A long list of physical indicators showing what
to look for, like reduced visibility, dense plankton blooms, slime, sedimentation,
bottom fog and smell. Ecological indicators like unoccupied territory,
missing organisms, patchines and symptoms of recent death.
Do indicator species have things in common? Which
organisms are good indicators of which threats? The young of all species
are good indicators of decay.
Many organisms have beneficial effects on their
surroundings, mitigating or postponing the ill effects of degradation.
When they die, their environment may go through a critical period of decline.
Many organisms display a kind of unhappiness
or ill health before dying. These are important warnings as they are visible
on organisms which have not yet disappeared and which may recover without
surrendering their space.
For comments, corrections or suggestions, please e-mail
the author Dr Floor Anthoni.
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indicators of doom
Seldom are the causes of degradation directly visible. They also have to
act over a period of time, usually when diving is unpleasant or impossible.
But fortunately there are many indicators, which taken together, give a
reasonable picture of the threat to the environment and the quality of
that environment.
Obvious indicators: Agents The most common indicator agents (media) are:
reduced visibility due to either mud or plankton, which have comparable
negative effects.
dense plankton blooms: dense plankton blooms always have a negative
effect on the environment.
snot or slime in the water column, acting as cultivation media for
bacteria, then raining down on organisms and covering these in a sticky
layer of disease. Often producing nutrients for matting microalgae (green
slime).
sedimentation covering organisms, often combined with planktonic
detritus and decomposing bacteria. It takes sunlight away from plants while
smothering fine-pored water breathers like sponges. By waving a hand or
one's fins over the substrate, one can get a good idea of recent sedimentation.
nephos or bottom fog: (Gk: nephos=cloud) the muddy bottom
does not have a clear boundary but the water gradually thickens to mud.
Very few organisms can live here, resulting in the equivalent of a dead
zone except that oxygen is still available.
dead zone: due to heavy rates of decomposition, all oxygen has been
used up and the only survivors are putrid bacteria.
smell: your sense of smell is a good scientific instrument, as it
can alert you that something is wrong. Dense plankton can be smelled. Rotting
estuaries and shellfish beds can be smelled. Sea water can be smelled and
tasted, and you can learn the differences between the west and east coast.
Unfortunately one cannot smell the water as a diver.
Zone indicators Everywhere in the world the rocky shore is zoned by three most important
limiting factors: drying above low tide, wave action and reduction in light.
Of these the bottom of the sunlit zone, is the most telling of degrading
water quality. Thus the lower boundary of the kelp is an important measure.
Note however, that the sandy bottom reflects so much light (almost 100%)
that widely spaced plants can live much deeper.
Thus the amount of kelp cover is also important. Fortunately, the transition
from full cover to sparse cover is rather sudden and this is what one looks
for. The maximum amount of cover (including younger plants) is also a good
indication.
When new recruits are not found under old kelp, this means that the
lower boundary is shifting upward as a result of degradation. So the lower
boundary of kelp recruits is an even stronger indicator of decay or health.
In general, the first indicators of degradation are found along habitat
boundaries, of which the photic (= light) boundary is the most telling.
This boundary runs roughly along a depth contour but climbs to the surface
at the entrances of caves and archways, which are therefore treasure troves
for investigation and monitoring. As this boundary shifts, space becomes
available for new organisms. Often these organisms are new to the area
or totally unknown or they may be foreign and introduced.
Traces left behind from recently disappeared
organisms Although some organisms will always be found missing due to normal
mortality, one does get a feel for abnormal mortality rates. By calculating
the ratio of traces over what was once there (= remaining organisms + traces),
one gets an idea of the rate of decay.
kelp holdfasts: these disappear in 6 months after the plant dies
pink paint 'prints': when organisms attach to the underlying pink
paint, they may shade it off sufficiently to deprive it from light such
that it dies. The difference between dead pink paint (white) and live (pink)
is very clearly visible as an imprint of the deceased organism. Pink paint
prints can remain for up to two years, first showing as white, then as
dark pink.
Prime real estate or hot spots Before touching on missing species we need to introduce the concept
of prime real estate, or the preferred places (hot spots)
for certain organisms. This is particularly important for species that
move around freely like schooling fish but it also applies to territorial
species.
As individuals die, their space becomes available. If that space is
more beneficial than that which is occupied by survivors, these will leave
their territories to move in next door. Thus organisms diffuse towards
hot spots. Because of this, the prime real estate is always fully occupied,
even after severe mass mortalities (after a while). One has to learn to
recognise the preferred places or hot spots but this is easy because they
are so obvious. It is more difficult to find the reasons why hot spots
are popular. Most hot spots are found in places that offer shelter against
storms, but fish return here during the evening. Thus
censusing (counting organisms) in sheltered places is best done by night.
The moment one finds fish missing from a hot spot, it almost certainly
means that a mass mortality happened very recently. Frequent visits thereafter
will see the hot spot fill up again by diffusion while their surroundings
remain depleted.
archway: an archway is a cave with two openings and usually also
has vertical walls. Often a current runs through an archway. Therefore
archways combine the three hotspot qualities mentioned below.
cave: caves offer the ultimate in shelter and also hide organisms
from predators. Most of the hot spots I know centre around a cave. Because
caves are closed, the water cannot move in and out. Thus sessile life thins
out as food becomes scarcer in the darkening depth of a cave. Deep caves
may not have enough supply of oxygen to shelter schools of fish.
bubble umbrella: a special case of roofing is provided by
the wavewash producing an umbrella of bubbles/foam. These shield underlying
schools of fish from attacks by birds, as they also reduce the sunlight.
When attacked by predatory fish, the prey fish hide behind and amongst
a curtain of bubbles. (knife fish, koheru, demoiselle)
vertical wall: Many vertical walls offer adequate shelter.
As waves are bounced back without loss in energy, vertical walls appear
sheltered even on very exposed coasts.
running current: currents import planktonic food from the surrounding
ocean. They are favourite hot spots for fish by day and all-round (diurnally)
for sessile plankton feeders like gorgoneans and sponges. Current hot spots
may be found in the wave wash by day (bubble umbrella), where fish won't
stay to rest.
promontory: where rocks jut out in the sea, tidal currents are strongest
and the sea bottom deepest, offering rich feeding opportunities to the
widest possible range of fish and sessile filter feeders. When exposed
to moderate cleansing wave action, one finds the leftover species
there.
Patchiness Patchiness describes the randomness (=erratic) occurrence of individuals
and species as a result of competition for space, rather than a single
species dominating all. Even habitat zones of a single species can be patchy
with regard to year classes. Stable, healthy environments look patchy.
Patchiness is a good indicator of health.
Missing individuals/species One cannot see missing individuals, but there are some clear indicators:
open empty space: space on the rocky shore is heavily competed for
by both plants and animals and is therefore a strong indicator. Every part
of the rock should be occupied, unless heavily grazed, but even then the
grazers must be visible and densely spaced (some grazers appear only by
night). Thus seeing empty rock, even when covered by pink paint, should
cause suspicion. The amount of cover in old individuals is a strong indication
of the quality of the environment.
f037722: example of a fully occupied two dimensions. Alas
these species cannot grow outward. Jewel anemones in a Goat Island archway.
f021711:fierce competition for the third dimension. Callyspongia
spp on Whangarei Harbour pier in the currents.
f048712: A fine example of fierce 3D-competition in a very
healthy environment. Poor Knights under a deep ledge.
loss of the third dimension: On a healthy shore, competition for
space is so fierce that there is "standing room" only. Once the surface
(2 dimensions) is fully covered, organisms compete for the third dimension,
outward from the substratum. Missing the third dimension is an early sign
of degradation.
closed canopy: a closed canopy indicates healthy competition for
space, but not all closed cover indicates health. If a closed kelp canopy
contains but one year class, this indicates a recent mass mortality after
which a single year class emerged. Healthy environments contain year classes
of all ages.
gaps: gaps between individuals such as an open kelp canopy; large
gaps between grazers,
insufficient grazing: almost all common organisms have evolved with
their grazers and predators, such that the absence of these is detrimental.
It shows up in too many old fronds, rotting fronds and invasive species
taking hold. When sea urchins graze insufficiently, poisonous blue-green
algae and dinoflagellate slime (Ostreopsis) may take over, causing
further death of all grazers.
matting algae, brown slime: an indication of poor grazing and missing
grazers in addition to increased nutrient levels. Note that all the points
mentioned here are overlapping such that the one verifies the other.
Missing year classes It is not always possible to estimate the age of individuals but almost
always one can distinguish this year's, last year's, mature and old species.
By measuring sizes exactly, scientists can obtain size distributions which
may indicate missing year classes. However, our simple method is very effective.
missing recruits: this year's recruits are easily visible, particularly
during night dives, but some remain cryptic (= hidden) like sea
urchins do. They can be found by turning a few stones or peering into cracks.
Recruits may be missing because they may not have arrived yet (this year's).
Missing recruits indicates a recruitment problem, usually in their planktonic
stages when they are extremely sensitive to water quality. Missing recruits
may suddenly appear as next year's yearlings.
missing one year olds (yearlings): could mean two successive years
of recruitment failure or a mass mortality of young ones.
lack of medium sized ones: indicates a problem which is often not
immediately evident.
lack of old individuals: the old ones are the sturdy ones, and because
of their larger size, are often able to survive disease. Their presence
is a strong indicator of environmental quality. Their absence means a mortality
event somewhere in the recent past.
Stunted growth and runts The difference between a small individual because of age and one because
of unfavourable growth conditions, is often difficult to see. Small anemones
almost certainly indicate poor availability of food. Runts (= the
smallest in a litter) may show unusual distorted shapes and growth on their
skins. Ironically, runts often survive better than others, perhaps because
they have coped from birth.
Pink paint on the outsides of shells may serve as a growth marker,
where recent growth is still free from the pink paint. The faster the shell
grows, the wider this margin.
Weakness/disease Weakness and disease may be the causes of runts, but they can also
be a recent phenomenon. Signs of disease are very strong signals of degradation
because the chance of observing them on long-lived organisms is small.
opportunistic species/ invasions: most species have defences against
being invaded by opportunistic species, but less so when they weaken, giving
opportunity to overgrowth. The invaders often kill themselves by killing
their host, which then detaches from the rock. It is most observed on old
individuals and is a strong indication of the beginning of degradation.
Plants are cleaned firstly by exuding (= sweating out) slime and
secondly by grazers such as parore and grazing snails. Note that some species
such as some seasquirts promote organisms to grow on their skins. Ironically,
some opportunistic species are beautiful in appearance (zoanthids, carpeting
species, some nudibranchs). In the 1970s yellow zoanthid anemones were
uncommon on the Poor Knights, but today they are very common.
stunted growth: indicates either disease or lack of food or old
age.
sudden rapid growth: can be an indicator of decay caused by reduced
competition for food.
colour of leaves: healthy plants show lush colours, thickness, slime
and bounciness, indicating healthy living tissues. (yellow/green/red=
good) but when insufficient light is available, this living tissue diminishes,
turning the leaves dark (black, grey, brown= bad)
drooping leaves: healthy plants are bushy and upright but sag and
droop when sick.
infections: the most common infections are whitish, like a fungal
infection. Dead tissue can turn white, black or brown and is usually brittle
or slimy.
dying and dead organisms: sick animals exude body fluids that attract
predators and scavengers: whelks, starfish, crayfish.
pink paint: as growth marker on paua, cooks turban and other snails
Displacement by more robust species Sometimes missing species are replaced by more robust species with
the same functionality, although this is unfortunately uncommon. In general,
when species disappear, the environment becomes less dense and less diverse.
maomao/ sweep: blue maomao prefers the warmer and clearer waters
of NE New Zealand, whereas sweep thrives in less favourable coastal conditions.
When sweep become more populous where they were not before, this is a sure
sign of degradation.
northern scorpionfish/ dwarf scorpionfish: as above.
koheru/ jackmackerel: as above.
purple urchin/ green urchin: as above, but less clearly understood.
banded perch/ half-banded perch: the banded perch has been replaced
by the half-banded perch in most places
reef octopus/ sand octopus: the reef octopus (Pinnoctopus cordiformis
) has become rare whereas the sand octopus (Octopus gibbsi )
more common.
Left-over species The species that once grew everywhere in areas more exposed to degradation,
can still be found in the best and most protected places on the reef. Look
underneath overhangs or inclining walls to find the left-over species representing
what once grew more profusely everywhere. Places rinsed by currents and
moderate wave action, such as around promontories, also show left-over
species. Often the left-over individuals grow larger than before due to
reduced competition for space and food. Ironically, left-over species are
profound indicators of degradation, as they enable one to look back in
the past, to see what once lived here profusely. They are like the exceptions
proving the rule. The rule being the omni-present result of
degradation, whereas the exceptions those hard-to-find niches not
yet affected.
Note that some plankton feeders do not live entirely from planktonic
food but also from algal cells embedded in their tissues (zooxanthella).
Various anemones are suspected of this as are several sponge species. For
them the availability of light is important, and they cannot live well
under overhangs and inside caves and archways. They are also affected by
the water becoming more turbid (=muddy, thick, opaque). Note also that
some species under overhangs cannot live on rock faces exposed to sunlight.
f029419: where stick bryozoa have disappeared from vertical
walls, they can still be found under overhangs.
f037717: leftover sponges under an overhang in the channel
to Rogers Cave, show what once lived around Goat Island a long time ago.
f037722: a gaudy carpet of leftover Corynactis jewel
anemones and other species at the entrance to Rogers Cave are all that
is left of an environment that began degrading a long time ago. But some
of this can still be found under ledges elsewhere. Goat Island marine reserve.
Left-over dead species Some species leave their hard shells behind which may remain for several
years. By making a record of the number of dead shells over living ones,
one can obtain a measure of decay. Sometimes one finds a shell trap with
debris rained from above. By inspecting this debris, one can also obtain
an impression of the recent past.
.
f041628: the ratio of dead hat urchins over living ones gives
an idea of recent mortality rates. Poor Knights. Left one dead and broken;
right one well alive, covering itself.
f042519: this stalked kelp may have been removed by storm,
grazing or decay. It takes about 6 months for it to rot away. It is surrounded
by organisms competing fiercely for space.
Increased species of decay Sometimes decay is accompanied by species that are typical of decay.
Such species adapt quickly in numbers by replicating profusely while living
short.
sea lice: Sea lice attack all organisms but are successful only
on weak or dying ones. An increase in sea lice, observed during a night
dive may indicate acute decay.
drooping sponges and seasquirt mats: typical
of badly degraded habitats are drooping sponges and drooping seasquirt
mats.
leafy bryozoans: certain bryozoan species are associated with rapid
decay
black and purple mushy sponges: these sponges are seen only in the
worst of places.
f011003: drooping sponges and colonial seasquirts are a sure
sign of serious decay. Houhora Harbour.
f040020: fast growing leafy bryozoa belong to degraded environments.
Whangaroa Harbour.
f011302: intestinal compound seasquirts and black mushy sponges
are sure signs of severe degradation. Houhora Harbour.
f040020: dark purple mushy finger sponges and lumps are a
sure sign of far advanced degradation. Port Fitzroy.
Indicator species The holy grail of water quality assessment are species that have a
narrow range of tolerance, such that they can be used as indicator species
like the hand on a voltmeter. But finding these is not likely since most
species tolerate a range of conditions such that their ranges overlap,
which is an ecological requirement for resilience. See separate chapter
below.
Colonisers When organisms vanish suddenly, space becomes available which will
be colonised. Often (but not always) recolonisation begins with short-lived
fast-reproducing species (like barnacles) followed by longer living species
and eventually replaced by a patchwork of long-lived species. Typical first
wave colonisers are:
jellyfish polyps: the scyphistoma polyps of jellyfish quickly occupy
vacant space under overhangs in degraded waters
barnacles: barnacles repopulate vacant space in shallow water and
they prefer wave action or currents.
seasquirts: the matting compound seasquirts grow rapidly over many
other species
matting bryozoa: matting bryozoa can quickly grow a thin veil over
many organisms, paving the way for others.
tube worms: the parchment tubeworm has recently taken hold where
mud collects, in the shallows inside sheltered pockets and in the deep
in between furrows and megaripples (= large ripples) in the sea
bottom.
Note that kelp recruits are also first-wave colonisers. Typical second-wave
colonisers are:
encrusting sponges:
various bryozoa:
anemones:
Consequences Every event WILL have ecological consequences because everything is
connected. Thus having observed the indicators of an event this year, one
can expect to observe its consequences next year, such as:
larger nest sites: due to fewer breeders and fewer nest raiders:
demoiselle, black angelfish, tripefins
more juveniles: lack of predators: bait fish, demoiselle,
whole jellyfish: not eaten by leatherjackets, snapper, parore, demoiselles
Indicator species
As shown in the previous chapters, there are many indicators of health
and decay. To focus on a few single species would only narrow one's vision.
Yet some things can be said about indicator species. The idea behind it
is that threats or changes in environmental conditions leave traces behind
in the surviving organisms. Ideally, indicator species should be:
common: easy to see and count and measure
unfished: not be fished for food so that the effect of fishing
plays no role.
long-lived: stable in numbers and densities in normal times such
that they tell the story of change.
immobile: not able to evade threats and abnormal conditions.
productive: reproduce every year such that there are various year
classes.
specific: sensitive to particular threats only: decay, sedimentation,
plankton poisons, industrial poisons, etc.
Indicators of decay should in addition be low in the food chain, such as
filter feeders like sponges. It should be noted that juveniles of any
species are good indicators by themselves since they appear more sensitive
to unforeseen circumstances, and particularly to eutrophication by bacterial
attack:
skins: juveniles have thinner skins that their adults, being more
sensitive to disease.
food: juveniles need to switch their types of food to match their
size as they grow older. They depend on small morsels, which are usually
also lower in the food chain.
reserves and stores: juveniles do not have large reserves and cannot
fast for prolonged periods. They have to eat practically every day.
Missing species Indicator species are typically not found in the laboratory but by
observation in the environment. Species that suddenly disappear are the
first candidates. Those that disappear more gradually next. A sudden disappearance
may be correlated to a recently observed event such as an oil spill or
an industrial spill or an unusual temperature. The disappearance may be
correlated to the area affected by the spill, and further testing in the
laboratory may confirm the species' sensitivity to the particular threat.
The following species have disappeared suddenly from various places:
red actinia anemone (Isactinia tenebrosa): living in shaded places
around the high tide mark, this species appears vulnerable to floating
chemical pollution such as oil slicks.
olive actinia anemone (Isactinia olivacea): living around the low
tide mark, this species is similarly affected.
mangrove mud whelk (Amphibola crenata): living on mud flats under
the high tide mark, this whelk appears affected by many threats.
red seaweeds: various red seaweeds have disappeared suddenly. Vidalia
colensoi is one, and Pterocladia capillacea.
sea urchins (Evechinus chloroticus): sea urchins die when grazing
brown
slime of various kind (dinoflagellate slime, blue-green algal scum)
various sponges: the Callyspongia species are hardy but sensitive
to plankton poisons
bearded brown mussel (Modiolus aerolatus): lives in clean shallow
sheltered waters which are also favourite places for humans to live by
and pollute.
nesting mussel (Modiolarca impacta): living subtidally
blue-dot triplefin (Notoclinops caerulepunctus): a 4 cm small rock
dwelling fish
long-finned triplefin (Ruanoho decemdigitatus): a 12cm long rock
dwelling fish
(incomplete)
The above list will be augmented (= made larger) with time. Do you have
suggestions?
The cleaning gang
If left unchecked, small algae will smother all rocks and larger seaweeds.
Planktonic scum will descend on all sandy sea bottoms. Dust will smother
sponges and other filter feeders. Decay and rot will set in. Fortunately
a large cleaning gang is omnipresent doing what they were designed to do,
to keep the environment clean. This metaphor is of course poetic, as these
various organisms just go about their business of finding food, not aware
that they provide a cleaning service to others, in doing so.
parore(Girella tricuspidata): the parore is a plant eater
which scrapes fine algae from the larger seaweeds, using its fused teeth.
Where parore have been caught for use as crayfish bait, the seaweeds look
decisively sick.
butterfish(Odax pullus): the butterfish is a plant eater
and is often seen biting round holes from the centres of kelp fronds. However,
it also scrapes fine algae like parore do. Where butterfish have been hunted
down by spearfishermen, the seaweeds suffer.
others: black angelfish(Parma alboscapularis) and silver
drummer(Kyphosus sydneyanus) and marblefish (Aplodactylus
arctidens) perform similar services but are less important because
they are not as common.
grazing snails: almost all grazing snails are indispensable cleaners
hermit crabs: hermit crabs are untiring cleaners, forever plucking
at organisms and thereby removing diseased tissues and invasive growths.
They are also tilling the sandy bottom while removing phytoplankton scum.
cushion stars(Patiriella regularis): by extending their
stomachs outside their mouths, cushion stars are able to dine on large
patches and they are not particular about the nature of their food. Aquarium
studies have shown that they survive the poisonous blue-green algae and
dinoflagellate slime. They are also effective scavengers, locking decaying
material up beneath their flat bodies. Cushion stars are extremely aware
of stress and home in on organisms that are about to become ill. In aquariums
I have observed them bringing a sick sponge to health. They are unaffected
by poisonous brown slime (ostreopsis) and clean it up.
sea cucumbers(Stichopus mollis): sea cucumbers are the vacuum
cleaners of the sea, mopping dust with their sticky mouthparts, while living
from detritus. They play an important role in keeping the environment free
from dust and detritus, and thus potential rot and suffocation.
f000832: Parore (Girella tricuspidata) seen stripping
fine algae from the coarse brown featherweed (Carpophyllum plumosum)
in a side-ways swipe. Parore are important environmental cleaners. Leigh
marine reserve.
f991027: parore scrape-marks on heavily polluted rock where
even the coralline algae known as pink paint, won't grow any longer.
A serious sign of degradation. Long Bay marine reserve, Auckland.
f040013: grazing snails remove invasive species from various
organisms. Here the top shell is no longer capable of removing the already
established bryozoan mats from stalked kelp in this highly degraded Whangaroa
Harbour.
f004917: a sea cucumber (Stichopus mollis) seen cleaning
heavily dusted yellow nipple sponges (Polymastia croceus). Other
sponge species also benefit. The sea cucumber excretes a solid turd which
confines decomposing bacteria. Near Mahurangi Harbour.
f041916: sea urchins (Evechinus chloroticus) prevent
slimy algae such as this poisonous dinoflagellate slime (Ostreopsis
sp.) from establishing. Once established, it also kills the sea urchins.
Little Barrier Island.
f039221: cushion stars (Patiriella regularis) graze
large surface areas and they tolerate many natural poisons, dinoflagellate
slime and decomposing bacteria. Parengarenga Hr.(on snow-white sand)
unhappiness
Many organisms display what could be called unhappiness or a sense of not
being well or ill health before dying. Such symptoms are important to recognise,
as the organism may stay alive or recover completely, being available for
next occurrence of the offending threat. I have been documenting such symptoms
only recently and do not have enough illustrative photographs, but their
number will undoubtedly grow.
Many gorgoneans, soft corals and anemones withdraw in case of adversity
but they also have cycles of rest which are entirely normal. Thus care
must be taken in explaining unhappiness from a temporary rest. However,
in a single dive many hundreds or thousands of individuals can be observed,
either corroborating or contradicting one another.
Unhappiness or ill-health can easily be seen in seaweeds as their fronds
and branches droop, assuming a collapsed appearance. Healthy seaweeds feel
slimy and bouncy while they hold their fronds up.
f042803: a sea urchin folding its spines is a sure sign of
unhappiness. The more spines folded, the less happy it is. Eventually it
dies. Poor Knights marine reserve.
f042719: this is a very unhappy yellow nipple sponge, (Polymastia
croceus) which is about to die. When Polymastia sponges become
hard, withdrawing their nipples, they are unhappy. This one is also grown
over by invading red algae, a sure sign of severe stress. Poor Knights
marine reserve.
f042628: green sea rimu with all its branches held upward,
is a sign of health, as also expressed by the red seaweeds. However, they
are insufficiently grazed, as is also the drooping stalked kelp centre-right.
Eventually this will lead to rot. Insufficient grazing points to a decline
in grazing fish, a sign of degradation. Poor Knights marine reserve.
f041022: unhappy seaweeds droop their branches. Float bladders
lack the gas to pull the branches up. These flexible weeds (Carpophyllum
flexuosum) are normally able to shed dust but cannot resist bacterial
attack. This photo shows the end of a habitat. Near Whangaroa Harbour.
