Benthic Substrate Research Articles

Diel Migration and Microhabitat Distribution of a Benthic Stream Assemblage

Macroinvertebrate microspatial distributions were determined on nonglazed brick substrates at three sites on the upper Colorado River. Site 1 was located above a reservoir, whereas Sites 2 and 3 were located 0.4 and 4.0 km, respectively, downstream from a deep-release dam. Replicate samples from each substrate surface (top, sides, front, back, and bottom) and from the interstices below brick substrates were collected during the day (ca 14:00–16:00) and at night (ca 21:00–23.00) in the summer and autumn of 1982. Although most macroinvertebrates occurred on "bottom" surfaces, "top," and "side" surfaces and the interstices were often utilized. Macroinvertebrates were least abundant on "back" and especially "front" surfaces. Total macroinvertebrate density on upper substrate surfaces was not significantly different at night compared with the day. However, there was a 47% increase in the density of Baetis spp. on upper surfaces during the night at Site 1, a diel shift in benthic substrate utilization that corresponded to drift periodicity. The density of Baetis spp. on upper surfaces during the night compared with the day was not significantly different at Sites 2 and 3. Large-sized Baetis spp. at Site 1, but not at Sites 2 and 3, used a greater proportion of upper substrate surfaces at night compared with the day.

Effects of discharge fluctuation and the addition of fine sediment on stream fish and macroinvertebrates below a water-filtration facility

A small, coastal stream in the San Francisco Bay area of California, USA, received the discharges from a drinking-water filtration plant. Two types of discharges were present. Discharges from filter backwashing were 3–4 times base stream flow, occurred 10–60 times per day, contained fine sediments, and each lasted about 10 min. The other discharge was a large, steady flow of relatively sediment-free water from occasional overflow of the delivery aqueduct which generally lasted several hours a day. Samples of invertebrates from natural substrates had significantly fewer taxa and lower density at the two stations below the backwash than at the two above. However, when stable artificial substrates were used, there were no significant differences among all four stations. The aqueduct apparently had no effect because the. invertebrate community at the station upstream of the backwash but downstream of the aqueduct was statistically similar to the station above the aqueduct. To test for acute toxicity, we exposed additional artificial substrates to short-term simulated backwash conditions. These exposures had no effect on invertebrate density or drift. Three-spine stickleback (Gasterosteus aculeatus) populations were also significantly reduced at the two downstream stations and were made up mostly of larger, adult fish. Prickly sculpins (Cottus asper), restricted to the most downstream station, were emaciated and had poor growth, probably as a result of scarce benthic food organisms. Artificial redds with eggs of rainbow trout (Salmo gairdneri) had significantly lower survival at two stations below the plant backwash (30.7% and 41.8%) than at the one above it (61.4%). Hatchery rainbow trout held in cages below the treatment plant from 7 to 37 days survived and continued to feed. Thus, the major effect of the water treatment plant on fish and invertebrates probably was not from acute toxicity in the discharges or the occasionally large discharge of clean water from the aqueduct, but was from the fluctuating backwash flows containing fine sediment that displaced small fish downstream and created unstable benthic substrates for invertebrates. The filter plant that we studied is a direct-feed type (that is, no sedimentation before filtration). These generally require greater frequencies of backwashing than do conventional plants and may therefore have greater biological impacts. Direct-feed plants are becoming increasingly popular throughout the world, for the most part because they are cheaper to build and operate. But if the associated biological problems are mitigated, then the cost savings of direct-feed compared to conventional plants may be lost.

Food acquisition by competing surfperch on a patchy environmental gradient

Black surfperch, Embiotoca jacksoni, and striped surfperch, Embiotoca lateralis, coexisted along steep sloping rocky habitats at Santa Cruz Island, California. The range of depths occupied (to 15 m) was characterized by a strong gradient in abundance of prey and a changing mosaic of substrate types from which surfperch harvested food. Availability of prey and diversity of benthic substrates were greatest in shallowest areas and both declined with increasing depth. Individuals of both surfperch species were residential within a narrow range of depths, with the result that different segments of their populations were consistently exposed to different foraging environments. These two phenomena (residential behavior combined with a gradient in availability of resources) resulted in variation in foraging behaviors and diets among individuals that resided at different depths. The pattern of within-population variation differed between the surfperch species. Black surfperch individuals achieved similar taxonomic diets and expended similar foraging effort at all depths, but deep-water foragers captured much less prey biomass per unit effort. The taxonomic composition of striped surfperch diets differed among depths, and although similar amounts of prey biomass were captured everywhere, individuals in deep areas expended much greater effort to obtain that level of food return. For both species, habitat profitability (food return to foraging effort) declined with depth. The difference in habitat profitability appeared to influence fitness components of both surfperches. Individuals occupying deep habitats were about 5% shorter in standard length than conspecifics of the same chronological age living in shallow areas; the disparity in body size resulted in an estimated difference in clutch size of 10–18%.

Importance of Snag Habitat for Animal Production in Southeastern Streams

Abstract The Satilla River in southeastern Georgia is a low gradient coastal plain stream with large quantities of woody debris (snags) along its banks. The major objective of this study was to assess the relative importance of the snag habitat as a site of invertebrate production in comparison to benthic habitats. This was accomplished from quantitative sampling of invertebrate habitats, analysis of drifting organisms, and gut analyses of the major fish species. Invertebrate diversity, biomass, and production were considerably higher on snag surfaces than in either sandy or muddy benthic substrates. Although snags represented a relatively small habitat surface (4% of total habitat surfaces), snags supported 60% of total invertebrate biomass and 16% of the production for a stretch of river. Drift densities from night samples collected throughout the year were relatively high, and approximately 78% of drifting invertebrate biomass originated from the snags. Four of the eight major fish species obtained at ...

Ripistes parasita (Schmidt) (Oligochaeta:Naididae), a Distinctive Oligochaete New to North America

Ripistes is a monospecific genus (containing only R. parasita (Schmidt)) easily distinguished from other naidid worms by the bundles of extremely long capilliform chaetae on body segments VI-VIII. Its occurrence in New York State is the first record of the genus outside the Palearctic region. In general, the New York specimens conformed to the morphological traits of the Palearctic material, but none were more than half as long as the known maximum length, some dorsal and ventral chaetae were somewhat shorter, and the penial chaetae were occasionally more numerous and always considerably longer. The New York specimens were collected from hardboard artificial substrate samplers, usually with several other species of naidids. The use of artificial substrates may have been instrumental in finding the species, since it is known to live on the surfaces of submerged objects, rather than on the benthic substrate per se.

Small Scale Diurnal Migrations by Heterocypris Incongruens (Ramdohr, 1808) (Ostracoda: Cyprididae) in a Temporary Pool, Ghana, West Africa

ABSTRACT Diurnal migrations of fresh-water ostracods, Heterocvpris incongruens (Ramdohr, 1808), from a muddy to a rocky benthic substrate in a small pool, are described. This is the first time that such benthic migrations have been noted for any microcrustacean. Possible explanations for the phenomenon are suggested.

Spatial and Temporal Distribution of Benthic Diatoms in Northern Lake Michigan

Benthic diatom communities were sampled from natural substrates along a depth tran- sect in northern Lake Michigan to examine spatial and seasonal distribution patterns and define assemblages of associated taxa. Information-theory diversity, evenness, and richness were signifi- cantly higher in deep assemblages than in shallow assemblages, with the boundary falling between 5 and 10 m in winter and fall, 10 and 20 m in spring, and 20 and 31 m in summer. Planktonic taxa are abundant on benthic substrates in the deep zone, primarily as dead fallout. In shallow water, large numbers of living planktonic taxa overwinter beneath the ice on benthic substrates. Cluster analysis of samples was used to identify and define diatom assemblages from deep, mid- depth, and shallow water. The deep-water assemblage contains motile and nonmotile benthic species that have been reported from alpine and boreal oligotrophic lakes. The mid-depth assemblage is rich in epipsammic taxa. The shallow-water assemblages contain cosmopolitan taxa that are collected often in nearshore plankton samples. These shallow assemblages do not persist throughout the year as do the deep and mid-depth assemblages. Cluster analysis of taxa provides further definition of species associations and the degree of cor- relation among species. Correlations among benthic taxa are strengthened when planktonic taxa are removed from the analysis, indicating that plankton fallout represents an addition of information which is poorly related to distribution of the benthic species. The most stable and diverse community is found at the deepest sampling depths where environ- mental conditions are most stable, the mid-depth community exists in fluctuating but predictable conditions, and the shallow assemblages occur in the zone of maximum physical fluctuation or natural stress. Substrate types are correlated with the species assemblages, but the high diversity of substrate types in shallow water does not support the most diverse assemblage. The discrete species assem- blages seen in an oligotrophic area of this large dimictic lake apparently respond sensitively to tem- porally and spatially dynamic environmental parameters.

Pozzolanic aggregates of fly ash in the sea

Pulverized fuel ash (pfa) readily forms pozzolanic aggregates when wetted, and these are common at sites of ash dumping at sea, where they can be up to 2 m across. Field observations on the structure and fauna of aggregates from an ash dumping ground off the Northumberland (UK) coast were undertaken in 1975, together with experimental studies of aggregation, to determine the influence of ash aggregates on the benthic substrate and the faunistic colonisation of aggregates in situ. The aggregates are of a soft sandstone consistency, but are persistent at the sea bed. Particle analysis of aggregates showed negligible contribution by inorganic particles other than the ash, and an overrepresentation of larger diameter particles (3.5 to 4 Φ) compared to pure ash. There was an exponential relationship between aggregation and ash content of experimental sediments. It is suggested that only 15 to 17% of the ash reaching the sea bed will be involved in aggregation. The naturally occurring aggregate fauna consisted of a sparse but diverse sessile epifauna, which depended on encrusting bryozoans for initial colonisation, and a few boring species (Zirfaea crispata, Hiatella arctica, Polydora flava). The presence of 7 yr-old Z. crispata in aggregates confirms their persistence at the sea bed, and indicates that the ash is not toxic.

The Feeding Ecology of the West Caribbean Green Turtle (Chelonia mydas) in Nicaragua

The stomach contents of 243 subadult and adult green turtles, Chelonia mydas, taken at their foraging grounds off the eastern coast of Nicaragua, were examined. The sex and site of capture of most of the turtles were known. Turtle grass, Thalassia testudinum, accounted for an average of 78.9 percent of the dry weight of the samples. The turtles were found to graze at the bases of the Thalassia plants where they obtained the youngest growth. They avoided those blades which were encrusted with epiphytic animals and plants. In decreasing order of abundance, the remaining food items comprised: other species of seagrasses (9.7%), algae (8.2%), benthic substrate (1.8%), and animal matter (1.4%). In the northern part of the Nicaraguan foraging range Thalassia accounted for nearly 90 percent of the diet, while in the more southerly portions fleshy red algae predominated. Turtles migrating between the feeding and nesting grounds travel near shore, at which time they consume greater amounts of Syringodium filiforme, red algae, and highly lignified terrestrial debris deposited at river mouths. No difference in the diets of the two sexes was recorded. THE AIM OF THIS STUDY is to enhance our generally limited knowledge of the ecology of the green turtle, Chelonia mydas, at its feeding grounds. Information obtained by tagging nesting females has made it possible to piece together migratory routes, the location of feeding grounds, and the time intervals between nestings. Virtually nothing, however, is known of the ecology of the animals away from the nesting beach. The green turtle colony that nests at Tortuguero, Costa Rica, is both the largest in the western Caribbean and the best studied in the world. Here, a tagging project conducted by Archie F. Carr, Jr. has been in progress for 27 years. At Tortuguero, females nest at intervals of two, three, and four years, with longer cycles possibly occurring. After laying between one and six clutches of eggs during a given nesting season, the females travel to their distant feeding grounds, and apparently remain there until the time again comes to migrate to Tortuguero (Carr et al. 1978). Because it has not been feasible to tag males, their movements remain unknown. However, it is assumed that they too return to the same feeding grounds after mating off the nesting beach. It has been postulated that conditions on the foraging pastures may determine the timing of the reproductive cycles (Carr and Carr 1970). The feeding grounds of most populations of green turtles are located some distance from their nesting beaches. Tag returns have demonstrated that the feeding grounds for approximately three-quarters of the Tortuguero turtles are the seagrass meadows that blanket the extensive continental shelf of eastern Nicaragua (Carr et al. 1978). Because food is generally unavailable, little or no feeding is believed to take place directly off the nesting beaches, or enroute between breeding and feeding sites. Mortimer (1976, in press) reviewed published accounts of green turtle feeding habits on a worldwide basis. The literature characterizes the turtle as an herbivore that is not averse to eating animals.In most parts of its range the green turtle forages primarily in seagrass pastures (Hirth 1971), e.g., in the western Atlantic north of the equator, in the central Pacific, and in the Indian Ocean (Frazier 1971). In areas where seagrasses are lacking-off the coast of Brazil, Tahiti, Hawaii (Balazs 1979a, b), the Galapagos Islands (Pritchard 1971), and the south African coast (Hughes 1974) -algae are the mainstay of the diet (Hirth 1971). In some localities, however, green turtle colonies that feed mainly on seagrasses occur within a few kilometers of others that forage exclusively on algae. This dichotomy has been reported along the west coast of Honduras (Carr 1952), in the Gulf of California (Felger and Moser 1973), in Fiji (Hirth 1971), in the Gulf of Aden (Hirth et al. 1973), and the Torres Strait of Australia (Nietschmann, in press). The present study is a quantitative analysis of stomach contents from adult green turtles captured on their feeding grounds off the east coast of Nicaragua (fig. 1). In most cases sex and sites of capture were known. The turtles were slaughtered either in Miskito Indian villages for local consumption, or in the two Nicaraguan meat-packing and exporting plants. MATERIALS AND METHODS STOMACH CONTENT ANALYSIS.-The guts of 243 BIOTROPICA 13(1): 49-58 1981 49 This content downloaded from 157.55.39.136 on Thu, 19 May 2016 04:17:56 UTC All use subject to http://about.jstor.org/terms

Monitoring river periphyton with artificial benthic substrates

The objective of this research was to identify the materials and methods necessary to study the attached algal community on a river bottom in deep water. The study site was the Susquehanna River near Falls, Pennsylvania. Artificial substrates of smooth glass, frosted glass, Vermont slate, ‘sandy slate’ (flagstone) and acrylic plate were placed on the stream bottom in detritus free sample holders by scuba divers. Both monthly and long-term cumulative samples were collected from the plates employing scuba and a Bar-Clamp sampler. River stones (natural substrates) were collected for comparison. Samples were analyzed in a Palmer Cell under a Bausch and Lomb research microscope. Diatoms were the most important colonizers of river stones, with the genera Nitzschia and Navicula most abundant. Highest periphyton densities occurred on natural substrates in winter with a maximum of 2.2 × 104 units/ mm2. Artificial substrates with one month exposure periods accumulated maximum periphyton density from May through October with relatively low densities in winter. Cumulative artificial substrates were most like river stones in patterns of colonization. Frosted acrylic is recommended for future studies employing benthic artificial periphyton substrates.

Assemblages of algae and invertebrates in Southern California Phyllospadix-dominated intertidal habitats

The assemblages of macroalgae and macroinvertebrates that coexist in intertidal Phyllospadix beds at seven sites in San Diego County, California, are described quantitatively. Most of the algae are attached to benthic substrates (68 of 71 species); one of the 90 recorded invertebrates is restricted to the blades of Phyllospadix species. The composite data, considered to be characteristic of beds of both P. torreyi S. Watson and P. scouleri W. Hook. at the sites sampled, are compared qualitatively with the biota in various other adjacent and nearby habitats. With the exception of four epibiotic taxa, found only on blades of the surfgrass, the organisms are not uniquely associated with habitats where Phyllospadix plants are present. No patterns of seasonal fluctuation were evident in either species abundance or occurrences. Several ubiquitous species were consistently found in larger numbers, but most were observed infrequently.

Distribution of benthos in a stagnant estuarine bay

In the summers of 1974 and 1975, profiles of temperature, salinity, and dissolved oxygen were made monthly at four stations in Kennebecasis Bay. Samples of the benthic fauna and substrate were also taken.Sediment particle size distribution did not vary between stations. Combustible organic content of sediments was highest at the head of the bay and lowest near the mouth.Surface water was generally of low salinity, high dissolved oxygen, and seasonally variable temperature. Bottom water showed a stable salinity of 18 to 20‰, stable temperature of 4 to 7 °C, and stable oxygen concentrations of 1.5 to 4.5 mg/ℓ.While the parameters just mentioned are thought to be uniform throughout Kennebecasis Bay, the observed distribution pattern of species and individuals in the benthic fauna was not uniform. Samples taken at the mouth of the bay produced greater numbers of taxa and abundance of fauna than samples from the head of the bay. It is proposed that this bay mouth-to-head gradient is related to infrequent saline water inflows reaching only lower parts of Kennebecasis Bay.

Distribution of Paralichthid Flounders (Bothidae: Paralichthys) in North Carolina Estuaries

Summer flounder,Paralichthys dentatus, and southern flouder,P. lethostigma, extensively use Pamilco Sound and adjacent estuaries as nursery areas. Young gulf flounder,P. albiguta, are rarely found. Flounders remain in the estuaries for the first 18–20 months of their life before moving into ocean waters. Benthic substrate and salinity are the two most important factors governing distribution. Southern flounder are most abundant in areas of low salinity and clayey silt or organic rich mud bottoms. Summer flounder are most abundant in areas of moderate to high salinities and sandy bottom.

Lugworm mortalities and a bloom of Gyrodinium aureolum Hulburt in the eastern Irish Sea, Autumn 1971

A bloom of the dinoflagellate Gyrodinium aureolum Hulburt in the eastern Irish Sea during September and October 1971 was accompanied by unusual mortalities of Arenicola marina L. and Echinocardium cordatunt Pennant. Observations in the field and laboratory suggest that the mortalities may not have been directly related to the occurrence of Gyrodinium but could have been a consequence of unusual climatic conditions which resulted in oxygen depletion in benthic substrates. The decomposition of the bloom possibly aggravated the situation.

THE EFFECT OF WATER MOTION ON ALGAL SPORE ADHESION1,2

The effects of water motion on the attachment of algal germ cells to benthic substrates were studied. Water motion was measured in the field and the forces on a germ cell attached to a substrate surface computed. Laboratory apparatus for simulating wave surge was developed, calibrated, and used for experiments on the spore attachment process. A“waterbroom,” producing water motion over the surface of a submerged substrate in a laboratory aquarium, closely simulates wave surge; it was calibrated by measuring static and dynamic pressures in the substrate’s boundary layer and determining whether the layer was laminar or turbulent.Preliminary tests with the waterbroom indicate that the adhesion of carpospores of Agardhiella tenera to a clean glass surface increases wih residence time, while that of Cryptopleura violacea decreases. Improved experimental data on Gracilariopsis sjoestedtii showed an increase in adhesiveness with residence time, from 10 hr to an asymptotic limit at 20. Once attached, the Gracilariopsis spores adhere firmly, resisting removal by shear forces nearly 100 times their weight.