水研センター研報，第32号，1−10，平成22年
Bull. Fish. Res. Agen. No. 32, 1‑10, 2010

Balance between harvesting pressure and protection: Implications
for barren ground formation in Hong Kong
P.O. Ang, Jr.

＊1

＊1

＊1

＊1

＊1

, K.Y. So , T.W. Li , F.F. Yeung. , S.Y. Wong.

＊1

and C.K. Woo

Abstract: In recent years, there is an increasing awareness of the importance of coastal
communities as ecological habitats. Marine protected areas (MPA) are being established andharvesting of marine organisms within these protected areas is being regulated. MPAs provide an opportunity for dynamic regulating mechanisms within coastal community to be examined. A case in point is the Tung Ping Chau Marine Park (TPCMP) in Hong Kong established in 2001. From October 2002 to March 2004, temporal variations in algal and herbivore
dynamics were observed in general monthly surveys. The density of herbivores in Lung
Lok Shui (LLS), one of the sites known to support extensive bed of, was low (0.762individual/100cm ) and herbivores did not appear to be an important factor in structuring
the algal community.
In 2006 to 2007, the population of the short-spined black urchinin2
creased significantly, from < 1 individuals/m in pre-MPA period to up to 40 individuals/m2,
likely a result of restricted harvesting of these urchins since the establishment of TPC asa marine park. One serious and unexpected consequence of this was the decimation of
population in LLS due to extensive urchin grazing. The cover ofwascompletely reduced, forming barren ground. Sea urchin grazing became the most important
structuring force in this coastal community and was previously put under check due to harvesting by human. A question can therefore be put forward as to how important is humanharvesting pressure on sea urchins, or other herbivores like fish, contributing to the dynamics of the coastal algal community. This factor may be more important than previously
thought.

Introduction

climate with mean sea water temperature ranging
from 14℃ in winter to 28℃ in summer. More thanHong Kong is located in the southern part of299 species of macroalgae (seaweeds) have been

mainland China to the east of the Pearl River,recorded within Hong Kong waters (Ang 2005).

the third largest river in China. True marine

These include temperate as well as tropical species.

environment is therefore found only along its

Their abundance is highly seasonal. Many of theseeastern coastline whereas the western coast isappear as turf that forms a thin carpet on thehighly influenced by the Pearl River outflow androcky surface especially during summer. Larger

hence is brackish. Rocky shores supporting marine

algal species appear mostly in late fall to spring.

algae are not extensive and these do not usually

Perennial to pseudo-perennial species like

extend to great depth beyond 10m below the chart

spp. provide the canopy to support large number ofdatum (CD). Largely because of the influence of thezooplankton and epiphytic flora and fauna (Ng 2009).

Pearl River, sea water around Hong Kong is highly

Changes in physical and chemical parameters

turbid. Hong Kong has a subtropical monsoonalin the environment, including tide, temperature

2010年 月 日受理（Received on July 1. 2010）＊1
Marine Science Laboratory, Department of Biology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China

P.O. Ang, Jr., K.Y. So, T.W. Li, F.F. Yeung. S.Y. Wong and C.K. Woo
and light are some of the forces structuring algalchanges in the environmental conditions.

communities. Biological interactions, including

Herbivory as a structuring force in Hong Kong

competition and herbivory, are also importantalgal communities is understudied. Large scale(So 2005). The level of intensity, periodicity andgrazing by sea urchins, resulting in barren groundregularity of these interactions at the temporal(isoyake) formation in many places around the worldand spatial scales can affect the abundances andis well documented (e.g. Watanabe and Harrold 1981,

diversities of algal populations at a particular

Vasquez

locality. Ultimately, the characteristics of individual

However, this phenomenon is largely unknown

species or populations, including their physical form,in Hong Kong until recently. This study explores

reproductive behavior, fecundity and functional

aspects of herbivory as a structuring force in Hongphysiology could also determine their tolerance toKong algal community, with particular focus on

1984, Himmelman & Nedelec 1990).

Fig. 1. Map of Hong Kong showing A. the location of Tung Ping Chau Marine Park (TPCMP) and other sites(marked with ★ ) with known abundance ofspp.; B. detailed picture of TPCMP with location of thesites mentioned in this study. (Photo Courtesy: AFCD of Hong Kong SAR Government)

Balance between harvesting pressure and protection: Implications for barren ground formation in Hong Kong
Materials and Methods

sea urchin grazing in a marine protected area,
the Tung Ping Chau Marine Park (TPCMP). Sea
urchins, especially the short-spined black urchin

Measurement of Algal Percentage Cover, are harvested resource in

Algal percentage cover in LLS was examinedHong Kong. They are prized for their gonads locallymonthly from December 2002 to March 2004.

or are harvested for export. The earlier study on

Seven 5m transects were laid parallel to the shore

the density ofin Tung Ping Chauhaphazardly. Four quadrats were placed on eachbefore it was designated as a marine park in 2001

transect which was marked with random points.

enables a comparison to be made on the density and

The random point quadrat was 25cm x 25cm insize of this sea urchin before and after marine park

dimensions, with 100 random points represented

designation. Furthermore, continuous monitoring of

by intersections of cross strings. Algae underneaththe phenology ofin the same

every random point were identified to the species

site made possible a correlation to be made between

level as much as possible. The percentage cover

the density of the urchins and that of the seaweed.

of each algal species was recorded by counting

The increase in the number of, mostthe number of random points that it covered. At

plausibly due to its protection after Tung Ping Chautimes when there was more than one layer of algae

was designated as a marine park, has brought someunder one point, the algae in the upper layer were

unexpected impact on the seaweed flora in therecorded first, and were then pushed to one side toprotected area.

expose and count the algae in the lower layer.
Some algae were difficult to identify
Study Site

Filamentous algae less than 1cm in length weregrouped as turf algae. Encrusting algae were also

Tung Ping Chau Marine Park (TPCMP) is locatedidentified as a group. No attempt was made toon the northeastern corner of Hong Kong territorial

examine the detailed species composition of the turf

water (Fig. 1). Because of its relative remoteness toor encrusting algae.

the highly urbanized Hong Kong, it still enjoys arelative protection from many human disturbances

Measurement of Herbivore Densitythat are characteristics of many other coastal areas

The position and number of quadrats were thein Hong Kong. A Ye Wan (AYW) and A Man Wan

same as those used in the measurement of algal(AMW), on the north to northeastern side of thepercentage cover described above. The number

island (Fig. 1), support a high cover (>50%) of hardof individuals of each herbivore species within thecorals. But high diversity of algae can also be found

25cm x 25cm quadrat was counted and identified

in their shallower rocky shores especially in winter.

to the lowest taxonomic level as much as possible.

Lung Lok Shui (LLS), on the other hand, is located

The sampling method for fishes was different. The

on the south to southwestern side of the island. It

observer would stay at 2m away from the plot andis exposed to strong waves especially in summer.

would count the number of fishes hitting the plot

It supported extensive beds offor two minutes. After recording, the number of, mainlyin the lower intertidal andand
Population ofin the subtidal.
extended all the way

individuals for each herbivorous species per quadrat,
including fishes, was standardized and expressed as
number of individuals/100 cm2 in the analyses.

to 10m depth below CD, forming one of the largest
seaweed beds in Hong Kong. The presence of thisextensive seaweed bed, together with high covers ofcorals in AYW and AMW, were the reasons behind

Density and size of
Other than the density of herbivores measured
above, the density of the sea urchinthe designation of Tung Ping Chau as a marine parkand its sizes in LLS were separately

in November 2001. Changes in algal and herbivore

measuredon a monthly basis in 2000, thendensities in LLS are the focus of this study.

in 2006-07 and 2008-09. Eight transect lines, each

P.O. Ang, Jr., K.Y. So, T.W. Li, F.F. Yeung. S.Y. Wong and C.K. Woo
20m long, were laid out haphazardly, in a direction

Statistical Analysis

perpendicular to the shoreline. A cave in LLS was

Relationships between the abundance of algae

used as a reference point to allow rough estimationand herbivores were tested by Pair-wise Pearsonof the position of the study site. All transect lines

Correlation. The percentage cover of algae andwere set at the shallow water region with depth

the density of herbivores, including herbivorous2

between ‑3 to ‑5 m CD. A 0.25 m quadrat was

fishes, were correlated. Furthermore, Canonicalplaced at 2m interval on the left side along each

Correlation was used to relate the abundance oftransect and all individuals of

found

the algal species and the density of herbivorous

inside the quadrat were counted. At the same time,

species in the whole community. Variables used in

the test diameter of each of these individuals of

the analysis were defined as the variables measured

was measured with a vernier caliper toin the study, such as the percentage cover ofthe nearest millimeter.

Canonical variates were thelinear combinations of these variables (Tabachnick

Phenology of& Fidell 1989). Two linear combinations of variables

Monthly monitoring for the growth andreproduction ofwere employed in this study, representing the algal

in LLS

species and the herbivorous species. Each species

has been on going since 1996. In each month, 100

was tested as one variable, unless the parametricindividuals of

assumptions of the analysis had been violated. In thewere haphazardly

selected and its maximum length from the baselatter case, the algal speciesof the holdfast to the tip of the longest lateral was

spp.,

measured to the nearest millimeter using a meter
stick. The number of individuals that became,

reproductive was also counted.

,
,

, and

were grouped as others.

Fig. 2. Mean percentage cover (%) of algae and mean density of herbivores(Individuals/100cm2) recorded in the general surveys from November 2002 to March
2004 in Lung Lok Shui. SD not shown.

Balance between harvesting pressure and protection: Implications for barren ground formation in Hong Kong
Herbivores like

,
,

,
,

and other small crabs were grouped as
small herbivores. The significance of each canonical2003, its density was 0.14 individual/100cm2. All
the other herbivores were also low in density at<0.3 individual/100cm2 all throughout the surveyed
period.

correlation was noted. For significant correlations,
their canonical loadings with values that were <0.3

Interactions between Algae & Herbivores

were not interpreted as they explained <10% of thevariance (Tabachnick & Fidell 1989).

Results of Pair-wise Pearson Correlation showedthat the cover of algae was not significantly
correlated with the density of the herbivores ( =Results‑0.112,> 0.05,= 15). For the results of CanonicalCorrelation, the first set was significant ( = 0.005)
Seasonal Variation in Algal Diversity and Cover
A total of 23 algal species were recorded in

between the two pairs of canonical variates with
encrusting algae having negative relationships with

LLS. The species richness of algae was highest

hermit crabs, the rock fisharound February to April 2003 and the maximum

and small herbivores. The alga

number of species found in any single month wasin contrast, had positive relationship with these

16. Diversity of the algae remained high throughout

three types of herbivores. The contributions from,the survey period with a peak shown in March 2003.

and hermit crabs were more

spp. were always the most dominant

important than those from the other variables.

species recorded.

The contribution from the sea urchin

The yearly mean percentage cover (±SD) of algae

was negligible.

was 93.6 ± 26.5%, ranging from 59% in August 2003
to 136% in December 2003 (Fig. 2). The peaks of algal

Density and size ofcoverage were in June 2003 and December 2003.

Comparing the density of

Although there was a significant drop in algal coversampled over the years, albeit at times using

in August 2003, the cover rebounded quickly. The

slightly different methods, it can be observed that

results of Kruskal-Wallis one-way ANOVA indicate

the number of these sea urchins was very low inthat the algal percentage cover was significantly

2000, ranging from 1.3 to 5.3 individuals/m2, anddifferent ( < 0.05, df = 14) among months.

remained low throughout 2003 to early 2004 (Fig.
3). The density, however, increased significantly by

Seasonal Variation in Herbivore Abundance andDiversity

2006. The mean density ofincreased2

from 5.5 individuals/m in September 2006 to 10.23

Seasonal variations of herbivore density wereindividuals/m2 in March 2007. In some quadrats, theobserved in LLS. The densities of all herbivores,

density could be as high as 40 individuals/m2. This

including fishes, increased in March 2003 and leveled

increase in March 2007 was a result of recruitment

off in May 2003. The density of the herbivoresof young urchins during winter (February andranged from 0.18 − 1.14 individual/100cm2 (Fig. 2)

March). This is reflected in the population structures2

with a mean of 0.76 individual/100cm . Eighteenofspecies of herbivores were recorded, with the−52% of the sea urchins were in the size range ofhighest diversity recorded in February 2003 and35−45 mm. In early 2007, the number of individuals

March 2004. The gastropod

having test diameter < 15mm increased to 21% in

was the dominant herbivore within the period

January and eventually to 32% in March (not all

surveyed with the highest density of 0.95 todata shown). A more detailed analysis on changes in2shown in Fig. 4. In October 2006, 39

1.17 individual/100cm recorded in April to June

the size structure of

2003. The density of the sea urchingiven in Li (2007). The mean density of

in LLS, TPCMP is

was very small and except for June 2003,

remained high (> 5 individuals/m 2) in 2008‑2009

was always less than 0.1 individual/100cm2. In June

(Fig. 3) with maximum density at 20 individuals/m2

P.O. Ang, Jr., K.Y. So, T.W. Li, F.F. Yeung. S.Y. Wong and C.K. Woorecorded in some quadrats.

Kong. Local villagers would collect these urchinsin late winter for their gonads. Even small sizes of

Phenology ofthese urchins are collected, especially by fishers

As typical for many

species.

from mainland China, and grown in cages until aexhibits an annual cycle of growthsuitable marketable size for export (pers. com. withand die-back. It has a slow growth period in

local villagers). This situation was also true in Tungspring to summer, a rapid growth period in thePing Chau in earlier years. On several occasions,fall, cumulating in the peak reproductive period in

we had directly observed the collection of these sea

early winter (December to January) before dying

urchins by these fishers underwater as well as byback in February to March. Over the years, thisthe local villagers. Each time, the collection was very

pattern has been consistent although the peakextensive and almost no urchin was left untouched.

period of growth and reproduction may differ

Since Tung Ping Chau was designated as aslightly from year to year (Fig. 3). Starting frommarine park in November 2001, all forms of plant

September to October 2006, however, the population

and animal collection are prohibited except withoffailed to attain a rapid increase

permission. Hook and line fishing is allowed but onlyin length. By December 2006, the mean maximum

in two designated sites. While local villagers could

length remained at only 13.4 ± 3.6 cm. In January

still collect the urchins for their local consumption,

and February 2007, only few reproductive plants

the large scale collection by other fishers is banned.

were found. Although some increase in length was

Our pre-marine park data on sea urchin density

apparent in March to June 2007, this was largely

clearly showed that the density was very low, anddue to development of the new shoots from thethis density remained low in a few years (2003-2004)

perennating holdfast. Thereafter, the population

immediately after large scale collection of the sea

completely disappeared and in 2008 to 2009, nourchins was banned. This low density populationindividual of

was found in the same

was likely maintained by harvesting pressure andwas reduced to

it took a few years for the population to increase insite (Fig. 3). The cover of0%.

size after harvesting was discontinued.
While no detailed monitoring on the density andDiscussion

sizes of

was carried out between 2004

and 2006, our regular monitoring of theSince our monitoring of the ecological condition

bed within the same period did not find them toof Tung Ping Chau in 1996, the presence of a large

be prominent. This situation changed in 2006 whenseaweed bed in LLS was a prominent feature.

visual inspection of the seaweed bed showed the

Although measurements of changes in the length

presence of many sea urchins. Our subsequentof thespp. in this bed were not carriedmonitoring of their density confirmed our suspicion

out every year, their presence could not be missed.

of the dramatic increase in their number. It is

Our earlier data indicated that the growth cycles ofapparent that the banning of larger scale sea urchin

the seaweeds, including the large

spp.

collection after Tung Ping Chau was designated aswere very regular for many years and herbivores

a marine protected area may have contributed towere not an important structuring force in thisthe dramatic increase in the sea urchin populations.

seaweed bed. This situation, however, had changed

As observed, this high density of sea urchins grazed

dramatically since 2006.

directly on
is a well known herbivore.

Its grazing effect and changes in its population

decimation of theand was responsible for thebed.

The presence of this large

bed itself

structure have been reported in other parts ofcould have provided the food needed by the urchins

Hong Kong (Chiu 1988) as well as in other partsfor rapid population growth. The large recruitmentof the Asia Pacific (Yoo1982, Yatsuya &in winter is timed with the presence of highest

Nakahara 2004). It is a harvested resource in Hongamount of seaweed biomass. The impact of sea

Balance between harvesting pressure and protection: Implications for barren ground formation in Hong Kongurchin grazing actually started in the shallower

individuals of

area of LLS. While individuals of

in lower intertidal and shallow subtidal were allandcould still be found in slightly deeper (-3 to -6 m

gone as of October 2006. In other parts of TPCMP,CD) subtidal area, albeit in a much reduced size,

like Lan Kwo Shui (LKS) and Lung Lin Tsui (LLT)

Fig. 3. Monthly mean length ( ± SD) of
from Lung Lok Shui, Tung Ping Chau Marine
Park over a 10 year period from 2000 to 2009. Data on the density of the sea urchins,when available, are also shown. Arrow A, time (Nov 21, 2001) when Tung Ping Chau was designated as a marine
park. Arrow B, time (Nov/Dec 2006) when decimation of the
population started to become clear. Notetime gaps in the X axis.

Fig. 4. Size frequency (%) of the test diameters of the sea urchinsin Tung Ping Chau
Marine Park. Only data for October 2006 and February 2007 are shown to illustrate the increase in the numberof small urchins in winter.

P.O. Ang, Jr., K.Y. So, T.W. Li, F.F. Yeung. S.Y. Wong and C.K. Woo(see Fig. 1 for their locations in TPCMP), which are

Would the dominance of barnacles prevent the

only a few hundred meters from LLS, large number

coming back of the algae, and lead to furtherofpersistence of the barren ground even after the

spp. remained during this same period.

A scenario could therefore be projected that thispopulation of sea urchins has declined?

bloom of sea urchin population most likely started

The formation of barren ground is an unexpectedin the shallow area of LLS in 2006. There could be

result of the protection of Tung Ping Chau as aother environmental conditions that contributed

marine park. This ran contrary to the very objective

to this bloom, e.g. warmer sea water temperatureof the marine park designation, which is to preserve(?). But the most likely scenario would have beenand protect the existing biodiversity, including thethat the release of sea urchins from harvesting

extensivepressure, coupled with the absence of any large

are expected to serve the functions of increasing

predators like fish and the presence of large amountthe biodiversity and abundance of protected species,of food in the seaweed bed, provided the impetus

preservation of genetic pools, and eventual spill

for its population expansion. This hypothesis couldof individuals (adults, juveniles or propagules) tofurther be confirmed with other developments

surrounding areas (Russ 2002). Our own studies,observed since 2006. The density of sea urchinsproviding both temporal and spatial comparisons ofremained high and in 2007 to 2008, these urchins

the mean density and diversity of fish before andhad moved on to decimate deeper populations ofafter Tung Ping Chau was designated as a marine

beds. Successful marine parks

in LLS, as well as populations of otherpark, indicated that there were increases in the

spp. in LKS and LLT. Extensive barren

fishery target species like the seagrass rabbitfish

grounds can now be observed throughout the west

, as well as other species likeand southwestern shore of Tung Ping Chau where

the yellowstripe scadlarge beds ofsilver sweeper

spp. used to stand. As of

April 2009, pockets ofcould still

prep., Lam

and the(Tam & Ang inin prep.). None of these, however,be found in LLT. These populations are currently

are the predatory fish that could prey on the sea

being monitored as they could serve as the source ofurchins.

recruits to the barren grounds should the populationofIn our survey of LLS in December 2008, somedecline in the near future.
Hong Kong fisheries are heavily overexploited

individuals belonging toandhad come back, mainly in theso the absence of any large predatory fish is not

lower intertidal and shallow subtidal areas. However,a surprise. Elsewhere outside TPCMP (or in thethe deeper areas remained barren with no signearlier years in TPCMP), harvesting pressure itself

ofserves as a top down control on the population of sea. Nonetheless, the return ofand, albeit very few

urchins, and indirectly on the seaweed populations.

of them, may provide some hope on the potential of

The question now is after the decimation of thenatural recovery of thebed.

seaweed bed in TPCMP, would the absence of

The unexpected formation of barren ground has

food resource then provide a bottom up control

implications for future management of TPCMP.

that would eventually lead to the decline of the

Several critical management questions need tosea urchin population? Or would the persistence ofbe addressed. In spite of the formation of barren

sea urchins lead to a phase shift in the community

grounds, should the system be left alone? Would

structure such that barren grounds would becomelarge predators eventually appear in the marine

the norm rather than the exception?

park to initiate a top down control on the population

One other indirect consequence of the formationof the sea urchins that would eventually lead toof barren ground is the recruitment of otherthe recovery of theinvertebrates, notably barnacles, on the newly

human step in to act as the top predator under

bed? Or should

opened space. The open areas cleared of

the unlikely scenario of natural appearance of otherspp. in LLS are now all covered with barnacles.

top predators? Finally, larger scale harvesting ofBalance between harvesting pressure and protection: Implications for barren ground formation in Hong Kongsea urchin is a more recent activity that probably

Kong. In: Echinoderm Biology. Burke R.D. (ed.).

started only in the last 20 or 30 years. There was

Balkema, Rotterdam, pp. 193‑204.

no record of what the environment was like prior

Himmelman, J.H. and Nedelec, H. 1990. Urchinto that. Is it therefore likely that barren groundforging and algal survival strategies in intensity

was actually thegrazed communities in eastern Canada. Can. J.

naturalsituation and seaweed

beds appeared only because of the removal of

Fish. Aquatic Sci. 47: 1011‑1026.

these major grazers by human? How important is

Lam Y.H., Lau P.L., Leung H.N., Sin Y.W., Tam M.C.,

human harvesting pressure on sea urchins, or other

Tam T.W. and Ang P.O. (in prep.) Changes inherbivores like fish, contributing to the dynamics

the fish assemblage structure in Tung Pingof the coastal algal community. What would be theChau Marine Park, Hong Kong: Effects ofother implications of this observed impact, i.e. onprotection.

the role of seaweed bed as a nursery and breeding

Li T.W. (2007) Population dynamics of the sea

ground for other fish and invertebrates? All theseurchinquestions inevitably point to the utility of setting

Chau Marine Park. Final Year Project Report,

up of the marine park itself and would need to be

Department of Biology, The Chinese University

examined more carefully!

in Tung Pingof Hong Kong.
Ng K.Y. (2009) The Faunal Assemblage Structure

Acknowledgmentsin the Seaweed Bed of
M.Phil. Thesis, The Chinese University of Hong

We would like to thank the Aquaculture, Fisheries

Kong.

and Conservation Department (AFCD) of the Hong

Russ G.R. (2002). Yet another review of marine

Kong SAR Government for permission to work inreserves as reef fishery management tools. In:

Tung Ping Chau Marine Park over these many

Coral Reef Fishes: Dynamics and Diversity in ayears. P.O. Ang would like to thank the Fisheries

Complex Ecosystem. Sale P. F. (ed.). Academic

Agency, Ministry of Agriculture, Forestry &Press, San Diego, CA, pp. 421‑443.

Fisheries of Japan for support to attend the Isoyake

So K.Y.E. (2005) Algal-herbivore Interactions in

Symposium held at the Tokyo University of Marine

Coastal Communities in Tung Ping Chau, Hong

Science and Technology (TUMST) in August,Kong. M.Phil. Thesis, The Chinese University of2008 and to Prof. D. Fujita of TUMST and otherHong Kong.

colleagues from the Fisheries Agency for support

Tabachnick B.G. and Fidell L.S. (1989) Usingand hospitality during the symposium and theMultivariate Statistics. HarperCollins Publishers

post-symposium field trip. This study was partly

Incorporation, New York.

supported by NSFC-RGC Grant N̲CUHK438/06 to P.
O. Ang, Jr.

Tam M.C. and Ang P.O. (in prep.) Spatial andtemporal comparison of fish assemblage
structures in a subtropical marine park before

References

and after its designation.
Vasquez J.A., Castilla J.C. and Santelices B. (1984)

Ang P.O. (2005) Studies of marine algae in HongKong. In: World Seaweed Resources. Critchley
A.T., Ohno M., Largo D. (eds.). ETI Information
Services Ltd., Wokingham, Berkshire, UK. Part
3.04.

Distributional patterns and diets of four speciesof sea urchins in giant kelp forest () of Puerto Toro, Navarino Island, Chile.
Mar. Ecol. Prog. Ser. 19: 55‑63.
Watanabe, J.M. and Harrold, C. 1981. Destructive

Ang, P.O. (2006) Phenology of

spp. ingrazing by sea urchins

spp.

Tung Ping Chau Marine Park, Hong Kong SAR,

in a central California kelp forest: Potential roles

China. J. Appl. Phycol. 18: 629‑636.

for recruitment, depth, and predation. Mar. Ecol.

Chiu S.T. (1988) Reproductive biology of(Echinodermata: Echinoidea) in Hong

Prog. Ser. 71:125‑141.
Yatsuya K. and Nakahara H. (2004) Density andP.O. Ang, Jr., K.Y. So, T.W. Li, F.F. Yeung. S.Y. Wong and C.K. Woo
reproduction of the sea urchin(A. Agassiz) in two different adjacent
habitats, the

and

area.

70: 233‑340
Yoo S. K., Hur S.B., Ryu H.Y. (1982) Growth andspawning of the sea urchin(A. agassiz).
15: 345‑358