Henry M. Page

Temporal and spatial patterns of growth in mussels Mytilus edulis on an offshore platform: relationships to water temperature and food availability

Abstract Temporal and spatial (depth) patterns of shell growth were studied in the mussel Mytilus edulis in relation to water temperature and potential food availability, at an offshore oil platform, Holly (ARCO), in the Santa Barbara Channel, California. Length-specific growth rates were highest from late May to July and at a depth of 9 m. The time to achieve a length of 50 mm from recruitment was estimated at 6–8 months. Growth rates were not correlated with water temperature, using multiple regression and correlation analysis. Temporal variation in the growth of 20- and 35-mm mussels correlated with chlorophyll a concentration at time lags of 2 and 4 wk, respectively. Variation in growth of mussels with depth was more closely associated with the concentration of particulate organic carbon than with chlorophyll a . Our results indicate that water temperature can be disregarded as an important factor in regulating mussel growth in California waters, but that growth could vary in association with well-documented regional variation in phytoplankton biomass.

Experimental evidence for filter-feeding by the hydrothermal vent mussel, Bathymodiolus thermophilus

We provide experimental evidence, using a high-pressure recirculating aquarium and radiolabeled bacteria, that the hydrothermal vent mussel. Bathymodiolus thermophilus, can clear and assimilate particulate organic matter. Our results support previous evidence that this mussel can filter-feed on particulate organic matter to supplement nutrients provided by endosymbiotic chemoautotrophic bacteria.

Role of filter-feeding in the nutritional biology of a deep-sea mussel with methanotrophic symbionts

The ability of an undescribed deep-sea hydrocarbon-seep mussel which contains endosymbiotic methanotrophic bacteria to clear, ingest, and assimilate radiolabeled bacteria (Vibrio pelagicus andEscherichia coli) and algae (Dunaliella tertiolecta) was compared with that of the bay musselMytilus edulis. The seep mussel, collected in August 1987 from the Louisana Slope in the Gulf of Mexico, was slower to clear bacteria and algae thanM. edulis. The ingestion and assimilation of filtered bacteria and algae was established from the presence of radiolabel in mussel tissues and feces. The seep mussel was somewhat less efficient in assimilating radiolabeled components from bacteria and algae thanM. edulis. The dietary carbon maintenance-requirement of the seep mussel could potentially be met at environmental concentrations of greater than 106 bacteria ml−1. At lower concentrations of particulate organic matter, filter-feeding could be an important source of nitrogen and essential nutrients not supplied by the endosymbionts.

Variation in the natural abundance of 15N in the halophyte, Salicornia virginica, associated with groundwater subsidies of nitrogen in a southern California salt-marsh

To provide insight into the importance of the salt-marsh ecotone as a sink for inorganic nitrogen in perched groundwater, measurements were made of the natural abundance of 15N in dissolved NO3-N and NH4-N and in the salt-marsh halophyte, Salicornia virginica, along an environmental gradient from agricultural land into a salt-marsh. The increase in the natural abundance of 15N (expressed by convention as δ15N) of NO3-N, accompanied by the decrease in NO3-N (and total dissolved inorganic N, DIN) concentration along the gradient, suggested that the salt-marsh ecotone is a site of transformation, most likely through denitrification, of inorganic nitrogen in groundwater. 15N enrichment in S. virginica (and the parasitic herb, Cuscuta salina), along the tidal marsh boundary, relative to high and middle marsh locations, indicated the retention of groundwater nitrogen as vegetative biomass. The correlation between δ15NSalicornia and δ15NNH4 suggested a preference for NH4-N over NO3-N during uptake by this plant. Groundwater inputs enhanced the standing crop, above-ground productivity, and nitrogen content of S. virginica but the ralative effects of pore water salinity and DIN concentration on these parameters were not determined. 15N enrichment of marsh plants by groundwater DIN inputs could prove useful in tracing the fate of these inputs in the marsh food web.

Experimental evaluation of biases associated with sampling estuarine fishes with seines

Beach seines are widely used to estimate the density and species richness of fishes in estuaries. We evaluated the causes and extent of bias in estimates from seines using a series of field experiments in small estuaries in southern California, USA. Seining in spatially paired areas that were either enclosed by block nets or not, revealed that seines used without block nets und erestimated density by more than 4-fold and species richness by more than 2-fold relative to blocked areas. Seining in paired blocked areas with seines of two lengths revealed that net length affected estimates of density, but not species richness; a 7.6-m long seine produced 1.6-fold higher estimates of total density than did a 15.2-m long seine due to increased catches of demersal fishes, but not midwater species. Paired sampling in blocked areas also revealed that many fishes initially evaded capture by the seine. Estimates of density but not species richness were significantly higher in areas through which a seine was swept 5 times compared to once. This was due to higher catches of demersal fishes but not midwater fishes in areas seined 5 times. Repeated seining through blocked areas revealed that the vast majority (90% or more) of species and individuals of midwater fishes were captured within the first 5 sweeps, compared to only about 50% of the individuals of demersal species. A mark-recapture study in blocked areas revealed lower probabilities of capture for demersal species relative to midwater species.

Local variation in reproductive patterns of two species of intertidal barnacles, Pollicipes polymerus Sowerby and Chthamalus fissus Darwin

Reproductive patterns, percentage of barnacles with egg masses together with size of egg masses, were studied for two species of intertidal barnacles, Pollicipes polymerus Sowerby and Chthamalus fissus Darwin, in three locations. Percentage with egg masses of both species was highest at lower intertidal levels. Seasonal changes were evident in the percentage of Pollicipes polymerus with egg masses and weight of egg masses of this species, standardized for barnacle size, varied with location and season. Weight of egg masses of Chthamalus fissus varied only with location. Weight of egg masses, as a percentage of body weight, ranged from 4 to 21% for Pollicipes and from 33 to 108% for Chthamalus. Estimates of annual reproductive effort for both species increased at lower intertidal levels. A high reproductive output of C. fissus that settle low intertidally may offset high mortality at this tidal level.

Effect of water temperature and food on energy allocation in the stalked barnacle, Pollicipes polymerus Sowerby

Abstract The effects of water temperature and food level on absorption efficiency, rate of oxygen consumption, molting rate, reproductive condition, energy content, and total production have been studied in the stalked barnacle, Pollicipes polymerus Sowerby. Absorption efficiency measured gravimetrically was high (≈94%) and unaffected by water temperature or food level. Absorption efficiency measured using an ash-ratio method was substantially less than that determined gravimetrically. The rate of oxygen consumption increased in the high food treatments and decreased in the starved treatment after 40 days. Molting rate, energy content, and total production were highest in the high food treatments. Reproduction was inhibited at warm water temperatures. The greater influence of food level than water temperature on production is probably related to the thermal regime experienced by these animals in the field.

Comparative effects of infaunal bivalves on an epibenthic microalgal community

Abstract The effects of three infaunal bivalves on an epibenthic microalgal community were studied in a tidal channel at Carpinteria Salt Marsh, California, USA. Sediment Chl a concentration was patchy, ranging from ≈ 1 to ≈ 5.5 μd·cm −2 . Chl a concentrations in 78.5-cm 2 sample plots was negatively correlated with the density of the deposit-feeder Macoma nasuta , but not the suspension-feeders Protothaca staminea and Tagelus californianus within those plots. In field experiments, M. nasuta inhibited the development of microalgal standing stock relative to P. staminea and Control treatments. The effect of M. nasuta on microalgae varied with clam density. M. nasuta also reduced existing microalgal standing stock but without affecting the relative abundance of common diatom species. Our results indicate that the random distribution of the deposit-feeding M. nasuta contributed to small-scale patchiness in microalgal standing stock, locally reducing the availability of microalgae to infaunal as well as epifaunal benthic consumers.

Effects of non-native Spartina patens on plant and sediment organic matter carbon incorporation into the local invertebrate community

The cycling of organic matter through food webs is a fundamental process that may be altered by the invasion of non-indigenous plants. We explored consequences of the invasion of non-indigenous Spartina patens to the composition of soil organic matter (SOM) and to detritivore and herbivore diets in the upper salt marsh within Corrubedo National Park, northwest Spain. We tested for the incorporation of S. patens carbon (C) into SOM and by detritivores and herbivores using stable isotope analysis, focusing primarily on detritivorous enchytraeid oligochaetes and herbivorous insects. Stable isotope results indicated that C derived from S. patens has been incorporated into SOM. Elevated densities of enchytraeids in stands of S. patens, and their incorporation of C derived from this plant, suggested that dense patches of S. patens may facilitate detritivore populations. In contrast, although insect herbivores used S. patens as habitat, there was little isotopic evidence for the widespread incorporation of S. patens-derived C by these consumers. The population and dietary response of enchytraeids to S. patens suggests that S. patens invasion could indirectly influence soil processes and pathways mediated by detritivore activity (e.g., soil respiration rates, nutrient retention and transformation, energy flow). The loss of food resources to insect herbivores alters local food webs. However, insect herbivores may move and feed on native plants elsewhere. As a result, insect populations may be less immediately impacted than soil detritivore populations by S. patens. Our study suggests that the influences of S. patens invasion extend beyond the more obvious changes in native plant abundance, to include differing responses in the cycling of organic matter between detritivore and insect herbivore food web pathways.

Sampling characteristics and biases of enclosure traps for sampling fishes in estuaries

We evaluated the sampling characteristics of enclosure traps in estuaries in southern California, USA. Using enclosure traps that sampled 0.25, 0.5, and 1-m2 footprints, we found that enclosure trap size significantly affected estimates of fish density and the precision of these estimates. The highest estimates were produced by the 0.5-m2 trap and the lowest by the 0.25-m2 trap. Precision of the density estimates improved with increasing trap size, while the proportion of zero values in the data sets decreased and estimates of species richness increased. The largest trap was difficult to use in the field and often did not function properly; thus we concluded that intermediate enclosure trap sizes offered the best compromise between statistical and logistical considerations. By examination of burrows in sediment cores taken in fished out enclosure traps, we found no evidence to support the widely held view that burrow-dwelling fishes evaded capture by hiding in burrows. We also used mark-recapture techniques to estimate recovery efficiency in 0.43-m2 enclosure traps. Recovery efficiency averaged 91% and did not differ significantly among estuaries or sampling stations within estuaries. Based on extensive netting within enclosure traps, we determined that in areas with dense fish populations (>90 fish 0.43-m−2), netting could be ceased after the first sweep that captured no fish with only a trivial effect on the estimate of density. In more sparsely populated areas, netting had to continue until 2–3 sweeps had captured no fish in order to obtain estimates of density that were within 90% of the actual values present. Overall, we found enclosure traps to be effective tools for sampling small, abundant fishes in shallow estuaries in southern California, but we recommend that care be taken when choosing trap size and sampling (netting) effort within traps in order to optimize their sampling characteristics.