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

Change in the distribution of a member of the strand line community: the seaweed fly (Diptera: Coelopidae)

1. Coastal organisms are predicted to be particularly susceptible to the impact of global warming. In this study the distribution and relative abundance of two coastal invertebrates, Coelopa frigida (Fabricius) and C. pilipes are investigated. 2. Coelopa pilipes has a more southerly distribution than C. frigida , and prefers a warmer climate. Coelopa pilipes is less resistant to sub-zero temperatures than C. frigida and its northerly distribution is probably limited by cold winter days. 3. The most recent distribution map of C. frigida and C. pilipes in northern Europe was published a decade ago and showed the northerly extent of the distribution of C. pilipes reaching the north coast of mainland Scotland but its complete absence from the Western and Northern Isles. 4. C. pilipes has now spread throughout the Western Isles and the Orkney Islands but is still absent from Shetland. There has also been an increase in the relative frequency of C. pilipes at sites harbouring coelopids on the British mainland. A similar pattern of distribution change along the west coast of Sweden is reported. 5. It is proposed that these changes have occurred primarily as a result of global warming and in particular due to the recent increase in winter temperatures. A number of other indirect effects may have also contributed to these changes, including a probable change in macroalgae distribution. The implications of these changes for the wrack bed ecosystem and at higher trophic levels are considered

Temperature responses of tropical to warm-temperate Atlantic seaweeds .2. Evidence for ecotypic differentiation in amphi-Atlantic tropical-Mediterranean species

Nineteen isolates of four amphi-Atlantic seaweed species with a tropical to warm-temperate/Mediterranean distribution (Microdictyon boergesenii, M. tenuis, Wurdenmannia miniata and Valonia utricularis) and one eastern Atlantic endemic (M. calodictyon) have been investigated for their temperature responses (tolerance limits and growth response curves). In all species, isolates survived undamaged at 30 degrees C but died at 33 or 35 degrees C. Growth occurred up to 30 degrees C in most isolates but no growth was observed at higher (33 degrees C) temperatures. Tolerance to low temperatures showed marked differences between and within species. In tropical isolates, damage generally occurred between 15 and 18 degrees C and plants grew at temperatures down to 18-20 degrees C. Isolates from warm-temperate localities (Canary Islands and Mediterranean) tolerated much lower temperatures (0-12 degrees C), and showed substantial growth at temperatures as low as 15-18 degrees C, which indicates ecotypic differentiation. It is hypothesized that these cold-adapted populations are descendants of populations which were isolated in the eastern Mediterranean during the last glacial episode and recolonized the western Mediterranean and Canary Islands at the onset of the interglacial

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

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

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

Oxidative stress and enzymatic scavenging of superoxide radicals induced by solar UV-B radiation in Ulva canopies from southern Spain

The generation of reactive oxygen species (ROS) and scavenging of the superoxide radical by superoxide dismutase (SOD) was studied in mat-like canopies of the green macroalga Ulva rotundata Bliding in a tidal brine pond system in southern Spain. Artificial canopies were covered with different cut-off filters, generating different radiation conditions. ROS and SOD were assessed after three days of exposure. ROS induced lipid peroxidation depended on the position of individual thalli within the canopy and on radiation conditions. Samples exposed to the full solar spectrum were most affected, whereas samples either exposed to photosynthetically active radiation (PAR) alone or UV radiation without PAR exhibited fewer peroxidation products. The activity of SOD appeared to be controlled by the impinging UV-A and UV-B radiation and also increased in response to oxidative stress. The results provide evidence for additive effects of high PAR and UV-B under field conditions and support the previously proposed hypothesis that UV-B effects are mediated by an inhibition of the xanthophyll cycle, which increases ROS production and, consequently, causes oxidative damage to components of the photosynthetic machinery, such as proteins and pigments [KEYWORDS: Macroalgae, photosynthesis, reactive oxygen species, superoxide dismutase, Ulva, UV radiation]