Jane April

Anita McCulloch

Central place foraging is the theory that animals will leave a fixed site in order to forage. The theory of central place foraging was first tested by Hamilton and Watt (1970) using roosting brids. This study proved
inconclusive, however, since it is difficult to monitor birds because of their high mobility. It is also difficult to measure the bird's amount of foraging. A less mobile, easily monitorable animal is needed. Limpets provide the perfect animal. They are move slowly, have small travel areas, and their radulas leave easily traceable marks. This study will test the clustering behavior of the high intertidal limpet, Lottia digitalis, in terms of foraging strategies and energetics. This study consists of original experimentation in the field, as well as in the laboratory, in an attempt to gain insight into limpet behavior and central place foraging.

Nearshore circulation patterns affected by shoreline irregularities, such as headlands and embayments, can modify circulation creating eddies and fronts that may affect larval recruitment. Several studies have looked at the circulation within larger bays and behind headlands, but few studies have focused on small-scale circulation on the order of several 100 m to a few km. The topographical generated secondary circulation (front) may affect the dispersal of larvae by: (1) acting as a barrier to larvae that have gone through part of their development offshore and are migrating to settlement sites onshore, or (2) exploiting these flow regimes to limit their dispersal. We investigated the nearshore small-scale circulation patterns and the effects on larval dispersal and settlement. At the mouth of Sunset Bay, Oregon, during the summer, there is a persistent front that is delineated by a band of foam and detritus. To identify and describe the front, vertical profiles of temperature, salinity, and chlorophyll a were obtained with a CTD. Inshore and offshore of the front, subtidal moorings containing settlement plates, Tuffys, and mooring larval collectors were sampled every other day. Concurrent with mooring sampling, vertical plankton tows were conducted to determine meroplankton distribution.

RESEARCH:

Estuarine Delivery and Transport Mechanisms:

Knowledge of the mechanisms responsible for larval dispersal, transport, and delivery is necessary to understand population maintenance and regulation of marine organisms. Population cycles are highly variable and often appear erratic. Advances in recruitment models, however, have been made with the incorporation of physical factors that regulate larval dispersal and transport. Several physical mechanisms of cross-shelf and nearshore larval transport have been documented, such as Ekman-driven surface water transport, internal waves, and tidal stream transport. Their role, however, in regulating patterns of larval delivery to the nearshore and estuaries is unclear for many fish species. The extent of larval exchange among nearshore and estuarine areas on local and regional scales is also poorly understood. Oregon’s coastal region is part of the North Pacific eastern boundary current where seasonal, wind-driven upwelling enhances production. Typically, periods of intense summer upwelling and winter downwelling are separated by transition periods, one in the spring and fall during which wind direction reverses frequently.
The proposed research will 1) determine the seasonal use of Coos Bay by larval and juvenile fishes on a daily frequency; 2) examine potential delivery mechanisms, such as wind-driven and tidal transport; 3) examine interannual patterns in fish use; and 4) test the hypothesis that coastal fishes spawn during winter downwelling events, possibly to reduce offshore loss due to advection. Daily light trap collections at three locations in Coos Bay, OR will be used to address these questions. Traps will be located in the Charleston Harbor’s outer boat basin and distant fleet facility and within the South Slough National Estuarine Reserve (SSNERR). Daily catch will be examined in relation to physical factors, including alongshore and cross-shore wind stress, upwelling indices, and sea surface temperature. Otolith microstructure analysis will be used to determine age and time of hatch to provide additional information on spawn timing and delivery patterns of selected species.

Regional Transport:

The analysis of trace elements in otoliths has been used to identify fish from distinct coastal areas and to reconstruct environmental histories. Laser-ablation inductively coupled mass spectrometry (LA-ICPMS) will be used to determine if otolith trace elements can distinguish adult and larval fishes from distinct sites along Oregon’s coast. Unique elemental signatures from adults along the coast would provide reference markers for the interpretation of larval signatures. Comparisons of signatures could then supply information on the regional extent of larval dispersal. Consistent site differences in otolith elemental fingerprints would aid the reconstruction of larval transport histories. The extent of larval exchange among nearshore and estuarine regions could then be estimated, thereby providing a tool to test the open population assumption.
Otolith elemental signatures of coastal benthic fishes, specifically the black rockfish (Sebastes melanops) and the staghorn sculpin (Leptocottus armatus), will be examined. The Cottidae (the sculpins) and Scorpaenidae (the rockfishes) are the most common and speciose families in the NE Pacific. The hypothesis that coastal populations of S. melanops and L. armatus are open with extensive larval exchange can be tested with otolith elemental analysis. Adults of each species will be collected with minnow trap (L. armatus), or seine (both species) or hook and line ( S. melanops) within the Rogue River region, Coos Bay, and the Columbia River estuary. Otoliths will be removed with glass probes, washed, air-dried, and stored in acid-washed plastic containers to avoid contamination. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) will be used to quantify isotopic concentrations. Ten to fifteen isotopes (including Fe57, Mg24/25, Mn55, Sr86/87) will be measured at three to five points along the otolith radius, depending on otolith size, and standardized relative to Ca44/48 concentrations. Those with adequate background levels and minimal interference will be used for statistical analysis. An ANOVA will be used to compare individual elements within and between locations. After identification of useful isotopes, discriminant function analysis can be used to further partition variance and examine relationships among locations and elements (Thorrold et al. 1988). If elemental signatures among adults are identified based on location, elemental signatures of otoliths from juveniles collected in the same locations will be similarly analyzed. If extensive dispersal occurs, juvenile signatures are expected to reflect a mixture of the signatures identified in adults. Alternatively, if larvae remain within a relatively narrow stretch of coastline, then elemental signatures are expected to be similar to those of local adults.