水研センター研報，第32号，47−50，平成22年
Bull. Fish. Res. Agen. No. 32, 47‑50, 2010

Comparisons between East-Asian isoyake and deforestation in global
kelp systems
Michael H. Graham＊1

Abstract: Seaweed deforestation (isoyake) is a conspicuous phenomenon in many
temperature/polar regions of the world and often results in strong ecological and economic
impacts to local human communities. The study of isoyake in East Asia (especially in Japan)
has a long history, however the resulting literature is generally inaccessible to researchersthat do not speak Asian languages. This study integrates knowledge of the causes and consequences of isoyake in East Asia into an emerging global model of the causes of deforestation in non-Asian kelp systems. Isoyake in southern regions of East Asia result from a concurrence of increased herbivory by fish and sea urchins of sub-tropical origin with periodsof decreased seaweed production due to poor oceanographic conditions. Such processes are
similar to those that cause deforestation in other warm-temperate kelp systems (southern California and northern New Zealand) and may be enhanced during periods of oceanwarming. Alternatively, isoyake in northern regions of East Asia result primarily from uncontrolled sea urchin grazing; inherently low kelp productivity in these regions cannot balance the high rates of kelp consumption. As such, these regions appear similar to other highlatitude/low productivity kelp systems in which large enduring sea urchin barrens often exist in the absence of external controls on sea urchin abundance (predation or harvestingby humans). Therefore, the diversity of causes of isoyake in East Asian systems appears toencompass the full range of deforestation processes described for high- to low-latitude kelp
systems worldwide. The unique situation in which high seaweed and herbivore diversity
coincide with high variability in oceanographic processes appears may make East Asian seaweed systems more vulnerable to perturbation than other temperate kelp systems.

Introduction

Graham2007). When kelps disappear, either

naturally or due to human activities, the ecologicalSeaweed forests are well recognized to provide

and economic consequences can be severe (Steneckessential habitat and energy to nearshore areas2002, Graham 2004). As such, there is growing

worldwide (Mann 1973, Dayton 1985, Barnes

interest in understanding general processes driving

and Hughes 1988, Duggins

kelp deforestation at a global scale.

Foster 2006, Graham

1989, Schiel &2008), with subsequent

Conspicuous seaweed deforestation was firstenhancement of local biodiversity, productivity, anddescribed in Japan in the 1800s and named

human economies (Steneck(Fujita, this issue). Over the last 100+ years an2007, Kang

2002, Graham2008). This is particularly

extensive literature has developed in Japanese,true for systems founded by kelps, large brown

and later Korean and Chinese, scientific journals

algae in the order Laminariales, which have some of

fueled by public and private interests in ecology

the highest productivities known amongst marine

and resource use of coastal seaweed forests. Most

autotrophs (Mann 1973, Jackson 1977, North 1994,

of this literature is in Asian languages and has

2010年 月 日受理（Received on July 1. 2010）* Moss Landing Marine Laboratories 8272 Moss Landing Road Moss Landing, Ca, USA, 95039
EMAIL: mgraham@mlml.calstate.edu

Michael H. Graham
been generally inaccessible to English-speaking

region. Isoyake caused by herbivory occurs on bothresearchers since the first description of kelp

natural and artificial reefs, and appears to be mostdeforestation in non-Asian systems (reviewed incommon in regions of low water motion.

Lawrence 1975). As such, isoyake research in East

In cold-temperate East Asia, isoyake can be

Asia has had little impact on the understanding ofobserved primarily in Japan on the west coast of

the causes of kelp deforestation worldwide. The

Hokkaido (Fujita, this issue) and in limited areas ongoal of this paper is to discuss the ecology of East

the west coast of Sakhlin Island, Russia (Galanin, thisAsian isoyake in light on a new model explaining

issue). Isoyake is not described for the east coast ofvariability in kelp deforestation at a global scale

Hokkaido. In these regions, the dominant kelps are(Grahamin prep.).

andThewest coast of Hokkaido has very low productivity
Dynamics of East-Asia kelp systems

relative to other kelp systems worldwide (Graham

Seaweeds are important taxa throughout East

entirely by overgrazing by the sea urchin,Asia, however, kelps are only important in the(Fujita, this issue). The

warm- and cold-temperate regions of Japan, South

only known control on sea urchin overgrazing in

Korea, China and Russia (Lüning 1990). Isoyake has

this region is high water motion in shallow water,

been described from each of these regions, althoughand harvesting by humans; sea urchin harvesting,the ecology of isoyake clearly differs between warm-however, is only possible outside of isoyake whereand cold-temperate systems, and it is useful to treat

sea urchin gonads are of marketable quality. In

these separately.

Russia, the observation of isoyake is recent andin prep.) and isoyake here is caused almost

In warm-temperate East Asian kelp systems,

coincides with declines in kelp farming productivity

isoyake can be observed in southern Japan (Honshu,(Galanin, this issue), potentially due to poor

Shikoku, Kyushu; Fujita, this issue), South Korea

oceanographic conditions.

(Kang, this issue), and China (Duan and Ming, thisissue).

Kelp productivity is moderate in these

Inclusion into a global deforestation model

regions relative to other kelp systems worldwide(Grahamin prep.), with the dominant taxa

beingandand

Japanese researchers have long understood,that isoyake results either when oceanographic(Lüning 1990). These kelps

conditions degrade kelp production entirely or whenappear to have adapted to high seasonal variability

kelp consumption exceeds kelp production.

Inin oceanographic conditions driven by fluctuations

addition to creating artificial habitats to compensate

in the strength and direction of the Kuroshio andfor isoyake, researchers have considered ways toJapan currents. As such, these systems naturally

either enhance kelp production or hamper kelp

degrade during late summer and autumn due toconsumption. This approach is entirely consistentregional ocean warming (Yokohama1987,with new ideas that have emerged from the study of1989). In recent decades, continued

kelp production and consumption in non-Asian kelp

ocean warming has resulted in greater stress to thesystems. Using ecological and oceanographic data,

kelps (SerisawaGraham

Haroun2004). Further, sub-tropicalsea urchins (Terawaki2002, Tamaki(Masuda(in prep.) found that kelp production

2001, Steneck

potential varies 30-fold between the lowest (Arctic)

2005) and herbivorous fishand highest (west South Africa) productivity

2000, Yamauchi2006) haveregions, driven by global variability in irradiance,

become common in southern waters of East Asia

ocean temperature, and nitrate concentrations.

during warm seasons, devastating local kelp forests.

Furthermore, kelp production potential decreased

Although predation in Asian kelp systems is poorly

predictably with increasing latitude and broad-scalestudied, there currently are no known conspicuous

enduring sea urchin barrens were restricted to highpredators on sea urchins and herbivorous fish in thelatitude systems. The conclusion from this study

Comparisons between East-Asian isoyake and deforestation in global kelp systems
was that high-latitude low-productivity kelp systems

conditions appear to be a primary cause of isoyake

were more likely to experience imbalance between

in warm temperate regions, with grazers inhibiting

kelp production-consumption than low-latitude

the return of kelp to natural abundances.

high-productivity systems.

SeaKelp production

urchins have a much more direct role in the causepotential from southern and northern Japan wereof isoyake in northern cold temperate regions, withwell predicted by the global model (Grahamocean warming playing a secondary role. However,inprep.).

it is still unknown whether isoyake are relatively

An additional conclusion of the global kelp

naturally states in East-Asian kelp systems, sincemodel was that low-latitude systems often have athe only modern control on sea urchin populations

greater diversity of factors that control herbivory

appears to be human harvesting, extreme water

populations. Seaweed diversity in warm-temperatemotion, or high levels of kelp productivity. The

regions is generally higher than high-latitude

absence of important sea urchin predators, besides

counterparts, and herbivore and predator

the sea otter, which has long been extinct from

populations are also generally more diverse due toJapan, is conspicuous.

proximity to the subtropics. In Japan, the southern
Acknowledgments

islands have a high diversity of kelp grazers
including various sea urchins, fishes, and snails,
coincident with regionally high diversity of kelps ofthe genera
andI wish to thank the National Research Institute ofFisheries Engineering, Tokyo University of Marine; these kelp taxa are complimented

by many species ofandScience and Techlology and the Fisheries ResearchAgency, Japan for inviting me to participate in thein the north. Sea urchin diseases are also relatively

International Symposium on Reduction of Seaweeds

warm water phenomena (Behrens and Lafferty 2004)

and Isoyake Recovery Technique in East Asia ,and sea urchin fisheries are often well establishedand for supporting my participation and travel. Inin lower latitudes. As such, the balance betweenparticular, Drs. D. Fujita and H. Kuwahara werekelp production-consumption can often be shifted

generous hosts and spent many hours helping me toin favor of kelp by a greater diversity of sea urchinbetter understand the functioning of Japanese kelp

controlling factors in low-latitude systems. Again,systems.

this perspective well explains many key differences
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