Short-Term Dynamics of Tidepool Fish Community: Diel and Seasonal Variation

Short-term temporal dynamics in a tidepool fish community were quantitatively examined through a series of direct observation at consecutive low tides in a temperate-subtropical intertidal of southwestern Japan. The visual observation was sufficiently effective compared with the capture by anaesthetics and allowed a continual, undisturbed monitoring. Species composition markedly varied between consecutive day versus night in spring-autumn, but not in winter. In contrast, species composition on consecutive days and on consecutive nights was relatively stable all through the year. The pattern of diel change in abundance varied among species and seasons. C. gulosus, Istiblennius sp. and Girella spp. showed the tendency of night-time occurrence, while B. fuscus individuals tended to occur by day. These trends of day–night differences were mainly observed in spring and summer and rarely in winter. Size differences between day and night were detected in B. fuscus, C. gulosus, Istiblennius sp. and Girella spp. This tidepool fish community demonstrated variation in abundance and body size on short time scales, which may be attributable to behavioural differences among species.     

Tidal activity pattern and feeding behaviour of the ophiuroid Ophiocoma scolopendrina on a Kenyan reef flat

Ophiocoma scolopendrina exhibits a distinctive pattern of feeding activity on intertidal reef platforms off Kenya. With the first wave of the flooding tide, dense aggregations of these ophiuroids (up to 320 m⁻²) engage in a 1–2 min burst of surface-film feeding, vigorously sweeping the air-water interface and associated sea foam with the ventral surface of 2–4 arms. Suspension feeding (with arms extended in the water column) is the primary feeding mode throughout the rest of the tidal cycle (involving 25–65% of the population at a time), while bottom feeding (with arms extended along the substratum) is infrequent (<10%). Field experiments showed that surface-film feeding is regulated by water depth and can be triggered by suspended particles. This feeding mode appears to be an adaptation to the intertidal habitat, enabling the ophiuroids to exploit a nutrient-rich surface film during a temporal refuge (low tide) from fish predation. Dense populations of O. scolopendrina may represent an important trophic link between producers of particulate organic material and higher-level consumers in coral reef environments.Tara Oak and Robert E. Scheibling contributed equally to this paper. The order of authorship is alphabetical     

Microbial deposits in upper Miocene carbonates, Mallorca, Spain

The Santanyí Limestone, a 30-35-m thick upper Miocene limestone succession cropping out in Mallorca, contains abundant microbialite deposits, the shape, microstructure and texture of which was controlled by environmental factors: depth, energy and salinity. Three main types of microbialites are distinguished: (1) domed (DNOS) and stratiform, mostly undulate (UNOS) non-oolitic stromatolites, (2) undulate oolitic laminites (UOL) and (3) domed-oolitic thrombolites (DOTs). Based on lithofacies associations and occurrence of microbialite types, the Santanyí Limestone succession is subdivided into five stratigraphic units (I to V) separated by sharp surfaces. Within units II, III and V, the vertical evolution of microbialites was induced by changes in accommodation space/depth: (1) intertidal/very-shallow subtidal conditions at the base were induced by flooding over a wide area, (2) continued sea-level rise caused submergence to subtidal conditions, and (3) a significant bathymetric decrease created the sharp surface bounding these units.In units II and III, NOS accumulated in variable energy and depth conditions, as buildups with thick, somewhat discontinuous and mostly non-isopachous lamination, surrounded by oolitic grainstones with wave and current structures and oolitic intraclasts. In contrast, thin and generally regular and smooth lamination of NOS in unit V suggests, along with the absence of oolite grainstones and macrobiota, calm and restricted, maybe more saline, conditions.UOL, consisting of oolitic layers separated by thin micritic laminae, developed adjacent to NOS in units II and III and to DOT at the lower part of unit III, in shallow-water and low-energy conditions. Both ooids and micrite laminae have evidence for biogenesis. Micritized ooids containing microbial remains are common. Micritic laminae in UOL and the dark micritic laminae in NOS are thought to represent bacterially enhanced calcite precipitation and lithification during periods of low sedimentation.Oolitic thrombolites containing macrobiota are only present in unit III. They represent deeper and open-marine conditions affected by high-energy events, in which microbially mediated precipitation favoured microbialite accretion and lithification.     

The effect of wrack composition and diversity on macrofaunal assemblages in intertidal marine sediments

Wrack (dead, washed-up seaweed and seagrass) buried in soft substrata may increase the organic content and alter the physical structure of sediments. These effects may influence the composition and structure of macrofaunal assemblages in the sediment. Such influences can be expected to vary according to the type and amount of wrack as well as the presence of invasive seaweeds in the wrack. In this study, we deliberately buried different amounts of the invasive species Sargassum muticum in isolation or mixed to the native species Ulva sp. and Fucus vesiculosus, in two intertidal sandflats to test some hypotheses about the response of macrofaunal assemblages. We tested whether (1) diversity of detritus (i.e. different mixtures), and (2) the amount of detritus of S. muticum influenced the composition and the relative abundance of macrofaunal assemblages. We also assessed whether the sediment organic carbon and the biomass of benthic microalgae varied depending on the diversity of detritus and the amount of detritus of S. muticum. Finally, we tested if these effects of wrack were consistent across sites. Results indicated that buried wrack affected the composition and structure of macrofaunal assemblages in short-term (i.e. 4 weeks), but there were no differences depending on detritus diversity or the amount of S. muticum. In addition, sediment organic matter and microalgal biomass were not affected by the addition of wrack. They instead varied greatly among small spatial scales (i.e. plots). Wrack composition or abundance of the invasive species S. muticum played thus a small role in shaping the structure of macrofaunal assemblages or the biomass of benthic microalgae in these intertidal sediments, probably because these sediments are frequently affected by various inputs of organic matter and benthic assemblages are already adapted to organically enriched sediments.     

Upstream Petroleum Degradation of Mangroves and Intertidal Shores: The Niger Delta Experience

This article was inspired by a field reconnaissance survey of outcrops along the Nembe‐Brass axis of the petroliferous Niger Delta. It reviews various tradeoffs of the impact of upstream petroleum (seismic and production) operations on the mangrove ecosystems in that region, the largest in Sub‐Saharan Africa. Mangroves and intertidal shores are considered critical to the economic well‐being of this region owing to the people's dual occupation in fishing and farming. The mangrove ecosystem provides a nutrient medium, which serves as a nursery and spawning ground for many fish species and other biota. Oil and gas activities might destroy these spawn areas, causing reduction in resource output and community pressure. Devegetation of the mangrove forest as a result of seismic delineation leaves the fragile soil exposed, unprotected, and susceptible to erosion. Again, loss of vegetation might discourage the natural role of plants in air purification (CO₂ utilization and O₂ production). The release of nutrients (organic N₂, NH₃, and NO$\rm{{_{3}^{-}}}$ ) and polyaromatic hydrocarbons (PAHs) to the environment, with the attendant increase in microbial load, increases biochemical O₂ demand (BOD) and depletes dissolved O₂ (DO) in H₂O to a level that is beyond the tolerance limit of organisms. This anoxic situation leads to asphyxiation and subsequent fish kill in affected areas. In order of increasing vulnerability, the mangroves and intertidal shores of the Niger Delta fall under categories 8 to 10 on the environmental sensitivity index (ESI) scale, which predisposes the areas to serious long‐term effects and clean‐up complexity. Thus, there is need to monitor mangrove systems and shoreline changes in the areas of considerable seismic and production activities, especially in the coastal Niger Delta, where pipeline corrosion due to salt intrusion into the swampy environment and ‘unsighted fingers’ of sabotage have increased the prevalence of oil spills.     

Influence of puffer predation on vertical distribution of mangrove littorinids in the Gulf of Nicoya, Costa Rica

The eastern Pacific puffer fish Sphoeroides rosenblatti (family Tetraodontidae) preys on the mangrove periwinkles Littorariafasciata and L. varia up to 13 cm above the water surface. Puffers capture snails by jumping partially out of the water and removing them by mouth from Rhizophora spp. prop roots. Field predation trials suggested puffer predation is intense, averaging 40.6% h⁻¹ on L. fasciata tethered at the water surface. L.fasciata <∼8 mm in shell length and L. varia <∼12 mm remained near or below the water surface and were easily crushed by puffers; gut content analyses showed that these snails were commonly eaten by puffers. L.fasciata >∼8 mm and L. varia∼12–16 mm were also crushed by puffers, but were generally located above their reach; these snails were much less abundant in puffer guts. L.varia >∼16 mm were abundant and some were submerged at high tide; however, none were found in puffer guts presumably because puffers encounter difficulty crushing these snails. S.rosenblatti is an important predator of L. fasciata and L. varia and appears to affect their vertical distributions. Received: 21 April 1998 / Accepted: 10 August 1998     

The decision to feed by a scavenger in relation to the risks of predation and starvation

Recent theoretical models have considered how nutritional status and predation risk affect the decision by an individual to forage. We consider the feeding behaviour of a scavenger under risk of predation. The intertidal gastropod Nassarius dorsatus Röding was used to test the following hypotheses: (1) a damaged conspecific should be a less preferred meal than a damaged predator or another species; (2) a scavenger should be able to discriminate between a damaged conspecific in the presence and one in the absence of its predator, preferring the latter; and (3) the decision by a scavenger to feed should reflect a trade-off between nutritional status and the above preferences. Results from the laboratory and field were consistent with predictions. Two hypotheses are suggested from the work: scavengers may generally be less willing to feed on carcases of conspecifics than on those of other species, and intertidal scavengers may commonly face a relative or absolute shortage of food.     

A Preliminary Study of Microalgae in the Intertidal Zones of the Deception Island,Antarctica

his paper first presents a report on the composition and distribution of microalgae in the intertidal zones of the Deception Island, Antarctica. These microalgae samples were collected from six mud-sand flats stations on 21 January 1987. 179 taxa of microalgae belonging to Bacillariophyta (125 species, 25 varieties and 2 forma, 34 genera), Cyanophyta (18 species and 2 varieties, 6 genera), Pyrrophyta (6 species, 4 genera) and Chrysophyta (1 species 1 genus) were observed. The six dominant microalgae in each habitat are Fragilaria bongrainii, F. oceanica, F. striatula, F. islandica, Navicula antarctica and Synedra kerguelensis var. antarctica. Rhabdonema arcuatum, Cocconeis antiqua and Licmophora gracilis are abundant in station 4, 5 and 6. Oscillatoria spp., Lyngbya antarctica, Phormidium antarcticum and Nodularia spp. are also abundant in station 1, 2 and 3. The values of diversity indice for microalgae varied from 2. 85 to 6.86. The values of similarity indice in microalgae composition between biotopes ranged from 32 to 79 for pairs of stations. Microalgal species composition and quantitative distribution are depended on per cent contents of mud-sand and claysilt at different stations.     

Seasonal Variations in Population Dynamics of Key Intertidal Molluscs at Two Contrasting Locations

The paper deals with the spatial and the temporal variability of the population dynamics of five key molluscan species at two rocky intertidal shores on the southern Saurashtra coastline of India. The intertidal belts of the two selected stations, Veraval and Diu, are about 100 km apart and differ in their coast characteristics and level of human interference. The slope and the substrate types of the two stations are not uniform and the exposure of intertidal belt of these predominantly rocky shores during low tides is also not significantly long. The study revealed that a general, species specific pattern of spatial and temporal variations existed in the population abundance and density of the species studied. There was considerable spatial variability in some species examined but most species showed no clear seasonal trends for the population abundance. The Veraval coast, in spite of being affected by heavy human interference, is still a favourable place for Chiton, Turbo cornatus and Turbo intercoastalis than Diu, though the latter is relatively less affected by anthropogenic influences. It appears that the subtratum type, short exposure duration and moderate wave action of the Arabian Sea are most active controlling factors for higher distribution of these species at Veraval.