The meiofauna of a flatfish nursery ground

Abstract

Plates I-II and Text-figs 1-4)The meiofauna was studied over a 10-year period on a flatfish nursery ground between the high-water mark and a depth of 10 m below low-water springs.The sediment was well sorted sand, with median diameter from 210 to 279 ji in the intertidal area and 160 to 208 ji in the subtidal. It was composed of medium rounded quartz, with the calcium carbonate content mainly 0-25 to 2-20 % by weight. Porosity was 33-39% and the coefficient of permeability ranged from 166 to 233 x io~2 cm per sec, indicating good drainage. The sand was usually over 90 % water-saturated, and seldom less than 60 %. The annual average concentration of particulate organic carbon was 205 /ig/g sand in the intertidal, and 684 fig/g at 5 m depth. Corresponding values for chlorophyll a were 0-75 and 4-50 /*g/g.The most numerous taxonomic groups were nematodes, copepods, turbellarians, gastrotrichs and tardigrades. Oligochaetes, polychaetes, coelenterates and archiannelids occurred in smaller numbers. Total meiofauna individuals averaged from 0-5 x 10 s to 6-7 x 10 6 per m 2 and the corresponding biomass from 279 mg to 1092 mg dry weight per m 2 . There was a distinct zonation of fauna, the richest populations occurring from around the level of mean low-water neaps on the beach to about 1 m depth below low water. The populations were most sparse in both numbers and species above mean highwater neaps.Below midtide level the bulk of the meiofauna was found in the upper 4 cm of sand, but there was a significant vertical migration apparently depending on the state of the tide, and a general downward movement during the winter. At higher beach levels the vertical distribution was less regular. During a 6-year period of detailed observation, significant overall annual change in the populations was detected only once, when, due to severe storms, there was a drastic decline in numbers, but recovery took place the following year.The optimum sediment for interstitial meiofauna appears to be well-sorted sand of median diameter about 230 fi, but other density-independent factors affecting the populations are discussed. On an exposed beach the typical meiofauna comprises a community of of high individual numbers with a stable and permanent set of species of great diversity. This is contrasted with the equivalent macrofauna community, and reasons for the differences in diversity discussed in terms of niche utilization.Meiofauna populations on exposed sandy beaches may be fuelled largely by soluble organic matter via bacteria attached to sand grains. No great interaction was shown with other groups on the beach and no significant transfer of material to higher trophic levels was observed. It is suggested that meiofauna in these circumstances may be largely at the top of a food chain. I N T R O D U C T I O NAs part of a comprehensive investigation of the food web in a sandy bay, a study has been made of the meiofauna, denned here as metazoans passing a 0-5 mm sieve. This paper deals with the composition, abundance and distribution of the...

An Ecophysiological Study of the Meiofauna of the Swartkops Estuary

“…This suggests that the lower limit for interstitial life, excluding nematodes, is considerably lower than 200 JJ.m. The nematodes, however, are capable of sliding in very small spaces and it has been postulated that the lower limit for these forms is 125 JJ.m (Mcintyre & Murison 1973).…”

Foraging patterns of two syngnathid fishes: importance of harpacticoid copepods

“…Some investigators have reported harpacticoid copepods to be unimportant to higher trophic levels (Marshal1 1970, McIntyre & Murison 1973, Heip & Smol 1976, but these studies are from unvegetated areas. More recent work from shallow water has shown that harpacticoids are a prevalent dietary item for some fishes, especially juveniles and smaller-sized species (e.g.…”

Influence of the tidal and rainfall cycles on the population structure and density of Mesacanthion hirsutum gerlach (nematoda, thoracostomopsidae) on a tropical sandy beach (Tamandaré Bay, Pernambuco, Brazil)

“…These great density variations can probably be linked to the dispersion and/or migration of the animals within the sediment or through the water column. Nematode migration to deeper sediment layers during high tides has already been reported by many authors (e.g., MCINTYRE; MURISON, 1973;PLATT, 1977); however, STEYAERT et al (2001) found in a temperate estuary that some species have the opposite behavior, increasing their densities in the upper layers of the sediment during the submersion periods (high tides).…”