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Marine habitat‐forming species often play critical roles on rocky shores by ameliorating stressful conditions for associated organisms. Such ecosystem engineers provide structure and shelter, for example, by creating refuges from thermal and desiccation stresses at low tide. Less explored is the potential for habitat formers to alter interstitial seawater chemistry during their submergence. Here, we quantify the capacity for dense assemblages of the California mussel, Mytilus californianus, to change seawater chemistry (dissolved O2, pH, and total alkalinity) within the interiors of mussel beds at high tide via respiration and calcification. We established a living mussel bed within a laboratory flow tank and measured vertical pH and oxygen gradients within and above the mussel bed over a range of water velocities. We documented decreases of up to 0.1 pH and 25 μmol O2 kg−1 internal to the bed, along with declines of 100 μmol kg−1 in alkalinity, when external flows were < 0.05 m s−1. Although California mussels often live in habitats subjected to much faster velocities, sizeable populations also inhabit bays and estuaries where such moderate flow speeds can occur > 95% of the time. Reductions in pH and O2 inside mussel beds may negatively impact resident organisms and exacerbate parallel human‐induced perturbations to ocean chemistry while potentially selecting for improved tolerance to altered chemistry conditions. [ABSTRACT FROM AUTHOR]

The close association between planktic foraminiferal assemblages and local hydrography make foraminifera invaluable proxies for environmental conditions. Modern foraminiferal seasonality is important for interpreting fossil distributions and shell geochemistry as paleoclimate proxies. Understanding this seasonality in an active upwelling area is also critical for anticipating which species may be vulnerable to future changes in upwelling intensity and ocean acidification. Two years (2012-2014) of plankton tows, along with conductivity-temperature-depth profiles and carbonate chemistry measurements taken along the north-central California shelf, offer new insights into the seasonal dynamics of planktic foraminifera in a seasonal coastal upwelling regime. This study finds an upwelling affinity for Neogloboquadrina pachyderma as well as a seasonal and upwelling associated alternation between dominance of N. pachyderma and Neogloboquadrina incompta, consistent with previous observations. Globigerina bulloides, however, shows a strong affinity for non-upwelled waters, in contrast to findings in Southern California where the species is often associated with upwelling. We also find an apparent lunar periodicity in the abundances of all species and document the presence of foraminifera even at very low saturation states of calcite. [ABSTRACT FROM AUTHOR]

Abstract Sediment transport past rocky headlands has received less attention compared to transport along beaches. Here we explore, in a field-based study, possible pathways for sediment movement adjacent to Point Dume, a headland in Santa Monica Bay, California. This prominent shoreline feature is a nearly symmetrical, triangular-shaped promontory interior to the Santa Monica Littoral Cell. We collected current, wave, and turbidity data for 74 days during which several wave events occurred, including one associated with a remote hurricane and another generated by the first winter storm of 2014. We also acquired sediment samples to quantify seabed grain-size distributions. Near-bottom currents towards the headland dominated on both of its sides and wave-driven longshore currents in the surf zone were faster on the exposed side. Bed shear stresses were generated mostly by waves with minor contributions from currents, but both wave-driven and other currents contributed to sediment flux. On the wave-exposed west side of the headland, suspended sediment concentrations correlated with bed stress suggesting local resuspension whereas turbidity levels on the sheltered east side of the headland are more easily explained by advective delivery. Most of the suspended sediment appears to be exported offshore due to flow separation at the apex of the headland but may not move far given that sediment fluxes at moorings offshore of the apex were small. Further, wave-driven sediment flux in the surf zone is unlikely to pass the headland due to the discontinuity in wave forcing that causes longshore transport in different directions on each side of the headland. It is thus unlikely that sand is transported past the headland (specifically in a westerly direction), although some transport of finer fractions may occur offshore in deep water. These findings of minimal sediment flux past Point Dume are consistent with its role as a littoral cell boundary, although more complex multi-stage processes and unusual events may account for some transport at times. Highlights • Currents, waves, and sediment transport were measured around a prominent headland. • Currents over 74 days were apex-ward on each side and reversing at the point. • Sand and mud transport are likely decoupled with sand ejected offshore. • Two flow separation regimes are proposed from current patterns around the point. • The headland is a likely littoral cell boundary for some sediment fractions. [ABSTRACT FROM AUTHOR]

Ocean acidification threatens many marine organisms, especially marine calcifiers. The only global-scale solution to ocean acidification remains rapid reduction in CO 2 emissions. Nevertheless, interest in localized mitigation strategies has grown rapidly because of the recognized threat ocean acidification imposes on natural communities, including ones important to humans. Protection of seagrass meadows has been considered as a possible approach for localized mitigation of ocean acidification due to their large standing stocks of organic carbon and high productivity. Yet much work remains to constrain the magnitudes and timescales of potential buffering effects from seagrasses. We developed a biogeochemical box model to better understand the potential for a temperate seagrass meadow to locally mitigate the effects of ocean acidification. Then we parameterized the model using data from Tomales Bay, an inlet on the coast of California, USA which supports a major oyster farming industry. We conducted a series of month-long model simulations to characterize processes that occur during summer and winter. We found that average pH in the seagrass meadows was typically within 0.04 units of the pH of the primary source waters into the meadow, although we did find occasional periods (hours) when seagrass metabolism may modify the pH by up to ±0.2 units. Tidal phasing relative to the diel cycle modulates localized pH buffering within the seagrass meadow such that maximum buffering occurs during periods of the year with midday low tides. Our model results suggest that seagrass metabolism in Tomales Bay would not provide long-term ocean acidification mitigation. However, we emphasize that our model results may not hold in meadows where assumptions about depth-averaged net production and seawater residence time within the seagrass meadow differ from our model assumptions. Our modeling approach provides a framework that is easily adaptable to other seagrass meadows in order to evaluate the extent of their individual buffering capacities. Regardless of their ability to buffer ocean acidification, seagrass meadows maintain many critically important ecosystem goods and services that will be increasingly important as humans increasingly affect coastal ecosystems., (© 2018 The Authors. Ecological Applications published by Wiley Periodicals, Inc. on behalf of Ecological Society of America.)

An extensive body of work suggests that altered marine carbonate chemistry can negatively influence marine invertebrates, but few studies have examined how effects are moderated and persist in the natural environment. A particularly important question is whether impacts initiated in early life might be exacerbated or attenuated over time in the presence or absence of other stressors in the field. We reared Olympia oyster (Ostrea lurida) larvae in laboratory cultures under control and elevated seawater pCO2 concentrations, quantified settlement success and size at metamorphosis, then outplanted juveniles to Tomales Bay, California, in the mid intertidal zone where emersion and temperature stress were higher, and in the low intertidal zone where conditions were more benign. We tracked survival and growth of outplanted juveniles for 4 months, halfway to reproductive age. Survival to metamorphosis in the laboratory was strongly affected by larval exposure to elevated pCO2 conditions. Survival of juvenile outplants was reduced dramatically at mid shore compared to low shore levels regardless of the pCO2 level that oysters experienced as larvae. However, juveniles that were exposed to elevated pCO2 as larvae grew less than control individuals, representing a larval carry-over effect. Although juveniles grew less at mid shore than low shore levels, there was no evidence of an interaction between the larval carry-over effect and shore level, suggesting little modulation of acidification impacts by emersion or temperature stress. Importantly, the carry-over effects of larval exposure to ocean acidification remained unabated 4 months later with no evidence of compensatory growth, even under benign conditions. This latter result points to the potential for extended consequences of brief exposures to altered seawater chemistry with potential consequences for population dynamics., (© 2013 John Wiley & Sons Ltd.)

Marine invertebrates commonly produce larvae that disperse in ocean waters before settling into adult shoreline habitat. Chemical and other seafloor-associated cues often facilitate this latter transition. However, the range of effectiveness of such cues is limited to small spatial scales, creating challenges for larvae in finding suitable sites at which to settle, especially given that they may be carried many kilometers by currents during their planktonic phase. One possible solution is for larvae to use additional, broader-scale environmental signposts to first narrow their search to the general vicinity of a candidate settlement location. Here we demonstrate strong effects of just such a habitat-scale cue, one with the potential to signal larvae that they have arrived in appropriate coastal areas. Larvae of the purple sea urchin (Strongylocentrotus purpuratus) exhibit dramatic enhancement in settlement following stimulation by turbulent shear typical of wave-swept shores where adults of this species live. This response manifests in an unprecedented fashion relative to previously identified cues. Turbulent shear does not boost settlement by itself. Instead, it drives a marked developmental acceleration that causes "precompetent" larvae refractory to chemical settlement inducers to immediately become "competent" and thereby reactive to such inducers. These findings reveal an unrecognized ability of larval invertebrates to shift the trajectory of a major life history event in response to fluid-dynamic attributes of a target environment. Such an ability may improve performance and survival in marine organisms by encouraging completion of their life cycle in advantageous locations.

Anthropogenic CO(2) is reducing the pH and altering the carbonate chemistry of seawater, with repercussions for marine organisms and ecosystems. Current research suggests that calcification will decrease in many species, but compelling evidence of impaired functional performance of calcium carbonate structures is sparse, particularly in key species. Here we demonstrate that ocean acidification markedly degrades the mechanical integrity of larval shells in the mussel Mytilus californianus, a critical community member on rocky shores throughout the northeastern Pacific. Larvae cultured in seawater containing CO(2) concentrations expected by the year 2100 (540 or 970 ppm) precipitated weaker, thinner and smaller shells than individuals raised under present-day seawater conditions (380 ppm), and also exhibited lower tissue mass. Under a scenario where mussel larvae exposed to different CO(2) levels develop at similar rates, these trends suggest a suite of potential consequences, including an exacerbated vulnerability of new settlers to crushing and drilling attacks by predators; poorer larval condition, causing increased energetic stress during metamorphosis; and greater risks from desiccation at low tide due to shifts in shell area to body mass ratios. Under an alternative scenario where responses derive exclusively from slowed development, with impacted individuals reaching identical milestones in shell strength and size by settlement, a lengthened larval phase could increase exposure to high planktonic mortality rates. In either case, because early life stages operate as population bottlenecks, driving general patterns of distribution and abundance, the ecological success of this vital species may be tied to how ocean acidification proceeds in coming decades.

Hydrodynamic forces dislodge and kill large numbers of organisms in intertidal and subtidal habitats along rocky shores. Although this feature of wave-driven water motion is well recognized, the mechanics of force imposition on compliant organisms is incompletely understood. Here we undertake a field examination of two processes that are thought to impose many of the more dangerous forces that act on flexible benthic seaweeds: impingement of breaking waves directly on emergent organisms, and inertial effects tied to the rapid deceleration of mass that occurs when a passively moving but attached organism abruptly reaches the extent of its range of motion. We focus on two common and important seaweed species: one intertidal kelp (Egregia menziesii) and one subtidal kelp (Macrocystis pyrifera). Results support the concept that wave impingement and inertial effects produce intermittent force transients whose magnitudes commonly exceed values readily attributable to drag. Peak force transients are elevated by as much as a factor of 3 relative to drag in both small and large individuals, consistent with smaller seaweeds being more susceptible to brief impingement forces, and larger seaweeds being more vulnerable to inertial forces. Because both wave impingement and inertial effects vary with the size of an organism, they may have the potential to influence the demographics of physical disturbance in an array of flexible species.