Emergence of chironomidae from Findley Lake in the coniferous forest of the cascade mountains after early and late thaws

Chironomidae were collected in floating emergence traps on 27.5 m deep Findley Lake in the coniferous forest of the Cascade Mountains, USA, from 1972 to 1975. There was considerable yearly variation in the date of thaw, the total number of Chironomidae that emerged and the relative abundance of each species. In 1972, 1973 and 1975 when there were early thaws, Tanytarsus and Procladius were the most common Chironomidae. Many of the common species started to emerge before the lake had completely thawed. In 1973 when most of the lake thawed June 7 and the surface water reached a maximum temperature of 19.25 °C in July, the Tanytarsus chinyensis group, Stictochironomus and Chironomus started to emerge from deep water when there was still ice along shore. Procladius nr gretis and Orthocladius started to emerge two days after the last ice had melted. In 1974 when most of the lake did not thaw until July 30–31, the surface water reached a maximum temperature of only 12.5 °C in August. Only a fifth as many Chironomidae emerged as in 1973. Most of these were Procladius and Orthocladius which had their maximum emergence when most of the lake was still frozen. The emergence of each species was reduced except Orthocladius. Procladius contributed the greatest biomass that emerged each year, but the second greatest biomass was contributed by different genera each year.     

Life cycle and production of Chironomidae (Diptera) from Lake Banyoles (NE Spain)

1. The life cycles and annual production of the eight most abundant species of chironomids (Prodadius cf. choreus, Tanypus punctipennis, Chironomus bernensis, Chironomus gr. plumosus, Cladopelma virescens, Microchironomus tencr, Tanytarsus gr. lestagei, and Cladotanytarsus atridorsum) were studied from sublittoral and profundal samples taken monthly in Lake Banyoles during 1987 at five sampling stations (depths ranging from 5 to 20 m). 2. The number of generations per year deduced from instar-frequency data varied from one to four, depending on the species, lake basin and depth. Annual temperature range, dissolved oxygen in the stratified period and presence of sulphide are the key factors that may explain the differences in the number of generations. 3. Production estimates were calculated using the size-frequency (SF) method corrected for the number of generations (SFG), and the increment-summation method (IS) when cohorts could be clearly deduced. 4. Production calculated with the SFG method gave results which were comparable with those of the IS method using smoothed-survivorship curves in the three species for which the use of the IS method was possible (C. virescens, M. tener and C. atridorsum). Using these methods production was estimated to range from 23–70 mg AFDW (ash-free dry weight) m^?2 yr^?1 at 12 m to 74–275 mg AFDW m^?2 yr^?1 in the sublittoral zone of the lake (5-m depth). 5. Calculation of production for the other five species using the size-frequency method with the number of generations (SFG) deduced from monthly instar-frequency data gave values ranging from 12 mg AFDW m^?2 yr^?1 (Chironomus bernensis at 20 m depth) to 3.75 g AFDW m^?2 yr^?1(Prodadius cf. choreus at 12 m). 6. Total chironomid production (with the SFG method) varied from 0.8 to 5 g AFDW m^?2 yr^?1 in the profundal and sublittoral, respectively. At each sampling station two species groups accounted for most of the production: Prodadius cf. choreus and Chironomus spp. Annual production/biomass ratio (P/B) varied from very high values for Prodadius (between 11 and 27, as four generations completed each year) to very low values for Chironomus gr. plumosus (2.20), which completed only one generation each year. The annual production of P. cf. choreus in Lake Banyoles is higher than any reported in the literature due to the completion of four generations and to the high densities of this species.     

The hemoglobin concentration ofChironomus cf.Plumosus l. (Diptera: Chironomidae) larvae from two lentic habitats

Hemoglobin concentrations ofChironomus cf.plumosus larvae were measured in two different habitats of the same pond. Larger larvae have higher hemoglobin concentrations than small larvae. There is strong indication that the animals of poorly oxygenated deep water, have higher hemoglobin concentrations than the animals from the well-oxygenated littoral zone.     

Chironomidae communities of the near-shore zone in Zegrzyńsky Reservoir,Poland

The structural differences in chironomid communities of the near-shore zone in Zegrzyski Reservoir corresponded to variations in sediments composition. Sandy bottom areas covered by a thin layer of mud were inhabited mostly byPolypedilum, Cryptochironomus andGlyptotendipes larvae.Cladotanytarsus andStictochironomus were often the most numerous in the shallower zone (0.2–0.5 m). Predatory Tanypodinae were found most commonly on the sandy bottom covered by well mineralized plant debris and loose silt. Extremely high numbers and biomass ofChironomus andGlyptotendipes larvae occupied the clay bottom covered by a thick layer of mud. On the basis of developmental stage distribution it was found that at least three generations ofChironomus andGlyptotendipes occurred during the study period (April–October 1988). The combined production estimate for these two taxa exceeds any reported for Chironomidae in lentic or lotic habitats.     

Growth-rates of Hippophae rhamnoides L.

Six populations of the sea buckthorn, Hippopha rhamnoides Lare sampled systematically and graphs of age against stem diameterplotted. Regression analyses are used to derive the mean girthincrease per annum for the whole of a population and for thepopulation divided according to the stem age, i e 0–10years and 11–40 years The six populations represent fivemajor edaphic types of the Spurn Peninsula (I) stable dunes,sheltered, sand depth > 1 m, (II) unstable dunes, sheltered,sand depth > 1 m; (III) unstable, exposed dunes, sand depth> 1 m; (IV) stable dunes, sheltered, sand depth < 1 mover coarse gravel and mud, (v) stable dunes, sheltered, sanddepth < 0.5 m over coarse shingle/sand mixture The annualgrowth increment for the whole population is shown to be greatestin the sheltered areas on deep sand, the highest figure recordedbeing 4.5 mm per annum The rate of growth for the plants upto 10 years old in the three populations on deep sand vanesbetween 3 88 and 4 5 mm per annum, whilst in shallow sand areasthe range is between 2 0 and 2.8 mm per annum Girth increasein plants over 10 years slows down to 2 92 mm per annum in shelteredareas on deep sand, is considerably retarded in exposed areason deep sand (1.53 mm per annum), and is least on shallow dunes(1 34 mm per annum).     

Instar distribution and biomass of Chironomidae larvae in Lago El Junco, Isla San Cristobal, the Galápagos

The distribution, abundance and standing crop biomass of chironomid larvae were determined at one-meter depth intervals along three radial transects. Samples were collected by coring soft sediments while diving. Three genera were found in the lake: Chironomus sp. (collector-filtering larvae), Ablabesmyia sp. (predatory larvae) and Goeldichironomus sp. (collector-filtering larvae). Standing crop densities of chironomids, averaged over the entire lake, varied from 30,594 larvae/m² to 11,428 larvae/m² at different depths. No statistically significant zonation in density was found for the two most common taxa, Chironomus sp. (87.8% of specimens) and Ablabesmyia sp. (9.0%), however the deepest zones (>4 m) had the lowest estimated densities. Significant differences in standing crop biomass were detected, with the 6 m depth having greatest biomass. The increase in standing crop biomass was a function of (1) lower frequency of first instars of Chironomus sp. and Ablabesmyia sp. at 6 m (2) higher average larval biomass of both species at 6 m and (3) very significant increase in average biomass of fourth instars of Chironomus sp. at 6 m compared to fourth instars at shallower depths. These results indicate that the lentic chironomids of this isolated oceanic habitat consist of a small number of species that are ecological generalists and tolerant of low oxygen concentrations.     

Influence of benthic organisms on solute transport in lake sediments

Increased inputs of nutrients into the waters of Lake Okeechobee has raised concern that the lake is becoming hypereutrophic. One aspect in understanding the overall cycling and dynamics of the nutrients in the system is the effect of benthic organisms on solute transport. Various diffusional models have been used to approximate the effect of benthic organisms on solute transport within sediments using diffusion coefficient values which represent the pooled contributions of molecular diffusion (D _s ) and enhanced solute mixing due to macrobenthos activity (D _i ). The objective of this study was to investigate the impact of benthic activity on solute transport by measuringD _s (i.e., no benthic activity) and an apparent-dispersion or mixing coefficientD _m (i.e., with benthic activity) for the four major sediment types of Lake Okeechobee, Florida using a reservoir technique. This method involved monitoring the depletion of a conservative tracer (tritiated water) from the overlying water (reservoir) resulting from transport into sediments using disturbed sediments repacked in cores (3.2 cm diam.) and undisturbed cores (3.2 to 12 cm diam.) obtained from the lake. Additional estimates ofD _m andD _s were also obtained by measuring tracer concentration profiles in the sediment cores at the end of a specified diffusion period. Molecular diffusion coefficients (D _s ) measured forrepacked cores of sand, littoral, mud and peat sediments ranged from 0.90 to 1.29 cm² d⁻¹, and estimates ofD _s were slightly higher in undisturbed cores without benthic organisms.D _m values for undisturbed cores of mud, sand and littoral sediments having macrobenthic populations ranged from 2.09 to 24.78 cm² d⁻¹; values that were 1.6 to 15 times higher than those in sediments without benthic activity. Undisturbed cores of varying diameter from mud sediments had similar estimates ofD _m for tritium; however, the undisturbed cores with larger diameters from littoral sediments yielded larger estimates ofD _m , reflecting the heterogeneity of benthic population densities and activity. Therefore,D _s estimates may not adequately represent transport processes for mud, sand and littoral sediments of Lake Okeechobee; hence careful consideration should be given to the role of benthic organisms in the overall transport of solutes across the sediment-water interface. A contribution of the Florida Agricultural Experiment Station Journal Series No. R-01150. A contribution of the Florida Agricultural Experiment Station Journal Series No. R-01150.     

Lipiniella arenicola (Chironomidae) compared withChironomus muratensis andCh. nudiventris: Distribution patterns related to depth and sediment characteristics,diet, and behavioural response to reduced oxygen concentrations

Density patterns ofLipiniella arenicola andChironomus muratensis were studied in Lake Wolderwijd (The Netherlands) using geostatistics, and compared with patterns of depth and silt contents of the sediment.L. arenicola was restricted to shallow (depth <1 m), sandy silt (silt content <5%), wind-exposed sediments.Ch. muratensis occurred all over the lake, but the highest densities were found in the sheltered silty North-West corner. Gut analyses of IV-instar larvae from the Ventjagers flats (Haringvliet, Lower Rhine-Meuse) showed thatL. arenicola fed by selectively grazing on benthic algae,Ch. muratensis by filtering and non-selective grazing, andCh. nudiventris by non-selective grazing. In the laboratory, behavioural responses to reduced oxygen concentrations were tested with the impedance conversion technique.L. arenicola was more sensitive to low oxygen concentrations (<3 mg l^–1) than bothChironomus species. It is argued that the differences in resistance to hypoxia and feeding behaviour are in accordance with the differences in distribution patterns. The restriction ofL. arenicola to the pure sand habitats is not attributable to an especially high sensitivity to low dissolved oxygen concentrations alone. Several behavioural adaptations enableL. arenicola larvae to live in the shallow, wind-exposed pure-sand habitats: the ability to select food items, tube strength, and site selection of ovipositing females or planktonic larvae.     

The production of five genera of Chironomidae (Diptera) in Lake Norman,a North Carolina reservoir

The production of five genera of chironomids collected at 4- and 8-m depths at four stations in Lake Norman, North Carolina, was estimated using the size-frequency method. To correct for multivoltinism, the estimates were adjusted by multiplying by 365/Cohort Production Interval. Ranges of production estimates (P) in milligrams dry mass m^-2 yr^-1 and production/mean annual biomass ratios (P/B ratios) for each genus over both depths were: Tanytarsus, P = 744 to 8788, P/BB = 66 to 176; Cladotanytarsus, P = 74 to 2387, P/B = 69 to 100; Stempellina, P = 19 to 412, P/ B = 74 to 132; Chironomus, P = 166 to 7293, P/ B = 50 to 70; Cryptochironomus, P = 92 to 398, P/ B = 71 to 221. These estimates are among the highest reported for chironomids, due primarily to the rapid larval development times estimated for these genera.     

Abundance,population dynamics and production of Chironomidae (Diptera) in an ul traoligotrophic lake in South Greenland

Macrozoobenthos of the ultraoligotrophic Lake 95 (61°N, 46°W, 8 ha, z_max=18 m, ) is composed of about 14 taxa dominated by 12 Chironomidae species. Abundance, life cycle, biomass and production were estimated for the six dominant taxa. Abundance declined fromca. 4150 at 2.5 m depth toca. 1400 ind m^–2 at 16 m depth and averagedca. 3200 ind m^–2 on a lakewide basis. By numbers,Heterotrissocladius changi andH. oliveri dominated the average fauna.H. changi was common at the 2.5 m and 5 m depth stations, whereasH. oliveri dominated from 5 m depth downwards. Chironomids showed mainly a 1-yr life cycle, but apparently bothHeterotrissocladius species had two contemporary cohorts with emergence in midsummer and late autumn/early spring, respectively. Average annual ratio was 4.2 and 4.6 forH. oliveri andH. changi, respectively. Annual production varied from 0.3 g ash-free dry weight (AFDW) m^–2 y^–1 at 16 m depth to 1.6 g AFDW m^–2 y^–1 at 2.5 m depthH. changi contributed 45%, fiveMicropsectra spp. 17% andH. oliveri 15% to total average production, which on a lakewide basis wasca. 1.1 g AFDW or 25 kJ m^–2 y^–1. Lake 95 thus belongs at the very low end of measured lake zoobenthic productions, which range from 10 kJ m^–2 y^–1 in Arctic lakes toca. 1600 kJ m^–2 y^–1 in highly eutrophic shallow lakes.     

Phytoplankton productivity in findley lake

Findley Lake is a dimictic, oligotrophic, subalpine lake located in the western Cascade Mountains, Washington. The lake is snow covered for most of the year so that the growing season was 3.5 months in 1971 and 4.5 months in 1972. Rapid melt of the lake's snow cover in summer allowed the sudden development of a phytoplankton productivity maximum (as measured by the ¹⁴C tracer method) of 86 mg m⁻² hr⁻¹ and a peak of 48 mg chlorophyll a per m¹ within two weeks of surface clearing in 1972, followed by a rapid decline of productivity and biomass. Annual production (between 10 October, 1971 and 21 October, 1972) was 36 g/m² in the 27.5 m water column. Autotrophic carbon assimilation during the snow-covered period was insignificant. The total production for the lake in 1972 was 530 kg carbon. The concentration of available nitrogen (NO₂ + NO₃ + NH₃ as N) at 15 m ranged from 12 to 76 mg/m³ while PO₄-P ranged from 0.5 to 8.3 mg/m³. In vitro nutrient enrichment experiments with natural phytoplankton communities from the lake indicated that while N and P together were growth limiting, P alone produced a growth response while N alone did not. Contributions to production from net-, nanno-, and ultraplankton were determined by fractional filtration of ¹⁴C-labeled phytoplankton samples. The nannoplankton, dominated by diatoms, accounted for 58% to 94% of productivity.     

The role of zoobenthos in energy flow in two shallow lakes

Net production of zoobenthos in two shallow and eutrophic lakes, i.e. the S-basin of Mývatn, Iceland (maximum depth 4.2 m, mean depth 2.3 m) and Hjarbæk Fjord, Denmark (maximum depth 6.5 m, mean depth 1.9 m) were calculated as 878 and 1093 kJ m^-2 yr^-1, respectively. The zoobenthos in both lakes was dominated by Chironomidae (Diptera) living partly as filtrators feeding on suspended particles (phytoplankton) and partly as surface feeders foraging on benthic algae and/or seston. Respiration and consumption were estimated from the literature. Net production efficiency averaged 0.41 and 0.48 in Hjarbæk Fjord and Mývatn, respectively. Ingestion was dominated by herbivorous chironomids, while detritivorous tubificids were insignificant. Zoobenthic production made up 86% of total secondary production (zooplankton plus zoobenthos) in both lakes. The trophic efficiency between net primary production and benthic net secondary production was 8% and 11% in Hjarbæk Fjord and Lake Mývatn S-basin, respectively.     

Moitessier's pea clam Pisidium moitessierianum (Bivalvia,Sphaeriidae): a cryptogenic mollusc in the Great Lakes

Pisidium moitessierianum Paladilhe, 1866, a small pea clam native to Europe, was identified for the first time from the lower Great Lakes basin based on an examination of historical collections of Pisidium performed by V. Sterki in 1894 and 1903 and new material collected during 1997 and 1998. During recent surveys, P. moitessierianum individuals were found in the St. Clair River delta, Lake St. Clair and western Lake Erie, but were not detected in the Detroit River or western Lake Ontario. Pisidium moitessierianum was collected on sand, silty sand and mud substrata from water depths ranging between 0.6 and 5.4 m. Populations occurred at an average density of 51 ind. m^–2 and included juveniles and adults. All individuals were less than 2.0 mm in length. We examined the structure of the umbos and hinge, surface sculpture and shape of the shell, and the anatomy of gills, mantle and nephridia in populations from the lower Great Lakes and Ukrainian inland basins (Dnieper River and Lake Beloye). The results indicated that the Great Lakes' pea clams match European specimens of P. moitessierianum in these conchological and anatomical characteristics. As with other nonindigenous sphaeriids in the Great Lakes, P. moitessierianum was likely introduced through shipping activities into the Great Lakes, possibly as early as the 1890s.     

The benthic communities of the saline lakes Abijata and Shala (Ethiopia)

Lake Abijata lies in a shallow depression (maximum depth 8–9.5 m); the water is green with phytoplankton and it supports large fish and bird communities. Lake Shala lies in a deep caldera (maximum depth reputedly 260 m); phytoplankton is sparse and fish and bird communities scanty.Lakes Abijata and Shala, sampled in January, 1985, had conductivities of 14 000 and 21 000 microSiemens cm^-1 at 25 °C respectively, mainly due to high sodium, carbonate and chloride ions. Calcium concentrations are very low.The benthic fauna was studied with an Ekman grab to a depth of 8.5 m in Abijata and 15.5 m in Shala and was found to be dense in both lakes but varying greatly in composition at different depths. In Abijata the benthos consisted mainly of Ostracoda and Chironomidae, and in Shala mainly of Tubificidae, Ostracoda and Chironomidae. There were very few Nematoda. No true halophilic species were found but the community consisted of euryhaline forms found also in non-saline waters. Predatory invertebrates were absent and many of the dominant species, notably of the Chironomidae, were different from those of non-saline lakes nearby.     

Scaling food chains in aquatic mesocosms: do the effects of depth override the effects of planktivory?

To assess the effects of physical dimension and planktivorous fish on phytoplankton standing crop, we repeated an experiment at different scales in plastic enclosures during summer 1995 in Lake Créteil, France. Enclosures were scaled for a constant surface (1.5 × 1.5 m) as depth was increased from 2.5 to 4.5 m. Even-link (zooplankton and phytoplankton) and odd-link (planktivorous fish, zooplankton and phytoplankton) food webs were established in both shallow and deep enclosures. Fish densities in the deep enclosures were scaled to allow comparisons with shallow ones for both in individuals m⁻² or individuals m⁻³. We explicitly designed this experiment to examine the scale-dependent behavior of the top-down mechanism of algal biomass control in lakes, and in particular to test the hypothesis of stronger cascading effects of fish on lower trophic levels at reduced depth. Both fish and enclosure size had highly significant effects on phytoplankton biomass over the duration of the experiment. No depth × fish interaction effects were observed. The presence of planktivorous fish enhanced phytoplankton biomass in both shallow and deep enclosures, although the reduction in depth generally produced a stronger effect. The mean concentration of chlorophyll a in the deep odd-link systems (ca 5 mg m⁻³) was lower than in the shallow even-link systems (ca 17 mg m⁻³). Statistical interpretation did not change when data were expressed as phytoplankton biomass per unit of surface area. Light limitation and zooplankton grazing are the most probable mechanisms explaining our results in these nutrient-enriched systems. Moreover, we found that the strength of the cascading effect of fish on plankton was not a function of depth. We believe that further studies on scaling effects should be conducted in order to improve our understanding of ecological patterns and to extrapolate results from micro/mesocosms to natural ecosystems. Received: 18 January 1999 / Accepted: 7 June 1999     

Production ecology of phyto- and zooplankton in a eutrophic pond dominated byChaoborus flavicans (Diptera: Chaobolidae)

Primary production of phytoplankton and secondary production of a daphnid and a chaoborid were studied in a small eutrophic pond. The gross primary production of phytoplankton was 290 gC m⁻² per 9 months during April–December. Regression analysis showed that the gross primary production was related to the incident solar radiation and the chlorophylla concentration and not to either total phosphorus or total inorganic nitrogen concentration. The mean chlorophylla concentration (14.2 mg m⁻³), however, was about half the expected value upon phosphorus loading of this pond. The mean zooplankton biomass was 1.60 g dry weight m⁻², of whichDaphnia rosea and cyclopoid copepods amounted to 0.69 g dry weight m⁻² and 0.61 g dry weight m⁻², respectively. The production ofD. rosea was high during May–July and October and the level for the whole 9 months was 22.6 g dry weight m⁻².Chaoborus flavicans produced 10 complete and one incomplete cohorts per year. Two consecutive cohorts overlapped during the growing season. The maximum density, the mean biomass, and the production were 19,100 m⁻², 0.81 g dry weight m⁻², and 11.7 g dry weight m⁻²yr⁻¹, respectively. As no fish was present in this pond, the emerging biomass amounted to 69% of larval production. The production ofC. flavicans larvae was high in comparison with zooplankton production during August–September, when the larvae possibly fed not only on zooplankton but also algae.     

Benthic community response (primarily Chironomidae) to nutrient enrichment and alkalinization in shallow,soft water humic lakes

A comparison of the benthic fauna found in two shallow lakes in the New Jersey Pinelands (USA) illustrated the impact of elevated pH and nutrients caused by residential and agricultural disturbance on a naturally acidic, poorly buffered aquatic environment. Detailed community analysis suggested that change in community composition was a better indicator of response to disturbance than biological diversity indices. Chironomidae (insecta) were the predominant components of the benthic macroinvertebrate assemblage of both undisturbed Oswego Lake (low pH, low nutrients) and Nescochague Lake (fluctuating pH, elevated nutrients). The genera Procladius, Tribelos, and Pagastiella dominated Oswego Lake, where as Zalutschia zalutschicola, Procladius, Dicrotendipes, and Tanytarsus dominated Nescochague Lake. Glyptotendipes was a common and unique member of the Nescochague Lake assemblage. Cluster analysis indicated that the chemical differences between lakes were the most important community determinants, although, within each lake, depth and substrate affected the local communities. Oswego Lake exhibited a depauperate nonchironomid benthic fauna typical of low nutrient, acid lakes. In turn, Nescochague Lake exhibited an enriched nonchironomid fauna including mollusks and planaria which were not found in Oswego Lake.     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Carbonate production by scleractinian corals at Aqaba,Gulf of Aqaba,Red Sea

Summary In a fringing reef at Aqaba at the northern end of the Gulf of Aqaba (29°26′N) growth rates, density, and the calcification rate ofPorites were investigated in order to establish calculations of gross carbonate production for the reefs in this area. Colony accretion ofPorites decreases with depth as a function of decreasing growth rates. The calcification rate ofPorites is highest in shallow water (0–5 m depth) with 0.9 g·cm⁻²·yr⁻¹ and falls down to 0.5 g·cm⁻²·yr⁻¹ below 30 m. Scleractinian coral gross production is calculated from potential productivity and coral coverage. It is mainly dependent on living coral cover and to a lesser extent on potential productivity. Total carbonate production on the reef ranged from 0 to 2.7 kg/m² per year, with a reef-wide average of 1.6 kg/m² perycar. Maximum gross carbonate production by corals at Aqaba occurs at the reef crest and in the middle fore-reef from 10 to 15 m water depth. Production is low in sandy reef parts. Below 30 m depth values still reach ca. 50% of shallow water values. Mean potential production of colonies and gross carbonate production of the whole reef community at Aqaba is lower than in tropical reefs. However, carbonate production is higher than in reef areas at the same latitude in the Pacific, indicating a northward shift of reef production in the Red Sea.     

Effects of temperature and sediment properties on benthic CO2 production in an oligotrophic boreal lake

1. Temperature and many other physical and chemical factors affecting CO₂ production in lake sediments vary significantly both seasonally and spatially. The effects of temperature and sediment properties on benthic CO₂ production were studied in in situ and in vitro experiments in the boreal oligotrophic Lake Pääjärvi, southern Finland. 2. In in situ experiments, temperature of the water overlying the shallow littoral sediment varied seasonally between 0.5 and 15.7 °C, but in deep water (≥20 m) the range was only 1.1–6.6 °C. The same exponential model (r² = 0.70) described the temperature dependence at 1.2, 10 and 20 m depths. At 2.5 and 5 m depths, however, the slopes of the two regression models (r² = 0.94) were identical but the intercept values were different. Sediment properties (wet, dry, mineral and organic mass) varied seasonally and with depth, but they did not explain a significantly larger proportion of variation in the CO₂ output rate than temperature. 3. In in vitro experiments, there was a clear and uniform exponential dependence of CO₂ production on temperature, with a 2.7‐fold increase per 10 °C temperature rise. The temperature response (slope of regression) was always the same, but the basic value of CO₂ production (intercept) varied, indicating that other factors also contributed to the benthic CO₂ output rate. 4. The annual CO₂ production of the sediment in Lake Pääjärvi averaged 62 g CO₂ m^?2, the shallow littoral at 0–3 m depth releasing 114 g CO₂ m^?2 and deep profundal (>15 m) 30 g CO₂ m^?2. On the whole lake basis, the shallow littoral at 0–3 m depth accounted for 53% and the sediment area in contact with the summer epilimnion (down to a depth c. 10 m) 75% of the estimated total annual CO₂ output of the lake sediment, respectively. Of the annual production, 83% was released during the spring and summer. 5. Using the temperature‐CO₂ production equations and climate change scenarios we estimated that climatic warming might increase littoral benthic CO₂ production in summer by nearly 30% from the period 1961–90 to the period 2071–2100.