Distribution of the alien ctenophore <Emphasis Type="Italic">Mnemiopsis</Emphasis><Emphasis Type="Italic">leidyi</Emphasis> in the Caspian Sea in August 2001

In this study, spatial and vertical distributions of the invasive ctenophore Mnemiopsis leidyi in the Caspian Sea were evaluated by using data collected at 41 stations during the August 2001 cruise. A comparison of data from different depths revealed that M. leidyi were generally confined to surface waters. The maximum size of the ctenophore was only 41-45 mm, and the bulk of individuals (85.5%) were <10 mm in length. The average and maximum biomasses of M. leidyi were calculated as 120 and 351 g wet weight m^-2, respectively. Whilst highest biomasses were observed in the western and central Middle Caspian Sea, hot spot areas of reproduction were present along the coasts of the western Caspian Sea, with abundance values of up to 2285 ind. m^-2. The impact of such high densities of M. leidyi is expected to be significant for the pelagic ecosystem of the Caspian Sea.     

Osteological development of the vertebral column and of the fins in Diplodus sargus (Teleostei: Perciformes: Sparidae)

The osteological development of vertebral column and fins in white sea bream, Diplodus sargus (Linnaeus, 1758) was studied. Vertebral ontogeny started at 5.7 mm total length (TL, post-fixation), with the formation of the first cartilaginous neural and haemal arches, and was completed by the full attainment of dorsal ribs (20.8 mm TL). The formation of vertebral centra occurred between 7.3 and 9.4 mm TL, but was fully completed only after the development of post- and pre-zygapophyses (26.0 mm TL). Pectoral supports were the first fin elements that started to develop (3.8 mm TL), followed by those of the caudal fin (5.2 mm TL), dorsal and anal fins (6.7 mm TL), and then by those of the pelvic fin (9.5 mm TL). The caudal fin of D. sargus was the first to develop fin rays and attain the full count of lepidotrichia (5.6-7.8 mm TL), but the last to attain the full count of dermatotrichia (7.9-16.0 mm TL). The next fins starting to present rays were the pectoral (6.5 mm TL) and the dorsal and anal fins (7.5 mm TL), while the pelvic fins were the last (11.5 mm TL). Following the caudal lepidotrichia (7.8 mm TL), the anal (10.5 mm TL), dorsal (12.0 mm TL), pectoral (11.4 mm TL) and pelvic fins (12.5 mm TL) were the next with fully completed ray counts. Finally, fin meristics were fully developed with the caudal dermatotrichia. The results are discussed in comparison with the fin and vertebral ontogeny of other teleosts.     

Changes in otolith microstructure and microchemistry during larval development of the European conger eel (<Emphasis Type="Italic">Conger conger</Emphasis>)

Otolith microstructure and chemical composition (Sr:Ca ratios) of the European conger eel (Conger conger) were examined during the larval developmental stages by scanning electron microscopy and wavelength dispersive spectrometer. Back-calculated hatching dates from the otolith microstructure of the developing leptocephali indicate a protracted spawning season from December to June. The early age of our developing specimens captured south of the Azores Islands suggests that the conger eel has another spawning area closer to Azores than the Mediterranean. Otolith increment width, which was relatively constant and narrow in the developing leptocephalus stage, increased sharply at age 170-250 days. Sr:Ca ratios in the otolith, which increased during the developing leptocephalus stage, showed a rapid drop coinciding with the increase in increment width. These coincidental changes were regarded as the onset of metamorphosis for this species. A close linear relationship between the age at metamorphosis and otolith growth rate indicates that the faster-growing larvae metamorphose earlier, suggesting that somatic growth should play an important role in the timing of metamorphosis. As shown in earlier work, the existence of an otolith marginal zone with unclear rings during metamorphosis prevents an accurate estimate of the larval stage duration of this species.     

A comparison of transport-related gill enzyme activities and tissue-specific free amino acid concentrations of Baltic Sea (brackish water) and freshwater threespine sticklebacks, Gasterosteus aculeatus, after salinity and temperature acclimation

The osmoregulatory abilities of one freshwater and two brackish water (Baltic Sea) populations of the euryhaline teleost fish Gasterosteus aculeatus were studied with respect to evolutionary physiology. Plasma osmolality, activities of Na⁺K⁺-ATPase, citrate synthase, creatine kinase in the gill and free amino acids in liver, axial muscle and pectoral fin muscle were measured. After transfer from 10 to 35 ppt at 15 °C, time-course changes of plasma osmolality and gill Na⁺K⁺-ATPase showed no significant fundamental differences between the freshwater and one of the Baltic Sea populations. In a multi-factorial experiment, each population was exposed to four different abiotic regimes. Both brackish water populations had high mortality in freshwater at 4 °C, which is discussed as a failure of osmotic regulation (reduced taurine concentrations). Freshwater specimens had higher levels of glycine in the axial and pectoral fin muscles compared to the brackish water populations. This is interpreted as a genetically based effect. In brackish (20 ppt) water of 15 °C, the freshwater population had high activities of Na⁺K⁺-ATPase, but low activities of creatine kinase, whereas both brackish water populations behaved in the opposite way. A fundamental difference between the freshwater and brackish water populations on the level of the osmoregulatory machinery was not observed. Received: 10 December 1998 / Accepted: 22 September 1999     

Stoichiometry of mesozooplankton in N- and P-limited areas of the Baltic Sea

The Baltic Sea is a very suitable site for stoichiometric studies, since its subbasins differ in their concentration of elemental components, and primary production can therefore be either nitrogen or phosphorus limited. To reveal if the nutrient limitation of mesozooplankton mirrors that of the primary producers, carbon, nitrogen and phosphorus content of both seston and grazers (Acartia sp., Centropages hamatus, Daphnia cristata, Eurytemora affinis, Limnocalanus macrurus, Temora longicornis) were measured in midsummer in the Baltic proper, the Gulf of Finland and the Gulf of Bothnia. The mineral ratios of the different taxa were equal, apart from L. macrurus with notably higher C:P and N:P ratios. Molar C:N ratios were relatively stable (5.1-6.3), whereas C:P and N:P ratios fluctuated more (41-144 and 6.6-24). However, zooplankton elemental composition and limitation did not depend on the limiting nutrient of the phytoplankton, the seston mineral ratio or the sea area. Both the seston-zooplankton elemental imbalance and the food threshold ratio indicated phosphorus limitation of most of the grazers. While L. macrurus may be C or N limited, the possible P deficiency of the other studied taxa suggests that the Baltic Sea zooplankton may act as a potential phosphorus sink, as the freshwater secondary producers do.     

Occurrence of marine resident tropical eel Anguilla bicolor bicolor in Indonesia

In order to understand the migratory history and habitat use of the tropical anguillid eels Anguilla celebesensis, A. marmorata, and A. bicolor bicolor, the otolith strontium (Sr) and calcium (Ca) concentrations were examined for eels collected in Indonesian waters. In A. bicolor bicolor collected in a lagoon, the change in Sr:Ca ratios outside the high Sr:Ca core generally indicated two patterns of habitat residence: (1) constant living in either brackish or sea waters with no freshwater life (25%) and (2) habitat shifts from fresh water to brackish or sea waters (75%). No A. bicolor bicolor had a general life history as a freshwater resident. A. celebesensis and A. marmorata from the uppermost freshwater lake showed freshwater life history patterns. The wide range of otolith Sr:Ca ratios in A. bicolor bicolor indicated that the habitat use of this tropical eel was facultative among fresh, brackish, and marine waters during the growth phase after recruitment to coastal areas similar to that for temperate eels. Thus, the migration of anguillid eels into fresh water is clearly not an obligatory.     

Elemental composition of otolith growth marks in three geographically separated populations of European hake (Merluccius merluccius)

The composition of the opaque and translucent bands in the otoliths of European hake (Merluccius merluccius) from three different populations (Celtic Sea, Galicia shelf and Cretan Sea) was analysed with wavelength dispersive spectrometry (WDS) and differences in Ca, Sr and Na were compared. The translucent bands (annual marks and checks altogether) were significantly richer in Sr and Ca and significantly poorer in Na than opaque bands. Results support the idea of a more compact arrangement of crystals in translucent bands compared to opaque. Analyses did not help to discriminate between putative annual marks and checks. Clear differences in the range of Sr/Ca variation across the otolith as well as in the composition of the otolith core were observed among the three populations. As a result it was possible to discriminate the natal origin of each fish using the composition of the otolith core in Ca, Sr and Na. Nevertheless, the overall pattern across the otolith was similar among the three populations suggesting the existence of ontogenetic trends. Variation of Na/Ca ratios was largely uninformative. Based on these results, a conceptual model for hake is proposed which integrates the different sources of otolith Sr/Ca variation: ambient Sr/Ca, endogenous cues (ontogeny) and exogenous cues (environment).     

Acoustical identification of the concentration layer of a copepod species,Calanus euxinus

Swimming trajectories of Calanus euxinus Hulsemann in the Black Sea were studied using an echosounder at 120 and 200 kHz. C. euxinus were acoustically discriminated with respect to vertical migration and swimming speed, according to dissolved oxygen (DO) concentration and the timing of migrations. Species became torpid in water with DO values <0.5 mg l^у. The time spent swimming under DO conditions between 2 and 5 mg l^у was insignificant, and varied greatly from the 10% to 25% of total time spent swimming under normoxic conditions (5-10 mg l^у). C. euxinus formed a concentration layer in the water of 1-3 m thickness. Upward migration was completed in about 3.5 h, starting 2.5 h before and ending 1 h after sunset (average rate: 0.95 cm s^у) in summer. Species ascended discretely from the suboxic to the lower boundry of the cold intermediate layer (CIL) at 0.82 cm s^у, and passed up the CIL and thermocline fast (2.3 cm s^у). Downward migration took less time (2 h), starting ~1 h before and ending ~1 h after sunrise. Swimming speed within the thermocline and CIL was 2.7 cm s^у; copepods subsequently returned to daylight depth at a sinking speed of 0.57 cm s^у. Total time for C. euxinus to settle to their nocturnal depth layer was about 5 h.     

A new record of the endosymbiont polychaete Veneriserva (Dorvilleidae), with description of a new sub-species, and relationships with its host Laetmonice producta (Polychaeta: Aphroditidae) in Southern Ocean waters (Antarctica)

A new record of the genus Veneriserva Rossi, 1984 (Polychaeta: Dorvilleidae) is reported, as an endosymbiont in the coelom of the polychaete Laetmonice producta Grube, 1877 (Aphroditidae) in the eastern Weddell Sea and off King George Island (Southern Ocean, Antarctica). The specimens studied were very similar to Veneriserva pygoclava Rossi, 1984; however, due to the greater morphological variability and larger dimensions of our specimens, as well as different host species and geographic locations, a new sub-species, V. pygoclava meridionalis, was erected. A total of 842 specimens of L. producta were examined, 163 of which hosted 209 symbionts (183 in the Weddell Sea samples and 26 in the King George Island samples). Symbiont prevalence was higher in the Weddell Sea samples, and increased with depth (max. 51% at stn 14, 850 m depth). Symbiont intensity was equal to one for 78% and to two for 19.6% of all hosts examined; a maximum of six symbionts per single host was observed. Mean symbiont density was equal to 0.36 and 0.07 for the Weddell Sea and King George Island host populations, respectively. A weak linear relationship was found between symbiont and host size. Eight symbiont specimens (all found at a single station, 850 m depth) were bearing eggs, ranging between 10 and 200 µm in diameter, while 13 specimens were observed in regeneration of the posterior part, suggesting the occurrence of both sexual and asexual reproduction. The way of feeding is still not clear; reduction of the jaw apparatus suggests a parasitic host-symbiont relationship, however, no evident damage was observed in the tissues of the host. These results point out that occurrence of polychaete endoparasites in large aphroditids may be a more frequent and widespread phenomenon than previously believed, and that more attention should be paid to this aspect also in temperate and tropical aphroditid species.     

Population development of the invader ctenophore Mnemiopsis leidyi, in the Black Sea and in other seas of the Mediterranean basin

In the last two decades of the twentieth century, the ctenophore Mnemiopsis leidyi (A. Agassiz) has invaded the Black, Azov, Marmara and Aegean Seas, and, recently, the Caspian Sea. Here, we compare its spatial and temporal distribution, seasonal dynamics and the time and duration of reproduction. We also discuss factors that control its abundance throughout its invasive range and its effect on ecosystems. Observations are based on the long-term field data collected by three research institutes. An analysis of the effects of temperature, salinity, prey (zoo- and ichthyoplankton) availability and predation (by ctenophores of the genus Beroe) on M. leidyi population size, and the effects of M. leidyi on zoo- and ichthyoplankton, and on fish populations in the Black and Azov Seas is also provided. With the Black Sea current, M. leidyi spreads to the upper layers of the Sea of Marmara, where it now occurs around the year. At regular intervals, the Black Sea current also takes it to the northern Aegean Sea. In contrast, it has to re-invade the Sea of Azov every spring or summer, dying out during winter when the temperature drops below 4°C. The warm summer and mild winter temperatures, relatively low salinity and abundance of prey in the Black Sea are close to optimal for M. leidyi, while they are suboptimal in the northern Aegean Sea, where salinity and temperature are often too high. In the Black Sea the absence of gelatinous and other predators led to an enormous ctenophore abundance for a decade, but with the appearance of Beroe ovata in 1999, M. leidyi abundance greatly decreased. Analysis of seasonal dynamics of M. leidyi in the Black Sea and in other seas of the Mediterranean basin indicates similarities in the timing of maximum abundance and biomass, in spite of some differences in the initiation and duration of reproduction. A peak biomass and density occurred in 1989 in the Black and Azov Seas and in 1990 in the other seas. The M. leidyi invasion negatively affected the ecosystems of the Black Sea and the Sea of Azov. The zooplankton, ichthyoplankton and zooplanktivorous fish stocks all underwent profound changes. Similar effects, but less pronounced, were recorded in the Sea of Marmara. Effects on Mediterranean food chains have, so far, remained insignificant. Salinity is probably supraoptimal here, and several predators prevent M. leidyi from reaching outbreak levels.     

Strontium/Calcium ratios in statoliths of the neon flying squid, Ommastrephes bartrami (Cephalopoda), in the North Pacific Ocean

Strontium to calcium ratios were observed along longitudinal sections of statoliths of nine neon flying squid, Ommastrephes bartrami (LeSueur, 1821), including three mature females (422 to 454 mm mantle length, ML; 207 to 306 d old) obtained from the North Pacific (27–35°N; 144–150°E) during winter and six immature males and females (187 to 226 mm ML; 126 to 164 d old) collected from 39°N; 145°E and 39°N; 169°W during summer. The distances between the nucleus (core) and the edge of the dorsal dome were approximately 660 to 690 μm in mature females and 450 to 510 μm in the immature squid. Sr/Ca ratios were determined at intervals of 30 μm between the nucleus and edge of the dorsal dome. Sr/Ca ratios were higher in areas near the nuclei and peripheral portions of the dorsal dome than in the middle portions of the statoliths (270 to 420 μm from the nuclei, corresponding to ages of 60 to 90 d) in mature females; thus a U-shaped pattern was evident. Sr/Ca ratios in the six immature squid decreased from nucleus to the dorsal dome; in three squid the ratios slightly increased toward the dorsal dome edge. The observed Sr/Ca ratios in immature squid were considered to represent younger portions of the U-shaped pattern. In the present study we discuss this pattern in relation to environmental and biological conditions of O. bartrami, which undertakes seasonal migrations between spawning grounds in the Subtropical Domain and feeding grounds in the Subarctic Domain and Transitional Zone in the North Pacific Ocean. Although Sr/Ca ratios are potentially affected by ambient water temperature and ontogenetic conditions, including somatic growth and statolith growth, it was impossible to evaluate each environmental and biological effect separately, as variations in these factors are complicated and effects could be interdependent. Received: 11 April 1997 / Accepted: 27 December 1997     

Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase. Received: 30 September 1999 / Accepted: 6 April 2000     

Early life history of tropical Anguilla leptocephali in the western Pacific Ocean

In order to examine the early life-history characteristics of tropical eels, otolith microstructure and microchemistry were examined in leptocephali of Anguilla bicolor pacifica (27.6-54.1 mm TL, n=20) and A. marmorata (22.0-47.3 mm TL, n=8) collected during a cruise in the western Pacific. A. bicolor pacifica occurred between 10°N and 15°N in the west and between 5°S and 10°N farther to the east. A. marmorata also occurred in two different latitudinal ranges in the Northern (15-16°N) and Southern Hemispheres (3-15°S) of the western Pacific. The increment widths in the otoliths of these leptocephali increased between the hatch check (0 days) and about an age of 30 days in both species, and then gradually decreased toward the otolith edge. Otolith Sr:Ca ratios showed a gradual increase from the otolith center to the edge. The ages of A. bicolor pacifica and A. marmorata leptocephali ranged from 40 to 128 days and from 38 to 99 days, respectively. Growth rates of A. bicolor pacifica and A. marmorata leptocephali ranged from 0.33 to 0.71 mm day^-1 and from 0.45 to 0.63 mm day^-1, respectively. These leptocephali had estimated growth rates that were spread out throughout most of the reported range of growth rates of the leptocephali of the temperate species, the Japanese eel and the Atlantic eels. Differences in the spatial distribution in relation to current systems, and the age and size compositions of the leptocephali of A. bicolor pacifica and A. marmorata suggested different spawning locations for these two species.     

Active pelagic migrations of the bivalve Macoma balthica are dangerous

The bivalve Macoma balthica migrates twice during the benthic part of its life cycle. During the spring migration (May-June), the newly settled spat (0-group) migrates to the nurseries in the high intertidal. Seven to nine months later, the bivalves migrate back to the low tidal flats and the subtidal (winter migration, 1-group). Both 0- and 1-group M. balthica use byssus threads for active pelagic migrations. As many M. balthica disappear during these migrations, we examined experimentally the importance of predation on 0- and 1-group M. balthica. Laboratory experiments using a circular aquarium determined predation rates on buried (no current) and drifting (current) 0- and 1-group M. balthica by several fish species (plaice, flounder, goby and whiting) and the shore crab. Under illuminated conditions, more M. balthica were consumed when migrating than when buried, whereas there was no difference between experiments in conditions of darkness. For the 0-group, predation rates on migrating and buried M. balthica in the dark were lower than in the light. The stomachs of pelagic fish in the Wadden Sea and Oosterschelde estuary did not contain M. balthica during winter migration. In the Wadden Sea, 1-group M. balthica primarily migrated at night. In conclusion, enhanced predation on drifting, as compared to buried, M. balthica may be the mechanism that explains enhanced mortality during migration in light, and may explain why M. balthica mainly migrates at night in the field. As we found no M. balthica in stomachs of pelagic fish, we do not know whether predation on byssus drifting M. balthica exists in the field. There are, however, some indications for fish predation on infaunal polychaetes during pelagic migrations.     

Evidence of a spawning area of <Emphasis Type="Italic">Anguilla</Emphasis><Emphasis Type="Italic">marmorata</Emphasis> in the western North Pacific

Leptocephali of the tropical eel Anguilla marmorata have been consistently collected in the same area of the North Equatorial Current (NEC) in the western North Pacific during three consecutive cruises in June and July of 1991 (N=28) and 1994 (N=20), and July and September of 1995 (N=27), indicating that this is a spawning area of this species. These leptocephali were collected from 130°E to 142°E and 12°N to 20°N, to the west of the Mariana Islands, in 20 tows in 1991, in 13 tows in 1994 and in 17 tows in 1995, indicating a widespread presence, but a relatively low abundance. Six of these specimens (16.3-36.0 mm total length) from the 1995 cruise, which were of the typical size range of these leptocephali, were genetically confirmed to be A. marmorata in a previous study. The consistent presence of recently spawned A. marmorata leptocephali (9-20 mm) in all 3 years, suggests that the western region of the NEC is the spawning area of the northern population of A. marmorata that was identified in a recent population genetics study. These leptocephali would thus be transported westward by the NEC and then transported north into the Kuroshio Current and toward Taiwan and Japan, or south toward the southern Philippines and into the Celebes Sea by the Mindanao Current. Available evidence indicates that A. marmorata may have potentially year-round spawning, and the presence of a spawning area of this species in the same region as that of Anguilla japonica suggests that the northern population of A. marmorata has evolved a spawning migration from East Asia, the Philippines and the Celebes Sea region to the NEC area, but differs from A. japonica by having some individuals that recruit to more southern areas.     

On the potential use of magnesium and strontium concentrations as ecological indicators in the calcite skeleton of the red coral (Corallium rubrum)

 The variability of magnesium, strontium and calcium concentrations in the two skeleton types (sclerites and axis) of the red coral (Corallium rubrum) was assessed by using X-ray fluorescence spectroscopy and microprobe analysis as a prerequisite for their use as ecological indicators. Axis cross sections showed light and dark circular growth bands corresponding to fast and slow growth, respectively. Using microprobe analyses the Mg and Sr concentrations ranged from 2.8 to 3.0% and from 0.21 to 0.29%, respectively, in the sclerites and from 2.4 to 3.0% and from 0.1 to 0.28%, respectively, in the axis. Mg/Ca and Sr/Ca ratios varied within sclerites (average, 12% for both ratios) and within the axis of single colonies (average, 20% for Mg/Ca and 48% for Sr/Ca). Sr/Ca ratios in the axis were lower in fast-growing branch tips than in older, more basal parts of the colonies, whereas the Mg/Ca ratio did not differ significantly between colony regions. Mg/Ca and Sr/Ca ratios in the axis decreased significantly with depth, and we estimated an increase of the Mg/Ca ratio of 0.004–0.006 per degree Celsius. In all depth layers, Sr/Ca ratios showed a significant direct relationship with skeleton density in axis cross sections, whereas there was no significant relationship for Mg/Ca. Overall, our data indicate that temperature promotes the incorporation of Mg in C. rubrum as in other calcite skeletons, whereas Sr concentrations are inversely related to growth rate. This preliminary study suggests that Mg and Sr concentrations in the axis of the red coral have a strong potential as ecological indicator for temperature and growth rate. Received: 3 March 2000 / Accepted: 30 August 2000     

Seasonal variation in ecophysiological patterns in macroalgae from an Arctic fjord. I. Sensitivity of photosynthesis to ultraviolet radiation

Marine macroalgae inhabiting Arctic coastal ecosystems are exposed to pronounced seasonal variations in the radiation regime, including harmful UVB radiation. This study presents the first data on the seasonal changes in the sensitivity of macroalgal photosynthesis towards UV exposure by comparing under-ice, clear-water and turbid-water conditions characteristic for late winter, spring and summer. Various brown (Laminaria saccharina, L. digitata, L. solidungula, Saccorhiza dermatodea, Desmarestia aculeata), red (Palmaria palmata, Devaleraea ramentacea) and one green macroalgal species (Monostroma aff. arcticum) were collected at the same water depth throughout the seasons in the Kongsfjord (Spitsbergen, Svalbard, Norway). Maximum quantum yield (F_v/F_m) and maximum photosynthetic electron transport rates (ETR_max) were determined immediately after collection, after 2 h exposure to artificial UV radiation and after 18 h recovery in dim white light. Photosynthesis of the studied species showed different responses depending on their morpho-functional and physiological characteristics, their life strategies, phenology and depth distribution. Within the genus Laminaria, maximum quantum yield of adult specimens of the deep-water species L. solidungula was most strongly UV sensitive. Adult L. saccharina exhibited a lower UV sensitivity than a 6-month-old specimen. Inhibition of photosynthesis after UV exposure remained at the same level throughout the study period, both in adult L. saccharina and S. dermatodea. However, adult specimens of L. saccharina collected in May showed partial recovery only, whereas photosynthesis of specimens from both species collected later recovered fully. D. aculeata exhibited a remarkable decrease of UV sensitivity during the study period. Photosynthesis of specimens collected under the ice was strongly inhibited by UV, but the degree of inhibition decreased during spring and summer. Concomitantly ETR_max values were low after UV exposure in specimens collected in June, but increased later in the season. P. palmata exhibited a relatively flexible response. Photosynthesis in specimens collected under the ice in June or in turbid water in July/August was relatively strongly inhibited; specimens collected during sunny periods and in clear water in spring showed a much lower degree of photoinhibition after UV exposure. The seasonal pattern of low/high ETR_max values in spring/summer is probably a characteristic of the life strategy of this species. The UV sensitivity of D. ramentacea exhibited a similar seasonal pattern. In M. aff. arcticum, UV sensitivity increased and ETR_max values decreased during the study period, reflecting the life strategy of this annual late winter/spring species. The physiological basis for the seasonal changes in UV sensitivity of photosynthesis is presented in a companion paper (this issue).     

Environmental and structural control of trace elements in barnacle shells

The shell composition of 5 species of barnacles [Balanus balanoides (L.), B. crenatus Bruguière, B. hameri Ascanius, Elminius modestus Darwin and Chthamalus stellatus (Poli)] collected from four different sites on the coast of North Wales and one site in the Irish Sea were studied using chemical, X-ray diffraction and electron-microprobe analyses. All the shells consisted of calcite. The trace substances studied were Mg, Sr, Na, Mn, PO₄, and SO₄. Other trace elements detected included Si, Li, Ba, Zn, Cl, and Al. For each species, Mn was the only element in the shell which varied significantly from one locality to another. Variation of concentration of Mn in the shells may be related to the variations of the concentration of Mn in the water, since concentrations in the shells were highest in (estuarine) waters containing high concentrations of Mn. In Balanus balanoides L. and Elminius modestus Darwin, the Mn:Ca and Mg:Ca ratios decreased with decreasing shore level and Sr:Ca varied in the opposite direction. When B. crenatus Bruguière, a subtidal and lower littoral species, and B. hameri Ascanius, a Continental-Shelf species, were compared with the intertidal, species B. balanoides and E. modestus, the Mn:Ca and Mg:Ca ratios followed the same decreasing trend, and the Sr:Ca ratios the same increasing trend with increasing depth. These variations may be related either to increased growth rate of the shells of each species or maxium temperature to which the species is exposed, or both. The differences between species are more consistently reflected, in the concentration of Mn. However, since the concentration, of Mn is correlated with the amount of organic matter in the shell, the specific variations may reflect only the variations in the amount of organic material in the shell of each species.     

Changes in otolith strontium:calcium ratios in metamorphosing Conger myrisaster leptocephali

Content ratios of strontium (Sr) to calcium (Ca) in the otolith of Conger myriaster metamorphosing leptocephali and elvers increased with increasing increment number from the core to the 110th increment and subsequently decreased. The otolith region from the 110th increment to the edge corresponded to the metamorphic stage. The Sr:Ca ratios in otolith edges of metamorphosing leptocephali were inversely related to metamorphic stage, suggesting that the changes in otolith Sr:Ca ratios were influenced by some physiological factor(s) rather than by environmental factors. Sr concentration in leptocephalus somatic tissues was high and decreased as metamorphosis progressed until the late metamorphic stage when the preanal myomere to total myomere ratio was 0.4. Ca concentration was constant throughout ontogenesis. Body Sr:Ca ratios markedly decreased as metamorphosis progressed. Decrease in somatic Sr concentration and the consequent decrease in body Sr:Ca ratios seemed to be associated with the breakdown of glycosaminoglycan (GAG) in gelatinous matrix, which is the major constituent of soft tissue in leptocephali. Catabolism of GAG may also cause a decrease in otolith Sr:Ca ratios during metamorphosis. In leptocephalus otoliths, Sr:Ca ratios may change in association with the synthesis and breakdown of GAGs during ontogeny. Received: 29 November 1996 / Accepted: 6 January 1997     

Predator-inducible changes in blue mussels from the predator-free Baltic Sea

Blue mussels, Mytilus spp., have inhabited the brackish Baltic Sea, an environment lacking predatory crabs and starfish, for several thousand years. In this paper we examined whether Baltic Mytilus that were transplanted to the North Sea showed predator-inducible plasticity like their "marine" conspecifics. Our experiments showed that native North Sea Mytilus changed their morphology when exposed to waterborne scents from shore-crabs and starfish. These predators induced different kinds of changes, with emphasis on shell thickness and adductor muscle size, respectively. Baltic Mytilus responded in a similar way to crab scents, whereas starfish scents had a relatively weak effect on the morphology. Crab and starfish scent induced strengthening of the byssal attachment in North Sea Mytilus, with crabs providing more stimulation than starfish. Baltic mussels also improved the byssal attachment when exposed to either of the predators, but the attachment strength, as well as the response to crabs, were relatively weaker than that of North Sea mussels. We conclude that inducible plasticity still is present in Baltic Mytilus, despite their recent evolution in a predator-free environment. There is probably no strong selective pressure against inducible plasticity, but it could also be maintained in the population by gene flow from Mytilus in the adjoining North Sea. The question whether Baltic Mytilus are M. edulis or M. trossulus may also be relevant for the present results.