Publications
Permanent URI for this collectionhttps://hdl.handle.net/1969.6/86487
Browse
Browsing Publications by Issue Date
Now showing 1 - 20 of 149
- Results Per Page
- Sort Options
Item Distributional notes of Harpacticoida (Crustacea: Copepoda) collected from the Beaufort Sea (Arctic Ocean)(1978) Montagna, Paul A.; Carey Jr., Andrew G.Forty-one species of large-size Harpacticoida have been sorted from Smith-McIntyre grab samples sieved through 1.00 and 0.2 mm aperture screens. Fifty-eight stations were occupied throughout the southwestern Beaufort Sea, ranging from Point Barrow, Alaska (USA) west, to Demarcation Point, the eastern border with Canada. The depth of the study area ranged from 5-3500 m. Harpacticus superflexus Willey and Stenhelia nuwukensis M. S. Wilson dominated the samples numerically. Though H. superflexus was ubiquitous, S. nuwukensis was restricted to a narrow range of shallow waters. The female to male ratio was 99:1. It is not known why there is such a preponderance of females, but sexually dimorphic characters may be absent or the smaller males may have passed through the sieve.Item Cervinia langi n. sp. and Pseudocervinia magna (Copepoda: Harpacticoida) from the Beaufort Sea (Alaska, U.S.A.)(Transactions of the American Microscopy Society, 1979) Montagna, Paul A.Two species of the family Cerviniidae have been collected from the Beaufort Sea off the coast of Alaska. Pseudocervinia magna (Smirnov, 1946) and Cervinia langi n. sp. were found in association. Lang (1936, 1948) described the new species as a variant of Cervinia synarthra Sars, 1911. However, C. langi is consistent and unique in the setation of its swimming legs and in details of the mandible and maxilliped. A key to the species and a table of salient morphological characters of the genus Cervinia are given. Appendages from the cephalothorax of P. magna are also figured, and its taxonomic position is discussed.Item Two new bathyal species of Pseudotachidius (Copepoda: Harpacticoida) from the Beaufort Sea (Alaska, U.S.A.)(Journal of Natural History, 1980) Montagna, Paul A.During the summer of 1977, the Oregon State University Benthic Group participated in a USCGC GLACIER cruise off the northeastern coast of Alaska, U.S.A. Two new species of Harpacticoida (Copepoda) were found from several of the bathyal stations occupied. Pseudotachidius brevisetosus sp. nov. occurred in 15 samples from 4 stations. Pseudotachidius bipartitus sp. nov. co-occurred with P. brevisetosus in 5 samples from 3 stations. The areal extent was not great, hut the depth ranged from 659-1144 m for the 3 stations where both species occurred. A single P. brevisetosus female was found at the fourth station, where the depth was 403 m. Pseudotachidius bipartitus is .most similar to Pseudotachidius vikingus Drzycimski, but differs from it and other members of the genus in that the endopod of the first leg is 2-segmented. Pseudotachidius brevisetosus is most nearly related to Pseudotachidius coronatus T. Scott, but differs from it in the setal arrangement of the fourth and fifth legs, and most importantly in the transformed endoped of the male second legs. The setal arrangements ofP. coronatus and Pseudotachidius similis T. Scott are in question, due to differing interpretations of the original descriptions. A re- examination of the literature is discussed so that the relationships of the new species are clearly defined. All figures were made with the aid of a camera lucida. The nomenclature and descriptive terminology are adopted from Lang (1948, 1965) and Coull (1977). The following abbreviations are used throughout the text: R = rostrum, A 1 -- antennule, A 2 = antennae, Md = mandible, Mxl = maxillula, Mx = maxilla, Mxp = maxilliped, P1-P6 = legs 1-6, CR = caudal rami, GF = genital field, Bend. = baseoendopodite. Body length measurements are from the base of the R to the base of the CR, excluding both. CR L/W (=length to width ratio) is measured from the inner proximal edge to the inner distal edge for length, and at the widest points for width.Item A New Species And A New Genus Of Cerviniidae (Copepoda: Harpacticoida) From The Beaufort Sea, With A Revision Of The Family(Proceedings of the Biological Society of Washington, 1980) Montagna, Paul A.Cercinia unisetosa n. sp. from the bathyal zone of the Beaufort Sea (Arctic Ocean) is unique in the Cervinia in that is possesses a reduced fifth leg, moderate length caudal rami, and only one seta on the bases of the mandible and the maxilliped. The discovery of the male of Pseudocervinia magna (Smirnov, 1946) proves that the species should be redesignated as a Cervinia as originally described. Expansicervinia glacieria n. gen, & n. sp. from the deep-sea of the same area proves to be unique in the Cerviniidae in three expansions; the ventral margins of second thoracic segment; the basal segment of the antennule; and the terminal endopodite of the second leg. The genus Stratiopontotes Soyer, 1970 is synonymized with Ameliotes Por, 1969. Keys to the genus Cervinia and the family Cerviniidae are presented.Item Decomposition of Spartina alterniflora in different seasons and habitats of a Northern Massachusetts salt marsh, and a comparison with other Atlantic regions(Estuaries, 1980-03) Montagna, Paul A.; Ruber, ErnestPackets of freshly harvested liveSpartina alterniflora were placed on the marsh surface, in a tidal ditch, in a pool contacting sides and bottom, and in the center-bottom of the same pool in September 1972. Rates of loss were the same for all four sites through day 242. After that packets on the marsh surface decomposed slower. A second experiment was begun in July only at the marsh surface and pool side sites. These lost dry weight much more rapidly than packets started in September. Populations of bacteria, fungi, diatoms, flagellates, ciliates and nematodes within the packets peaked within 60 days then decreased proportionately with the loss of dry weight in packets through day 242. After this, bacterial numbers decreased more rapidly presumably in response to a qualitative change in the packet material. Populations of flagellates and ciliates also declined rapidly after day 300. This decline occurred in new packets at around this date as well. In a limited set of samples 12 taxa were analyzed for date or detritus-age dependent occurrence. Of these, eight were data dependent, two were dependent on packet age, and two could not be determined from the data.Item Production of dominant emergent vegetation and of pool algae on a northern Massachusetts salt marsh(Bulletin of the Torrey Botanical Club, 1981) Ruber, Ernest; Gillis, Gregory; Montagna, Paul A.Cover frequency for the emergent vegetation of three representative sections of a salt marsh is presented. Annual production values are calculated using the ash-free dry weights of a series of harvests of standing live and dead crops, and estimating export or decomposition losses from the standing crops from data on litterbag-losses. Production values are provided for tall and dwarf Spartina alterniflora, S. patens, Distichlis spicata, Juncus Gerardi, Salicornia europaea, Typha angustifolia and Scirpus olneyi, the last two being based on end-of-season harvests only. These species account for from 88 to 96% of the emergent cover of these marsh sections. Salt marsh pool production and cover values are obtained and integrated for 8 months of the year. Such pools comprise from 0 to 26% of the sections studied. These data provide a baseline for studies of energy transfer in this marsh.Item Sampling Design and Enumeration Statistics for Bacteria Extracted from Marine Sediments(American Society for Microbiology, 1982) Montagna, Paul A.The spatial and temporal distributions of marine bacteria were studied at both a muddy and a sandy subtidal site in North Inlet, S.C. The sampling design was hierarchical, since subsampling (by a dilution series) of the sediments was necessary to count bacterial cells using acridine orange epifluoresence microscopy. The cell count data fit a log-normal distribution. The abundance of bacteria was 1011 g−1 (dry weight) of mud and 109 g−1 (dry weight) of sand. Variance component analyses demonstrated that variation due to the subsampling procedures was always statistically significant. Thus the common practice of counting 20 fields from one filter preparation is inadequate for estimating the true bacterial population variance in marine sediments. It is recommended that replication of the subsampling level be performed. Standardization of data (by dry weight of sediment) decreased sampling variance at the mud site but not at the sand site, implying that bacteria are more homogeneously distributed in sand than in mud.Item Morphological adaptation in the deep-sea benthic harpacticoid copepod family Cerviniidae(Crustaceana, 1982) Montagna, Paul A.Por (1964) suggested that deep-sea harpacticoids were adapted to an "epipelic way of life", by means of a "gradual elongation of limbs". To test this hypothesis I examined four closely related Arctic species to determine if such a predicted gradient of morphological characteristics exists with increasing depth. The deep-sea macrobenthos is highly diverse (Sanders & Hessler, 1969), and harpacticoid copepod assemblages follow this trend (Coull, 1972). Species and genera from the family Cerviniidae are often dominant members of deep-sea benthic copepod communities (Brodskaya, 1963; Por, 1964; Por, 1969; Coull, 1972; Dinet, 1977; Montagna & Carey, 1978). Thus, members of the Cerviniidae are especially good for testing hypotheses about the deep-sea. In general, deep-sea harpacticoids are found patchily distributed at cm and m scales (Thistle, 1978), in agreement with Jumar's (1975) ''grainmatching model". Disturbance/predation is probably also important in structuring these communities since harpacticoids are negatively correlated with the presence of sessile surface-deposit feeding polychaetes (Thistle, 1979). In this study I pro vide information about the nature of speciation in deep-sea harpacticoids.Item Arctic Sea Ice Faunal Assemblage: First Approach to Description and Source of the Underice Meiofauna(InterResearch, 1982) Carey, Jr., Andrew G.; Montagna, Paul A.The ice meiofaunal assemblage in shallow Stefansson Sound off the northern coast of Alaska included Polychaeta, Nematoda. Rotifera and Crustacea. The crustaceans conlprised calanoid copepods, nauplii, 2 species of harpacticoids (Halectinosoma neglecturn and Pseudobradya sp.) shared with the benthos and a cyclopoid copepod (Cycloplna gracilis), probably a benthic epiphytic form. Much of the ice meiofaunal assemblage was dominated by larvae and juveniles. The ice taxa were sparse in numbers (100-1,000 tlmes less than the sediments) and depauperate in specles (e.g. 2 species of harpacticoids versus 28 in the sediments). The ice meiofauna appears to be derived from both sediments and water column. We hypothesize that during sprlng the undersurface of nearshore sea ice acts as a substrate for benthic recruitment and for nourishment of a highly selected fauna. However, the meiofauna is too sparse to be significant in the food web or energy budget in the protected nearshore Beaufort Sea.Item Live controls for radioisotope tracer food chain experiments using meiofauna(InterResearch, 1983) Montagna, Paul A.malin poisoned samples are inadequate for measuring the amount of label to be subtracted as control values for certain food chain studies that employ radioactive tracers. In some studies, tracer is added just before incubation to label 'food' during the feeding study. Commonly, parallel, poisoned incubations are used to distinguish between biotic and abiotic label incorporation. But, a poisoned control does not account for label that could enter a consumer via active transport, epicuticular microfloral uptake, or grazing on labeled, non-food particles. Experiments were performed to test if label uptake is greater in live non-grazing than dead organisms. Marine benthic meiofauna incoporate from 3 to 133 times more tracer when they are alive and not grazing than when they are formalin killed. These results suggest that control experiments with live animals be performed to measure all processes by which label can enter consumers in food chain experiments.Item In situ measurement of meiobenthic grazing rates on sediment bacteria and edaphic diatoms(InterResearch, 1984) Montagna, Paul A.A radioactive tracer technique was used to measure meiofaunal grazing on bacteria and diatom communities in natural sediments. Radioactive '4C-glucose and 14C-bicarbonate were used to label heterotrophs (bacteria) and autotrophs (diatoms), respectively. The labeled compounds were added to undisturbed sediment cores and incubated for 4 h at in situ temperatures. After incubation, radioactivity was determined for the sediment (microbes) and the major meiofaunal taxa. To quantify meiofaunal grazing on microbes, a 3-compartment model was used where: available label is not limiting, microbial uptake is linear, and meiofaunal uptake is hyperbolic. The formula to calculate meiofaunal grazing rate (k) is: k = 2f/t, where f = fraction of meiofaunal radioactivity (DPM) relative to microbial radioactivity at time t. Although microbial actlvity was greater in summer than winter, there were no differences between meiofaunal grazing rates in winter and summer Total meiofaunal ingestion of microbes was dominated by polychaetes. Preliminary results suggest that, on the average, 3 % of the bacteria and 1 % of the diatom communities were removed per hour Thus turnover times of approximately 30 h for bacteria and 6.5 d for diatoms are apparently sufficient to maintain the microbial community in steady state under the meiofaunal grazing regime. This meiofaunal grazing pressure (60 pg bacterial C and 27 pg diatom C ingested 10 cm-2 h-') probably represents a significant stimulatory effect on the microbial community.Item Benthic metabolism in a natural coastal petroleum seep(InterResearch, 1986) Montagna, Paul A.; Bauer, James E.; Prieto, Maria C.; Hardin, Dane; Spies, Robert B.The rates of 3 processes known to be mediated by microbial metabolic activity were measured in the sediments of a shallow-water (18 m depth) natural petroleum seep and a nearby non- seep area near Santa Barbara, California. Measurements of oxygen flux, hydrocarbon degradation, and sulfate reduction were made in the sediments of 3 stations wlth varying amounts of petroleum seepage. At the seep, 1 station was at the margin of active seepage while the 2nd station (20m away) had moderate seepage. A 3rd non-seep station was 2.4 km away from the petroleum seep area. Total oxygen flux was not staustically different among the 3 stations studied. Rates of sulfate reduction and hydrocarbon degradation were greater at seep than non-seep sites. Within the seep area, greater rates of sulfate reduction and hydrocarbon degradation were found at the station of moderate seepage than at the margin of active oil and gas seepage. The greater rates of metabolism at the seep correlate with previous findings of higher amounts of ATP and macrolnfauna at the seep. We hypothesize that the higher abundances of infauna and concentrations of ATP at the seep are sustained by heterotrophlc bacterial degradation of petroleum and the consumption of those bacteria by infauna.Item Temporal variability and the relationship between benthic meiofaunal and microbial populations of a natural coastal petroleum seep(Yale Peabody Museum, 1987) Montagna, Paul A.; Bauer, James E.; Toal, Jon; Hardin, Dane; Spies, Robert B.Previous studies of the Isla Vista petroleum seep in the Santa Barbara Channel found much higher abundances of macrofauna and concentrations of adenosine triphosphate (ATP) in sediments near petroleum seepage compared to those from nonseep areas. To further assess the possible effect of petroleum on organisms at the base of benthic food webs, population abundances of meiobenthos and their suspected microbial food (bacteria and diatoms) were measured biweekly for one year at three stations with differing petroleum exposure. Determinations of suspended particulate matter and the abundance and gut contents of juvenile fishes were also made at seep and nonseep stations.Nematodes and bacteria had higher abundances in areas of active petroleum seepage than in areas of moderate seepage (within 20 m) or no seepage (1.4 km away). Bacterial productivity (based on the frequency of dividing cells) was 340% greater in sediments from areas of active seepage compared to those from a nonseep station. Sediments within the seep, but away from active seepage, had rates of bacterial productivity 15 times greater than a nonseep comparison site. Densities of harpacticoid copepods and their probable principal food, diatoms, were not affected by petroleum seepage. Suspended organic matter caught in settling traps was not different between seep and nonseep stations. In addition, there was no evidence that predation pressure by juvenile fish on meiofauna was different between stations.The higher bacterial biomass and productivity in areas of petroleum seepage are consistent with the hypothesis that petroleum carbon is available for assimilation by sediment bacteria. The enhanced level of microbial carbon associated with the petroleum seep is available for consumption by benthic invertebrates and could explain the higher abundances of macrofauna and meiofauna found there.Item Partitioning radiolabeled thymidine uptake by bacteria and meiofauna using metabolic blocks and poisons in benthic feeding studies*(Marine Biology, 1988) Montagna, Paul A.; Bauer, J. E.Techniques exist which allow for the measurement of in situ grazing rates of meiobenthos on sedimentary bacteria and microalgae. Radiolabeled substrates are incorporated into microbes which serve as food for meiofauna and which themselves also become labeled during feeding. However, during in situ grazing experiments, meiofauna may become radiolabeled by a variety of non-feeding processes. Proper controls to correct for these extraneous routes of labeling have been developed in the present study. The use of [methyl-3H] thymidine (3HTdR) in studies of meiofaunal grazing on bacteria has two unique advantages: (1) it is incorporated only into prokaryotic macromolecules, and (2) bacterial incorporation of 3HTdR may be selectively blocked by several inhibitors which are non-toxic to meio faunal grazers. Coupled with formalin-killed control treat ments, the use of these inhibitors makes it possible to accu rately determine the partitioning of radiolabel into meiofauna during grazing into adsorptive, absorptive and grazing components. A saturated solution of nalidixic acid and 5'-deoxythymidine was found to be most effective in inhibiting water-column bacterial uptake and incorporation of 3HTdR, and had no toxic effects on meiofauna. The inhib itor was found to immediately block bacterial incorporation of 3HTdR and was as effective at 20% saturation as at 100%. The presence of sediment reduced the effectiveness of this inhibitor by 50%. Solutions of the inhibitor with excess undissolved material, however, completely blocked sediment bacterial uptake of 3HTdR. Employing these techniques during in situ grazing experiments showed that up to 83% of total meiofaunal uptake of 3H-label may be attributable to non-grazing processes. Experiments conducted in slurried sediments yielded grazing rates which were the same as those from intact cores. Furthermore, meiofaunal grazing rates on multiple food sources (e.g. bacteria and diatoms) may be determined synoptically by adding isotopically-distinct sub strates (e.g. 3HTdR and H14CO3) to the same experimental incubation.Item Vertical distribution of microbial and meiofaunal populations in sediments of a natural coastal hydrocarbon seep(Yale Peabody Museum, 1989) Montagna, Paul A.; Bauer, James E.; Hardin, Dane; Spies, Robert B.We studied the vertical distribution of microbes and meiofauna in natural hydrocarbon seep sediments to determine if there was a relationship between profiles of benthic trophic structure and the unique biogeochemical conditions present at the seep. Three stations in the Santa Barbara Channel represented a gradient of natural petroleum seepage, from very active, to moderate, to none. Seasonal differences were examined by sampling in the three major oceanographic seasons, upwelling (April), mixed (July), and Davidson (December). Densities of microbes and meiofauna were highest in July, and decreased in winter. All population sizes decreased with increasing depth in the sediment. Harpacticoids and Chl a were practically restricted to the surface sediments. Harpacticoids and Chl a were more dense (number per unit volume or strata of sediment) and abundant (number per unit area of sediment or sum of the strata) at the comparison site than at the seep sites. Density and abundance of nematodes, bacteria cell counts, and bacterial biomass were greater at the station with the most active seepage rates. Bacterial biovolumes appeared constant among sediment depths and stations, but cell biovolumes were larger in July. The data are consistent with the hypothesis that organic enrichment via petroleum utilization is responsible for increased abundances of bacteria and nematodes at the seep. There were strong correlations between densities of harpacticoids and microalgae, and densities of nematodes and bacteria. These links indicate that seeping petroleum might have an enhanced effect on the detrital (bacterial based) food web, but a toxic effect on the grazing (microalgal based) food web.Item Microbial biogeochemistry and heterotrophy in sediments of a marine hydrocarbon seep(Limnology and Oceanography, 1989) Bauer, James E.; Montagna, Paul A.; Spies, Robert B.; Prieto, Maria C.; Hardin, DaneVertical profiles of sediment and pore-water constituents and rates of microbially mediated geochemical processes were determined in surficial sediments (0-7-cm depth) of three stations in and around Isla Vista hydrocarbon seep off Santa Barbara, California. Measurements were made of pore-water alkalinity (total and carbonate), pH, Eh, dissolved oxygen, sulfate, and sulfide, total sedimentary organic carbon (TOC) and nitrogen, ATP, sulfate reduction and dark bicarbonate uptake and incorporation, and oxygen flux across the sediment-water interface in benthic chambers. In general, alkalinity, pH, sulfide, TOC, ATP, and all rate processes were greatest in sediments of that station (A) with active seepage and decreased with increasing distance from the seep. Sulfate depletion and extremely low Eh values occurred in station A sediments. At a station (B) with lower seepage rates than station A, sedimentary and pore-water constituents and rate processes were intermediate those measured at station A and a station (C) without seepage. Pore-water and sedimentary constituents as well as oxygen flux were strongly correlated with total extractable sedimentary hydrocarbons (TEH) measured at each station and for each corresponding depth interval. All parameters exhibited seasonal differences that may have been temperature-dependent. The greater concentrations of TEH, sulfide, and alkalinity with increasing sedimentary depth indicate that seep sediments are a source of these constituents to the water column and a sink for 02 and S042-. The strong heterotrophic, and possibly chemoautotrophic, character of seep sediments resembles that of other organically enriched systems. The diagenesis of petroleum hydrocarbons is a function of the biogeochemical patterns and microbial heterotrophic activities in surficial sedimentItem The effect on freshwater inflow on macrobenthos in the Lavaca River delta and upper Lavaca Bay, Texas(Contributions in Marine Science, 1991) Kalke, R.; Montagna, Paul A.A two year study on the effects of freshwater inflow on macrobenthos at selected sites in the upper portion of the Lavaca River and Bay was conducted from November 1984 through August 1986. Lowest densities occurred in lakes, and highest densities occurred in creek deltas. Sediment grain size did not have a significant effect on spatial distributions. The first year of the study had higher inflow rates than the second year. Temporal changes of inflow had a larger effect on spatial variability, because freshwater species had extended ranges during the high-flow year. Temporal variation in the benthic community during the study was caused by population changes of low salinity species, and this was associated with high inflow rates during the first year. Freshwater inflow is apparently necessary to induce the recruitment oflow salinity species in the upper bay. Chironomid larvae and the polychaete, Hobsonia florida, increased in density approximately 4 weeks after an inflow event. In contrast, the mollusks, Mulinia lateralis and Macoma mitchelli, had increased densities during the low inflow period resulting in high benthic biomass. Streblospio benedicti, a surface deposit-filter feeder, and Mediomastus californiensis, a burrowing deposit-feeder, were also positively correlated with increasing salinity during low inflow periods. Chlorophyll-a concentration in the surface water increased with inflow, indicating primary production was stimulated by inflow, and then decreased with increased salinity and increased filter feeder biomass. Non-molluskan benthic biomass was similar during wet and dry periods, and had a positive relationship with chlorophyll-a concentration. The amount, timing, and inter-annual variation of inflow influence both the spatial and temporal abundance and biomass ofbenthic macrofauna.Item Photosynthetic response of natural assemblages of marine benthic microalgae to short- and long-term variations of incident irradiance in Baffin Bay, Texas.(Journal of Phycology, 1992-02) Blanchard, Gerard F.; Montagna, Paul A.This study was designed to understand the high variability characterizing primary production rates of microphytobenthos. The photosynthetic efficiency (αB) and photosynthetic capacity (PBmax) of the microphytobenthos were measured at different times of the day on two different dates (8 May and 7 July 1990). In July, unusually low light conditions were caused by the development of a brown tide (chrysophytes). Both light-limited and light-saturated photosynthesis changed at hourly and monthly scales. There was a linear relationship between αB and PBmax, suggesting a common response to environmental factors [αB= 0.0075(±0.00063)·PBmax+ 0.00097(±0.0071), R2= 0.94]. Incident irradiance at the sediment-water interface was the primary physical factor that explained variability of both αB (84%) and PBmax (92%). Temperature had a negative but minor effect that explained an extra 8% and 2% of the variance, respectively. There was no diel rhythm of αB and PBmax and incident irradiance was regulated by wind-induced currents. Therefore, microphytobenthos photosynthesis seemed to be primarily controlled by wind events in Baffin Bay.Item The effect of freshwater inflow on meiofaunal and macrofaunal populations in the Guadalupe and Nueces Estuaries, Texas(Estuaries, 1992-09) Kalke, Richard D.; Montagna, Paul A.Two estuaries with very different inflow characteristics were compared to test the hypothesis that benthic standing crops are enhanced by freshwater inflow. Assuming predation pressure is similar in both estuaries, this would imply that freshwater inflow enhances secondary production. The Guadalupe Estuary had 79 times more freshwater inflow than the Nueces Estuary, and a third of the salinity. The Guadalupe had higher macrofaunal densities and biomass than the Nueces, and both parameters increased with decreasing salinity within the Guadalupe Estuary. Macrofauna density increased with increasing salinity in the Nueces Estuary, due to invasion by marine species. However, meiofauna population size responds differently than macrofauna. Meiofaunal densities were higher in the low-inflow Nueces Estuary, and increased with increasing salinity in both estuaries. Macrofauna diversity increased with salinity, both within and between estuaries. The macrofauna response supports the hypothesis that increased freshwater inflow stimulates secondary production. A review of past benthic studies in these estuaries and the historical climatic patterns indicate that wet years with high inflow result in increased macrofaunal productivity. Since, macrofaunal diversity decreased with lower salinity both within and between the estuaries, the enhanced productivity is due to increases by freshwater and estuarine species that can tolerate low salinities. Increased macrofaunal densities are associated with decreasing meiofaunal densities. The latter result could be due to either increased macrofaunal competition with or predation on meiofauna, or a lack of low-salinity tolerance by meiofauna.Item Dwarf surfclam Mulinia lateralis (Say, 1822) populations and feeding during the Texas brown tide event(National Shellfisheries Association, 1993) Montagna, Paul A.In 1990, there was an unusual brown tide bloom of an aberrant Chrysophyte sp, in Baffin Bay and Laguna Madre near Corpus Christi, Texas. Coincident with the bloom was a dramatic loss of shellfish in Baffin Bay and Laguna Madre, The dominant clam, Mulinia lateralis. disappeared for about two years. Wc performed a series of experiments to determine if disappearance of M. lateralis was related to negative feeding interactions with the brown tide organism, Radioactive tracers were used to compare feeding rates on brown tide, Isochrysis galbana, DUllalielia tertioleera. and Heterocapsa pygmeae. At low cell concentrations « I,000 cells' ml" I), M. lateralis grazing rates (ccll . h-I) increased with concentration and were similar among the microalgal species. At higher concentrations, grazing rates on lsochrysis were inhibited, but remained the same for the other microalgal species. Assimilation efficiency by M. lateralis was lowest on Heterocapsa, and was about the same for the three other species of algae. The high grazing and assimilation rates of brown tide by M. lateralis indicate that the loss of the clam population was not likely caused by a negative trophic effect of the brown tide. Other bloom factors, e.g. reproductive effects or toxic effects, may have contributed to the concomitant loss of the clam population and the occurrence of brown tide. It is also possible that non-bloom factors, e.g. natural population variability increased predation pressure, could have caused the population loss. The reduced populations of filter feeders could have been partially responsible for conditions conducive for the brown tide bloom.