Inhibitory effects of red algal extracts on larval settlement of the barnacle Balanus improvisus

We examined the chemical antifouling properties of four sublittoral red algae, Chondrus crispus, Delesseria sanguinea, Osmundea ramosissima, and Polyides rotundus, which are all rarely fouled in the field. Two different approaches were used. Firstly, we tested the effects of lipophilic crude extracts on the settlement behaviour of cyprid larvae of the co-existing barnacle Balanus improvisus. Secondly, in a settlement preference experiment, we tested whether B. improvisus cyprid larvae settle on living algae when given a choice between natural algal surfaces and control surfaces. With this procedure, we were able to test both if the algae inhibit recruitment of cyprids, and if this inhibition is a result of chemistry. The settlement of B. improvisus larvae was strongly inhibited at concentrations estimated to be potentially ecologically relevant for all of the tested extracts. However, only C. crispus significantly inhibited settlement in the preference experiment, even though there was also a tendency for settlement inhibition on P. rotundus and O. ramosissima. In contrast, D. sanguinea seemed to stimulate settlement. This contradiction probably resulted from an extraction of metabolites that naturally occur only inside the alga. However, as this study shows, a combination of settlement assays with whole-cell extracts and preference tests of ecologically relevant fouling organisms on natural algal and control surfaces may be a useful procedure to avoid erroneous conclusions regarding natural antifouling roles of compounds based on settlement assays with only whole-cell extracts. Furthermore, this study also shows that production of inhibitory metabolites may explain the low degree of fouling, especially by B. improvisus, on C. crispus.Communicated by L. Hagerman, Helsingør     

Herbivory in the gammarid amphipod Aora typica: relationships between consumption rates, performance and abundance across ten seaweed species

This paper reveals a substantial capacity for herbivory of seaweeds in the gammarid amphipod Aora typica, adults eating seven of ten taxonomically and morphologically diverse seaweed species offered to them in a no-choice assay. The green algae Ulva spathulata and Enteromorpha intestinalis were consumed at the highest rates in both no-choice (2.3–2.5 mg blotted weight individual⁻¹ day⁻¹) and multiple-choice assays (0.5–1.3 mg blotted weight individual⁻¹ day⁻¹). Adult A. typica collected from two different species of brown seaweeds had very similar feeding preferences to each other. Juvenile A. typica grew to reproductive maturity on the green algae E. intestinalis and U. spathulata, and the brown algae Carpophyllum maschalocarpum and Ecklonia radiata. In common with previous studies on members of other amphipod families, survivorship of juvenile amphipods was positively correlated with feeding preferences of adults across seaweed species (r ²=0.43, P=0.04). However, densities of A. typica on seaweeds in the field (excluding the intertidal E. intestinalis and U. spathulata) were not significantly correlated with feeding preferences of adults (r ²=0.07, P=0.5) or survivorship of juveniles (r ²=0.17, P=0.31). This suggests that either host seaweeds are not a major dietary component of these amphipods in nature, or that the host’s value as a food source is overridden by other properties such as the degree of shelter it affords from larger consumers. This study provides the first demonstration that a member of the cosmopolitan amphipod family Aoridae is capable of consuming a diverse range of seaweeds.     

The role of different types of detached macrophytes in the food and habitat choice of a surf-zone inhabiting amphipod

Allorchestes compressa is the dominant macroinvertebrate species in wrack accumulations on surf zones of south-western Australia. These amphipods were provided with a choice of macrophyte material representing brown and red algae and seagrass in a series of preference experiments in the laboratory and field. Feeding experiments showed that A. compressa exhibited a strong preference for particular types of macrophytes (P < 0.01). Amphipods primarily consumed brown algae, with 69–98% of the biomass of Ecklonia radiata and 64% of the biomass of Sargassum sp. lost over the experiments. This study has shown that the amphipod A. compressa exhibits a clear preference for brown algae over red algae and seagrass as food. In terms of habitat preference, tank experiments using a series of pair-wise comparisons showed that, in the absence of fish predators, A. compressa selected seagrass as its preferred habitat over the other types of wrack (P < 0.001). When satiated or starved, between 68 and 83 and 79 and 98% of amphipods were found in Amphibolis and Posidonia, respectively. In contrast, field-cage experiments revealed that A. compressa preferred either mixed wrack, brown algae or red algae over seagrass as a habitat (P < 0.01). The contrasts between results from the laboratory and field suggest that other factors such as the presence of predators, water flow and light could influence habitat choice in the surf zone. This study shows that allochthonous material transported to surf zones from other habitats therefore play different roles in driving secondary production in this shoreline habitat.     

Ecology of a corallivorous gastropod,<Emphasis Type="Italic"> Coralliophila abbreviata</Emphasis>, on two scleractinian hosts. II. Feeding,respiration and growth

Coralliophila abbreviata is a corallivorous gastropod that has been observed to cause large feeding scars on reef-building corals on Floridian and Caribbean reefs. We detected differences in the population structure (length-frequency distribution and sex ratios) of C. abbreviata populations living on two coral host taxa, Acropora palmata and Montastraea spp., in the Florida Keys in a previous study. We hypothesize that diet (host) has a major influence on snail population structure and, thus, we characterize metabolism, feeding and growth for snails residing on these coral taxa. Here, we present results of a reciprocal transplant experiment demonstrating that the taxon of the host influences snail growth rates, as indicated by changes in shell and body tissue weight. Regardless of the host from which they were drawn, snails resident on A. palmata grew faster than those resident on Montastraea spp. Thus, diet influences snail population structure. However, the tissue of Montastraea spp. provides more N and C per area of tissue than that of A. palmata. Respiration rates and tissue composition of snails collected from the two host taxa did not differ. Therefore, snails feeding on Montastraea spp. should have to consume less tissue per day to satisfy their metabolic requirements compared to snails feeding on A. palmata. Feeding rates for snails on A. palmata were measured in the laboratory over 48 h (1–9 cm² coral tissue snail⁻¹ day⁻¹) and estimated from feeding scars observed in the field (weekly mean rate of 1.07 cm² coral tissue snail⁻¹ day⁻¹). The lack of definition of snail feeding scars on Montastraea spp. required the calculation of coral tissue consumption rates based on estimated minimum carbon requirements. Calculated feeding rates for C. abbreviata were 0.13–0.88 cm² coral tissue day⁻¹ snail⁻¹, when feeding on Montastraea spp., and 0.44–3.28 cm² coral tissue day⁻¹ snail⁻¹, when feeding on A. palmata. The calculated range for the latter is consistent with measured rates. Thus, C. abbreviata exhibits high variation in growth parameters in response to environmental variability and/or food source. At mean levels of snail density on reefs off Key Largo, Fla., 20% of A. palmata colonies lose between 1.32 and 9.84 cm² tissue day⁻¹, while 50% of Montastraea spp. colonies lose between 1.04 and 7.04 cm² tissue day⁻¹. Together with published coral tissue regeneration rates, these results suggest that if sustained, such rates of predation could have a serious effect on the viability of these coral populations on Florida's reefs.     

Competitive interactions between two fucoid algae with different growth forms,<Emphasis Type="Italic"> Fucus serratus</Emphasis> and<Emphasis Type="Italic"> Himanthalia elongata</Emphasis>

Competitive interactions between two fucoid algae with different growth forms, Fucus serratus L. and Himanthalia elongata (L.) S.F. Gray were examined both in the laboratory and on a shore of the Isle of Man, Irish Sea. The growth of germlings of both species declined with increasing density, irrespective of whether they were with cohorts or rival species, indicating that intra- and interspecific competition occurred between germlings. H. elongata suppressed the performance of F. serratus at the germling stage by virtue of its larger initial size, and at the mushroom stage by forming a miniature canopy with the caps of the adjacent plants. In a field experiment, the mortality of H. elongata juveniles generally increased in mixtures with F. serratus and was highest when F. serratus were 50% of the plants. At the juvenile stage, the negative effect of F. serratus on H. elongata was more severe than the other way round. This was because F. serratus grows predominantly upwards, whereas H. elongata had already begun to expand laterally at the distal end. If F. serratus survives in sparse mixed stands with H. elongata juveniles, it can overgrow them and inhibit their subsequent survivorship and growth, probably by both shading and physical sweeping. H. elongata and F. serratus maintain their discrete monospecific stands because of the varying outcomes of mutual competitive exclusion resulting from their differing growth patterns. Thus it is possible for them to co-occur at a similar shore height.Communicated by O. Kinne, Oldendorf/Luhe     

Feeding selectivities of the marine cladocerans<Emphasis Type="Italic"> Penilia avirostris</Emphasis>,<Emphasis Type="Italic"> Podon intermedius</Emphasis> and<Emphasis Type="Italic"> Evadne nordmanni</Emphasis>

We conducted grazing experiments with the three marine cladoceran genera Penilia, Podon and Evadne, with Penilia avirostris feeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02–8.8 mm³ l^–1, plankton assemblages grown in mesocosms at different nutrient levels), and with Podon intermedius and Evadne nordmanni feeding on the plankton community found in summer in Hopavågen Fjord (NE Atlantic, Norway, 0.4 mm³ l^–1). P. avirostris and P. intermedius showed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively. E. nordmanni preferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were >2.5 µm, for all cladocerans. P. avirostris showed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits for P. intermedius were 135 µm long and 60 µm wide; those for E. nordmanni were 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment for P. avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher for P. intermedius than for E. nordmanni. With increasing food concentrations, the clearance rates of P. avirostris showed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates of P. avirostris, P. intermedius and E. nordmanni were 25.5, 18.0 and 19.3 ml ind.^–1 day^–1, respectively. Ingestion rates at similar food concentrations (0.4 mm³ l^–1) were 0.6, 0.8 and 0.9 g C ind.^–1 day^–1.Communicated by O. Kinne, Oldendorf/Luhe     

Ecology of a corallivorous gastropod,<Emphasis Type="Italic"> Coralliophila abbreviata</Emphasis>, on two scleractinian hosts. I: Population structure of snails and corals

Despite their potential importance in structuring reef communities, invertebrate corallivores and their population structures are poorly understood. We found distinct differences in the population structures (length-frequency distribution and sex ratio) of the corallivorous gastropod Coralliophila abbreviata residing on two coral-host taxa, Montastraea spp. and Acropora palmata, in the Florida Keys. In each of two survey years, around 50% of the Montastraea spp. colonies were infested, with a mean snail density of eight snails per infested colony (range 1–45), while around 20% of A. palmata colonies harbored three snails per infested colony (range 1–23). Variation in patterns of snail occurrence was also observed within a host taxon. A. palmata occurred in low- and high-density stands (0.4 and 1 colony m^–2, respectively, at the initial survey) at different sites. Hurricane Georges struck the area in September 1998. When resurveyed in 1999, density of colonies in low-density stands had decreased by 75% to 0.1 colonies m^–2. This decrease was accompanied by a doubling in the proportion of colonies infested with snails (from 19% to 46%) and an increase in snail density per infested colony (from 3.7±3.3 SD to 5.4±4.6 SD) as snails apparently concentrated on surviving A. palmata. In contrast, sites with high density A. palmata stands (thickets) retained colony densities of about ~1 colony m^–2 among years, while snail infestation increased only from 9% to 14% of colonies surveyed and snail density essentially remained unchanged (from 2.7±1.8 to 2.9±1.9 snails per infested colony). Snails collected from Montastraea spp. were shorter than those from A. palmata in low-density stands and were longest on A. palmata in thickets. On both host taxa, female snails were longer than males. The sex ratio of snails on Montastraea spp. hosts was even (1:1), while that of snails on A. palmata was skewed (70% males). Factors that could explain observed differences in size structure and sex ratio between Coralliophila populations on the two coral host taxa include: differential susceptibility to predators, influence of host tissue nutritional quality and/or secondary metabolite content, and genetic differences (cryptic species). The host-specific characteristics of C. abbreviata populations imply that the impact of gastropods on reef communities will vary with the coral species composition.     

Early life histories in the bryozoan<Emphasis Type="Italic"> Schizobrachiella sanguinea</Emphasis>: a case study

Mediterranean populations of Schizobrachiella sanguinea seem to span a wide range of contrasting benthic habitats. We have studied adult, larval, and recruit populations of S. sanguinea from sublittoral (approximately 10 m depth) communities at Blanes (Spain, NW Mediterranean). At the study site, the species colonises semi-obscure caves and, to a lesser extent, communities of sciaphilic algae. Our first goal was to show the periods of brooding, larval release, and recruitment. Plankton was collected about twice a week between July 1998 and June 2000 over an artificial reef. A total of 303 larvae were collected in 23 of the 102 days of sampling. At the study site the species shows a single, annual larval release period, which occurs from late March to June–July every year. Recruits were found from late May to late August 1999 and in late May 2000. A recruitment peak was observed in July 1999 and again in late May 2000. The presence of brooding adults corresponded to the periods of larval supply and recruitment. Our second goal was to investigate the causes of the variable distribution of the species along several communities in the north-west Mediterranean Sea. We describe adult distribution and the dynamics of larval supply, recruitment of early (15 days from settlement) and late (4 months from settlement) recruits. Patterns of larval presence and early recruit distribution along the communities on the reef did not reflect the adult distributions, whereas this was closely matched by the distribution of late recruits. Post-recruitment mortality strongly affected recruits of the PA (photophilic algae) and SA (sciaphilic algae) communities, whereas it was very low in the communities of SOC (semi-obscure caves). Mortality of recruits was density independent and colony survivorship in the SA communities, where recruitment was the highest, appeared strongly affected by competition with brown algae. Like the majority of cheilostomate bryozoans, S. sanguinea releases a coronate larva capable of active swimming and positive reaction to light. Such swimming abilities may allow larvae to actively select the substrate on which to settle and to avoid unsuitable substrates. It seems that larval behaviour does not explain the preference of S. sanguinea for sciaphilic habitats. High post-recruitment mortality due to various factors, especially competition with fast-growing algae, seems particularly relevant in determining the adult distributions observed.Communicated by S.A. Poulet, Roscoff     

Availability of ammonium influences photosynthesis and the accumulation of mycosporine-like amino acids in two<Emphasis Type="Italic"> Porphyra</Emphasis> species (Bangiales,Rhodophyta)

The effect of ammonium concentration on photosynthetic activity estimated as in vivo chlorophyll fluorescence, i.e. maximal quantum yield (F_v/F_m) and electron transport rate (ETR) and on the accumulation of mycosporine-like amino acids (MAAs), chlorophyll a (chl a), biliproteins (BP) and soluble proteins (SP) in the red algae Porphyra leucosticta Thuret in Le Jolis collected from Lagos (Málaga, Spain) and Porphyra umbilicalis (Linnaeus) J. Agardh from Helgoland (Germany) was evaluated. Discs of both species were incubated with three ammonium concentrations (0, 100 and 300 µM) under artificial PAR and UV radiation for 7 days. Photosynthetic activity decreased under the culture conditions due to UV radiation and ammonium availability. The decrease of both F_v/F_m and maximal ETR was related to ammonium supply, i.e. the lowest decrease occurred in algae growing with the highest concentration of ammonium. In both species, after 7 days of culture, the content of chl a, BP and SP was higher under 300 µM than that under 0 and 100 µM ammonium. In both species, the content of MAAs was increased under 300 µM ammonium compared to the initial value, whereas a decrease under 0 and 100 µM ammonium was observed only in P. leucosticta. The content of MAAs in P. umbilicalis did not present significant differences compared to the initial value, probably because of the high initial content of MAAs. In both Porphyra species, four MAAs were identified: shinorine, porphyra-334, palythine and asterina-330. However, P. leucosticta modified its MAA pattern during the incubation time, reaching the same percentages found for P. umbilicalis, which did not show any change during the experimental period. P. leucosticta exhibited a decrease in BP/SP and BP/chl a ratios through the incubation time and an increase in MAAs/BP. The ratio MAAs/chl a did not show any variation with time or treatment, as was also true for all ratios in P. umbilicalis. In summary, ammonium supply diminished the decrease of F_v/F_m, increased the content of photosynthetic pigments (chlorophyll and biliprotein) and soluble protein, and stimulated of the accumulation of MAAs in the red algae P. leucosticta and P. umbilicalis.Communicated by O. Kinne, Oldendorf/Luhe     

Distributional ecology and food habits of the banded blennyParaclinus fasciatus (Clinidae): a resident in a mobile habitat

An ecological study of the banded blennyParaclinus fasciatus (Steindachner, 1876) showed that the fish is tolerant of physical/chemical conditions in the shallow subtidal area of Apalachee Bay, Florida (USA). Population density ofP. fasciatus was unrelated to physical/chemical characteristics and seagrass biomass at field stations. A strong correlation was found between numbers ofP. fasciatus captured and abundance of unattached red algae (drift algae) at the field sites, although seasonality in population density was related to summer spawning. Spawning began at approximately 28°C. The life span of the clinid is probably little longer than 1 yr. Long-term variation in population size was also demonstrated.P. fasciatus was found to be a highly specialized carnivore which consumes only a few species of amphipods and shrimps; however, major seasonal variation in diet occurred. Variations in food habits were related to known patterns of prey abundance in Apalachee Bay. The most important prey species taken byP. fasciatus, includingCymadusa compta andHippolyte zostericola, are associates of red algae masses, further substantiating the close functional relationship of the clinid with its algal habitat which moves about the bay. The driftalgae habitat is probably an important source of shelter, food, and dispersal for the banded blenny. The eurytolerance ofP. fasciatus makes it particularly well adapted for life in an unusual, mobile habitat.Gontribution No. 173 of Harbor Branch Foundation, Inc.     

Feeding in dominant Antarctic copepods—does the morphology of the mandibular gnathobases relate to diet?

This study should clarify the importance of morphology and stability of the mandibular gnathobases for the diet of Antarctic copepod species. The gnathobase morphology of the dominant copepod species Calanoides acutus, Calanus propinquus, Ctenocalanus citer, Rhincalanus gigas, Metridia gerlachei, Stephos longipes, Microcalanus pygmaeus and Paraeuchaeta antarctica from the Southern Ocean was investigated in detail by means of a scanning electron microscope. The mandibular gnathobases of C. acutus, C. propinquus and C. citer have relatively short and compact teeth. These species feed mainly on diatoms and are able to crack the silicious diatom frustules with their mandibular gnathobases by directed pressure. In contrast the teeth of the mandibular gnathobases of P. antarctica are very long and pointed. The nutrition of this species consists predominantly of other smaller copepod species. The motile prey can be held by skewering, using the gnathobases, and then eventually minced. The mandibular gnathobases of P. antarctica have notably more small bristles than those of the other investigated copepod species. These bristles are probably associated with receptors and could serve to locate the prey. The morphology of the gnathobases of R. gigas and M. gerlachei is between that of P. antarctica on the one side and that of C. acutus, C. propinquus and C. citer on the other. Based on the morphology of its gnathobases the copepod species S. longipes, which has to date been found to feed primarily on phytoplankton, mainly ice algae, must also be considered a zooplankton feeder. The investigation showed that M. pygmaeus has gnathobases with surprisingly long and pointed teeth, indicating that this species very probably feeds both on phyto- and on zooplankton organisms. While the mandibular gnathobases of the males of C. propinquus, R. gigas, M. gerlachei and S. longipes have the same morphology as the females of the respective species, in the other four investigated copepod species the males have reduced (C. acutus, C. citer and M. pygmaeus) or completely missing mandibular gnathobases (P. antarctica). The teeth of the gnathobases of all studied species with the exception of M. gerlachei consist of a different material than the remaining parts of the gnathobases. This material seems to be silicate, which probably enhances the stability of the gnathobase teeth.Communicated by O. Kinne, Oldendorf/Luhe     

A critical habitat for Mediterranean fish resources: shelf-break areas with<Emphasis Type="Italic"> Leptometra phalangium</Emphasis> (Echinodermata: Crinoidea)

This paper considers the potential role of the crinoid Leptometra phalangium as an indicator of highly productive areas along the shelf break that can sustain large biomasses of benthopelagic fish and recruits. The structure of fish assemblages in the central Mediterranean Sea (central-western coast of Italy), analysed on the basis of surveys carried out in summer and autumn from 1997 to 2001, revealed the presence of a well-defined group of species on the shelf break. This area, occurring at a depth of between 120 and 170 m, is characterised by detritic organogenic sediments colonised by the crinoid L. phalangium, a suspension-feeding macro-epibenthic species confined in the Mediterranean to the shelf-break area. Its abundance in the studied area can reach 12–15 ind. m^–2. A total of 121 species belonging to 66 families of demersal organisms (crustacean decapods and stomatopods, cephalopods, selaceens and teleosteens) were caught at shelf-break stations from September to October. The species which typified the assemblage were the fishes Trisopterus minutus capelanus, Merluccius merluccius, Glossanodon leioglossus, Argentina sphyraena, Capros aper, Macroramphos scolopax and Lepidotrigla cavillone, the crustacean decapod Parapenaeus longirostris and the cephalopods Illex coindetii and Todaropsis eblanae. Detritic shelf-break stations showed a higher abundance of demersal organisms than stations distributed on muddy bottoms in the same depth range (100–200 m). Such differences appeared to be significant in September–October, when a clear increase in benthopelagic zooplanktivorus species, such as Glossanodon leioglossus, Trachurus trachurus, Trachurus picturatus, was found. The length structure of species occurring on the shelf break showed that for some of them the selection of this area is related to specific phases of their life cycle. Significant highest abundance of recruits and juveniles was observed for Merluccius merluccius, Helicolenus dactylopterus, Phycis blennoides, Parapenaeus longirostris and Capros aper in at least one of the two seasons. Similarly, an increased abundance of spawners of red mullet Mullus barbatus and four-spotted megrim Lepidorhombus boscii was observed on the shelf break. Results of this study may have important consequences for management of fish stocks and assemblages in the central Mediterranean. The co-occurrence of high densities of L. phalangium and benthopelagic fish, occurring mainly with juveniles and spawners, strongly indicates a potential role of L. phalangium as an indicator of highly productive areas around the shelf break. Such areas appear to play a major role in the production of some of the most abundant and commercially important fish species, such as the Mediterranean hake and red mullet.Communicated by R. Cattaneo-Vietti, Genova     

Comparing macroalgal food and habitat choice in sympatric, tube-building amphipods, Ampithoe lacertosa and Peramphithoe humeralis

For small tube-building amphipods that live on the algae they consume, food and habitat are tightly linked. This study compared two closely related amphipods to determine whether the species’ algal preferences are based on the food value of the algae or on some other aspect of their algal habitat. Ampithoe lacertosa and Peramphithoe humeralis are both abundant on Shannon Point beach (Anacortes, Washington, USA; 48°30.542′ N, 122°41.070′ W) but specialize on different algae. In observations and laboratory experiments conducted July–September 1997, 2007, and 2008, the two species exhibited markedly different choices of food and habitat when offered six common macroalgae. Ampithoe lacertosa ate all algae offered, but preferentially built tubes on the green alga Ulva lactuca. Survival was relatively low among juveniles maintained on single species diets, except when they were fed Mazzaella splendens. Conversely, P. humeralis consumed primarily the brown kelp Saccharina latissima, Alaria marginata, and Desmarestia ligulata and preferred those species for tube building. Juvenile P. humeralis could not survive on a diet of U. lactuca or M. splendens. While A. lacertosa builds simple, temporary tubes and relocates frequently, P. humeralis is a highly thigmotactic species that builds long-term, complex tubes on the alga it prefers to eat. Feeding and habitat preferences of the two species were not clearly linked to nitrogen content of the algae, C:N ratio, or toughness of the algal tissue. Instead, preferences of the species may be related to their mobility and the permanence of the tubes they build. Ampithoe lacertosa and P. humeralis also use different feeding strategies; the former appears to mix algae to produce a high-quality diet, while the latter is more selective and has a capacity for compensatory feeding. The species are abundant on the same protected rocky shores, but specialize on different algae for habitat and food. Results suggest that the nutritional requirements of these sympatric mesograzers differ considerably and even closely related species can exhibit divergent behavioral strategies.     

In situ beziehungen zwischen nahrungsangebot und aufgenommener Nahrung bei 5 Blennius-Arten (Pisces) des Mittelmeeres

Eight epiphytal samples were taken from the upper littoral at Banyuls-sur-Mer (French Mediterranean coast) and the fauna living on the thalli of algae or between bivalves was examined. Intestinal food contents of 67 specimens of 5 Blennius species (B. trigloides, B. canevae, B. sphinx, B. incognitus, and B. dalmatinus) occurring in the same biotope were also investigated. The epiphytal samples consisted of a rich supply of amphipods, bivalves, and algae. Amphipods are the preferred food of the Blennius species examined. These fishes also consume large amounts of copepods and algae, and small quantities of halacarids, bivalves, and ostracods. In addition to serving as a substrate for the main food-animals of the fishes, the algae themselves constitute an important food source. Presumably, for these reasons, the fishes remain close to the area inhabited by the algae on rocky substrates.     

Habitat use by sponge-dwelling brittlestars

Cryptic organisms often associate with sessile invertebrates for refuge in space-limited environments. To examine interspecific habitat associations on coral reefs, tube- and vase-shaped sponges were surveyed for associated brittlestars at six sites on the coral reefs off Key Largo, Florida. Of 179 sponges encountered, Callyspongia vaginalis was the most abundant (43.0%), followed by Niphates digitalis (39.7%), and Callyspongia plicifera (4.5%). Three of eight sponge species surveyed did not differ from C. vaginalis in two physical refuge characteristics: oscular diameter and inner tube surface area. Brittlestars (416 total), all of the genus Ophiothrix, were only found in C. vaginalis, N. digitalis, and C. plicifera. The most abundant brittlestar, O. lineata (326), occurred on C. vaginalis (99.0%) and N. digitalis (1.0%), while O. suensonii (67) occurred on C. vaginalis (79.1%), N. digitalis (19.4%), and C. plicifera (1.5%). There was no pattern of co-occurrence of O. lineata and O. suensonii on C. vaginalis. The abundance of O. lineata increased with surface area of C. vaginalis. Differential habitat use was observed in O. lineata, with small individuals (<5 mm disk diameter) located inside and on the surface of sponge tubes and large individuals (5 mm) solely inside tubes. The number of large O. lineata in C. vaginalis never exceeded the number of tubes per sponge, and tagged O. lineata remained in the same sponge for at least 3 weeks. In density manipulations, no pattern of intraspecific competition among large O. lineata was observed; however, there was evidence for interaction between size-classes. Brittlestars selected live sponge habitat over a non-living refuge, suggesting a mechanism for sponge habitat recognition. Sponge-dwelling brittle stars prefer some tube- and vase-shaped sponge species despite similar oscular diameters and surface areas. Surprisingly, these preferred sponge species are known from previous studies to be chemically undefended against generalist fish predators; therefore, brittlestars that inhabit these sponges do not gain an associational chemical defense. Sponge habitat use by O. lineata may be governed by intraspecific interactions to maintain habitat and access to food. While past studies have suggested that O. lineata is an obligate sponge commensal, the present study suggests that O. lineata has a species-specific association with the tube-sponge C. vaginalis.Communicated by O. Kinne, Oldendorf/Luhe     

Elemental sulfur in the gills of three species of clams containing chemoautotrophic symbiotic bacteria: a possible inorganic energy storage compound

Sulfur content and fine structure were studied for tissues of three species of clams, Lucinoma annulata, Calyptogena elongata and Lucina floridana, which inhabit sulfide-rich environments and whose gills harbor symbiotic sulfur bacteria. Lucinoma annulata and C. elongata were dredged from the Santa Barbara basin, California, USA, at a depth of 480 to 490 m, and Lucina floridana were dug from below the roots of seagrasses in Saint Joseph Bay, Florida, at a depth of 0.25 to 2m. Foot tissue of Lucinoma annulata, without symbionts, had a total sulfur content of 1.4±0.1 (SD) mg 100 mg^-1 dry weight of tissue (%DW). The symbiont-containing gill tissue of different individuals of L. annulata varied in color from dark red to pale yellow, and the total sulfur content was 2.5±0.4% DW in red gills and was 5.6±3.3 % DW in the yellowest gills. Maintenance of L. annulata in the laboratory for 21 d in the absence of sulfide resulted in the loss from the gill of yellow deposits which were elemental sulfur in the form of liquid-crystalline sulfur globules rather than solid orthorhombic sulfur crystals. The foot tissue did not contain elemental sulfur. When examined by freeze-etch microscopy, sulfur globules were found only within bacteria and not in the animal host cytoplasm. Sulfur globules were confined to the periplasmic space of the bacteria. C. elongata and Lucina floridana resembled Lucinoma annulata in the physical form and distribution of elemental sulfur. The absence of elemental sulfur in the animal cytoplasm suggests that its formation from sulfide is not a detoxification scheme to protect animal tissue from sulfide toxicity. The sulfur deposits probably represent inorganic energy reserves that permit the symbiotic bacteria to function even during the temporary absence of external sulfide.     

Growth inhibition and formation of morphologically abnormal cells of <Emphasis Type="Italic">Akashiwo sanguinea</Emphasis> (Hirasaka) G. Hansen et Moestrup by cell contact with <Emphasis Type="Italic">Cochlodinium polykrikoides</Emphasis> Margalef

We investigated the growth interaction between Cochlodinium polykrikoides and Akashiwo sanguinea using bi-algal cultures. When cultured together, morphologically abnormal cells of A. sanguinea appeared and the growth of A. sanguinea notably decreased. When C. polykrikoides and A. sanguinea were cultured separately in inner and outer wells separated by a membrane with a pore size of 3 μm, neither species showed suppressed growth and no morphologically abnormal cells of A. sanguinea were observed. Furthermore, filtrates from C. polykrikoides cultures did not affect the cell morphology or the growth of A. sanguinea. When the abnormal cells of A. sanguinea were transferred from bi-algal cultures into fresh medium and cultured as a mono-algal culture, cells recovered their normal morphology and multiplied. Therefore, the growth inhibition and formation of morphologically abnormal cells of A. sanguinea would be induced by constant cell contact with C. polykrikoides.     

Early reproduction and development of dominant calanoid copepods in the sea ice zone of the Barents Sea—need for a change of paradigms?

Reproduction and growth of the dominant copepods Calanus finmarchicus, C. glacialis, C. hyperboreus and Pseudocalanus minutus were studied on transects across the sea ice zone of the northern Barents Sea in May and June 1997. C. glacialis and C. finmarchicus were numerically dominant and also the largest component of the biomass. C. hyperboreus was rather rare. Moderate levels of phytoplankton and eventually high concentrations of ice algae supported maximum egg production rates of 53.6 and 48.5 eggs female^–1 day^–1 of C. glacialis in May and June, respectively. Results of incubation experiments were supported by a tremendous abundance of C. glacialis eggs in the water column ranging from 7×10³ to 4.4×10⁴ m^–2 in May and from 9.8×10³ to a maximum of 9.7×10⁴ m^–2 in June. In contrast, C. finmarchicus spawned only in the vicinity of the ice edge, at a maximum rate of 30 eggs female^–1 day^–1. Egg sacs of P. minutus were often observed in the preserved samples, but contained only few eggs, which may be due to loss during sampling. The presence of considerable concentrations of young stages in May and June indicated successful recruitment of C. glacialis and P. minutus. Back calculation using published stage duration estimates indicates March/April as the begin of the reproductive and growth period for these species under the first-year ice of the Barents Sea. Hence, secondary production in the study area starts at the same time as in open water regions and polynyas in the northern North Atlantic. Although the role of ice algae in the nutrition of copepods was not clarified here, the significant relationship between phytoplankton chlorophyll and egg production of C. glacialis suggests that high reproductive activity has already been achieved at moderate food concentrations.Communicated by O. Kinne, Oldendorf/Luhe     

Ciliated epibionts on the Arctic sympagic amphipod<Emphasis Type="Italic"> Gammarus wilkitzkii</Emphasis> as indicators for sympago–benthic coupling

In September 2003 specimens of the sympagic amphipod Gammarus wilkitzkii were sampled in drifting pack ice above 50 m water depth and in the pelagic/benthic environment beneath in the coastal waters off Svalbard (Norway). Abundance values ranged between 1.5 and 8 individuals m^–2 for the pelagic/benthic and the sympagic environments, respectively, and showed corresponding sex ratios of 1:1.4, favoring males. In the ice a significantly higher number of juveniles prevailed. In contrast, ovigerous females were more abundant among pelagic/benthic living specimens. Approximately 25% of the individuals hosted ciliated epibionts of the genera Ephelota, Cryptacineta, Acineta, Podophrya (all suctoria), and Epistylis (peritrichia). Cryptacineta and Ephelota were the most abundant epibionts on this amphipod species. Female specimens of G. wilkitzkii showed the highest degree of infestation (>2,100 individual epibionts per amphipod specimen: indE/A) followed by juveniles (>1,200 indE/A) and males (>220 indE/A). Highest densities of epibionts were found on anterior body parts with the antennae bearing up to 130 individuals. This is the first sighting of epibionts on crustacea from the sympagic environment. We interpret them as biomarkers that indicate the existence of sympago–benthic coupling processes between the ice and the underlying waters and the seafloor. The population structure and the proportion of infested specimens are equal for the amphipods sampled from both the sympagic and the pelagic/benthic environment, indicating the existence of exchange (coupling) processes between the two habitats. Considering the annual ice cycle, local ice drift patterns, and the shallow water depth in the sampling area, we hypothesize that ice amphipods spend ice-free periods near the seafloor where they may serve as basibionts for protozoans and eventually re-colonize the ice with the onset of ice formation. Our observations strongly emphasize that shallow coastal areas serve as both retention (rather than sink) areas for ice fauna during ice-free periods, and as stepping-stones for re-colonizing the ice when the ice is formed in winter.Communicated by M. Kühl, Helsingor     

Comparison of hemolytic activity in eight species of polychaetes

Hemolytic capacity was investigated in homogenates of eight species of polychaetes, belonging to five different orders.Nainereis laevigata, Orbinia cuvieri, Cirriformia tentaculata, Notomastus latericeus, Arenicola claparedii andPetaloproctus terricola were collected during February 1990 from the coastal lagoon of Acquatina (Puglia, Italy).Nereis sp. (from the Yellow Sea, Japan) andMarphysa sanguinea (from Venice lagoon, Italy) were both purchased from a retail shop in Lecce (Italy). Homogenates from only three species [Nainereis laevigata andO. cuvieri (family Orbinidae, order Orbinia) andP. terricola (family Maldanidae, order Capitellida)] induced hemolysis in sheep red blood cells. Important differences in hemolytic titers, Ca- or Mg-dependence and in timecourse responses were noted between the three hemolytic species. On the other hand, thermolability and proteinase-inhibitor resistance (with the exception ofO. cuvieri) were features common to all three. Electrophoretic analysis revealed that hemolysis was mediated by apparently only one protein inN. laevigata andP. terricola, with no correlation between them or with the proteins responsible for hemolysis in the oligochaeteEisenia fetida andrei (Lumbricidae). No lytic protein was localized in hemolyticO. cuvieri homogenate, which was also the only homogenate to be partially inhibited by benzamidine, but not by phenylmethylsulfonyl fluoride or soybean trypsin inhibitor. These results underline the extreme variety existing among the species constituting the polychaete group.