Turf Communities Research Articles

Effects of unidirectional and oscillatory water flow on nitrogen fixation (acetylene reduction) in coral reef algal turfs, Kaneohe Bay, Hawaii

Rates of acetylene reduction (nitrogenase activity) by algal turf communities from Kaneohe Bay, Oahu, Hawaii, were measured as a function of increasing water flow speeds under unidirectional and oscillatory flow regimes in an enclosed incubation chamber. Water flow speeds, shear stress, and turbulence intensities were measured with thermistor probes in the chamber and over the turfs in the field. The thickness of the boundary layer varied significantly and linearly with bulk water flow speeds in the field. Although the boundary layer in the chamber also decreased with increasing flow speeds, turbulence intensity and flow speeds in the chamber were mostly lower than those typically measured in the field. Rates of acetylene reduction were positively related to water flow speed. Oscillatory water flow, which increased turbulence intensity five times, resulted in a significant increase in acetylene reduction compared to unidirectional flow. Even at the lowest mean flow speeds measured in the field (<0.1 m s −1), mean rates of acetylene reduction (27 nmol ethylene cm −2 h −1±11 SD) were high under oscillatory flow. Equivalent high rates under unidirectional flow were not achieved until flow speed was more than doubled. The slope of log–log linear regressions of acetylene reduction versus flow speed was 0.5 for both oscillatory and unidirectional regimes. This result suggests that acetylene reduction rates in the chamber were controlled by mass transfer of a rate-controlling solute, such as acetylene or oxygen (inhibitory to nitrogenase), through a laminar diffusion boundary layer. Because coral reefs exist in areas of very low nitrogen availability, nitrogen fixation is fundamentally important for coral reef primary production and biogeochemistry. Yet, current understanding of nitrogen fixation on coral reefs has been derived primarily from measurements made under unnatural conditions of no or low water flow. This study lends support to the importance of water flow as a major control of the metabolism of organisms occupying coral reefs.

Grazing effects on nitrogen fixation in coral reef algal turfs

This study addressed whether grazing by the sea urchin Diadema antillarum influenced rates of nitrogen fixation by algal turf communities on Caribbean coral reefs. Because the turfs were nitrogen-limited, we also assessed whether newly-fixed nitrogen was important for supporting net primary productivity by the turfs. We measured acetylene reduction in turfs grown in treatments excluding or including D. antillarum in the presence of other herbivores at 3 m water depth on Tague Bay forereef, St. Croix, U.S. Virgin Islands. These were the first measurements of acetylene reduction on coral reefs under quasi-natural conditions of high water-flow and photosynthetic oxygen generation. Rates of acetylene reduction under these conditions were as high as any measured previously in coral reef communities (mean 7.6 nmol C2H4 cm−2 h−1). Algal turfs grazed by D. antillarum and other herbivores had chlorophyll-specific acetylene reduction rates up to three times higher than when D. antillarum was excluded. High rates of nitrogen fixation by the turfs were sufficient to meet <2% of the nitrogen required to support net chlorophyll-specific primary productivity over 24 h. Grazer-mediated increases in nitrogen fixation do not appear responsible for a parallel enhancement of net primary productivity. Algal turfs at this site must be dependent primarily on external sources of nitrogen.

Quantum Efficiency and Photosynthetic Production of a Temperate Turf Algal Community

A preliminary investigation of the production and photosynthetic efficiency of a temperate, sub-tidal, turf algal community using in situ measurements of photosynthesis and respiration is reported. Results indicated that temperate turfs have high biomass specific productivity, but are less productive on an areal basis than either the surrounding macro-algal community or their tropical counterparts. Net 24 h production ranges between 12 and 78 mmol O2 m-2 d-1 (corresponding to a carbon fixation rate of 0.1–0.9 g C m-2 d-1). Inefficient use of the available substrata, due to the early successional nature of these communities, is considered to be the cause of this low productivity. A quantum efficiency of 0.034 µmol O2 µmol photons-1 and a sub-saturating light itensity of 134–210 µmol photons m-2 s-1 indicate that photosynthetic saturation was easily achieved and suggests that self-shading in the turf community was not significant.

Spatial Variation in an Algal Turf Community with Respect to Substratum Slope and Wave Height

A mid-shore colonial algal turf community is described. Samples were analysed to determine if species composition, invertebrate epiphyte density, algal mat biomass, and the amount of sediment trapped among algal thalli differed with respect to substratum slope and wave height.Colonial algal turf was approximately 1–3 cm in height and predominantly composed of a mixture of four species of eurythermal red algae, including Gelidium crinale (Turner) Lamouroux (Rhodophyceae: Gelidiales), Centroceras clavulatum (C. Agardh) Montagne, Polysiphonia denudata (Dillwyn) Kuetzing, and Bryocladia cuspidata (J. Agardh) De Toni (Rhodophyceae: Ceramiales). More delicate algae and algal epiphytes were found at stations with lower mean wave height, while non-epiphytic coralline algae were found only at stations with higher mean wave height. Algal mat mass was significantly greater on horizontal slopes than on vertical slopes, but did not differ with respect to wave-height levels. Algal mats trapped significantly more sediment on horizontal slopes with lower mean wave height.Densities of the three most abundant invertebrate epiphytes appeared to be related to sediment deposition. Like sedimentation patterns, disparities in population densities on different substratum slopes increased with lower mean wave height. The highest densities of the amphipods Elasmopus rapax Costa and Hyale frequens Haswell (Crustacea: Peracarida) occurred on horizontal slopes at stations with significantly lower mean wave height. The highest densities of the tree oyster Isognomon bicolor C.B. Adams (Mollusca: Pterioida) were on vertical slopes at stations with significantly lower mean wave height. Barnacle epiphytes occurred in higher densities at stations receiving greater mean wave height, while dominant species of other crustaceans and molluscs had higher densities at stations with significantly lower mean wave height.

Haraldiophyllum infossum sp. nov. (Delesseriaceae, Rhodophyta), a Diminutive Turf-forming Red Alga from the South-western Pacific

Haraldiophyllum infossum sp. nov. is a small red alga that is partially buried by sponges and ascidians in the turf community often under stands of Ecklonia radiata (C. Agardh) J. Agardh. Blades are monostromatic with conspicuously dentate margins and arise from creeping stolons. Spermatangial and tetrasporangial sori form elongate, interrupted patches along the mid-region of the blades. Features allying the new species with the genus Haraldiophyllum include growth by means of many marginal initials, blades that are monostromatic except at their base and where reproductive structures are borne, absence of microscopic veins, procarps that are scattered over the surface of the fertile frond and which are associated with two groups of sterile cells and one group of cover cells, and carposporangia that are borne singly and terminally on gonimoblast filaments

Effects of algal turf canopy height and microscale substratum topography on profiles of flow speed in a coral forereef environment

Water motion can be an important variable affecting the recruitment, metabolism, growth rates, feeding efficiency, and distribution of aquatic organisms. Recent studies suggest that flow speed may be an important factor regulating primary productivity of reef algal turf communities. We measured profiles of flow speed over algal turfs with different canopy heights and over algal turfs growing on substrata that varied in microtopography. Profiles over sea urchin‐grazed algal turfs with low canopy heights and algal turfs growing on topographical high points indicate that the boundary layer is dominated by turbulent eddies. In contrast, flow over algal turfs with higher canopy heights and those growing within depressions in the substratum is influenced more by viscous forces that may lead to diffusion‐limited metabolism of these algal communities. These data demonstrate that flow speeds over coral reef algal turfs exhibit spatial variation over small spatial scales and temporal variation that is dependent on ambient flow speeds. Our results predict microscale variation in algal turf metabolism and suggest that photosynthetic rates of this component are likely to be below maximum capacity for a significant portion of the time.

Valeriemayagen. nov. (Rhodophyta), with a discussion of apical organizations within the Delesseriaceae

Valeriemaya gen. nov. is described from subtidal habitats along the New South Wales coast of eastern Australia and assigned to the red algal family Delesseriaceae. Valeriemaya geminata sp. nov., designated the generitype, and V. maculata sp. nov. are assigned to this genus. Plants in both species form a small component of the turf community of the rocky reef flora, occurring from the lowest littoral to a death of 20 m. They consist of clusters of mostly simple, lanceolate blades arising from holdfasts that may be discoid or well-developed, spreading systems of terete, branched axes firmly clasped to the substratum. V. geminata is distinctive in having a pair of ovate tetrasporangial sori mid-way along the erect blades, a habit in which erect blades recurve toward the substratum, attaching by means of rhizoidal tufts and producing new blades, and in its lack of vesicular cells, whereas V. maculata is distinctive in having single, large, ovate, tetrasporangial sori located at the bases of the blades, a habi...

In situcarbon dioxide levels in cushion and turf forms ofGrimmia antarcticiat Casey Station, East Antarctica

Grimmia antarctici is abundant on the Bailey and Clark Peninsulas, Wilkes Land, East Antarctica. It grows as a turf in wet locations and as cushions at relatively dry sites. This paper documents substantial differences in the internal CO2 concentration of cushion and turf communities during the growing season. In November, CO2 levels in the rhizo/phylloplane of both growth forms were close to ambient (around 350 ppm). Over the next two months the levels increased tenfold in turf but remained essentially constant in cushions. This means that the actively growing shoot tips of turf would be photosynthesizing at optimal CO2 concentration (i.e. close to CO2 saturation) for most of the summer. Photosynthesis in cushions, on the other hand, would be severely limited by CO2. These findings may account for the observations of Kappen et al. (1989), made at the same field sites in January 1986, that turf photosynthesizes at higher rates than cushions under simulated field conditions and is more resistant to photoinhibition.

Ecological and Physiological Investigations in Continental Antarctic Cryptogams: I. Vegetation Pattern and its Relation to Snow Cover on a Hill Near Casey Station, Wilkes Land

Summary The vegetation of the summit region of a small ice:free hill in the inner part of the east-Antarctic Bailey Peninsula, Windmill Islands, was recorded by 105 releves along various transects. It was analysed by the Braun-Blanquet phytosociological method, by a divisive polythetic procedure and tested by an ordination analysis. An epipetric Usnea sphacelata- and a Rinodina olivaceobrunnea -moss turf community were described as distinct communities and additionally a transient community. The vegetation is highly dependent on the extension and duration of a shallow snow cover, because snow is the main water source for the poikilohydrous cryptogams. This was shown by recording regularly the changes of snow cover in 5 quadrats of the summit region. The photophilous, wind- exposed vegetation of this hill resembles ecologically that of high arctic and alpine regions. The dominance of Neuropogon species is characteristic of the Antarctic and also the Andine region, in equivalent arctic-alpine communities Umbilicaria species are the most prominent element. The epibryic and epigeic Rinodina olivaceobrunnea -moss turf community has no identical counterpart in the arctic and alpine region.

Environmental Determinants of Spatial Pattern in the Vegetation of Pb-Zn Mines in Southwestern Wisconsin

-Vegetation colonizing Pb-Zn mine waste in Wisconsin in patchily distributed with two distinct communities, open and closed turf. Analysis of environmental variables indicates that the closed turf community occurs in areas of finer soil texture, higher nitrogen and moisture levels and lower Zn concentrations. Open turf occurs on sites of greater environmental stress. Nitrogen mineralization rates are comparable between communities. Significant reduction of environmental stress occurs with advancing successional age. Soil moisture and total N increase with mine age, while Zn concentrations decline. Application of mulch to the open turf increased biomass, but no significant increase occurred after fertilization. This suggests that the factors limiting vegetation success in the open turf are related to the severe environment of the tailings surface, not to nutrient levels. Fertilization produced a biomass increase in the closed turf, but many species were unresponsive to added nutrients, a behavior consistent with characterizing them as stress-tolerant sensu Grime.

Biology of surgeonfish Acanthurus nigrofuscus with emphasis on changeover in diet and annual gonadal cycles

A 3 yr study was conducted on the feeding biology and reproductive strategies of Acanthurus nigrofuscus (Acanthuridae, Teleostei) found along the coral reefs of the Gulf of Aqaba and forming there the major biomass of algivorous fish. The diet of this surgeonfish is based on algae selected from turf communities growing on subtidal rocky surfaces. At some sites A. nigrofuscus form schools that migrate daily from nocturnal refuges in coral reefs to foraging sites on the intertidal, covering distances of 500 to 600 m. During summer the main food items are brown and red algae; in winter, lush green algae. This changeover appears to provide the food-base for accumulation of fat and recrudescence of gonadal activity initiating in March-Apnl. Reproduction occurs in large schools of 2000 to 2500 fish and on selected sites, continuing from May to September. Spawning occurs daily from 1800 to 1830 h, after which the fish depart for their night refuges. Peak of gonadal activity is in July-August, after whch an increase of pre- and postovulatory atretic bodes is prominent. In female post-spawned gonads, cysts of spermatogonia appear and remain until renewed normal activity in February-March. Histological evidence and possible explanation of this phenomenon are provided.

Environmental factors influencing decomposition rates in two Antarctic moss communities

Rates of disappearance of dead material of Polytrichum alpestre and Chorisodontium aciphyllum from a moss turf community and of Drepanocladus uncinatus, Calliergon sarmentosum and Cephaloziella varians from a moss carpet community, measured using litter bags over 2 years, were 1.5% year-1. Decomposition potential, estimated using loss in tensile strength of cotton strips inserted into the different bryophytes on the two sites, was also low. Ranking the five plant species in order of decomposition potential, from highest to lowest, gave D. uncinatus, C. aciphyllum, C. sarmentosum, P. alpestre and C. varians. The time taken for the tensile strength of the cotton strips at depths of 1–3 and 4–6 cm beneath the surface to decline by 50% varied from 1–2 years under the first two species to 3–4 years beneath the last two species. The main causes of these slow rates were low temperatures, short active season and low pH. Differences in decomposition between species, sites and with depth were related to temperature, nutrient status, water content and anaerobic conditions. Variation in anaerobic conditions beneath D. uncinatus, C. sarmentosum and C. varians in the moss carpet resulted in wide variation of decomposition rate beneath these species and with depth beneath C. varians. The peat in the moss turf was aerobic and experienced higher temperatures, but the average decomposition rate was no higher than in the moss carpet, because the peat was of a poorer quality and had a lower pH.

Relationships between primary production and ii radiance in coral reef algal communities1

Shallow water algal turf communities are the major primary producers on coral reefs. High rates of primary production are maintained despite extremely high light intensities and exposure to ultraviolet wavelengths. The relationships between the light intensity and primary production in these assemblages are typical of algae adapted to a high light environment [low α (initial slope), high Ik (saturating light intensity), and high Ic (compensation point light intensity)]. Seasonal variations in algal standing crop due to herbivory and daylength result in some characteristic photoadaptive changes in a, Ik, and Ic, and changes in Pnetmax rate s (maximum net photosynthetic rate achieved at light saturation) on both a chlorophyll a and an areal basis. Exposure to UV wavelengths results in significantly higher respiration rates but no changes in α, Pnetmax, or Ik, when compared with these parameters for the same algal communities incubated at the same light intensities without UV wavelengths. The apparent lack of photoinhibition in these algae allows calculation of the daily integrated production from the P vs. I parameters. This integrated production is highest in July (3.1 ± 0.2 g C m−2 d−1) and is reduced by 30% from this maximum in December (2.1 ± 0.1 g C m−2 d−1).

A subtidal transect in Jervis Bay, New South Wales

Long‐term variations in the intertidal algal flora of the entire rock platform at Plantation Point, Jervis Bay, are described by May (1981). The study now reported presents similar long‐term changes in the flora of a subtidal region of the same headland, observed within the same period of time.This first detailed report of subtidal macroalgal communities in New South Wales describes a several‐year study of the benthic communities along a transect in the upper sublittoral region of a rocky headland at Plantation Point, Jervis Bay.Eighty‐nine species of algae were recorded, five of which were previously unrecorded for New South Wales.The area studied is dominated by the large brown algae Ecklonia radiata and Phyllospora comosa, large areas of which were cleared periodically by storms. Turf, shade and crustose coralline algal communities also were present.Storms, seasonal variation and longer term changes all affected the abundance and distribution of the algal species growing along the transect and hence the floristic composition of the area.

Nutrient turnover studies in alpine ecosystems : IV. Communities of the Central Alps and Comparative Survey.

The nutrient relations of five treeless plant communities on acid soils above siliceous rock of the Central Alps are investigated. Three of these communities, situated on Mt. Patscherkofel, are dominated by dwarf shrubs of the Ericaceae family: Loiseleurietum (P 1, 2175 m NN), Loiseleuria heath (P 2, 2000 m NN), and Vaccinium heath (P 3, 1980 m NN). The other two are bound to higher elevations (2500 m NN, at Timmelsjoch): Caricetum curvulae (T 1), forming the mats, and Salicetum herbaceae (T 2), covering the snow-beds.Phytomass productivity decreases with increasing altitude in the sequence P 3-P 2, P 1-T 1-T 2.Compared with the turf communities of the Northern Calcareous Alps, nitrogen reserves and experimental net-mineralization of the soils (0-15 cm) are extremely low in P 1, P 2, and P 3 (<0.5 g N/m2 mineralized per GS1). The fluctuation of N in the living above-ground phytomass during the GS is also low (about 1.6 g/m2 in P 1 and P 2; 2.2 g/m2 in P 3, although it exceeds the values of net mineralization. Additional uptake through mycorrhizal fungi or activation of mineralizing microbes in the rhizosphere by exudation is assumed.The P- and K-reserves are extremely small in the humic soils of P 2 and P 3, but somewhat higher in the more mineral soil of P 1. Mean lactatesoluble P of the three sites is low (0.3 g/m2 or less) whereas Klact (2.7-3.3 g/m2) is higher than the lowest level found in some turf communities, e.g. Caricetum firmae. The amounts of P in the phytomass are in the range of those of the turf communities and agree with the gradation in the mean Plact values (P 1 and P 3>P 2). There are, however, almost no discernible fluctuations of P in the phytomass, and the K-fluctuations are far below the mean Klact level.The Timmelsjoch communities generally have higher N/C-, P/C-, and K/C-ratios in the soils compared with those of Mt. Patscherkofel, although the N-reserves (g/m2) and the K-reserves (of T 1 only) are lower. The Plact values are higher than those from Mt. Patscherkofel and also exceed those of the calcareous turf communities. Klact is low in T 1 whereas in T 2 it is in the range of P 1, P 2, and P 3. Compared with T 1, T 2 has distinctly higher amounts of the three nutrients in the soils and a higher net mineralization of N, as well as higher values in the phytomass components and in the fluctuation of the latter.In conclusion, a general view is given (Fig. 9) of the most important nutrient parameters of the communities represented in this series, including some others of lower altitudes.

A preliminary study of algal turf communities of a shallow coral reef lagoon using an artificial substratum

The growth, productivity and species composition of algal turf communities growing on glass microscope slides at various sites in the lagoon of One Tree Island,Capricorn Group, Great Barrier Reef, Australia (23° 30′ S, 152° 06′ E) were measured, and the possible use of algal communities growing on artificial substrates for ecological studies was assessed. Colonization of the bare glass slides by bacteria, green and blue-green algae was rapid. After 3 months, the slides had become covered by filamentous and crustose algae [e.g. Sphacelaria tribuloides Meneghini, Herposiphonia tenella (C. Agardh) Naegeli, Tenarea sp. etc.] and invertebrates (e.g. Spirorbis sp.). Crustose coralline algae settled evenly over the surface of the slide but were soon removed from the slide centre by grazing fish. Eventually, thicker crustose corallines [e.g. Porolithon onkodes (Heydrich) Foslie] from the less grazed edges of these slides began to overgrow the slides, providing a different substrate for growth of algal species such as Lophosiphonia spp. and Laurencia papillosa (Forsskål) Greville, etc. Various differences in species composition were observed between the different sites and depths. In general, the glass slide communities were less diverse than those on nearby natural substrates, presumably due to the hardness of the glass slides.

Snowmobile Impact on Three Alpine Tundra Plant Communities

This paper describes the effects of 1,020 passages of snowmobiles, made over two winters, on three regularly winter-snow-free alpine tundra plant communities. A cushion-plant community on a 7-degrees slope showed a 31% reduction in total living plant coverage due to snowmobile impact. Destruction was greatest to soil lichens, rock lichens, and the cushion-plants Arenaria obtusiloba, Arenaria fendleri, Paronychia sessiliflora var. pulvinata, Silene acaulis, Eritrichium aretioides, and Phlox pulvinata. Graminoids generally survived to increase in importance. On a flat site, a cushion-plant community with Kobresia myosuroides as its most important species, showed the greatest loss of living-plant coverage, namely 46%. This was due primarily to the destruction of Kobresia, although Selaginella densa, Arenaria obtusiloba, Hymenoxys acaulis, and Eritrichium aretioides, also showed heavy losses. In a Kobresia turf community, destruction was decidedly less severe than in the cushion-plant communities, reduction in total living plant coverage being only 19%. It is suggested that the closed nature of the Kobresia turf, with its stiff tussocks, enables it to absorb impact well. It is recommended that snow-mobile travel be confined to Kobresia or similar turfs, when such travel is necessary under snow-free conditions.