Leaf choice by crustaceans in a mangrove forest in Queensland

The feeding behaviour of leaf eating crustaceans feeding on leaves shed by Avicennia marina, Bruguiera gymnorhiza and Rhizophora stylosa in the mangrove forest at Myora Springs, Queensland, Australia was studied between 1980 and 1984. Individual Sesarma erythrodactyla (carapace >9 mm long), one of the most abundant species of crabs in the forest, processed approximately half a leaf from any of the three species of mangroves in 24 h under laboratory conditions. of the amount of leaf material processed, 20% was lost from the mandibles due to sloppy feeding, 68% was egested as faeces and 12% converted into crab biomass. Crabs processed more leaf material at 30°C than at 20°C. S. erythrodactyla preferred leaves of A. marina to those of the other two species, probably because leaves of A. marina have a lower tannin and a higher nitrogen content. Of the other two species, B. gymnorhiza was preferred to R. stylosa. Among leaves of R. stylosa, S. erythrodactyla exerts a strong preference for aged rather than freshly fallen, and for thick rather than thin leaves. The mesofauna (carapace length <9.0 mm) which processed dead mangrove leaves comprised juveniles of S. erythrodactyla, the crab Ilyograpsus paludicola, the isopod Exosphaeroma alata and the amphipods Orchestia sp. and Melita sp. These species processed between 0.2 and 24.7 mg dry wt of a leaf per individual over a period of 4 d. Of this, 72 to 85% was egested as faeces. The significance of leaf eating crabs to nutrient cycling in mangrove forests is discussed. I conclude that leaf processing by crustaceans shortens the time span between leaf fall and consumption of leaf material by organisms. This may have the effect of conserving leaf biomass inside the mangrove forest.     

Role of grapsid crabs, Parasesarma erythrodactyla, in entry of mangrove leaves into an estuarine food web: a mesocosm study

The influence of the crab Parasesarma erythrodactyla on the entry of the organic matter derived from Avicennia marina mangrove leaves in a sub-tropical mangrove ecosystem of southeast Queensland, Australia, was simulated using tidal mesocosms. Degradation of mangrove leaf organic matter was followed by analysing the fatty acid composition, carbon, and nitrogen isotopic signatures of the surface sediment and suspended particulate organic matter (SPOM) with and without the presence of crabs. Assimilation of mangrove organic matter by P. erythrodactyla was also assessed by stable isotope and fatty acid analyses in tissues and faeces. Results of the chemical tracer analyses question the adaptability of P. erythrodactyla to a diet comprised exclusively of mangrove leaves, and suggest that these organisms were dependent on additional food sources in their natural environment. Crab processing of senescent leaves significantly accelerated the transfer of mangrove organic matter to the surface sediments, as shown by a higher C/N ratio, a higher contribution of long-chain fatty acids and a more depleted C isotopic signature of sediment samples in the mesocosms with crabs compared to those without crabs.     

Competition and interaction between Neosarmatium smithi (Crustacea: Grapsidae) and Terebralia palustris (Mollusca: Gastropoda) in a Kenyan mangrove

 In a Kenyan mangrove, we studied the interactions between the gastropod Terebralia palustris and the crab Neosarmatium smithi when foraging on decaying mangrove leaves. Interactions are considerable on account of their wide overlap in zonation (Rhizophora mucronata belt), food items (mangrove leaves) and activity window (diurnal low water). The snails find a leaf by a systematic transecting of the platform and eat the leaf after crawling on to it, usually en masse. The crabs rarely venture beyond 80 cm from their burrows, and once they find a leaf they quickly drag it back into their burrow, probably to reduce the strong intra-specific competition. A crab is able to drag a leaf away even if a number of snails are already feeding on it, by strongly pulling the leaf away or by pushing the snails off the leaf. The success of the “thief ” depends on both the crab's size and the number of snails on the leaf. Received: 25 July 1999 / Accepted: 27 April 2000     

Leaf consumption by <Emphasis Type="Italic">Sesarma plicata</Emphasis> in a mangrove forest at Jiulongjiang Estuary,China

The feeding ecology of Sesarma plicata (Grapsidae: Sesarminae), the most abundant crab species in a mangrove forest dominated by Kandelia candel at Jiulongjiang Estuary, China, was investigated through field and laboratory experiments. Feeding preference and consumption rates were determined on mature, senescent and decomposed leaves of Kandelia candel, Bruguiera gymnorrhiza and Aegiceras corniculatum. In the laboratory, S. plicata preferred leaves of K. candel over those of B. gymnorrhiza and A. corniculatum, and consumed significantly more decomposed leaves than mature and senescent ones, irrespective of crab size. Field experiments with limited power failed to reveal detectable species preferences despite more consumption of K. candel, but decomposed leaves of each species were again preferred. Leaf characteristics associated with preference changed with plant species and leaf state. Low tannins and high water content characterized the preference for decomposed state of leaves. Species preference was significantly and negatively related to crude fibers and C:N ratios for mature leaves, and crude fiber for senescent leaves, but significantly and positively related to water content for decomposed leaves. Leaf consumption rates averaged for all leaf categories from laboratory no-choice feeding experiments were 0.101, 0.055 and 0.017 gDW ind⁻¹ d⁻¹ for large, medium and small crabs, respectively. In this forest, mean density of S. plicata was 20.5 ind m⁻² as assessed by a manual catching method. Leaf litter removal rate during neap tides by sesarmid crabs was about 1.33 gDW m⁻² d⁻¹ in April 2006. The leaves removed by crabs were grazed on the sediment surface or taken into crab burrows, shredded and stored before being eaten.     

Vertical migrations in the tree crab Sesarma leptosoma (Decapoda,Grapsidae)

Sesarma leptosoma, somewhat similar to the Atlantic related species, Aratus pisonii, is an East-African mangrove crab which spends its entire life on the roots and branches of mangrove trees (mostly Rhizophora mucronata, Bruguiera gymnorhiza and Ceriops tagal). S. leptosoma never enters the water, nor does it ever venture onto the free mud surface at low tide. Part of the day and night it remains on the lower parts of the mangrove aerial roots, which are often encrusted with a wet algal mat of Bostrichia spp., searching for food and water. Twice a day, from ca. 06:00 to 08:00 hrs in the morning and 16:00 to 18:00 hrs in the afternoon, many of the crabs migrate as far as the leaves at the top of the tree on which they feed. However, they only spend a brief period among the leaves, from ca. 07:00 to 10:00 and 17:00 to 19:00 hrs, after which time they make their way back towards the roots again in two downward migrations. In the morning, the downward migration brings all the crabs back to the roots, but in the evening not all the crabs take part in the downwards migration and some of them pass the whole night in the tree tops. A comparison of the migration time patterns for two different periods of the year (June–July and November) shows that the number of crabs migrating along the tree trunk is modulated by the spring-neap tidal cycle, while the onset of daily migration seems to be controlled mostly by the light level and/or other climatological cues. The adaptive significance of this migratory behaviour is discussed. Observations reported in our study were made in Mida Creek, Dabaso, Kenya in 1991 and 1992.     

Growth and spawning in the pectinid Chlamys opercularis in relation to temperature and phytoplankton concentration

Groups of queens, Chlamys opercularis (L.), were maintained under semi-natural conditions for a period of 18 months while growth rates and spawning conditions were monitored. Temperature and phytoplankton standing crop (as chlorophyll a) were also measured. The data suggest that only 1 major growth ring is formed in 1 year (in spring), although disturbance rings may be present. Rings are the result of the build-up of a number of small growth increments (striae) formed as successive lamellae are laid down. One lamella is probably laid down during 1 day, but a lamella is not necessarily laid down every day. Lamellae are laid down most regularly when temperature is moderately high and food availability is good. It seems likely, however, that poor food availability can limit growth and thus restrict the formation of lamellae even under field conditions. Spawning does not seem to induce the formation of growth checks.     

Control of microbial growth and of amphipod grazing by water-soluble compounds from leaves of Zostera marina

The role of minor components of the leaves of Zostera marina L. in altering the activity of micro-organisms directly (and indirectly by affecting amphipod grazers) was investigated in laboratory experiments, using plants collected at Roberts Bank (49°2N; 123°8W) on the west coast of Canada. Water-soluble extracts of eelgrass leaves inhibited the growth of a micro-alga (Platymonas sp.) and many marine bacteria at concentrations equivalent to as little as 10 mg dry leaf l^-1. The potency of leaf extracts was higher (1) in young, actively metabolizing tissue than in older leaves, and (2) in leaves collected during rapid growth in summer 1980 than during the following winter. Water-soluble inhibitors (especially phenolic acids) may explain the low biomass of epiphytes on actively growing leaves. Three phenolic acids inhibited the test micro-organisms at concentrations as low as 0.3 mg l^-1; caffeic acid was more potent than either protocatechuic or gentisic acid. Extracts of young leaves also inhibited grazing by amphipods [Eogammarus confervicolus (Stimpson)] on dead leaves. The time required for leaching of soluble inhibitors may account for the delay between the loss of leaves from the plants and the onset of grazing. Thus, interactions among the biotic components of the detritus ecosystem may be significantly modified by minor compounds in the leaves of Z. marina     

Feeding and mouthpart morphology in the semaphore crabHeloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

The mouthparts of the Australian semaphore crabHeloecius cordiformis (H. Milne-Edwards, 1837) are described. Male and female semaphore crabs were observed and collected from mangrove swamps around the south side of Botany Bay, Australia between 1983 and 1987. Semaphore crabs inhabit mangrove mud/sand flats between the midlittoral intertidal zone and the supralittoral fringe of bordering saltflats. Scanning electron micrographs provide detailed pictures of mouthpart morphology and the setae present on the third, second, and first maxillipeds; the second and first maxillae; and the mandibles. Amongst other setal types, spoon-tipped, corn, and bottle-brush setae are described. While semaphore crabs are primarily deposit feeders (microphagous), they have well developed mandibles and are, therefore, also able to eat larger plant and animal material (macrophagous). A brief comparison is made between the mouthparts of semaphore crabs and fiddler crabs (Uca spp.), since the two genera are closely related, occupy similar niches, and resemble each other in appearance. This comparison reveals that while the second maxilliped setal morphology differs between the two genera (Heloecius possesses corn setae,Uca possesses spoontipped setae) these setae may have similar functions. The feeding behaviour ofH. cordiformis is related to substrate composition, burrow construction and various mouthpart specialisations. It is conlcuded that, within the context of the present study, certain structural e.g. mouthpart modifications allowing both scavenging and deposit feeding, and behavioural modifications e.g. mound building in wet muddy habitats, enable semaphore crabs to occupy a wide range of habitat types within the mangrove.Please address all correspondence and requests for reprints to Dr Maitland at his present address at the University of the Witwatersrand     

Feeding ecology of the mangrove crab <Emphasis Type="Italic">Ucides cordatus</Emphasis> (Ocypodidae): food choice,food quality and assimilation efficiency

Food preferences, consumption rates and dietary assimilation related to food quality were investigated for the large semi-terrestrial and litter-consuming mangrove crab Ucides cordatus cordatus (Ocypodidae, L. 1763) in northern Brazil. Stomach contents were composed of mangrove leaves (61.2%), unidentified plant material and detritus (28.0%), roots (4.9%), sediment (3.3%), bark (2.5%), and animal material (0.1%). U. cordatus prefers Rhizophora mangle over Avicennia germinans leaves despite a higher nitrogen content, lower carbon to nitrogen (C/N) ratio and lower tannin content of the latter. Also, assimilation rates for senescent R. mangle leaves (C: 79.3%, N: 45.4%) were higher than for A. germinans leaves (C: 40.6%, N: 9.1%). Faeces composition indicates that A. germinans leaves were more difficult to masticate and digest mechanically. The leaf-ageing hypothesis, according to which crabs let leaves age in burrows to gain a more palatable and nutritive food, was rejected for U. cordatus since N content, C/N ratio and the abundance of microorganisms did not differ significantly between senescent leaves and leaves taken from burrows. The low microbial biomass on leaf surfaces and in the sediment indicates its minor importance for the nutrition of U. cordatus. It is concluded that high ingestion and assimilation rates of a R. mangle diet together with the consumption of algae allow for a high intake of C, N, and energy. The data suggest that the digestibility of mangrove leaves by U. cordatus is not hampered by tannins. This may have provided a competitive advantage over other leaf-consuming invertebrates unable to digest mangrove litter with high tannin concentrations. Due to the large stock biomass of U. cordatus in the study area, a great amount of finely fragmented faeces is produced (about 7.1 ton dry matter ha⁻¹ year⁻¹ in a R. mangle forest) which is enriched in C, N and bacterial biomass compared to the sediment. The decomposition of mangrove litter, and thus nutrient and energy transfer into the sediment, is greatly enhanced due to litter processing by U. cordatus.     

Nematode assemblages from <Emphasis Type="Italic">Avicennia</Emphasis><Emphasis Type="Italic">marina</Emphasis> leaf litter in a temperate mangrove forest in south-eastern Australia

Meiofauna from Avicennia marina leaf litter in a temperate mangrove forest was enumerated, and the nematode assemblages compared on the bases of leaf colour (used as a guide to leaf age) and shore horizon where samples were collected. Twenty-one putative nematode species were collected from 48 leaf litter samples. Univariate analyses indicated that neither the colour of the leaf nor the shore horizon significantly affected abundance of nematodes. However, of the four (2Ƕ) treatment groups, rarefaction curves revealed highest diversity on brown leaves from under the shade of the tree canopy (H'=0.751ǂ.126 SE, n=17). Species diversity of leaf litter nematodes was lower in this temperate mangrove system than reported from tropical mangrove studies. ANOSIM tests confirmed a significant effect of shore horizon on nematode assemblages. The dominant feeding group among nematodes was non-selective deposit feeders (7/21 species, but 77% of all nematodes). Epigrowth grazers were represented by 8/21 species of nematodes, but only 19% of the total number. Excised leaves became skeletonised by about 15 weeks. Shorter temporal scales of life cycles of nematodes compared with leaf degradation, and the dynamic nature of epibiontic assemblages, probably explain the similar assemblage structure on yellow and brown leaves.     

Responses of nymphs of desert locust,Schistocerca gregaria to volatiles of plants used as rearing diet

Summary Gregarious nymphs of the desert locust,Schistocerca gregaria (Forsk.) (Orthoptera: Acrididae) were more attracted to volatiles from mechanically damaged food plants used for rearing than to either the undamaged or damaged food plants not used as diet in Y-tube olfactometer assays. Comparative analysis of the volatile emissions from plants used for rearing and food plants not used for rearing,e.g. Sorghum bicolor, Pennisetum clandestinum, Schouwia thebaica, wheat (Triticum sp., var. Nyangumi),Zygophyllum simplex, Heliotropium undulatum andTribulus terrestris was carried out by GC, GC-EAD and GC-MS. Significant quantitative and qualitative differences were found in the volatile emissions and olfactory responses of nymphs in GC-EAD assays. Up to 33 compounds were identified in volatiles of the plants of which 9 evoked EAGs. EAG-active components included common green leaf compounds (E)-2-pentenal, (E)-2-hexenal, 4-methyl-3-pentenal, (E)-3-hexenyl acetate, (Z)-3-hexenyl acetate, (Z)-2-hexenyl acetate, (Z)-3-hexen-1-ol and (Z)-2-hexen-1-ol. (Z)-3-Hexenyl butyrate and (Z)-3-hexenyl isovalerate were detected in stimulatory amounts only in the volatiles ofS. thebaica. (E, Z)-2,6-Nonadienal was detected as a component in the volatiles ofT. terrestris and was highly stimulatory. In EAG assays with seven common green leaf volatiles, (Z)-3-hexenyl acetate was most stimulatory while hexanal was the least. No significant differences were recorded between antennal responses of males and females to the tested compounds. These results are discussed with regard to current hypotheses on host plant recognition through detection of their airborne volatiles and the learning behaviour by nymphs ofS. gregaria.     

Molecular evidence for multiple lineages in the gorgonian family Plexauridae (Anthozoa: Octocorallia)

Octocorals are diverse and abundant on many marine hard substrates, and, within this group, members of the family Plexauridae are an important component of tropical reef assemblages, especially in the Caribbean. To understand historical relationships within this large and diverse assemblage, and to test the monophyly of the family and some of its genera, DNA sequences of two mitochondrial loci (msh1 and ND2, ~1,185 bp) were analyzed from 46 species in 21 genera from deep and shallow waters in the tropical western Atlantic and in the tropical western and eastern Pacific (plus 9 taxa in the closely related Gorgoniidae and 1 species of the more distantly related Alcyoniidae). Five strongly supported clades were recovered. Three large clades correspond roughly to the Plexauridae, Paramuriceidae, and Gorgoniidae, and two smaller clades were comprised of taxa previously assigned to several families. Astrogorgia sp. did not group with any of the clades. The mutual relationships among the five clades remain unclear. Several genera previously regarded as unrelated appear to be grouped among the three families; e.g. Hypnogorgia sp. (Paramuriceidae) falls within a clade consisting of both Pacific and Atlantic Muricea spp. (Plexauridae), while Swiftia sp., Scleracis sp., and an Atlantic Thesea sp. (all Paramuriceidae) group with the gorgoniids. In several instances, genera containing Atlantic and Pacific species were recovered as monophyletic (Muricea spp., Bebryce spp.). However, in at least three cases (Echinomuricea spp., Thesea spp., Villogorgia spp.), placement of Atlantic and Pacific species in the same genus may reflect convergence of sclerite morphology. The results indicate a strong need for reexamination of octocoral taxonomy using a combination of molecular, morphological, and chemical evidence.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00227-005-1592-y.Communicated by J.P. Grassle, New Brunswick     

Leaf volatiles and polyphenols in pear trees infested byPsylla pyricola. Evidence of simultaneously induced responses

Summary Feeding by the homopteranPsylla pyricola on leaves of pear trees induces the production of volatile compounds, such as (E,E)--farnesene and methyl-salicylate, as well as the production of polyphenols. The inference on induction is based on GC-MS and HPLC chromatograms from the same samples ofPsylla infested leaves, leaves from the same pear tree beforePsylla infestation and uninfested leaves from other pear trees.Psylla infestation greatly enhanced the production of volatiles ((E,E)--farnesene, methyl-salicylate and others) and triggered the production of new polyphenols, characterized by much longer retention times.However, the responses to infestation depend critically on leaf age (defined by leaf distance to apex). With respect to the leaf volatiles it appears that infested, old leaves produce fewer compounds and lower amounts of the volatiles than infested, young leaves. Moreover, there seem to be differences in pattern. Relative to (E,E)--farnesene, methyl-salicylate was found in much lower amounts in heavily infested, old leaves. With respect to polyphenols it was found that infested old leaves collected in August have polyphenols with the same retention times, but more or less equal amounts as uninfested young leaves collected in May. This shows thatPsylla infestation causes the induced response mostly in young leaves.The induced leaf volatiles may act as synomones to heteropteran bugs. As shown elsewhere,Anthocoris nemoralis responds significantly to (E,E)--farnesene and methyl-salicylate when offered in pure form against clean air in a Y-tube olfactometer. The effect of polyphenols on the performance ofP. pyricola is not yet known. Hence, a role in direct defence is still to be investigated.     

Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

The feeding activity of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in 1978–1979 using various foods (natural particles, monospecific algal cultures, and artificial food) under different conditions of temperature and salinity. Experiments with Amphidinium sp. or Tetraselmis maculata as food showed that the ingestion rate increased with food concentration according to an asymptotic or a linear relationship. Although of slightly smaller size, T. maculata was ingested at a higher rate than Amphidinium sp. Large maximum daily rations (up to 150% of body carbon with Amphidinium sp. and up to 250% with T. maculata) were attained. These values, which greatly exceed those generally obtained with marine copepods, could result from adaptation of the feeding processes of this copepod to its very rich trophic environment. A significant correlation was demonstrated between ingestion rate and fecal pellet production using T. maculata as food. Therefore, daily fecal production was used as an index of feeding activity in experiments carried out with natural food, T. maculata cultures and artifical food (Tetramin). Increased temperature generally resulted in an activation of grazing and filtration rates and of fecal production at low temperatures (10° to 15°C), but a strong decrease was observed over 22°C. Differences of 10 S over or under the natural salinity level led to a decrease in fecal production, suggesting unachieved acclimatization to salinity variation due to a too short acclimation period before the experiments. Fecal pellet production was higher during the day than during the night. It depended also on the quality of food used: high values were obtained with T. maculata, Phaeodactylum tricornutum, Rhodomonas sp. and Chlamydomonas sp., low values with Chlorella sp. and Amphidinium sp., and medium values with natural food material. The assimilation rate (A) was calculated by Conover's methods. A significant negative correlation was obtained between A and the ash content of the food. High assimilation rates were attained with chlorophycean algae, while natural particulate food produced variable assimilation rates, depending on the amount of inorganic material present.

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Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

     

Use of time, space and food resources in the mangrove climbing crab Selatium elongatum (Grapsidae: Sesarminae)

The activity patterns and use of space of the mangrove dweller Selatium elongatum were studied in the field, in combination with gut content analyses for evaluation of the crab's natural diet. This sesarmine crab proves to be one of the most adapted to climbing and living on mangroves. Moreover, S. elongatum showed a strong preference for being active at high tide, both during the day and night, always along the trunks a few centimetres above the water level, feeding on floating algae and mangrove leaves. Larger males were always recorded within activity areas into which they allow females and smaller males but exclude males of the same size, which probably compete for females. These results confirm that, in spite of the homogeneous herbivorous diet, little niche overlap exists among the several sesarmine crabs inhabiting the East African mangroves, all being leaf consumers segregated on the basis of their horizontal and vertical zonation, and/or of their activity rhythm. Received: 28 September 1998 / Accepted: 14 June 1999     

Physiological responses to fluctuation in temperature of salinity in invertebrates. Adaptations ofAlpheus viridari (Decapoda,Crustacea),Terebellides parva (Polychaeta) andGolfinigia cylindrata (Sipunculida) to the mangrove habitat

The snapping shrimpAlpheus viridari (Armstrong, 1949), the polychaeteTerebellides parva Solis-Weiss, Fauchald and Blankensteyn 1990, and the sipunculanGolfingia cylindrata (Keferstein, 1865) are commonly found in the same mangrove habitat, where they experience frequent, acute fluctuations in temperature and salinity. Ecological studies indicate a temporal variation, including occasional absence, in the distribution of bothG. cylindrata andT. parva; this fed us to examine the physiological adaptations of the three species (collected at Western Bay, Twin Cays, Belize in 1985, 1986 and 1988). Each was subjected to acute, repeated exposure to either control (35 S) and decreased (25 S) salinity or to control and increased (45 S) salinity. Ability to regulate water and ion content (g H₂O or mol g^-1 solute free dry wt) was examinedA. viridari behaved as a hyperosmotic conformer at decreased salinity but as an osmoconformer at increased salinity. Regardless of direction of salinity change,A. viridari regulated water content through change in Na⁺, K⁺, and Cl^– contents. In contrast,G. cylindrata behaved as an osmoconformer and did not demonstrate ability to regulate water content.T. parva behaved as an osmoconformer, showed incomplete regulation of water content via change in Na⁺, K⁺, and Cl^– contents but had limited survival following exposure to 45 S. Each species was also exposed to change in temperature. Species were subjected to acute, repeated exposure either to control (28°C) and decreased (21°C) temperature or to control and inereased (35°C) temperatureA. viridari regulated water and ion content under both experimental conditions. In contrast,T. parva did not regulate water and ion content under either experimental temperature.G. cylindrata did not regulate water and ion content during exposure to decreased temperature and did not survive exposure to increased temperature. ForA. viridari, weight specific oxygen uptake rates (mg O₂ g^-1 ash-free dry wt) were determined. Exposure to decreased salinity or to increased temperature resulted in a small sustained elevation in O₂ uptake. It is concluded that, unlikeA. viridari, T. parva andG. cylindrata are only marginally adapted to withstand the salinity and temperature stresses, respectively, of the mangrove habitat. The inability ofT. parva andG. cylindrata to fully adapt to extremes in the mangrove habitat could well explain the temporal variation seen in the distribution of these two species.Contribution number 380. Caribbean Coral Reef Ecosystems, National Museum of Natural History, Smithsonian Institution     

Sources of carbon and dietary habits of new Lessepsian entry<Emphasis Type="Italic"> Brachidontes pharaonis</Emphasis> (Bivalvia,Mytilidae) in the western Mediterranean

The sources of carbon and the dietary habits of Brachidontes pharaonis (Mollusca, Bivalvia), a new Lessepsian entry in the western Mediterranean, living in a cooling vat of a saltworks system in western Sicily (MED), were assessed by estimating throughout a season the relative abundance of a stable carbon isotope (¹³C) in particulate organic matter (POM), sedimentary organic matter (SOM), primary organic matter sources (seagrasses, sand microflora, macroalgae), Brachidontes pharaonis and its biodeposition material. In the saltworks the most enriched primary food source potentially fuelling the saltworks food web was Cymodocea nodosa (seasonal average –7.9±0.6), Laurencia papillosa and Cystoseira sp., which represented the predominant macroalgae (seasonal average –19.0±1.0) and sand microflora ¹³C (–14.7±0.11). POM annual mean ¹³C was –17.4±0.9, and that of SOM was –17.0±2.3. The seasonal mean isotopic value of B. pharaonis was –14.7±0.7; while its faeces was more depleted (–17.7±2.4), while the pseudofaeces (–14.6±3.6) was similar to somatic B. pharaonis in composition. Our study showed that Brachidontes assimilated mostly mixed sedimentary organic carbon re-arranged via a detritus route dominated mainly by macroalgae and sand microflora and that it was able to exploit almost all the predominant carbon sources available in its colonised environment both directly (sand microflora) and indirectly via the POM/SOM detritus route. These carbon sources incorporated most of the environmental variability relative to the isotopic composition of primary producers (about –11 throughout the year).Communicated by R. Cattaneo-Vietti, Genova     

Dietary effects on oocyte yolk-composition inCapitella sp. I (Annelida: Polychaeta): Fatty acids and sterols

In 1988, immatureCapitella sp. I (initial biomass 80µg dry wt) were raised on four diets: Gerber cereal, TetraMin fish food,Ulva sp., and benthic diatoms. After 2 wk of culturing different populations on these diets, eggs were dissected from gravid females, frozen and analyzed for fatty acid and sterol composition. Eggs produced by worms on different food types were discriminated by fatty acid composition in a principal component analysis (PCA), with 18:1⁹, 18:2, 20:5 and 20:4 fatty acids showing the greatest differences between experimental groups. The sterol profiles of all eggs were dominated by cholesterol (cholest-5-en-3-ol) and cholest-5,24-dien-3-ol (>60%). A PCA of egg sterols discriminated between adult diets with cholesterol, 23,24-dimethyl-cholesta-5-en-3-ol, cholest-5,24-dien-3-ol and a C-29 stenol showing the greatest differences. In field populations ofCapitella sp. I, oocytes produced at different times of the year may have different levels of lipids depending on their dietary availability during vitellogenesis. Variations in oocyte composition may influence larval growth and development and thus have an impact on population dynamics. Alternatively, variations in fatty acid and sterol composition of oocytes may allow us to identify the food resources utilized by this species.     

Changes in nutrient content and stable isotope ratios of C and N during decomposition of seagrasses and mangrove leaves along a nutrient availability gradient in Florida Bay,USA

The decomposition of the mangrove Rhizophora mangle and the seagrass Thalassia testudinum was examined using litterbags along a natural gradient in nutrient availability. Seagrass leaves had a higher fraction of their biomass in the labile pool (57%), compared to mangrove leaves (36%) and seagrass rhizomes (29%); the overall decomposition rates of the starting material reflected the fractionation into labile and refractory components. There was no relationship between the N or P content of the starting material and the decomposition rate.

Nutrient availability had no influence on decomposition rate, and mass was lost at the same rate from litterbags that were buried in the sediment and litterbags that were left on the sediment surface. The dynamics of N and P content during decomposition varied as a function of starting material and burial state. N content of decomposing mangrove leaves increased, but seagrass rhizomes decreased in N content during decomposition while there was no change in seagrass leaf N content. These same general patterns held for P content, but buried seagrass leaves increased in P content while surficial leaves decreased. δ¹³C and δ¹⁵N changed by as much as 2‰ during decomposition.     

Relationship between bottom characteristics and benthic organisms in the shallow water of Oppa Bay,Miyagi

An investigation was conducted to examine the species composition, abundance and biomass of benthic macrofaunal invertebrates in Oppa Bay, Miyagi Prefecture, Japan, in August 1984. Among 212 species identified, nearly half (105) were Polychaetes. Usually five species, Ampharete sp. 1, Neosabellides sp. 1, Nephtys polybranchia, Chaetozone sp. 1, and Lumbrineris longifolia were numerically dominant. The faunal features of dominant species were clearly divided into two areas using two indicator species, Amphalete sp. 1 and Neosabellides sp. 1. The former species decreased in numbers in the area from the river to the bay mouth, while the latter increased. Sediments consisted of sand at the river mouth and in the northern bay; and of silt-clay in the central bay, bay mouth and southern part of the bay. Gradients of species diversity (H) were expressed as a function of distance by linear regression. The relationship was positive (r=0.812) from the river to the bay mouth accompanied by increasing depth; and negative (r=-0.906) from northern to southern parts of the bay in proportion to the increase of silt-clay in sediments.