zoning		The ecological factors that are most influential on the zoning that occurs on the intertidal rocky shore. (on this page)
principles		A vast number of principles to guide our investigations and observations. Living in the sea and in the intertidal in particular, is spectacularly interesting. (on this page, 14 pages)
species interaction		The reasons why one species lives mainly here while another is found there, does not only depend on physical factors but also on biotic factors such as competition, predation and so on. However, the sea has some surprises in store. (on this page)
zone builders		Which organisms are so successful that they build the distinguishable zones? Also view some examples, showing what to look for. (4 pages)
feeding methods		Although the rocky intertidal is not a closed ecosystem, due to the vast open sea bordering it, one still finds all methods of feeding here. Also tips for doing a rocky shore study. (3 pages)
further reading		Books and references (on this page)
what's new?		A log of recent changes to this section (on this page)

 

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When  one traverses a snowy mountain in a mediterranean or tropical climate from its top down to its base, one comes across several distinctive zones, identified as follows:

• permanent snow: the area with permanent snow has no plant life as temperatures are too cold and the snow would lay over any plant or plant seedlings.
• snow-free in summer but snowed over in winter: as there exists no sudden onset of summer or sudden ending, this is  a zone with a substantial gradient.
• scree or broken rock: on the top of this zone one finds a minefield of broken rock and sharp stones continually sliding down-hill. The rock is broken here because of successive freezing and thawing which gives enormous strength to water seeping into cracks and pores. This zone is not very inhabitable because no suitable soil is found, but some lichens may survive.
• alpine meadows: where the snow stays away for a suficiently long time, and where soil develops, one finds a most diverse community of flowering plants, mosses and lichens, in patches according to shelter, moisture and warmth.
• scrub forest: dwarfed and crippled trees dare to grow where the temperature is insufficient for good growth, soils are frozen most times and at times heavy snowfall is experienced. Wind speeds at this altitude are also high. The scruffy trees grow to shoulder height but one can distinguish some species that belong to the mountain forest.
• montane forest: the mountain forest needs sufficient temperature to grow a productive soil that may freeze over, as in a temperate winter. Trees and shrubs may lose their leaves in winter as in winter-deciduous (leaf-dropping) forests.
• (sub) tropical forest: the temperature is always high enough for good soil development and there is no need for dropping leaves in winter, but in case the summer brings predictable droughts, some trees and shrubs may be summer-deciduous.
• coastal forest: the make-up of the forest is influenced by the sea, such as by salt spray and strong winds.

The sea may experience the seasons too, being iced over at times in cool climates. Ice over water reflects and absorbs most sunlight, thus seaweeds will die. But most of the world's seas and coasts do not freeze over, although frost may threaten creatures at low tide. Temperature and the amount of light play a role for ocean productivity, but there does not exist something like soil, except in very sheltered inlets (sand and mud flats).  The diagram shown here shows typical coastal zoning in a temperate climate. The intertidal (the subject of this chapter) is driven by the tide. No tide, no intertidal, but there may exist a splash zone in case of waves. Thus the intertidal zone is clearly defined by the movement of the tide. Below it extends the infralittoral (photic zone) and circalittoral zone (demarcated by lack of light to grow plants, or inadequate quantity of light). These two zones are also clearly defined as they depend on the clarity of the water. In murky water the photic zone may be as shallow as 3m, whereas in a clear blue sea of 30m visibility, the photic zone may extend down to 35m until also the quality of the light becomes insufficient.

But there is another zone inside the photic zone (infralittoral), demarcated by the worst storms. Severe storms generate deep waves (swell) that can cause severe damage even when the centre of such a storm passes 1000km away from the shore. This powerful swell of some 200m deep (half of the wave length of 400m), arriving at the continental shelf of 200m deep, experiences the shallowing sea bottom as a hindrance, which absorbs the swell's energy. As such deep waves travel further over an ever shallowing sea bottom, they lose more and more energy. Thus the maximum energy that the most severe waves can deliver to the coast, depends on the depth of the sea bottom. The deeper the bottom, the worse the worst waves are. [note that this has not yet been confirmed by mainstream science]. For more about waves, read oceanography/waves/
In New Zealand, as in many other places, such devastating deep waves cause a barren zone between the strong and flexible stringy seaweeds and the more fragile stalked kelp. This zone is then occupied by powerful grazers such as sea urchins (Evechinus chloroticus), abalone or paua (Haliotis spp.) and Cooks turban shell (Cookia sulcata). Such grazers are then able to prevent seaweeds from establishing themselves in the barren zone, in effect keeping this zone barren, while also extending it here and there. Terrestrial grazers such as sheep and cattle do something similar on pasture and hoofed grazers (ungulates) in the tropical savanna habitat.

The shape of the shore also depends on wave action, and like landscapes, seascapes adjust their shapes for minimal loss in either erosion or opportunity for life. Read our Least Loss Landscapes hypothesis [which is not yet backed by mainstream science]. The effect of this is that shores with massive wave exposure (and thus deep sand bottoms) develop into vertical walls that bounce waves back while absorbing only the least of their energy. Ironically, these steep rock walls provide shelter as waves roll up and down without much shearing (currents). At the most sheltered shores we find a shape that shears the wave at its top, as in a swimming pool's wave-absorbing channel along all sides. Waves then shear over shallow platforms that are covered in life, thus minimising erosion of the rock and damage to life.
It must also be noticed that the sunlight has a profound influence on the shape of the shore, such that shaded shores (less life) are always steeper under water than sunlit ones (abundant life).

The intertidal is defined by zones caused by the moon tide and sun tide. When they work together, the tide is larger, which is called a spring tide. In between occur the neap tides. For more about tides, read oceanography/tides/. Note that most places in the world have two tides each day, but there exist places with only one tide each day, and even ones with no tide at all. Most places have between 1 and 3m of tide swing, but places exist with up to 10m between high and low tide.
Thus the intertidal zones can be defined clearly:
 

splash zone or maritime zone: the zone above high spring tide, that is regularly sprayed or washed by waves. On exposed shores the splash zone is wide, whereas on sheltered shores it becomes essentially absent. Above the splash zone begins the terrestrial world, marked by lichens (white, black, orange crusts) that are resistant to salt spray. Characteristic of the splash zone is that sometimes for many days in succession, during calm weather, the sea does not get there. upper tide zone (supra littoral fringe): the water comes here only twice each month during spring tides. mid tide zone (eulittoral zone): the water comes here twice daily but also retreats twice daily. lower tide zone (sublittoral fringe): the water recedes from here only twice each month during spring tides. The diagram shows how the three zones are substantially altered by wave action, which also blurs their distinction.

Compared to mountain zoning which covers several kilometres of altitude, the zoning on the shore happens within a few metres. Also the living conditions can change profoundly over short distances, due to irregularities like ledges, cracks, stones and so on. Of course, waves can make this fine distinction of zoning somewhat vague, and so can the shape of the shore. Here are some new factors to consider:

• topology: the shape of the shore determines very much its character. A vertical rock wall for instance is not attractive for snails because, once dislodged and falling into the deep, they cannot make it back. A shore with rock flats is rich in grazing snails and other organisms, particularly when it also has loose stones on it, but it may not extend to the upper tide zone. Deep cracks  and pools invite for high biodiversity.
• rock hardness: the hardness of the rocky shore also plays an important role. When the rock is soft , such as some sandstones, it erodes too quickly for plants and barnacles to settle on, and even when they do, they are all too easily dislodged. When a rock is very hard such as granite, many organisms cannot attach because dissolution of the rock is part of their method. A hard rock cannot be bored into by rock-boring clams such as piddocks and date shells. Thus it remains unpitted and less attractive for other organisms. Medium hardness rock which can be dissolved by acids appears to invite highest biodiversity.
• life protects: where the shore is hard enough for a permanent cover of life, erosion suddenly becomes minimal as wave damage occurs to living organisms that can repair the damage. Where degradation is rife to such extent that it reduces the live cover, shore erosion suddenly accelerates. Muddy water for instance, takes the light away for a protective (plant) cover to grow.
• wave-wash: waves make the intertidal a hell to live on. Where the shore is deep and wave action during storms very strong, only few organisms can survive (barnacles and stringy seaweeds). Most biodiversity is found at medium wave action. In calm places one would expect even more biodiversity, but pollution from the land in the form of mud, now makes life difficult. Waves also blur the distinction between upper, mid and lower tide zones. However, waves also have a positive rinsing effect, removing dust and sedimentation and poisonous slime.
• sand: some sand inside rockpools makes them more attractive for sand-burrowing organisms like scavenging whelks, worms and some clams but large amounts of sand can cause 'sand-blasting' in storms with loss of life. Also large amounts of sand nearby can occasionally cover the shore entirely, thereby killing almost all life.
• fresh water: every rain during low tide showers organisms in fresh water, which by osmosis tends to make organisms swell and die. For this reason many organisms can seal their shells securely to the substrate, avoiding this threat. Fresh water fills rock pools only at the very top because fresh water is lighter than salt water, and is thus unable to cause real hardship to those living beneath. Crustaceans and seaweeds are sensitive to fresh water. Where fresh water intrudes, marine life recedes. Freshwater springs are particularly life threatening in coral lagoons.
• degradation: land-based degradation has caused seas to be 'sick' from sediment and decomposing bacteria. In general, coasts near big rivers suffer from degradation more than coasts with small water catchments. Seas are 'sicker' near the main land and become 'healthier' further out towards the edge of the continental shelf. Water quality affects shore biodiversity, even though many animals are quite resilient. For more information, read our decay section.
• disasters: disasters occur occasionally. They can be natural such as large storms or hurricanes or can be man-made such as oil slicks. Recovery from a disaster is faster in a healthy sea than in a sick sea, reason why even natural disasters have a man-made component.

One would also expect that intertidal zoning is fixed and predictable, as the zonation diagrams shown above, suggest. But after some investigation, one finds that this is not so. Why?
Of all the abiotic (physical) environmental factors discussed above, the tidal range, exposure, shore shape and substrate are the most important ones. Because each has its own 'sorting sequence', the resulting zones are quite variable.
 
 

0701180: located behind a barrier rock, which shelters this coast, stringy seaweeds are threatened by drying out at spring low tide. The greenish zone is the mid intertidal. Pied shags are drying themselves after a day's fishing. The reef flat is rich in organisms and tide pools abound with seaweed species. The seaweeds are cartilage weed (Xiphophora chondrophylla), flapjack (Carpophyllum maschalocarpa) and just visible stalked kelp (Ecklonia radiata).

0701183: Never Fail Rock is an exposed rock in a 50m deep sea). The spring tide covers no more than 2m (compare with the birds). It is a very calm sea now at spring low tide and stringy seaweeds (Carpophyllum maschalocarpa) are having a hard time. This is the sheltered side of the rocks, and white bird excrement shows a curved splash zone where it is washed away. The greenish zone is the eulitteral.

0701157: the intertidal in a healthy  sea: high biodiversity of seaweeds and other life. Every bit of rock is covered in long-lived sea life. Stalked kelp dares to grow in the lower littoral fringe. East coast Mercury Islands.

f218219: the intertidal in a degraded sea: low biodiversity. Reef stars (Stichaster australis) surviving desiccation (drying out) while reaching for the black band of flea mussels. Much of the shore is not covered in long-lived sea life. No coralline pink paint! West Coast.

f009525: rock pools with seaweeds while all exposed rock is covered in life, a healthy environment at Goat Island marine reserve. This reef flat is found at the mid to lower littoral and there is no upper littoral or splash zone. There are many broken rocks, some large, accommodating high biodiversity. Featherweed and flapjack in the pools. Abundant coralline pink paint.

f991016: a degraded rocky shore at low tide, showing little variety and poor cover. The pink paint (Lithothamnion sp.) is almost entirely absent, making the shore subject to rapid erosion. Long Bay marine reserve. The white crusts consist of rock oysters and plicated barnacles.

f219610: a potentially interesting rocky shore with rocky undulations capturing large rockpools and boulders littered everywhere. Yet this is a very degraded shore with poor diversity and cover, due to the release of treated sewage at the point in the distance. Whangaparoa Peninsula. Very little pink paint.

f219722: a low tide platform at a very exposed shore has gutters full of seagrass, caused by a high input of mud and nutrients. Near Napier.

f222332: a seaweed washup after a storm, although natural, can cause tremendous loss of life as seaweeds rot away and decomposing bacteria kill sensitive life. A natural disaster such as this has a man-made component: sea urchins died by eating a highly poisonous dinoflagellate slime and this invited the kelp to grow in the urchin barren zone where storms would take them out. The dinoflagellate Ostreopsis slime was caused by unnaturally high nutrient loads in the water which is man-made.

f219317: intertidal zoning on a sheltered evenly sloping shore continues in the vegetation above. Note how low the barnacle zone is relative to the sublittoral fringe of brown seaweeds. Note also the grey, orange and black lichens so close to the top of the intertidal zone. Entrance to Whangarei Harbour.

• roots/leaves: land plants need roots to find water in the soil and to transport water and nutrients through 'pipes' (vessels) to their leaves. They pump water up as water evaporates from their leaves. Land plants do not like rock as they need soil for their moisture, nutrients and recycling of decaying matter. In the sea it is an upside down world. Seaweeds do not like sand because it is constantly on the move and seedlings would not be able to survive. Seaweeds find their moisture and nutrients all around, so they do not need roots or pipes and pumps for that matter. They absorb nutrients while exchanging gases through their leaves. Seaweeds can exist only on a substrate such as rock and their roots (holdfasts) serve only to hold on to the rock. Note that eelgrass and mangroves (both vascular plants) do live in mud/sand, but only in very sheltered harbours where their wandering roots (stolons) secure them against being washed out. Note that botannically speaking, vascular plants have leaves but seaweeds, mosses, ferns and palms have fronds. But in this section we will use the words leaf and stem freely.
• waves: because water is 800 times denser than air, the force of waves can be very destructive, but there are several survival strategies.
• flexibility:  For seaweeds it doesn't pay to be rigid like a tree but to yield to the water movement instead. The stringy bladderweeds follow this principle. And just in case there are no waves, they have gas-filled float bladders to keep them upright. Note that the stalked kelp is kept upright by its stiffness, even though its stalk can flex and yield to water movement. Observe how all bladderweeds with flat stems have a corkscrew 'foot' that allows them to bend in all directions. Note that trees have both rigidity (in stems and branches) and flexibility (in leaves).
• streamline: where the water rushes fast over the rock (shearing force), it pays to have a streamlined shape. Limpets and chitons have such a shape as they are flat, with a large suction foot. But such a shape cannot move and turn easily. It also claims a large patch of the shore, just for sleeping. This shape is also worst for being stepped upon. When humans walk on the shore, their weight pushes down onto the shore through a small surface under the shoe. Limpets never evolved with such a threat, reason why people can easily break their shells. This is one reason it is desirable to visit the rocky shore on bare foot.
• strong shell: a strong shell protects not only against being sand-blasted but also against being rolled around when dislodged. A strong shell also protects against predation as it can less easily be broken or drilled into. Many shore creatures have strong shells, particularly those living on exposed surfaces.
• large foot: particularly the grazing snails have a large foot to secure themselves.
• small size: being small reduces the water's drag, but more importantly, enables creatures to find a sheltering crack or pit.
• water breathing: in order to survive being submerged for hours, organisms need to be able to breathe water through gills. Although some mammals (dolphins, whales) and other terrestrial animals (turtles, snakes) can be amazing in their breath-holding, they eventually need to surface and none would be able to last attached to the intertidal.
• uni-directional flow: it is interesting to note that water breathers arrange for a flow of water over their gills in one direction. They cannot afford the extra energy to stop the water, and accelerate it in the reverse direction, such as all air breathers do. Air is 800 times lighter than water and its flow can be reversed without much loss in energy.
• cold-blooded: an animal that breathes water cannot be warm-blooded because the water comes in close contact with the blood, over a large area (gills). There would not be enough energy to stay warm. All submerged animals must therefore be cold blooded (poikilotherm) and this allows them to shut down over considerable periods.
• on stand-by: cold blooded animals are able to go on stand-by (shutting down) because they do not need to expend energy staying warm. For instance, the difference between a human sleeping (80-100Watt) and working hard (300W) is not large. When 'shut down' for the night, humans still expend a considerable amount of energy on warmth. The ability of going on 'stand-by' allows organisms to stay out of water for considerable time periods, some even up to two weeks (barnacles, periwinkles). The moment they become inundated, they are then able to switch on and continue their meal.
• drying out: drying out (desiccation) is one of the severest threats to those staying out of the water. To counter this problem, organisms have developed several strategies:
• survival pack: organisms store extra water. Snails lock a few drops of water up over their gills and insides. Through this water they can still breathe a little. By quickly removing a snail from the rock and turning it over, one can see it withdrawing deeper into its shell while sacrificing its 'survival pack'. Seaweeds store extra water by being puffed up (crusting seaweeds and others). The survival pack also helps against overheating by allowing some of the water to evaporate, which causes cooling.
• huddling: by huddling together, organisms can retain more moisture than each in isolation. They also shelter one another against drying winds while also minimising exposure to sunlight.
• finding cracks: cracks in the rock and any discontinuity (sudden change) in the surface, invites hairy algae to grow larger than usual because grazing them is difficult. These algae lock up moisture, which helps other organisms to survive. Cracks can also provide shade against direct sunlight.
• finding shade: avoiding direct sun exposure by seeking the shaded side of a rock helps considerably.
• hiding under stones: stones offer the perfect shelter from wind and sunlight while also providing a solid roof against browsing seabirds. That is why turning stones when studying the rocky shore, provides the most unusual finds. The larger the stone, the more likely it will stay in place amidst wave action, and the more diversity can be found underneath, and also older organisms.
• heating/cooling: once exposed to the air, intertidal organisms are affected by the sun's heat and the drying effect of wind. On a winter day, organisms can become frozen before the tide returns. Survival strategies against overheating and cooling are similar to those against drying out, see above. To counter extreme frost, some marine creatures have 'anti-frost' compounds in their blood.
• increased metabolism: many sea creatures are seen 'basking' in the sun in shallow water (sharks, pelagic fish, sting rays, and many more). This is not for tanning or for feeling the heat of the sun but to warm up. As the surface layer can be 4-6ºC higher in summer, it improves metabolism (food digestion & growth) and could also bring a sense of well-being. Thus creatures who 'bask', grow faster and make more spawn than those who don't. Likewise, being able to stay out of the water, and thus able to warm up, could mean a higher growth rate and egg production.
• oxygen release: gases like oxygen and carbondioxide dissolve well in water, and more so in cooler water. Thus when water warms up, gases tend to escape, which means that their availability increases. Fish seek warming waters for their increased oxygen levels, which may also increase their metabolism.
• exposure to degradation: we discovered that degradation in the sea is caused mainly by planktonic decomposing bacteria that are capable of causing infection. The chance of infections is proportional to the time being exposed to it. Thus being able to live outside the water for some time, reduces the chance of dying. It is a good idea to spend a short time submerged to feed, followed by a long time to digest the food. For more on degradation, visit the decay section.
• salinity: when sea water evaporates, it becomes more salty, which accelerates fluid loss from organisms through osmosis (water moving from a weaker concentration in the body, to a denser one outside). Rockpools may become too salty to survive in. But all marine organisms need to 'drink' salt water while excreting salt, in order to stay moist, so added salinity is easy to cope with for animals, although less so for plants.
• size: size matters considerably for survival. Being small reduces the drag of the waves, requires less energy to maintain, while one's weight is easier to carry in the presence of gravity (out of the water). Rockpool fishes are from necessity small. Being small is a disadvantage against predation as escape is too slow and a thick shell unaffordable. But predators who have to be larger than their prey, are disadvantaged by being less capable of surviving out of the water or on wave-exposed surfaces.
• weight/gravity: while submerged, most organisms are almost weightless. But being out of the water requires them to carry their full weight, reason why they do not like to move around. An octopus for instance, a strong mollusc, is hardly capable of movement above water. Many molluscs like grazing snails, limpets, chitons and abalone are remarkably strong because they need to resist strong water movement. But being attached strongly goes against movement. Thus they either move while lightly attached, or stay put while strongly attached.
• hydraulics: many underwater creatures (molluscs, echinoderms) master a mysterious force, that of hydraulics. A snail withdraws into its shell by expelling water and shrinking. For instance, it extends a siphon to half its body length by hydraulic forces. It sucks to the rock like a suction cup, and once 'stuck', requires very little energy to maintain suction. This enables them to remain stuck firmly in place while 'on stand-by'. A snail or clam can burrow straight into the sand by mysterious techniques, of which hydraulics is a part. It can also suddenly emerge from under stones while lifting these with ease. It can disappear in a crack or under a stone by shifting its shape to suit. A weight-less army tank would not be able to do any of this.
• oxygen: in order to survive, animals need oxygen and plants carbondioxide. But both can go on 'stand-by', surviving long periods of oxygen starvation. Note also that above water there is still oxygen and CO2, although less easily available.
• feeding: for most intertidal animals, feeding stops once the tide goes out.
• fishes: rockpool fishes claim their large territories when the tide is in, and they retreat to rock pools which they share with their rivals in a kind of 'truce'. When the tide is in, they show how remarkably adapted they are to wave-wash, with their large breast fins clinging onto the rocks and speeding to and fro in the shallowest of water.
• grazing snails: when the tide is out, they stop feeding and go on stand-by. Only inside rockpools can one find grazing snails, limpets and chitons.
• echinoderms: some starfish are able to survive out of water (cushion star). They stay moist by keeping water between their frilly tubefeet on top. On a sand flat they are able to transport water by means of their tubefeet, from underneath to their backs. Submerged echinoderms like sea urchins and brittle stars continue feeding as normal.
• predation: also predation stops when the tide is out, but once on its prey, a predator will not let go, because the meal may take a week. Predators such as the dark and white rock shells (Haustrum sp.) have a large space under their shells which acts as a mitten (glove) to hold the prey and a survival pack of water, while allowing them to attach as well.
• body plans: more so than the terrestrial environment, the sea has a much larger 'arsenal' of body plans in the form of ancient designs that still occupy unique and often important functions today. The body plans are reflected in the various phyla, the main groups of life, some of the most obvious in the animal kingdom are mentioned here:
• Porifera: the sponges are sessile animals that protect themselves by being inedible or rightout poisonous or by having spiky glass skeletons. Sponges in general grow only slowly and need to be submerged.
• Cnidaria (=Coelenterata): the flower animals with stinging cells. These are the coral builders in the tropics but in the temperate climates play a lesser role: anemones, gorgonians, solitary corals, jellyfish. The flower animals have a very simple form: just a stomach with a mouth, surrounded by tentacles. They are very soft and like to stay under water.
• Ectoprocta (=Polyzoa=Bryozoa): the mat forming moss animals are tiny flower animals living inside tiny boxes, complete with lid. These boxes join up in regular patterns. They too like to remain submerged as under stones.
• Brachiopoda: the ancient lamp shells that look like molluscs with two shells.
• Annelida: the round worms and bristleworms that play an important role in decomposing dead animals. They also include the plankton-feeding tube worms. Worms form an important food source for others.
• Arthropoda: the joint-legged ones, of which the Crustaceans are the most common on the shore: shrimps, crabs. Also the numerous but largely invisible sea slaters and sand hoppers. Crustaceans live inside an external skeleton and in order to grow, must discard their old skeleton to grow a new, bigger one. This is called moulting. Having many legs leads to diversification, reason why crustaceans have adapted to many kinds of feeding.
• Mollusca: the soft-bodied ones including inkfish, shells, clams, chitons, limpets and nudibranchs. Molluscs do not have fixed shapes and can adapt to the size of the environment. They represent a huge diversity in the sea. Most molluscs are hermaphrodites, being male and female at the same time. This enables them to live in seclusion while multiplying without mates.
• Echinodermata: the prickly skinned ones: sea urchins, starfish, sea pens and sea cucumbers. Echinoderms also live inside an external skeleton made of many individual plates, separated by living tissue. They can grow by growing each plate separately. They can also shrink in size to suit the amount of food they can get. Some sea stars can reproduce by splitting. Having many tubefeet, they too have adapted to a wide range of food: grazing, scavenging, predating, detritus feeding, plankton feeding.
• Chordata: the ones with a spinal cord. Of course mammals, birds, reptiles and amphibians belong to this phylum, but also the Classes:
• Ascidiacea: the ascidians or sea squirts. These live from phytoplankton by sieving the water through a fine bag.
• Osteichthyes: the bony fishes: the little fishes found on the rocky shore. There is no space for big ones.

The science of ecology teaches the following classical species interactions:

• neutral: not benefiting or damaging either species
• competition: competition for space, for food, for shelter.
• association: one species is usually but not necessarily and not exclusively associated with another. For instance, barnacles make the surface rather rough and unsuitable for medium-sized grazing snails, but little ones can negotiate the rough terrain and even find shelter inside empty barnacle shells, even when they are not normally found at this altitude without barnacles.
• negative: benefiting one but damaging another
• predation: predators eat others, thereby killing an individual and reducing the numbers in a population or community. Yet predation can be beneficial because often the weak and sick are targeted, and they help limit populations before these run out of food, which can cause unpleasant death while the health of the population weakens.
• parasitism: a parasite benefits from exploiting its host, whereas the host loses.
• positive: one species benefits another and vice versa
• commensalism: occurs when an individual obtains a benefit from a different species without damaging it.
• mutualism: occurs when an individual obtains a benefit from another species and, at the same time, the second species obtains a benefit from the first one. Mutualism is not obligated, which makes it different from symbiosis.
• symbiosis: species benefiting one another but also depending on one another.  If one of the symbiotic individuals perishes, the other also perishes by losing the source from which it was obtaining a benefit.

• social dominance: the stratification of groups into a society given by the influence that one individual or one group of individuals has on the other individuals or groups into the same society.
• social hierarchy: the stratification of the individuals that consists in the domination that an individual has on the other individuals of the same population.
• territoriality: the demarcation and defense of a physical area that is defined by an individual or by a group of individuals.
• intraspecific competition: happens when two or more individuals of a population try to obtain a factor needed by all individuals from the environment where they inhabit.
• effectively: if the competition is brought to a harmful struggle between two of the stressed individuals of a population
• unintentionally: if the competition does not imply a deadly or harmful ritual, but a natural application of abilities to achieve a required factor.
• agonistic behavior: if the contest implies a risk-free ritual of threatening and submissive behavior
• ritualistic competition: if the competition does not imply a ritual

One method of scientific study of the intertidal zone is by laying out a measuring tape and measuring species densities along the tape. The species counts can then be depicted in the form of a kite diagram as shown in this example of grazing molluscs. The width of the black kite represents the number of individuals found within a defined quadrat. (Note, however, that the kite diagram shown here is more conceptual than representing actual numbers.) Students are then asked to explain why certain species are found where they are, why some overlap with one another and others don't, using all the knowledge explained before. In our example, all species shown are grazers which suggests that competition should be a major biotic factor as well as exposure to desiccation (drying out). However, also some important information is missing. To begin with, it does not show where the high and low tide marks are. One should also know that this is a shaded and reasonably sheltered shore, reason why the grazing slug Onchidella is found here, crawling out of their hideouts, grazing the sea weeds above. So the zone builders not shown on the diagram are important biotic factors as well. For instance Siphonaria is usually associated with the blood crust Ralfsia or Gelidium. One should also know that this is an almost vertical shore, reason why Cellana ornata is found and Melagraphia is lower down than usual. The message here is that there are many hidden clues before one can understand the ecology behind this diagram of grazers. But there is more to consider.

If one were to study the same area of shore over a long time period (longer than 10 years), one may notice that the kite diagram changes seasonally and annually, and often quite suddenly too. So in the end, our entire toolbox of ecological factors proves to be of no use. None of the explanations we can muster holds true over a sufficient span of time. Why? Why does ecology in the sea appear to make no sense?

There are a number of invisible ecological factors that we do not find on land:

• imported food: we mentioned this before. Much if not most of the food input to the rocky shore comes from places far away as an inexhaustible supply. For barnacles who feast on dead and living zooplankton therefore food is not limiting; only space is. Even grazers like limpets take in a lot of nutritious detritus supplied from afar. Slime tracks from snails can serve to trap detritus, eaten by same snails, or which bacteria can convert to nutrients and so on.
• imported nutrients: for algae living on the shore, there is a never limiting supply of new nutrients. For them mainly the amount of sunlight and warmth are limiting.
• bacteria as food: only in the soil can one find organisms living from bacteria, but in the sea the bacteria can assume the plankton's main biomass. Furthermore every surface (even fish skins and seaweed skins) is covered in dense mats of bacteria that can be eaten. Nearly all surface grazers consume the fast growing bacteria as substantial parts of their diets.
• bacteria as killers: one of the largest ecological factors in the sea, and so far entirely overlooked by mainstream science, is the planktonic decomposer guild (an association of heterotrophic bacteria) that also brings disease. Sea water is not only thin nutritious soup but also thin infectious sewage. Living in the sea is a delicate balancing act, and living in the intertidal does not exempt. Bacteria can suddenly change the goal posts, causing major habitat shifts and mass mortalities. [see our discoveries that have not yet been confirmed by mainstream science, and principles of degradation]
• broadcast spawning: on land the offspring are born near their parents, so we can understand how populations grow (gradually and predictably) and describe that in mathematical formulas. Sea organisms however, produce excessive amounts of spawn, most of which serves as food for others. So the number of offspring born on suitable habitat is entirely unpredictable. From one day to the next, a shore may become overwhelmed with the offspring of a single species. Likewise, the offspring from a mollusc may be born hundreds of kilometres away.
• offspring from successful survivors are not born where their survival skills matter: this is related to the previous factor, which makes evolution and adaptation on land faster than in the sea. this leads to the following:
• all seas are connected whereas on land there are isolated pockets like islands, and land separated by rivers, ice and mountain ranges.
• visitors from other habitats: on land only birds who can fly long distances can become visitors from other habitats, but the rocky shore, even the estuarine flats, are so narrow that visitors who do not live there, are common and can have a decisive influence. Wading birds on mudflats are a good example, but with a rising tide come a large array of marine visitors who have only one thing in mind: exploitation. Even little triplefins (small fish without float bladder) become redoubtable predators, picking off all newly settled barnacles while operating from a rockpool many metres away. Visiting herbivorous fish (weed eaters) may in one visit have more influence than all the resident grazers together all week. The intertidal habitat is incredibly narrow.
• failure is more important than success: in terrestrial (land-) ecology we think in terms of survival of the fittest, which sprouts from the foundation that offspring are few and born near their parents. From this observed fact we then explain behaviour designed to propagate the genes of the fittest (best suited). On land, survival is important. In the sea with broadcast spawning, long planktonic larval stages and larvae drifting on currents, this paradigm (way of thinking) is no longer defensible. On the intertidal shore where life is brutal and short, failure becomes the dominant selector. In other words, on land the fittest are selected by survival during life, resulting in advantage during reproduction, whereas in the sea they are deselected by failure during birth (recruitment). So we can understand the intertidal (and the sea) only from this perspective. Look at intertidal zoning and try to understand it in terms of failure as the big selector! [Reader please note that this point is highly counter-intuitive and controversial and is perhaps unsuitable for teaching]

Now we've come full-circle with the most important ecological factor saved for last. Read this chapter again, but now from the paradigm (way of thinking) that failure (death) is more important than success (survival). Also consider this: