Daphne: a new multimetric benthic index for the quality assessment of marine coastal environment in the Northern Adriatic Sea

A new benthic index, named Daphne, is proposed for the Northern Adriatic coastal area, near the Po river delta. It is based on six characteristics of the community that do not require in-depth taxonomic expertise: number of mollusc species, % of bivalves, % of polychaetes, abundance of the opportunistic species Corbula gibba, % of amphipods and number of 'typical mollusc species' that are individuated by multivariate analysis. The application of the index in selected stations along a gradient of decreasing disturbance shows that it is simple to use in regular monitoring campaigns and that the results are consistent with environmental quality data in the special conditions of this area subjected to considerable river runoff. The index can be used in addition and as a complement to more widespread indices (such as M-AMBI); a comparison of the two indices performance is discussed.     

Bioaccumulation of platinum group metals on some fish species ( Oreochromis niloticus,Penaeus laspisulcates,Scylla serrate,Galaxias brevipinnis and Mollusc ) in the Pra estuary of Ghana

Catalytic converters have been designed to solve the problem of pollution from automobiles. However, recent studies have shown that the platinum group metals (PGMs) that are used in the design are being deposited alongside highways. The objective of this study was to measure the levels of PGMs that bioaccumulate in Oreochromis niloticus, Penaeus laspisulcates, Scylla serrate, Galaxias brevipinnis and Mollusc in the river Pra estuary along a major highway in Ghana. Chemical analysis using neutron activation analysis showed accumulation of the PGMs in all the biota species analysed. The S. serrate and mollusc showed higher accumulation than the other species. The mollusc and the other fish species in the estuary are consumed in Ghana, and therefore there is the need to educate the population on the effect of the PGMs on their health.     

Evaluation of sampling methods for the estimation of structural indices in forest stands

The paper is about the accurate (i.e. unbiased and precise) and efficient estimation of structural indices in forest stands. We present SIAFOR, a computer programme for the calculation of four nearest-neighbour indices, which describe the spatial arrangement of tree positions, the distribution pattern of species, and the size differentiation between trees. The study uses SIAFOR as a sampling simulator in eight completely stem-mapped forest stands of varying area and structural complexity. We statistically evaluate two sample types (distance and plot sampling), comparing sampling error, bias and minimum sample size for index estimation. We introduce the concepts of measurement expansion factor (MEF) and design expansion factor (DEF) for the technical evaluation of sample type efficiency (optimal sample type). Results indicate that sampling error can reach high levels and that minimum sample sizes for index estimation often amply exceed the limit of 20% of tree density or 20 trees per species per hectare, that we set as the highest feasible sample size in normal situations. We found clear feasibility limits (in terms of minimal tree densities and reachable accuracy levels) for the estimation of all investigated indices. Generally, equal or higher sample sizes are needed for plot sampling than for distance sampling to reach equal accuracy levels. Nevertheless, plot sampling resulted more efficient for the estimation of tree size differentiation at low to medium accuracy levels. For all other investigated indices distance sampling resulted more efficient than plot sampling. Minimum sample size increases with accuracy and is negatively correlated with tree density. At a given accuracy level minimum sample size is highest for the estimation of relative mingling and lowest for tree size differentiation; furthermore it is generally lower in large stands than in small ones. Because of the consistency of our conclusions in all of the investigated stands, we think they apply in most stands of similar area (between 1 and 10 ha) and species diversity (not more than four species).     

Correlations between physiological responses of four aquatic plant species and river water quality

The Jiushanwai channel is located in the Lucheng district of Wenzhou City, China. Four aquatic plant species (Canna indica, Cyperus alternifolius, Myriophyllum verticillatum, and Lythrum salicaria) were planted on floating-beds constructed in a north-south layout along this channel. Five sites were sampled during spring, summer and autumn. The physiological characteristics (content of chlorophyll and soluble protein, activity of peroxidase and catalase) of the plants and the corresponding water quality were determined and correlations between these indices were analysed. The physiological indices of the plants and water quality changed regularly at the five sampling sites. Myriophyllum verticillatum was the most sensitive species to water quality changes, whereas Lythrum salicaria was least sensitive. Of the physiological indices examined, soluble protein content was most sensitive to water quality changes. The physiological indices of M. verticillatum are deemed to be most suitable to indicate river water quality.     

Reproductive effort in four species of intertidal limpets

Reproductive effort was measured in 4 species of intertidal limpets: Cellana tramoserica (Sowerby) Notoacmea petterdi (Tenison Woods), Patella peroni Blainville and Patelloida alticostata (Angas) from south-eastern Australia. Field studies between 1971 and 1975 enabled indices of reproductive effort to be obtained using both gonad to body weight ratios and energy budgets. The ratio of annual gonad production to somatic tissue energy content is highest for Patella peroni (2.19). The ratios for C. tramoserica and Patelloida alticostata are lower but similar (1.02), and N. petterdi has the lowest ratio (0.78). The percentage of assimilated energy allocated to reproduction is also highest in Patella peroni (26.6%), but this index of reproductive effort is similar for the other three species (10.3 to 12.9%). Consequently, these 4 species are ranked in different orders with respect to reproductive effort, depending upon which index is used. However, the difference between both indices is small, and is less than has usually been anticipated. The difference is interpreted as being the result of the low metabolic rate of N. petterdi rather than as evidence for the inadequacy of one of the indices of reproductive effort.     

Seasonal reproduction of the brachiopod Frieleia halli and the scaphopod Cadulus californicus at bathyal depths in the deep sea

Two benthic species of invertebrates from the physically seasonless bathyal depths of the San Diego Trough off southern california USA showed highly synchronous reproductive cycles. Although the common pattern in the deep-sea benthos seems to be year-round reproduction, these two species are exceptions. The brachiopod Frieleia halli Dall spawned between January and April (1971) and the scaphopod mollusc Cadulus californicus Pilsbry and Sharp in late summer between July and October. Furthermore, F. halli. has maintained a predictable annual gametogenic cycle for three years (1970–1972). Several factors are suggested as possibly important in synchronizing their reproductive cycles, but no single environmental cue can be conclusively demonstrated as a definite influence.     

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.     

Relationship between bottom characteristics and benthic organisms in the shallow water of Oppa Bay,Miyagi

An investigation was conducted to examine the species composition, abundance and biomass of benthic macrofaunal invertebrates in Oppa Bay, Miyagi Prefecture, Japan, in August 1984. Among 212 species identified, nearly half (105) were Polychaetes. Usually five species, Ampharete sp. 1, Neosabellides sp. 1, Nephtys polybranchia, Chaetozone sp. 1, and Lumbrineris longifolia were numerically dominant. The faunal features of dominant species were clearly divided into two areas using two indicator species, Amphalete sp. 1 and Neosabellides sp. 1. The former species decreased in numbers in the area from the river to the bay mouth, while the latter increased. Sediments consisted of sand at the river mouth and in the northern bay; and of silt-clay in the central bay, bay mouth and southern part of the bay. Gradients of species diversity (H) were expressed as a function of distance by linear regression. The relationship was positive (r=0.812) from the river to the bay mouth accompanied by increasing depth; and negative (r=-0.906) from northern to southern parts of the bay in proportion to the increase of silt-clay in sediments.     

Long-term variation of organochlorine residues and assemblages of epibenthic organisms in a shallow North Florida (USA) estuary

A 4-year study (1972–1976) determined long-term trends of organochlorine residues (DDT, DDE, DDD, PCB's, mirex) and trawl-susceptible organisms in a shallow, river-dominated estuary in North Florida (Apalachicola Bay, USA). Moderate levels of such compounds were found in various species prior to the restricted use of DDT in 1972. A subsequent precipitous decline in organochlorine besidues was attributed to decreased upland usage, major flushing of the river basin in early 1973, and various factors associated with estuarine function. No mirex was found in sediments or aquatic organisms. Apparently, the half-life of organochlorines is relatively short in this bay system. Various statistical methods were used to test the relationships of different physico-chemical and biological parameters. During the 4-year study period, seasonal river flow fluctuations dominated water color, turbidity, salinity, nutrients (NO₃), chlorophyll a, and the temporal succession of fishes in the bay. Certain long-term trends of fish associations were noted; relative dominance of key fish species declined and stabilized while bay-wide species richness and diversity increased with time. Qualitative changes in species representation determined the long-term pattern of community variability. This was consonant with a distinctive fish fauna during the first year of sampling. The bay anchovy Anchoa mitchilli was dominant during 9 of the first 12 monts of the project; this influenced the time-related changes in community indices. Temporally clustered fish associations reflected the importance of river flow in the estuarine environment. Direct correlation of fish distribution with the rapid disappearance of organochlorine compounds was complicated by aperiodic natural phenomena such as storms and river fluctuations. Population and community trends appeared consistent with other studies showing similar patterns of dominance of stress-resistant fish populations and related changes in community parameters. In this case, the relatively predictable annual succession of fish associations allowed an appraisal of key forcing functions. Due to the high level of seasonal and annual biological variability in this estuary, there were some problems in the application of linear statistical models to the data base. Although the long-term trend of relative species representation is useful as an index of stress, new techniques are needed to analyze extensive field data so that functions such as trophic interactions are included in the estimation of causal relationships. There are indications that such effects could be related to the impact of organochlorine compounds on estuarine systems.     

Soleidae macroparasites along the Portuguese coast: latitudinal variation and host–parasite associations

Parasite assemblages are increasingly being used as indicators of their hosts’ biology and ecology, especially for economically important marine species such as the Soleidae. In this study, seven species inhabiting Portuguese coastal waters were examined for external and internal macroparasite infections using standard procedures: Dicologlossa cuneata, Microchirus azevia, Microchirus variegatus, Solea lascaris, Solea senegalensis, Solea solea and Synaptura lusitanica. Despite being closely related, these species present different life history patterns and ecological preferences which were expected to be mirrored by their macroparasite assemblages. The aim of the study was, therefore, to study the variation of these assemblages, within and between host species, along the Portuguese coast in order to evaluate the importance of the hosts’ features and environmental factors in the assemblage compositions. Flatfish were obtained seasonally from commercial fishing vessels operating in three areas (northern, central and southern) along the Portuguese coast. Prevalence and mean abundance were calculated and tested for differences between host sex, areas and seasons. The host specificity index and the importance of the host–parasite relationship were computed based on mean abundance. The total number of parasite individuals, species richness, total prevalence, total mean abundance, diversity and evenness were also calculated. A canonical correspondence analysis (CCA) was performed using prevalence and mean abundance data. A total of 44 macroparasite species were found. No significant differences were observed in prevalence and mean abundance between sexes and sampling seasons but, for three of the parasite species, significant differences were found between areas. The highest values of the parasitological and ecological indices were generally registered in the hosts S. lascaris and S. senegalensis and in the southern area. The CCA using the prevalence data revealed the differentiation of S. lascaris samples, which was mainly related to the total prevalence and to the number of important species of macroparasites. When using mean abundance data, the CCA revealed the differentiation of D. cuneata from the south, S. lascaris from the three areas and S. senegalensis from the south, mainly related to total prevalence and richness. The differences found between infection levels and assemblages’ composition were mainly due to differences in hosts’ diet, namely prey type consumption, given that most macroparasites found were transmitted through the food web. However, environmental factors were also important given that they regulate the distribution of ectoparasites and the availability of prey, and therefore the infections’ pattern. These findings were in agreement with the ones from similar studies performed in other species, revealing the importance of parasites as indicators of their hosts’ ecology.     

Between introgression events and fragmentation, islands are the last refuge for the American crocodile in Caribbean Mexico

Habitat loss and degradation in the Mexican Caribbean, caused by the development of tourism, have decreased the potential nesting area for the American crocodile (Crocodylus acutus) and have fragmented the populations of the Yucatan peninsula. Our study investigated five populations (three continental: North, South, Sian Ka’an, and two insular: Cozumel, Banco Chinchorro) of C. acutus in the Mexican Caribbean using seven different inter simple sequence repeat (ISSR) markers as tools for genetic variability and population differentiation. Three classification methods were tested and compared: distance analysis, self-organizing map, and Bayesian methods, to evaluate the resolution of each method with ISSR markers. The 77 loci selected revealed a high variability between populations (polymorphism from 17% for Sian Ka’an to 75% for Banco Chinchorro) with a total polymorphism of 84% and a global coefficient of gene differentiation (G _ST ) of 0.296, but low values of Nei’s Gene diversity (from 0.065 for Sian Ka’an to 0.233 for Banco Chinchorro). Our results suggest elevated inbreeding in all local populations with higher indices for Banco Chinchorro and lower indices for Sian Ka’an. Three independent classification methods gave similar results, and suggested that most continental individuals are admixtures, with different levels of introgression, with the sympatric species Crocodylus moreletii. We propose that the islands/atolls remain the sole areas with genetically “pure” American crocodiles and we discuss these results for future conservation of this endangered crocodile species.     

Reproductive periodicity in the euryalinid snake star Astrobrachion constrictum in a New Zealand fiord

The euryalinid snake star Astrobrachion constrictum (Farquhar), a normally deep-water species, exists within SCUBA diving range in New Zealand flords, and thus presents a unique opportunity for study. A population of A. constrictum in Doubtful Sound was investigated from February 1990 to July 1994 to determine the reproductive cycle. Unlike most ophiuroids, the gonads of A. constrictum are positioned along the aboral coelom in the proximal portion of the arms. The proximal 2 to 3 cm of the arms of individuals were thus removed on an approximately monthly basis for histological examination of the gonads. Image analysis was used to determine oocyte size-frequency distributions. A gonad index was calculated for each individual based on the ratio of cross-sectional area of the gonads to cross-sectional area of the arm. Maturity indices were calculated based on stage of development of the gonads of each individual. A. constrictum has a period of enhanced breeding activity in April–June, after which both the gonad and maturity indices decline. The increase in gametogenic activity during these months was correlated with rising sea temperature within the fiord. Although the females showed an annual pattern of gonad development, oogenesis was continuous throughout the year, with oocytes at different stages of development present in the gonads. Males also showed continuous spermatogenesis and, although the same annual pattern of gonad development was evident as seen in the females, it was less marked. The presence of females with large oocytes and ripe males throughout the study indicates that breeding in the Doubtful Sound population is prolonged, and possibly continuous, as found in many deep-sea ophiuroids.     

Restoration of the Kishon River

The Kishon River, which is now an industrial sewage canal, may be turned into a recreational area in two stages, and by approximately 20 million dollar investment.

Stage A: The wastewater is treated in order to avoid polluted effluents from entering the river.

Stage B: The river water is treated in order to turn the river into a recreational area.     

The fish fauna of a seasonally closed Australian estuary. Is the prevalence of estuarine-spawning species high?

The fish at sites located throughout the large, seasonally closed Wilson Inlet, on the southern coast of Western Australia, were sampled bimonthly between September 1987 and April 1989. Seine nets were used to sample nearshore shallow waters, while gill nets were employed in slightly more offshore and deeper waters. Twenty species were recorded in the shallows, of which the three species of atherinid and the three species of goby comprised >97% of the total catch. In terms of number of individuals, the 27 species recorded in gill nets in the deeper waters were dominated by Cnidoglanis macrocephalus and Platycephalus speculator, and to a lesser extent Engraulis australis, Aldrichetta forsteri, Sillaginodes punctata and Arripis georgianus. Fifty-five percent of the species recorded in the nearshore shallow waters and 18% of those in offshore deeper waters spawn within Wilson Inlet; these species contributed 98.5 and 63.0%, respectively, to the total catches in those waters. Classification and ordination showed that the composition of the fauna in the shallows was similar at all sites throughout the large basin and did not change conspicuously with season. However, the composition of catches taken in offshore waters differed between the lower part of the basin and the middle and upper regions of the basin, which in turn differed from those in the saline reaches of a tributary river. The four diagnostic species of the lower estuary were all marine species, while the three diagnostic species in the river included a marine species (Mugil cephalus) that often penetrates far upstream in other systems, and a species which was confined to the rivers (Acanthopagrus butcheri). The composition of the fish fauna in the offshore waters of the lower estuary between the middle of spring and middle of autumn was different in 1987/1988 (when the estuary mouth was open for only the first two months of that period) from that in 1988/1989 (when the mouth was open for the whole of that period). This difference is related to the greater number of marine species that were retained in the first of these years, when the estuary was open to the ocean for only a short period. The greater retention of marine species in 1987/1988 than in 1988/1989 probably reflects a far lower level of freshwater flusing and/or a less marked decline in salinity.     

Tree species diversity and its relationship to stand parameters and geomorphology features in the eastern Black Sea region forests of Turkey

We studied the effects of stand parameters (crown closure, basal area, stand volume, age, mean stand diameter number of trees, and heterogeneity index) and geomorphology features (elevation, aspect and slope) on tree species diversity in an example of untreated natural mixed forest stands in the eastern Black Sea region of Turkey. Tree species diversity and basal area heterogeneity in forest ecosystems are quantified using the Shannon-Weaver and Simpson indices. The relationship between tree species diversity basal area heterogeneity stand parameters and geomorphology features are examined using regression analysis. Our work revealed that the relationship between tree species diversity and stand parameters is loose with a correlation coefficient between 0.02 and 0.70. The correlation of basal area heterogeneity with stand parameters fluctuated between 0.004 and 0.77 (R2). According to our results, stands with higher tree species diversity are characterised by higher mean stand diameter number of diameter classes, basal area and lower homogeneity index value. Considering the effect of geomorphology features on tree species or basal area heterogeneity we found that all investigated relationships are loose with R < or = 0.24. A significant correlation was detected only between tree species diversity and aspect. Future work is required to verify the detected trends in behaviour of tree species diversity if it is to estimate from the usual forest stand parameters and topography characteristics.     

Using three-dimensional surface area to compare the growth of two Pocilloporid coral species

Many facets of coral research require coral colony surface area estimates. This study developed a relationship between the two-dimensional (2D) projected area and the three-dimensional (3D) whole colony surface area for two commonly studied Indo-Pacific coral species: Pocillopora damicornis and Stylophora pistillata. The surface index function was used to measure the growth of colonies in situ around Heron reef on the southern Great Barrier Reef. The results show that while growth between the two species was not significantly different when measured in two dimensions, the 3D area showed significantly different growth rates with S. pistillata growing at almost double the rate of P. damicornis. The study demonstrates that it is possible to make reliable estimates of the 3D surface area of entire colonies of these complex branching coral species, using the plan view of the coral and a pre-determined surface index function. In addition, this study shows that the 3D surface area provides a more useful measure of colony growth than the traditional methods of either 2D area or longest dimension.     

Coexistence and reproductive isolation of the sympatric echinoids<Emphasis Type="Italic"> Diadema savignyi</Emphasis> Michelin and<Emphasis Type="Italic"> Diadema setosum</Emphasis> (Leske) on Kenyan coral reefs

The sympatric echinoids Diadema savignyi and D. setosum coexist in shallow reef lagoons throughout East Africa. The reproductive strategies of these echinoids were studied to investigate reproductive isolation as a possible mechanism for maintaining the coexistence of these closely related species. The annual reproductive cycle and lunar periodicity were determined by gonad index measurements, histological examination of gametogenesis, and induction of spawning with injections of KCl. The peak reproductive period of D. savignyi coincided with the north-east monsoon period (when light and temperatures are high) as gonad indices were high (>8%) beginning in February and peaked at 9.7% in May. Gonad indices subsequently rapidly decreased (by 26%) in June at the beginning of the cooler south-east monsoon period. However, the presence of sperm and ova in most months of the year indicates continuous gametogenesis with reduced reproductive effort during the cooler months. The annual cycle for D. setosum showed less of a seasonal trend as gonad indices remained above 7% throughout much of the year but tended to be highest when temperatures were lower. This is the first confirmation of continuous reproduction in these two species at the equator. The reproductive patterns of both species remained consistent over 2 years of sampling. Both species exhibited a synchronized lunar spawning periodicity during the 3 months sampled, with D. setosum spawning on lunar days 8–10 and D. savignyi spawning after the full moon (lunar days 17–18). Whereas spawning in D. savignyi was very tightly synchronized, 20% of D. setosum individuals still spawned after the peak spawning period. The coexistence of these closely related species appears to be maintained by temporal reproductive isolation during the lunar spawning period reinforced by seasonal differences in reproductive effort.Communicated by O. Kinne, Oldendorf/Luhe     

The Capacity of Australia's Protected‐Area System to Represent Threatened Species

Abstract: The acquisition or designation of new protected areas is usually based on criteria for representation of different ecosystems or land‐cover classes, and it is unclear how well‐threatened species are conserved within protected‐area networks. Here, we assessed how Australia's terrestrial protected‐area system (89 million ha, 11.6% of the continent) overlaps with the geographic distributions of threatened species and compared this overlap against a model that randomly placed protected areas across the continent and a spatially efficient model that placed protected areas across the continent to maximize threatened species’ representation within the protected‐area estate. We defined the minimum area needed to conserve each species on the basis of the species’ range size. We found that although the current configuration of protected areas met targets for representation of a given percentage of species’ ranges better than a random selection of areas, 166 (12.6%) threatened species occurred entirely outside protected areas and target levels of protection were met for only 259 (19.6%) species. Critically endangered species were among those with the least protection; 12 (21.1%) species occurred entirely outside protected areas. Reptiles and plants were the most poorly represented taxonomic groups, and amphibians the best represented. Spatial prioritization analyses revealed that an efficient protected‐area system of the same size as the current protected‐area system (11.6% of the area of Australia) could meet representation targets for 1272 (93.3%) threatened species. Moreover, the results of these prioritization analyses showed that by protecting 17.8% of Australia, all threatened species could reach target levels of representation, assuming all current protected areas are retained. Although this amount of area theoretically could be protected, existing land uses and the finite resources available for conservation mean land acquisition may not be possible or even effective for the recovery of threatened species. The optimal use of resources must balance acquisition of new protected areas, where processes that threaten native species are mitigated by the change in ownership or on‐ground management jurisdiction, and management of threatened species inside and outside the existing protected‐area system.     

Grazing as a measure against grass encroachment in Dutch dry dune grassland: effects on vegetation and soil

A grazing experiment was started in 1984 and 1989 respectively, in two parts of a dune grassland in the nature reserve ‘Zwanenwater’, North Holland; a third part with similar geology and topography was used as a control area and not grazed. An evaluation of the effects of grazing on vegetation patterns, species composition, vegetation structure and humus form was made with the help of vegetation maps from 1986 and 1992 as well as field surveys. Dense tall-grass communities dominated byAmmophila arenaria increased over the period 1986–1992 in the grazed areas, and especially in the non-grazed area (increase in area to 20 %, 22 % and 50 %, respectively). Open communities decreased in the grazed areas, but are still prevalent, while in the ungrazed area they virtually disappeared, with the result that the present percentage areas are 53 %, 38 % and 17 %. Field survey data were classified by TWINSPAN producing four vegetation types. These occur more or less equally in grazed and ungrazed areas, albeit with different percentage areas: (1) open vegetation dominated byCorynephorus canescens; (2) open vegetation characterized byKoeleria macrantha; (3) heathland dominated byEmpetrum nigrum; and (4) tall-grass communities dominated byAmmophila arenaria. Within a vegetation type, species composition was only marginally affected by grazing regime. Within the open communities the number of species, vegetation height, vegetation cover and soil organic horizons were not affected by grazing. In the tall-grass communities the number of species was significantly larger and the height of the vegetation significantly lower in the area grazed since 1984. In the heathland community the number of species and cover of the moss layer were significantly higher in the 1984 area and ectorganic and endorganic horizons significantly thicker in the ungrazed area. It is suggested that these effects are the result of an increased availability of light, but possibly also of a decreased stock of organic matter and nutrients, due to a decreased input of litter and accelerated rates of decomposition. Nomenclature: Van der Meijden et al. (1992) for phanerogams; Corley et al. (1981) for mosses; Grolle (1983) for hepatics.     

Spatio-temporal patterns in the diversity of demersal fish communities off the south coast of South Africa

The diversity of ecological communities has been the focus of many studies. Because biodiversity provides several indicators used in an Ecosystem Approach to Fisheries (EAF) to track changes in fish communities, we investigated the spatial and temporal patterns in the diversity of some demersal fish communities subjected to varying fishing pressure. Depth and catch rate were the most important predictors in explaining changes in diversity followed by longitude and survey year. Diversity, as measured by the various indices except for taxonomic distinctness (∆*), initially declined with increasing depth to about a depth of 80 m, then increased to about 150 m after which it declined. Taxonomic distinctness index (∆*) showed an increase in the taxonomic heterogeneity of the demersal community below the 300-m isobath. Diversity remained relatively constant with increase in longitude to around 24°E (which has the lowest diversity) after which it increased. The assessment of the temporal trend in diversity indicates that survey year has a significant effect on all diversity indices except for ∆*. Diversity increased and dominance declined with time. This may be result of a decline in the abundance of dominant species or an increase in the abundance less dominant species, or a combination of both effects. Multivariate analysis of the set of diversity indices showed three groups of indices: those reflecting species richness (S, Margalef’s d), those measuring mainly taxonomic relatedness (∆*), and those balancing the richness and evenness components of diversity (J′, H′, λ, ∆, Hill’s N1, and Hill’s N2). The relationship between evenness, catch rate, and size was also investigated. Size classes with highest evenness were found to have lowest catch rate and vice versa. This highlights the need to consider the size and trophic level of species when linking diversity to the functioning of ecosystems.