Dominant Polychaete Research Articles

Benthic associations in bathyal and hadal depths off the Pacific coast of north eastern Japan: physiognomies and site factors

Off north-eastern Japan, the continental slope is rather narrow. It slopes steeply down to a depth of 1000m, but then forms a flat terrace between 1000 and 3000 m. Beyond 3000m the slope drops steeply down to the axis of the Japan Trench (7500m). Only one community type occurs in the upper bathyal zone (200–600m), an Ophiura association whose physiognomy is a “turf” of ophiuroids. The middle bathyal zone (600–1200m) is occupied by two types of community. The predominant community is an association characterized by an asteroid, Ceramaster, and a demersal fish, Sebastolobus, which has no characteristic physiognomy. The second is a comatulid community, which occurs on the shoulder of the slope as a comatulid “park”. The lower bathyal zones (1200–3000m) is inhabited by two distinct associations one of which has two facies. Most of the terrace area is occupied by an amphiurid association. In the plateau-like areas where there is a higher flow regime, there are sporadic, or sometimes rather dense stands of a coelenterate — the Radicipes facies. Whereas at the deeper site current are slower and the sediment is muddy, a Megayoldia — Ascorhynchus facies occurs in which a bivalve and a gigantic pycnogonid are found associated with amphiurids. The other community-type is a tubicolous-polychaete association which consists of a dominant polychaete species with a rather thin sandy tube which is associated always with a caprellid. This association is found on a shoulder-like topography, where bottom currents are expected to be constant and sediment is sandy. In the axis of the Japan Trench, where the sediment is soft mud, a small globular bivalve, Kelliella, is numerically dominant, which is associated with a holothurian, Elpidia, and a demersal fish, Careproctus. Nearby where the topography is a gentle slope, the community is typified by a dominant isopod, Storthyngura sp., accompanied by a bivalve, Spinula, and an actiniarian, Galatheanthemum.

Contribution of the polychaete, Neanthes japonica (Izuka), to the oxygen uptake and carbon dioxide production of an intertidal mud-flat of the Nanakita River estuary, Japan

The benthic oxygen consumption and carbon dioxide production of undisturbed and sieved sediment cores with various values for the biomass of polychaetes collected from the intertidal mud-flat of Nanakita River estuary of Japan were measured simultaneously. The benthic oxygen consumption and carbon dioxide production increased in proportion to the biomass of a dominant polychaete species Neanthes japonica (Izuka). This increase was not explained by the respiration of the animals alone. The residual increase in benthic O 2 and CO 2 fluxes may be due to mineralization processes in the burrow wall and enhanced diffusion caused by the pumping activity of the worms. From the average biomass of polychaetes at the study site, total benthic O 2 and CO 2 fluxes were estimated to be 5.2 mmol·m −2·h −1 and 7.3 mmol·m −2·h −1, respectively, at 20 ° C. The worms were responsible for 79% of the total O 2 flux and 73% of the total CO 2 flux but the respiration of the worms accounted for only 53% of the total O 2 flux and 36% of the total CO 2 flux. The residual enhanced fluxes were 26% and 37% for the total O 2 and CO 2 fluxes, respectively.

General characteristics of benthic faunas on the Amazon inner continental shelf with comparison to the shelf off the Changjiang River, East China Sea

Major patterns of bacteria, meiofauna, and macrobenthos distributions were examined from muddy sediments on the inner continental shelf near the Amazon River. The spatial distributions and functional groupings of the fauna were compared with faunal distributions on the East China Sea shelf off the Changjiang (Yangtze) River and used to assess the impact of long-term, large-scale physical processes on benthic community structure in shelf environments. Both areas are influenced by large discharges of fresh water and suspended solids, and have inner-shelf mud deposits. On the Amazon shelf, macrofauna were generally small in size or absent from highly mobile, muddy sediments on the inner shelf. Significant numbers occurred only in relatively stable sediments offshore or to the south or northeast of the mud belt. Macrobenthos reached greatest densities (3915 m −2) in a general area of firm muddy sediments (Stas 79 and 88) interbedded with sand and burrowed by the ghost shrimp Callianassa sp. At these stations, diversity was greatest, particularly in the dominant polychaete taxon. Macrofauna in the East China Sea, particularly epifaunal species, were reduced in abundance and biomass in inner-shelf areas of most active accumulation near the Changjiang River. However, macrofauna were 50–100 times more abundant (ranging to 10,000 m −2) than at sedimentologically comparable locations on the Amazon shelf. For areas of reduced deposition on the East China Sea shelf, diversity was also greater, with 50 species per sample as opposed to a maximum number of 19 per sample of comparable size on the Amazon shelf. Bacterial and meiofaunal abundances were low nearshore on the Amazon shelf compared with farther offshore or, in the case of meiofauna, other shelf environments. Average bacterial abundances for the top 10 cm of sediments ranged from 1.3 to 21 × 10 9 g −1 on the Amazon shelf and from 7.1 to 22 × 10 9 g −1 on the East China Sea shelf. Meiofauna on the Amazon shelf varied from none in the nearshore mobile mud belt to 2045 (10 cm −2) offshore on firm silty clay sediments. These densities compare with 66 (10 cm −2) near the Changjiang River mouth and 4870 (10 cm −2) farther offshore. Nematodes dominate the meiofauna on both shelves. The high degree of physical disturbance and unstable nature of the seabed coupled with reduced detrital food availability in bottom sediments appear to be the major factors limiting faunal abundances, controlling the taxonomic diversity of the meio- and macrofaunal species, and determining the functional groups of macrobenthos on the Amazon inner shelf, and, to a lesser extent on the East China Sea inner shelf.

陸奥湾におけるマクロベントスの時空間分布

In order to elucidate the conditions of food environments for righteye flounders Limanda herzensteini and L. yokohamae in Mutsu Bay, Aomori Prefecture, the distributions of macrobenthos were investigated by analyzing grab samples obtained at approximately 300 stations chiefly from March 1980 to February 1983. Faunal composition in the bay was correlated with the mud contents in the bottom sediments. In the extensive mud bottom in offshore area polychaete annelids predominated, representing 82.8% of the total number of macrofauna. Most of the dominant species, Scalibregma inflatum, Paraprionospio pinnata, and Maldane sarsi, were chiefly abundant in East Bay. So macrofaunal biomass and density in West Bay were consistently lower than those in East Bay. The densities of S. inflatum and Ampharete sp. increased remarkably in spring and decreased in autumn and winter, while no seasonal periodicity was found in fluctuations in den-cities of Lumbrineridae and M. sarsi. There is a general tendency that the macrofaunal biomass in offshore area attains peak in summer and lowest in winter. But such a periodicity was not found in East Bay since the autumn of 1980 because of remarkable increase in density of M. sarsi. Results of cluster analysis showed that the community structure of macrofauna in offshore area varied largely with fluctuations in abundance of dominant polychaetes by seasons and years.

Field experiments on the role of epibenthic predators in determining prey densities in an estuarine mudflat

A series of caging experiments was performed on an estuarine mudflat at three seasons of the year, in which Carcinus maenas L. and Pomatoschistus microps (Kroyer) were either excluded from, or allowed to prey upon, the benthos in order to determine to what extent infaunal abundance and mortality was a result of predation by epibenthic predators. The difficulties of conducting and interpreting the results of such experiments are recognized. The benthic macrofauna of this mudflat is dominated numerically by small annelids and there is evidence that adult C. maenas can cause significant increases in the oligochaete component of this assemblage, probably as a result of disturbance caused by its burrowing activity. Juvenile C. maenas on the other hand significantly reduced the abundance of small annelids, particularly the dominant polychaete Manayunkia aestuarina (Bourne) and could be responsible for year-to-year variations in abundance of this species. The role of fish predators (in this case P. microps) is more problematical but it is suggested that in the densities at which they occur naturally on the mudflat they have little direct effect on the abundance of prey species. There is no evidence that seasonal mortality of small annelids is reduced in the absence of predation and this is taken to indicate that not all mortality is due to epibenthic predation. Certain changes in relative abundance of the component species of the harpacticoid copepod community were discerned but it is suggested that the plasticity of their reproductive potential is such that the effect of predation on the group as a whole is usually masked.

Algal-faunal interactions in a mat ofUlva fenestratain false bay, Washington

Abstract The events associated with the annual formation of algal mats in a shallow bay were studied for 36 months. Maximum net primary production, estimated from change in weight of thalli (compound production) in mesh bags plus weight of algae which amphipods may have eaten, was 10.2% · day−1 for Ulva fenestrata and 20.8% · day−1 for Monostroma fuscum. The compound production of Ulva was 8.0% · day−1 in June and 1.4% day−1 other months. In the laboratory Eogammarus confervicolus consumed 0.21 mg Ulva · mg amphipod−1 · day−1. At this rate the amphipod population could have consumed over half of the annual net production of Ulva (46.3 metric tons). Wind and tidal patterns in the bay May through September were favorable for the formation of Ulva mats, 400–1200 g · m−2. After the mats were dispersed when environmental patterns changed in October, 8–20% of the algal biomass could be accounted for in the sediment. Numbers of the dominant polychaete, Rhynckospio glutaea, declined as the biomass of the mat increased. Oligochaete numbers declined 4–10 fold in the fall and winter as did the quantity of organic matter in the sediment.

Impact of a combined sewer overflow on the abundance, distribution and community structure of subtidal benthos

A biological survey of the subtidal fauna near an intertidal combined sewer overflow (CSO) discharging into Puget Sound, Washington, USA, was conducted during April and May, 1977. The purpose of this study was to determine the effect of the CSO on the surrounding marine invertebrate communities. The shallowest subtidal sites studied (9 m below MLLW) appeared to be more affected by the CSO than deeper sites (13 and 24 m below MLLW). The subtidal area affected, as reflected in the levels of organic material, heavy metals and pesticides in the sediments, as well as the composition of the benthic macrofauna, appeared to be highly localised. The numerically dominant species at sites closest to the CSO was the polychaete Capitella capitata while the abundance of the bivalve Axinopsida serricata increased with distance from the CSO. Burrowing deposit feeders were the numerically dominant polychaete feeding type at sites nearest the CSO. Surface deposit feeders were more abundant at sites farther from the CSO, perhaps due to reduced sedimentation rates. Site-classification analyses indicated that sites adjacent to the CSO were more similar to one another than to sites which were farther away and apparently less affected. The positions of the sites along the first three principal component ordination axes were significantly correlated with depth and volatile organics (traceable to the CSO) in the sediments.

Distribution of western beaufort sea polychaetous annelids

Depth and depth-related processes appear to exert primary control over the distributional patterns of species of polychaetous annelids in the western Beaufort Sea (Cape Halkett to Barter Island, Alaska). Species richness and total polychaete abundance are maximal along the outer continental shelf and upper continental slope. Stations exhibiting the most similar polychaete assemblages are located at similar depths. However, some species distributions appear to correlate better with sediment type than with depth. Maximum abundance occurs deeper on the continental slope to the west, and station clusters generated by non-hierarchical clustering (using the dominant polychaete species data) are not sorted strictly by depth. In a canonical analysis of discriminance, the station clusters were projected onto a two-dimensional plane in “species space”. The first and second canonical variables of the station clusters correlate with sediment grain-size distributions, suggesting a relationship between polychaete distribution patterns and the sedimentary environment. This relationship is further substantiated when sediment grain-size distributions for each station are plotted on a tertiary diagram: the stations are grouped and ordered in a pattern similar to that generated by the canonical analysis of discriminance.