Competition between red kangaroos (Macropus rufus) and sheep (Ovis aries) in the arid rangelands of Australia

Abstract Competition between red kangaroos and sheep in the more arid areas of Australia was examined by means of a large-scale manipulative experiment incorporating two replicates of each of three treatments: sheep-only, kangaroo-only and a sheepAangaroo mixture. The study was conducted over two years during which time pasture conditions varied markedly. Competition was intermittent, occurring only during a period of climatically related food depletion (semi-drought). At this time there was a large increase in kangaroo densities due to an influx of kangaroos from neighbouring areas. Competition reduced live-weight in sheep but had no significant impact on wool production. This effect was linked to diet selection. Competition caused red kangaroos to favour paddocks destocked of sheep but had no detectable effect on the condition of kangaroos.     

Diet overlap between small ruminants and the European hare in a Mediterranean shrubland

Seasonal diets of goats, sheep and European hares (Lepus europaeus) were examined using microhistological analysis of feces collected when these herbivores grazed together in a typical Mediterranean shrubland. Approximately half of the total diet content of goats was shrubs (mainly kermes oak, Quercus coccifera), while that of hares was grasses (mostly brush grass, Chrysopogon gryllus). Sheep had a more balanced diet consisting mainly of grasses, forbs, and shrubs. Dietary overlap between goats and sheep was high throughout the year. In contrast, there was very low dietary overlap between small ruminants and hares. Dietary diversity was high in spring and low in winter across all species, with sheep in general displaying higher dietary diversity across all seasons than goats and hares. Goats had intermediate and hares had low dietary diversity across all seasons. Communal grazing by small ruminants and hares ensures that there is a more uniform use of the available forage resources than if a single herbivore is left to graze an area.     

Water usage and diet preferences of free ranging kangaroos, sheep and feral goats in the Australian arid zone during summer

In much of the arid rangelands of Australia the common large mammalian herbivores are the native marsupials, the Red kangaroo ( Megalein rufa ) and the Euro ( Mucropus robustus ), and the introduced eutherian species, the domestic sheep ( Ovis aries ) and the feral goat ( Capra hircus ). In the north west of New South Wales a study was carried out to examine the patterns of water usage during summer of these species when they were free ranging in the same area. Drinking frequencies, water turnovers, electrolyte concentrations and diet preferences were determined and information obtained on movements and dispersal from watering points.
The marsupials had a much lower water usage than either of the eutherians. The tritiated water turnover of the goats was three times and that of the sheep four times the value obtained for kangaroos. While much of the difference between the marsupials and eutherians appeared to be due to fundamental physiological differences the high water usage of sheep was in part related to the high intake of halophytic plants in their diet.
The water turnovers of the Red kangaroos and Euros were not found to be different. Drinking studies and urine osmolalities suggested, however, that the open plains dwelling Red kangaroos had a higher water requirement than the hill inhabiting Euro.
The principal components of the diets of the Red kangaroo were grasses; of the Euro, grasses and shrubs; of goats, trees and shrubs; of sheep, halophytic shrubs.     

Water use and feeding patterns of the marsupial western grey kangaroo (Macropus fuliginosus melanops) grazing at the edge of its range in arid Australia,as compared with the dominant local livestock,the Merino sheep (Ovis aries)

Western grey kangaroos (Macropus fuliginosus melanops) are large, foregut fermenting herbivores common to Australia's southern woodlands and shrublands, but they extend well into semiarid habitats at the north-eastern edge of their range. At this range boundary, western grey kangaroos occupy open chenopod (saltbush) shrubland, along with Australia's other large native kangaroos, as well as with extensive pastoral stock, primarily the wool-breed merino sheep. In this habitat, within a large naturally vegetated enclosure (16 ha), western grey kangaroos grazing sympatrically with merino sheep spent much of the day resting under shade trees, and fed mainly during the evening and early morning, mainly on grasses and flat-leaved chenopods. On this diet, western grey kangaroos had water turnovers similar to those of red kangaroos, at 1.1 L d⁻¹. Sheep, however, used 7.7 L of water each day. Thus, although the sheep were twice the average body mass of kangaroos, the sheep used more than seven times as much water. This level of water use by sheep was almost half that previously reported for sheep at the same site feeding mainly on salt-laden chenopods (ca. 12 L d⁻¹), but was consistent with other studies showing lower water usage by sheep feeding on trees and low-salt shrubs; foregut (rumen) contents of our sheep comprised 35% tree browse. Overall, our data do not support suggestions that western grey kangaroos are limited mainly by water at this arid range-boundary. Notably, the western grey kangaroos’ feeding behaviours were consistent with those of other arid-zone kangaroos, highlighting distinctive differences in the ecological physiology of the foregut fermenting kangaroos and the ruminant sheep.     

Trophic interactions between two medium-sized mammals: the case of the native Dolichotis patagonum and the exotic Lepus europaeus in a hyper-arid ecosystem

As medium-sized herbivores, the exotic Lepus europaeus (European hare) and the native Dolichotis patagonum (mara) have been considered ecological equivalents. These species coexist in Ischigualasto Provincial Park, a hyper-arid ecosystem with scarce food resources. Our objective was to evaluate diet composition, relationship between diets and food availability, and trophic relationships between both herbivores. Collection of feces and vegetation sampling were made in the Mesquite woodland community. Diet composition was analyzed by microhistological analysis of feces. In both seasons, shrub species represented the most abundant cover type in the area, and annual forbs and grasses appeared in the wet season. Herbivores showed similar dietary ecology: shrubs were the main food items along the year, showing a higher plasticity compared to their diets in other ecosystems, where they selected mostly grasses. The mara selected shrubs such as Atriplex sp. and Prosopis torquata, whereas the European hare selected Cyclolepis genistoides, Atriplex sp., and Bulnesia retama. During the wet season, both herbivores supplemented their diets with grasses and annual forbs. In the dry season, there was increased consumption of cacti, such as Tephrocactus sp. The mara and the European hare are likely close ecological equivalents, in terms of dietary similarity, and they showed strong dietary overlap across the dry season (over 60 %). Thus, we can assume the existence of a potential trophic competition between mara and European hare, especially during the season when food resources are scarce. These results can be important for the management of drylands in South America, where populations of threatened herbivorous species, such as the mara, coexist with exotic animals, sharing spatial and trophic resources even in protected areas.     

Modelling digestive constraints in non-ruminant and ruminant foregut-fermenting mammals

It has been suggested that large foregut-fermenting marsupial herbivores, the kangaroos and their relatives, may be less constrained by food intake limitations as compared with ruminants, due mainly to differences in their digestive morphology and management of ingesta particles through the gut. In particular, as the quality of forage declines with increasing contents of plant fibre (cellulose, hemicelluloses and lignin; measured as neutral-detergent fibre, NDF), the tubiform foregut of kangaroos may allow these animals to maintain food intakes more so than ruminants like sheep, which appear to be limited by fibrous bulk filling the foregut and truncating further ingestion. Using available data on dry matter intake (DMI, g kg(-0.75) d(-1)), ingesta mean retention time (MRT, h), and apparent digestibility, we modelled digestible dry matter intake (DDMI) and digestible energy intake (DEI) by ruminant sheep (Ovis aries) and by the largest marsupial herbivore, the red kangaroo (Macropus rufus). Sheep achieved higher MRTs on similar DMIs, and hence sheep achieved higher DDMIs for any given level of DMI as compared with kangaroos. Interestingly, MRT declined in response to increasing DMI in a similar pattern for both species, and the association between DMI and plant NDF contents did not support the hypothesis that kangaroos are less affected by increasing fibre relative to sheep. However, when DEI was modelled according to DDMIs and dietary energy contents, we show that the kangaroos could meet their daily maintenance energy requirements (MER) at lower levels of DMI and on diets with higher fibre contents compared with sheep, due largely to the kangaroos' lower absolute maintenance and basal energy metabolisms compared with eutherians. These results suggest that differences in the metabolic set-point of different species can have profound effects on their nutritional niche, even when their digestive constraints are similar, as was the case for these ruminant and non-ruminant foregut fermenters.     

Dietary Overlap Between Huemul and Livestock in Los Alerces National Park,Argentina

ABSTRACT We evaluated the potential for interspecific competition for forage between huemul (Hippocamelus bisulcus) and livestock in Los Alerces National Park, Argentina. We studied winter diets based on microhistological analysis of fecal samples. Huemul selected herbs and shrubs, sheep showed preference for herbs and grasses, and cattle selected grasses. As predicted for small-bodied species, huemul had a narrower dietary niche than did larger bodied cattle. Competition for forage would be more likely between huemul and sheep than between huemul and cattle. Our results might be helpful to managers in areas where domestic and wild ungulates live in sympatry in order to reduce competition, especially in wintering areas where food is scarce.     

Spatial and Dietary Overlap Creates Potential for Competition between Red Snapper (Lutjanus campechanus) and Vermilion snapper (Rhomboplites aurorubens)

Understanding the complex nature of direct and indirect species interactions is a critical precursor to successful resource management. In the northern Gulf of Mexico fisheries ecosystem, red snapper (Lutjanus campechanus) and vermilion snapper (Rhomboplites aurorubens) are two commercially harvested species within a larger reef fish complex. These two species share similar habitats and diets; however, little is known about how these species partition habitat and dietary resources. In this study we examined the extent of spatial and dietary overlap between red snapper and vermilion snapper, and experimentally compared their feeding behavior. Field data from multiple gear types demonstrates that red snapper and vermilion snapper frequently cohabited reefs in the northern Gulf of Mexico, and Pianka’s niche overlap indices suggest significantly overlapping diets. Experimental manipulations show that red snapper are the dominant forager of the two species, as red snapper foraging alone ate more shrimp per fish than vermilion snapper in both the single species (p = 0.003) and mixed species (p = 0.02) treatments. In addition, red snapper ate significantly more shrimp per fish in the mixed species treatment than in the single species treatment (p = 0.04). Vermilion snapper shrimp consumption per fish did not differ significantly between mixed and single species treatments. Cumulatively, our results suggest that spatial and dietary overlap could lead to competition between red and vermilion snapper in the study area; however, conclusively determining the existence of such competition would require further research.     

Thermoregulation by kangaroos from mesic and arid habitats: influence of temperature on routes of heat loss in eastern grey kangaroos (Macropus giganteus) and red kangaroos (Macropus rufus)

We examined thermoregulation in red kangaroos (Macropus rufus) from deserts and in eastern grey kangaroos (Macropus giganteus) from mesic forests/woodlands. Desert kangaroos have complex evaporative heat loss mechanisms, but the relative importance of these mechanisms is unclear. Little is known of the abilities of grey kangaroos. Our detailed study of these kangaroos' thermoregulatory responses at air temperatures (T(a)) from -5 degrees to 45 degrees C showed that, while some differences occur, their abilities are fundamentally similar. Both species show the basic marsupial characteristics of relatively low basal metabolism and body temperature (T(b)). Within the thermoneutral zone, T(b) was 36.3 degrees + or - 0.1 degrees C (X + or - SE) in both species, and except for a small rise at T(a) 45 degrees C, T(b) was stable over a wide range of T(a). Metabolic heat production was 25% higher in red kangaroos at T(a) -5 degrees C. At the highest T(a) (45 degrees C), both species relied on evaporative heat loss (EHL) to maintain T(b); both panting and licking were used. The eastern grey kangaroo utilised panting (76% of EHL) as the principal mode of EHL, and while this was so for red kangaroos, cutaneous evaporative heat loss (CEHL) was significant (40% of EHL). CEHL appeared to be mainly licking, as evidenced from surface temperatures. Both species utilised peripheral vascular adjustments to control heat flow, as indicated by changes in dry conductance (C(dry)). At lower temperatures, C(dry) was minimal, but it increased significantly at T(a) just below T(b) (33 degrees C); in these conditions, the C(dry) of red kangaroos was significantly higher than that of eastern grey kangaroos, indicating a greater reliance on dry heat loss. Under conditions where heat flows into the body from the environment (T(a) 45 degrees C), there was peripheral vasoconstriction to reduce this inflow; C(dry) decreased significantly from the values seen at 33 degrees C in both kangaroos. The results indicated that, while both species have excellent thermoregulatory abilities, the desert red kangaroos may cope better with more extreme temperatures, given that they respond to T(a) 45 degrees C with lower respiratory evaporation than do the eastern grey kangaroos.     

Biomass and shoot production of Carex rostrata and Equisetum fluviatile in unfertilized and fertilized subarctic lakes

The emergent macrophytes were studied in two, small subarctic lakes in 1972–1980. One of the lakes, Hymenjaure, was fertilized with phosphorus in 1972–1974 and with both phosphorus and nitrogen in 1975. The emergent vegetation in the lakes consisted mainly of Carex rostrata Stokes and Equisetum fluviatile L. The maximum shoot biomass of C. rostrata varied between 12–25 g dry wt. m^?2 during the investigation years, corresponding figures for E. fluviatile were 10–21 g dry wt. m^?2. The yearly shoot production of the emergent macrophytes ranged from 6 to 21 g dry wt. m^?2 during the study. The natural variations in growth of both species between the years were mainly regulated by summer temperature. Carex rostrata was able to benefit from increased phosphorus supply, when more shoots were produced within its stands. Growth of individual shoots, though, was still regulated by summer temperature. Equisetum fluviatile increased its phosphorus uptake as an effect of the fertilizations, but production was not affected.     

Soil seed densities and emergence patterns in pastures in the seasonally dry tropics of northeastern Australia

Germinable seed densities in the surface (0–10 cm) soil of pasture communities growing at Lansdown, near Townsville, were measured during the late dry season before the first germinating rain and again during the following wet season after germination but before the input of new seed. Seedlings emerging in the field were counted at approximately weekly intervals during this period to determine emergence patterns. Twelve communities were sampled in 1980–81 and six were re-sampled in 1981–82. During the late dry season germinable seed densities ranged from 5000 to 40 000 seeds m^-2. Seeds of the introduced legume, Stylosanthes hamata, were present in all pastures. There were many seeds of annual grasses (Digitaria ciliaris and Brachiaria miliiformis) and sedges (Cyperus and Fimbristylis spp.) but only few seeds of perennial grasses (both native and introduced). Soil seed densities were much lower during the wet season than during the preceding dry season, particularly for the grasses. Emergence commenced and approximately 70% of all seedlings emerged on the first major rainfall of the wet season. The subsequent emergence pattern varied between years. In 1980–81 there was a gradual and continuous increase in seedling numbers under the continuously moist conditions which prevailed. In 1981–82 further emergence occurred in discrete events related to rainfall and intervening dry periods. Maximum seedling densities exceeded 34 000 seedlings m^-2 including 29 000 grass seedlings (mainly annual species). The implications of these results for species survival and pasture composition are discussed.     

Feed intake and digestion in the maned wolf (Chrysocyon brachyurus): Consequences for dietary management

Captive maned wolves (Chrysocyon brachyurus) often consume diets high in prey and meat items even though they are omnivorous in the wild. These soft, high protein diets may exacerbate conditions of gingivitis and cystinuria in this species. Feed intakes were monitored in wolves provided with prey and meat-based diets (3 periods) and subsequently with extruded dog chows and small amounts of prey (2 periods). Digestibilities of each type of diet were measured with the indigestible marker chromic oxide. Dry matter intakes were similar between diets (374–584 g · 30 kg^?1 · d^?1), even though dietary protein content was reduced from 44% to 29% of dry matter. Digestibility of dry matter was unaltered by these dietary changes (77% of high prey diet vs. 73% of chow diet), but fecal consistency changed to softer stools at lower intakes of prey. Estimated metabolizable energy intakes of wolves (501–674 kJ · kg^?0.75 · d^?1) were similar to the maintenance requirement for domestic dogs (525 kJ · kg^?0.75 · d^?1), suggesting a similar energy requirement for maintenance of the wolves. The metabolizable energy derived from protein in the high prey diets was 37%, whereas that of the chow diets was only 27%. These levels exceed estimates of protein requirements for maintenance (4.3–21.8%) and growth (11.5–20.3%) in domestic dogs and may thus exceed those of the wolves. Dietary management of maned wolves should minimize excess protein intake by limiting prey consumption and acclimating animals to extruded diets for domestic dogs. Further research is required to formulate diets for long-term management of cystinuria in maned wolves. © 1994 Wiley-Liss, Inc.     

Comparative feeding ecology of two herbivorous damselfishes (Pomacentridae: Teleostei) from the Gulf of California,Mexico

Two species of benthic damselfishes from the Gulf of California, Mexico, use contrasting behaviors when feeding on benthic algal communities. The small (±70 g) Cortez damselfish, Eupomacentrus rectifraenum (Gill, 1862), feeds selectively from a multi-species algal mat, eats fleshy red and green algae and ignores brown and calcareous algae. The giant blue damselfish, Microspathodon dorsalis (Gill, 1862), is a large (±450 g), lethargic, nonselective feeder which grazes on a near monoculture of a fleshy red alga, Polysiphonia sp. Feeding activity for both species is low in the morning peaks during late afternoon, and drops sharply as night approaches. Based on feeding rates, gut-filling times, and weights of gut contents, Cortez damselfish process six to eight full guts of food and giant blue damselfish three full guts of food per day. The algal mat exhibits high standing crops (291–618 g dry wt · m^?2) and low productivity, but the preferred food of the Cortez damselfish (Ulva) appears to colonize the mat frequently and grow rapidly. The Polysiphonia dominated community on giant blue damselfish territories exhibits low standing crops (23 g · m^?2) and high productivity (34–47 times that of the mat per gram algae). Even though the feeding behaviors and resources used by the two damselfishes differ, both species eat similar food (delicate red and green fleshy algae, and depend on rapid colonization and/or high productivity to maintain their primary foods in the grazed algal community.     

贺兰山同域分布岩羊和马鹿的夏季食性

2008年78月贺兰山对同域分布的岩羊和马鹿粪便进行采集,利用粪便显微分析法对二者夏季食性进行了研究。从10个沟系中一共收集了297堆岩羊和305堆马鹿粪便,每堆中捡拾2粒粪粒,组成40个复合样本进行分析。结果表明,夏季在岩羊采食的19科35种(属)植物中,针茅(29.74%)、早熟禾(18.82%)、内蒙古邪蒿(10.30%)、灰榆(7.76%)、冰草(7.47%)是其主要食物,针茅是岩羊夏季的大宗食物;夏季在马鹿取食的11科18种(属)植物中,小红柳(36.26%)、山杨(23.10%)、灰榆(16.84%)等是其主要食物,小红柳为马鹿夏季的大宗食物。夏季岩羊采食植物中,乔木占8.67%,灌木占3.97%,禾本科草本占69.43%,非禾本科草本占17.94%;马鹿采食植物中,乔木占89.61%,灌木占5.38%,禾本科草本占1.03%,非禾本科草本占3.99%。从食物多样性和食物生态位宽度来看,岩羊的Shannon-Wiener指数高于马鹿,而马鹿的Pielou均匀性指数和食物生态位宽度指数高于岩羊,岩羊和马鹿共有9种食物重叠,生态位重叠指数为65.17%。     

Preference for different inorganic nitrogen forms among plant functional types and species of the Patagonian steppe

We have explored species–specific preferences for nitrate (NO₃ ^?) and ammonium (NH₄ ⁺) as an alternative niche separation in ecosystems where nitrogen (N) is present mostly in inorganic forms. The Patagonian steppe is dominated by shrubs and grasses. Shrubs absorb water and nutrients from deep soil layers, which are poor in N, while grasses have the opposite pattern, absorbing most of their water and nutrients from the upper layers of the soil. We hypothesized that the preferences of shrub and grass for inorganic N forms are different and that the rate of potential N uptake is greater in shrubs than in grasses. To test this hypothesis, we grew individuals of six dominant species in solutions of different NH₄ ⁺:NO₃ ^? concentration ratios. Nitrate uptake was found to be higher in shrubs, while ammonium uptake was similar between plant functional types. The NH₄ ⁺:NO₃ ^? uptake ratio was significantly lower for shrubs than grasses. Shrubs, which under field conditions have deeper rooting systems than grasses, showed a higher N absorption capacity than grasses and a preference for the more mobile N form, nitrate. Grasses, which had lower N uptake rates than shrubs, preferred ammonium over nitrate. These complementary patterns between grasses and shrubs suggest a more thorough exploitation of resources by diverse ecosystems than those dominated by just one functional type. The loss of one plant functional group or a significant change in its abundance would therefore represent a reduction in resource use efficiency and ecosystem functioning.     

Distribution and production of Chironomidae (Diptera) in the lower course of the Grabia River (Central Poland)

SUMMARY.

• 1 A fifth-order section of the Grabia River was investigated over two years: 1984/85 (low water level) and 1985/86 (high spate). Chironomidae (thirty-nine species) dominated the macrobenthos in both years.
• 2 In 1984/85 (mean annual water temperature 10.2°C), the number of Chironomidae species in coarse sediment was highest in spring (thirty-three species) while in sand it was highest in summer (fifteen species). A decrease in species richness was recorded in autumn and winter at each of the established sites. The estimated Chironomidae production for the whole river section was 5.37 g dry wt m^?2 yr^?1, but it differed widely amongst the study sites, ranging from 3.75 to 12.07 g m^?2 yr^?l.
• 3 In 1984/85 (mean annual temperature 8.1°C) there occurred a summer spate which was more intense than any recorded over the previous 20 years. This substantially reduced the number of species, the greatest reduction being in the coarse sediment, which was buried with sand during the spate. Production for the whole section decreased to 1.17 g m^?2 yr^?1, and the variability amongst sites ranged from 1.04 to 1.45 g m^?2 yr^?1.

     

Dietary composition of wildebeest (Connochaetes taurinus) kongoni (Alcephalus buselaphus) and cattle (Bos indicus), grazing on a common ranch in south-central Kenya

This paper gives the results of a study conducted at Game Ranching Ltd, situated at the Athi Kapiti Plains, Kenya, to determine the dietary composition of cattle (Bos indicus L), kongoni (Alcephalus buselaphus Pallas) and wildebeest (Connochaetes taurinus Burchell), through two forage growing seasons (wet and dry). The dietary preferences and overlaps between the species were also determined. The diet preference of the three herbivores was determined using a microhistological analysis technique. The three dominant grasses in the ranch: Themeda triandra Fork, Digitaria macroblephara (Hack.) Stapf and Penisetum mezianum Leeke, formed the major diets of the animals. The browse component of the diets increased during the dry season by about 100% for all the animal species, with cattle always having twice as much browse as the wild herbivores. However, the animals selected similar diets in terms of plant species during both seasons but were more selective during the wet season. Dietary overlaps were always above 75%, but more than this during the dry season. The dietary overlaps were lower between cattle and wild herbivores than between the wild herbivores. The diet preference index for the animals differed from season to season, and from plant to plant.     

High rates of net primary production and turnover of floating grasses on the Amazon floodplain: implications for aquatic respiration and regional CO2 flux

We investigated whether rates of net primary production (NPP) and biomass turnover of floating grasses in a central Amazon floodplain lake (Lake Calado) are consistent with published evidence that CO₂ emissions from Amazon rivers and floodplains are largely supplied by carbon from C4 plants. Ground‐based measurements of species composition, plant growth rates, plant densities, and areal biomass were combined with low altitude videography to estimate community NPP and compare expected versus observed biomass at monthly intervals during the aquatic growth phase (January–August). Principal species at the site were Oryza perennis (a C3 grass), Echinochloa polystachya, and Paspalum repens (both C4 grasses). Monthly mean daily NPP of the mixed species community varied from 50 to 96 g dry mass m^?2 day^?1, with a seasonal average (±1SD) of 64±12 g dry mass m^?2 day^?1. Mean daily NPP (±1SE) for P. repens and E. polystachya was 77±3 and 34±2 g dry mass m^?2 day^?1, respectively. Monthly loss rates of combined above‐ and below‐water biomass ranged from 31% to 75%, and averaged 49%. Organic carbon losses from aquatic grasses ranged from 30 to 34 g C m^?2 day^?1 from February to August. A regional extrapolation indicated that respiration of this carbon potentially accounts for about half (46%) of annual CO₂ emissions from surface waters in the central Amazon, or about 44% of gaseous carbon emissions, if methane flux is included.     

Population dynamics and production of the tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) in the littoral of Lake Sibaya

SUMMARY. Seasonal changes in population structure, standing stock levels and production of Caridina nilotica were studied at three sites in the littoral margins of subtropical Lake Sibaya between January 1975 and March 1976. Average population density at these sites declined from a maximum of c. 1400 to a minimum of c. 350 individuals per m² (3.4–0.4 g m^?2 dry wt) during the study, possibly as a result of emigration into peripheral vegetation inundated by rising lake levels. Shrimps bred perennially and, although egg stocks and instantaneous birth rates (b) were highest during summer, no corresponding increases in populaton density were observed, suggesting that the seasonally higher birth rates were offset by higher mortality rates. Population size structure and size-specific sex ratios did not change seasonally to any marked extent. Relative abundance declined with size and females grew larger than males. Clutch size increased linearly as a function of female carapace length. Estimates of overall mean annual somatic production (g m^?2 year^?1 dry wt) for the three sites between January 1975 and January 1976 ranged between c. 132 (egg-ratio method), 37.5 (summation of growth increments) and 24 (Hynes-Hamilton method) at an annual mean standing stock level of 2.7 g m^?2 dry wt (calorific value, 20.34 kJ g^?1 dry wt). Production at sites 1, 2 and 3 decreased in line with declining annual mean standing stocks (5.32, 3.67 and 0.23 g m^?2, respectively). The growth increment method gave an overall mean annual P/B value of 13.9. Egg production amounted to a further 5.6, 3.6 and 0.1 g m^?2 year^?1 dry wt (calorific value, 28.01 kJ g^?1) at sites 1, 2 and 3, or 2.7 g m^?2 year^?1 on average.     

Seasonal abundance and distribution of drift algae and seagrasses in the mid-Indian river lagoon,Florida

The distribution of seagrasses in a 15-ha area in the mid-Indian River lagoon on Florida's central east coast was mapped. Halodule wrightii Aschers. dominated in shallow (< 0.4 m) and Syringodium filiforme Kutz. in deeper water (> 0.5 m). Thalassia testudinum Banks ex König occurred as scattered patches. Areal coverage of monospecific stands of the three major seagrasses was: Syringodium 35%, Halodule 14%, Thalassia 6% and bare sand 21%. Mixed species stands, mostly Syringodium with Hallodule, covered 25% of the total study area. Above-ground seagrass biomass was maximum in summer (June–July) and minimum in late winter (February–March). Summer maxima ranged from 60 g dry wt. m^?2 for Syringodium to ～ 300 g dry wt. m^?2 for Thalassia, with Halodule intermediate at 160 g dry wt. m^?2.Because distribution of unattached benthic macroalgae (“drift algae”), primarily Gracilaria spp., was highly aggregated, aggregations were first mapped, followed by stratified quadrat sampling in order to estimate total drift algal abundance. In April 1982, high-density patches covering a few hectares averaged 409 g dry wt. m^?2. At maximum abundance, averaged over the entire 15-ha mapped area, drift algal biomass was 164 g dry wt. m^?2; mean above-ground seagrass biomass was only 49 g dry wt. m^?2. Other large expanses of the lagoon had similar accumulations of drift algae; densities of some accumulations exceeded 15 000 g dry wt. m^?2. Year-to-year variability of seagrass and drift algal abundance was high and may be related to variations in light levels.Drift algae harbor high densities of animals and at times may be quantitatively more important locally than seagrasses in terms of habitat, nutrient dynamics and primary production.