第六讲第二节
大型底栖海藻生态
主要内容
? What are seaweeds?
? 底栖藻类固着生长
? 对光的需求产生形态上的适应
? Seaweed的种类：绿藻、褐藻、红藻
? Grazers,competition and defence
? Seaweed as part of an ecosystem
? The rigours of seaweed life
? Wherever seaweeds grow they have to
compete for space,inorganic nutrients and
light,They are also in constant danger of being
grazed on by gastropods（腹足动物）,fish,
sea slugs（海蛤蝓） and sea urchins（海胆）
and have some sinister tactics for putting off
predators.
? An,army”of Littorina snails grazing green seaweeds form a rock
surface (Fig,p59)
Fighting for space
? 1)种内竞争：
? when there is mass settling and germination of
spores of the same species in a confined area,
competition naturally occurs between the
thalli(叶状体 ).
? In general this results in an inverse relationship
between density and size,This is particularly
applicable to stands of fast-growing,short-lived
species such as Ulva(石莼 ),Bangia（红毛菜）,
Enteromorpha（浒苔） and Porphyra（紫菜）,
? Those much slower growing encrusting
coralline species compete for space,they end
up growing into and over each other,
sometimes becoming quite indistinct（模糊的）
as individuals.
? 2）种间竞争：
? 并不一定是大的藻类在空间竞争中就获得优势，
例如大型褐藻 Egregia laevigata（优秀藻）就竞
争不过较为小型的红藻，因为这些小型的藻类能
够快速地占领空间，使得大型褐藻的孢子难以附
着并萌发。
? 3）与动物的空间竞争：
barnacles（藤壶）,mussels（贻贝）等也
是大型藻类空间的竞争对手。
There are mechanisms by which seaweed
inadvertently(不经意地 ) helps to strip the
creatures from the rocks,so creating a space
in which to grow,
The robust Postelsia(囊沟藻 ) inhabits parts
of the shore that are also occupied by barnacles
and mussels,Small Postelsia have been seen
growing firmly attached to barnacles,When they
reach a certain size,the increased drag causes
the seaweed,together with the attached
barnacle,to be ripped from the rock surface,
The bare area of rock is immediately colonised
by Postelsia spores.
? 4) 附生植物 epiphytes
One of the most effective ways to gaining an
advantage in the quest for space and light is to
grow on the surface of a moving animal or on
the surface of another seaweed.
Most seaweeds,from encrusting corallines
(钙质的 ) to large membranous species,can
grow as epiphytes,but very few seaweeds
have to live this way.
? Fig.p65
Most epiphytic species are fast growing,short-lived
and filamentous,for example,丝状的红藻 Polysiphonia
lanosa（多管藻）经常附生于 Ascophyllum（囊叶藻）
的叶状体上。
Generally,epiphytes do not grow on rapidly
growing parts of the thallus.Therefore Laminaria(海带 )
and Macrocystis(巨藻 ) stipes(叶柄 ) may have large
standing crop of epiphytes whereas the rapidly growing
fronds(叶面 ) or blades are largely free of epiphytes,
Fast-growing species such as Ulva and Porphyra are
rarely covered with epiphytes—they simply grow too
fast for the epiphytes to take hold.
? 5) 防止被附生植物附着
Epiphytes can harm their hosts by blocking
out the light and taking up nutrients from the
surrounding water,Layer of epiphytes can act
as effective barriers to exchange processes,
including gaseous exchange,reducing the
host’s growth rate,
? Some species,including Chondrus crispus(皱波角叉
菜 ),Halidrys siliquosa（角长角藻）,regularly slough
（脱落） their surfaces,thereby ridding themselves of
any build up of epiphytes.
? Enteromopha intenstinalis（肠浒苔） constantly
produces new cell wall layers,while shedding outer
layers of the wall,to ensure that it remains epiphyte
free.
? Some species produce chemical deterrents to prevent
epiphytes settling,Phenolics(苯酚 ) and halogenated
lipids（卤化油脂） are thought to play such a role.
Trying not to be eaten,Adaptations
in benthic algae against grazing
? 1）藻体形态 Algal morphology
Many grazers show considerable species selectivity
and this may be related to algal morphology or size,
Grazing difficulty increases from microalgae (diatoms,
blue-green algae) through filamentous（丝状体，如刚
毛藻、水云）,foliose（叶状体，如石莼）,corticated
（带外皮的，如软骨藻）,leathery form（革状种类，如
海带、墨角藻）,cartilaginous form（软骨质形态，如仙
掌藻、珊瑚藻） and ultimately to crustose coralline
algae（壳状、珊瑚状藻类，如石枝藻）,
? Some algae are able to grow fast enough to escape
grazing by becoming too large for grazers to deal with
them.
? 对于某些具有不同类型生活史的藻类来说，可以通过藻
体不同阶段的形态变化来减轻动物的捕食压力，如
Scytosiphon lomentaria(萱藻 )，其叶状体阶段生长很快，
抵御蜗牛（ Littorina littorea ）捕食的能力很低，其壳状
体很少被蜗牛所取食；在蜗牛活动最活跃的夏季，尽管
环境条件很适合叶状体生长，但是萱藻还是以壳状体形
式存在，以降低动物捕食压力。
? Littorina littorea 喜欢吃皱波角叉藻（ Chondrus crispus）
的孢苗，但是对成体却不感兴趣。
? 南太平洋岛屿
中的某些马尾
藻与喇叭藻等
的叶状体变得
很粗糙以及多
刺，可以有效
地抵御动物的
捕食,如图喇叭
藻 Turbinaria；
2）特殊的栖息地 Special habitat
? Rock-boring algae which often abound on coral
reefs,although suffer from poor light,are
protected from most grazers due to their
special habitat.
3) 藻体表面钙化
Calcification of surface
? 在热带海域，植物群落缺少大型种类，许多种类
以钙化的形态存在，例如珊瑚藻科植物，其钙化
形态对在高捕食压力下具有重要的存活意义。如
钙质红藻 Peyssonnelia squamaria(耳壳藻）
（左），钙质绿藻 Halimeda copiosa（仙掌藻）
（右上），钙质褐藻 Padina boergesenii（团扇
藻） （右下）
4）释放有毒化学物质 Release of
toxic chemical compounds
? 绿藻、褐藻、红藻中的某些种类能释放诸如萜类化合物、
多酚、生物碱等化合物，这些化合物的存在能有效地抵
制动物的捕食；
? 一般来说，能释放有毒物质的种类大多局限于热带海域，
因为在热带海域中动物的捕食压力（尤其是鱼类的捕食
压力）很大，使得底栖藻类产生进化上的相应机制；
? 例如,Laurencia obtusa (凹顶藻 )能通过产生溴化物来
逃避很多草食动物的捕食，如海胆等，溴化物对海胆的
卵具有很强的毒性；
? 某些藻类的藻体中含有相当高分量的丹宁酸，使得它们
散发出异常的气味，口感差，使其它动物不喜欢吃；
? 褐藻经常能产生一些酚类化合物，他们是一些抗
菌化合物，也能使无脊椎动物不去吃它们；
? 网地藻中的一些热带种类能产生大量萜类化合物，
如在网地藻 Dictyota中萜类化合物的含量能达到
藻体干重的 5％；
? 褐藻中的海带、绿藻中的羽藻、红藻中的海门冬
和柏桉藻，能累积大量的碘，碘的释放过程能阻
止动物的捕食；
? 某些藻类分泌的有毒化合物能通过食物链传递给
人类，例如，从齿形蕨藻（ Caulerpa serrulata）
的藻体中已经分离出蕨藻红素和蕨藻毒素两类化
合物，它们能对小鼠造成毒害作用，在热带海域
密集的海藻床上，这些毒素通过无脊椎动物、鱼
类，进而传递给人类，对人的健康造成影响；
? 一些有毒的珊瑚鱼类，其毒性是通过摄食某些有
毒藻类而获得的，如从易氏鞘丝藻和巨大鞘丝藻
中获得的毒素，能对人体造成皮肤病；
? 酸藻藻体的液泡中
含有硫酸，其浓度
足以将海胆的牙齿
腐蚀掉。
Herbivores are not all bad
? Though seaweeds are food for a whole host of
herbivores,in general less than 10% of
biomass tends to be actively grazed,Many of
the molluscs（软体动物） that appear to be
grazing on the seaweeds are actually eating
the films（膜） of epiphytic（附生植物的）
microalgae and bacteria that grow on the
surfaces of the seaweed.
? 适当的捕食压力能提高藻类的多样性，例如海胆
对海藻床造成破坏，主要是通过破坏大型藻的固
着器等，使藻体从固着物上脱落漂走，这样就那
些因大型藻类的遮荫作用而生长不良的种类长起
来，提高生物多样性。
?,House building” amphipods(片脚类动物 ) and
“farming, fish
Some surprising associations have developed
between seaweeds and grazing animals,Some
species of sea slug(海蛤蝓 ),for example,graze
specifically on seaweeds that contain agents for
deterring(阻止 ) fish,By storing the anti-grazing agent in
its own tissues the sea slug then has a deterrent to
stop itself being predated upon by fish.
A Caribbean amphipod constructs enclosures from
Dictyota(网地藻 ) thalli,encouraged by chemicals
released by the Dictyota itself,The chemicals are
released to deter fish grazing,and the enclosures
therefore also protect the amphipods form predatory
fish.
There are even examples of,farming fish”(species
of tropical damselfish(小热带鱼 )) that maintain
specific stands of seaweed by careful selective
grazing,Sometimes they maintain,pastures” (牧场 ) of
just on species or a limited number of species over
large expanses of reefs.
The effect of grazing and
competition on zonation
? It is a commonly held view that the upper limits
of a particular species on the shore are set by
the tolerances to one or more of the physical
stresses,such as desiccation(干燥 ),salinity,
temperature,light,etc,while the lower limits
are set by the effect of grazing and competition.
? In the subtidal zone light is the obvious single
more dominant factor in determining the
distribution of seaweeds and zonation patterns.
? The intertidal region is somewhat more
complicated since none of the physical,stress
factors” act in isolation,Rather than being a
response to one particular stress,distribution
limits result from the interaction of several
factors prevailing(占优势的 ) at a particular
place on a shore.
? A more accurate interpretation of the causes of
zonation is probably that the,potential” limits
of the distributions of a species are set by
physical and chemical limitations,The actual
distribution on a shore is finely tuned(调节 ) by
biological interactions such as grazing
pressure and competition,
Seaweed as part of an ecosystem
? The total weight,or biomass,of seaweed on a shore
can be impressive,especially when subtidal kelp
forests are considered,
? The productivity of seaweed communities is equal to,
or in many cases greater than,that of terrestrial plant-
based systems,
Laminaria-dominated communities,2 kg carbon per m2
Postelsia(囊沟藻 ) communities,up to a massive 14 kg carbon per m2
intensive alfalfa(紫花苜蓿 ) crops,1-2 kg carbon per m2
Temperate tree plantation or grassland,less than 1 kg carbon per m2
? 1) 食物来源 Seaweed as a food source
? Seaweeds are part of a complex ecosystem involving
many different types of animals,Many of the finer(好的 )
seaweeds are valuable food sources,yet the larger
species are not grazed on to a great extent.
In the case of laminaria(海带 ),for example,only
about 1% of the thallus is directly eaten by herbivores
such as gastropods（腹足动物）,sea urchins（海胆）
and fish.
? Bits and pieces constantly break off from the main
thallus and provide food for debris feeders such as
crabs,sea cucumbers(海参 ) and amphipods(片脚类动
物 ),The smaller fragments are rich supplies for filter-
feeding organisms such as mussels（贻贝）,
barnacles（藤壶）,tunicates（被囊类）,anemones
（海葵） and polychaete worms(多毛类 ).
? Detached seaweeds washed up on the shore are
another valued resource.
? 2) 分泌粘液 Mucus producers
? Seaweeds release sugars and amino acids into
the water as a result of damage or due to
regulation of their metabolism in response to
environmental stress.
? These substances are referred to as dissolved
organic matter (DOM) and it is thought that up
to 30% of the carbon assimilated by Laminaria
may be released in the form of DOM.
? The seaweeds play a role in the regulation of
bacterial activity within coastal waters,As the
bacteria break down the DOM,nutrients such
as nitrogen and phosphorus are released back
into the water and can be taken up again by
the seaweed for new growth.
? 3) seaweed as shelter
? These assemblages of seaweeds and animals attract
fish for the rich pickings the provide,But it isn’t just the
food that attracts the fish since the dense growth of
seaweed form an effective refuge from larger predators
such as birds and dolphins,
? Shoals(鱼群 )of plankton-eating fish hide amongst
stands of seaweed,coming out of cover to feed only at
certain times of the day,Some fish have an elaborate
camouflage（伪装）,such as the sargassum fish
(Histrio histrio)
七,Seaweed life
大型海藻生活的环境
? The region between the ocean and the land is
a demanding place in which to live,It is a place
of extremes dominated by tides and waves,
Seaweeds have to be able to cope with the
rise and fall of the tides.
1,Tidal patterns 潮汐规律
? There are three main classes of tidal cycles:
1) Diurnal tide 全日潮
with one high and one low water per day,
for example,parts of the Gulf of Mexico
2) Semiduirnal tide 半日潮
with two high and two low tides in a day
for example,Atlantic coastline
3) Mixed tide 混合潮、不规则半日潮
occur twice a day but the highs and the lows are of
unequal amplitudes.
for example,Pacific ad Indian Ocean coasts
What causes the tides?
? Tides are produced by the gravitational（万有
引力） effects of the moon and to a lesser
extent the sun.
? Spring tides 大潮 the moon and sun are in
line with the earth,which occurs twice a month
? Neap tides 小潮 the moon and sun are at
right angles and have,on average,20% lower
amplitudes than spring tides.
Seaweeds and tides
? Any seaweed that
grows on the shore
between the
lowest and the
highest tide levels
will be exposed to
the air at some
point,maybe once
or twice a day,
2,Zone of the shore
? Certain species are specific to particular
regions or zones,The zones are delineated by
critical tide levels that govern how long the
region is submerged or exposed.
? Whether a species can grow in a particular
zone depends on its tolerance to desiccation,
temperature stress,salt stress and wave action.
Three zones of the shore
? Intertidal or littoral zone 潮间带
The shore that lies between the extreme high water of
spring tides and the extreme low water of spring tides.
? Supralittoral zone 潮上带
The region above the littoral zone that receives spray.
? Subtidal or sublittoral zone 潮下带
The permanently submerged region that lies beyond the
extreme low watermark.
The intertidal zone
? Worldwide studies have identified three regions with
the intertidal zone,
? 1) there is an uppermost strip of desiccation-tolerant
lichens(苔藓、地衣 ) or cyanobacteria that often have
obvious populations of littorinid snail(滨螺 ).
? 2) the next zone down the shore comprises a wide
diversity of seaweeds together with barnacles(藤壶 )
and limpets(帽贝 ),
? 3) the lowermost part of the intertidal zone harbours a
diverse community of seaweed species including red
encrusting and coralline algae.
The subtertidal zone
? The kelps of temperate and some tropical
shores grow within this zone,The lowermost
region of this zone is never exposed to the air
and is dominated by a variety of large canopy-
forming seaweeds with diverse understorey
communities of predominantly red and brown
species.
? Still further down,where light hardly penetrates,
is home to encrusting red algae.
3,the problems of desiccation（干
燥）
? Seaweed living in the intertidal zone may face
long periods out of water,but there are various
strategies for keeping water loss to a minimum.
? Even when seaweeds do dry out they have a
remarkable ability to recover once the tide
returns.
Safety in numbers
? Understorey layer
The consequence of this sort of layered structure is that it
is only those fronds lying on the surface that will be
exposed to the harsh condition.
? Tufts(一簇 ) of filaments
When the tide goes out the tufts
actually retain a lot of water between
the filaments so that even after they
have been exposed to the air for a
considerable time the interior of the
tuft remains moist.
Preventing water loss
? Desiccation can be extreme such that intertidal
seaweeds can lose up to 90% of their tissue.\
water when exposed to the air,especially if
there is a breeze(风 ) and humidity is low.
? The speed with which this happens depends
largely on the surface area to volume ratio of a
thallus,the larger this ratio,the faster the water
losses,Small seaweed,branched seaweed.
? Some seaweed could withstand a certain
amount of desiccation due to the present of
polysaccharides within their inner cortex(皮质 )
or medulla(髓 ) that bind with water,Other
seaweeds exude mucus that helps to slow
down the rate of evaporation,
潮间带藻类光合作用的变化
? The most obvious factor that determined
whether or not a species can survive long
periods out of the water is whether it is able to
photosynthesis in the air.
? As long as the seaweeds do not dry out,many
species photosynthesis in air at rates similar to
those measured when they are fully
submerged,However,as they begin to dry out
their ability to photosynthesis diminishes.
? For example,photosynthesise if Laminara,
even when mildly desiccated,is greatly
reduced whereas Ulva continues
photosynthesis down to 35% water loss,Some
species of Fucus photosynthesise when
desiccated down to tissue water contents of
less than 30%.
? Seaweeds recover their full photosynthetic
rates within hours.
? A rare example of
Pelvetia canaliculata
(沟鹿角菜 ) in which
periods out of water
are absolutely
essential,If it is
submerged for more
than 6 hr,it actually
starts to decay.
4,Dealing with salt stress
? In most oceans around the world there are
about 35 grams of salt in every litre of water.
? There are notable exceptions to this,such as
the Baltic Sea,which has much reduced
salinities of between three and 10 due to tis
large influx of freshwater,while the Arabian
Gulf,Mediterrancean and Red Sea have
salinities up to 45or more due to high rates of
evaporation and their semi-enclosed nature.
? When seaweeds are exposed to rain at low
tide,they experience a dramatic reduction in
salt concentration,In contrast,when water
evaporates from the surfaces of seaweeds,
salts in the remaining water become greatly
concentrated,Both lowered and eleated
changes cause a severe strain on the cells of
the seaweeds,requiring swift metabolic action
to prevent permanent damage.
? In some regions,such as Moroccan(摩洛哥 ) estuary,
the evaporation of water is so extreme that o seaweeds
can survive.
Salt and osmosis(渗透作用 )
? In normal seawater the cells of a seaweed are in
balance with the water outside of the cells.
? When salinity in the external water goes down,it
creates an osmotic imbalance that results in water
being taken up by the cells,By lowering the cellular
concentrations of ions such as potassium(钾 ),
sodium(钠 ) an chloride(氯化物 ),as well as sugars and
organic compounds to restore the osmotic equilibrium
to one close to that before the salinity ha been reduced.
? When the salinity of the external water
increases the reverse process take place,The
higher concentration of external salts causes
water to be lost from the cells,again in direct
proportion to the increase in salinity.The cells
have to restore the osmotic balance by taking
up ions,or producing greater cellular
concentrations of sugars and organic
compounds.
Salinity tolerance varies
? Seaweeds have differing capabilities for making these
osmotic adjustments and hence varying tolerances to
salinity changes,In general,seaweeds growing higher
on the shore tend to have greater tolerance than
species found lower on the shore.
? Many intertidal seaweeds may withstand salinities
ranging from 0-100,whereas many subtidal species
are killed by only slight changes in salinity,or at best
have limited tolerance of salinities from 20-50.
? Metabolic rates are severely reduced for most species
in extremely low and high salinities,
Effect of temperature on saline
stress
? Temperature can have a significant influence
on how well seaweeds survive saline stress.
? Species normally grow within a certain
temperature range and at temperatures at
either extreme of this range the ability to
withstand salinity stress is generally reduced,
5,Temperature stress
? The geographical distribution of seaweed
species is largely dictated by temperature
tolerance.
? There are species of seaweed that re restricted
to tropical waters which narrow temperature
tolerances close to 30℃,while species in the
Antarctic rarely survive temperatures above
13℃,
? Difference life cycle stages may also be
sensitive to different temperature range,
? Temperature tolerance,and therefore
geographical distribution,is also modified by
the ability of a species to withstand other
stresses,such as salinity and desiccation,
especially at extreme high and low
temperatures.
Seasonal temperature changes
? Seasonal changes in water temperatures are
large gradual and species that live permanently
submerged are not often exposed to sudden
shifts in temperature,
? Metabolic rates change with these seasonal
variations due to the effects of temperature on
chemical reaction rates,enzyme metabolism
and biophysical processes,
? At the lower end of the temperature range for a
particular species,growth rates will be slower
than at higher temperatures,and often there
will be temperatures at which growth is optimal
although these may vary with the different life
cycle stage.
A hot summer
? In the intertidal zone seaweeds exposed during
periods of low tide may be subjected to
temperature extremes may outside the normal
limits set by seawater temperature.
? For example,Porphora
A freezing winter
? Differences in
freezing tolerance
play a role in
determining the
distribution of
seaweeds on the
shore,
6,Water movement
? Another
challengin
g aspect of
seaweed
life is the
relentless
action of
the waves,
? The turbulent motion of seaweeds that is
induced by currents and waves is not all bad,
? The currents and waves of coastal regions
mean that seaweeds are constantly supplied
with nutrient-rich water (water can quickly
become depleted where movement is low and
where large stands of seaweed are present),
? Constant water motion also distributes light in
the water more evenly.
? In regions where wave action is strong,grazing by
herbivores is significantly reduced,Turbulent water
also keeps the seaweed in constant motion,allowing
the diffusion of nutrients and gases to and from the
frond.
? Nereocystic(腔囊藻 ) 在流动速度快的水体中，叶片很平
滑，以降低藻体被海浪冲击下来的危险；但在流水缓慢
的地方，由于藻类大量生长，为了获取营养盐，腔囊藻
变得有褶边，增加表面积来吸收营养盐。
It pays to be flexible
? The difference between seaweed and trees or
bushes on land
? A key to the success of the seaweeds is their
flexible nature,expecially those with long stipe.
? The flexible stipes allow the thalli to bend in the
direction of the water movement.
? Seaweeds adapt their shape to reduce drag
depending on their location,the same species
growing on exposed or sheltered stretches of
coast can look quite different,In general,wave-
exposed forms are smaller and may have
narrower blades.
Growth strategy
? Despite having smooth blades and a flexible stipe,
seaweeds suffer considerable damage from surf and
wave action,The fronds of species such as Laminaria
are frequently broken off at the tips or lacerated into
strips,
? Sea palm,Postelsia(囊沟藻 ) is one of the most
tenacious seaweeds to survive high-energy wave
environments,The secret of its success seems to be
that it has exceptionally strong holdfasts combined with
highly flexible stripes.
大型底栖海藻生态
主要内容
? What are seaweeds?
? 底栖藻类固着生长
? 对光的需求产生形态上的适应
? Seaweed的种类：绿藻、褐藻、红藻
? Grazers,competition and defence
? Seaweed as part of an ecosystem
? The rigours of seaweed life
? Wherever seaweeds grow they have to
compete for space,inorganic nutrients and
light,They are also in constant danger of being
grazed on by gastropods（腹足动物）,fish,
sea slugs（海蛤蝓） and sea urchins（海胆）
and have some sinister tactics for putting off
predators.
? An,army”of Littorina snails grazing green seaweeds form a rock
surface (Fig,p59)
Fighting for space
? 1)种内竞争：
? when there is mass settling and germination of
spores of the same species in a confined area,
competition naturally occurs between the
thalli(叶状体 ).
? In general this results in an inverse relationship
between density and size,This is particularly
applicable to stands of fast-growing,short-lived
species such as Ulva(石莼 ),Bangia（红毛菜）,
Enteromorpha（浒苔） and Porphyra（紫菜）,
? Those much slower growing encrusting
coralline species compete for space,they end
up growing into and over each other,
sometimes becoming quite indistinct（模糊的）
as individuals.
? 2）种间竞争：
? 并不一定是大的藻类在空间竞争中就获得优势，
例如大型褐藻 Egregia laevigata（优秀藻）就竞
争不过较为小型的红藻，因为这些小型的藻类能
够快速地占领空间，使得大型褐藻的孢子难以附
着并萌发。
? 3）与动物的空间竞争：
barnacles（藤壶）,mussels（贻贝）等也
是大型藻类空间的竞争对手。
There are mechanisms by which seaweed
inadvertently(不经意地 ) helps to strip the
creatures from the rocks,so creating a space
in which to grow,
The robust Postelsia(囊沟藻 ) inhabits parts
of the shore that are also occupied by barnacles
and mussels,Small Postelsia have been seen
growing firmly attached to barnacles,When they
reach a certain size,the increased drag causes
the seaweed,together with the attached
barnacle,to be ripped from the rock surface,
The bare area of rock is immediately colonised
by Postelsia spores.
? 4) 附生植物 epiphytes
One of the most effective ways to gaining an
advantage in the quest for space and light is to
grow on the surface of a moving animal or on
the surface of another seaweed.
Most seaweeds,from encrusting corallines
(钙质的 ) to large membranous species,can
grow as epiphytes,but very few seaweeds
have to live this way.
? Fig.p65
Most epiphytic species are fast growing,short-lived
and filamentous,for example,丝状的红藻 Polysiphonia
lanosa（多管藻）经常附生于 Ascophyllum（囊叶藻）
的叶状体上。
Generally,epiphytes do not grow on rapidly
growing parts of the thallus.Therefore Laminaria(海带 )
and Macrocystis(巨藻 ) stipes(叶柄 ) may have large
standing crop of epiphytes whereas the rapidly growing
fronds(叶面 ) or blades are largely free of epiphytes,
Fast-growing species such as Ulva and Porphyra are
rarely covered with epiphytes—they simply grow too
fast for the epiphytes to take hold.
? 5) 防止被附生植物附着
Epiphytes can harm their hosts by blocking
out the light and taking up nutrients from the
surrounding water,Layer of epiphytes can act
as effective barriers to exchange processes,
including gaseous exchange,reducing the
host’s growth rate,
? Some species,including Chondrus crispus(皱波角叉
菜 ),Halidrys siliquosa（角长角藻）,regularly slough
（脱落） their surfaces,thereby ridding themselves of
any build up of epiphytes.
? Enteromopha intenstinalis（肠浒苔） constantly
produces new cell wall layers,while shedding outer
layers of the wall,to ensure that it remains epiphyte
free.
? Some species produce chemical deterrents to prevent
epiphytes settling,Phenolics(苯酚 ) and halogenated
lipids（卤化油脂） are thought to play such a role.
Trying not to be eaten,Adaptations
in benthic algae against grazing
? 1）藻体形态 Algal morphology
Many grazers show considerable species selectivity
and this may be related to algal morphology or size,
Grazing difficulty increases from microalgae (diatoms,
blue-green algae) through filamentous（丝状体，如刚
毛藻、水云）,foliose（叶状体，如石莼）,corticated
（带外皮的，如软骨藻）,leathery form（革状种类，如
海带、墨角藻）,cartilaginous form（软骨质形态，如仙
掌藻、珊瑚藻） and ultimately to crustose coralline
algae（壳状、珊瑚状藻类，如石枝藻）,
? Some algae are able to grow fast enough to escape
grazing by becoming too large for grazers to deal with
them.
? 对于某些具有不同类型生活史的藻类来说，可以通过藻
体不同阶段的形态变化来减轻动物的捕食压力，如
Scytosiphon lomentaria(萱藻 )，其叶状体阶段生长很快，
抵御蜗牛（ Littorina littorea ）捕食的能力很低，其壳状
体很少被蜗牛所取食；在蜗牛活动最活跃的夏季，尽管
环境条件很适合叶状体生长，但是萱藻还是以壳状体形
式存在，以降低动物捕食压力。
? Littorina littorea 喜欢吃皱波角叉藻（ Chondrus crispus）
的孢苗，但是对成体却不感兴趣。
? 南太平洋岛屿
中的某些马尾
藻与喇叭藻等
的叶状体变得
很粗糙以及多
刺，可以有效
地抵御动物的
捕食,如图喇叭
藻 Turbinaria；
2）特殊的栖息地 Special habitat
? Rock-boring algae which often abound on coral
reefs,although suffer from poor light,are
protected from most grazers due to their
special habitat.
3) 藻体表面钙化
Calcification of surface
? 在热带海域，植物群落缺少大型种类，许多种类
以钙化的形态存在，例如珊瑚藻科植物，其钙化
形态对在高捕食压力下具有重要的存活意义。如
钙质红藻 Peyssonnelia squamaria(耳壳藻）
（左），钙质绿藻 Halimeda copiosa（仙掌藻）
（右上），钙质褐藻 Padina boergesenii（团扇
藻） （右下）
4）释放有毒化学物质 Release of
toxic chemical compounds
? 绿藻、褐藻、红藻中的某些种类能释放诸如萜类化合物、
多酚、生物碱等化合物，这些化合物的存在能有效地抵
制动物的捕食；
? 一般来说，能释放有毒物质的种类大多局限于热带海域，
因为在热带海域中动物的捕食压力（尤其是鱼类的捕食
压力）很大，使得底栖藻类产生进化上的相应机制；
? 例如,Laurencia obtusa (凹顶藻 )能通过产生溴化物来
逃避很多草食动物的捕食，如海胆等，溴化物对海胆的
卵具有很强的毒性；
? 某些藻类的藻体中含有相当高分量的丹宁酸，使得它们
散发出异常的气味，口感差，使其它动物不喜欢吃；
? 褐藻经常能产生一些酚类化合物，他们是一些抗
菌化合物，也能使无脊椎动物不去吃它们；
? 网地藻中的一些热带种类能产生大量萜类化合物，
如在网地藻 Dictyota中萜类化合物的含量能达到
藻体干重的 5％；
? 褐藻中的海带、绿藻中的羽藻、红藻中的海门冬
和柏桉藻，能累积大量的碘，碘的释放过程能阻
止动物的捕食；
? 某些藻类分泌的有毒化合物能通过食物链传递给
人类，例如，从齿形蕨藻（ Caulerpa serrulata）
的藻体中已经分离出蕨藻红素和蕨藻毒素两类化
合物，它们能对小鼠造成毒害作用，在热带海域
密集的海藻床上，这些毒素通过无脊椎动物、鱼
类，进而传递给人类，对人的健康造成影响；
? 一些有毒的珊瑚鱼类，其毒性是通过摄食某些有
毒藻类而获得的，如从易氏鞘丝藻和巨大鞘丝藻
中获得的毒素，能对人体造成皮肤病；
? 酸藻藻体的液泡中
含有硫酸，其浓度
足以将海胆的牙齿
腐蚀掉。
Herbivores are not all bad
? Though seaweeds are food for a whole host of
herbivores,in general less than 10% of
biomass tends to be actively grazed,Many of
the molluscs（软体动物） that appear to be
grazing on the seaweeds are actually eating
the films（膜） of epiphytic（附生植物的）
microalgae and bacteria that grow on the
surfaces of the seaweed.
? 适当的捕食压力能提高藻类的多样性，例如海胆
对海藻床造成破坏，主要是通过破坏大型藻的固
着器等，使藻体从固着物上脱落漂走，这样就那
些因大型藻类的遮荫作用而生长不良的种类长起
来，提高生物多样性。
?,House building” amphipods(片脚类动物 ) and
“farming, fish
Some surprising associations have developed
between seaweeds and grazing animals,Some
species of sea slug(海蛤蝓 ),for example,graze
specifically on seaweeds that contain agents for
deterring(阻止 ) fish,By storing the anti-grazing agent in
its own tissues the sea slug then has a deterrent to
stop itself being predated upon by fish.
A Caribbean amphipod constructs enclosures from
Dictyota(网地藻 ) thalli,encouraged by chemicals
released by the Dictyota itself,The chemicals are
released to deter fish grazing,and the enclosures
therefore also protect the amphipods form predatory
fish.
There are even examples of,farming fish”(species
of tropical damselfish(小热带鱼 )) that maintain
specific stands of seaweed by careful selective
grazing,Sometimes they maintain,pastures” (牧场 ) of
just on species or a limited number of species over
large expanses of reefs.
The effect of grazing and
competition on zonation
? It is a commonly held view that the upper limits
of a particular species on the shore are set by
the tolerances to one or more of the physical
stresses,such as desiccation(干燥 ),salinity,
temperature,light,etc,while the lower limits
are set by the effect of grazing and competition.
? In the subtidal zone light is the obvious single
more dominant factor in determining the
distribution of seaweeds and zonation patterns.
? The intertidal region is somewhat more
complicated since none of the physical,stress
factors” act in isolation,Rather than being a
response to one particular stress,distribution
limits result from the interaction of several
factors prevailing(占优势的 ) at a particular
place on a shore.
? A more accurate interpretation of the causes of
zonation is probably that the,potential” limits
of the distributions of a species are set by
physical and chemical limitations,The actual
distribution on a shore is finely tuned(调节 ) by
biological interactions such as grazing
pressure and competition,
Seaweed as part of an ecosystem
? The total weight,or biomass,of seaweed on a shore
can be impressive,especially when subtidal kelp
forests are considered,
? The productivity of seaweed communities is equal to,
or in many cases greater than,that of terrestrial plant-
based systems,
Laminaria-dominated communities,2 kg carbon per m2
Postelsia(囊沟藻 ) communities,up to a massive 14 kg carbon per m2
intensive alfalfa(紫花苜蓿 ) crops,1-2 kg carbon per m2
Temperate tree plantation or grassland,less than 1 kg carbon per m2
? 1) 食物来源 Seaweed as a food source
? Seaweeds are part of a complex ecosystem involving
many different types of animals,Many of the finer(好的 )
seaweeds are valuable food sources,yet the larger
species are not grazed on to a great extent.
In the case of laminaria(海带 ),for example,only
about 1% of the thallus is directly eaten by herbivores
such as gastropods（腹足动物）,sea urchins（海胆）
and fish.
? Bits and pieces constantly break off from the main
thallus and provide food for debris feeders such as
crabs,sea cucumbers(海参 ) and amphipods(片脚类动
物 ),The smaller fragments are rich supplies for filter-
feeding organisms such as mussels（贻贝）,
barnacles（藤壶）,tunicates（被囊类）,anemones
（海葵） and polychaete worms(多毛类 ).
? Detached seaweeds washed up on the shore are
another valued resource.
? 2) 分泌粘液 Mucus producers
? Seaweeds release sugars and amino acids into
the water as a result of damage or due to
regulation of their metabolism in response to
environmental stress.
? These substances are referred to as dissolved
organic matter (DOM) and it is thought that up
to 30% of the carbon assimilated by Laminaria
may be released in the form of DOM.
? The seaweeds play a role in the regulation of
bacterial activity within coastal waters,As the
bacteria break down the DOM,nutrients such
as nitrogen and phosphorus are released back
into the water and can be taken up again by
the seaweed for new growth.
? 3) seaweed as shelter
? These assemblages of seaweeds and animals attract
fish for the rich pickings the provide,But it isn’t just the
food that attracts the fish since the dense growth of
seaweed form an effective refuge from larger predators
such as birds and dolphins,
? Shoals(鱼群 )of plankton-eating fish hide amongst
stands of seaweed,coming out of cover to feed only at
certain times of the day,Some fish have an elaborate
camouflage（伪装）,such as the sargassum fish
(Histrio histrio)
七,Seaweed life
大型海藻生活的环境
? The region between the ocean and the land is
a demanding place in which to live,It is a place
of extremes dominated by tides and waves,
Seaweeds have to be able to cope with the
rise and fall of the tides.
1,Tidal patterns 潮汐规律
? There are three main classes of tidal cycles:
1) Diurnal tide 全日潮
with one high and one low water per day,
for example,parts of the Gulf of Mexico
2) Semiduirnal tide 半日潮
with two high and two low tides in a day
for example,Atlantic coastline
3) Mixed tide 混合潮、不规则半日潮
occur twice a day but the highs and the lows are of
unequal amplitudes.
for example,Pacific ad Indian Ocean coasts
What causes the tides?
? Tides are produced by the gravitational（万有
引力） effects of the moon and to a lesser
extent the sun.
? Spring tides 大潮 the moon and sun are in
line with the earth,which occurs twice a month
? Neap tides 小潮 the moon and sun are at
right angles and have,on average,20% lower
amplitudes than spring tides.
Seaweeds and tides
? Any seaweed that
grows on the shore
between the
lowest and the
highest tide levels
will be exposed to
the air at some
point,maybe once
or twice a day,
2,Zone of the shore
? Certain species are specific to particular
regions or zones,The zones are delineated by
critical tide levels that govern how long the
region is submerged or exposed.
? Whether a species can grow in a particular
zone depends on its tolerance to desiccation,
temperature stress,salt stress and wave action.
Three zones of the shore
? Intertidal or littoral zone 潮间带
The shore that lies between the extreme high water of
spring tides and the extreme low water of spring tides.
? Supralittoral zone 潮上带
The region above the littoral zone that receives spray.
? Subtidal or sublittoral zone 潮下带
The permanently submerged region that lies beyond the
extreme low watermark.
The intertidal zone
? Worldwide studies have identified three regions with
the intertidal zone,
? 1) there is an uppermost strip of desiccation-tolerant
lichens(苔藓、地衣 ) or cyanobacteria that often have
obvious populations of littorinid snail(滨螺 ).
? 2) the next zone down the shore comprises a wide
diversity of seaweeds together with barnacles(藤壶 )
and limpets(帽贝 ),
? 3) the lowermost part of the intertidal zone harbours a
diverse community of seaweed species including red
encrusting and coralline algae.
The subtertidal zone
? The kelps of temperate and some tropical
shores grow within this zone,The lowermost
region of this zone is never exposed to the air
and is dominated by a variety of large canopy-
forming seaweeds with diverse understorey
communities of predominantly red and brown
species.
? Still further down,where light hardly penetrates,
is home to encrusting red algae.
3,the problems of desiccation（干
燥）
? Seaweed living in the intertidal zone may face
long periods out of water,but there are various
strategies for keeping water loss to a minimum.
? Even when seaweeds do dry out they have a
remarkable ability to recover once the tide
returns.
Safety in numbers
? Understorey layer
The consequence of this sort of layered structure is that it
is only those fronds lying on the surface that will be
exposed to the harsh condition.
? Tufts(一簇 ) of filaments
When the tide goes out the tufts
actually retain a lot of water between
the filaments so that even after they
have been exposed to the air for a
considerable time the interior of the
tuft remains moist.
Preventing water loss
? Desiccation can be extreme such that intertidal
seaweeds can lose up to 90% of their tissue.\
water when exposed to the air,especially if
there is a breeze(风 ) and humidity is low.
? The speed with which this happens depends
largely on the surface area to volume ratio of a
thallus,the larger this ratio,the faster the water
losses,Small seaweed,branched seaweed.
? Some seaweed could withstand a certain
amount of desiccation due to the present of
polysaccharides within their inner cortex(皮质 )
or medulla(髓 ) that bind with water,Other
seaweeds exude mucus that helps to slow
down the rate of evaporation,
潮间带藻类光合作用的变化
? The most obvious factor that determined
whether or not a species can survive long
periods out of the water is whether it is able to
photosynthesis in the air.
? As long as the seaweeds do not dry out,many
species photosynthesis in air at rates similar to
those measured when they are fully
submerged,However,as they begin to dry out
their ability to photosynthesis diminishes.
? For example,photosynthesise if Laminara,
even when mildly desiccated,is greatly
reduced whereas Ulva continues
photosynthesis down to 35% water loss,Some
species of Fucus photosynthesise when
desiccated down to tissue water contents of
less than 30%.
? Seaweeds recover their full photosynthetic
rates within hours.
? A rare example of
Pelvetia canaliculata
(沟鹿角菜 ) in which
periods out of water
are absolutely
essential,If it is
submerged for more
than 6 hr,it actually
starts to decay.
4,Dealing with salt stress
? In most oceans around the world there are
about 35 grams of salt in every litre of water.
? There are notable exceptions to this,such as
the Baltic Sea,which has much reduced
salinities of between three and 10 due to tis
large influx of freshwater,while the Arabian
Gulf,Mediterrancean and Red Sea have
salinities up to 45or more due to high rates of
evaporation and their semi-enclosed nature.
? When seaweeds are exposed to rain at low
tide,they experience a dramatic reduction in
salt concentration,In contrast,when water
evaporates from the surfaces of seaweeds,
salts in the remaining water become greatly
concentrated,Both lowered and eleated
changes cause a severe strain on the cells of
the seaweeds,requiring swift metabolic action
to prevent permanent damage.
? In some regions,such as Moroccan(摩洛哥 ) estuary,
the evaporation of water is so extreme that o seaweeds
can survive.
Salt and osmosis(渗透作用 )
? In normal seawater the cells of a seaweed are in
balance with the water outside of the cells.
? When salinity in the external water goes down,it
creates an osmotic imbalance that results in water
being taken up by the cells,By lowering the cellular
concentrations of ions such as potassium(钾 ),
sodium(钠 ) an chloride(氯化物 ),as well as sugars and
organic compounds to restore the osmotic equilibrium
to one close to that before the salinity ha been reduced.
? When the salinity of the external water
increases the reverse process take place,The
higher concentration of external salts causes
water to be lost from the cells,again in direct
proportion to the increase in salinity.The cells
have to restore the osmotic balance by taking
up ions,or producing greater cellular
concentrations of sugars and organic
compounds.
Salinity tolerance varies
? Seaweeds have differing capabilities for making these
osmotic adjustments and hence varying tolerances to
salinity changes,In general,seaweeds growing higher
on the shore tend to have greater tolerance than
species found lower on the shore.
? Many intertidal seaweeds may withstand salinities
ranging from 0-100,whereas many subtidal species
are killed by only slight changes in salinity,or at best
have limited tolerance of salinities from 20-50.
? Metabolic rates are severely reduced for most species
in extremely low and high salinities,
Effect of temperature on saline
stress
? Temperature can have a significant influence
on how well seaweeds survive saline stress.
? Species normally grow within a certain
temperature range and at temperatures at
either extreme of this range the ability to
withstand salinity stress is generally reduced,
5,Temperature stress
? The geographical distribution of seaweed
species is largely dictated by temperature
tolerance.
? There are species of seaweed that re restricted
to tropical waters which narrow temperature
tolerances close to 30℃,while species in the
Antarctic rarely survive temperatures above
13℃,
? Difference life cycle stages may also be
sensitive to different temperature range,
? Temperature tolerance,and therefore
geographical distribution,is also modified by
the ability of a species to withstand other
stresses,such as salinity and desiccation,
especially at extreme high and low
temperatures.
Seasonal temperature changes
? Seasonal changes in water temperatures are
large gradual and species that live permanently
submerged are not often exposed to sudden
shifts in temperature,
? Metabolic rates change with these seasonal
variations due to the effects of temperature on
chemical reaction rates,enzyme metabolism
and biophysical processes,
? At the lower end of the temperature range for a
particular species,growth rates will be slower
than at higher temperatures,and often there
will be temperatures at which growth is optimal
although these may vary with the different life
cycle stage.
A hot summer
? In the intertidal zone seaweeds exposed during
periods of low tide may be subjected to
temperature extremes may outside the normal
limits set by seawater temperature.
? For example,Porphora
A freezing winter
? Differences in
freezing tolerance
play a role in
determining the
distribution of
seaweeds on the
shore,
6,Water movement
? Another
challengin
g aspect of
seaweed
life is the
relentless
action of
the waves,
? The turbulent motion of seaweeds that is
induced by currents and waves is not all bad,
? The currents and waves of coastal regions
mean that seaweeds are constantly supplied
with nutrient-rich water (water can quickly
become depleted where movement is low and
where large stands of seaweed are present),
? Constant water motion also distributes light in
the water more evenly.
? In regions where wave action is strong,grazing by
herbivores is significantly reduced,Turbulent water
also keeps the seaweed in constant motion,allowing
the diffusion of nutrients and gases to and from the
frond.
? Nereocystic(腔囊藻 ) 在流动速度快的水体中，叶片很平
滑，以降低藻体被海浪冲击下来的危险；但在流水缓慢
的地方，由于藻类大量生长，为了获取营养盐，腔囊藻
变得有褶边，增加表面积来吸收营养盐。
It pays to be flexible
? The difference between seaweed and trees or
bushes on land
? A key to the success of the seaweeds is their
flexible nature,expecially those with long stipe.
? The flexible stipes allow the thalli to bend in the
direction of the water movement.
? Seaweeds adapt their shape to reduce drag
depending on their location,the same species
growing on exposed or sheltered stretches of
coast can look quite different,In general,wave-
exposed forms are smaller and may have
narrower blades.
Growth strategy
? Despite having smooth blades and a flexible stipe,
seaweeds suffer considerable damage from surf and
wave action,The fronds of species such as Laminaria
are frequently broken off at the tips or lacerated into
strips,
? Sea palm,Postelsia(囊沟藻 ) is one of the most
tenacious seaweeds to survive high-energy wave
environments,The secret of its success seems to be
that it has exceptionally strong holdfasts combined with
highly flexible stripes.
