Alan C. Trimble

Compliant Realignment of Binding Sites in Muscle: Transient Behavior and Mechanical Tuning

The presence of compliance in the lattice of filaments in muscle raises a number of concerns about how one accounts for force generation in the context of the cross-bridge cycle--binding site motions and coupling between cross-bridges confound more traditional analyses. To explore these issues, we developed a spatially explicit, mechanochemical model of skeletal muscle contraction. With a simple three-state model of the cross-bridge cycle, we used a Monte Carlo simulation to compute the instantaneous balance of forces throughout the filament lattice, accounting for both thin and thick filament distortions in response to cross-bridge forces. This approach is compared to more traditional mass action kinetic models (in the form of coupled partial differential equations) that assume filament inextensibility. We also monitored instantaneous force generation, ATP utilization, and the dynamics of the cross-bridge cycle in simulations of step changes in length and variations in shortening velocity. Three critical results emerge from our analyses: 1) there is a significant realignment of actin-binding sites in response to cross-bridge forces, 2) this realignment recruits additional cross-bridge binding, and 3) we predict mechanical behaviors that are consistent with experimental results for velocity and length transients. Binding site realignment depends on the relative compliance of the filament lattice and cross-bridges, and within the measured range of these parameters, gives rise to a sharply tuned peak for force generation. Such mechanical tuning at the molecular level is the result of mechanical coupling between individual cross-bridges, mediated by thick filament deformations, and the resultant realignment of binding sites on the thin filament.

Factors Preventing the Recovery of a Historically Overexploited Shellfish Species, Ostrea lurida Carpenter 1864

ABSTRACT The Olympia oyster, Ostrea lurida Carpenter 1864,† in estuaries along the Pacific coast of North America, experienced overexploitation throughout its range in the late 1800s, resulting in commercial extinction before 1930. Significant harvest restrictions and marine reserves were established in Washington State by 1897 to protect new recruits, and harvest pressure has been negligible for the past 80 y. Nevertheless, O. lurida remains locally rare. This study focuses on the contemporary dynamics of the remnant population of O. lurida in Willapa Bay, Washington, historically home to the largest native oyster fishery on the coast, with a broad focus on factors preventing recovery. Failed recovery could be because of reproductive limitation, or to poor postrecruitment performance. In this case, reproductive limitation seems unlikely, because historical (1947 to 1983) and modern (2002 to 2006) records reveal 5-fold higher annual spatfall for O. lurida than introduced Pacific oysters (Crassostrea gigas.) However, O. lurida remains rare and C. gigas is commercially exploited from natural recruitment. To evaluate the effects of abundant C. gigas in intertidal areas on O. lurida settlement patterns, strings of C. gigas shell were placed at two tidal elevations in three habitat types—open mud, eelgrass beds of Zoster a marina, and C. gigas reefs. Settlement of O. lurida was significantly higher on the shell strings placed in the C. gigas reefs at both tidal heights. To evaluate postrecruitment demography, juvenile O. lurida were outplanted at three tidal elevations at five sites, and fouling organisms were manipulated to test for competition. Short emersion times (8% greater exposure) reduced survival by 80% relative to subtidal treatments, but did not affect growth rates of survivors. Naturally-setting competitors, mostly nonindigenous, depressed survival by 50% and growth by 20%. In a third experiment, manipulating the density and stability of shell substrate, O. lurida was easily moved or buried when outplanted in a thin, unconsolidated layer. These results indicate that recovery has been hampered by the removal of dense subtidal native oyster shell accumulations during exploitation, by direct competition from exotic species, and by the appearance of novel introduced oyster shell settlement substrate in the intertidal zone. This altered web of interactions influencing O. lurida serves as a model for beginning to explore the failed recovery of overfished species in rapidly changing coastal systems.

The Nearly Forgotten Oyster: Ostrea lurida Carpenter 1864 (Olympia Oyster) History and Management in Washington State

ABSTRACT Overexploited fisheries are a worldwide problem. Restoration efforts aimed at these fisheries often involve a combination of reduced catch, hatcheries, and habitat improvement. The native oyster of western North America, Ostrea lurida,† was commercially extinct in most locations more than a century ago. In this paper, we track the history of its management for insight into its demise and failed recovery in Washington State. We document six phases of management: open access, aquaculture, control of water pollution sources, substitution by nonindigenous oysters, harvest regulations and marine reserves, and restoration. Three general lessons emerge from this historical analysis, which may apply generally to exploited fisheries that fail to recover. First, the introduction of substitute species led to neglect of the native species for many decades. Second, reserves were not fully protected and instead were designed for commercial removal of newly settled oysters, thus they largely failed. Finally, current restoration efforts are hampered by several biological problems, including water pollution, invasive competitors and predators, and habitat loss.

The Willapa Bay Oyster Reserves in Washington State: Fishery Collapse, Creating a Sustainable Replacement, and the Potential for Habitat Conservation and Restoration

ABSTRACT Oysters have been an important resource in Washington state since the mid 1800s and are intimately associated with recent history of the Willapa Bay estuary, just as they have defined social culture around much larger U.S. east coast systems. The Willapa Bay oyster reserves were set aside in 1890 to preserve stocks of the native oyster Ostrea lurida in this estuary, but these stocks were overfished and replaced with the introduced Pacific oyster Crassostrea gigas during the late 1920s. Pacific oysters have spawned and set naturally in this estuary on a fairly regular basis since that time, and have formed the basis of a sustainable fishery established on state oyster reserves. The fishery is managed as an annual sale of oysters to private aquaculture interests. Oysters are harvested mostly by hand from intertidal tracts, usually moved to better growing areas closer to the estuary mouth, and shell is required to be returned to the reserves to perpetuate the fishery. Although oyster harvest for human consumption will remain an important social management goal, these bivalves have been shown to provide a suite of other ecosystem functions and services. A survey of the reserves suggests that they represent 11.2% of the intertidal habitat in Willapa Bay and cover substantial subtidal areas as well. A comparison with historical maps suggests that most of the low intertidal area in the reserves formerly populated by native oysters is now covered primarily with eelgrass (Zostera marina), which potentially serves as important habitat for numerous other organisms, including juvenile salmon, Dungeness crab, and migratory waterfowl like black Brant. Native oysters can still potentially be restored to some of these areas, but the value of both introduced oysters and eelgrass as habitat and ecosystem engineers also deserves attention, and the reserves provide an excellent place to elucidate the role of these additional conservation targets at the landscape scale.

Evaluation of Olympia Oyster (Ostrea lurida Carpenter 1864) Status and Restoration Techniques in Puget Sound, Washington, United States

ABSTRACT The Olympia oyster of Washington State, USA (Ostrea lurida†) was heavily exploited (1850 to 1940), declined dramatically, and has subsequently failed to recover, although it still supports small aquaculture operations. This paper documents the distribution and abundance of O. lurida in one of the last remaining locations where it forms extensive beds: the North Bay Oyster Reserve in south Puget Sound. We monitored recruitment every 2 wk between May and September 2004 and found a small recruitment peak in late July, which was much later than reported for these oysters when they were abundant throughout Puget Sound. We also experimentally tested two factors that could influence recovery: tidal elevation and substrate type. We established 1 m2 plots at three tidal elevations (-0.3, 0, +0.3 m MLLW) with six substrates: bare, gravel, crushed shell of Crassostrea gigas (Pacific oyster), whole C. gigas shell, whole shell of O. lurida, and live O. lurida. The plots were set up May 21, 2004 and measured for recruitment on October 16, 2004 and April 11, 2005 by collecting material from a 0.0125-m2 area of each plot. Recruitment improved at low tidal elevations and differed across substrates. Ostrea lurida shell consistently provided a better recruitment substrate than gravel or bare plots, but shell treatments could not be distinguished statistically. Postrecruitment mortality occurred in all treatments; however the rates of mortality were not significantly different by elevation or substrate treatment. Habitat restoration (low intertidal and subtidal shell areas) should promote the recovery of O. lurida where natural recruitment still occurs.

Variability in Carbon Availability and Eelgrass ( Zostera marina ) Biometrics Along an Estuarine Gradient in Willapa Bay, WA, USA

Because photosynthesis requires CO2, carbon limitation in aquatic environments could restrict primary production and provide signals in tissue chemistry. We took advantage of spatial variability of aqueous [CO2] in estuaries to examine within-estuary variation in biometrics of intertidal eelgrass (Zostera marina) during peak summer production. As expected from the sensitivity of carbonate equilibria to pH, aqueous [CO2] increased along an ocean-to-river gradient in Willapa Bay, WA, USA. The scale of pH variability also changed, reflecting weather-driven upwelling near the ocean, tidal advection near rivers, and reduced diel fluctuation up-estuary. Z. marina studied at eight sites in the bay integrated across these different temporal fluctuations in water chemistry to exhibit increased tissue carbon and depleted δ13C up-estuary. However, seagrass production did not change as expected from aqueous [CO2]. Instead, small standing biomass occurred at sites with organic-rich sediments or high wave energy, investment in branching showed trends along the estuarine gradient that changed seasonally, and specific growth rates based on leaf extension did not shift with the estuarine gradient or with standing biomass. These results reinforce that estuarine seagrasses are likely to experience modified mean pH and variability due not only to ocean acidification in the strict sense (anthropogenic CO2 absorbed from the atmosphere) but also from land use, upwelling, and feedbacks from biological processes. However, responses via productivity may be less evident than in tissue chemistry.

A Low-Cost, Data-Logging Salinity Sensor

In this paper, we present the design, development and testing of a novel low-cost, data-logging salinity sensor. The sensor was designed keeping size, cost and functionality in mind. The sensor can be submersed in water for up to two weeks (all electronics are completely sealed) while salinity is recorded onboard at user-defined intervals. The data is then downloaded to a computer in the laboratory, after which the sensor is recharged, cleaned for biofouling and ready to be used again. Our initial laboratory testing shows the sensor prototype is functional and can be calibrated to compute conductivity, hence salinity, of ocean water.

First report of Phoronis ovalis from Africa and its effect on mussel hosts

Phoronis ovalis is a cosmopolitan, shell-boring phoronid worm reported from 24 locations worldwide in temperate latitudes, but not previously from Africa. We identified a shell-boring phoronid in Namibia that is morphologically similar to P. ovalis and subsequently surveyed its latitudinal and tidal elevational range, host distribution, and evidence for long-term occupation of this shoreline. Phoronis ovalis in Namibia leaves characteristic burrows in its hosts (0.2 mm diameter), primarily the native brown mussel Perna perna. In all, eight additional host species were identified, including one barnacle, four gastropods and three bivalves. The distribution of P. ovalis was strictly subtidal, where it reached 99% prevalence in P. perna at some sites. Latitudinally, it occurs at least from the northern border of Namibia (17.4° S) to Walvis Bay (22.74° S). Its long-term presence was evident in subfossil shells. We hypothesised that extensive shell-boring could be energetically costly to the host due to the need for ongoing shell repair. Perna perna with higher phoronid infestation made thicker shells, which were less dense. In addition, colonised mussels had lower body condition (dry meat weight relative to internal shell volume), which implies a significant energetic cost to the host.

Similar oyster reproduction across estuarine regions differing in carbonate chemistry

In laboratory studies, shellfish larvae often respond negatively to augmented [CO2], but no prior tests have related wild bivalve larval performance and carbonate chemistry spatiotemporally. The geography of Willapa Bay (Washington, USA) naturally generates two distinct regions of carbonate chemistry where non-native Pacific oysters (Crassostrea gigas) dominate the intertidal fauna and successfully reproduce. On the river-influenced east side, pCO2 is higher and alkalinity lower, which both contribute to reduced aragonite saturation state (Xaragonite 1.3– 1.5) relative to the west side receiving low watershed inputs (Xaragonite 1.8–1.9). pHsws is also >0.1 lower on the east vs. west sides. Despite this difference in field conditions, no biological signal related to carbonate chemistry was apparent in oyster reproduction based on coupled chemical–biological comparisons over three summers. Instead, survival was equal between the two sides of the bay, and settlement was equal or higher on the low-Xaragonite, low-pH east side. In a temporal comparison of four larval cohorts, settlement differed by two orders of magnitude and increased with water temperature. These field data on oyster reproduction illustrate that population-level effects may not emerge in higher mean [CO2] conditions, with possible decoupling due to local adaptation, spatio-temporal heterogeneity, or higher sensitivity to other axes of environmental variability such as temperature.