Predation and the Control of the Sea Urchin Echinometra viridisand Fleshy Algae in the Patch Reefs of Glovers Reef, Belize

The massive reduction in sea urchin Diadema antillarum populations since the mid-1980s has been associated with large increases in the abundance of fleshy algae on many Caribbean reefs despite the availability of other sea urchin and finfish grazers. This study examined the ecology of a grazer living sympatrically with D. antillarum, the common and abundant sea urchin Echinometra viridis. I examined the role that finfish and invertebrate predators play in controlling the distribution of E. viridis as well as the ability of this sea urchin to control exposed fleshy algae on the patch reefs of the Glovers Reef Atoll lagoon. I found that the major predators of this sea urchin were Calamus bajonado (jolthead porgy), Balistes vetula and Canthidermis sufflamen (queen and ocean triggerfish), Lachnolaimus maximus (hogfish), and a gastropod, probably Cassis madagascariensis. The abundance of E. viridis is constrained by predation, which restricts E. viridis to cryptic locations, such as crevices. Sea urchins bit a smaller percentage of experimental algal assays than finfish. Finfish herbivory was associated positively with patch reef topographic complexity. Unexpectedly, E. viridis abundance was positively correlated with fleshy algal abundance, but negatively correlated with the frequency of finfish bites. Predators restrict E. viridis to crevices and therefore reduce their influence on exposed fleshy algae, even at moderately high population densities (up to 10 per square meter). Since net benthic primary production of coral reefs is most strongly associated with herbivory on exposed surfaces, it would appear that E. viridis is unable to maintain the same production as reefs dominated by D. antillarum. Received 5 November 1998; accepted 2 June 1999.     

Intraguild predation and interference competition on the endangered dragonfly <Emphasis Type="Italic">Aeshna viridis</Emphasis>

We examined the effects of intraguild predation (IGP) and interference competition on an endangered dragonfly, Aeshna viridis Eversm. (Odonata: Anisoptera). A. viridis is rare in Europe due to the decrease in suitable habitats harboring the macrophyte Stratiotes aloides L. Stratiotes plants are the principal oviposition substrate for A. viridis females and protect the larvae of A. viridis from fish predation. In our study lakes A. viridis larvae are sympatric with larvae of Aeshna grandis and Aeshna juncea. The susceptibility of A. viridis larvae to IGP by similar-sized larvae of A. grandis and A. juncea was tested in a laboratory predation experiment. Microhabitat use of A. viridis and A. grandis was studied in the laboratory to determine the possible effects of interference competition on the spatial distribution of A. viridis larvae. Our results show that at least in laboratory conditions, A. viridis is susceptible to IGP and interference competition. In competition, A. grandis larvae dominated the middle and outer portion of S. aloides rosettes whereas A. viridis stayed in the inner parts. When A. grandis larvae were absent, A. viridis colonized the middle and outer parts of the rosettes. We conclude that asymmetric predation between odonate larvae of equal size can be intense, and that both IGP and interference competition affect A. viridis. Although natural habitat complexity diminishes their impact, these interactions may nevertheless influence the distribution of A. viridis in S. aloides waters and restrict its microhabitat use in S. aloides rosettes.     

Reproductive cycles of the sympatric excavating sponges Cliona celata and Cliona viridis in the Mediterranean Sea

Abstract. Clionaids are excavating sponges, which live in and grow into calcareous substrates. We studied the sexual reproductive cycles of two clionaid sponges coexisting in a Mediterranean coastal basin (Porto Cesareo, Italy), Cliona viridis and Cliona celata, by analyzing monthly tissue samples of ten specimens of each species collected over a 2‐year period. From May to June of the second study year, supplementary samples were taken weekly. Up to 90% of the specimens of C. viridis and 70% of those of C. celata sampled were reproductive during the study. In both species, but particularly in C. viridis, reproductive investment, measured as the percentage of sponge tissue occupied by gametes, was high. Oocytes were present almost year‐round in both species, except for a 1–4‐month period after zygote release. In contrast, spermatogenesis occurred most frequently in May in both species, when (May–June) oocytes reached their greatest diameters. Cliona viridis and C. celata are hermaphrodites, with oocytes and spermatic cysts coexisting in 10% of the studied individuals in the first year of the study, and in 30% during the second. No developing embryos or larvae were incubated in the sponge tissues, and fertilization was not observed. Temperature may play a role in triggering some important phases of the reproduction of these Cliona, such as oocyte maturation and spermatogenesis, which occurred when water temperature increased from 17°C to 25°C between May and June.     

Molecular Phylogenetic Relationships Between Prostanoid-Containing Okinawan Soft Coral (<Emphasis Type="Italic">Clavularia viridis</Emphasis>) and Nonprostanoid-Containing <Emphasis Type="Italic">Clavularia</Emphasis> Species Based on Ribosomal ITS Sequence

To study phylogenetic relationships among Okinawan soft corals of the genus Clavularia, the ribosomal internal transcribed spacer sequences of host corals and the 18S rDNA sequences of symbiotic algae were analyzed. The molecular phylogenetic trees of hosts showed that a prostanoid-containing species, Clavularia viridis, is deeply diverged from other species of Clavularia which do not biosynthesize the prostanoids as the main secondary metabolites. Comparison of their trees suggested poor phylogenetic concordance between hosts and symbionts.     

The diatom flora of the Salton Sea, California

We report on diatom species of the Salton Sea, a highly saline (43 g l^–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.     

Accumulation, depuration and distribution of cadmium and zinc in the green-lipped mussel Perna viridis (Linnaeus) under laboratory conditions

Ecotoxicological tests were conducted in the green-lipped mussel Perna viridis under laboratory conditions. Different rates of accumulation and depuration in soft tissues are found and this might be due to different mechanisms of metal binding and regulation. At the end of depuration, Cd levels in soft tissues of P. viridis were 10–30 times higher than before exposure, while Zn levels in soft tissues were almost similar to levels before exposure. These results indicate that P. viridis is a good biomonitoring organism for Cd but Zn levels might be actively regulated. It remains uncertain whether P. viridis is a good biomonitoring organism of environmental Zn contamination. However, the positive patterns, although different rates, of accumulation and depuration for Cd and Zn support the use of P. viridis as a biomonitoring agent for such metals.     

Caprellid assemblages (Crustacea: Amphipoda) in shallow waters invaded by <Emphasis Type="Italic">Caulerpa racemosa</Emphasis> var. <Emphasis Type="Italic">cylindracea</Emphasis> from southeastern Spain

Growth of the invasive algae Caulerpa racemosa var. cylindracea in shallow habitats may influence the faunal assemblage composition. We studied its effects on caprellid assemblages associated with shallow-water habitats of hard and soft bottoms from the SE Iberian Peninsula (native rocky-bottom algae, C. racemosa from hard and soft bottoms, and Caulerpa prolifera, Cymodocea nodosa and Posidonia oceanica from soft bottoms). Samples were taken in two different sampling periods (September 2004 and March 2005). A total of seven caprellid species were identified, with important differences in their distribution in different habitats. Total abundance of caprellids was very high in March on native algae on hard bottoms, and on C. racemosa on both soft and hard bottoms. On both hard and soft bottoms, abundances of Caprella hirsuta recorded from C. racemosa were low. On the other hand, a higher abundance of other species, namely C. acanthifera, C. santosrosai, Phtisica marina and Pseudoprotella phasma, was recorded from C. racemosa. The results indicate that C. racemosa may have a positive influence on some caprellid species, while seasonal changes are also evident. It is concluded that introduced C. racemosa may serve as a new habitat, promoting and maintaining caprellid populations in shallow Mediterranean habitats.     

Space partitioning by stony corals soft corals and benthic algae on the coral reefs of the northern Gulf of Eilat (Red Sea)

The major faunistic and floristic components occupying space on the coral reefs of the northern Gulf of Eilat (Red Sea) are stony corals, soft corals and benthic algae. The percent living coverage of the three components and the relative abundance of the different species of each component were studied by line transects, on the reef flats and the upper forereef zones of nine localities. A wider and higher range of living coverage values of stony corals were recorded at the upper fore-reef zones (18.30–49.09%) compared with the reef flats (5.50–31.66%) at the different stations. The most abundant stony corals on the reef flats areCyphastrea microphthalma, Stylophora pistillata, Favia favus, Porites lutea, Platygyra lamellina and the hydrozoanMillepora dichotoma. The fire coralM. dichotoma dominates the upper fore-reef zone in most of the stations. The average percent living coverage of soft corals on the reef flats ranged between 0.20 and 17.06%, and on the upper fore-reef zones between 1.68 and 15.13%. Seventy percent of the total living coverage of the soft coral community is contributed by 2 to 3 species. They tend to form large monospecific carpets, such as those composed ofSinularia sp.,Sarcophyton glaucum andLobophytum pauciflorum. The common benthic algae on the coral reef studied occur as turfs or macroscopic noncalcareous algae. They play a significant role in occupying space, especially on the reef flats. The most abundant algae recorded in all localities are the turfsSphacelaria tribuloides, Jania sp. and the macroscopic non-calcareous algaeTurbinaria elatensis andColpomenia sinuosa. Comparison between reef flats and upper fore-reef zones, in terms of average living cover of stony corals, shows that the variation among the reef flats is grater than the variation among the upper fore-reef zones. However, there is no significant variation in the average living coverage of soft corals between these two zones. Annual living-coverage values of algae on the reef flats are significantly higher than those of the upper fore-reef zones. Extremely low tides occurring periodically but unpredictably at Eilat cause mass mortality of the benthic communities on the reef flats reopening new spaces for settlement. The coexistence of stony corals, soft corals and algae on the reef ecosystem is due to different biological properties of each component. Opportunistic life histories of certain stony corals and most algae enable quick colonization of newly opened spaces. Lack of predators, high tolerance against abiotic factors and ability to form large aggregates of colonies are suggested as possible factors supporting the existence of soft corals in shallow water. Biological factors such as competition, predation and grazing pressure play an increasingly important role in controlling space utilization by the components studied with the advancement of succession.     

Composition of a molluscan assemblage associated with macrophytes in Menzel Jemil (Bizerte lagoon,SW Mediterranean Sea)

The molluscan species composition and diversity associated with macrophytes was studied throughout 1 year at Menzel Jemil station (Bizerte lagoon, north‐west of Tunisia). A total of 7,539 individuals belonging to 13 species were collected. The molluscan assemblage was mainly composed of gastropods (98.12%, nine species), followed by bivalves (1.88%, four species). Hydrobia acuta ranked first with 49.97% of total abundance, followed by Bittium reticulatum (17.97%), Tritia mutabilis (11.38%), Haminoea navicula (8.98%), Phorcus articulatus (5.17%) and Cerithium vulgatum (3.94%). The large number of juvenile molluscs collected confirms the importance of macroalgae and seagrass for mollusc recruitment. Significant temporal variations of species richness, density and diversity indices of the mollusc assemblage have been observed during the year. Multivariate analyses applied to our data revealed significant relationships between the macrophyte composition and associated molluscan assemblage. The BIOENV analysis indicated that water temperature, phosphates concentration and macrophyte biomass were environmental variables most closely associated with the temporal variation of molluscan assemblage.     

Three wild Lithuanian strawberry species and their pollinators

The European wild strawberry species Fragaria vesca L., Fragaria viridis Weston, and Fragaria moschata Weston are sympatric and bloom concurrently, introducing the possibilities of cooperation and competition for pollinators. We studied the pollination biology of strawberries that were grown in rectangular plots at a field site near Vilnius city in Lithuania. The number of open flowers, the number of insects visiting flowers, and the plot area covered by strawberry plants were recorded. Wild strawberries were visited by solitary bees (38.5%), flies (31.4%), and other hymenopterans (21%; ants accounted for approximately 98% of this group). Coleopterans, lepidopterans and honey bees together represented less than 10% of the insects recorded on strawberries. Fragaria viridis and F. moschata flowers were more attractive to pollinators than those of F. vesca. The main visitors of F. viridis were small solitary bees; those of F. moschata were ants, while F. vesca flowers were visited by solitary bees, ants and flies in comparable numbers. We discuss competition for pollinators and the possible impact of climate fluctuation on strawberry-pollinator interactions.     

Late Glacial and Holocene Ostracoda of the Gulf of Gdańsk,the Baltic Sea,Poland

To trace environmental changes in water hydrology and salinity in the Late Glacial to Holocene of the Gulf of Gdańsk, a south‐eastern bay of the Baltic Sea within the maritime zone of Poland, the distribution of ostracod valves was studied in 20 sediment cores collected from both the shallow‐ and deep‐water zones (depth 10.9–67.5 m). The studied sediment sequences yielded ca. 3000 valves of 21 ostracod species, of which only five are known to live today in the Gulf, which has a present maximum depth of 118 m and water salinity up to 7–8‰. The majority of the studied sediment layers that contained ostracod valves corresponded to the period of the Late Glacial to Mid‐Holocene and was dominated by non‐marine species, of which the most common were Candona neglecta (present in 17 cores), Cytherissa lacustris (15 cores) and Candona candida (14 cores). By clustering classification five major ostracod assemblage types were recognised in the studied cores. Initial assemblage types dominated mostly by inhabitants of the profundal/sub‐littoral zones of modern oligo‐mesotrophic lakes (C. lacustris and C. neglecta) in some sediment sequences were replaced in stratigraphical order by the assemblages dominated by brackish‐water species (Cyprideis torosa or Cytheromorpha fuscata). The structure and species composition of the distinguished ostracod assemblage types as well as their successional transitions indicate that the studied sediments were deposited initially in the Late Glacial in freshwater lacustrine conditions, and subsequently, during the Holocene marine transgression, covered by marine sands. The present results confirm and consolidate inferences based on previously published data on ostracods from the western part of the Gulf of Gdańsk as well as on other biotic (molluscs, diatoms) and abiotic (seismoacoustic) indices from this area (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Changes in subtidal habitat following mass mortality of sea urchins in Botany Bay,New South Wales

On two occasions, between June and October 1986 and April/May 1988, mass mortality of the sea urchin Centrostephanus rodgersii occurred at Bare Island in Botany Bay, New South Wales. Following the widespread disappearance of C. rodgersii in August 1986, the abundance of filamentous and foliose algae increased and crustose corallines declined. There was also a large, but shortlived, increase in the density of limpets, particularly Patelloida alticostata, which then fell to nearly zero after 15 months. In October 1986, the habitat found at other sites in Botany Bay was consistent with a recent disappearance of C. rodgersii. At all sites a complex assemblage of non-crustose algae developed, the species composition of which differed among sites. A large recruitment of C. rodgersii was observed at all affected sites in February 1987 and January 1988. These individuals grew quickly and reached a mean size of approximately 35 mm test diameter at the end of their first year.     

Depth-related radiolarian assemblage in the water-column and surface sediments of the Japan Sea

Plankton tows and surface sediments from the Japan Sea, a marginal sea of the northwestern Pacific, were examined to study the depth distribution of modern radiolarians. The depth distribution patterns between the living assemblage in the water-column and the thanatocoenose in surface sediments are similar to each other, indicating that the depth-related assemblage in sediments is closely related to the living depths of major species. Four clear restrictions of many species to discrete depth zones are recognized in the water-column, from the surface down to 2000 m: (1) upper subsurface-water species, which are abundant from 40 to 120 m (Larcopyle butschlii juvenile form, Spirocyrtis subscalaris, Spongodiscus resurgens and Lipmanella virchowii); (2) lower subsurface-water species, which are abundant from 40 to 300 m (Larcopyle butschlii adult form, Ceratocyrtis histricosa and Spongotrochus glacialis); (3) intermediate-water species, which have population maxima from 160 to 300 m (Ceratospyris borealis); and (4) deep-water species, which have maxima between 1000 and 2000 m (Cycladophora davisiana and Actinomma boreale). Only a few specimens of A. boreale were found in the water-column ranging from 1000 to 2000 m depth, although this is a dominant species in surface sediments from depths below 2000 m of which the dominance increases with water depth. A. boreale may live mainly in the bottom water. Cycladophora davisiana and A. boreale, which characterize the Japan Sea deep assemblage, are naturally shallow or intermediate dwellers in other oceans. On the other hand, the typical deep-dwellers (e.g. Cornutella profunda, Cyrtopera languncula and Peripyramis circumtexta) of other oceans have not been found in the Japan Sea. Such a peculiar deep assemblage is a result of the deep circulation system in the Japan Sea and the shallow depths of the sills around it.     

Metatrancriptomic analysis from the Hepatopancreas of adult white leg shrimp (<Emphasis Type="Italic">Litopenaeus vannamei)</Emphasis>

The amoeba, Mayorella viridis contains several hundred symbiotic green algae in its cytoplasm. Transmission electron microscopy revealed strong resemblance between symbiotic algae from M. viridis the symbiotic Chlorella sp. in the perialgal vacuoles of Paramecium bursaria and other ciliates. Although it is thought that the M. viridis and symbiotic algae could be model organisms for studying endosymbiosis between protists and green algae, few cell biological observations of the endosymbiosis between M. viridis and their symbiotic algae have been published. In this study, we characterized the specificity of endosymbiotic relationships between green algae and their hosts. Initially, we established stable cultures of M. viridis in KCM medium by feeding with Chlorogonium capillatum. Microscopic analyses showed that chloroplasts of symbiotic algae in M. viridis occupy approximately half of the algal cells, whereas those in P. bursaria occupy entire algal cells. The symbiotic algae in P. bursaria contain several small spherical vacuoles. The labeling of actin filaments using Acti-stain? 488 Fluorescent Phalloidin revealed no relationship between host actin filaments and symbiotic algal localization, although the host mitochondria were localized around symbiotic algae. Symbiotic algae from M. viridis could infect algae-free P. bursaria but could not support P. bursaria growth without feeding, whereas the original symbiotic algae of P. bursaria supported its growth without feeding. These data indicated the specificity of endosymbiotic algae relationships in M. viridis and P. bursaria.     

Microalgal biotechnology: Carotenoid and glycerol production by the green algae <Emphasis Type="Italic">Dunaliella</Emphasis> isolated from the Gave-Khooni salt marsh,Iran

In this study, carotenoid and glycerol production in two unicellular green algae (Dunaliella salina and D. viridis) isolated from the Gave-Khooni salt marsh grown in media containing five different salt concentrations (0.17, 1, 2, 3, and 4 M NaCl) were evaluated under sterile conditions. Algae growth decreased as the medium salinity increased. Optimum growth of D. salina and D. viridis were obtained at 2 and 1 M NaCl, respectively. As salinity increased, glycerol and carotenoid production were increased in D. salina, whereas lower values for these products were produced in D. viridis under the same conditions. Furthermore, the cell color of D. salina changed from green to orange-red following accumulation of carotenoid, but the color of D. viridis was not changed. Thereby, it seems that the Iranian D. salina may be suitable for carotenoid production (betacarotene) on a large scale. In addition, since carotenoid compounds enhance the efficiency of photosynthesis and glycerol synthesis, it appears that the pathway for glycerol production and mechanisms of salt tolerance in D. viridis are unique from those of D. salina.     

Sub-ice algal assemblages of the Barents Sea: Species composition,chemical composition,and growth rates

Summary The ice algae of the Barents Sea were studied from 1986 to 1988. With a few exceptions, the ice algal assemblages were dominated by pennate diatoms. From March to early June there was a transition from a mixed population of both centric and pennate diatoms at the start into a well developed Nitzschia frigida assemblage. Nutrier ts in ice-covered regions were high in spring, and high N/C and protein/carbohydrate ratios indicated no nutrient deficiency in the ice algae. The N/P ratios were lower than 15, but comparable to ratios of three ice algae species grown in culture at -0.5 °C and various light conditions. The Si/N ratios were lower than corresponding ratios from the Canadian Arctic and the Antarctic. The chemical composition revealed that silicate limited growth cannot be excluded. The cells were heavily shade-adapted the entire spring season, with high Chl/C ratios (0.045–0.084), comparable to the cultures growing at low irradiances. The growth rates in the cultures peaked at 50 mol m^-2s^-1 with maximum rates of 0.6–0.8 div. day^-1, both for 12 and 24 h day lengths. The low growth rates for the May assemblages (max 0.20 div. day^-1) indicated strong light limitation by self-shading. Adaptation experiments showed that some ice algae are highly adaptable, while others are not able to adjust to new irradiances. Their growth rates are inhibited by high irradiances and this may affect the distribution in the field.     

A modern soft-bottom, shallow-water crinoid fauna (Echinodermata) from the Great Barrier Reef, Australia

A recent preliminary survey revealed that 12 species of unstalked crinoids occur on a gentle sandy slope (12–18 m depth) at Lizard Island, Great Barrier Reef, Australia; five of which are also found on coral reefs. The other seven appear to constitute a unique assemblage restricted to unconsolidated substrates, where most cling to algae or hide beneath rubble or sponges. Members of this assemblage exhibit all of the basic feeding postures found among reef-dwelling species. However, Comatula rotalaria, which lacks anchoring cirri and bears uniquely differentiated short and long arms, exhibits a posture different from other living crinoids. Quantitative transects reveal apparent depth-related differences in species composition: C. rotalaria dominated the 12 transects in 12–13 m (84% of 82 specimens), while Comatella nigra, Comatula cf. purpurea, Amphimetra cf. tessellata and Zygometra microdiscus accounted for 96% of 54 specimens observed along 12 transects in 16–17 m.     

Endosymbiotic bacteria associated with the intracellular green algae ofHydra viridis

Gram-negative bacteria 4.5–5.5 μm in length and 1.2 μm in diameter are found in gastrodermal cells of three stains of freshwater green hydras,Hydra viridis (Ohio and Carolina from North America, Jubilee strain from England). They are motile via single polar flagella. They were detected in live animals, Jensen stained material, and electron micrographic sections. Bacteria lose motility quickly upon release from hydra cells. Green hydras harbor strain-specific numbers of chlorellae in these cells. Other tissue types lack algae. The chlorella-hydra symbiosis can be disassociated and the partners grown separately; transfer of photosynthate from algae to hydra occurs. Here we report the presence of endocellular bacterial vesicles specifically associated with cells that contain the symbiotic chlorellae. No cells that contained algae and lacked bacteria were seen. Vesicles, especially conspicuous in sexually mature green hydras, are probably produced upon extrusion from the cell. They contain either algae and bacteria or bacteria alone and are often expelled to the surrounding medium via the coelenteron. Bacteria are absent in nerve cells, interstitial cells, nematocysts, mucous cells, sperm, and probably in most of the other cell types that lack algae. They are present in at least one cell type that lacked algae: the columnar ovarian cells. Bacteria were lost in “bleached” hydras, those induced to lose their algae by high intensity light in a solution of DCMU, a standard inhibitor of photosynthesis. They were absent in a fourth strain of green hydra (Connecticut Valley,H. viridis) and inH. fusca andH. littoralis, two freshwater nonsymbiotic hydras. All of the hydra lacking bacteria contain conspicuous lipid droplets in their cells. The presence of large numbers of bacteria has implications for interpretations of metabolic exchange between host and algal symbionts and for extrapolation of metabolic data from strain to strain ofH. viridis.     

Analysis of the blennioid assemblages associated with different rocky shore habitats in the Ligurian Sea

The differences among blennioid assemblages (families Blenniidae and Tripterygiidae) on different habitats were assessed at two localities of the Ligurian Sea, namely Arenzano and Riva Trigoso. The assemblage composition and species relative density were evaluated visually on four different habitats of diverse wave exposure and substratum orientation (macro‐habitat characteristics): two vertical intertidal and subtidal habitats (exposed and sheltered rockwalls) and two horizontal subtidal habitats (semi‐exposed flat rock and boulders and pebbles). Each habitat was also characterized in relation to micro‐habitat features, such as substratum complexity, heterogeneity and amount of algae cover. Patterns of differences among habitats in assemblage variables and fish density, and the influences of macro‐ and micro‐habitat features on these patterns were studied at small (within localities) and large (across localities) spatial scales. Higher values of species richness (S), diversity and evenness (J) were generally associated with vertical habitats, as a result of a positive correlation with substratum orientation. The presence of an intertidal zone in the rockwall habitats may partially explain the observed differences in assemblage variables between vertical and horizontal habitats. The strength of relationships between S, and J and the other investigated habitat variables (exposure, complexity, heterogeneity and algae cover) varied greatly depending on spatial scale. All these relationships were positive, except for complexity. Significant variation in the assemblage total density among habitats was recorded only at Arenzano, where a larger number of fishes were counted on rockwalls rather than on the horizontal habitats. The positive effect of orientation on fish total density was strictly dependent on spatial scale. Fish total density showed a negative correlation with complexity and a positive correlation with heterogeneity, both relationships being unaffected by spatial scale. The unexpected relationship with complexity was probably due to the fact that, in the most complex habitat (i.e. boulder and pebbles), the potential positive effect of high complexity on fish density might be overcome by the negative influence of other environmental features, such as horizontal orientation and low wave exposure. Complexity and heterogeneity thus seemed good predictors of fish total density, but their role needs to be carefully interpreted. The most marked differences in species composition and relative density were found between rockwalls and the other habitats, mostly due to an unbalanced distribution of some stenoecious species. Variations in species relative density were related to different combinations of both macro‐ and micro‐habitat features, and these relationships usually changed depending on spatial scale.     

Seasonal variation in a low shore Fucus serratus (Fucales,Phaeophyta) population and its epiphytic fauna

Seasonal variation in a Fucus serratus assemblage was studied on the Isle of Man, UK over a 13-month period. Algal cover varied greatly, related to shedding reproductive fronds and winter storms. Peak reproduction was recorded in the autumn. There was little change in density of plants, the population was dominated by a bank of germlings (<20 cm) and an adult mode between 50–70 cm. An indistinct third component of recruiting juveniles was present when gaps in the canopy formed. Seasonal variation in the algae was reflected in the population dynamics of the mobile epiphytes such as Littorina mariae and Lacuna pallidula, which exhibited annual life histories. Sessile species (such as bryozoans) utilized the algae year round, dominating the perennial stipes and lower fronds, which were not shed. Other species utilized the algae in a transient fashion: some feeding on the algae (e.g. Idotea), or other epiphytic animals (e.g. Nucella). Fucus serratus, therefore, provides a variety of spatially and temporally variable niches that explain the diversity of epiphytic animal species that exploit this alga.