Local complexity in patterns of canopy–benthos associations produces regional patterns across temperate Australasia

Across subtidal coasts of temperate Australasia, canopy–benthos associations are mostly understood from broadly defined studies of kelp forests within eastern Australia and north-eastern New Zealand. We tested the hypotheses that (1) benthic assemblages differ between monospecific stands of Ecklonia radiata and stands that comprise E. radiata mixed with other canopy-forming species, (2) patterns observed locally (i.e. within sites 1–10 km apart) match those observed among regions (>1,000 km apart) for which (3) eastern Australia and northern New Zealand are representative of other regions of temperate Australasia. Benthic assemblages almost always differed among monospecific, mixed, and open stands indicating that failure to distinguish between superficially similar habitats can lead to over-generalised conclusions about the ecology of kelp forests. Patterns of differences among stands did not change between western and southern Australia but differed from eastern Australia, and patterns from all regions were distinct from New Zealand (WA=SAEANZ). Whilst local patterns were complex, the major morphological groups that often characterise benthos (i.e. encrusting coralline algae and turf-forming algae) revealed patterns that could be related across space from local to regional scales. These findings demonstrate that knowledge about the configuration of canopy-forming species will improve confidence about the representativeness of results and that any local complexity need not impede searches for generality when the spatial limits of patterns are also understood.Communicated by M.S. Johnson, Crawley     

Morphology of<Emphasis Type="Italic"> Ecklonia radiata</Emphasis> (Phaeophyta: Laminarales) along its geographic distribution in south-western Australia and Australasia

Ecklonia radiata (C. Ag.) J. Agardh is a common macroalga on reefs in the warm-temperate parts of the southern hemisphere. It is a dominant habitat-former and as such has a strong structuring effect on associated algal assemblages. Morphological variation in E. radiata potentially affects its interactions with the surroundings and contributes to confusion about its taxonomy. We quantified the magnitude of morphological variation in fully developed E. radiata sporophytes across Australasia and tested the hypotheses that E. radiata has different morphology at different locations and that the degree of morphological difference depends on spatial distances among locations. A total of 11 morphological characters were sampled from 11 locations along the Australian coastline from Kalbarri in Western Australia to Sydney in New South Wales as well as from Doubtful Sound, New Zealand. Most morphological characters varied considerably from one location to another. For example, the average (±SE) thallus length was 135.2±12.5 cm in Kalbarri and only 69.7±5.5 cm in Sydney. There were no consistent spatial patterns of variation among individual morphological characters, and, generally, variations among individual characters were poorly correlated (-0.5< R<0.5). This suggests that individual morphological characters develop independently of each other in response to processes operating at different spatial scales. Multivariate measures of morphology were found to be different among some locations and similar among others (-0.37=Clarke's  R=1), but there was no correlation (Spearman's R=0.08) between morphological similarity and distance between locations. Consequently, our results do not support clinal variation in E. radiata morphology. Rather, they suggest the presence of discrete morphologically different populations, in which the morphology at any one location reflects multiple forcing factors operating on different morphological characters at different spatial scales.     

Metacommunity influences on community richness at multiple spatial scales: a microcosm experiment

Large-scale processes are known to be important for patterns of species richness, yet the ways in which local and larger scale processes interact is not clear. I used metacommunities consisting of five interconnected microbial aquatic communities to examine the manner in which processes at different scales affect local and metacommunity richness. Specifically, I manipulated the potential dispersal rate, whether dispersal was localized or global, and variation in initial community composition. A repeated-measures ANOVA showed that a low dispersal rate and intermediate distance dispersal enhanced local richness. Initial assembly variation had no effect on local richness, while a lack of dispersal or global dispersal reduced local richness. At the metacommunity scale, richness was enhanced throughout the time course of the experiment by initial compositional variation and was reduced by high or global dispersal. The effects of dispersal were contingent on the presence of initial compositional variation. The treatments also affected individual species occupancy patterns, with some benefiting from large-scale processes and others being adversely impacted. These results indicate that the effects of dispersal on species richness have a complex relationship with scale and are not solely divisible into "regional" vs. "local" scales. Finally, predictions of the manner in which dispersal rate structures communities appear dependent upon species compositional variation among communities.     

Variability over space and time in the genetic structure of the winged kelp Alaria marginata

The genetic structure of Alaria marginata Postels & Ruprecht was investigated spatially and seasonally using amplified-fragment length polymorphisms (AFLP). Using one primer, 206 scoreable bands were produced. Individual plants that were separated by as little as a few decimeters to >100 km could be distinguished, and followed an isolation-by-distance model. Genetic similarity (average April data) ranged from 76% for patches (a few decimeters in diameter), to 71% for individual kelp stands (15 m across) and 67% for a group of stands separated by 185 km. Greater genetic similarity of patches occurred at a wave-sheltered site than at a wave-exposed site. The lower wave action may limit meiospore dispersal, resulting in patches of related sporophytes. Genetic similarities between A. marginata stands indicated a pattern of gene flow that is consistent with local currents. In one stand, genetic similarities were markedly different between seasons. This seasonal pattern may be the result of different age groups dominating the sampled stands over time. The genetic structure of A. marginata comprises local scale (patch and within-stand) heterogeneity and larger scale (between-stands) homogeneity. Received: 30 September 1998 / Accepted: 26 October 1999     

Coral recruitment: a spatio-temporal analysis along the coastline of Eilat,northern Red Sea

Recruitment rates of stony corals to artificial substrates were monitored for 2 years at 20 sites along the coast of Eilat, northern Red Sea, to compare with those recorded at other coral reef locations and to assess variation in recruitment at several spatial scales. Coral recruitment was low compared to that observed on the Great Barrier Reef in Australia, but was similar to levels reported from other high-latitude reef locations. Pocilloporids were the most abundant coral recruits in all seasons. Recruitment was twofold higher during the first year than during the second year of study. There was considerable spatial variability, with the largest proportion of variance, apart from the error term, attributable to differences between sites, at a scale of 10² m. Spearmans ranked correlation showed consistency in spatial patterns of recruitment of pocilloporid corals between years, but not of acroporid corals. During spring, when only the brooding pocilloporid coral Stylophora pistillata reproduces at this locality, most coral recruitment occurred at central and southern sites adjacent to well-developed coral reefs. During summer, recruitment patterns varied significantly between years, with wide variation in the recruitment of broadcasting acroporid corals at northern sites located distant from coral reefs. Settlement was low at all sites during autumn and winter. This work is the first detailed analysis of coral recruitment patterns in the Red Sea, and contributes to the understanding of the spatial and temporal scales of variation in this important reef process.Communicated by O. Kinne, Oldendorf/Luhe     

Genetic subdivision within the eastern Australian population of the sea anemoneActinia tenebrosa

An electrophoretic survey of allozyme variation revealed substantial genetic differentiation within the eastern Australian population ofActinia tenebrosa. This differentiation appears to reflect the effects of both asexual reproduction and limited gene flow among local populations separated by up to 1050 km. Variation was assessed within groups of 27 to 55 adults sampled between September 1985 and December 1988 collected from small areas of shore within each of 24 local populations. All individuals were collected from stable rock platforms, with the exception of Boulder Bay, where some sea anemones were removed from small mobile boulders. High levels of variability were detected for each of seven enzyme-encoding loci. The patterns of genotypic variation detected imply that local populations are maintained by predominantly asexually generated recruitment. Levels of multi-locus genotypic diversity within samples were consistently less than 50% of the level expected for sexual reproduction with free recombination. This was reflected by the detection of relatively low numbers of multi-locus genotypes and significant departures from expectations for single-locus Hardy-Weinberg equilibria within 17 of the 24 local populations. Standardised genetic variances (F _ST ), calculated from the genotypes of all individual adults were typically much greater than those expected for marine organisms with widely dispersed larvae. The former values were reduced, but were still extremely large when clonal genotype frequencies were substituted into the calculation. These data imply that although widely dispersed larvae may be an important source of initial colonists, levels of gene flow among established local populations are low. Furthermore, cluster analysis revealed a clear subdivision of the population into northern and southern groups. However, this subdivision was largely explained by strong clinal variation at a GPI-encoding locus. For this locus, allele frequencies ranged from fixation of the A allele in samples from the 12 most northern sites to near fixation of the alternative B allele in southern samples. Subdivision of the eastern Australian population is consistent with the predicted off-shore movement of the Eastern Australian Current close to the border between Victoria and New South Wales. However, the split into northern and southern regions, as evidenced by the variation forGpi, could reflect patterns of gene flow and/or other factors such as natural selection or the recent patterns of colonisation.Contribution No. 78 from the Ecology and Genetics Group of the University of Wollongong     

Competitive interactions between two fucoid algae with different growth forms,<Emphasis Type="Italic"> Fucus serratus</Emphasis> and<Emphasis Type="Italic"> Himanthalia elongata</Emphasis>

Competitive interactions between two fucoid algae with different growth forms, Fucus serratus L. and Himanthalia elongata (L.) S.F. Gray were examined both in the laboratory and on a shore of the Isle of Man, Irish Sea. The growth of germlings of both species declined with increasing density, irrespective of whether they were with cohorts or rival species, indicating that intra- and interspecific competition occurred between germlings. H. elongata suppressed the performance of F. serratus at the germling stage by virtue of its larger initial size, and at the mushroom stage by forming a miniature canopy with the caps of the adjacent plants. In a field experiment, the mortality of H. elongata juveniles generally increased in mixtures with F. serratus and was highest when F. serratus were 50% of the plants. At the juvenile stage, the negative effect of F. serratus on H. elongata was more severe than the other way round. This was because F. serratus grows predominantly upwards, whereas H. elongata had already begun to expand laterally at the distal end. If F. serratus survives in sparse mixed stands with H. elongata juveniles, it can overgrow them and inhibit their subsequent survivorship and growth, probably by both shading and physical sweeping. H. elongata and F. serratus maintain their discrete monospecific stands because of the varying outcomes of mutual competitive exclusion resulting from their differing growth patterns. Thus it is possible for them to co-occur at a similar shore height.Communicated by O. Kinne, Oldendorf/Luhe     

Genetic structure of the subtidal red alga Delisea pulchra

We used random amplified polymorphic DNA (RAPDs) to examine small-scale spatial genetic structure in the red alga Delisea pulchra (Greville) Montagne at two locations near Sydney, Australia. We examined genetic structure among plants at four spatial scales ranging from 2 km apart down to <50 cm apart between locations, among sites within locations, among quadrats within sites, and among plants within quadrats. Haploid stages of D. pulchra were absent from the populations studied, suggesting that they are maintained through asexual reproduction of diploid plants. Consistent with this, we found that 19 RAPD phenotypes scored in this study had multiple individuals, indicating the presence of clones in these populations. However, there were no RAPD phenotypes common to two locations separated by only 2 km. Analysis of molecular variance revealed that strong genetic differences occurred between plants from these two locations, with 46.3% of the total genetic variation occurring at this scale, most probably reflecting limited gene flow. Within each location, <25% of the genetic variation was attributable to differences among sites or quadrats, indicating gene flow at those smaller scales. Most of the variation within each location occurred at the smallest spatial scale, among plants within 0.25 m² quadrats. Nonetheless, some pairwise genetic distances (φST) between sites or quadrats within locations were large, indicating some genetic divergence on smaller scales. Genetic distance was independent of spatial distance within both locations, suggesting that fine-scale differences within locations were most probably caused by variation in fine-scale patterns of water movement or fine-scale natural selection. We assessed the impact of one potential selective agent, grazing sea urchins, on the fine-scale genetic structure of D. pulchra. There was no evidence that grazing by sea urchins affected the genetic structure of D. pulchra. In combination with demographic data, our results indicated that local populations of D. pulchra within locations were relatively open and that fine-scale genetic structure was probably constrained by gene flow. At the larger scale however, strong genetic differentiation indicated little gene flow between locations and restricted dispersal of spores. Received: 22 April 1999 / Accepted: 29 November 1999     

Chitinolytic enzymes in the digestive system of marine fishes

Chitinase, exo-N-acetyl--D-glycosaminidase (NAGase) and lysozyme activities were assayed in the digestive tract of 6 species of marine fishes: Myxine glutinosa (cyclostome), Chimaera monstrosa (holocephalan), Squalus acanthias, Etmopterus spinax, Raja radiata (elasmobranchs) and Coryphaenoides rupestris (teleost). Strong chitinase activity was found in the gastric mucosa of the elasmobranchs (S. acanthias, E. spinax and R. radiata) and the teleost (Coryphaenoides rupestris). A remarkably high chitinase activity occurred in the pancreas of the stomachless holocephalan fish Chimaera monstrosa. NAGase activity was strong in the digestive tract of all species. It could be concluded that marine fishes with diets consisting largely of chitinous invertebrates may display high chitinase and NAGase activities in their digestive system; however, only low chitinase activity was found in the intestine of the cyclostome Myxine glutinosa. Coryphaenoides rupestris gastric mucosa chitinase had one optimum activity at pH 1.25, whereas S. acanthias chitinase had two optima, at pH 1.6 and 3.6. The NAGase pH-activity curves from S. acanthias and R. radiata gastric mucosa displayed similar optima, at pH 4.5 and 4.25 respectively. Chimaera monstrosa pancreatic chitinase had a very strong optimum around pH 8 to 10, and one less strong at pH 3. These enzyme activities could not be separated by gel filtration or isoelectric focusing. The pI (isoelectric point) was approximately 4.9 for both enzymes. The molecular weight of the C. monstrosa pancreatic chitinase was estimated to be approximately 43 000. Lysozyme activity was absent or extremely weak in the material studied.     

Chemical defense: incorporation of diet-derived pyrrolizidine alkaloid into the integumental scales of a moth (<Emphasis Type="Italic">Utetheisa ornatrix</Emphasis>)

Summary. Evidence is presented that pyrrolizidine alkaloid acquired by Utetheisa ornatrix (Lepidoptera, Arctiidae) as a larva from Crotalaria foodplants is incorporated in part into the scales of the adult. A single forewing of a male or female moth may contain in the order of 6 to 13 g monocrotaline in its scale cover or about 1 to 2% of the moths systemic monocrotaline content. Based on estimates of the number of scales per forewing, the monocrotaline content of individual scales is calculated to be in the order of 0.1 and 0.2 ng monocrotaline per male and female scale, respectively. This amounts to concentrations of about 1 and 3%, values roughly at a par with the average systemic concentration (0.5-0.6%) previously determined for monocrotaline in Utetheisa. It is argued that the presence of pyrrolizidine alkaloid in the moths scale coating could account for the promptness with which adult Utetheisa are rejected by spiders. It is suggested further that chemical impregnation of scales with substances deterrent to predators may be more widespread among insects than generally assumed.     

In situ exudation of phlorotannins by the sublittoral kelp Ecklonia radiata

Exudation of phlorotannins (polyphenolics) was measured in situ from the sublittoral kelp Ecklonia radiata at two locations near Sydney, New South Wales, Australia during 1992–1993. Minimally disruptive techniques were used in which individual plants were enclosed within clear plastic bags in order to concentrate exudates. Rates of exudation from E. radiata were low relative to most previous studies, with a mean rate (averaged across four seasons and two sites) of 5.5 g g (dry wt)^-1 h^-1. Exudation was greatest in summer and least in winter at one site, but there were no seasonal differences at a second, more protected site. There was no measurable diurnal variation in exudation rates. Exudation after a period of heavy storms was not significantly different from exudation during calm weather, but severe physical damage to the kelp did increase exudation. Our results suggest that exudation of phlorotannins in temperate Australian waters may be less ecologically important than has been suggested for coastal systems in the Northern Hemisphere.     

Acanthochromis polyacanthus,a fish lacking larval dispersal,has genetically differentiated populations at local and regional scales on the Great Barrier Reef

Acanthochromis Gill is a monotypic genus within the damselfish family Pomacentridae, erected for an unusual species [A. polyacanthus (Bleeker)] that uniquely lacks larval dispersal. Instead, offspring are reared in the parental territory, in the manner of cichlids, and fledged into the surrounding habitat. Phenotypic and genotypic variation was surveyed on the basis of body colouration and 7 polymorphic loci in 19 populations from 5 regions of the central and southern Great Barrier Reef (GBR). Variation in both characters was found at regional and local scales. Two colour morphs were recognised: a bicoloured morph from the three northern regions and a uniform dark morph from the two southern regions. Isozyme analysis showed a similar pattern with greatest variation between the different morphs, but also with significant variation at both regional and local scales within morphotypes. Heterozygosity was maximal in the central populations, which, together with other measures of variability, suggests a mixing of separate gene pools in this region and denies species status to the two morphotypes despite numerous fixed differences in allele frequencies between the most distant populations. The presence of fixed differences in multiple alleles between populations separated by 1000 km indicates negligible gene flow over such distances and long isolation of these gene pools. These patterns may reflect recolonisation of the GBR after the last sea-level rise by fish from two stocks. Founder effects and random drift in small populations after colonisation are probably the major sources of the local and regional variations observed at smaller spatial scales. This diversity has been maintained among populations at all scales by the very low levels of gene flow possible without an effective strategy for larval dispersal between coral reefs.     

Use of Historical Logging Patterns to Identify Disproportionately Logged Ecosystems within Temperate Rainforests of Southeastern Alaska

The forests of southeastern Alaska remain largely intact and contain a substantial proportion of Earth's remaining old‐growth temperate rainforest. Nonetheless, industrial‐scale logging has occurred since the 1950s within a relatively narrow range of forest types that has never been quantified at a regional scale. We analyzed historical patterns of logging from 1954 through 2004 and compared the relative rates of change among forest types, landform associations, and biogeographic provinces. We found a consistent pattern of disproportionate logging at multiple scales, including large‐tree stands and landscapes with contiguous productive old‐growth forests. The highest rates of change were among landform associations and biogeographic provinces that originally contained the largest concentrations of productive old growth (i.e., timber volume >46.6 m³/ha). Although only 11.9% of productive old‐growth forests have been logged region wide, large‐tree stands have been reduced by at least 28.1%, karst forests by 37%, and landscapes with the highest volume of contiguous old growth by 66.5%. Within some island biogeographic provinces, loss of rare forest types may place local viability of species dependent on old growth at risk of extirpation. Examination of historical patterns of change among ecological forest types can facilitate planning for conservation of biodiversity and sustainable use of forest resources. El Uso de Patrones Históricos de Tala para Identificar Ecosistemas Talados Desproporcionadamente en Bosques Lluviosos Templados del Sureste de Alaska Albert & Schoen 11‐839     

Spatial patterns of spawning in the coral-reef damselfish Dascyllus albisella

Reproductive patterns of the endemic Hawaiian damselfish Dascyllus albisella were examined around the island of Oahu for 5 m in 1992. Daily variation in spawning was studied at four spatial scales: individual territories; reef transects; whole patch reefs; and locations separated by>20 km. A 6 d, non-lunar nesting cycle was found for individual males, and a synchronized, 6 d, nonhinar spawning cycle was found within reef transects, whole patch reefs, and locations. Spawning synchronicity was maintained among reefs within a location. However, spawning among locations was found to be asynchronous, limiting the spatial scale of reproductive synchrony to>1 km but<20 km. Inherent benefits of synchronous reproduction are discussed for D. albisella, but only the localized swamping of planktonic predators may be an inherent benefit of synchronous spawning for this species. Alternatively, synchronous spawning among populations may exist from adults tracking local, favorable environmental conditions rather than having evolved towards an inherent benefit of synchronization.     

Lysozyme,chitinase and exo-N-acetyl-β-D-glucosaminidase (NAGase) in lymphomyeloid tissue of marine fishes

Lymphomyeloid (haemopoietic) tissues produce or store blood cells — among these leucocytes rich in lysosomal enzymes. The thymus, unlike the other lymphomyeloid tissues found in fish, produces exclusively lymphocytes. The carbohydrate-hydrolysing enzymes lysozyme (EC 3.2.1.17), chitinase (EC 3.2.1.14) and exo-N-acetyl--D-glucosaminidase (NAGase; EC 3.2.1.30) were assayed in various lymphomyeloid tissues of the cartilaginous fish Chimaera monstrosa, Squalus acanthias, Etmopterus spinax and Raja radiata, and in the thymus of the marine teleost Lophius piscatorius. Lysozyme activity was high in the cranial lymphomyeloid tissue of C. monstrosa; in Leydig's organ (oesophageal lymphomyeloid tissue) and the spleen from E. spinax; and in Leydig's organ, the epigonal organ and the spleen from R. radiata. Little or no lysozyme activity was found in Leydig's organ and the epigonal organ of S. acanthias, or in the thymus of C. monstrosa, R. radiata and L. piscatorius. The pH optima for lysozyme activities lay between 4.8 and 5.4 when assayed photometrically. Chitinase was most active at pH 1 in Leydig's organ from R. radiata, and at pH 2.7 in the epigonal organ from S. acanthias. The chitinolytic activity in Leydig's organ of E. spinax may be due to lysozyme. The optimum for NAGase activity in Leydig's organ from R. radiata lay at pH 4.0, that from S. acanthias and E. spinax at pH 4.5. The role of the enzymes in the defense against microorganisms and parasites is discussed.     

Differences in kelp morphology between wave sheltered and exposed localities: morphologically plastic or fixed traits?

The ability of algae to change the shape of their thallus in response to the environment may be of functional and ecological importance to the alga, with many species of macroalgae exhibiting a great range of morphological variation across wave exposure gradients. However, differences in morphology detected between sheltered and exposed environments cannot determine whether such differences represent plastic responses to the local environment or whether morphology is genetically fixed. This study tested for differences in the morphology of the common kelp, Ecklonia radiata, between wave sheltered and exposed environments, and reciprocally transplanted juveniles to distinguish the nature of such differences (i.e. plastic vs fixed traits). Differences between exposure environments were consistent with known effects of exposure (i.e. a wide, thin thallus at sheltered sites and a narrow, thick thallus with a thick stipe at exposed sites). The reciprocal transplant experiment confirmed that morphological plasticity was the mechanism enabling this alga to display different patterns in morphology between exposure environments. Individuals transplanted to the exposed environment underwent a rapid and extreme response in morphology, which was not apparent in individuals transplanted to the sheltered environment that responded more slowly. These results suggest that stressors typical of sheltered environments (i.e. diffusion stress) may not be as influential (if at all) compared to stressors typical of exposed environments (i.e. breakage, dislodgement) in differentiating morphological characters between exposure environments.     

Ecological studies on a tropical limpet Cellana radiata

Some aspects of the habitat zones, distribution pattern, and population density with reference to tidal levels of the tropical limpet Cellana radiata (Born) are presented. Observations have also been made on the homing behaviour of the limpet. Unlike the temperate limpets, no migration to different tidal levels during different seasons was observed in C. radiata.     

Flowering of the seagrass Posidonia oceanica in a north-western Mediterranean coastal area: temporal and spatial variations

Sexual reproduction in Posidonia oceanica (L.) Delile is likely to be highly variable both in space and time. However, there has been little effort to identify at what spatial scale variability exists in the distribution and abundance of reproductive shoots or the magnitude of these variations. Such information is important for elucidating several aspects of the reproductive strategy of this species. Here, by using a reconstructing technique, I estimated the rate at which flowering events occurred over the last decades in three P. oceanica meadows along the coastline of the north-western Mediterranean (Italy). Then, variation in inflorescence frequency (i.e. the percentage of shoots that flowered in a particular year of the total number of shoots present in the sample in that year) was examined on a hierarchy of spatial scales, ranging from a few metres to meadows separated by tens of kilometres over a 3-year period. Separate analyses were also conducted to examine the patterns of spatial variability of several plant characteristics (i.e. shoot age and density of vegetative shoots) that may influence the timing of flowering. In total, ten reconstructed flowering events were recorded during the period 1983–1999. Despite the similar climatic conditions experienced in the three meadows surveyed, no inflorescence scars were found in one meadow. In the other two meadows, the flowering rate fluctuated considerably from year to year (0–26%), and simultaneous flowerings were detected only in 3 years (1993, 1994 and 1995). The pattern of spatial variability in the inflorescence frequency varied among years. An investigation of the flowering events recorded along the north-western Mediterranean coast reveals that in the studied period flowering also occurred across a broad range of meadows. Therefore, flowering could be a far more widespread phenomenon in this sector of the Mediterranean basin than previously thought. Analysis of variance showed significant variation in 1993 at the mean inflorescence frequency on very small scales (metres to tens of metres), whereas variation was not found at any of the scales investigated in 1994 and 1995. Overall, variation in the inflorescence frequency within individual meadows (65–93%) was at least an order of magnitude greater than that among separate meadows (0.5–19%). Patterns of spatial variation in the plant characteristics examined did not reflect those of flowering. It may be hypothesised that internal rhythms of populations, in conjunction with changes in environmental conditions, which are consistent over relatively large spatial (kilometres), are involved in the control of flowering induction. Environmental heterogeneity (in terms of nutrient availability) on a very local scale (metres to tens of metres) and intrinsic factors might affect the distribution of reproductive shoots within P. oceanica meadows.Communicated by R. Cattaneo-Vietti, Genova     

Weak climatic control of stand-scale fire history during the late holocene

Forest fire occurrence is affected by multiple controls that operate at local to regional scales. At the spatial scale of forest stands, regional climatic controls may be obscured by local controls (e.g., stochastic ignitions, topography, and fuel loads), but the long-term role of such local controls is poorly understood. We report here stand-scale (<100 ha) fire histories of the past 5000 years based on the analysis of sediment charcoal at two lakes 11 km apart in southeastern British Columbia. The two lakes are today located in similar subalpine forests, and they likely have experienced the same late-Holocene climatic changes because of their close proximity. We evaluated two independent properties of fire history: (1) fire-interval distribution, a measure of the overall incidence of fire, and (2) fire synchroneity, a measure of the co-occurrence of fire (here, assessed at centennial to millennial time scales due to the resolution of sediment records). Fire-interval distributions differed between the sites prior to, but not after, 2500 yr before present. When the entire 5000-yr period is considered, no statistical synchrony between fire-episode dates existed between the two sites at any temporal scale, but for the last 2500 yr marginal levels of synchrony occurred at centennial scales. Each individual fire record exhibited little coherency with regional climate changes. In contrast, variations in the composite record (average of both sites) matched variations in climate evidenced by late-Holocene glacial advances. This was probably due to the increased sample size and spatial extent represented by the composite record (up to 200 ha) plus increased regional climatic variability over the last several millennia, which may have partially overridden local, non-climatic controls. We conclude that (1) over past millennia, neighboring stands with similar modern conditions may have experienced different fire intervals and asynchronous patterns in fire episodes, likely because local controls outweighed the synchronizing effect of climate; (2) the influence of climate on fire occurrence is more strongly expressed when climatic variability is relatively great; and (3) multiple records from a region are essential if climate-fire relations are to be reliably described.     

Patterns in reproductive dynamics of burrowing ghost shrimp Trypaea australiensis from small to intermediate scales

Many studies have examined latitudinal differences in reproduction of marine invertebrates, but few have measured variation at small to intermediate scales (kilometres to hundreds of kilometres), which may confound comparisons across broader geographic regions. Here, we examined variation in the reproductive biology of a little-studied species of burrowing ghost shrimp (Trypaea australiensis) at spatial scales ranging from km (between sites within estuaries) to 100s of km (among estuaries), over a 2-year period in south-eastern Australia. Sex ratios of populations were consistently biased towards females through time and space. Although reproduction started in summer months across all spatial scales, there was a pattern of earlier spawning from southern to northern estuaries. Integration of results from previous studies of T. australiensis supported a similar pattern of earlier breeding from high to low latitudes. Fecundity of shrimp increased linearly with female size, but the relationship varied inconsistently across the different spatial scales. Similarly, sizes at maturity varied from small to intermediate scales and observed patterns were not consistent with general predictions e.g. shrimp were smaller and ovigerous at smaller sizes at sites in the southern-most estuary, compared to estuaries further north. We found no differences in the sizes of embryos across the different spatial scales, but confirm that T. australiensis employs a strategy of high fecundity and small embryo size compared to other thalassinidean shrimp. Our results suggest that factors at smaller scales (e.g. food availability) may be important in affecting reproductive dynamics of T. australiensis, but further research is needed in testing hypotheses about patterns observed here. A lack of similar studies on other marine organisms remains an impediment to understanding life-history strategies and the sustainable management and conservation of populations.