Climb and flight speeds of shorebirds embarking on an intercontinental flight:Do they achieve the predicted optimal behaviour?

Most Arctic-breeding waders wintering in West Africa cover the first 4000 km of their northward journey in spring by a single flight to western Europe. We examined the extent to which waders economize their night behaviour during departure by comparing climb rates and forward night speeds with predictions based on flight mechanic theory and the relevant morphological measurements made of birds collected on the site. With an optical range finder, we followed 98 wader necks on their departure from Banc d'Arguin in Mauritania, We also measured wind speed and direction at different altitudes by tracking helium-filled balloons and thus were able to deduce airspeeds from groundspeeds of the departing flocks. Of the nine species examined, six showed the predicted negative relationship between climb rate and airspeed, although only one was statistically significant. By normalizing the data, we found a statistically significant negative correlation across all species. Although 17% of the observed climb rates were greater than the predicted theoretical maximum, the average observed climb rate was lower than the predicted optimum and the average observed airspeed was higher. The absolute deviations of climb rates fr om theory may have been because of the existence of pockets of rising and sinking air at the boundary of desert and ocean. That the absolute deviations in average climb rate and airspeed followed the predicted negative relationship is in accordance with the current theory of flight mechanics

Bioerosion and sediment ingestion by the Caribbean parrotfish Scarus vetula and Sparisoma viride:Implications of fish size, feeding mode and habitat use

Erosion rates and sources of sediment ingested were quantified for the 2 most abundant parrotfish species on a leeward fringing reef of Bonaire, Netherlands Antilles: Scarus vetula and Sparisoma viride. Direct estimates of erosion by different size classes were obtained from daily feeding rates and grazing scar frequency, scar volume and substrate density. Foraging preference and distribution of fish on the reef were used to examine patterns of bioerosion at 2 spatial scales: reef zones and individual substrates used for grazing. Sediment mass ingested by fish provided an independent check on erosion rates, and was partitioned according to source. S. vetula, employing a scraping feeding mode, removed less material from grazed substrates than similar sized S. viride, which forages by excavating the substrate. Erosion rates increased strongly with fish size in both species. The (indigestible) carbonate derived from epilithic algae accounted for all sediment ingested by juvenile fish. In adult fish, the proportion of freshly eroded carbonate substrate ingested increased with fish size. The distribution of adults of these large scarids over different reef zones determines the rate of bioerosion on a large spatial scale. The highest bioerosional rates occur on the shallow reef (ca 7 kg m(-2) yr(-1)), and they decrease with depth. Parrotfish foraging preferences, and the effects of food type and skeletal density of substrates on the size of the grazing scars, cause large differences in bioerosional rates on a small spatial scale. The highest rates of bioerosion occur on substrates infested with boring algae and of low skeletal density, while high-density substrates and substrates covered with crustose corallines undergo lower rates. Living coral is rarely eaten by scarids, and largely escapes erosion by grazing

Plastic growth of the herbivorous reef fish Sparisoma viride: field evidence for a trade-off between growth and reproduction

The growth of different Life phases and social categories of the protogynous parrotfish Sparisoma viride was studied on a fringing reef on Bonaire (Netherlands Antilles) using mark-recapture procedures and by taking repeated stereographic measurements of free-swimming fish. Weight-growth was best described by the Putter/von Bertalanffy growth equation for all categories, allowing comparison of specific growth rates (dW/Wdt) using analysis of covariance with W-(1/3) as the covariate. Growth was retarded by Peterson discs, but no effect of fin clips was detected. Adjusted for size differences, growth of juveniles was fastest, followed by sexually inactive terminal phase (TP) males living in groups. Initial phase (IP) females and territorial TP males (spawning daily) showed the lowest growth rates. Growth rate of territorial males was negatively correlated with their average spawning rate. All adult categories showed seasonal variations in growth, the highest rates occurring in the warmest season (August to October). A possible effect of depth on growth is confounded by differences in social and reproductive status. Growth of group TP males showed a weak positive correlation with their condition. Gross growth efficiencies were estimated by combining data on growth and body composition with previously published data on food intake and assimilation. Growth efficiency is highest for protein, ranging from 50.6% of food intake for juveniles to 0.12% for territorial males. Corresponding values are 6.25 to 0.01% for ash-free dry weight and 7.9 to 0.01% for energy. The high abundance of small, sexually inactive group TP males (early sex-changers) in our S. viride population is related to their fast growth. We suggest that these 'bachelors' trade growth against current reproduction and thereby enhance their chance to acquire the status of a territorial male with high reproductive success. Insight into intraspecific variation in growth improves the accuracy of trophodynamic models and increases our understanding of complex Life history patterns in fish

Seasonal dynamics of Sargassum ilicifolium (Phaeophyta) on a shallow reef flat in the southern Red Sea (Eritrea)

The seasonality of Sargassum ilicifolium was studied in the southern Red Sea by monitoring thallus density, thallus size and the initiation, growth, reproduction and survivorship of primary laterals. Thallus density showed slight but significant seasonal variation; it was highest at the end of the hot season and lowest at the end of the cold season. Mean thallus and lateral lengths peaked in the second half of the cold season. Initiation of new laterals was highest in the first half of the cold season. High lateral densities suppressed new lateral initiation. In the first month after initiation, laterals grew out to the same length as those formed earlier in the year. Thus, elongation rates of young laterals were highest during the period of maximum canopy height. In older laterals, growth rates decreased with length, due to increased tissue loss. Growth rates were independent of reproductive status. Reproduction occurred in the second half of the cold season and was independent of lateral size, but laterals had to be at least 1 to 2 mo old before reproducing. Highest loss rates of laterals occurred at the end of the growth season. Survivorship was independent of lateral size or reproductive status. Loss rates were lowest in the hot season. We conclude that there is no direct trade-off between reproduction and growth/survival of the laterals, and that the dynamics of S. ilicifolium are directly related to the seasonal extremes in environmental conditions. Morphogenetic responses at the level of individual laterals also contribute to the overall phenological patter

Seasonal patterns of biomass, growth and reproduction in Dictyota cervicornis and Stoechospermum polypodioides (Dictyotales, Phaeophyta) on a shallow reef flat in the southern Red Sea (Eritrea)

Seasonal patterns in thallus length, biomass, reproduction, total biomass m-2 and size structure were monitored in populations of Dictyota cervicornis and Stoechospermum polypodioides on a shallow reef flat in the southern Red Sea. These tropical reef flats are exposed to extreme temperatures of about 34°C in summer and to temperatures of about 25°C in winter. Both species showed peaks in length, biomass and reproduction in winter; macrothalli were absent in summer. Thallus length, biomass and the proportion of reproductive thalli showed a strong negative correlation with seawater temperature. Young thalli first appeared in November, following a drop in seawater temperature from about 33 to 31°C. Macroscopic thalli had disappeared in May, when temperatures had reached the same values as those at the start of the growth season (33°C). When reef substrata collected in summer were kept at sub-ambient temperatures (29¿31°C), macroscopic thalli of D. cervicornis developed. Size structure varied over time, probably because of non-synchronous development and tissue loss among thalli. Reproduction was size-dependent. We conclude that D. cervicornis and S. polypodioides have highly seasonal patterns of growth and reproduction related to the seasonal variation in the environment, especially temperature

Inaugural Meeting

Quantitative data are presented to assess the trophic role of scarids on the fringing coral reef of Bonaire (Netherlands Antilles): with particular emphasis on the stoplight parrotfish Sparisoma viride. Average herbivore biomass on the reef was 690 kg ha(-1), 22% of which was accounted for by S. viride. From data on relative gonad weights, daily spawning frequencies, and egg numbers obtained by stripping, with previous estimates of somatic growth and energy intake, a gross efficiency (GE: somatic plus gamete production/consumption) of 23% was obtained. This is a factor of five to seven lower than the GE suggested to be valid for most aquatic ecosystems, including coral reefs. To investigate one potential cause for our low estimate, overestimation of food intake, our intake estimates were compared with published values for other herbivorous coral reef Bah. This yielded a relationship (daily C intake = 0.0342 x W(0.816); wet body mass W in g) with high correlation (r(2) = 94.6%, n = 13), which shows that the intake estimates agree well with other published data. Averaged over the year, primary production at 0-3 m depth was 17.2 kg C ha(-1) day(-1) while herbivore consumption was estimated at 17.4 kg C ha(-1) day(-1), indicating an ecotrophic efficiency (EE, the fraction of total production at one trophic level that is consumed by all predators) of 100%. This suggests strongly that the food intake estimates are realistic, since no changes in algal biomass were observed over the study period. The two scarids for which food intake was actually measured in our own study area, were estimated to consume 55% of the algal production in the shallow reef (S. viride, 20%; Scarus vetula, 35%). This is lower than expected if consumption were proportional to biomass (S. vb ide, 22%; S. vetula, 40% of herbivore biomass in the shallow reef). Consequently, a minimum estimate of 88-91% can be inferred for the EE of these two species. Multiplied by GE, this yields a transfer efficiency (TE, the fraction of production passing from one trophic level to the next) of 2%. For coastal and coral systems the primary production required (PPR) to sustain fisheries was estimated to be 8.3%, which was based on a TE of 10%. The present estimates show that the TE of a major herbivore at our reef is at least a factor of five lower. Assuming that the estimate is representative for all scarids (comprising 70% of the herbivore standing stock), it can be concluded that the PPR to sustain coral reef fisheries may be as high as 40% of the total primary production. The low value reported before, might suggest that the effect of fishing mainly affects target populations but not the lowest trophic levels. II is argued that our estimate is more realistic for coral reefs supporting high scarid biomass and explains better the many reports of coral destruction due to algal overgrowth at exploited reefs. (C) 1998 The Fisheries Society of the British Isles

Ontogenetic, social, spatial and seasonal variations in condition of the reef herbivore Sparisoma viride

We studied the condition of stoplight parrotfish, Sparisoma viride, collected from the fringing reef of Bonaire (Netherlands Antilles) between March 1987 and October 1991. To this end, we compared length-weight relationships using analysis of covariance. The condition of different life phases [juveniles, initial phase (IF) and terminal phase (TP) adults] and social categories (territorial and group adults) is compared in different seasons, taking into account spatial variability along a depth gradient. Variations in condition are related to differences in behaviour, the use of space and the distribution of food. The average length-weight relationship of fish with empty guts is described by the equation: W-Empty - 9.115 x 10(-6) x FL(3.140) (n = 386, R(2) = 99.82%, W in g, FL in mm). Territorial TP males were found to be in poorest condition, whereas (sexually inactive) group TP showed the best and IP fish an intermediate condition. These differences are ascribed to varying investments in territory defence and reproduction, which affect condition more than, the vertical distribution of food. All categories were Sn minimum condition between May and July, the season with longest day lengths and increasing water temperatures. This seasonal effect cannot be ascribed to increased reproductive effort and suggests that the higher energetic demands due to the longer active period of fish are not completely met by increased food uptake. It is inferred that food may be a limiting factor at times