Substratum Preferences Research Articles

Characterization of the typical fish community of inland waterways of the north-eastern lowlands in Germany

A representative number of 11 inland waterways of the north-eastern lowlands in Germany was surveyed between 1992 and 1994 using different fishing methods. Data were pooled for sites and waterways. From the 234 sites investigated, a total of 53 432 fish were collected and 29 species recorded. The typical fish assemblage of the waterways was subdivided into three defined classes according to presence and relative abundance of species: reference, accompanying and minor species. The fish fauna was characterized by the dominance of roach (Rutilus rutilus) and perch (Perca fluviatilis). Both fish species showed a mean abundance of 70·61 % (SD=10·91 %), whereas more than half of the species recorded had a relative abundance < 1%. Two trends could be identified in the fish assemblage owing to human influences: an increase in the dominance of roach and perch and a decrease in species number. In particular, intolerant fish with a preference for sand or gravel substrata and current diversity have become rare and endangered. The typical fish assemblage of waterways in the lowlands differed from that in the uplands with respect to the higher abundance of rheophilic lithophils in the uplands. © 1997 John Wiley & Sons, Ltd.

Relationships between recruitment and postrecruitment processes in lagoonal populations of two coral reef fishes

Pomacentrus amboinensis Bleeker and Dascyllus aruanus (L.) exhibit similar large scale patterns in recruitment to One Tree lagoon, southern Great Barrier Reef. They recruit in greatest numbers near the windward perimeter compared with the centre of the lagoon, and at the perimeter, recruit preferentially to deeper sites (4–8 m depth). This pattern was observed in recruitment to standard coral heads of Pocillopora damicornis (L.), a preferred substratum transplanted to a range of locations and depths. As substratum was held constant, spatial variation in recruitment was not determined by the availability of suitable habitat. Patterns in growth and mortality of the two fish species were monitored for juveniles transplanted to another set of standard coral heads, in order to determine whether post-recruitment processes would reinforce or disrupt patterns established at the time of recruitment. The two species exhibited contrasting patterns. Pomacentrus amboinensis exhibited faster growth and better survivorship at deeper sites, regardless of the location in the lagoon, reinforcing the initial pattern. Dascyllus aruanus exhibited faster growth at perimeter sites and significantly better survivorship at central sites, patterns that would tend to disrupt the initial pattern. Within locations, individuals exhibiting slower growth rates ( Pomacentrus amboinensis) or smaller initial size ( Dascyllus aruanus) had reduced life expectancy. The results suggest that location selection by settlers of Pomacentrus amboinensis results in improved growth and/or survival. This was not the case for Dascyllus aruanus, which is probably more influenced by the presence of conspecifics. However, even for Pomacentrus amboinensis, large-scale patterns probably reflect constraints on habitat selection. Recruitment in Pomacentrus amboinensis was consistently lower to sites immediately down current of other reefs, regardless of their position. I suggest that the absence of recruits of both species to central sites indicates that this region is a recruitment-shadow. Juveniles settle in preferred habitat at the first opportunity after entering the lagoon, leaving much of the preferred habitat in the centre of the lagoon unoccupied. Patterns are initially recruitment-determined, but either reinforcement or disruption mean that the numerical abundance of adults cannot be predicted on the basis of recruitment data alone.

Substratum preferences by larvae of three species of midge (Diptera: Chironomidae)

Three chironomid midge (Diptera: Chironomidae) species (Cricotopus sylvestris (Fabricius); Psectrocladius limbatellus (Holmgren), Tanytarsus fimbriatus Reiss and Fittkau) live at high densities and dominate the midge assemblage found in slow sand filter beds. After filter beds are drained and cleaned, the substratum consists of sand of different particle sizes, but once beds are refilled and in operation, organic material accumulates on the sand and Cladophora grows. In laboratory experiments, we found that larvae of the three midge species preferred different substratum types: C. sylvestris preferred sand to both Cladophora and organic material, P. limbatellus preferred Cladophora, and Tanytarsus sp. preferred organic material. Some evidence of preference for one particle size was also found, but compared with substratum types, this was neither as marked or contrasting between the three species. The contrasting preferences that we found in the laboratory suggest that the substratum will influence the microdistribution of the three species in filter beds, and provide further evidence of the importance of substratum in midge assemblages.

Response of mud crab (Panopeus herbstii) megalopae to cues from adult habitat

During the summer of 1995, we investigated the response of mud crab megalopae (Panopeus herbstii Milne-Edwards) to cues associated with adult habitat. Natural rock/shell substratum and the rock-associated seaweed, Fucus vesiculosus L., both induced metamorphosis of competent megalopae; natural sand substratum did not induce metamorphosis. Structural mimics of preferred substrata induced metamorphosis only when covered with natural biofilm. Clean mimics did not induce metamorphosis. Water-soluble exudates from preferred substrata showed weak induction of metamorphosis. Exudates from adult P. herbstii elicited a similar weak response. Exudates from another species of crab and from two fish predators did not induce metamorphosis. We conclude that water-soluble cues associated with major components of preferred adult habitat induce the metamorphic molt of P. herbstii megalopae. The three-dimensional structure of the substratum is not important in induction of metamorphosis, but the biofilm associated with preferred substratum plays a critical role. It is not clear whether the biofilm produces the water-soluble cue or simply provides a tactile stimulus that works in conjunction with the soluble cue.

Interspecific competition and habitat selection by the riverine dragonfly Onychogomphus uncatus

1. Substratum selection by the burrowing larvae of the dragonfly Onychogomphus uncatus was examined in an artificial laboratory stream at different larval densities and in the presence of one of three other dragonfly species.2. The larvae of O. uncatus, as well as those of the other species, clearly preferred gravelly sand substratum rather than gravel or stone.3. At low larval density (71.4 m–2) in the stream, 83% of the O. uncatus were found in gravelly sand. An increase of larval abundance in the stream to 202.4 specimens m–2 resulted in greater density in all substrata, but this increase was proportionally lowest in gravelly sand.4. The presence of a second species had various effects on the microdistribution of O. uncatus. In the presence of Gomphus simillimus or Cordulegaster boltoniiimmaculifrons the distribution of O. uncatus changed significantly; their density increased in the normally less preferred substrata. This effect is interpreted as asymmetric interspecific interference. The presence of a third species, Onychogomphus forcipatus unguiculatus, had no effects.

Induction of Metamorphosis in Larvae of a Sponge

Elevated exogenous KC1 and CsCl are effective artificial metamorphic triggers for many, but not all, invertebrate larvae. Neither taxonomic nor functional patterns in their effectiveness, however, are apparent. In our experiments, elevated exogenous KC1 promoted metamorphosis of larvae of the demosponge Aplysilla sp., but only when applied simultaneously with a biofilmed artificial substratum. Although the presence of this artificial substratum alone significantly enhanced settlement over seawater controls, its effectiveness was further augmented significantly in the presence of elevated KC1, indicating a synergistic interaction. Exposure of larvae to a 2-min pulse of 30 mM KC1 promoted metamorphosis as effectively as continuous exposure to 30 mM KC1. Moreover, 30 mM CsCl proved an effective trigger of metamorphosis both in the absence and presence of a biofilmed substratum. As with KC1, the CsCl data indicate the presence of a synergistic interaction between CsCl and the biofilmed substratum. This report provides preliminary insights into the induction of settlement and metamorphosis of sponges, metazoans which lack established sensory and neuronal elements, and it permits comparison with responses of eumetazoans. Additional key words: Porifera, Aplysilla, KC1, CsCl, settlement Sponges represent a grade in metazoan evolution for which the presence of neuronal cells and differentiated receptor cells is unconfirmed (Harrison & De Vos 1991). Additionally, sponge larvae are considered generally nonspecific in substratum preferences at settlement and metamorphosis (Bergquist 1978). The receptor site(s) and the internal pathway(s) of the metamorphic response in sponges remain unexplored. Elevated concentrations of exogenous K+ (as KC1) are effective in inducing larval settlement and metamorphosis in species of a wide range of marine invertebrates including a hydrozoan (Spindler & Muller 1972; Muller & Buchal 1973), a polychaete (Yool et al. 1986), at least 15 gastropods (Baloun & Morse 1984; Yool et al. 1986; Pechenik & Heyman 1987; Hubbard 1988; Davis et al. 1990; Todd et al. 1991; Inestrosa et al. 1993; Pechenik & Gee 1993; Campos et al. 1994; Gibson & Chia 1994; Yang & Wu 1995), a bivalve (Nell & Holliday 1986), a phoronid (Herrmann 1979), a brachiopod (Freeman 1993), 5 bryozoans (Eiben 1976; Stricker 1989; Wendt & Woollacott 1995), and 3 echinoderms (Cameron et al. 1989; Pearce & Scheibling 1994). Evidence indicates, however, that supplemental K+ is not a global inducer as aTo whom correspondence should be addressed. it is ineffective in stimulating settlement and metamorphosis in species of certain other marine invertebrates (at least at the concentrations tested) including 2 corals (Morse et al. 1988), 2 bivalves (Eyster & Pechenik 1987; Gustafson et al. 1991), 2 echinoderms (Rowley 1989; Johnson et al. 1991), and 2 ascidians (Grave & Nicoll 1940; Lynch 1961). In the barnacle Balanus amphitrite, supplemental K+ even inhibits settlement (Rittschof et al. 1986). Inspection of these data reveals little in the way of phylogenetic patterns in larval responses to K+. Only in 3 taxa (echinoderms, gastropods, and bryozoans) are responses of more than 3 species established. In gastropods and bryozoans, excess K+ was uniformly effective as an inducer of settlement and metamorphosis. In contrast, data on echinoderms (and smaller data sets on cnidarians and bivalves) indicate that larvae of some species within each group are affected by elevated K+ whereas others are not. Responses of larvae within deuterostome and protostome assemblages are also mixed. Finally, where response to elevated K+ varies within a clade, it does not correlate with overall differences in known features of developmental and larval biology. At present, an encompassing synthesis of K+ induction remains elusive from phylogenetic perspectives. To expand on this taxonomic baseline This content downloaded from 157.55.39.186 on Sun, 09 Oct 2016 06:18:30 UTC All use subject to http://about.jstor.org/terms Woollacott & Hadfield and to address the induction pathway in sponges, we examined responses of larvae of the demosponge Aplysilla sp. to elevated exogenous K+ and Cs+. Aplysilla sp. retains its early developmental stages and releases short-lived parenchymella larvae that are anenteric and, presumably, incapable of feeding on particulate matter (Woollacott & Hadfield 1989 [as Dendrilla cactus]; Woollacott & Pinto 1995). Most of the larval surface is comprised of a uniform field of flagellated (monociliated) cells. The anterior end (that facing forward during swimming) is cap-like and formed by larger flagellated cells. The posterior pole bears a tuft of long flagella. On release, larvae are initially strongly positively phototactic, but the strength of this response gradually diminishes during the swimming period.

The structure and components of European estuarine fish assemblages

This paper discusses the structure of fish assemblages using information from 17 European estuarine areas (in the British Isles, Portugal, Belgium, France, the Netherlands, Germany, Norway and Spain). Binary (presence/absence) and quantitative data for each assemblage have been used to assess the assemblage structure according to taxonomy (i.e. species identity). Following this, a total of 29 functional guilds were created in order to describe the use made of an estuarine area for each taxon encountered: feeding preferences, reproduction type, substratum preferences (for bottom dwelling fish) and position within the water column (vertical preference guild). The paper focuses on the designation and determination of the proportions of the guild members of the fish assemblage within each estuary. Ecological guilds within the assemblage include estuarine residents, marine juvenile migrants, catadromous and anadromous migrants, marine seasonal users, and freshwater and marine adventitious species. Feeding guilds include detritivores, planktonic feeders, infaunal croppers and sediment ingesters, piscivores, and active predators of mobile crustaceans. Reproduction guilds include planktonic and demersal spawners and those using brood-protection. The substratum preference indicates the proportions of sand, mud, rock and vegetation dwellers, and the vertical preference denotes benthic, demersal or pelagic species. The analysis has allowed both the estuaries to be grouped according to taxonomic and guild similarity and the characterisation of a typical European estuarine fish assemblage. Within the limits posed by differing sampling methods, times of sampling and survey rationale, there is a high similarity between estuaries. The data indicate common patterns of estuarine usage irrespective of the differences between the estuaries although such patterns cannot be interpreted fully given the incomplete knowledge of their physical and anthropogenic characteristics.

Sediment preference in juvenile pacific flatfishes

Behavioural preference tests were used to determine if sediment selection played a role in habitat choice. Four species of juvenile pleuronectids were given a choice of eight sediments in a carousel and final choices were recorded after 20 h. Juvenile flatfishes demonstrated strong selection for sediments less than 500 μm. Juvenile starry flounder ( Platichthys stellatus) selected larger particles with increasing fish size. Starry flounder under 25 mm in length chose mud, 50–80 mm fish chose mud and mixed mud sediments and larger juveniles (>150 mm) confined themselves to find sand. Juvenile halibut ( Hippoglossus stenolepis) at 50–80 mm preferred a combination of mud and fine sand and were spatially segregated. Yellowfin sole ( Pleuronectes asper) at 50–80 mm showed a slight preference for mud and mixed mud sediments over sand, a selection that became stronger in larger (>150 mm) fish. Juvenile rock sole ( Pleuronectes bilineatus) at 50–80 mm preferred substrata of sand and mixed sand nearly 90% of the time. All species seldom selected sediments which were too coarse to allow the flatfishes to bury themselves, such as granular or pebble substrata. The results of these laboratory studies can be used to predict the distribution of juvenile flatfishes in a nursery area.

Microbial production and degradation of γ-aminobutyric acid (GABA) in the abalone larval settlement habitat

Abstract By producing or degrading gamma-aminobutyric acid (GABA), microbes may affect the settlement of abalone (Haliotis) larvae. GABA was not detectable in extracts of crustose red algae (CRA) which are the preferred settlement substratum for Haliotis larvae. The CRA surfaces and their associated biofilms did not produce GABA from glutamate, and GABA production from putrescine required gabaculine (transaminase inhibitor). The GABA-degrading activity on the CRA surfaces was removed by surface-sterilisation. It ranged from 0.45 to 1.12 nmol cm−2 h−1 with insignificant seasonal variation. Removal of grazing molluscs from CRA-covered stones led to the growth of a visible biofilm and markedly increased GABA degradation in 2 weeks. Within a few days of placing clean, sterile glass surfaces in the settlement environment, biofilms with GABA-degrading activity developed, and after 11 weeks incubation the GABA degradation rate on glass marbles was 0.37 nmol cm−2 h−1. GABA was not completely oxidised, and the products of GABA metabolism showed similar chromatographic behaviour to alanine and glutamate. In the typical New Zealand Haliotis settlement habitat, GABA is not likely to play a significant role as an inducer of abalone larval settlement because on the preferred settlement surfaces it is not readily produced from its precursors but it is easily degraded.

Life History and Habitat of the Endangered Dwarf Wedgemussel Alasmidonta heterodon (Bivalvia:Unionidae)

The reproductive cycle, population demographics, and habitat use of the dwarf wedgemussel (Alasmidonta heterodon) were studied in populations from the Tar River, North Carolina, and Aquia Creek, Virginia, during 1991 and 1992. The mussel is a long-term brooder, spawning in late summer and becoming gravid in fall. Laboratory infestations with glochidia on 15 species of fish confirmed three hosts for A. heterodon: tessellated darter (Etheostoma olmstedi), Johnny darter (E. nigrum), and mottled sculpin (Cottus bairdi). Six species of sunfishes, four minnows, one sucker, and one catfish tested in the laboratory did not serve as hosts. Age and growth characteristics were calculated using a thin sectioning technique on valves collected from the Tar River, Aquia Creek, and Neversink River, New York. As computed by the von Bertalanffy equation, the dwarf wedgemussel reaches a maximum length of 38.70 mm, 45.26 mm, and 45.84 mm in the Tar River, Aquia Creek, and Neversink River, respectively. There were significant differences in growth rates of A. heterodon from the Tar River and Aquia Creek and between populations in the Neversink River and Aquia Creek. There was no significant difference in growth rate of populations from the Tar and Neversink rivers. Age-class distribution of live mussels collected at the three sites was estimated using age-length keys. The Tar River population included year classes from 4 to >6 years. Excessive shell erosion prevented the aging of older individuals and thus, a key to include larger live individuals. The age class distribution of the Aquia Creek population ranged from 2 to 9 years, while the Neversink River population was represented by age 1 to 8 year classes. The von Bertalanffy growth equations for the Tar River, Aquia Creek, and Neversink River populations were as follows: L_t = 38.70 mm (1-e^{-0.299(t+0.251)}; L_t = 45.26 mm (1-e^{-0.260(t+0.244)}); and L_t = 46.84 mm (1-e^{-0.207(t+0.335)}), respectively. Habitat-suitability experiments were conducted in the laboratory to determine preferred substratum size and water velocity. Dwarf wedgemussels always preferred the finer substratum offered, but little preference was shown for lotic versus lentic flow regimes.

Fish feeding on mobile benthic invertebrates: influence of spatial variability in habitat associations

Patterns of habitat association and foraging were examined for a group of tropical goatfishes (family Mullidae) that feed on mobile benthic invertebrates at Lizard Island (Great Barrier Reef). All goatfish possess barbels that disturb the substratum during feeding. Foraging methods were examined for the six most common species and used in conjunction with data on habitat associations to estimate the distribution and potential impact on the benthic invertebrate assemblage of foraging-related disturbance. Particular species exhibited broad habitat associations which differed little over two surveys (January 1989, January 1990). All species showed different preferences for the substrata they foraged. Preferences for substrata exhibited by the most common reef-associated species, Parupeneus multifasciatus, differed among locations separated by 1 km, between sites 150 m apart, and between depths (shallow and deep). Habitat preferences changed with ontogeny. Based on their habitat associations and foraging preferences, species were divided into habitat generalists and specialists. Specialists associated primarily with soft sediments. Habitat generalists, such as P. multifasciatus and P. cyclostomus, are likely to have an impact on their mobile invertebrate prey that is localised, diffuse and transitory, making any experimental analysis difficult and expensive. Habitat specialists form a guild of fishes with complementary feeding modes that efficiently exploit soft sediments and are more amenable to experimental manipulation. Experiments designed to detect the impact of foraging by these fishes must be repeated at different locations and times and must account for depth differences in foraging pressure.

Larvae of a colonial ascidian use a non-contact mode of substratum selection on a coral reef

The rate at which larvae successfully recruit into communities of marine benthic invertebrates is partially dependent upon how well larvae avoid benthic predators and settle on appropriate substrata. Therefore, to be able to predict recruitment success, information is needed on how larvae search for settlement sites, whether larvae preferentially settle on certain substrata, and the extent to which there are adequate cues for larvae to find these substrata. This article describes how larvae of the colonial ascidian Diplosoma similis find settlement sites on a coral reef. Direct field observations of larval settlement were made on a fringing reef in Kaneohe Bay, Oahu, Hawaii, between September 1985 and April 1986. A comparison of the substrata that larvae contacted prior to settlement relative to the percentage cover of these substrata on the study reef suggests that larvae are using a non-contact mode of substratum identification to locate suitable settlement sites. This mode of substratum identification allowed 74% of larvae to evade predation by benthic organisms who would otherwise have eaten larvae if they had been contacted. Of those larvae that evaded predation, 88% subsequently settled on the same two substrata upon which most adults are found (dead coral or the green alga Dictyosphaeria cavernosa). This pattern of settlement was probably a result of active selection, since the two substrata cover only 14.4% of the reef's surface and currents had little effect on the direction in which larvae swam. An important contributing factor to the high success rate of larval settlement on suitable substrata was the lack of any temporal decay in substratum preference. It is concluded that for Diplosoma similis larval supply is a sufficient predictor of larval settlement rate. However, for marine invertebrates whose larvae are passively dispersed and exhibit a greater temporal decay in substratum preference, larval settlement should generally have a greater dependency on spatial variation in the abundance of benthic predators and suitable substrata.

Substratum selection by juvenile plaice ( Pleuronectes platessa L.): Impact of benthic microalgae and filamentous macroalgae

Preference by juvenile plaice for vegetated or unvegetated substratum was investigated in laboratory experiments to study the impact of recent changes in vegetation structure in shallow nursery areas on the recruitment of plaice. The experiments were done in circular tanks with filtered flow-through sea-water. The tanks were divided into two parts, one with bare sediment and the other with mat-forming benthic microalgae or patches of filamentous macroalgae ( Enteromorpha intestinalis and Rhizoclonium spp.) attached to small cobbles. Substratum preference were tested for different size-classes of juvenile plaice, ranging in size from 11 to 50 mm. Recently metamorphosed (11–15 mm) and post-settlement (16–26 mm) juveniles showed a significant preference for bare sediment compared with areas containing patches of filamentous algae. Post-settlement juveniles (16–26 mm) also exhibited a significant preference for bare sediment compared with sediment covered with mat-forming benthic microalgae. The differences in substratum selection disappeared 6 to 8 weeks after settlement in individuals that were 35 to 50 mm in total length. Field sampling verified that density of plaice (17–34 mm) was significantly lower in vegetation patches than in areas of bare sediment.

Substratum preference of the tropical estuarine crabs, Uca tangeri Eydoux (Ocypodidae) and Ocypode cursor Linne (Ocypodidae)

The vertical and horizontal distribution of two burrowing mud crabs, (Ocypodidae) and Ocypode cursor Linne 1758 (Ocypodidae) are described for the Bonny Estuary (7° 00' E: 4° 20′ N), S. Nigeria. Substratum preference is the most prominent factor influencing distribution, but lack of tolerance to low salinities (< 6%o) is also important, and prevents Ocypode cursor from occurring close to freshwater. The two species have slightly different sediment organic content and grade size requirements. Ocypode cursor was concentrated in well drained sandy sediment above mid-tide-level, whilst Uca tangeri was found in water-logged areas slightly above and below Mid-tide-level. This vertical demarcation is attributed to differential feeding and burrowing adaptations related to different substrata, rather than to differential tolerances to desiccation.

Transitional ecological requirements for early juveniles of two sympatric stichaeid fishes,Cebidichthys violaceus andXiphister mucosus

The distribution patterns, diets, and substratum (refuge) requirements of early juveniles of two sympatric stichaeid fishesCebidichthys violaceus andXiphister mucosus, were investigated in a rocky intertidal habitat at Diablo Canyon, California. Monthly investigations were conducted at low tide for four consecutive months, to assess ontogenetic differences in distribution, diet, and refuge requirements within and between the two species. Distinct differences in vertical zonation were exhibited by both stichaeids throughout the study. Interspecific zonation patterns were similar to those recorded for adults of both species. Diet analyses showed that early juveniles of both stichaeids were zooplanktivorous, differing markedly from the primarily herbivorous diets of adults. Changes in diet were largely due to the selection of larger prey taxa as both fishes, and their mouth size, grew over the study period. Predation by both fishes on water-column planktors (calanoid copepods, zoea and polychaete larvae) was greatest following initial intertidal settlement and habitat establishment by early juvenile fishes. Greater dependence on substrate-oriented and/or benthic prey (harpacticoid copepods, gammarid amphipods and mysid shrimp) was exhibited by both fishes as they grew in size. Affinities for sand, gravel, and pebbles during monthly field surveys were similar for both species throughout the study. As the fishes grew, their substratum preferences changed in relation to the substrata which provided the best refuge. Results from laboratory experiments indicated that young stichaeids select very specific substrata based on fish age (size) and substratum suitability (i.e. adequate refuge). Similarities in diet and substratum preferences, and changes in those preferences over time, appear to be the result of morphological similarities (body size and shape and mouth gape) for both species at a given age.

Influence of Current Velocity on Substratum Selection by Naucoridae (Hemiptera): An Experimental Approach Via Stream Simulation

Microhabitat preferences of three sympatric naucorids ( Ambrysus circumcinctus Montandon, Limnocoris lutzi La Rivers, and Cryphocricos hungerfordi Usinger) from the South Llano River of central Texas were evaluated in laboratory experiments. Each species was individually subjected to all paired contrasts produced from three substratum size classes (coarse gravel, small pebble, and small cobble). Within each contrast, three trials were conducted, each involving a different current velocity (slow, 6.6 ± 0.1 cm/s; intermediate, 9.8 ± 0.1 cm/s; and fast, 13.7 ± 0.5 cm/s). The gravel substratum was never preferred; moreover, preference in the pebble versus cobble contrast, when present, was only shown for the cobble substratum. Overall, A. circumcinctus exhibited consistent substratum preferences (cobble> pebble> gravel) independent of current velocity. C. hungerfordi preferred cobble over either gravel or pebble substrata; however, a synergistic effect between current velocity and substratum size was detected in the gravel versus pebble contrast. Finally, L. lutzi exhibited the highest degree of velocity-dependent substratum selection. Laboratory analyses corroborated field investigations and offered insight into the influence of interacting abiotic variables on the microdistribution of Naucoridae.

Ecology of Pectinatella magnifica (Bryozoa) in an Alabama Oxbow Lake: Colony Growth and Association with Algae

Colonies of the bryozoan Pectinatella magnifica commonly occur on submersed substrata in an oxbow lake (Touson Lake) in the floodplain of the Black Warrior River, Alabama. Seasonal growth patterns, substratum preference, and potential effects of bryozoan colonies on algal assemblages attached to artificial and natural substrata were determined. Colony growth on artificial substrata (pine sticks) and natural ones (dead cypress twigs and aquatic plants) was monitored at biweekly intervals from the appearance of bryozoans during early autumn to the loss of colonies from substrata in late December. Maximum colony growth occurred during late September and early October. Some colonies reached up to 65 cm in length and 10 cm in diameter. Colonies showed no preference among the substrata examined, but young colonies always developed first on the shaded side of the substratum. The presence of bryozoan colonies affected the composition of attached algae. Blue-green algae (90%) dominated on surfaces enclosed by the colonies and also within the gelatinous colony matrix, whereas surfaces uncolonized by Bryozoa developed mixed communities of diatoms (78%), blue-green algae (12%), and green algae (11%).

Central and peripheral neurite outgrowth differs in preference for heparin-binding versus integrin-binding sequences

Neurons of the CNS and PNS differ in their response to fibronectin (FN) and proteolytic fragments of FN. The 33 kDa C-terminal cell and heparin-binding fragment of FN, in particular, is a strong promoter of CNS neurite outgrowth. To define further the neurite-promoting activity of the 33 kDa fragment, and to investigate further the differences between PNS and CNS responses to FN and the 33 kDa fragment, we contrasted neurite outgrowth by CNS and PNS neurons on three synthetic peptides representing sequences from this fragment of FN: two heparin-binding peptides, FN-C/H I and FN-C/H II (McCarthy et al., 1990), and an integrin-binding peptide, CS1 (Humphries et al., 1987). Spinal cord (SC) neurons, from the CNS, differed from dorsal root ganglion (DRG) neurons, from the PNS, with respect to substratum preference for heparin-binding versus integrin-binding peptides. SC neurite outgrowth was greatest on the heparin-binding peptide FN-C/H II, while DRG neurite outgrowth was greatest on the a4 beta 1 integrin-binding peptide CS1. To test whether the difference in substratum preference was due to differences in the molecular mechanism by which SC and DRG neurons interact with the 33 kDa fragment of FN, anti-beta 1 integrin antibodies and/or soluble heparin were added to the cultures as potential inhibitors of integrin-mediated or proteoglycan-mediated interactions with FN. SC neurite outgrowth was much more sensitive to the effect of heparin than anti-beta 1 integrin, indicating SC neurite outgrowth may involve predominantly a heparin-sensitive mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting the horizontal migration of the amphipod Pontoporeia affinis Lindström. II. Effects of temperature, salinity and substratum

Pontoporeia affinis Lindström was subjected to temperature gradients, increased salinity and different substrata in narrow aquaria 3 m long and its swimming activity was recorded by pairs of photocells. By dividing the aquaria with intersecting walls during the day, when the animals hid in the sediment, the activity recorded in separate sections during subsequent nights revealed that Pontoporeia migrates towards the warmer end of the aquarium. Preference for soft substrata dominates temperature preference. Increased salinity activates swimming activity even during the day. Partly using a new IR video-recording method, increased temperature was found to decrease swimming activity. The new method is described in detail.

The influence of periphyton, detritus and shelter on invertebrate colonization of aquatic bryophytes

SUMMARY1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization.2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship.3. Reducing substratum ‘stem’ density (i.e. ‘shelter’) in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low‐density substrata. Abundances of most of the twenty‐two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced.4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty‐two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site.5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrital biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty‐two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty‐two taxa were significantly related to the measured variables, of which exposure time was most important (four taxa).