Ocean current variability and the spawning season of Hawaiian reef fishes

Synopsis The spawning patterns of four Hawaiian reef fishes with similar reproductive habits, but different biogeographic distributions were studied from September 1980 to October 1981. Two species are Hawaiian endemics [Centropyge potteri (Pomacanthidae) and Chaetodon multicinctus (Chaetodontidae)] and the other two have pan-tropical Pacific distributions [Ctenochaetus strigosus and Zebrasoma flavescens (Acanthuridae)]. All showed increased spawning activity from January to July, the prevalent pattern among a majority of coastal marine fishes in Hawaii. Environmental correlatives to the period of peak reproduction include cycles of (a) daylight length and temperature which probably function as proximate cues and (b) seasonal variations in ocean current patterns which may ultimately affect survival of larvae and dispersal. Peak reproduction takes place during months when (1) mesoscale eddies most likely occur, and (2) the probability is greatest of drifting objects remaining near the islands.     

Small and impoverished regional species pools constrain colonisation of restored river reaches by fishes

1. Using an extensive data set from 18 river restoration projects in the lower mountain ranges of Germany and 5462 river reaches in their surroundings, we estimated the spatial extent of the regional fish species pool from which restored river reaches are colonised. 2. Restoration resulted in a marginally significant increase in fish species richness; however, restored reaches still deviated markedly from natural reference conditions. Nearly all (96.6%) species occurring in restored reaches were present in reaches within a distance of 5 km up‐ or downstream of the restored reach. 3. Species richness in restored reaches was correlated with species richness within a 5‐km species pool. This relationship was more pronounced for common than for rare fishes and applied to both the total number of fish species at the restored reach and the number of additional fish species that were not present at unrestored conditions. 4. The richness of the regional species pools was greatly impoverished. On average, only 50% of all species considered to represent natural reference assemblages were present. The limited success in establishing natural fish assemblages in restored reaches was attributed to spatial limitation (e.g. due to fragmentation) and an impoverished regional species pools from which restored reaches recruit. 5. We recommend that integrated river restoration management should consider not only the abiotic prerequisites of successful restorations, but also the structure and quality of the regional species pool.     

Strip counts as a means of determining densities and habitat utilization patterns in lake fishes

Synopsis The strip count method of determining fish densities was investigated for a small lake in a series of inshore sites that differed in their physical and biological characteristics and in the communities of fishes present. Overall total numbers of fish, number of species, ratio of commonest to total species, and 2nd commonest to total species, were investigated. Counts were made during time of the feeding peaks.Repeatability of the method was tested by series of five traverses at 10-minute intervals and was good both for total numbers of fish and ratio of commonest species to total fish. However, it varied with the habitat type, being excellent for small semi-isolated weedy sites, good for gravel-bottom sites, but only fair in open sandy bays where the strip was laid in the middle of an extensive area of homogeneous habitat.Series of comparative counts made (a) between morning and afternoon on the same day and, (b) between successive mornings, to determine how constant populations were between these time intervals, proved to be within the same general range but were significantly different by the Mann Whitney U test at the = 0.05 level.In small lakes the strip count method proves to have considerable potential in the study of habitat specializations, taxocene structures, and relative abundances.     

SMURFs: standard monitoring units for the recruitment of temperate reef fishes

I evaluated a standard monitoring unit for the recruitment of reef fishes (SMURF) as a tool for ascertaining spatial and temporal patterns of reef fish recruitment in central California, USA. SMURFs consisted of a 1.0×0.35 m dia. cylinder of fine mesh plastic grid that contained a folded section of larger mesh plastic grid. SMURFs collected new recruits of 20 species of fish with 92% of the individuals collected from 10 species, mostly rockfish (genus Sebastes). An experiment varying depth of SMURFs in the water column (surface, mid-depth, or bottom) showed that surface SMURFs collected the greatest diversity of species and significantly greater abundance for eight species, with two species having significantly greater abundance on mid-depth SMURFs and three species having significantly greater abundance on bottom SMURFs. A comparison of cumulated recruitment from SMURFs that varied in sampling frequency (removal of new recruits every 1-3, 7, or 28 days) suggested that increasing the time between sampling caused a significant decrease in recruitment estimates for some species but not for others. To determine how well temporal patterns of recruitment to SMURFs reflected patterns to nearby reefs, I compared within season temporal patterns of recruitment to SMURFs with that at nearby reefs, estimated by visual transect surveys conducted on scuba. Temporal patterns of recruitment to SMURFs were significantly and positively related to early recruitment on reefs for one group of benthic-algal associated rockfish species when diver surveys were lagged by 30 days (r=0.87) and for another group of canopy-algal associated rockfish species when lagged by 5 days (r=0.72). SMURFs appeared to be an effective and efficient method for indexing relative rates of delivery of competent juveniles for many temperate nearshore reef fishes.     

Behavioral thermoregulatory abilities of tropical coral reef fishes: a comparison with temperate freshwater and marine fishes

Synopsis Eight species in six different families of tropical marine reef fishes from the Indo-West Pacific region (Naso lituratus, Zebrasoma.flavescens, Balistes fuscus, B. vidua, Forcipiger longirostris, Echidna zebra, Cromileptes altivelis, Canthigaster jactator) were tested for ability to thermoregulate behaviorally in electronic shuttleboxes. All of these species preferred mean temperatures between 20 and 30°C, but differed considerably in thermoregulatory precision. All species avoided lethal high or low temperatures (i.e., they did not die during the tests), and some species thermoregulated as precisely as temperate species. Some temperate species prefer higher temperatures (above 30°C) than do these tropical reef species.     

Phylogeography and the conservation of coral reef fishes

Here we present a review of how the study of the geographic distribution of genetic lineages (phylogeography) has helped identify management units, evolutionary significant units, cryptic species, and areas of endemism, and how this information can help efforts to achieve effective conservation of coral reefs. These studies have confirmed the major biogeographic barriers that were originally identified by tropical species distributions. Ancient separations, identified primarily with mtDNA sequence comparisons, became apparent between populations on each side of the barriers. The general lack of correlation between pelagic larval duration and genetic connectivity across barriers indicates that life history and ecology can be as influential as oceanography and geography in shaping evolutionary partitions within ocean basins. Hence, conservation strategies require a recognition of ecological hotspots, those areas where habitat heterogeneity promotes speciation, in addition to more traditional approaches based on biogeography. Finally, the emerging field of genomics will add a new dimension to phylogeography, allowing the study of genes that are pertinent to recent and ongoing differentiation, and ultimately providing higher resolution to detect evolutionary significant units that have diverged in an ecological time scale.     

The influence of plant cover on surfperch abundance at an offshore temperate reef

Synopsis At an offshore reef near Santa Barbara, southern California, young-of-year (young) of five surfperch species (Embiotocidae: Embiotoca jacksoni, E. lateralis, Hypsurus caryi, Rhacochilus toxotes, Damalichthys vacca) once thrived in a dense kelp understory of Pterygophora californica and Laminaria farlowii, but disappeared after a severe storm in February, 1980 deforested their habitat. Measurements of fish density and kelp cover made before deforestation indicated that the young surfperch appeared in the spring and disappeared in the fall as cover increased and declined. Adult surfperch and large kelp bass (Paralabrax clathratus), which can eat young but not adult surfperch, remained all year. We tested to see if kelp cover was an essential refuge for the young by pruning back (thinning) kelp blades from one of two transects. The thinning caused a significant redistribution of young which clearly avoided open spaces, but not of adults which are less vulnerable to predation. Measurements of fish density made after the storm-induced deforestation showed that adult surfperch and kelp bass still remained abundant even after the young surfperch were gone. Only after an abrupt reforestation in 1983, more than a year after the present study was terminated, were young once again seen on the reef. Although young surfperch may seek tiny prey living on kelp blades, most lines of evidence indicated that the distribution of the young is more a response to risk of predation. Hence the extent of kelp understory was probably the main determinant of the survival of young surfperch on the reef.     

Assemblages of dytiscid predators and culicid prey in relation to environmental factors in natural and clear-cut boreal swamp forest pools

Assemblages of diving beetles (Dytiscidae) and mosquito immatures (Culicidae) were studied during 1987–1988 in 40 small, more or less temporary, snowmelt pools in spruce swamp forest and clearings at the Arctic Circle in Sweden. Larger pools were warmer than smaller ones, and clearing pools were warmer than forest pools. Temperature differences between pools remained high until late July. Twenty-one dytiscid species, representing three guilds, occurred in the pools, and individual pools had 1–13 species. Ten species occurred in both habitats. A few stenotopic species of boreal swamp forests had in clearing pools apparently been replaced by some species with a preference for more productive, often man-made habitats. Six Aedes species were collected in the clearing pools. Five of these were found in the forest pools, of which three had no mosquito larvae. Dytiscid assemblages in both habitats and culicid assemblages in clearing pools showed strong nested patterns.Abundance and species richness of both culicids and dytiscids were higher in clearing than in forest pools with an area >2 m² after that the effects of pool area had been accounted for (MANCOVA). In both habitats, abundance and species richness of both culicids and dytiscids were strongly and positively correlated with a linear combination of pool area, depth and temperature (Canonical Correlation). Increasing drought frequency of pools had a negative, less significant effect on the biota. In the clearing, the abiotic correlations with abundance were somewhat weakened chiefly by the relatively low abundance values from the largest pool.Distribution and mean abundance of individual dytiscid species were positively related in the clearing pools. Flying dytiscids were trapped in the larger (1.6 m²), but not in the smaller (0.07 m²) artificial pools, and the immigration rate was markedly higher on clearings than in forest. Dug pools were colonized faster on clearings than in forest. Even the flightless Hydroporus melanarius colonized dug pools during the first year.     

Temporal patterns in ambient noise of biological origin from a shallow water temperate reef

A systematic study of the ambient noise in the shallow coastal waters of north-eastern New Zealand shows large temporal variability in acoustic power levels between seasons, moon phase and the time of day. Ambient noise levels were highest during the new moon and the lowest during the full moon. Ambient noise levels were also significantly higher during summer and lower during winter. Bandpass filtering (700-2,000 Hz and 2-15 kHz), combined with snap counts and data from other studies show that the majority of the sound intensity increases could be attributed to two organisms: the sea urchin and the snapping shrimp. The increased intensity of biologically produced sound during dusk, new moon and summer could enhance the biological signature of a reef and transmit it further offshore. Ambient noise generated from the coast, especially reefs, has been implicated as playing a role in guiding pelagic post-larval fish and crustaceans to settlement habitats. Determining a causal link between temporal increases in ambient noise and higher rates of settlement of reef fish and crustaceans would provide support for the importance of ambient underwater sound in guiding the settlement of these organisms.     

The biogeography of lower Mesoamerican freshwater fishes

Aim This paper examines the importance of regional processes in determining the patterns of distribution and diversity of lower Mesoamerican freshwater fishes. Location We focused our analyses on the lower Mesoamerican region, which we define to include all the rivers of Panama and Costa Rica. The geographic boundaries are the Colombian Choco to the south and Lake Nicaragua to the north. Methods We described the biogeographical provinces of lower Mesoamerica (LMA) using presence/absence data of primary and secondary LMA freshwater fishes. We conducted subsequent analyses at the spatial resolution of the biogeographical provinces and described patterns of community composition, species richness, endemism, range size, and the permeability of dispersal barriers between biogeographical provinces. Results This study represents the first attempt since that of W. A. Bussing in 1976 to investigate the biogeographical regions of Mesoamerica, and our analyses demonstrate increased regional complexity in biodiversity patterns relative to previous studies. Changes in community composition across LMA clearly highlight the importance of both extrinsic geological processes and intrinsic biological differences among freshwater fish species in shaping the dispersal and diversification histories of the LMA freshwater fish fauna. The influence of biology and geology is also exemplified by patterns of endemism and turnover between biogeographical provinces, which suggests that the relative importance of regional speciation and dispersal varies spatially across the LMA landscape. Finally, it would seem to follow that secondary freshwater fishes will have larger range sizes than primary fishes as a result of the increased salinity tolerance posited for the former group, and thus the increased probability of dispersal along coastlines. We did not, however, find a significant difference between the average range size of primary and secondary freshwater fishes, indicating that the putative differences in physiological tolerance to seawater between the two groups are not reflected in their distribution patterns at the scale of LMA. The geometric distribution of range size of LMA freshwater fishes suggests that dispersal of both primary and secondary freshwater fishes along coastlines must be infrequent. Main conclusion The observation that regional processes exerted a strong influence on the assembly and maintenance of LMA freshwater fish communities has important consequences for both theory and conservation. We suggest that large‐scale biogeographical analyses are required to illuminate the backdrop upon which local interactions play themselves out, supporting a top‐down approach to the study of biological diversity. Our results also identify areas of high conservation priority, providing a baseline for informing conservation strategies for freshwater fishes in LMA. We conclude by calling for conservation planning and action that acknowledges the importance that regional processes play in determining patterns of organismal diversity, and that incorporates these processes in strategies to conserve remnant biological diversity.     

Impact of municipal effluents and hydrological regime on myxozoan parasite communities of fish

Increased productivity from sewage effluents can enhance species richness locally. Results from a study of spottail shiners (Notropis hudsonius) in 1999 showed that prevalence and the mean number of myxozoan parasite species per host were higher downstream of the wastewater outflow from the Island of Montreal than upstream in the St. Lawrence River, Quebec, Canada. This was attributed to organic enrichment of the sediments which presumably lead to increased densities of oligochaetes, the alternate hosts, downstream of Montreal. Spottail shiners subsequently were collected every August/early September in 2001–2004 to examine the stability and repeatability of these patterns. Prevalence and mean number of myxozoan species per fish typically were again higher downstream of the sewage source each year compared to upstream, although there was no significant difference in these measurements pooled across years between localities immediately upstream and downstream of the effluent outflow. Density of the oligochaete Limnodrilus hoffmeistereri, a common alternate host of myxozoans, was much higher at two downstream localities than at an upstream one. At a larger spatial scale, mean myxozoan infracommunity richness across sites in the St. Lawrence River was negatively correlated with mean water levels measured in the 3 months prior to fish sampling. Results suggest that on a local scale, variations in prevalence and diversity among localities are influenced by municipal effluents, but that at a landscape scale annual variations across sites are affected by the hydrological regime and climate. In effect, water level fluctuation had a landscape-wide impact that was superimposed over pollution-induced local variations.     

Diel distribution patterns of fishes in a temperate large lowland river

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid‐channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes.     

Long‐term population trends in three grassland insect groups: a comparative analysis of 1951 and 2009

Development of farming practices has caused drastic changes in European agricultural landscapes during the past 50 years. As a consequence of these changes, insect diversity is widely expected to decline. We performed a comparative analysis with long‐term data of three insect groups: Auchenorrhyncha, Heteroptera and Orthoptera. In 2009, we revisited nine grassland sites in northern Germany that were originally sampled in 1951 using the same techniques and during a similar time frame. We found that the insect community exhibited no consistent trends between years. Species richness of Auchenorrhyncha and Heteroptera increased on plot level as well as on landscape level but remained unchanged for Orthoptera. Abundance of Auchenorrhyncha and Orthoptera significantly decreased, while Heteroptera increased. There is a strong trend towards homogeneity in community composition for Heteroptera and a weak one for Auchenorrhyncha. The frequency and abundance of species preferring disturbed and/or eutrophic habitats increased, whereas the number of species preferring low‐productive habitats declined. This trend is especially pronounced in Auchenorrhyncha. Generalistic species were more abundant in relative proportions as well as in absolute numbers. We hypothesize that these trends arise from alterations of Central European landscapes because of agricultural intensification over the last several decades.     

The role of herbivorous fishes and urchins in coral reef communities

Synopsis Herbivorous fishes and invertebrates are conspicious elements of coral reef communities where they predominate both in numbers and biomass. Herbivores and the coral reef algae on which they feed represent a co-evolved system of defense and counter-defense. Algal species have developed toxic, structural, spatial and temporal defense or escape mechanisms, while the herbivores employ strategies that involve anatomical, physiological and behavioral adaptations. Current research demonstrates that many reef fishes are highly selective in the algae they consume. Food selection in these fishes may be correlated with their morphological and digestive capabilities to rupture algal cell walls. Sea urchins select more in accordance with relative abundance, although certain algal species are clearly avoided.The determinants of community structure on coral reefs have yet to be established but evidence indicates a strong influence by herbivores. Reef herbivores may reduce the abundance of certain competitively superior algae, thus allowing corals and cementing coralline algae to survive. We discuss how the foraging activities of tropical marine herbivores affect the distribution and abundance of algae and how these activities contribute to the development of coral reef structure and the fish assemblages which are intimately associated with reef structure.This paper forms a part of the proceedings of a mini-symposium convened at Cornell University, Ithaca, N.Y., 18–19 May 1976, entitled Patterns of Community Structure in Fishes (G. S. Helfman, ed.).     

Abundance and species richness patterns of diving beetles (Coleoptera, Dytiscidae) from exposed and protected sites in 98 northern Swedish lakes

Forty species of predaceous diving beetles (Coleoptera, Dytiscidae) were collected in sweepnet samples from 98 boreal lakes in northern Sweden. Samples from protected sites with vegetation had significantly more specimens and species than those from exposed sites without vegetation in the same lakes. No geographically based differences, e.g. latitudinal or in distance from the coast, were found. These gradients were 200 and 150 km long, respectively. Species' distribution in terms of occurence at number of sites was positively correlated with the mean abundance of the species. The relationship between species' abundance and body length was characterized by the lack of large, abundant species. Partial least square regressions on dytiscid abundance and species richness showed low predictive power of lake area, altitude and water chemistry. The seven environmental variables used explained at best 15.3 and 24.4% of the total variance in abundance and species richness, respectively. The results are compared to activity trap catches of dystiscids in lakes in an adjacent region. A majority of the species occured in both materials. However, species occuring in high proportion in one of the materials, were rare in the other material. The mean body length of the species caught more efficiently with traps was not larger than that of those overpresented in net sampling. Based on this study and the available literature data, the regional species pool of boreal lake dytiscids is estimated to 30–40 species. It is still an open question if lake assemblages are markedly poorer than those found in the development of vegetation, whereas the impact of water chemistry is small.     

热带森林树种多度和丰富度空间分布特征研究

用巴拿马50 hm2森林动态监测样地内直径≥1 cm的树种资料,分析了该样地树种多度(个体数)和丰富度(物种数)及其方差和变异系数在6个取样尺度(5 m×5 m,10 m×10 m,20 m×20 m,25 m×25 m,50 m×50 m,100 m×100 m)的变化规律.结果显示:(1)由于多度的可加性,不同取样尺度在样地内树种多度的变化表现出一致性;随取样尺度的增加,多度方差呈线性增加,而变异系数呈线性减小.(2)丰富度随取样尺度的变化较为复杂,随取样尺度的增加,丰富度方差呈非线性变化,在取样尺度为25 m×25 m时方差最大;变异系数随取样尺度的增加而呈线性减小.研究表明,大尺度的多度值可以由小尺度的多度值通过外推法估计,而丰富度却不能,在生物多样性的保护和管理中不能简单地从一个取样尺度的生物丰富度推测另一个取样尺度丰富度.     

Growth and reproduction in Canthigaster valentini (Pisces,Tetraodontidae): a comparison of a toxic reef fish with other reef fishes

Synopsis The growth and reproduction of Cantigaster valentini were studied in two sites at Lizard Island, Australia. C. valentini was found to be a gonochore, with a sex ratio very close to 1:1; sexes could be distinguished externally. The growth (in length) of known individuals from both sites was measured at least every two months over two years. Growth rates of males and females decrease as their sizes increase. Growth rates differ between sexes and between sites: males generally grow faster than females and individuals at Mermaid Cove generally grow faster than individuals at Palfrey Island. Spawning is demersal, it occurs daily between 0800 and 1600h, and continues year-round. For females the interval between successive spawnings varies from about 4 days in the warm-water season to about 10 days in the cool-water season. From a comparison of local reproductive output and local recruitment survivorship of larvae in the plankton was estimated to be much higher than in another species (Pomacentrus wardi) for which a similar estimate was available. We suggest that some aspects of the reproductive strategy of C. valentini differ from other, non-toxic reef fishes in ways consistent with a reduced threat of predation upon adults, eggs, and larvae: courtship and spawning are unhurried and occur throughout most of the day; spawning is unrelated to lunar cycles; there is no parental care or defense of fertilized eggs; and embryos often hatch on rising tides.Centre for Environmental and Urban StudiesSenior author's present address: School of Biological Sciences F07, University of Sydney, Sydney 2006, N.S.W., Australia