Carl M. Way

Substrate roughness, velocity refuges, and macroinvertebrate abundance on artificial substrates in the lower Mississippi River

Articulated concrete mattress blocks (ACM) are now used almost exclusively for erosion control of banks along the lower Mississippi River (LMR) and provide habitat for macroinvertebrates and fishes which could not otherwise colonize the unstable substrate of the natural river channel. We studied the distribution and abundance of macroinvertebrates in the LMR on ACM blocks with smooth, rough, and grooved surfaces. Additionally, the effects of block surface modifications on substrate velocity profiles were determined at three flow velocities in a laboratory flume using a thermistor-based current meter. Total density of macroinvertebrates and the densities of individual taxa were significantly different on the three surface types after 3 mo of colonization; rough blocks had 1.4× greater densities than smooth blocks, and densities on grooved blocks were 2.3× higher than smooth and 1.6× higher than rough blocks. The caddisfly Hydropsyche orris and the amphipod Corophium lacustre were significantly denser on grooved than on the other block types. In a flume, velocities in groove bottoms were 7-24× lower than ambient water column velocities (0.12, 0.23, and 0.44 m/s) and increased significantly from 1 mm to 65 mm above the block surface at all flume velocities. For all surface types there was a negative relationship between height above the block surface and measured variance in velocities and a positive relationship between flume velocities and the measured variance in velocity readings which could be attributed to increased turbulence over the block surfaces. In the field, H. orris in grooves built retreats with the anterior opening containing the feeding nets extending up into the near-surface flows over the grooves. Low velocity eddies in the grooves provided a velocity refuge while still allowing the feeding structures to contact feeding flows over the block surface. Grooved blocks in the LMR supported, on average, more than twice the invertebrate density as smooth blocks, and are recommended for future deployment of mattress blocks.

Reproductive strategies in the freshwater sphaeriid clam,Musculium partumeium (say), from a permanent and a temporary pond

SummaryReproduction was studied in two populations ofMusculium partumeium from temporary and permanent ponds. Adults of the single annual generation from the ephemeral pond have an annual selection ratio of 25:1 with 37.03 μgC per newborn, and an intrinsic rate of increase (r) of 0.0084 day-1. Fall-born adults from the permanent pond have an annual selection ratio of 38:1, 21.82 μgC per newborn and anr of 0.0115 day-1; springborn adults have an annual selection ratio of 136:1 (107:1 for their contribution to fall birth and 29:1 for the spring birth period) with newborns of 24.21 μgC and anr of 0.0304. The trade off between quantity and quality of young is discussed in terms of adaptive strategies.

The Use of Two Modified Breder Traps to Quantitatively Study Amphidromous Upstream Migration

Amphidromous stream fauna represent three phyla that have a tropical distribution among oceanic islands, with a few continental representatives. This lifecycle involves marine larval development, with postlarval migration, growth and reproduction as adults occurring in freshwater streams. Many tropical archipelagoes are on the brink of heavy commercial development, threatening freshwater resources in tropical regions. Because of this threat and the isolated nature of tropical islands, quantitative studies are needed to better understand this unique lifecycle. In this paper, we present the use of two modifications of the original Breder trap to study the migration dynamics of tropical amphidromous fish and shrimp postlarvae. The first modification was used in a cemented and channelized stream. The second modification was used in two streams with natural substrates of large, embedded and immovable boulders and basalt outcrops. Quantitative trapping was standardized by time and numbers of traps used, to give results presented as postlarvae trap−1 h−1. The number of traps used in the natural streams was based on channel width at the trapping location (i.e., equal number of traps per meter), thus providing equivalent trapping effort between streams of different sizes and flow magnitude. Both trap designs were useful for quantitative monitoring of postlarvae over several months and years, among different streams, and were equally practical for assessing diel and species-specific migration dynamics. Postlarval recruitment of Hawaiian amphidromous species showed temporal variation between months and years within the same stream, significant differences between two streams of different flow magnitude, and distinct diel patterns in diurnal and nocturnal fish and shrimp migration, respectively. A direct correlation between stream flow and total fish postlarval migration was documented.

The Life History of Leptoxis dilatata (Conrad) (Prosobrancia: Pleuroceridae) from the Laurel Fork River, West Virginia

-The life cycle of the prosobranch gastropod, Leptoxis dilatata, from a third order Appalachian Mountain stream was studied during 1984-1985. This population was semelparous and biennial, with individuals living approximately 23-26 months. Eggs were laid in late April through early May and hatched by late June. Young snails grew (0.03 mm/day) over the late summer and autumn months before cessation of growth in the winter. Overwintering juveniles began rapid growth (0.04 mm/day) again in March, attaining shell lengths of approximately 10 mm by August. This cohort reproduced in the 2nd yr of life at shell lengths of 12-14 mm. This study and other published life cycles indicate that individuals in the genus Leptoxis are typically semelparous and have a long prereproductive period. Individual longevity appears to be a function of environmental variables such as food quality and quantity.

Comparative bioenergetics of permanent and temporary pond populations of the freshwater clam, Musculium partumeium (Say)

The population energetics of a temporary and a permanent pond population of Musculium partumeium in Southwest Ohio were studied. In the permanent pond (surface area = 396 m2, maximum depth = 0.7 m) the population was bivoltine and iteroparous whereas in the temporary pond (surface area = 1042 m2, maximum depth = 0.9 m) the population was usually univoltine and semelparous.Growth and biomass were assessed as total organic carbon and total nitrogen to provide estimates of productivity and seasonal changes in C:N for each generation. Productivity (non-respired assimilation = growth + reproduction; N-R.A. = G + R) was 6939 mgC·m−2·a−1 (3858 and 3353 mgC·m−2·a−1 for each generation) and 1661 mgC·m−2·a−1 for the permanent and temporary pond populations respectively. The average standing crop biomass (B) was 606.8 mgC·m−2 (357.5 and 249.3 mgC·m−2 for each generation) and 231.9 mgC·m−2 with overall productivity: biomass ratios of 11.4 and 7.2 for the permanent pond and temporary pond populations respectively.Respiration rates were converted to carbon equivalents (respired assimilation = R.A.) and used to evaluate the components of total assimilation (T.A. = R.A. + N-R.A.) and the efficiency of partitioning this energy to N-R.A. for G and R. When expressed as a percentage, the production efficiencies (100 × N-R.A.:T.A.) were 50.4 and 62%, and the reproductive efficiencies (100 × R:N-R.A.) were 26.4 and 18% for the permanent and temporary pond populations respectively. The reproductive efficiencies for populations of these viviparous clams are greater than those for most oviparous molluscs.The comparative information on the energetics of these populations does not completely fit any theoretical consideration of reproductive effort or life-history strategy. These data are discussed in relation to selection for population success in temporary ponds.

Two modified Breder traps for quantitative studies of tropical amphidromous migration

Amphidromy is a life cycle of fauna found throughout the tropics and subtropics, including representatives from three phyla. Amphidromy involves a life cycle of oceanic larval development, with postlarval migration into streams where growth and reproduction take place. With increasing industrial and urban development in tropical regions, demands for freshwater are continuously growing, resulting in the construction of dams and diversions that break the freshwater continuum necessary for the amphidromous life cycle; thus, jeopardizing many populations of native and endemic tropical stream fauna. Because of this, more quantitative studies are needed to better understand this unique life cycle, which heretofore, has been relatively little studied compared to tropical terrestrial communities. As such, new and quantitative methods are needed to study the immature stages (e.g., postlarvae) associated with amphidromy. In this paper, we introduce two modifications of the original Breder trap that have been designed specifically for standardized, quantitative monitoring of amphidromous postlarval migration. In addition, the two modified traps can be used in a variety of stream settings from natural bed substrates to modified channels with little heterogeneity. The first modification is made of acrylic, with a flat bottom useful in channelized streams or streams with relatively flat, unnatural benthic substrate (e.g., concrete). The second modification is an affordable trap made from polyvinylchloride (PVC) compression couplings, to be used in streams with natural benthic substrates, particularly those with large, embedded and immovable boulders and bedrock outcrops. Both traps were designed for continuous water flow through the traps, providing the necessary rheotactic cue for migrating amphidromous postlarvae, and ameliorating deficiencies of earlier traps not intended for tropical amphidromous fauna. We also make recommendations for standardized use of these traps to facilitate data comparisons among studies.