Composition and temporal fluctuations of inshore juvenile fish populations in the Kornati Archipelago, eastern middle Adriatic

Temporal fluctuations of species composition and abundance of fish juveniles in the National Park Kornati were studied over 12 months from January to December 1992. A total of 40 168 individuals, representing 24 families and 69 species, were collected using a 50 m long beach seine. The community was dominated numerically by a few species: Atherina hepsetus (45.90%), Sarpa salpa (21.21%), Diplodus vulgaris (10.49%), and Symphodus ocellatus (6.98%), constituting over 84.58% of the total catch. Similarity between patterns in the abundance of the 17 most common species were examined using correlation matrix-based principal component analysis. Results were compared to the abiotic factors leading to the conclusion that only a low amount of variation in the abundance field can be explained by temperature, salinity and dissolved oxygen. Received: 23 March 1997 / Accepted: 11 April 1997     

Habitat structure and complexity as determinants of biodiversity in blue mussel beds on sublittoral rocky shores

Habitat-forming, ecosystem engineer species are common in most marine systems. Still, much uncertainty exists about how individual and population-level traits of these species contribute to ecosystem processes and how engineering species jointly affect biodiversity. In this manipulative field experiment, we examined how biodiversity in marginal blue mussel beds is affected by blue mussel (1) body size, density and patch context and (2) presence of fucoid and algal structures. In the study area, bladder-wrack (Fucus vesiculosus), filamentous algae and blue mussels (Mytilus edulis) coexist at shallow depths in a variety of patch configurations and offer complex habitats with a high variability of resources. We hypothesized that complexity in terms of mussel bed structure and algal presence determines species composition and abundance. Results from the experiment were compared with macrofaunal communities found in natural populations of both engineering species. Results show that the physical structure and blue mussel patch context are important determinants for species composition and abundance. Results further show that the presence of algal structures positively affects diversity in blue mussel habitats due to increased surface availability and complexity that these algae offer. This study shows that blue mussel beds at the very margin of their distribution have an indisputable function for promoting and maintaining biodiversity and suggest that facilitative effects of habitat-modifying species are important on Baltic Sea rocky shores with fundamental importance to community structure.     

Population structure,northern range limit,and recruitment variation in the intertidal limpet Lottia scabra

The northern range limit of the intertidal limpet Lottia scabra is Cape Arago, Oregon (43°N), where adult survival is excellent, the population is small (<300), and recruitment is low; the range limit may be set by limited recruitment. Between June 2012 and March 2013, 25 sites from the middle of the species range (33°N) to Cape Arago were sampled and population size frequency distributions, densities, and nearest neighbor distances were compared to the amount of rocky and sandy shore and kelp bed size. North and south of 37°N, the densities of new recruits averaged 22 and 86 m^?2, respectively. This shift was associated with the range limit of Macrocystis pyrifera kelp beds; we hypothesize that slower currents in M. pyrifera beds may limit larval dispersal leading to higher recruitment. North and south of 40°N, adult density averaged <1 and 458 m^?2, respectively, with the species absent from many sites to the north. This shift was associated with a sharp drop in the amount of rocky shoreline and an increase in uninhabitable sandy shore. Near the northern range limit, >80 % of the individuals were solitary and may be unable to spawn successfully. Recruitment at Cape Arago was infrequent and likely due to self-recruitment. This study suggests that the range limit was set by the absence of M. pyrifera and too little rocky shore leading to high larval wastage, low settlement, low population densities, and, due to an Allee effect, very small effective population sizes.     

Direct estimation of natural mortality rates for littoral marine fishes using populational data from a marine reserve

 Visual censuses conducted in a marine reserve (Medas Islands) were used to estimate the natural mortality rates (M) for five common fish species in the NW Mediterranean Sea (Coris julis, Diplodus annularis, D. sargus, Serranus cabrilla and Symphodus roissali). Visual censuses of these same five species were also performed at three sites in unprotected areas of the coast where both commercial and sport fishing activity was normal. Censuses were conducted over a 3 year period. Estimates of M in the 3 years displayed scant seasonal or interannual variation, which may mean that the populations were in equilibrium during that period. The results of this study showed that the relationships between M and the growth parameters and maximum life span were unclear, and considerable caution is therefore recommended when using indirect methods of estimating M based on those parameters. For certain species the values of M were equal to or greater than the estimated total mortality in the exploited areas. The virtual absence of piscivorous predators in the unprotected area as a consequence of the high level of fishing in that area contrasts with the high abundance of such predators in the marine reserve. Since predation is the main contributor to M, estimated mortality in the unprotected areas is attributable nearly entirely to fishing. It is suggested that M may vary according to alterations taking place in conditions in the ecosystem inhabited by a species and thus that use of a value of M for a pristine population cannot be extrapolated to exploited areas. Received: 18 January 2000 / Accepted: 14 July 2000     

Reproductive ecology of the azooxanthellate coral <Emphasis Type="Italic">Tubastraea coccinea</Emphasis> in the Equatorial Eastern Pacific: Part V. Dendrophylliidae

The reproductive ecology of Tubastraea coccinea Lesson, an azooxanthellate tropical scleractinian coral, was studied over various periods from 1985 to 2006 at four principal eastern Pacific locations in Costa Rica, Panamá, and the Galápagos Islands (Ecuador). This small (polyp diameter 0.8–1.0 cm), relatively cryptic species produced ova and planulae year round, including colonies with as few as 2–10 polyps. Of 424 colonies examined histologically, 13.7% contained both ova and sperm. Mature ova varied in diameter from ∼300 to 800 μm and the time from spawning and fertilization of oocytes to release of brooded planulae was about 6 weeks. Planulae were 0.5–1.5 mm long and they settled and metamorphosed on a variety of substrates after 1–3 days. Spermaries, though more difficult to distinguish in histological sections, were present throughout the year. Spent spermaries were never observed in sections, but several colonies in Panamá and the Galápagos Islands released sperm from night one to night five after full moon, indicating the potential for cross-fertilization among colonies. Planula release was observed at Uva Island (Panamá) in March, May, June, and July, and in general planula presence was higher at warm ocean temperatures at all sites, whether or not the sites were influenced by seasonal upwelling. Annual fecundity estimates for T. coccinea are comparable with other high fecundity brooding species, including the zooxanthellate Porites panamensis, with which it co-occurs in Panamá. Tubastraea coccinea is widely distributed in the tropical Indo-Pacific and has colonized substrates in the western Atlantic. In addition to the reproductive characteristics described in the present study, other features of the biology of T. coccinea, such as an ability to withstand conditions that produce bleaching and mortality in zooxanthellate species, may account for its widespread, low-latitude distribution in multiple oceans. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

Temporal and spatial components of variability in benthic recruitment,a 5-year temperate example

Deployment of artificial substrata is a common method of investigating early community development and recruitment, but rarely are such experiments of long enough duration to include even year time scales. We placed replicate, machined-slate panels (15×15 cm) in the intertidal and at depths of 6 and 12 m at two sites of differing flow rate at Lough Hyne, SW Ireland. These were serially replaced every 30–60 days for a period of 5 years (1997–2002), except in the intertidal (2000–2002). The number and identity of all recruits were recorded. Recruitment varied over several orders of magnitude both on temporal and spatial scales. The greatest source of variability was between the intertidal (with few species or recruit numbers) and the subtidal zones (many species, some with thousands of recruits per panel per 30 days). Highest levels of recruitment occurred at the low-flow site (Labhra Cliff). Here, recruitment was dominated by the serpulid polychaete, Pomatoceros sp., reaching ~4000 individuals per panel per 30 days. Highest species richness occurred, however, at the high flow site (Whirlpool Cliff). At this site more colonial forms (e.g. bryozoans) settled. Season was found to be the dominant pattern explaining subtidal recruit and species number variability. Year, however, was the dominant temporal pattern explaining change in diversity (Shannon–Wiener H). In space, depth explained most variability of recruit numbers, whereas site explained more variation in species richness. Both these spatial factors contributed similarly to variability of diversity (H). Recruitment has long been known to vary considerably over large spatial scales, such as with latitude and isolation, but we that show changes of a similar magnitude in recruitment can occur across small spatial scales. Individual taxa showed varied temporal patterns of recruitment including continuous, regular seasonal fluctuations and irregular pulses in particular years.     

Seasonality of polypide recycling and sexual reproduction in some erect Antarctic bryozoans

The seasonality of polypide cycling has been investigated for three species of erect bryozoans from Antarctica: Isoseculiflustra rubefacta (Kluge, 1914), Nematoflustra flagellata (Waters, 1904) and Himantozoum antarcticum (Calvet, 1905). Approximately ten colonies of each species were collected monthly by SCUBA divers over a 14 mo period during 1992/1993, and the status of each individual zooid was classified as differentiating/regenerating, active (feeding autozooids), degenerate (brown body) or sexually reproductive (ovicells present, or zooid containing a larva). Polypide cycling in all three species was distinctly seasonal. New zooids formed at the growth margin and typically contained actively feeding polypides for ≃9 mo before these polypides degenerated into brown bodies in the austral winter (June). Very few polypides were active in the period from June to August, when water-column food levels were at their lowest; after this period new polypides differentiated. Individual zooids typically underwent a total of five (I. rubefacta and N. flagellata), or at least four (H. antarcticum) complete polypide cycles before becoming senescent. Polypide lifetimes generally became shorter as the age of the zooid increased. Sexual reproduction was also distinctly seasonal in these species, with bands of ovicells or sexually reproductive zooids being formed each year in late summer once a given colony had grown to a threshold size (or age). Larvae were then brooded for ≃10 mo before being released in January/February (N. flagellata) or February/March (H. antarcticum). The seasonal patterns of polypide cycling are related clearly to the variations in food availability, and these species appear to have the longest zooid lifetime (≃5 yr) and the slowest polypide cycling (once per year with polypide lifetimes up to 10 mo) reported for any bryozoan so far. Received: 7 May 1995 / Accepted: 19 November 1997     

Reproductive development of the barnacle Chthamalus malayensis in Hong Kong: implications for the life-history patterns of barnacles on seasonal, tropical shores

Hong Kong, lying just below the Tropic of Cancer (22°17′N, 114°09′E), experiences a strongly seasonal environment, with a cool almost temperate winter and a hot, tropical, summer. Histological sectioning of the gonads of the high-shore barnacle, Chthamalus malayensis Pilsbry, showed a seasonal trend in the development of its reproductive organs. Four stages of female gonad development were identified according to the cell types present: post-spawning, resting, growth and mature stages. The female gonad was mature from April to November, which was related to seawater temperatures, and entered a resting phase from December to March. Although the male gonad showed a seasonal developmental trend and reached maximum maturity in summer, the seminal vesicles were full of spermatozoa and functional throughout the year. The reproductive season of this species is therefore solely dependant upon the maturity of the female gonad. The estimated maximum number of broods per year was up to 10 and the maximum number of eggs produced per brood can reach 3,000 eggs. The minimum size for female gonad maturity was 6 mm rostro-carinal diameter (RCD) at which size, the barnacles were ~6-month old. Sperm production occurred at a smaller size (2 mm=2-month old). Compared with Chthamalus montagui and Chthamalus stellatus from temperate regions, C. malayensis produced a greater number of broods per year, had a longer reproductive period and faster gonad development. Chthamaloid barnacles in tropical regions may, therefore, invest more energy per year in reproduction during their life span. Contrary to the seasonal gonad developmental pattern of C. malayensis in the present study, however, C. malayensis in Singapore (which experiences only slight seasonal variation) had mature female and male gonads throughout the year, further supporting the strong role of climatic conditions effecting the reproductive biology of barnacles.     

Comparative analysis of macrofaunal species richness and composition in Posidonia oceanica, Cymodocea nodosa and leaf litter beds

We investigated macrofaunal species richness and composition in Posidonia oceanica, Cymodocea nodosa and Leaf litter beds within a coastal area of the Gulf of Oristano in proximity of the Cabras lagoon (western Sardinia, Italy). A total of 124 taxa were found, of which 116 were identified at the species level. They were analyzed based on both taxonomic and substrate affinity classification. Presence/absence analysis revealed that P. oceanica, C. nodosa and Leaf litter were all characterized by a conspicuous number of soft-bottom polychaetes (e.g., Prionospio multibranchiata and Ampharete acutifrons) and crustaceans (e.g., Corophium sextonae and Dynamene bidentatus), also known as detritivores. There were also major differences between the three habitats investigated. Consistent with its structural complexity, P. oceanica showed the highest species richness [E(S ₅₀)] and the most diversified macrofaunal assemblages, both in terms of taxonomic groups and taxa associated with different substrates. The two seagrasses, however, showed a similar species composition and differed from Leaf litter for the exclusive presence of hard-bottom species (e.g., the tunicate Phallusia fumigata) and seagrass-associated species (e.g., the polychaete Syllis garciai and the decapod Paguristes syrtensis). In contrast, Leaf litter showed the most differences between the habitats, and was characterized by the bivalves Abra alba and Cerastoderma glaucum, not found in seagrass beds, and by Loripes lacteus and Ruditapes decussatus. Leaf litter also had the highest content of organic matter (26.7% ± 1.4) and total organic carbon (10.3% ± 0.4). Our results confirmed the facilitative role of living seagrasses, in particular P. oceanica, as related to their structural complexity, for numerous species from different substrates (e.g., hard bottom species). This study also showed that leaf litter beds act as a particular environment where sediment instability, leaf breakdown, and organic matter enrichment and decomposition strongly influence animal distribution. Finally, our results highlighted the ecological and trophic importance of seagrass-derived detritus and the associated macroinvertebrate detritivores within seagrass-dominated systems.     

Seagrass and algal beds as nursery habitats for tiger prawns (Penaeus semisulcatus and P. esculentus) in a tropical Australian estuary

We evaluated the importance of seagrass and algae to two species of tiger prawns (Penaeus semisulcatus and P. esculentus) by detailed sampling at four sites (two seagrass, two algae) in the Embley River estuary, and through sampling 26 sites in 7 adjacent estuaries at one time of year. Samples of tiger prawns were collected in the Embley River estuary with a small beam trawl at night every 2 wk from September to May for 2 yr (1990 to 1992). The two seagrass sites, which were 11 and 13 km from the river mouth, showed less seasonal variation in salinity than the two algal sites, which were 15 and 20 km from the river mouth. The algal beds at the two upstream sites almost disappeared during the wet season, but the biomass of seagrass did not change significantly between the wet and dry seasons. The grooved tiger prawn (P. semisulcatus), the main species at all sites, comprised 88% of the total tiger prawn catch over the two years. They were found at all sites during the pre-wet season, but after the onset of the wet season, they disappeared along with the algae, from the upstream sites. The brown tiger prawn (P. esculentus) was found almost exclusively (97% of the total catch) on the seagrass sites downstream. In the study of several estuaries, juvenile P. semisulcatus were caught at all 26 sites, and P. esculentus were caught in much smaller numbers, at 16 sites. Approximately equal numbers of P. semisulcatus were caught in seagrass and algal beds in the pre-wet season. Very few individuals >10 mm carapace length of either species, were caught. The results from this study highlight the importance of algal beds during the pre-wet season as nursery areas for one species of tiger prawn (P. semisulcatus).     

Fish assemblages in seagrass beds are influenced by the proximity of mangrove forests

Mangrove forests and seagrass beds frequently occur as adjacent habitats in the temperate waters of southeastern Australia. At low tide when fish cannot occupy mangroves they might utilise adjacent habitats, including seagrass. We first sampled small fish from seagrass beds close to and far from mangroves in the Pittwater estuary, NSW, Australia. Seagrass beds close to mangroves had a greater density of fish species than beds far from mangroves (close: mean 16.0 species net⁻¹, SE 1.0; far: 13.2, 1.3; P < 0.05). In particular, juvenile fish were in greater densities near to than far from mangroves (close: 5.3, 0.4; far: 3.1, 0.4; P < 0.05). We then sampled the mangrove forests during the high tide and seagrass beds during the low tide, in beds along a continuum of distances from mangroves. Multivariate analysis showed that fish assemblages differed with distance from mangroves, and the differences were attributed to the composition of the fish assemblage (i.e. presence/absence of fish species), not the abundances of individual species. In particular, fish that utilise mangrove forests at high tide were found in greater species densities and species richness in seagrass nearer to mangroves. A negative relationship was found between the density of mangrove-utilising fish species and the distance of the bed from mangroves (R ² = 0.37, P < 0.05). This confirms the important connectivity between mangroves and seagrass for fish in temperate Australian waters.     

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

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

Quantitative analysis of foraging behaviour in a field population of the South American sun-star Heliaster helianthus

Foraging behaviour in the South American sunstar Heliaster helianthus (Lamarck) was investigated quantitatively on a subtropical rocky shore in central Peru. H. helianthus feeds mainly on two mussel species, Semimytilus algosus (Gould) and Perumytilus purpuratus (Lamarck). A sequence of foraging behaviour was described and observations were made of the timing of attacks on mussel beds by sun-stars. Although H. helianthus is capable of foraging out of water, an unusual trait for asteroids, the timing of such foraging appears to be well adjusted to avoid the risk of prolonged heat and desiccation. Foraging activity began 4 h 52 min before high tide and 3 h 19 min after high tide, with a mode between 2 h 30 min and 2 h before high tide. Fifty-two percent of all foraging activity began between 3 h 30 min and 2 h before high tide, while only 12.4% began after high tide. This suggests that H. helianthus mainly relies upon changes in the rate of tidal increase as a cue to begin foraging. Foraging activity ceased between 3 h 40 min before and 4 h 29 min after high tide, with 48% ending between 2 and 0.5 h before high tide. The duration of foraging ranged from 19 to 190 min, with values between 30 and 80 min accounting for 67.4% of all observations. The median duration was 62 min. No significant correlation was detected between the time when foraging activity commenced and its duration. The intensity of foraging activity varied on consecutive days, with a general pattern of decreasing intensity after a day of relatively high activity. Foraging location in relation to a mussel bed was analysed on a marked, 8 m stretch of rocky shore. The numbers of foraging H. helianthus observed on different sections of the shore were related neither to the width of the mussel zone nor to the vertical position of the lower edge of the mussel zone, indicating that sun-stars do not rely upon these factors to assess prey availability and that ideal free distribution with regard to prey abundance does not occur on the spatial scale examined.     

Comparative species composition and relative abundance of decapod crustaceans in marine habitats of Panamá

The community structure of the decapod crustacean fauna of 7 tropical, shallowwater, marine habitats (sandy beaches, mangrove swamps and rocky intertidal habitats on both the Pacific and Caribbean coasts of Panama, and Pocillopora damicornis coral habitat of the Bay of Panama) were examined and analyzed for species composition and relative abundances. Collections from the 7 habitats yielded 4361 individuals, representing 236 species. The number of species per habitat was (Pacific, Caribbean): sandy beach (16, 7); mangrove (20, 17); P. damicornis (53); rocky intertidal (78, 67). There were more species represented by more individuals in the Pacific habitats. An index of faunal similarity was calculated for each pair (Pacific-Caribbean) of habitats. This index is the number of ecologically similar congeneric species which occurred in both habitats expressed as a percentage of the total number of species present in the pair of habitats. For the sandy beach communities there were three Pacific species which were similar to three Caribbean species, a similarity of 6/23 or 26%. The index of similarity for the mangrove communities is 54% and for the rocky intertidal communities it is 37%. The P. damicornis community has affinities with the Pacific rocky intertidal community (18%), with that of the Caribbean rocky intertidal (16%) and with that of Indo-West Pacific pocilloporid corals (20%). A few specialized species dominated each of the communities. The habitats and the number of species accounting for over half of the individuals present are (Pacific, Caribbean): sandy beach (1, 1); mangrove (4, 4); P. damicornis (5); and rocky intertidal (3, 6). Most of the species in each community were represented by one or a few individuals.     

Comparison of mussel bed community between two intertidal mytilids Septifier virgatus and Hormomya mutabilis

Mussel bed community structure of two intertidal mytilids, Septifer virgatus (Wiegmann) and Hormomya mutabilis (Gould), whose beds were contiguous vertically on a rocky intertidal shore (Wakayama Prefecture, Japan), was compared between 1982 and 1983. In the upper S. virgatus bed, crustaceans and bivalves were dominant in terms of both number of individuals and biomass. There were three barnacle species representative of the epizoans, two isopods and one amphipod as mobile fauna, and two bivalves as infauna. The lower H. mutabilis bed supported virtually no epizoans or mobile fauna. Infaunal free-ranging polychaetes and sipunculids were dominant in terms of both number of individuals and biomass. The H. mutabilis bed contained a much greater amount of sediment than did the S. virgatus bed, and the interstices among individual H. mutabilis and among their byssal threads were filled with sediment. The biomass of six of nine species dominant in the S. virgatus bed was negatively correlated with the amount of sediment. Recruitment of these faunal assemblages into artificial mussel clumps was examined in mussel enclosure experiments, and a negative sediment effect in H. mutabilis clumps was detected for one isopod and one limpet species. Factors causing the differences between two mussel bed communities are discussed, focusing on the effects of sediment.     

Differences in feeding ecology among three co-occurring species of wrasse (Teleostei: Labridae) on rocky reefs of temperate Australia

The foraging behaviours and dietary compositions of three co-occurring labrids (Ophthalmolepis lineolatus, Notolabrus gymnogenis and Pictilabrus laticlavius), which are conspicuous on rocky reefs in temperate south-eastern Australia, were investigated between 2003 and 2005. SCUBA observations at two locations showed that the feeding intensity, and hence the associated effects of these fishes on rocky reef invertebrate prey, was temporally consistent. Relative differences in the contributions of ingested prey and use of different feeding microhabitats demonstrated that the feeding ecology differed significantly among the three species. Thus, O. lineolatus fed on proportionately higher volumes of polychaetes, polyplacophorans, marginellid gastropods (especially Austroginella sp.), bivalves and echinoids, which were sighted opportunistically in a wide selection of microhabitats, but particularly in sand/rubble. Ambush hunting was used regularly by smaller N. gymnogenis and all sizes of P. laticlavius to forage on amphipods, small decapods and small gastropods at algal bases or fronds and Diopatra dentata tubes. Amphipods were similarly important in the diet of smaller O. lineolatus. Larger N. gymnogenis foraged opportunistically over an increased reef area and made greater use of microhabitats that offered minimal prey refuge (e.g. sand/rubble, bare rock/steel) from which common prey, in particular decapods, were obtained. The significant intra- and inter-specific differences in dietary compositions, allied with differences in the use of feeding microhabitats, would facilitate co-occurrence of these three conspicuous species and contribute to maintaining high richness of labrid species in reef systems. Echinoids were regularly consumed by each species but they made a moderate contribution to the diet of only O. lineolatus, which suggests that only one of the three labrids is likely to play a significant role in regulation of echinoid densities in these rocky reef habitats. However, the broad diets and diverse forging strategies employed by these labrid species imply that they have a system-wide influence on invertebrate prey on rocky reefs.     

Variation and persistence of the middle rocky intertidal community of central Chile,with and without human harvesting

Humans are an important intertidal predator in central Chile. Following a five-year study we report on the effects of the exclusion of humans from the rocky intertidal at Las Cruces, central Chile. The middle intertidal of harvested and non-harvested areas diverged in species diversity and composition during the experiment. In harvested areas the middle intertidal rocky shore was dominated throughout the study by a monoculture of mussels, Perumytilus purpuratus. When humans were excluded, the middle intertidal community switched to one dominated by barnacles (predominantly Jehlius cirratus and Chthamalus scabrosus); this community has persisted for at least three years, despite the presence of forces e.g. mussel larvae, that have the potential to alter the community structure. Such changes were mediated by the muricid gastropod Concholepas concholepas, a key-stone predator. As a consequence of the above changes, the species diversity, H', (primary space occupiers) in the non-harvested area increased from H'=0 at the beginning of the study in 1983 (when the middle intertidal community was dominated by mussels), to values ca H'=2 toward the middle of the study in 1984 (which coincided with the maximum predatory impact of C. concholepas) and subsequently decreasing to ca H'=0.5 at the end of the study in 1987 (when the middle intertida community was dominated by barnacles).Please address all correspondence to J. C. Castilla, Department of Zoology, University of Washington, Seattle, Washington 98195, USA, until March 1990     

Peculiar growth dynamics of the surfgrass <Emphasis Type="Italic">Phyllospadix japonicus</Emphasis> on the southeastern coast of Korea

The surfgrass Phyllospadix japonicus is endemic to exposed shores of the northeastern Pacific Ocean. Unlike the majority of seagrasses, P. japonicus grows on rocky substrata. The specific physical features of the habitat are likely related to the peculiar ecological characteristics of P. japonicus. However, few studies have been conducted thus far on the growth dynamics of Phyllospadix spp., largely due to the turbulent water conditions in its habitat. P. japonicus is a dominant seagrass species, and it plays critical ecological roles on the eastern coast of Korea. Here, we examined its growth dynamics for the first time on the Korean coast. We measured shoot density, biomass, leaf production, phenology, morphology, tissue nutrient content, as well as environmental factors including underwater photon flux density (PFD), water temperature and water column nutrient concentrations from March 2003 to December 2005. Shoot density, biomass, leaf productivity and morphological characteristics exhibited significant seasonal variations; maximum values of these variables occurred in winter and early spring, and the minima were recorded in late summer and early fall. PFD and water temperature were, respectively, positively and negatively correlated with leaf production. Nutrient availability fluctuated substantially, but there was no evidence of distinct seasonal variation, nor was it correlated with leaf production. Leaf chlorophyll concentrations were correlated strongly with leaf production, whereas tissue nutrient contents were unrelated to leaf production. Maximum potential seed production ranged from 1,200 seeds m⁻² in 2004 to 3,445 seeds m⁻² in 2003; however, seedlings were rarely detected through the observation period. Thus, P. japonicus meadows at the study site appeared to persist through vegetative propagation. Leaf C content varied bimodally, with peaks in spring and fall. Leaf N content was minimal during months in which leaf productivity was lowest. These patterns in tissue nutrient content are clearly different from those of the majority of soft-substratum seagrasses and appear to relate to the reduced physiological tolerance of high temperature in P. japonicus compared to other temperate seagrasses.     

Heavy Metals in Macroalgae of Havana's Northern Littoral,Cuba

Copper, iron, lead, manganese, and zinc contents were determined in various phyla of macroalgae typical of the rocky mesolittoral zone of Cuba and widely distributed in the Caribbean Region. the samples were collected in different zones along the shores of Havana City which are more or less influenced by anthropogenic activities. Differences in metal contents were observed due to seasonal variations and differences between sampling sites. of the analyzed species, only one brown alga, Padina vickersiae is considered as a suitable candidate for the monitoring of metal contamination.     

Tidal height,rather than habitat selection for conspecifics,controls settlement in mussels

Settlement is a major determinant of intertidal populations. However, the energy costs of lost larvae are very high. Accordingly, arrival and attachment on suitable substrata are essential requirements for species’ survival. On the intertidal, the presence of cues left by adult or juvenile conspecifics could be vital for the successful establishment of larvae arriving on the shore. Two mussel species, the indigenous Perna perna and the invasive Mytilus galloprovincialis, co-occur on the lower eulittoral zone on the south coast of South Africa. P. perna dominates the low and M. galloprovincialis the high mussel zones, with co-existence in the mid mussel zone. This study tested the hypothesis of settlement selectivity for conspecifics in these two mussel species, to understand whether the final adult distribution of mussels on the shores is determined by active behavioural and chemical mechanisms. Preferential selection by larvae for conspecifics was tested in the field during the peak settlement period in 2004 in natural mussel beds across zones and through manipulative experiments in the mid-zone where the species co-exist. On natural beds, settlement was determined by counts of settlers attached over 48 h onto artificial collectors. Collectors were placed on beds of P. perna and M. galloprovincialis present at both high- and low-adult densities, as well as in mixed beds. On such natural beds, settlers of both species consistently favored low-zone P. perna beds. Settlement patterns over 24 h onto experimentally created mussel patches consisting of P. perna, M. galloprovincialis or the two species combined beds, set in the mixed zone, did not conform with the results of the natural beds study: settlers of both species settled with no discrimination among different patches. The results indicate that mussels, which are sedentary, lack attraction to conspecifics at settlement. This highlights the importance of tidal height in setting settlement rates, and of post-settlement events in shaping populations of these broadcast spawners.