Bruce C. Coull

Field evidence that shrimp predation regulates meiofauna

SummaryThe grass shrimp Palaemonetes pugio, a suspected predator/disturber on meiofauna, and other large natant forms (>2 mm) were selectively excluded from microecosystem tanks for nine months during which time replicability between the tanks was established. Subsequently, shrimp were reintroduced into one of the four tanks via an aquarium and the meiofauna populations monitored in the “shrimp” and control tanks. In the presence of the predator/disturber, total meiofauna, nematode, oligochaete, and polychaete densities were significantly lower than in control tanks. In the presence of the predator/disturber, total meiofauna, nematode, oligochaete, and polychaete densities were significantly lower than in control tanks. Shrimp predation/disturbance significantly reduced meiofauna abundance in this salt marsh habitat but it did not alter the species diversity of the dominant taxon. The meiobenthos displayed characteristics common to other biologically regulated assemblages and our data provide the first field evidence of macrofaunal control of meiofauna community structure.

The response of meiofauna to sediment disturbance

Abstract The meiobenthos inhabiting an intertidal mud bar were disturbed by hand-turning the sediment of a 9-m 2 area with a shovel and monitoring the subsequent recolonization process. The immediate impact of the disturbance on this community dominated by Nematoda (91%), Copepoda (4%) and Foraminifera (4%), was to remove more than 70% of the meiofauna. However, after only one tidal cycle, total numbers of nematodes, copepods, foraminiferans and other meiofauna taxa were at predisturbance and control (similar 9-m 2 site on the same flat) density values. Nematode species assemblages rapidly adapted to the disturbance and changed little over time. Foraminifera showed insignificant fluidized flocculent upper layer of sediment was probably the major dispersal mechanism in this community, and foraminiferans seem to be the least able to use this mechanism. The meiobenthos of this habitat is described as a well-dispersed and dynamic community able to rapidly adjust to small-scale disturbances. However, the meiobenthos may not recover from all disturbances, because resilience was only determined for a limited physical disturbance.

Perspectives of Marine Meiofaunal Ecology

Meiofauna research has seen an increased ecological emphasis in the last ten years. The period prior to 1970 was primarily descriptive but current research is directed more toward testing hypotheses using the meiofauna. There is a fairly large descriptive base and generalities from a worldwide data set indicate that there are unique opportunities for additional studies. In this paper we present an overview of the historical development of meiofaunal research and a synopsis of the present knowledge, and provide our perceptions as to where meio fauna research needs to be directed. Hypothesis testing in the field, the role of meiofauna in total benthic energetics, and biological control mechanisms appear to be most fruitful avenues for future research.

The relationship between abundances of meiofauna and their suspected microbial food (diatoms and bacteria)

Abstract Samples were taken bi-weekly for one year at a sand site and a mud site in the North Inlet Estuary, Georgetown, South Carolina, for meiofauna, their suspected microbial food (bacteria and diatoms), and associated physical factors. Linear regression techniques were used to correlate food abundance and physical factors with the density of meiofaunal taxa. At both sites diatoms positively correlated with meiofauna taxa, but bacteria did not. Physical factors were not correlated with meiofaunal or microbial abundances at the sand site. Whereas, at the mud site meiofauna and diatom abundances were positively correlated with the depth of the redox layer and inversely correlated with temperature. Peaks of meiofaunal abundance did not follow peaks of food abundance. Analysis of copepods at the species level indicated that taxa response was due to the response of the dominant species. Even though some correlations existed, this study suggests that copepod species and meiofauna at the gross taxonomic level do not respond to changes in potential food abundance. Physical factors apparently influence both meiofauna and diatoms in the same fashion. However, bacterial abundance was not positively correlated with any of the factors studied.

Biogenic structure and its effect on the spatial heterogeneity of meiofauna in a salt marsh

Abstract Meiofauna samples collected around and between Spartina plants had either negative correlations with root biomass or no correlation. If, as predicted by earlier workers, meiofauna are attracted to micro-oxygenated zones around roots, there should have been a positive association between meiofauna and roots. Nematodes had higher densities around Uca pugnax (Smith) burrows than in controls, but copepods were less abundant, although the cause is unknown. Biogenic structures significantly affect meiofauna distribution and must be taken into account when quantifying meiofauna in areas with much structural heterogeneity.

Nematode/copepod ratios for monitoring pollution: A rebuttal☆☆☆

Abstract The nematode/copepod ratio recently proposed by Raffaelli & Mason is not a valid tool for assessing pollution. We found many discrepancies in the original paper and felt obliged to point them out. There was no quantitative assessment of contagion; and seasonal variation was great, two factors which could alter the ratio. We partitioned the original data into Raffaelli & Masons and others and found that the ratio was not significantly correlated with grainsize when using the literature values. There are several exceptions to their statement that nematodes dominate in organically enriched sites and that there are not copepods in deep water samples. We do not believe that reducing the very complex meiofaunal community structure to a single ratio is appropriate and are concerned that those not familiar with the meiofaunal literature will try to use this ratio method as a panacea for assessing pollution before its validity is fully known.

Juvenile spot (Pisces) and grass shrimp predation on meiobenthos in muddy and sandy substrata

Abstract Experiments were conducted to determine whether, when given the choice, juvenile spot (Leiostomus xanthurus Lacepede) or the grass shrimp (Palaemonetes pugio Holthius) would feed on meiobenthos in both muddy and sandy sediments or whether meiofauna from one sediment type would be preferred. Specially designed aquaria were used to collect and transport sandy and muddy sediments from the field into laboratory sea-water tables. Predators were allowed to feed on meiofauna in aquaria containing an all-mud substratum, an all-sand substratum, or a combination substratum with one side sand and the other mud. Given no sediment choice (all-mud or all-sand), juvenile spot fed upon meiofauna in both sediment types. When fish were presented with a choice (half-mud and half-sand), however, spot clearly demonstrated a preference for feeding on meiofauna in muddy substrata. Predation by juvenile spot resulted in the significant removal of seven of nine meiobenthic taxa. In contrast, grass shrimp removed only two taxa.

Fish predation on meiobenthos : field experiments with juvenile spot Leiostomus xanthurus Lacépède

While it is now accepted that meiofauna are an important food source for numerous juvenile fish, the impact of predation on field populations of meiofauna remains controversial. We conducted a field-caging experiment to determine the role of predation in structuring meiobenthic communities in situ. Cages excluding predators and cages enclosing low and high densities of juvenile spot Leiostomus xanthurus Lacepede, a common estuarine fish from the southeastern U.S.A., were placed on a mudflat in a randomized complete block design to determine the in situ effects of juvenile spot predation on meiobenthos. Juvenile spot predation was only significant for those prey taxa or species with a high proportion of their population in the top few millimeters of sediment. Copepods and their nauplii, specifically the epibenthic species, were most affected by juvenile spot predation.

Field experimentation in meiofaunal ecology

Field manipulations with meiofauna have become popular research tools recently. Over 40 experiments manipulating meiofauna have been conducted including natural experiments. Investigator induced experiments include pollution experiments, colonization (non-pollution) experiments, trophic-interaction experiments, organism-substrate experiments and others. We review the contributions of these investigations.To adequately interpret manipulative experiments we provide a protocol and procedures section which emphasizes what is necessary for experimentation with meiofauna. These include: establishing an hypothesis, experimental design, controls, time scale of the experiment, taxon in question, replicating and coupling laboratory and field experiments.We suggest several areas where we feel meiofauna manipulations will provide fruitful research answers in the future and urge meiofauna experimentation in the following areas: food for higher trophic levels; habitat complexity: prey refuges; pollution ecology; competition; suspension: drift of meiofaunal taxa and nutrient remineralization. None of these research areas are easy, but with ingenuity should provide exciting and provocative areas for research.

Zonation of meiobenthic copepods in a southeastern United States salt marsh

Abstract Studies in various regions of southeastern U.S. Spartina alterniflora marshes indicate distinct zonation patterns of the meiobenthic copepods. Transversing a water depth gradient from the subtidal at the bottom of a tidal creek to the high intertidal marsh, one species, Microarthridion littorale , occurs along the entire gradient. Other species are common along certain large portions of the gradient and still others are restricted to subhabitats. Potential reasons for the observed distribution patterns include water depth, tidal exposure, and presence or absence of both vegetation and macrofaunal disturbers/predators.