Dynamic zonation of Nerita plicata,N. undata and N. textilis (Prosobranchia: Neritacea) populations on a rocky shore in Kenya

Vertical zonation of Nerita plicata Linnaeus, N. undata Linnaeus, and N. textilis Dillwyn, inhabiting the rocky cliffs of Nyali, Kenya, was studied through several spring-neap tidal cycles from November to December (northeastern monsoon) 1981 and May to July (southeastern monsoon) 1982. For the first time, a monsoon-related cycle of migration in Nerita plicata and N. undata, superimposed on the shorter term spring-neap cycle is demonstrated. Both species rest predominantly in the upper eulittoral zone and the littoral fringe. N. plicata and N. undata rest at significantly higher levels during the southeastern monsoon (SEM) than during the northeastern monsoon (NEM) (P<0.001). On and around neap-tide days N. plicata, N. undata, and N. textilis occupy significantly distinct mean resting positions (P<0.001) in both seasons; N. undata being the highest in the SEM, followed by N. plicata, with N. textilis always in the lowest level. In the NEM, N. plicata and N. undata sometimes change order. On and around springtide days in both seasons, the upper two species, N. plicata and N. undata, rest close together with no significant difference in their mean resting positions, but with both significantly higher than N. textilis (P<0.001). Both the spring-neap and the monsoon migrations of N. plicata and N. undata are interpreted as either direct or indirect responses to wave action.     

Nocturnal feeding migrations of Nerita plicata,N. undata and N. textilis (Prosobranchia: Neritacea) on the rocky shores at Mkomani,Mombasa, Kenya

The vertical zonation of the three common rocky shore neritids at Mkomani, Mombasa, Kenya, Nerita plicata Linnaeus, N. undata Linnaeus, and N. textilis Dillwyn, as a function of feeding migrations and of size, was studied from 28 February to 24 March 1983. These snails perform feeding migrations at night starting at around mid-ebb tide and return to their resting positions with the flood tide. They remain in their resting positions throughout the day until the next nocturnal ebb tide. The direction of migration is sizerelated, with the larger snails of each species moving in the opposite vertical direction to the smaller ones, so that the populations as a whole exhibit no statistically significant net vertical displacement. The larger individuals of two of the species, N. plicata and N. undata, invariably move downwards to their feeding levels, while the smaller individuals move upwards; the larger individuals of N. textilis display a different pattern of migration, moving downwards on and around spring-tide days and upwards on and around neap tide days, while the smaller individuals move in the opposite directions. N. textilis rest above their feeding level around spring tides, and below that level around neap tides. It is demonstrated how these nocturnal migratory feeding rhythms are integrated into the spring-neap and seasonal cycles of the snails' daytime resting positions. The adaptive significance of these migrations is also discussed.     

Mating success of male hermit crabs in shell generalist and shell specialist species

Summary The reproductive behavior of two species of diogenid hermit crabs was studied in Hawaii. In the shell generalist, Clibanarius zebra, male reproductive success varied little with size, although the largest males were less successful in obtaining copulations than were medium-large males. Male and female size were positively correlated, in successful pairs, thus larger males had the potential to fertilize more eggs when they were successful in obtaining a copulation. Female fecundity in C. zebra was not affected by species of gastropod shell inhabited once female size was taken into account. Male copulatory success was very strongly influenced by the species of gastropod shell inhabited. Males in Trochus or Nerita shells had greatly reduced reproductive success compared to males in Turbo or Nassarius shells. This result was due both to (1) males in Trochus especially dropping and otherwise poorly handling females during precopulatory behavior and (2) females not responding to precopulatory behavior patterns executed by males in Trochus and Nerita. Transferring males from good to bad shapes of shells and vice versa showed that male success was a function of shell type inhabited and not some correlated feature of the crabs. In the shell specialist, Calcinus seurati, which is found primarily in Nerita shells as an adult, males in Nerita shells were quite successful in obtaining copulations.     

Nuclear and mitochondrial DNA markers indicate unidirectional gene flow of Indo-Pacific to Atlantic bigeye tuna (<Emphasis Type="Italic">Thunnus obesus</Emphasis>) populations,and their admixture off southern Africa

A sharp genetic break separates Atlantic from Indo-Pacific bigeye tuna (Thunnus obesus) populations, as the frequencies of two major mitochondrial (mt) DNA types ( and ) found in this species are different across the tip of southern Africa. The level of nucleotide divergence between mtDNA types and is of the same order as that between reproductively isolated taxa. To further investigate the genetic structure of bigeye tuna over its distribution range and in the contact zone off southern Africa, bigeye tuna samples collected between 1992 and 2001 (including samples from a previous mtDNA survey) were characterized for four nuclear DNA loci and for mtDNA. Nuclear markers did not support the hypothesis that and mitochondria characterize sibling species. Significant allele-frequency differences at one intronic locus (GH2) and one microsatellite locus (µ208) were found between Atlantic and Indo-Pacific samples, although the level of nuclear genetic differentiation (Weir and Cockerhams =0.025 to 0.042) was much lower than in mtDNA ( =0.664 to 0.807). Probabilistic Bayesian assignment of individuals to a population confirmed that southern African bigeye tuna samples represent a simple mixture of individuals from Atlantic and Indian stocks that do not interbreed, with a higher contribution from Indian Ocean individuals (about 2/3 vs. 1/3).Communicated by M.S. Johnson, Crawley     

Photosynthetic characteristics of nanoplankton and picoplankton from the surface mixed layer

Nanoplankton and picoplankton primary production has been studied at two oceanic stations in the Porcupine Sea-bight and at one shelf station in the Celtic Sea. At both sites, low wind conditions in June and July 1985 resulted in greatly reduced vertical turbulent mixing and a secondary, temporary thermocline developed in what is usually a well-mixed surface layer; as a result, there was physical separation of the phytoplankton within two zones of the surface mixed layer. The photosynthetic characteristics of three size fractions (>5 m, <5 to >1 m and <1 to >0.2 m) of phytoplankton populations from the two zones have been measured. Phytoplankton was more abundant at the oceanic stations and chlorophyll a values were between 1.3 and 2.2 mg chlorophyll a m^-3, compared with 0.3 to 0.6 mg chlorophyll a m^-3 at the shelf station; at both stations, numbers of cyanobacteria were slightly higher in the lower zone of the surface mixed layer. There was no effect of the temporary thermocline on the vertical profiles of primary production and most phtosynthesis occurred in the surface 10 m. Photosynthetic parameters of the three size fractions of phytoplankton have been determined; there was considerable day-to-day variation in the measured photosynthetic parameters. Assimilation number (P _m ^B ) of all >5 m phytoplankton was lower for the deeper than for the surface populations, but there was little change in initial slope (a ^B ). The small oceanic nanoplankton (<5 to >1 m) showed changes similar to the >5 m phytoplankton, but the same size fraction from the shelf station showed changes that were more like those shown by the picoplankton (<1 m) viz, little change in P _m ^B but an increase in a ^B with depth. Values of a ^B were generally greater for the picoplankton fraction than for the larger phytoplankton, but values of adaptation parameter (I _k )(=P _m ^B /) were not always less. There was little evidence to support the hypothesis that these populations of picoplankton were significantly more adapted to low light conditions than the larger phytoplankton cells. When photosynthetic parameters of the picoplankton were normalised to cell number (P _m ^C /a ^C ) rather than chlorophyll a, P _m ^C was comparable to other published data for picoplankton, but a ^C was much lower. The maximum doubling time of the picoplankton at saturating irradiance is calculated to be ca. 8.5 h for the oceanic population and ca. 6.2 h for the shelf population.     

The enantiomeric composition of monoterpene hydrocarbons in the defensive secretions ofNasutitermes termites (Isoptera): Inter- and intraspecific variations

Summary Frontal gland secretions of termite soldiers of the speciesNasutitermes costalis, N. ephratae, N. nigriceps, N. rippertii, andN. hubbardii were analyzed. The chiral compositions of the monoterpene hydrocarbons were investigated by means of two-dimensional gas chromatography. Two of them, 3-carene and-pinene were present in the form of (–)-enantiomers of high purity in the majority of the samples. The other monoterpenes,-pinene, camphene, sabinene, limonene, and-phellandrene, exhibited a great variation in the enantiopurity between different species.-Pinene and limonene varied significantly even between different colonies within the species.N. costalis was the only species with an invariable composition of the secretion, independent of the locality or origin.     

The effect of temperature-salinity combinations on survival and growth of juvenile Patiriella pseudoexigua (Echinodermata: Asteroidea)

Adult Patiriella pseudoexigua were collected in October 1989 from Wanlitung, Taiwan and then induced to spawn in the laboratory. Post-metamorphosed juvenile P. pseudoexigua were reared on a diet of benthic algae Navicula sp. at 25°C and salinity (34). Six weeks after metamorphosis, juvenile P. pseudoexigua at ca. 400 m in radius were reared on a diet of benthic algae Navicula sp. at different combinations of temperatures (20, 25, 30°C) and salinities (26, 30, 34) for 40 d. Both temperature and salinity had a significant effect on juvenile survival and growth. Juveniles survived best (>90%) at 25°C and 34 and grew best (to ca. 750 m in radius) at 30°C and 34. Variation in juvenile size was small immediately after metamorphosis and increased with time.     

Stable isotopic investigation of physiological and environmental changes recorded in shell carbonate from the giant clam Tridacna maxima

The aragonitic shell of the photosymbiont-bearing bivalve Tridacna maxima contains a record of the physiological and environmental changes the organism has experienced during its lifetime. This record is preserved as chemical and microstructural variations throughout the shell. Stable isotopic analyses of oxygen (¹⁸O/¹⁶O) and carbon (¹³C/¹²C) in shell carbonate were combined with growth increment studies to interpret the shell record of specimens collected from the Rose Atoll (Lat. 14°31S; Long. 168°10W) in April 1982. The seasonal water temperature cycle is recorded in the oxygen isotopic signature of the clams, permitting the recognition of annual cycles in the ¹⁸O profile. The total number of these cycles corresponds to the age of a specimen, while the cycle length is a measure of the yearly growth rate. Large-amplitude cycles, reflecting year-round calcification, characterize the early portion of the growth record. With the onset of sexual maturity and slower growth at an age of approximately ten years, the cycles decrease in amplitude and become more erratic. During this later growth phase calcification is limited to the cooler months of the year, perhaps in response to a re-ordering of energy priorities between growth and gametogenesis. A growth curve developed from the ¹⁸O profile indicates rapid juvenile shell growth followed by slower growth thereafter producing a lifespan of several decades. Carbon isotopic analyses of T. maxima were compared to analyses of the symbiont-barren gastropod Terebra areolata collected from the same locality in April 1984. A 2 depletion in the ¹³C composition of T. maxima shell carbonate is attributed to a symbiontenhanced metabolic rate and an increased flow of isotopically light, respired CO₂ into the carbon pool used in calcification. Such a depletion may prove useful in identifying the presence of photosymbionts in extinct species of fossil mollusks.     

Examples of post-mortality alteration in Recent brachiopod shells and (paleo)ecological consequences

Post-mortality alteration of brachiopod shells under normal environmental conditions leads to high taphonomic loss, and to a poor contribution to the biodetrital soft sediment. The successive stages of alteration which shells undergo are: (bio)degradation of the organic matrix shell softening structural disaggregation or/and mechanical fragmentation; these processes depend on the shell structure (number of layers) and composition (organic and inorganic components), but very little on environmental conditions, except for the dissolution of inorganic shell constituents. Among the Brachiopoda, three types of alteration occur to different types of shells — Type I: two-layered chitino-phosphatic shell (species ofLingula andGlottidia) displays a rapid degradation of the organic matrix and mechanical abrasion, leading to total disappearance of the shell in 2 to 3 wk; Type II: two-layered carbonate shell, e.g.Terebratulina spp. [but notNotosaria nigricans (Sowerby) which may constitute a fourth shell type], exhibits degradation of the organic matrix of the secondary layer, shell softening, and structural disaggregation leading to shell disintegration in 6 to 7 mo with a concomitant contribution of calcitic microfibres to the sediment; Type III: three-layered carbonate shell, e.g.Gryphus vitreus (Born), undergoes organic degradation of the secondary layer, fragmentation of the anterior two-thirds of the shell, and slow degradation (because of the thick tertiary layer) of the posterior portion of the shell, with dissolution of the inorganic components (mainly in the tertiary layer) which make a relatively minor contribution to the sediment.     

Genetic variation among life-history stages of mussels in a<Emphasis Type="Italic"> Mytilus edulis–M</Emphasis>.<Emphasis Type="Italic"> trossulus</Emphasis> hybrid zone

The mussel species Mytilus edulis L. and M. trossulus Gould coexist and hybridize throughout a large area that includes the north coast of Maine and Atlantic Canada. Previous studies provided genetic evidence for limited hybridization between the two species for mussels >15 mm. The present study used two genetic markers (ITS, Glu-5) to examine the genetic composition of early life-history stages by sampling veliger and pediveliger larvae, juveniles (<2.0 to 15.0 mm shell length) and adults (>15 mm shell length) in Trinity Bay, Newfoundland, during three consecutive years (1995–1997) to determine if differential mortality limits the relative abundance of hybrids. The relative frequency of the two species and the different hybrid genotypes was similar among the larvae, juveniles and small adult mussels. The double hybrid genotype (F₁-like) was the rarest genotype observed. There was no evidence for differential mortality during the early life-history stages, and factors limiting production of hybrids appear to operate before the late larval stage. The observed frequency of hybrids is probably due to a combination of pre- and postzygotic reproductive isolating mechanisms operating early in the mussels life history. M. trossulus dominated the early life-history stages, possibly due to a higher population density and a greater reproductive output than M. edulis. Differential mortality may explain the observed decrease in frequency of M. trossulus and increase in frequency of M. edulis with increasing shell length. A similar frequency of hybrid mussels from larvae to the size class of 55 mm shell length may indicate a rate of mortality intermediate between the two parental species. The M. edulis–M. trossulus hybrid zone appears to be maintained by reproductive isolating mechanisms limiting the production of hybrids and life-history differences that allow the two species to coexist.Communicated by J.P. Grassle, New Brunswick     

Biochemical composition of Nyctiphanes australis and its possible use as an aquaculture feed source: Lipids,pigments and fluoride content

Nyctiphanes australis contained, on a dry weight basis, an average of 52% crude protein and 5.0 to 9.5% lipid. The fatty acid profile of N. australis was markedly unsaturated, with a mean total 3 fatty acid content of 48.6±2.4% of total fatty acids. N. australis contained high levels of the essential long-chain polyunsaturated fatty acids eicosapentaenoic (EPA, 20:53) and docosahexaencic (DHA, 22:63), ranging from 16.6 to 36.5% and 11.1 to 24.8%, respectively. The concentration of total carotenoids ranged from 137 to 302 g g^–1 dry wt, with no significant differences in concentrations found with season or life stage. The carotenoids were comprised of 79.5% astaxanthin and 20.5% canthaxanthin. The lipid and pigment compositions of N. australis suggest that the species could serve as a suitable feed source for cultured salmonids. Like other euphausiids, N. australis contained high levels of fluoride, with a seasonal range between 277 and 3507 g g^–1 dry wt. The high fluoride levels found in N. australis would not detract from its potential as a feed source for salmonids because ingested fluoride is largely absorbed by the skeleton.     

Functional feeding morphology of the euphausiid Nyctiphanes australis

The structure of the feeding basket, mandible and stomach armature of the krill Nyctiphanes australis (G. O. Sars, 1883) was examined by scanning electron microscope with the aim of predicting its diet. N. australis were collected during February 1986 and October 1986 to February 1987 in Otago Harbour, New Zealand (45° 50 S; 170° 37 E). Predictions based on the functional morphology were tested by examining stomach contents with SEM. Intersetule distances of the feeding basket (1 to 7.5 m) are finer than in other krill species, suggesting that N. australis can efficiently collect nanoplankton-sized particles (2 to 20 m). The mandibular edge index (0.74) matched the edge index of Meganyctiphanes norvegica. This indicates, in contrast to the fine feeding-basket setulation, that N. australis has a mandible resembling that of predominantly carnivorous krill species. The ratio of mandibular palp length to mandible width is 3.2±0.2, or relatively longer than the elongate palp thought to be indicative of herbivorous habit in Euphausia superba. The fine structure of the molar shows specialized surfaces which differ from those of other krill species. The internal armature of the stomach is heavily spinose, as is common in krill of herbivorous habit. Layers of various-shaped spines at differing densities were observed. The functional morphology suggests that N. australis is an opportunistic omnivore. The stomach contents tentatively support this prediction, containing fragments of phytoplankton and detrital material. However, stomach contents were generally amorphous, making identification of dietary components in the field difficult.     

Spatial variation and ontogenic shifts in the isotopic composition of Mediterranean littoral fishes

Stable carbon and nitrogen isotope signatures have been determined for littoral fishes from three localities in the Balearic Islands (NW Mediterranean) for trophic assessment. Variation in the isotopic composition was examined at multiple levels: the individual organism, individual populations (ontogenetic variation) and at area effects (different islands). Cluster analyses based on ¹³C and ¹⁵N resulted in two very different dendrograms for the fish assemblages from Menorca and Formentera. In both schemes, congeners of the genera Diplodus and Labrus did not cluster together, suggesting that closely related species do not necessarily feed on similar foods. Significant differences in ¹⁵N were detected between locations for Scorpaena porcus, Scorpaena scrofa and Sciaena umbra, and significant differences in ¹³C were detected for Scorpaena porcus and Scorpaena scrofa. Overall there were significant spatial differences in the trophic position of littoral fishes among the three Balearic Islands, and fishes from Palma, Mallorca tended to feed at a higher trophic level than fishes from either Menorca and Formentera. Large-scale geographic comparisons, using earlier data from three sites in western Mallorca and in Corsica revealed that throughout the western Mediterranean generally, the average trophic level of fishes differs remarkably little. However, large discrepancies were observed in ¹⁵N for individual species, notably Scorpaena porcus, D. annularis, D. vulgaris and Serranus scriba. ¹³C composition of fishes did not seem to change greatly among the locations, although marked discrepancies were observed for D. puntazzo and Mullus surmuletus. Given the large-scale patterns we have observed, it is possible that the extent of multichannel omnivory which has been purported to exist in complex aquatic systems, may have been greatly overstated. Regression of ¹⁵N and ¹³C with fish body size revealed clear and significant trends for some species. In particular, ¹⁵N appeared to increase with body length in the macrocarnivorous fishes Scorpaena porcus, Scorpaena scrofa, Serranus scriba and Sciaena umbra. Trends were less apparent in animals which feed primarily on small benthic invertebrates, notably the four Diplodus species (D. vulgaris, D. sargus, D. annularis, D. puntazzo), and the labrids Labrus viridis and L. merula.Communicated by J.P. Thorpe, Port Erin     

Nitrogen regeneration by two surf-zone mysids,Mesopodopsis slabberi andGastrosaccus psammodytes

Nitrogen regeneration by two surf zone mysids,Mesopodopsis slabberi andGastrosaccus psammodytes, was determined under laboratory conditions. The mysids were collected from the lower Sundays River estuary, South Africa, from early spring 1984 to late summer 1985. The forms of nitrogen excreted and the effects of mass, temperature and feeding on excretion rate were determined for each species at three experimental temperatures. Comparison of the forms of nitrogen excreted revealed only slight differences between species, with ammonia the major form and urea and amino acids the secondary excretory products in both cases. Mass significantly influenced the rate of ammonia excretion at all experimental temperatures, with no significant difference in slope (common b=0.602) detected between species. During the day sediment deprivation resulted in a 15% and 20% increase in mean ammonia excretion rates of juvenile and adultG. psammodytes respectively, whereas no significant differences were found at night. The mean ammonia excretion rates of fedM. slabberi andG. psammodytes were 2 and 2.5 times higher than starved excretion rates, respectively.G. psammodytes andM. slabberi recycle 139 to 150 g N per running meter of surf zone per year and 1 007 to 1 208 g N m^-1 yr^-1, respectively. Togehter this constitutes 10% of total phytoplankton nitrogen requirements in the surf zone.     

Variability of shell growth and morphology of the wall-plate junctions of the intertidal barnacle Tesseropora rosea (Cirripedia: Tetraclitidae)

Variability in shell growth and morphology of the wallplate junctions of Tesseropora rosea (Krauss) were studied in 1983 in New South Wales, Australia, at two sites with differing wave exposure. The wall-plate junctions, a combination of dado (geometrically interlocking) and lap bints, increase in complexity with age, but do not differ between sites. The number of parietal tubes is fixed at settlement and does not differ between sites, but differs among wall plates in a manner consistent with their evolutionary history (rostrum > laterals > carina). The number of secondary septa increases with age, but does not differ between sites. In epilithic T. rosea, growth of the alae contributes to orifice enlargement. Epizoic T. rosea (on limpets) have conspicuous radii and display diametric growth. At the more exposed site, the shell wall was sleeper, and the aperture length, height and weight of the shell increased at a faster rate than at the less exposed site, but the maximum height of the shell was less. These differences appear to be due to a combination of greater feeding rates and greater erosion rates at the exposed site. The greater maximum height attained at the more sheltered site may be due to greater individual longevity. Juveniles at the sheltered site had thinner septa in the laterals than those at the exposed site. Septa in adults were rhinner at the exposed site, but this is due to age differences between sites in the adult populations.     

Response of a soft-bottom harpacticoid community to stingray (Dasyatis sabina) disturbance

The recolonization by harpacticoid copepods of patches disturbed by stingrays [Dasyatis sabina (LeSeur)] feeding in a subtidal (2–3 m depth) site off the Florida gulf coast (Lat. 29°54.55N, Long. 84°31.45W) was followed. Samples from disturbed patches could no longer be distinguished from control samples in terms of numbers of harpacticoids 29 h after disturbance. No species became significantly disproportionately abundant during the recovery suggesting that small-scale natural disturbances are not an important organizing force in this community.     

Monitoring spatio-temporal variation in molluscan grazing pressure in seasonal, tropical rock pools

In Hong Kong, low-shore rock pools support a patchy mosaic of different successional stages of crustose coralline algae. Echinoid and molluscan grazers are abundant in these low-shore rock pools and spatial and temporal variation in grazing pressure is thought to play an important role in structuring these assemblages. Direct records of graze marks using a modified wax-disc method were used to monitor spatial (different pools) and temporal (periods, 3 or 4 days each; spring vs. neap tides; summer vs. winter) variations in grazing pressure. Radula marks of Chlorostoma argyrostoma, Lunella coronata and Nerita albicilla were common in all pools. Grazing pressure was highly variable with tidal state and season but also within these two factors. Lunella and Nerita exerted highest grazing pressure at neap tides during summer, whilst Chlorostoma exerted highest grazing pressure in winter. Although overall patterns of temporal variation were similar and consistent in all pools, there was between pool variation in grazing pressure and individual species showed different patterns. Within the seasonal and tidal variations, large period-to-period differences were found for all species, illustrating small-scale temporal variation. Fine-scale spatial and temporal patterns of variation in grazing pressure of different species, therefore, contribute to the highly dynamic nature of these low-shore rock pools.     

Modification of shell formation in the giant clam Tridacna gigas at elevated nutrient levels in sea water

The effect on shell formation of Tridacna gigas by sea water supplemented for 3 mo with ammonium (5, 10 M, N) and phosphate (2, 5, 10 M, P), separately or in combination, was examined. Exposure to N and N+P significantly enhanced shell-extension rates, but significantly reduced shell weights at equivalent size. Scanning-electron microscopy further revealed structural alterations in the outer shell layer, such as misshapen aragonite crystals, irregular crossed-lamellar orientation, and relatively porous shell microstructure. These observations are consistent with results of X-ray diffractometry on the shells which show distinct shifts in the positions of reflections from the (012) and (200) crystal planes relative to the control, indicating changes in crystal lattice parameters following addition of nutrients.     

Spatial and temporal shifts in stable isotope values of the bottom-dwelling shrimp<Emphasis Type="Italic"> Nauticaris marionis</Emphasis> at the sub-Antarctic archipelago

Spatial and temporal dynamics of carbon and nitrogen stable isotope signatures of the bottom-dwelling caridean shrimp Nauticaris marionis were measured during April and May between 1984 and 2000 in the vicinity of Marion Island (the Prince Edward Islands, Southern Ocean). There was one trophic-level enrichment in bulk ¹⁵N and ¹³C signatures between small (<20 mm long) and large (>20 mm) specimens of N. marionis, suggesting distinct trophic differentiation among major shrimp size groups. Both ¹⁵N and ¹³C values of N. marionis increased with the depth, reflecting changes in their diet. There were no clear temporal trends in bulk ¹⁵N signatures of N. marionis. However, compound-specific ¹⁵N measurements of amino acids indicated that N. marionis from the inter-island realm occupied the trophic level of second order carnivores, while similarly sized shrimps in the near-shore realm were at the trophic level of first order carnivores. Compound-specific measurements also identified a change in the source of inorganic nitrogen at the base of the food web between the inter-island and near-shore realms. In contrast to the bulk ¹⁵N values, a significant shift in bulk ¹³C values of N. marionis was observed between 1984 and more recent years. This temporal change appears to be linked to changes in the overall productivity of the Prince Edward Island inter-island system, which could be linked to global climate change.Communicated by J.P. Thorpe, Port Erin     

Isozymes and general protein patterns as taxonomic markers in the taxon Nephtyidae (Annelida Polychaeta)

Seven Nephtys species and one species of the genus Aglaophamus (collected from different European tidal and subtidal locations between 1989 and 1991) were compared with respect to six isozyme systems (-amylase, esterase, hexokinase, malate dehydrogenase, malic enzyme, phosphoglucoseisomerase) as well as with respect to general protein patterns with non-specific staining. The proteins were obtained from the tissue (proboscis, individual segments) of single individuals, the species of which had previously been accurately determined, and were separated by isoelectric focusing (IEF) in polyacrylamide gels. The enzymes were identified by their specific catalytic activities, and the general proteins were visualized by silver staining. All the isozymes proved to be monomorphic within each of the various polychaete populations. With a single exception, it was impossible to distinguish geographically separated populations of the same species, because the band patterns were completely consistent within the species. The individual enzymes varied in their suitability for species differentiation. Only with respect to esterase and -amylase could all species be distinguished; the other enzymes studied were identical in morphologically similar species. In contrast, each species could be identified by its general protein pattern, although some species differed from others in the position of a few bands only. Individuals of N. hombergii, N. caeca and N. cirrosa with abnormally shaped parapodia, as well as juvenile nephtyids, could be unequivocally assigned to their respective species by IEF. Only in the case of N. longosetosa were two morphological variants found to differ in their electrophoretic characteristics; one of them is interpreted as a new species, not previously described.