during low tide and cement sandgrains together thus stabilizing the surficial deposit. Under benign microclimatic conditions in Pauatahanui Inlet, New Zealand, these mucoid films with bound surface sediments peel off the substratum and float onto the surface of incoming tidal waters. Large numbers of meiofaunal organisms are carried aboard these films which can subsequently be rafted considerable distances (10's of metres) at the whim of tidal currents and winds. Locally abundant epibenthic copepods are most prone to be passively conveyed in this way, and numbers on rafts are dependent on both microspatial and temporal factors that control population density at the site. Tiny naupliar stages of the harpacticoid Parastenhelia megarostrum dominate the rafted population, due to their intimate clinging association with surflcial particles. Survivorship is high in individuals that have undergone raftlng; rafts thus function as effective agents of dispersal for intertidal epibenthic meiofauna. Along with active migration by cra~vling and passive water column transport, this is the third significant pathway of small-scale within-locality dispersal for meiofauna to be revealed and investigated. It must be considered as a contributing mechanism of recruitment for meiofaunal organisms known to rapidly recolonlze disturbed or denuded habitat.

Meiofaunal emergence from intertidal sediment measured in the field: significant contribution to nocturnal planktonic biomass in shallow waters

“…The joint occurrence of all identified harpacticoid species in both the water column above and in the superficial sediment layer of the intertidal sandflats may in part be an artefact of (1) the stronger sampling effort in the water column (>500 samples of seawater but only 50 sediment samples), and (2) may result from passive suspension of some of the rarer species by wave action and tidal currents or sediment rafting (Hicks, 1988). In any case, the species list is subject to seasonal change.…”

Active and passive aspects of meiobenthic copepod dispersal at two sites near I Mustang Island, Texas

“…However there is evidence of exceptions to this pattern. Meiobenthic copepods have been shown to have a passive dispersal mechanism in low-energy intertidal areas through sediment rafting (Hicks 1988a). On a high-energy intertidal beach in Oregon (USA) copepods displayed a large amount of active behavior by positively responding to microbially-enriched sediment (Kern & Taghon 1986), as has also been observed in laboratory studies under conditions of no-flow (Decho & Fleeger 1988a).…”

Tidal and diel fluctuations in abundance of meiobenthic copepods on an intertidal estuarine sandbank

“…In a n attempt to determine the swimming potential of this species, experiments using emergence traps showed that, unlike members of an adjacent seagrass copepod assemblage, P. megarostrum did not actively emerge from the sediment and undertake bouts of swimming activity during high tidal periods (Hicks 1986). Evidence from this and other studies (Hicks 1984(Hicks , 1988) strongly suggests that this species, in particular young stages of the population, has great fidelity to sediment particles.…”

“…P. megarostrum is, however, a moderately sized species that is more superficial in its occupancy of bottom deposits. It does not actively swim into emergence traps during high water (Hicks 1986), and in situ stereomicroscope observations (Hicks 1988) have revealed that the smallest individuals, nauplii and copepodites particularly, are more conspicuous on the sediment surface than are the large females that tend to live about 1 mm or so deeper. Thus smaller individuals are predisposed to passive resuspenslon during the flood and ebb of the high water phase.…”

“…A number of workers have addressed issues in relation to tidal (e.g. Bell & Sherman 1980, Palmer & Brandt 1981, Fleeger et al 1984, Decho 1988, Hicks 1988 or diel events (e.g. Boaden & Platt 1971, Armonies 1988, Walters 1988), but in each case the time course of sampling has been either too constrained or too irregular to determine the magnitude or frequency of any inherent cyclic phenomena.…”