Effects of temperature and nutrients on microscopic stages of the bull kelp (Nereocystis luetkeana, Phaeophyceae).

Warming ocean temperatures have been linked to kelp forest declines worldwide, and elevated temperatures can act synergistically with other local stressors to exacerbate kelp loss. The bull kelp Nereocystis luetkeana is the primary canopy-forming kelp species in the Salish Sea, where it is declining in areas with elevated summer water temperatures and low nutrient concentrations. To determine the interactive effects of these two stressors on microscopic stages of N. luetkeana, we cultured gametophytes and microscopic sporophytes from seven different Salish Sea populations across seven different temperatures (10-22°C) and two nitrogen concentrations. The thermal tolerance of microscopic gametophytes and sporophytes was similar across populations, and high temperatures were more stressful than low nitrogen levels. Additional nitrogen did not improve gametophyte or sporophyte survival at high temperatures. Gametophyte densities were highest between 10 and 16°C and declined sharply at 18°C, and temperatures of 20 and 22°C were lethal. The window for successful sporophyte production was narrower, peaking at 10-14°C. Across all populations, the warmest temperature at which sporophytes were produced was 16 or 18°C, but sporophyte densities were 78% lower at 16°C and 95% lower at 18°C compared to cooler temperatures. In the field, bottom temperatures revealed that the thermal limits of gametophyte growth (18°C) and sporophyte production (16-18°C) were reached during the summer at multiple sites. Prolonged exposure of bull kelp gametophytes to temperatures of 16°C and above could limit reproduction, and therefore recruitment, of adult kelp sporophytes.

Quantifying the effectiveness of shoreline armoring removal on coastal biota of Puget Sound.

Shoreline armoring is prevalent around the world with unprecedented human population growth and urbanization along coastal habitats. Armoring structures, such as riprap and bulkheads, that are built to prevent beach erosion and protect coastal infrastructure from storms and flooding can cause deterioration of habitats for migratory fish species, disrupt aquatic-terrestrial connectivity, and reduce overall coastal ecosystem health. Relative to armored shorelines, natural shorelines retain valuable habitats for macroinvertebrates and other coastal biota. One question is whether the impacts of armoring are reversible, allowing restoration via armoring removal and related actions of sediment nourishment and replanting of native riparian vegetation. Armoring removal is targeted as a viable option for restoring some habitat functions, but few assessments of coastal biota response exist. Here, we use opportunistic sampling of pre- and post-restoration data for five biotic measures (wrack % cover, saltmarsh % cover, number of logs, and macroinvertebrate abundance and richness) from a set of six restored sites in Puget Sound, WA, USA. This broad suite of ecosystem metrics responded strongly and positively to armor removal, and these results were evident after less than one year. Restoration responses remained positive and statistically significant across different shoreline elevations and temporal trajectories. This analysis shows that removing shoreline armoring is effective for restoration projects aimed at improving the health and productivity of coastal ecosystems, and these results may be widely applicable.

Restricted ranges in physical factors may constitute subtle stressors for estuarine biota.

Biotic trends along estuarine gradients can be affected by co-varying processes ranging from large-scale oceanographic to local-scale physico-chemical effects. As a baseline for future process studies, we investigated the distinct gradients in species richness and biomass in pebble-sand shorelines along the estuarine axis of Puget Sound, and the scales of variation of some of their physical correlates. Higher richness and biomass at beaches at the more marine end of the Sound are temporally consistent and seen in all trophic groups. Variables that correlate with biotic patterns include relatively subtle increases in beach surface and sediment temperatures and decreases in nearshore salinity near the head of the estuary, but not more localized parameters such as sediment grain size or porewater salinity. To understand whether these variables are true forcing functions of community structure, we are performing experimental work.

Experimental studies of herbivory and algal competition in a low intertidal habitat.

Ecological factors regulating the species composition and abundance of the plant assemblage in the low intertidal zone were studied in the semiprotected San Juan Islands in Washington state. In particular, the roles of an abundant herbivore (the chiton Katharina tunicata) and competition among plants were evaluated experimentally. Densities of Katharina were manipulated in large areas to establish 3 treatments: Katharina removals (N=2), controls (N=2), and Katharina addition (N=1). These sites were monitored for 4 years. Over this time, algal abundance and diversity increased in the Katharina-removal areas; algae in most functional groups proliferated, and a multi-storied intertidal kelp bed eventually developed. In the Katharina-addition, the abundance of all plants except crusts, diatoms, and surfgrass decreased, and overall diversity declined. Control sites underwent year-to-year fluctuation in the abundance of the most conspicuous alga, Hedophyllum sessile, but remained otherwise unchanged.At the end of the third year, the dominant space occupiers (the large brown algae) were removed from half of each of the Katharina removal and control areas. These kelps positively affect abundances of Katharina but are negatively correlated with limpet numbers. In the absence of competition from the kelps, the abundance and diversity of most other algal groups increased. This change was especially dramatic in the areas lacking both chitons and kelps, indicating that herbivory and competition have negative, additive effects on smaller algae. However, even in the absence of Katharina, abiotic disturbance (desiccation and storms) apparently mediates the competitive dominance of the kelps.

Heteromorphic algal life histories: The seasonal pattern and response to herbivory of the brown crust, Ralfsia californica.

Little is known about the natural history of crustose phases of heteromorphic algae. A qualitative model describing their life history strategies has hypothesized that the morphologies and seasonal occurrences of the two phases evolved largely in response to variable grazing pressure. Crustose phases are predicted to occur when grazing is intense, and erect phases when grazing is reduced. The brown algal crust Ralfsia calfornica, which is the non-obligatory alternate phase of Scytosiphon lomentaria and/or Petalonia fascia, was studied on San Juan Island, Washington, USA. Both phases inhabit pools in the midto upper-intertidal zone, with the crust reaching maximum abundance between 1.8 and 2.3 m. The crust undergoes radical and predictable seasonal fluctuations in abundance, with a maximum in March-April and minimum in August. The erect phases are winter annuals, with maxima in January-April. Thus the crustose and erect phases show high temporal overlap. Colonization studies on new substrata showed that: 1) the crust is ephemeral, with a lifespan of 7-12 months, 2) it reproduces throughout the year and its propagules rapidly colonize new substrata at almost any time, while 3) erect phases appear only during the winter. Manipulations of limpets indicated that they do not directly graze the crust and are not responsible for its seasonal fluctuations in abundance; however, they are crucial to its persistence because they remove potential competitors. The crust fits poorly into models relating morphology to successional status in that it is ephemeral and opportunistic yet is grazer-resistant and grazer-dependent. Furthermore, both the crust and its erect phases are most abundant in the winter, when grazing appears to be least intense. Thus this heteromorphic complex exhibits interesting characteristics not predicted by current models.