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1.
Recolonisation of previously dry channels by stream invertebrates was studied in the Rakaia River during winter 1981 and summer 1982. The winter experiment continued for 42 days, with stable low flows, whereas the summer experiment was characterised by fluctuating large flows which caused it to be abandoned after 27 days. The fauna was dominated numerically by Chironomidae, a leptophlebiid mayfly (Deleatidium), and oligochaetes during the winter, and by Deleatidium alone during the summer. Recolonisation was considered complete after 33 days in winter and 15 days in summer. Flow fluctuations were the main factor affecting colonisation rates, and it was assumed that drift was the main source of colonising animals. Small freshes during low‐flow periods in winter resulted in a rapid increase in total density of invertebrates and number of taxa present and also affected the population structure of Deleatidium larvae in colonisation baskets. Before these freshes numbers had increased steadily over a 27 day period. In summer large floods during high flow periods initially decreased benthic invertebrate numbers in samples but numbers increased rapidly once the flood had passed. This appears to be the first study of its kind on a large unstable river system.  相似文献   

2.
The effects of the 3 main wastewater discharges on the benthic fauna of the Manawatu River were studied between March 1979 and January 1980. At least 4 replicate Surber samples were taken from each of 6 sites, on 5 occasions during this period. Deleatidium sp. (Ephemeroptera), Hydora sp. (Coleoptera), and the Chironomidae were the most useful indicator organisms, according to a ranking system based on the occurrence of significant differences (P<0.05) between populations at different sites. These taxa exhibited significant differences between sites in about 70% of all inter‐site comparisons, using Mann‐Whitney U‐tests. The Coefficient of Similarity was successful at summarising the comparisons between the clean‐water and down‐stream sites, ranging between 95% similarity to the clean‐water site for a recovery site in winter, and less than 10% similarity to the clean water site for the lower reaches in summer. It is suggested that relative indices may be more appropriate than absolute indices for measuring water pollution. Water quality, indicated by species diversity, was generally good (allowing for the effects of agricultural runoff), although midsummer organic loading induced marked changes in benthic species composition, including the disappearance of Deleatidium sp. from several sites.  相似文献   

3.
Drift was collected over 24‐h periods in five rivers in South Island, New Zealand, to determine whether diel periodicity was consistent across a range of river types, and whether the pattern was similar for different life stages/sizes of selected taxa. Total drift density (numbers per 100 m3 ) of aquatic invertebrates was greater at night than during the day in all rivers; peak abundance occurred shortly after sunset in clear water rivers and shortly before sunrise in a turbid, glacier‐fed river. Densities of drifting Deleatidium spp., Nesameletus spp. (both Ephemeroptera), Aoteapsyche spp., and Hydrobiosidae (both Trichoptera), were generally greater at night than during the day. However, the timing of peak abundance in the drift for other common taxa varied between rivers. Larger Deleatidium spp. larvae (> 1.00 mm head width) were more common in the drift at night than during the day in all rivers. However, this was not apparent for Aoteapsyche spp. and Hydrobiosidae, for which diel differences in the size of drifting animals were not consistent even within the same river. The propensity for some aquatic invertebrates to drift at night may influence fish feeding behaviour, particularly with respect to the timing of feeding and the species or life history stages of their prey.  相似文献   

4.
人工参礁在中国刺参(Apostichopus japonicus (Selenka))养殖业中被广泛应用,本文调查了2008年春、秋季刺参池塘中一种塑料人工礁表面的生物群落结构.采用沉积物捕捉器的方法调查了刺参池塘人工礁表面碳、氮、磷的循环及参礁的生态特征.结果表明,春季礁体底栖动物生物量及生物多样性高于秋季,底栖动物均集中在礁体外表面的缝隙内,4月礁体表面颗粒物,底泥沉积物总有机碳(TOC)平均含量分别为41.9 mg/g 和2.45 mg/g;总氮(TN)平均含量分别为4.1 mg/g 和0.2 mg/g.10月礁体表面颗粒物,底泥沉积物 TOC 含量分别为27.5 mg/g 和3.1 mg/g; TN 平均含量分别3.1 mg/g 和0.3 mg/g.4月 TOC, TN 沉积量分别达到711.2 mg/(m2·d)和70.7 mg/(m2·d);10月 TOC, TN 沉积量分别为804.9 mg/(m2·d)和87.3 mg/(m2·d).4月人工礁表面叶绿素/脱镁叶绿素(Chl a/Pheophytin)>1,表明礁体活体藻类较多.10月人工礁表面 Chl a/Pheophytin<1表明礁体表面降解颗粒物质较多.人工礁为刺参提供遮蔽场所,其表面生物膜为刺参提供优质食物,同时可增加池塘底面积,增强养殖系统稳定性.  相似文献   

5.
Abstract

The water chemistry, flora, and fauna of Lake Rotokawa (38° 37.8’ S, 176° 11.2'E) was studied in 1975–76. The mean pH is 2.1 and thermal inflows may elevate the mean summer temperature of the surface waters 4.2°c above that of nearby cold water Lake Rotongaio (18.9°c). The temperature range of surface water was from 10.1 °c in winter to 23.1°c in summer. The major anions were SO4 2? 679 g.m?3, and Cl‐ 314 g.m?3. Mean concentrations of major cations were Na+ 224 g.m?3, K+ 28.9 g.m?3, Ca2+ 13.3 g.m?3, and Mg2+ 2.6 g.m?3.

Two species of flagellate algae were recorded, of which Euglena anabaena was predominant. Only two benthic macroinvertebrates were found, larvae of Chironomus zealandicus, mean density 253 per square metre, and Helobdella sp., 1.3 per square metre.

The Parariki Stream was influenced by thermal springs in its upper and lower reaches, being cooler (24–25°c) about halfway along its length than near its source (27.8–39.0°c) or confluence (26.5°‐28.0°c) with the Waikato River. In the cooler stretch of the stream where unidentified benthic algae were not limited by high temperature, chlorophyll and total pigment increased from 3.9 to 377.9 mg.m?3 and from 17.5 to 534.4 mg.m?3 respectively, and nutrient levels fell (NO3‐N, 22–10.5 mg.m?3; NH4‐N, 6440–230 mg.m?3; and PO4‐P, 51–19 mg.m?3).  相似文献   

6.
江苏小庙洪牡蛎礁大型底栖动物多样性及群落结构   总被引：1，自引：1，他引：0  
基于2011年春季的生态调查资料,报道了江苏小庙洪自然潮间带牡蛎礁大型底栖动物的多样性及其群落结构。通过16SrDNA基因序列分析发现,在小庙洪牡蛎礁内分布有3种牡蛎(熊本牡蛎Crassostrea sikamea、近江牡蛎C.ariakensis和密鳞牡蛎Ostrea denselamellosa),其中分布于潮间带区的造礁活体牡蛎为熊本牡蛎,其平均密度和生物量分别为(2199±363)ind/m2和(12361±1645)g/m2。在该牡蛎礁内记录到定居性大型底栖动物(不包括3种牡蛎)共计43科66种,礁体大型底栖动物的总栖息密度和生物量分别达到(2830±182)ind/m2和(499.59±35.41)g/m2,显著高于邻近的软相潮间带泥(沙)质滩涂[密度(102±29)ind/m2;生物量(53.10±22.80)g/m2]和潮下带泥滩[密度(140±60)ind/m2;生物量(43.23±22.37)g/m2](P<0.001)。  相似文献   

7.
长江河口北支上口不规则周期潮流的动力机制   总被引：1，自引：1，他引：0  
裘诚  朱建荣 《海洋学报》2012,34(5):20-30
数值模拟和动量分析长江河口北支上口枯季大潮期间 1 d内出现"四涨四落"不规则周期涨落潮流现象。长江河口北支上口 1日内两次涨潮流和两次落潮流为常规涨落潮流,受外海半日潮流控制,两次涨潮流和落潮流为非常规涨落潮流。北支上口非常规的涨潮流处于南支落潮的末期,范围小,流速弱,历时约2 h;表层主要是垂向黏滞项和水平扩散项与正压项间的作用,南向的垂向黏滞项起着决定的作用,底层则是斜压项与正压项间的作用;北支上口非常规涨潮流是北风、盐度锋面产生的南向斜压压强梯度力和南支末期落潮流的牵引作用共同造成的;径流抑制非常规涨潮流的产生,持续时间随径流量的增加呈指数递减,当径流量达到22 300 m3/s时,非常规涨潮流现象消失。北支上口非常规落潮流处于南支涨潮流的初期,由于在北支上口南支的涨潮流早于北支涨潮流,导致南支水体进入北支,形成北支上口第二次落潮流,范围较大,流速较强,历时约2.5 h,从表层至底层主要是垂向黏滞项与非线性平流项和正压项之间的作用。本文揭示了北支上口 1 d内出现"四涨四落"不规则周期涨落潮流的动力过程和机制。  相似文献   

8.
Lobster impoundments are dammed coastal embayments utilised to hold American lobsters (Homarus americanus) before shipping to market. The impacts of lobster impoundments on the environment have not been previously studied. Here, the digestive functioning of American lobsters was examined to assess the quantity and quality (TVS, total volatile solids) of lobster faeces produced under the temperatures and feeding regimens these animals were subjected to during the impoundment period. Overall it was determined that quantity and quality of faeces did not differ among the experimental temperatures (5, 10, and 15°C), and that animals fed every 1–2 days produced greater quantity and quality of faeces than those fed every 3–18 days, or those animals fed less than every 18 days. As a first estimate of organic matter production in active lobster impoundments, it was calculated that a typical lobster impoundment produced 0.79 ± 0.35 (average ± 1 SD) g TVS m‐2 day‐1 during the impoundment period, equivalent to 3.11 ± 0.60% of the total weight of lobsters stocked into the impoundment. This level of organic matter production is below the level produced by other aquaculture operations, and that at which benthic impacts might be expected.  相似文献   

9.
Infaunal bivalve molluscs on the flood tidal delta of Tauranga Harbour, north‐eastern New Zealand, were surveyed twice over a 6‐month period, with the aim of assessing shellfish resources, assessing the magnitudes of temporal and spatial variability in abundances, and identifying potentially important processes. The surveys identified a total of 31 bivalve taxa from 27 sites. Species richness per site ranged between 0 and 9, and varied greatly in space and time, as did two other measures of diversity. Extremely high densities of bivalves (>20 000 m‐2) were encountered at several sites. Densities of several abundant species varied greatly in time, as a result of recruitment pulses. The abundances of the three species that dominated the fauna (Paphies australis, Tawera spissa, and Ruditapes largillierti) had characteristic spatial scales on the order of 200 m. Comparisons of size frequency distributions for individual sites suggested that mortality or emigration in the first year of benthic life was high. Substantial populations of bivalves occur on Centre Bank, and the most abundant of these are greatly influenced by events early in their lives.  相似文献   

10.
Silicic acid (DSi) benthic fluxes play a major role in the benthic–pelagic coupling of coastal ecosystems. They can sustain microphytobenthos (MPB) development at the water–sediment interface and support pelagic diatoms when river DSi inputs decrease. DSi benthic fluxes have been studied at the seasonal scale but little is known about their dial variations. This study measured the amplitude of such variations in an intertidal area over an entire tidal cycle by following the alteration of DSi pore water concentrations at regular intervals over the flood/ebb period. Furthermore we independently estimated the potential DSi uptake by benthic diatoms and compared it to the variations of DSi pore water concentrations and fluxes. The microphytobenthos DSi demand was estimated from primary production measurements on cells extracted from the sediment. There were large changes in DSi pore water concentration and a prominent effect of tidal pumping: the DSi flushed out from the sediment at rising tide, occurs in a very short period of time, but plays a far more important role in fueling the ecosystem (800 μmol-Si m−2 d−1), than diffusive fluxes occurring throughout the rest of the tidal cycle (2 μmol-Si m−2 d−1). This process is not, to our knowledge, currently considered when describing the DSi cycling of intertidal sediments. Moreover, there was a large potential MPB requirement for DSi (812 μmol-Si m−2 d−1), similar to the advective flow periodically pumped by the incoming tide, and largely exceeded benthic diffusive fluxes. However, this DSi uptake by benthic diatoms is almost undetectable given the variation of DSi concentration profiles within the sediment.  相似文献   

11.
Abstract. Cell‐specific fluorescence characteristics were used to characterize the light tolerance of the toxic benthic dinoflagellate Gambierdiscus toxicus. The fluorescence parameter Fv : Fm was measured using pulse amplitude modulation (PAM) fluorometry on individual cells collected from foliose red algae growing in the sub‐tidal margin of South Water Cay, Belize. Samples were collected over several days during sunny and cloudy conditions and compared to samples incubated in situ. The data from individual cells were used to generate both Fv : Fm frequency histograms and averages. Maximum individual cell values of Fv : Fm reached 0.81 in pre‐dawn samples, a value near the theoretical maximum for PAM fluorometry. In field samples from macroalgal hosts, average Fv : Fm values declined only slightly during the day, but cells incubated in bottles under 47 % incident sunlight showed a significant mid‐day depression. In freshly collected samples, near‐maximum Fv : Fm values could be found in individual cells during the entire day; however, the frequency histograms indicated a greater range in Fv : Fm values during the afternoon than in the morning. In contrast, cultures of G. toxicus showed a tight distribution around a mean. Field samples showed a rapid recovery to near‐maximum Fv : Fm within 2 min when assayed using a standardized actinic light series. Similar results were obtained in laboratory cultures of G. toxicus grown at 73 µmol photons · m‐2 · s‐1, but not at 383 µmol photons · m‐2 · s‐1. These data provide empirical support for suggestions that G. toxicus exploits the three‐dimensional structure of the algal host thallus to minimize light exposure. This strategy permits G. toxicus, a high‐light intolerant species in culture, to thrive in shallow, well‐lit tropical seas. It may also partially explain the observed preference of G. toxicus for complex, foliose macroalgae as hosts.  相似文献   

12.
Five stations along a transect from the western shore of Biscayne Bay, Florida to the Florida Current were sampled monthly for one year. The variability and amount of seston particulate organic carbon, adenosine triphosphate, chlorophyll a, primary production and zooplankton decreased along the seaward transect. The greater inshore biomass and variability of seston were the result of the allochthonous input of detritus and inorganic nutrients via terrestrial runoff. Annual primary production in this subtropical coastal lagoon ranged from 13 to 46 g C m?2 yr?1. Chlorophyll a in the bay ranged from 1 to 3 mg chlorophyll a m?2. In contrast, chlorophyll a in the surface centimetre of the sediment ranged from 50 to 300 mg chlorophyll a m?2. In this clear, shallow (2 to 3 m), oligotrophic lagoon, over 90% of total primary production is by submerged macrophytes and benthic algae. The high zooplankton biomass in the bay is most likely sustained by macrophyte detritus and the resuspension of benthic diatoms by the high winds associated with summer squalls and winter cold fronts.  相似文献   

13.
Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH4) and nitrate (NO3) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO3, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with 14C-based sediment accumulation rates and dry bulk density. Average NH4 and NO3-effluxes were 7.4 ± 19 μmol m−2 d−1 (n = 7) and 52 ± 30 μmol m−2 d−1 (n = 14), respectively, during the period 1996–2000. During the same period, the DON-flux was 11 ± 5.6 μmol m−2 d−1 (n = 5) and the denitrification rate was 5.1 ± 3.0 μmol m−2 d−1 (n = 22). Temporal and spatial variations were only found in the benthic NO3 fluxes. The average burial rate was 4.6 ± 0.9 μmol m−2 d−1. On average over the sampling period, the recycling efficiency of the PON input to the sediment was 94% and the burial efficiency hence 6%. The DON flux constituted 14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 ± 5 and 7 ± 1 Tg N year−1, respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3–12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean.  相似文献   

14.
In December–January of 2010 the spatial distribution of the phytoplankton production characteristics was studied along transects in the vicinity of the Greenwich meridian (I) and in the Drake Passage (II). On transect I, the surface chlorophyll a concentration and primary production varied from 0.11 up to 3.57 mg/m3 and from 4.38 up to 37.47 mgC/m3 per day, respectively. The chlorophyll a in the photosynthetic layer and the integrated primary production varied from 10.7 up to 66.1 mg/m2 and from 83 to 646 mgC/m2 per day, respectively. On transect II in the surface layer, the chlorophyll a concentration changed within the range of 0.09–1.02 mg/m3 and the primary production ranged from 2.08 to 9.49 mgC/m3. The integrated values ranged from 6.32 to 38.29 mg/m2 and from 41 to 221 mgC/m2 per day, respectively. The moderate means of themaximum quantum yield (F v/F m) on transects I and II (0.41 and 0.35, respectively) testify to the low activity of the phytoplankton’s photosynthetic apparatus. The studied water areas in the Southern Ocean differed both in the phytoplankton biomass expressed in the chlorophyll a concentration values and in the conditions of the primary production formation.  相似文献   

15.
Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m−2) is similar to phytoplankton production (6–10 g C m−2). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m−2 yr−1. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m−2 yr−1 is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m−2 yr−1 of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m−2 yr−1 was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.  相似文献   

16.
Data are presented on biomass, mortality, growth, and production of fish populations inhabiting two small streams in the Wairarapa district of the North Island of New Zealand. The main water of both streams contained a mixed population of bullies (Philypnodon breviceps Stokell), brown trout (Salmo trutta Linn.), and eels (Anguilla dieffenbachii Gray, and A. australis schmidtii Phillipps). The headwater tributaries of one of the streams contained a large population of Galaxias divergens Stokell and a few eels, but other fish species were absent. All species of fish appeared to be using the same food supply of small benthic invertebrates, mainly ephemeropteran and dipteran larvae. Biomass of benthos per unit area was appreciably higher in the headwater tributary examined than in the main waters downstream. Mean annual stock of benthos in the tributary (Hinau north branch) was 19.75 g/m2, in the Hinau main water 10.71 g/m2 and in the Hinaki main water 13.47 g/m2 Nevertheless, production per unit area from the nearly monospecific fish population in the Hinau north branch (14.28 g/m2) was less than that of the mixed populations in the main waters (24.17 g/m2 in the Hinau, 73.54 g/m2 in the Hinaki). Possibly fish production in the headwaters might be greater if the species composition of fish was more diverse.  相似文献   

17.
During three icebreaker cruises in the Arctic Ocean under different sea-ice conditions in 2002, undisturbed benthic surface sediments were collected and assayed for the presence of a short-lived (t1/2=53 d), particle-reactive cosmogenic radionuclide, 7Be, that is solely derived from atmospheric deposition. Under largely ice-covered conditions in May–June 2002, we did not detect this radionuclide in benthic surface sediments, despite significant inventories present in ice-rafted snow on the overlying sea ice (mean=86.8 Bq m−2±32.0 SD; n=9). During the July–August 2002 Shelf–Basin Interactions (SBI) cruise aboard the USCGC Healy and during a simultaneous cruise of the CCGS Sir Wilfrid Laurier on the Bering and Chukchi Shelf, which occupied the same general region following retreat and dissolution of Arctic ice cover, the 7Be present in this snow as well as surface deposition on to the sea ice-free water surface was detected in many benthic surface sediments, including some as deep as 945 m in Barrow Canyon. Inventories of 7Be in sediments were as high (60 Bq m−2) as the entire decay-corrected inventory present earlier in some snow samples collected on the sea-ice cover. Other deposition indicators such as the inventories of sediment chlorophyll, sediment oxygen respiration rates and 234Th-derived export fluxes also showed post-ice melt particle deposition and vertical transport, but in most cases the 7Be deposition was not tightly correlated with these other indicators, suggesting that 7Be sedimentation may not be controlled by the same processes. Our observations indicate that materials in sea ice, including contaminants, particulate organic, and mineral matter originating from atmospheric deposition or entrained in continental shelf sediments and rafted onto sea ice, can be rapidly transported to depth. The re-distribution of these materials as sea-ice drifts and eventually melts has the potential for impacting Arctic Ocean biogeochemical cycles and contaminant concentrations in areas of the Arctic remote from the original point of deposition.  相似文献   

18.
In situ measurements of ammonium and carbon dioxide fluxes were performed using benthic chambers at the end of spring and the end of summer in two soft-bottom Abra alba communities of the western English Channel (North Brittany): the muddy sand community (5 m, about 10% of surface irradiance) and the fine-sand community (19 m, about 1% of surface irradiance). High rates of ammonium regeneration were measured in the two communities at the end of summer (296.03±40.07 and 201.7±62.74 μmolN m−2 h−1, respectively) as well as high respiration rates (2.60±0.94 and 2.23±0.59 mmolC m−2 h−1, respectively). Significant benthic gross primary production (up to 6.11 mmolC m−2 h−1) was measured in the muddy sand community but no benthic primary production was measured in the fine-sand community. It suggests that microphytobenthic production values used in simulations previously published for these two communities were overestimated while values of community respiration were underestimated. The study confirms that this benthic system is heterotrophic and strengthens the idea that an important pelagic-benthic coupling is required for the functioning in such coastal ecosystems.  相似文献   

19.
The composition, density and community structure of the benthic macrofauna were investigated in sediments of the Campeche Canyon in the SW Gulf of Mexico. Total macrofaunal density ranged from 9466±2736 ind m−2 at the continental shelf station to 1550±195 ind m−2 in the canyon. Density values significantly diminished with distance from the coast and depth; only a few stations in the center of the canyon displayed larger density values (E-37 with 4666±1530 ind m−2, E-36 with 5791±642 ind m−2 and E-26 with 6925±2258 ind m−2). Densities were positively correlated to organic nitrogen in the sediment (r=0.82) and coarse silt (r=0.43), and negatively with depth (r=−0.74) and distance from the coast (r=−0.68). At all stations, the polychaete worms contributed most to the multi-species community structure. The nematodes and Foraminifera displayed their highest densities in the center of the canyon. The biomass values declined significantly with depth. We conclude that the macrofauna density and biomass changed in response to organic matter contents in the sediment, both with distance from the coast and with depth.  相似文献   

20.
The effects of New Zealand freshwater crayfish or koura (Paranephrops planifrons: Parastacidae) on organic matter processing, sediment accumulation, and benthic invertebrate communities were investigated using four replicate treatments of 0 (control), 4–5 (medium), and 8–11 (high) similar‐sized koura in 0.5 m2 artificial stream channels colonised by benthic invertebrates from a pasture stream, Waikato, New Zealand. Wineberry (Aristotelia serrata) leaf packs were placed in each channel and after 7 weeks the leaf matter remaining was significantly lower in both medium and high koura channels than in controls. The amount of sediment (surficial cover by fines and weight of suspendable sediment) was also significantly reduced in high koura density channels. Densities of invertebrates other than crayfish were not significantly different among treatments; however, taxa richness and invertebrate biomass were significantly lower in high koura channels than in controls. Our results suggest that freshwater koura may play a keystone role in structuring benthic invertebrate communities either directly through predation, or indirectly by sediment bioturbation and increasing organic matter processing rates.  相似文献   

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