Kelp forests are phyletically diverse, structurally complex and highly productive components of coldwater rocky marine coastlines. This paper reviews the conditions in which kelp forests develop globally and where, why and at what rate they become deforested. The ecology and long archaeological history of kelp forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in kelp forest biodiversity. Global distribution of kelp forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed kelp forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread kelp deforestation. Such deforestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deforestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the widespread extirpation of this herbivore, and kelp forests have returned in some locations but, for the first time, these forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish- to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of kelp forests were examined to determine their long history with humans and project the status of future kelp forests to the year 2025. Fishing impacts on kelp forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited kelp forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin populations and probably small-scale deforestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of kelp forests over vast areas. Despite southern California having one of the longest known associations with coastal kelp forests, widespread deforestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse kelp forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on kelp forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to kelp forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring populations of functionally important species in these systems.

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Kelp forest ecosystems: biodiversity, stability, resilience and future

Empirical parameterization of setup, swash, and runup

1. Introduction 2. Observation techniques 3. Description of ocean waves 4. Statistics 5. Linear wave theory (oceanic waters) 6. Waves in oceanic waters 7. Linear wave theory (coastal waters) 8. Waves in coastal waters 9. The SWAN wave model Appendices References Index.

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Waves in Oceanic and Coastal Waters

An abrupt change in the large-scale boreal winter circulation pattern over the North Pacific was observed during the mid-1970s. Most notably, this change was marked by a southward shift and intensification of the Aleutian Low and prevailing westerlies over the mid-latitude central and eastern Pacific. Associated changes in diverse North Pacific climatological, hydrological, and biological variables have been noted by numerous researchers. Intriguingly, the timing of these changes in the extra-tropical circulation was coincident with a shift in the background state of the coupled ocean-atmosphere system over the tropical Pacific. These changes include increases in SST over broad regions of the central and eastern tropical Pacific and an eastward displacement of the region of persistent convection in the western Pacific. This paper presents a variety of observed data and model results to describe the climate shift, and to understand some of the links within the coupled climate system that produced it. Five main findings are emphasized: (1) evidence of abrupt, simultaneous, and apparently related changes can be found in many fields and in many model results; the climate shift is not an artifact, (2) over the tropical Pacific the climate change represents a shift in the state of the coupled ocean-atmosphere system, some aspects of which resemble features associated with El Nino episodes. However, the shift in state is not well characterized as due to a change in the frequency of intensity of El Ni~no episodes; it is better described as a change in background mean state, (3) when forced with observed SSTs, both a very simple atmospheric model and a full general circulation model (GCM) qualitatively simulate aspects of the decadal-scale shift over the tropical Pacific, (4) when forced with observed surface wind stress, two ocean models of the tropical Pacific, in which surface heat fluxes are parameterized as Newtonian damping, reproduce some aspects of the near-equatorial decadal SST signal. However, the models do not reproduce the large changes in SST observed at higher latitudes of the tropical Pacific, suggesting that altered surface heat fluxes dominated in producing these changes, and (5) an important new finding of this study is the success of a GCM in reproducing important aspects of the observed mid-1970s shift in winter northern hemisphere circulation. Comparative analyses of the observed and GCM simulated circulation suggest the altered patterns of tropical Pacific SST and convection were important in forcing the changes in the mid-latitude circulation, a finding corroborated by recent GCM experiments.

Decadal-scale climate variability in the tropical and North Pacific during the 1970s and 1980s: observations and model results

Seaweeds are ecologically important primary producers, competitors, and ecosystem engineers that play a central role in coastal habitats ranging from kelp forests to coral reefs. Although seaweeds are known to be vulnerable to physical and chemical changes in the marine environment, the impacts of ongoing and future anthropogenic climate change in seaweed-dominated ecosystems remain poorly understood. In this review, we describe the ways in which changes in the environment directly affect seaweeds in terms of their physiology, growth, reproduction, and survival. We consider the extent to which seaweed species may be able to respond to these changes via adaptation or migration. We also examine the extensive reshuffling of communities that is occurring as the ecological balance between competing species changes, and as top-down control by herbivores becomes stronger or weaker. Finally, we delve into some of the ecosystem-level responses to these changes, including changes in primary productivity, diversity, and resilience. Although there are several key areas in which ecological insight is lacking, we suggest that reasonable climate-related hypotheses can be developed and tested based on current information. By strategically prioritizing research in the areas of complex environmental variation, multiple stressor effects, evolutionary adaptation, and population, community, and ecosystem-level responses, we can rapidly build upon our current understanding of seaweed biology and climate change ecology to more effectively conserve and manage coastal ecosystems.

Effects of climate change on global seaweed communities

The storm-related mortality rates of adult Macrocystis pyrifera in a Southern California giant kelp forest were determined over several winter storm seasons and compared with the hydrodynamic attributes of the most energetic storms. The data include stormy and relatively benign years and an exceptional storm which resulted in almost total destruction of a major Macrocystis forest. High orbital velocities (associated with large, high frequency waves), the presence of breaking waves, and entanglement by drifters were found to increase mortality through stipe breakage or holdfast failure. Longshore variability in wave intensity was found to affect kelp mortality rates. The data suggest that wave breaking may be an important factor in determining the inner boundary of the kelp bed.

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Storm wave induced mortality of giant kelp, Macrocystis pyrifera, in Southern California

orbital velocities (associated with large, high frequency waves), the presence of breaking waves, and entanglement by drifters were found to increase mortality through stipe breakage or holdfast failure. Longshore variability in wave intensity was found to affect kelp mortality rates. The data suggest that wave breaking may be an important factor in determining the inner boundary of the kelp bed.

http://cdip.ucsd.edu/SCBPS/DOCS/Publications/Article/storm_wave_induced_mortality.pdf

Storm Wave Induced Mortality of Giant Kelp, Macrocystis pyrifera, in Southern

The coastline of San Diego County, California, is characterized by steep seacliffs cut into 5 to 115 m high uplifted marine terraces. Over the past few decades, rapid population growth in the area has promoted a substantial increase in cliff-top development, despite a limited understanding of the long-term cliff erosion rates and their controlling factors. Wave erosion at the base of the seacliff is usually assumed to be a basic driving mechanism of coastal cliff retreat. We investigated the influence of waves on seacliff erosion by comparing high-resolution, long-term seacliff erosion rates to wave parameters (height, energy, and power or energy flux) in 10 m of water, the break-point, and at the cliff toe. Seacliff erosion rates range from 3.0 cm/yr in well-lithified Cretaceous sandstone to 43.0 cm/yr in unlithified Pleistocene sands. The wave parameters were calculated using the California Data Information Program (CDIP) Southern California Refraction-Diffraction Model (SCRDM), an empirical relationship for breaking wave height, and a new term we define as relative power at the cliff toe. Directional wave data from offshore South-Central California were used to initialize the model. The distribution of wave power in 10 m of water and at the breakpoint and cliff toe appears to be inversely related to historical seacliff erosion rates at our study sites. As a result, our findings suggest that waves, while an important mechanism of seacliff erosion, are secondary to material properties in the overall retreat of San Diego seacliffs. Along the San Diego coastline, material strength appears to largely determine seacliff stability and the rate and manner of retreat.

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The Relationship Between Incident Wave Energy and Seacliff Erosion Rates: San Diego County, California

This paper considers the feasibility of tapping a number of potential sources of energy in the oceans, assesses their magnitude in relationship to projected world needs, and discusses some means for avoiding environmental degradation.

The ocean as a power resource

Seiche measured within a small (0.6 by 0.6 km), shallow (12-m depth) harbor is dominated by oscillations in several narrow infragravity frequency bands between approximately 10−3 and 10−2 Hz. Energy levels within the harbor are amplified, relative to just outside the harbor in 8.5-m depth, by as much as a factor of 20 at the lowest (grave mode) resonant frequency (∼10−3 Hz) compared to amplifications of roughly 5 at higher resonant frequencies (∼10−2 Hz). At nonresonant frequencies, energy levels observed inside the harbor are lower than those outside. These amplifications are compared to predictions of a numerical model of seiche excited by linear, inviscid long waves impinging on a harbor of variable depth. The amplification of higher-frequency (∼10−2-Hz) seiches is predicted within a factor of about 2. However, at the grave mode (10−3 Hz), the observed amplification decreases with increasing swell and seiche energy levels, possibly owing to the sensitivity of this highly amplified mode to dissipation not included in the inviscid model. The energy levels of higher-frequency seiche within the harbor were predicted from the offshore sea and swell spectra by the ad hoc coupling of the linear model for the amplification of harbor modes with a nonlinear model for the generation of bound infragravity waves outside the harbor. The predictions are qualitatively accurate only when the swell is energetic and bound waves are a significant fraction of the infragravity energy outside the harbor.

Richard J. Seymour

Papers

Storm wave induced mortality of giant kelp, Macrocystis pyrifera, in Southern California

Storm Wave Induced Mortality of Giant Kelp, Macrocystis pyrifera, in Southern

The Relationship Between Incident Wave Energy and Seacliff Erosion Rates: San Diego County, California

The ocean as a power resource

Excitation of seiche observed in a small harbor