Freezing And Mechanical Failure of A Habitat-forming Kelp in The Rocky Intertidal Zone.

Kelp and other habitat-forming seaweeds in the intertidal zone are exposed to a suite of environmental factors, including temperature and hydrodynamic forces, that can influence their growth, survival, and ecological function. Relatively little is known about the interactive effect of temperature and hydrodynamic forces on kelp, especially the effect of cold stress on biomechanical resistance to hydrodynamic forces. We used the intertidal kelp Egregia menziesii to investigate how freezing in air during a low tide changes the kelp's resistance to breaking from hydrodynamic forces. We conducted a laboratory experiment to test how short-term freezing, mimicking a brief low tide freezing event, affected the kelp's mechanical properties. We also characterized daily minimum winter temperatures in an intertidal E. menziesii population on San Juan Island, WA near the center of the species' geographic range. In the laboratory, acute freezing events decreased the strength and toughness of kelp tissue by 8 to 20% (change in medians). During low tides in the field, we documented sub-zero temperatures, snow, and low canopy cover (compared to summer surveys). These results suggest that freezing can contribute to frond breakage and decreased canopy cover in intertidal kelp. Further work is needed to understand whether freezing and the biomechanical performance in cold temperatures influence the fitness and ecological function of kelp, and whether this will change as winter conditions, such as freezing events and storms, change in frequency and intensity.

Latitudinal variation in long-term stability of North American rocky intertidal communities.

Although long-term ecological stability is often discussed as a community attribute, it is typically investigated at the species level (e.g. density, biomass), or as a univariate metric (e.g. species diversity). To provide a more comprehensive assessment of long-term community stability, we used a multivariate similarity approach that included all species and their relative abundances. We used data from 74 sites sampled annually from 2006 to 2017 to examine broad temporal and spatial patterns of change within rocky intertidal communities along the west coast of North America. We explored relationships between community change (inverse of stability) and the following potential drivers of change/stability: (a) marine heatwave events; (b) three attributes of biodiversity: richness, diversity and evenness and (c) presence of the mussel, Mytilus californianus, a dominant space holder and foundation species in this system. At a broad scale, we found an inverse relationship between community stability and elevated water temperatures. In addition, we found substantial differences in stability among regions, with lower stability in the south, which may provide a glimpse into the patterns expected with a changing climate. At the site level, community stability was linked to high species richness and, perhaps counterintuitively, to low evenness, which could be a consequence of the dominance of mussels in this system. Synthesis. Assessments of long-term stability at the whole-community level are rarely done but are key to a comprehensive understanding of the impacts of climate change. In communities structured around a spatially dominant species, long-term stability can be linked to the stability of this 'foundation species', as well as to traditional predictors, such as species richness.

Linking Physiology To Ecological Function: Environmental Conditions Affect Performance And Size Of The Intertidal Kelp Hedophyllum Sessile (Laminariales, Phaeophyceae).

For autogenic ecosystem engineers, body size is an aspect of individual performance that has direct connections to community structure; yet the complex morphology of these species can make it difficult to draw clear connections between the environment and performance. We combined laboratory experiments and field surveys to test the hypothesis that individual body size was determined by disparate localized physiological responses to environmental conditions across the complex thallus of the intertidal kelp Hedophyllum sessile, a canopy-forming physical ecosystem engineer. We documented substantial (> 40%) declines in whole-thallus photosynthetic potential (as Maximum Quantum Yield, MQY) as a consequence of emersion, which were related to greater than 10-fold increases in intra-thallus MQY variability (as Coefficient of Variation). In laboratory experiments, desiccation and high light levels during emersion led to lasting impairment of photosynthetic potential and an immediate > 25% reduction in area due to tissue contraction, which was followed by complete loss of structural integrity after three days of submersion. Tissue exposed to desiccation and high light during emersion had higher nitrogen concentrations and lower phlorotannin concentrations than tissue in control treatments (on average 1.36 and 0.1x controls, respectively), suggesting that conditions during emersion have the potential to affect food quality for consumers. Our data indicate that the complex thallus morphology of H. sessile may be critical to this kelp's ability to persist in the intertidal zone despite the physiological challenges of emersion and encourage a more nuanced view of the concept of "sub-lethal stress" on the scale of the whole individual.

Temperature affects susceptibility of intertidal limpets to bird predation.

High temperatures resulting in physiological stress and the reduced ability to resist predation can have life-or-death consequences for an organism. We investigated the effects of temperature on the susceptibility to predation for an ectothermic intertidal mollusc (the owl limpet, Lottia gigantea) and its predator (the black oystercatcher, Haematopus bachmani). The ability of L. gigantea to resist bird predation during low tide is determined by the tenacity of attachment to the rock. We developed a transducer to measure the force of predatory attacks on limpets by a captive black oystercatcher, and tested the hypothesis that exposure to warm temperatures during low tide emersion would affect the limpet's ability to resist dislodgement in trials with a morphometrically accurate beak mimic and a live bird. In beak mimic trials, four times as many limpets exposed to warm low tides were removed, as compared with limpets exposed to cool low tides or in 'no low tide' submerged conditions. Minimum time before limpet removal in captive bird trials was more than six times longer for limpets in cool low tide or no low tide treatments compared with limpets in the warm low tide treatment. We measured shear forces up to 36.63 N during predatory strikes. These direct measurements of the forces exerted by a living oystercatcher provide context for interactions with multiple prey species. Our data suggest that naturally occurring variation in body temperatures among individual prey items in the field could be an important driver of predator-prey interactions and subsequently community patterns.

Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery.

Disease outbreaks can have substantial impacts on wild populations, but the often patchy or anecdotal evidence of these impacts impedes our ability to understand outbreak dynamics. Recently however, a severe disease outbreak occurred in a group of very well-studied organisms-sea stars along the west coast of North America. We analyzed nearly two decades of data from a coordinated monitoring effort at 88 sites ranging from southern British Columbia to San Diego, California along with 2 sites near Sitka, Alaska to better understand the effects of sea star wasting disease (SSWD) on the keystone intertidal predator, Pisaster ochraceus. Quantitative surveys revealed unprecedented declines of P. ochraceus in 2014 and 2015 across nearly the entire geographic range of the species. The intensity of the impact of SSWD was not uniform across the affected area, with proportionally greater population declines in the southern regions relative to the north. The degree of population decline was unrelated to pre-outbreak P. ochraceus density, although these factors have been linked in other well-documented disease events. While elevated seawater temperatures were not broadly linked to the initial emergence of SSWD, anomalously high seawater temperatures in 2014 and 2015 might have exacerbated the disease's impact. Both before and after the onset of the SSWD outbreak, we documented higher recruitment of P. ochraceus in the north than in the south, and while some juveniles are surviving (as evidenced by transition of recruitment pulses to larger size classes), post-SSWD survivorship is lower than during pre-SSWD periods. In hindsight, our data suggest that the SSWD event defied prediction based on two factors found to be important in other marine disease events, sea water temperature and population density, and illustrate the importance of surveillance of natural populations as one element of an integrated approach to marine disease ecology. Low levels of SSWD-symptomatic sea stars are still present throughout the impacted range, thus the outlook for population recovery is uncertain.

Genomics-fueled approaches to current challenges in marine ecology.

As a result of recent advances in genomic technology, a 'tool set' is emerging that can be used by marine ecologists to gain new perspectives on central questions in the field. Techniques such as gene expression profiling using DNA microarrays, when placed in an ecological context, stand to advance greatly our understanding of how organisms respond to abiotic and biotic stresses. Here, we target areas in which adding genomics to ecological and physiological investigations will significantly advance our understanding of crucial issues ranging from the general biological effects of environmental temperature changes on individuals and communities to the interactions between symbionts in coral bleaching. At a time when both short- and long-term perturbations of marine ecosystems are increasing in severity, this kind of integrative approach could generate new and exciting hypotheses about the functioning of marine organisms and communities.