Peter N. Slattery

Destruction and Opportunity on the Sea Floor: Effects of Gray Whale Feeding

Gray whales (Eschrichtius robustus) are highly disruptive bottom feeders that remove infaunal invertebrate prey and sediments by suction. The response of the benthos to gray whale feeding was examined in the primary feeding grounds of the Bering Sea and in an ecological analog of these prey communities along the west coast of Vancouver Island. Prey communities were dominated by ampeliscid and other amphipod crustaceans that formed dense tube mats. Large feeding excavations (often 2-20 M2) were rapidly colonized by scavenging lysianassid amphipods, especially Anonyx spp., that attacked injured and dislodged infauna. Many of the attacked animals were small crustaceans ( 2 mo. Early colonists were characterized by much greater abundances inside excavations relative to the adjacent tube mat. Two numerically dominant groups of tube-dwelling amphipods were not charac- terized by a large pulse of abundance inside excavations. Ampelisca and Protomedeia gradually col- onized pits. They also swam less frequently than the early colonists, and probably had more infaunal habits. Gray whale feeding clearly has a dramatic impact on the structure of benthic communities, and also may enhance the population size of several secondary prey.

Effects of crustacean predators on species composition and population structure of soft-bodied infauna from Mcmurdo sound, Antarctica

Abstract A tanaid crustacean (Nototanais), and especially a phoxocephalid amphipod (Heterophoxus), regulate the species composition and population-size structure of soft-bodied infauna (primarily polychaete worms) by preying on small species and small individuals of large species. Small individuals of soft-bodied infauna are rare in this dense infaunal assemblage (over 100000/m2) from Antarctica. The evidence for the regulatory role of the peracarid crustaceans comes from gut contents; from laboratory experiments where the crustaceans consume spionid larvae or juveniles and small polychaete species; from field experiments where the abundances of crustaceans and small polychaetes are negatively correlated after the colonization of defaunated sediments; from exploring the role of depth refuges in the sediment; and from community patterns along a gradient in water depth where crustacean abundance is negatively correlated with the abundance of small species and small individuals of large polychaete species. B...

Walrus feeding disturbance: Scavenging habits and recolonization of the Bering Sea benthos☆

Walruses (Odobenus rosmarus Illiger) influenced the structure of macrobenthic assemblages in a variety of ways as they excavated their major bivalve prey from soft sediments. Benthic animals were attracted to discarded bivalve shells and they colonized pits and furrows made during prey excavation. Discarded shells contained soft tissues that were eaten by several invertebrate scavengers. The most abundant and widespread scavenger was the sea star, Asterias amurensis Lutken. Sea stars out-competed brittle stars (Amphiodia craterodmeta Clark) for fresh scavenging events. They also attacked brittle stars under shells in the laboratory, and thus may have obtained two meals from discarded shells by eating remnant tissue and by consuming animals that used the shell as a habitat. In nature, brittle stars were abundant under discarded shells. In experiments, brittle stars invaded shells with soft tissue in the absence of sea stars, but not in their presence. In other experiments, brittle stars were most abundant under shells with soft tissue, but were also attracted to shells without organic matter. Large brittle stars were more abundant under shells than in the surrounding bottom, and the reverse was true of small individuals. Bottom communities recovered gradually inside experimental feeding excavations, which were not invaded by large numbers of opportunistic infaunal or epifaunal invertebrates. This is in contrast to gray whale feeding excavations, which are colonized by a large number of opportunistic peracarid crustaceans.

Patterns of survival and behavior in Antarctic benthic invertebrates exposed to contaminated sediments: field and laboratory bioassay experiments

Benthic invertebrates were exposed to chemically contaminated sediments (primarily petroleum hydrocarbons) from a well-defined pollution gradient around McMurdo Station, Antarctica in a series of field and laboratory bioassay experiments. The patterns of survival and behavior in these experiments corresponded to patterns observed in standard U.S. Environmental Protection Agency laboratory bioassays. The contaminated end of the pollution gradient is Winter Quarters Bay where total hydrocarbons are as high as 4500 μg·g sediment−1. Mortality of Heterophoxus videns K.H. Barnard, a phoxocephalid amphipod crustacean, in standard laboratory bioassays was highest in sediment from Winter Quarters Bay, high in sewage outfall sediments, and generally decreased in sediments from increasing distances from the bay. Similar survival patterns were documented for several other crustacean species. Amphipods, tanaids, and cumaceans consistently avoided sediments from Winter Quarters Bay in the survival bioassays and were more abundant in uncontaminated sediments in laboratory habitat choice experiments. Fewer H. videns and the heart urchin, Abatus shackletoni Koehler, burrowed into Winter Quarters Bay sediment compared with uncontaminated sediment in field and laboratory assays. We exposed H. videns and Eudorella splendida Zimmer, a cumacean, to Winter Quarters Bay and uncontaminated sediments for 10 and 28 days in field bioassays. Greater mortality was evident in Winter Quarters Bay sediment but the difference between treatments was not significant. In contrast, when benthic communities were transplanted along the pollution gradient and sampled a year later, there were dramatic changes in community structure in Winter Quarters Bay, less at the edge of the bay, and little at an uncontaminated site. Overall, these assays showed similar patterns of increased survival decreased avoidance of sediment along a steep and well-defined pollution gradient.

Scavenging and Other Feeding Habits of Lysianassid Amphipods (Orchomene spp.) from McMurdo Sound, Antarctica

SummaryThe distribution and scavenging habits of the two most abundant lysianassid amphipods in McMurdo Sound differ markedly. Orchomene plebs lives primarily in deep water (>100 m), where planktonic and benthic food is sparser and scavenging events are less common and predictable than in shallower water. Orchomene plebs is common in shallow areas (<100 m) only under the Ross Ice Shelf and along the western McMurdo Sound. Here Weddell seals frequent tidal cracks in which they discard carrion and defecate; otherwise food is scarce. Orchomene pinguides lives on shallow (<10 m) wave-cut benches that are rich in food along the eastern McMurdo Sound. They, along with other omnivorous invertebrates which scavenge the food-rich eastern sound benches, are rare from shallow water along the western sound. The eastern benches are bathed by dense plankton blooms and harbor a high biomass of benthic diatoms and invertebrates. Scavenging events there were observed throughout the year. Orchomene plebs is larger and more motile, and came to laboratory carrion and baited field traps more rapidly and in greater numbers than O. pinguides. The crop contents of O. plebs contained only amorphous organic matter that suggested a scavenging habit. Crops of O. pinguides contained not only amorphous organic matter but also invertebrate prey, especially planktonic copepods that impact the bottom during winter.

LIFE HISTORIES OF INFAUNAL AMPHIPODS FROM SUBTIDAL SANDS OF MONTEREY BAY, CALIFORNIA

ABSTRACT Members of the amphipod families Phoxocephalidae and Haustoriidae are small, mobile, efficient sand-burrowers. Three species are particularly dominant in the crustacean zone on subtidal sands of Monterey Bay. Life history traits of two phoxocephalids and one haustoriid characterize them as annual, univoltine, and producing a few, large eggs. However, the two families differ in several significant ways: time of year that they reproduce, sex ratios, swimming behavior, and diet. These contrasts reflect greater specialization, including method of reproduction, in the haustoriids. These differences suggest that the phoxocephalids retain typical gammaridean amphipod reproductive methods which compromise their burrowing life-style through disadvantageous morphological and behavioral characteristics.

Habitat-Related Benthic Macrofaunal Assemblages of Bays and Estuaries of the Western United States

Data from 7 coastwide and regional benthic surveys were combined and used to assess the number and distribution of estuarine benthic macrofaunal assemblages of the western United States. Q-mode cluster analysis was applied to 714 samples and site groupings were tested for differences in 4 habitat factors (latitude, salinity, sediment grain size, and depth). Eight macrofaunal assemblages, structured primarily by latitude, salinity, and sediment grain size, were identified: (A) Puget Sound fine sediment, (B) Puget Sound coarse sediment, (C) southern California marine bays, (D) polyhaline central San Francisco Bay, (E) shallow estuaries and wetlands, (F) saline very coarse sediment, (G) mesohaline San Francisco Bay, and (H) limnetic and oligohaline. The Puget Sound, southern California, and San Francisco Bay assemblages were geographically distinct, while Assemblages E, F and H were distributed widely along the entire coast. A second Q-mode cluster analysis was conducted after adding replicate samples that were available from some of the sites and temporal replicates that were available for sites that were sampled in successive years. Variabilities due to small spatial scale habitat heterogeneity and temporal change were both low in Puget Sound, but temporal variability was high in the San Francisco estuary where large fluctuations in freshwater inputs and salinity among years leads to spatial relocation of the assemblages.

Effect of sample area and sieve size on benthic macrofaunal community condition assessments in california enclosed bays and estuaries

Benthic macrofauna are used extensively for environmental assessment, but the area sampled and sieve sizes used to capture animals often differ among studies. Here, we sampled 80 sites using 3 different sized sampling areas (0.1, 0.05, 0.0071 m(2)) and sieved those sediments through each of 2 screen sizes (0.5, 1 mm) to evaluate their effect on number of individuals, number of species, dominance, nonmetric multidimensional scaling (MDS) ordination, and benthic community condition indices that are used to assess sediment quality in California. Sample area had little effect on abundance but substantially affected numbers of species, which are not easily scaled to a standard area. Sieve size had a substantial effect on both measures, with the 1-mm screen capturing only 74% of the species and 68% of the individuals collected in the 0.5-mm screen. These differences, though, had little effect on the ability to differentiate samples along gradients in ordination space. Benthic indices generally ranked sample condition in the same order regardless of gear, although the absolute scoring of condition was affected by gear type. The largest differences in condition assessment were observed for the 0.0071-m(2) gear. Benthic indices based on numbers of species were more affected than those based on relative abundance, primarily because we were unable to scale species number to a common area as we did for abundance.

Microhabitats and Population Densities of California Legless Lizards, with Comments on Effectiveness of Various Techniques for Estimating Numbers of Fossorial Reptiles

Abstract We studied the cryptic fossorial legless lizard (Anniella pulchra) in a 1.57-ha area of sand dune on the coast of central California. This is the largest and most dense population of A. pulchra (N = 3,582; 0.228/m2) known to date. We documented distribution of animals through systematic removal and relocation of lizards at the site and with GIS analyses. Lizard density was high near shrubs and where soil moisture was greater but lower in disturbed soils and in iceplant. We also conducted time-constrained searches and coverboard surveys to analyze the efficacy of standard survey methods for legless lizards. Moderate-impact time-constrained searches were more effective in establishing presence of lizards when compared to low-impact time-constrained searches and coverboard surveys. Our data show that standard methods may not be effective in establishing presence or absence of this lizard at low densities. None of the survey methods was effective in predicting the density of lizards actually present.