Vertical distribution of coralline algae in the rocky intertidal of northern Chile

Studies on crustose corallines present in the intertidal region at three localities in northern Chile (30°S), show that these algae are well represented in exposed and protected sites, reaching up to 90% cover. Species composition differs between sites with the common occurrence of species or morphological variants of Spongites and a single taxon attributed to Phymatolithon at the most exposed sites, and species of Lithophyllum and Titanoderma at more protected localities. The two Lithophyllum taxa recorded are distinguished by the presence/absence of protuberances, cell size and degree of calcification, while Titanoderma taxa are segregated by the thickness of the thallus, hypothallic and perithallic cell size and shape. Spongites taxa are distinguished on the basis of external morphology and anatomical features such as cell size, degree of calcification and percentage of fusions between cells. The variability of these features within each species is still unknown thus, the taxa remain without specific epithet until further studies. Examination of specific types recorded for nearby regions are also required in order to clarify the taxonomy of the group in these coasts.     

The distribution of benthic marine algae

Hitherto only gametangial and carposporangial phases of Thuretellopsis peggiana Kylin have been reported. A study of this rare member of the Dumontiaceae (Cryptonemiales) in culture has disclosed the existence of an encrusting tetrasporangial phase, previously unknown, whilst the life history has been shown to be of the ‘Bonnemaisonia’ type.     

The horizontal distribution of plankton in a deep, oligotrophic lake—Loch Ness, Scotland

1. The horizontal distribution of plankton in Loch Ness, a deep, oligotrophic lake with a simple trench morphometry, was studied on three occasions in 1993. Samples were collected from ten stations spaced along the length of the loch and the abundance of algae, bacteria, protozoa, rotifers and crustacean zooplankton was determined. 2. Horizontal variability was found to be greatest for the metazoan zooplankton and for the algae, especially two cryptomonad flagellates. Bacteria and heterotrophic protozoa showed relatively little horizontal variability. The degree of horizontal variability was not sufficient seriously to affect studies of the seasonality of plankton abundance conducted from a single sampling station. 3. Gradients of plankton distribution along the length of the loch were dependent on the recent wind history. The direction of the gradient could readily reverse with a shift in wind direction. These results indicate that the horizontal distribution of plankton in Loch Ness is more dependent on wind-induced water circulation patterns than on differential growth of plankton in water masses of differing chemistry.     

Refuge function of marine algae complicates selection in an intertidal snail

Species with restricted gene flow often show trait-shifts from one type of environment to another. In those rock-dwelling marine gastropods that lack larval dispersal, size generally decreases in wave-exposed habitats reducing risk of dislodgement, while increases in less exposed habitats to resist crab-crushing. In Littorina fabalis, however, snails of moderately exposed shores are generally much larger (11–14 mm) than snails of sheltered shores (5–8 mm). Observations from the White Sea (where crabs are not present) indicate that in the absence of crabs snails are small (6–7 mm) in both habitats. We assumed that the optimal size for L. fabalis in the absence of crabs is less than 8 mm, and thus that increased size in moderately exposed habitats in areas with crabs might be a response to crab predation. In a crab-rich area (Sweden) we showed that crab predation is an important mortality factor for this snail species in both sheltered and moderately exposed habitats. In sheltered habitats, snails were relatively more protected from crab-predation when dwelling on their habitual substrate, fucoid algae, than if experimentally tethered to rocks below the algae. This showed that algae function as snail refuges. Snail dislodgement increased, however, with wave exposure but tethering snails in moderately exposed habitats showed that large snails survived equally well on rocks under the algae as in the canopy of the algae. Thus in sheltered habitats a small snail size is favored, probably due to life-history reasons, while increased risk of being dislodged from the algae refuges promotes a large size in moderately exposed habitats. This study shows an example of selection of a trait depends on complex interactions of different factors (life-history optimization, crab predation, wave induced dislodgement and algal refuges).     

Biodegradation of photosynthetically produced extracellular organic carbon from intertidal benthic algae

14C-labeled extracellular products of a natural microphytobenthic community and two species of benthic diatoms (Nitzschia hybridaeformis and Amphora coffeaeformis) were fractionated into extracellular dissolved organic carbon (14C-EDOC), organic carbon extracted with EDTA (14C-EDTA-extractable OC) and extracellular polymeric substances (14C-EPS). The biodegradation of this labeled extracellular organic carbon by bacteria in sediments was examined to determine the processes of enzymatic degradation of photosynthetically-produced extracellular organic carbon from microphytobenthos in an intertidal flat ecosystem. In addition, primary production as well as extracellular enzyme activities (beta- and alpha-glucosidase) were measured to evaluate the possible relationship between organic carbon production and microbiological degradation at the Isshiki intertidal flat in Mikawa Bay, Japan. With all three 14C-fractions extracted from a natural microphytobenthic assemblage and two species of benthic diatoms, more than 50% of the added substrates were mineralized within 24 h by the bacterial community in sediments. At that time, the percentage of high-molecular-weight compounds (>5 K MW) to total MW compounds of 14C-EDTA-extractable OC and 14C-EPS fractions decreased within 24 h from 50.9 to 6.6% and 74.5 to 11.1%, respectively. In situ, beta- and alpha-glucosidase activity in sediment was higher than in the seawater column (at a depth of 1 m), though the photosynthetic production of microphytobenthos was equal to that of phytoplankton. Based on our previous studies that microphytobenthos produced much more extracellular products than phytoplankton, it is assumed from these results that carbon flowing into the microbial loop through the mediation of enzymatic degradation of extracellular products in a benthic system exceeds that in the overlying water column.     

Effects of consumers and enrichment on abundance and diversity of benthic algae in a rocky intertidal community

Human alteration of nutrient cycling and the densities of important consumers have intensified the importance of understanding how nutrients and consumers influence the structure of ecological systems. We examined the effects of both grazing and nutrient enrichment on algal abundance and diversity in a high-intertidal limpet-macroalgal community on the South Island of New Zealand, a relatively nutrient-poor environment. We used a fully factorial design with three levels each of grazing (manipulations of limpet and snail densities) and nutrients (nutrient-diffusers attached to the rock). Top-down control by grazers appears to be the driving organizing mechanism for algal communities in this system, with strong negative effects of grazing on algal diversity and abundance across all levels of nutrient enrichment. However, in contrast to the conclusions drawn from the analysis of the whole algal community, there was an interactive effect of grazing and enrichment on foliose algae, an important component of the algal system. When herbivory was reduced to very low levels, enrichment generated increases in the abundance and biomass of foliose algae. As expected, top-down control was the primary determinant of algal community structure in this system, controlling abundance and diversity of macrophytes on the upper shore. Contrary to expectations, however, increased nutrients had no community-wide effects, although foliose algal abundance increases were greatest with high nutrients and reduced grazing. It seems likely that most of the corticated algal species have limited capacity to respond to nutrient pulses in this nutrient-poor environment.     

Complex phylogenetic distribution of a non-canonical genetic code in green algae

Background  

A non-canonical nuclear genetic code, in which TAG and TAA have been reassigned from stop codons to glutamine, has evolved independently in several eukaryotic lineages, including the ulvophycean green algal orders Dasycladales and Cladophorales. To study the phylogenetic distribution of the standard and non-canonical genetic codes, we generated sequence data of a representative set of ulvophycean green algae and used a robust green algal phylogeny to evaluate different evolutionary scenarios that may account for the origin of the non-canonical code.     

Why overgrowth of intertidal encrusting algae does not always cause competitive exclusion

Encrusting algae are well-known to be able, for long periods, to withstand shading and overgrowth by other organisms. How this is achieved remains a mystery. It had been proposed that connections with unshaded (non-overgrown) parts of the thallus may allow transfer of nutrients to the shaded part. From this model, I proposed and tested the hypothesis that shaded patches of the intertidal red alga, Hildenbrandia rubra, would survive overgrowth longer, or better, when connected to unshaded thallus than when experimentally separated from surrounding alga. Experimental treatments were shading (black or transparent 80 mm perspex discs or no cover) and scraping (scraped around the disc to remove contacts, a control for effects of scraping, no treatment). The 9 orthogonal combinations of cover and scraping were applied to 3 independent, random replicates (i.e. 27 plots) in each of four randomly chosen sites.

In all 4 sites, over 13 months, shaded H. rubra survived in greater abundance (as % cover) where in contact with surrounding thallus. In one site, there was no effect of shading unless the thallus was isolated. In two sites, shading reduced cover, but was more deleterious where the thallus was isolated. In the fourth site, there were artefacts due to a perspex cover, but still less cover of alga where it was isolated.

This encrusting alga can withstand a long period of complete shading, provided there is connection to unshaded thallus. Interpreting or predicting overgrowth interactions in terms of competitive outcomes is therefore dependent on consideration of whether the overgrown species is actually being affected. It also depends on the duration of overgrowth and, as shown here, the extent to which connectivity with unshaded thallus is effective at preventing or reducing any consequences. Observations and experiments that do not ascertain these are difficult to interpret.     

The Loch Eil project: The bacterial flora and heterotrophic nitrogen fixation in sediments of Loch Eil

The organically enriched sediments of Loch Eil reduced acetylene (fixed nitrogen) at a higher rate than sediments in the Firth of Lome and other near shore marine locations. Sulphate-reducing bacteria (SRB) were implicated in nitrogen fixation although fixation rates did not correlate with the SRB numbers found in these sediments. The data suggest that a negative relationship may exist between nitrogen fixation and the sulphide content of sediments.     

The vertical distribution and seasonal abundance of intertidal microalgae on a rocky shore in New South Wales

The abundance of intertidal microalgal food resources was estimated on shores at Cape Banks (Botany Bay, New South Wales) by indirect assays of the concentration of chlorophyll on and in the surface of sandstone rocks. Examination of the relationships between chlorophyll concentration and weight and area of rock samples allowed valid assays to be made despite uncontrollable variations from replicate to replicate in the amount of rock sampled. Microalgal cells were also sampled directly by brushing them from the surface of the rock. The relationship between amount of chlorophyll in samples, and the number of microalgal cells in immediately adjacent brushed areas indicated a relatively constant amount of chlorophyll per cell at different heights and on different parts of the shore throughout different seasons of the year. These preliminaries determined that assays of chlorophyll provided reliable, repeatable estimates of the number of microalgal cells present.Replicated sampling at five heights on a transect spanning the mid-shore regions of a sheltered shore dominated by grazing gastropods, at approximately monthly intervals from 1977 to 1979, revealed a vertical gradient of increasing abundance of microalgae towards the bottom of the shore, except during summer. This trend was not correlated with decreasing abundance of microalgal grazers. During summer, the abundance of microalgae declined abruptly at all levels. The decrease was greatest at the lower levels, resulting in little or no difference among the abundances of microalgae at the five heights during summer. The seasonal changes were again unrelated to any major changes in densities of grazers. These trends confirm the general patterns of distribution of intertidal microalgae in previous studies in other parts of the world. The present data are discussed with respect to problems of interpretation of microalgal food resources for intertidal grazers.     

The physico-Chemical limnology of Loch Lomond

Loch Lomond, the largest freshwater lake in Britain, is physically divided into a number of distinct basins by geological structures. The northern part of the loch is long, narrow and deep whilst the southern area is broad and shallow with many islands scattered throughout it.The water chemistry of the loch is dictated by the geology of catchment and the quality of the rivers flowing into it. The two major rivers, the Falloch and the Endrick Water, are both of good quality with low nutrient content. Consequently, the loch is regarded as oligotrophic, though the southern area verges towards being mesotrophic.     

The diatom assemblage of a marl core from Linton Loch

Summary

Diatom data from Linton Loch show five diatom assemblage zones, together with stratigraphic evidence indicating some aspects of the development of the lake basin during the Flandrian. Results show an early Flandrian dominance of planktonic diatom species in the lake waters with the later development of epiphytic species as the hydrosere encroached. Following deforestation in the catchment, water levels rose in the basin when benthic diatoms became dominant.     

Scale-dependent patterns of macrofaunal distribution in soft-sediment intertidal habitats along a large-scale estuarine gradient

We investigated the pattern of distribution of intertidal soft-bottom fauna in streams and lagoons of the Uruguayan coast at three spatial scales. The Río de la Plata and the Atlantic Ocean produce on this coast a large-scale gradient in salinity, defining a freshwater (west), an estuarine (central) and a marine (east) region. Within each region, there are several streams and coastal lagoons (sites) that define a second scale of variability. A third scale is given by intertidal gradients within each site. Species richness and total abundance was low in the freshwater west region and high in the central and east regions. The community in the west region was characterized by the clam Curbicula fluminea; in the other regions, it was dominated mainly by the polychaete Heteromastus similis. The polychaete Nephtys fluviatilis was more abundant in the east region, while another polychaete, Laeonereis acuta, characterized the central region. Sediment fractions did not vary significantly at this scale. At the scale of the sites, species richness and total macrofaunal abundance were higher in coastal lagoons than in streams. Coarse sands were more common in coastal lagoons, while medium and fine sand characterized the sediment in streams. Within each site, species richness and total abundance increased towards the lower intertidal level; the macrofauna of the upper levels were a subsample of the fauna occurring at the lower levels. There was also a significantly lower proportion of fine sand at the upper level. At regional scales, the observed patterns may be indirectly or directly related to the gradient in salinity, through differential physiological tolerance to osmotic stress. At the scale of the sites, variability may be explained mainly by geomorphological and sedimentological differences between lagoons and streams. Variation among levels may be related to gradients in desiccation, colonization and predation.     

The distribution and abundance of algae in saline lakes of Saskatchewan,Canada

Collections of algae, mainly planktonic, were made from 41 saline lakes in southern Saskatchewan ranging in salinity from 3.2 to 428 g l^-1. Algae in 7 phyla, 8 classes, 42 families, 91 genera and 212 species and varieties were identified. Fourteen species were restricted to hypersaline (50 g l^-1) waters and eleven of these were diatoms. In general, species diversity was inversely related to lake salinity. Algae that were important community constituents over a broad spectrum of salinities were the green algae Ctenocladus circinnatus, Dunaliella salina and Rhizoclonium hieroglyphicum, the blue-green Lyngbya Birgei, Microcystis aeruginosa, Oscillatoria tenuis, O. Utermoehli and Nodularia spumigena and the diatoms Melosira granulata, Stephanodiscus niagarae and Chaetoceros Elmorei. In general green algae were dominant when lake salinity exceeded 100 g l^-1 although diatoms played important roles in most of these highly saline lakes except for Patience Lake.     

Choline and inositol distribution in algae and fungi

Inositol and choline were present in varying amounts among the species of Rhodophyta, Phaeophyta, Chlorophyta, and Euglenophyta examined. However, in the two members of the order Fucales (division Phaeophyta) examined, no detectable amounts of choline were found. In contrast, the species of Cyanophyta examined contained no detectable amounts of either choline or inositol. All species of the fungal classes Phycomyceteae, Ascomyceteae, and Basidiomyceteae collected contained both inositol and choline in varying amounts. The red, brown, and blue-green algae usually contained much less inositol and choline than do plant and animals sources, but the fungi and the algae Chlorella and Euglena contained amounts comparable to those present in plant sources.     

Scales of spatial patterns of distribution of intertidal invertebrates

Few comparative studies of spatial patterns at different scales have examined several species in the same habitat or the same species over a range of habitats. Therefore, variability in patterns among species or among habitats has seldom been documented. This study quantifies spatial patterns of a suite of intertidal snails and a species of barnacle using a range of statistical techniques. Variability in densities was quantified from the scale of adjacent quadrats (over a distance of centimeters) to tens of kilometers. Significant differences in abundances occurred primarily at two spatial scales. Small-scale differences were found at the scales of centimeters or 1–2 m and, for many species on many shores, these accounted for most of the variability in abundances from place to place. These are likely to be determined by behavioural responses to small-scale patches of microhabitat. Large-scale differences in abundance were also found in most species at the scale of hundreds of meters alongshore. These are likely to be due to variation in recruitment (and/or mortality) because of limited dispersal by adults of these species. There was little or no additional variation among shores, separated by tens of kilometers, than was shown among patches of shore separated by hundreds of meters. Identification of the scale(s) at which significant differences in abundance are found focus attention on the processes (and the scales at which these processes operate) that influence patterns of distribution and abundance. Some of the advantages and disadvantages of various procedures are discussed.