Temporal Changes In Species Composition Research Articles

Diatom (Bacillariophyceae) flora of early Holocene freshwater sediments from Skalafjord, Faeroe Islands

Abstract. Relative abundance data of diatom (Bacillariophyceae) species were generated for sediment core SKPC-01B from the Skalafjord, Faeroe Islands. The record shows distinct temporal changes in species composition. In the lowermost 65 cm of the 230 cm long core a species-rich freshwater diatom assemblage was found. Most of the taxa observed in this section are typical of oligotrophic to dystrophic lakes in northern Europe (Scandinavia, Iceland and Spitsbergen). Above this interval the diatom flora is dominated by marine taxa. The change from a freshwater to a marine flora is inferred to be caused by rising sea-level that took place about 7700–6400 years BP. Drastic changes in the diatom species composition within the transitional core section show that environmental change in the Skalafjord took place in several pulses. The first stage included strong inflow (possibly catastrophic) of marine waters. As a possible trigger of this phenomenon the tsunami released by the Storegga Slide is proposed. Before the final flooding by marine waters, freshwater conditions were re-established within the Skalafjord. These results have important implications for the interpretation of the palaeogeographical development of the Eysturoy area. Hence, it is suggested that the Storegga Slide led to inflow of marine waters at a distinctly lower water level in the area of the Skalafjord than proposed in recent publications and that the inundation of the threshold in the fjord happened after the tsunami.

Use of Faunal Indicators for Assessing the Impact of a Port Enlargement near Bilbao (Spain)

In order to assess the effects of the execution of the ‘Port of Bilbao Enlargement Project’, epifauna living on hard substrata and environmental parameters were quantitatively investigated from 1994 to 1996. A programme of repeated non-destructive sampling at 8 stations was carried out during the construction period of a breakwater and the filling operations on the shoreline. A correlation analysis was used as a method to extract potential indicator species of particular environmental conditions measured in the field. We postulate that the remaining species (about 80% of the total species data set), insensitive to any of the investigated environmental factors, were unnecessary for the purposes of assessing the environmental impact caused by the port building works. Classification and ordination techniques were then conducted at two contrasting levels by using the full species data set and the selected faunal indicator data subset. All plots showed separation of sampling sites in 3 major groups, which were easily related to the perturbations caused by a siltation gradient from the estuary mouth. This suggests that the amount of effort required in the enumeration of all the organisms sampled may be dramatically reduced by identifying only faunal indicators of environmental discontinuities in the field. So far, the engineering works developed on the western side of the bay have not caused dramatic temporal changes in species composition, or at least they have not had an effect that was larger than the variations detected among the study sites due to siltation from the estuary mouth.

Longitudinal and temporal patterns of benthic coarse particulate organic matter in the Ag�era stream (northern Spain)

Benthic coarse particulate organic matter (CPOM) was studied between November 92 and December 93 at four sites along the longitudinal gradient of the Aguera stream system (Northern Spain). CPOM was sorted in four main categories: leaves (several species), fruits and seeds, twigs and debris. Headwater site showed higher densities of total CPOM, leaves and twigs than downstream reaches, but no regular longitudinal pattern of change was noticed. The ranges of mean CPOM standing stock at the sampling sites were 20.5–74.1 g AFDW m−2 (site B), 9.9–47.7 g AFDW m−2 (site 5), 4.3–21.4g AFDW m−2 (site 7) and 9.8–37.9 g AFDW m−2 (site 9). The particulate matter at downstream sites was in a more advanced stage of breakdown probably as a result of processing and transport from upstream reaches. Leaves species composition of benthic CPOM clearly reflected the type of riparian vegetation at each site. The timing of inputs and the hydrologic regime appeared to act together influencing temporal dynamics of benthic CPOM. A gradual temporal change in species composition of benthic leaf litter was observed under natural mature deciduous forest: first alder, later chestnut and finally oak.

Postfire Regeneration of a Mediterranean Heathland in Southern Spain

Fire is a recurrent disturbance in the vegetation of Mediterranean climate regions. Most of the woody species (16 out of 19) in a Mediterranean heathland community, in the Strait of Gibraltar region of southern Spain, sprouted from subterranean vegetative organs after a wild-fire. Dominant sprouters were the prostrated oak Quercus lusitanica, three gorses, Genista tridens, G. tridentata and Stauracanthus boivinii, and a heath, Erica scoparia. About 100 seedlings m-2 of 14 woody species were censused in the first three years after fire. The highest density of seedlings was recorded for heather (Calluna vulgaris), a rockrose (Cistus populifolius subsp. major) and a gorse (Genista triacanthos). Woody vegetation covered up to 85% of the soil surface in the third year after fire. At this stager the community was co-dominated by the sprouters Quercus lusitanica (21%), Genista tridentata (21%) and Stauracanthus boivinii (20%), and the seeder Cistus populifolius subsp. major (20%). A total of 52 herbaceous species, many of them (35) perennials, was recorded, showing a temporal change in species composition. The role of fire influencing community diversity and the consequences for the conservation of heathlands in the Strait of Gibraltar region, are discussed.

Trophic structure and diversity in some litter inhabiting microarthropods of monoculture and natural forest ecosystems

Temporal changes in species composition of litter insect communities of Shevroys, as well as their trophic diversity involving mycophagous and predatory species are examined with reference to natural forest as well as monoculture systems.

The spatial and temporal distribution of an epiphytic algal community in a shallow prairie‐parkland lake – Alberta, Canada

In Hastings Lake (longitudes 113°15′ and 53°50′N), a shallow eutrophic lake, the spatial and temporal changes in species composition. diversitv. standing crops, and primary productivity of the epiphytic algae attached to Phragmnes australis and Scirpus validus were investigated in relation to the physico‐chemical environment. Of the dominant species, cyanophycean algae (Lyngbya diguetii and Calothrix sp.) developed best in the 25 cm region below the water surface, while the chlorophycean alga, Stigeoclonium nanum and the diatoms (Cocconeis placentula, Gomphonema parvulum and Rhoicosphenia curvata) did so in the 50 cm and 75 cm regions, respectively. Certain dominant species persisted throughout, interrupted by “shock periods” which created spring, summer, and autumn peaks. Species diversity indices increased with depth, and generally decreased spring through winter. Standing crop maxima occurred within the top 25 cm of the host stems, and showed spring and larger autumn peaks before declining to low. yet significant winter levels. Productivity, too, was greatest in the top 25 cm region, and again peaked in the spring and autumn. Cross incubation studies elucidated vertical and seasonal relationships among productivity, photosynthetic index, and efficiency, and productivity efficiency. An interplay of “sun and shade” adapted populations within the community was found. The epiphytic algae displayed but a muted seasonal response to physico‐chemical fluctuations: however, there was an association with overall nutrient changes as determined by meq HCO3−I−1.

Distribution of shallow-water epibenthic macrofauna in Moreton Bay, Queensland, Australia

The distribution of epibenthic penaeid prawn postlarvae has previously been shown to relate to the degree of marine influences in the flora, sediment and water conditions in littoral and infralittoral habitats in Moreton Bay. The postlarvae are part of a complex faunal assemblage of approximately 400 mobile epibenthic species. Samples of the assemblage from stations situated throughout Moreton Bay were analysed by multivariable methods, to detect whether the environmental influences volated to the distribution of penaeid prawns, were related to the fauna as a whole. This was found to be so. The fauna occurred in two groups in areas of either less marine or more marine influences. Animals in the first group were less diverse, with distributions unrelated to depth or presence of seagrasses, but related to the level of marine influences between geographical areas sampled. Animals in the second group were closely related to depth and presence of seagrasses, but no overall differences were attributable to marine influeces apart from those attributable to depth. Temporal changes in species composition were smaller than spatial changes, and changes in relative abundance were, in both groups, related to differences between (i) summer and winter, and (ii) spring and the rest of the year.

An assessment of principal component analysis for description of phytoplankton periodicity in Lake Wingra

Principal component analysis ordinates temporal changes in species composition in samples collected regularly from March 1970 throughout August 1973. The results indicate two compositionally stable periods (winter and summer) separated by spring and autumn transition periods where composition changes rapidly. Each transition appears distinct; spring compositional changes do not simply mirror autumn changes. Some seasonal information is lost when samples for both years are simultaneously considered. Nine physico-chemical factors are examined as potential correlates of compositional change, individually, and through an environmental ordination.

SEASONAL CHANGES IN THE COMMUNITY STRUCTURE OF THE MACROBENTHOS INHABITING THE INTERTIDAL SAND AND MUD FLATS OF BARNSTABLE HARBOR, MASSACHUSETTS

1. A quantitative sampling survey of the benthic macrofauna inhabiting the intertidal sand and mud flats of Barnstable Harbor, Massachusetts, was conducted to describe general community structure and examine temporal changes in species composition.2. Classification analysis delimited coarse and fine sand, mud, muddy-sand, and gravel-mud benthic species associations. The 32 species used in the inverse classification analysis were partitioned into 10 species groups, reflecting spatial distributional patterns. Many of the species were both dominant and ubiquitous, masking discrete species groupings.3. The majority of macrobenthos at Barnstable Harbor were deposit-feeders which comprised more than 90% of all organisms sampled. The deposit-feeders normally dominate mud and muddy-sand sediments. Suspension-feeders were most abundant in fine sands. The relationship of sedimentary parameters affecting the distribution of both trophic groups proposed by Sanders is generally supported.4. While no significant changes were evident in species diversity, evenness, or species number throughout a 19 month sampling period, classification analysis delimited seasonal clustering of both samples and species groupings. These patterns were repeatable over a two year period suggesting that dynamic "equilibrium," not successional change was occurring.5. Seasonal clustering patterns of some species were related to the appearance of different zoogeographic faunal province elements. Typical warm-temperature Virginian components and cold-temperate Nova Scotian species were commonly found in late summer and winter, respectively.