The mussel Mytilus californianus is a competitive dominant on wave—swept rocky intertidal shores. Mussel beds may exist as extensive monocultures; more often they are an everchanging mosaic of many species which inhabit wave—generated patches or gaps. This paper describes observations and experiments designed to measure the critical parameters of a model of patch birth and death, and to use the model to predict the spatial structure of mussel beds. Most measurements were made at Tatoosh Island, Washington, USA, from 1970—1979. Patch size ranged at birth from a single mussel to 38 m2; the distribution of patch sizes approximates the lognormal. Birth rates varied seasonally and regionally. At Tatoosh the rate of patch formation varied during six winters from 0.4—5.4% of the mussels removed per month. The disturbance regime during the summer and at two mainland sites was 5—10 times less. Annual disturbance patterns tended to be synchronous within 11 sites on one face of Tatoosh over a 10—yr interval, and over larger distances (16 km) along the coastline. The pattern was asynchronous, however, among four Tatoosh localities. Patch birth rate, and mean and maximum size at birth can be used as adequate indices of disturbance. Patch disappearance (death) occurs by three mechanisms. Very small patches disappear almost immediately due to a leaning response of the border mussels (0.2 cm/d). Intermediate—sized patches (<3.0 m2) are eventually obliterated by lateral movement of the peripheral mussels: estimates based on 94 experimental patches yield a mean shrinking rate of 0.05 cm/d from each of two principal dimensions. Depth of the adjacent mussel bed accounts for much of the local variation in closing rate. In very large patches, mussels must recruit as larvae from the plankton. Recovery begins at an average patch age of 26 mo; rate of space occupation, primarily due to individual growth, is 2.0—2.5%/mo. Winter birth rates suggest a mean turnover time (rotation period) for mussel beds varying from 8.1—34.7 yr, depending on the location. The minimal value is in close agreement with both observed and calculated minimal recovery times. Projections of total patch area, based on the model, are accurate to within 5% of the observed. Using a method for determining the age of patches, based on a growth curve of the barnacle Balanus cariosus, the model permits predictions of the age—size structure of the patch population. The model predicts with excellent resolution the distribution of patch area in relation to time since last disturbance. The most detailed models which include size structure within age categories are inconclusive due to small sample size. Predictions are food for large patches, the major determinants of environmental patterns, but cannot deal adequately with smaller patches because of stochastic effects. Colonization data are given in relation to patch age, size and intertidal position. We suggest that the reproductive season of certain long—lived, patch—dependent species is moulded by the disturbance regime. The necessary and vital connection between disturbance which generates spatial pattern and species richness in communities open to invasion is discussed.

Intertidal landscapes: disturbance and the dynamics of pattern [Mytilus californianus, mussels]

The nonconsumptive effects (NCEs) of predators on prey behavior and physiology can influence the structure and function of ecological communities. However, the strength of NCEs should depend on the physiological and environmental contexts in which prey must choose between food and safety. For ectotherms, temperature effects on metabolism and foraging rates may shape these choices, thereby altering NCE strength. We examined NCEs in a rocky intertidal food chain across a latitudinal sea surface temperature gradient within the Gulf of Maine. The NCEs of green crabs (Carcinus maenas) on the foraging, growth, and growth efficiency of prey snails (Nucella lapillus) were consistent across a broad (~8.5 °C) temperature range, even though snails that were transplanted south consumed twice as many mussels (Mytilus edulis) and grew twice as much as snails that were transplanted north. The positive effects of warmer temperatures in the south allowed snails under high risk to perform similarly to or better than snails under low risk at cooler temperatures. Our results suggest that for prey populations residing at temperatures below their thermal optimum, the positive effects of future warming may offset the negative effects of predation risk. Such effects may be favorable to prey populations facing increased predation rates due to warmer temperatures associated with climate change. Attention to the direct and indirect effects of temperature on species interactions should improve our ability to predict the effects of climate change on ecological communities.

Effects of predation risk across a latitudinal temperature gradient

Prey often retreat into the safety of refuges for protection from predators. This shift into refuge can reduce foraging opportunities, escalating the costs of risk and the strength of nonconsumptive effects. Such costs, however, may be shaped by the variation in resources that refuges harbor for prey foraging (i.e., refuge quality), and change dynamically via impacts on prey state. Despite its potential importance, we lack an explicit understanding of how refuge quality impacts prey performance under risk. Using a rocky intertidal food chain, we examined the interaction between predation risk and the amount of resources available for prey in refuge. We found that refuges with more resources greatly reduce the costs of refuge use, and that nonconsumptive effects are thereby weakened by as much as one-half, with especially strong impacts on prey growth and growth efficiency. These results suggest that failure to consider refuge quality could result in overestimation of the negative effects associated with prey refuge use.

Refuge quality impacts the strength of nonconsumptive effects on prey.

Manipulative field experiments provide a window into the complexity of nature. Yet there is concern that we lack resolution by conducting experiments on a scale that is too small and short to include the relevant complexity of the study system. We addressed this issue by asking how and why the scale (local and global spatial extent, spatial grain, duration) and complexity (number of species, factors, treatment combinations) of experiments performed on marine hard substrata (rocky intertidal, RI; coral reef, CR; rocky subtidal, RS; mangrove root, MR) has changed by assessing 311 total experiments published since 1961 in Ecology and Ecological Monographs and since 1967 in Journal of Experimental Marine Biology and Ecology. We show that the local spatial extent and all metrics of complexity increased as a positive, log-linear function of time. In contrast, the size of experimental units (spatial grain) decreased with time. Quantile regression analysis revealed that these trends are largely driven by changes ...

/pdf/towards-an-integration-of-scale-and-complexity-in-marine-4scpl2rugm.pdf

Towards an integration of scale and complexity in marine ecology

Recovery from disturbance is a key element of ecosystem persistence, and recovery can be influenced by large-scale regional differences and smaller local-scale variations in environmental conditions. Seagrass beds are an important yet threatened nearshore habitat and recover from disturbance by regrowth, vegetative extension and dispersive propagules. We described recovery pathways from small-scale disturbances in the seagrass Zostera nigricaulis in Port Phillip Bay, a large embayment in southeastern Australia, and tested whether these pathways differed between 5 regions with different hydrodynamic conditions and water quality, and between sites within those regions. Recovery pathways were broadly consistent. When aboveground biomass was removed, recovery, defined as the point at which disturbed areas converged with undisturbed controls, took from 2 to 8 mo, but when we removed above-and below-ground biomass, it took between 2 and 13 mo. There was no evidence of recovery resulting from sexual reproduction at any sites regardless of the presence of seeds in the sediment or flower production. We found no differences in recovery at the regional scale, but we found substantial differences between local sites. At some sites, rapid recovery occurred because seagrasses grew quickly, but at others, apparent recovery occurred because regrowth coincided with overall declines in cover of undisturbed areas. Recovery time was unrelated to seagrass canopy height, biomass, percentage cover, stem density, seed bank density, epiphyte cover or sediment organic matter in seagrass adjacent to disturbance experiments. This study highlights the importance of understanding fine-scale variation in local recovery mechanisms, which may override or obscure any regional signal.

/pdf/recovery-pathways-from-small-scale-disturbance-in-a-4u45xt90vr.pdf

Recovery pathways from small-scale disturbance in a temperate Australian seagrass

A major challenge facing ecology is to better understand how large-scale processes modify local-scale processes to shape the organization of ecological communities. Although the results of ecological experiments are repeatable on local scales, different results often emerge across broad scales, which can hinder the development of general predictions that apply across the geographical range of a community. Numerous studies in the southern Gulf of Maine have shaped our understanding of community organization and dynamics on New England rocky intertidal shores, where consumers strongly control recovery from disturbance on sheltered shores, and high invertebrate recruitment and competition for space dictate recovery on wave-exposed shores. It is unclear, however, whether the effects of consumers and recruitment variation on resulting community organization in this region apply more broadly to rocky intertidal habitats throughout the Gulf. We characterized variation in rocky intertidal community structure at 34 sites throughout the Gulf of Maine and experimentally examined the influence of consumers (present, absent) and wave energy (wave-exposed, sheltered) on community recovery from disturbance in the northern and southern Gulf. Our results reinforced previous work in the southern Gulf, because consumers dictated the recovery of fucoid algae and mussels on sheltered shores, whereas high barnacle and mussel recruitment and competition for space shaped recovery on wave-exposed shores. However, on sheltered shores in the northern Gulf, neither consumers nor barnacle and mussel recruitment impacted recovery, which was dominated by fucoid algae. Moreover, recovery on wave-exposed shores in the northern Gulf was quite distinct from that observed in the southern Gulf; barnacle and mussel recruitment was negligible and fucoid algae dominated recovery, including the long-term establishment of Ascophyllum nodosum, which is largely absent from wave-exposed shores in the southern Gulf. Thus, distinct community types emerged in the northern and southern Gulf despite their sharing of many of the same species. These patterns likely emerged because of regional differences in coastal oceanography that modulate the recruitment of barnacles and mussels. Hence, increased attention to regional factors should provide key insight into how rocky-shore communities are organized in the Gulf of Maine and elsewhere.

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/13-1106.1

Elizabeth S. Bryson

Papers

Broad‐scale geographic variation in the organization of rocky intertidal communities in the Gulf of Maine