Storm barrens of northern New Zealand

by Dr J Floor Anthoni (2009)
www.seafriends.org.nz/enviro/habitat/storm_barrens.htm
The general idea of urchin barrens is that they are abnormal and that sea urchins have multiplied, while creating barren areas, because snapper and crayfish populations (their predators) have been decimated by people. So sea urchins and their barrens are a bad thing. However, nothing could be further from the truth, as this page shows. Dr Anthoni discovered that the barren zone is created by large storms, and that urchins may or may not establish themselves there. Storm barrens are highly productive and diverse and a sign of good environmental health.
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introduction Storm barrens were discovered by Dr Anthoni in an extensive habitat survey done in 1993, work that has not been disproved. But please note that mainstream scientists are not supportive of this idea (yet).
rules for storm barrens Because storm barrens are caused by a physical process, we can define a number of rules about them. This helps in further understanding the marine environment.
other barren areas Barren zones or areas are places where large seaweeds cannot grow because storms remove them. We must not confuse them with places where there is not enough light or where there is surface wave action.
What are the main grazers of New Zealand's storm barrens?
examples Examples of storm barrens in northern New Zealand and the Kermadec Islands
References to scientific journals.
Related chapters Related chapters on this web site:
Hauraki Gulf Survey 1993: our measurements of habitat zoning after the kelpbed death of 1993, leading to many discoveries.
The snapper-urchin-kelp myth: how scientists misinterpreted the disappearance of the urchin barrens, a major scandal.
Scientific research in NZ debunked: a critical dissection of some marine research done in NZ relating to urchin barrens.
Introduction to marine habitats: what it means to live in the sea.
Images of stalked kelp and its ecology.

-- Seafriends home -- marine environment index - marine habitat index -- updated:20070330,20070728,20090416,20120513,



 
Introduction
Every ocean shore in the world is subjected to the forces of waves, which is the main sorting factor for what species live where along a depth profile, as the wave's force rapidly declines with depth. In addition there is the influence of light, or lack thereof. As one goes deeper, light intensity and quality diminish until eventually plants can no longer grow. This depends on the orientation of the coast (sunny or shaded side) and the turbidity of the water, and of course the light sensitivity of the main habitat-forming seaweeds. The resulting habitat zoning is also subjected to unusual events like major storms (hurricanes) that may cause major damage only once every few years.

After one such major event, a massive plankton bloom at the end of 1992, the kelp forest in a large area died and was successively removed by a tropical cyclone (hurricane) in January 1993. After the storm we did a preliminary survey and found good reasons to follow it up with a more thorough one in the (southern) winter of 1993 (See Hauraki Marine Survey 1993). Because we looked at many factors, we also made many discoveries, such as the full extent of the kelpbed death. For every site we recorded habitat boundaries along a vertical transect down the shore. This led to the first record of actually measured habitat boundaries (they were previously guessed at).

For some time we suspected that the depth of the sand bottom restricts waves as wave theory predicts, such that the maximum strength of the worst storm waves is proportional to the depth of the sand bottom. Hurricane waves are typically spaced over 400m apart, extending to a depth of 200m. When they arrive at the continental shelf, they are hindered by the sand bottom which becomes shallower as the waves approach land, draining their energy accordingly. So, by sorting the transects by their bottom depth, we could place them in order of worst wave exposure, and a consistent zoning diagram emerged.
 
 

underwater zoning diagram northern New Zealand underwater zoning diagram northern New Zealand
From left to right wave exposure from exposed to sheltered. The top two zones are taken by stringy seaweeds which give way abruptly to a barren zone, bordering the kelp forest. The kelp forest is bordered by the sand bottom with occasionally a narrow fringe of sponges.
Above right a three-dimensional view with typical shore profiles plotted. Please note that the urchin barrens (pink) end when the bottom is shallower than 15m, and that a tough seaweed like the featherweed (Carpophyllum plumosum) takes over. Note that this diagram could be extended further into the sheltered shallows, but this was not the purpose of our survey. We also didn't record zoning on shaded shores. Note also that exposed shores become steeper as they become deeper.

 
storm barrens relative to sea bottomBarrens without urchins
To our surprise, we discovered that some barrens were not populated by urchins. Some of these were grazed by the strong grazing Cook's turban snail (Cookia sulcata) and some by the rainbow paua (Haliotis iris) but there were also some that had no grazers at all. Instead the barrens (that are devoid of kelps), were populated by colourful communities of turfing calcareous algae (pink turf), sponges and anemones. When we plotted these against the depth of the sand bottom, they followed a straight line. Note that sites 24 and 22 were located in very strong currents, known to erode the sand bottom as they shear past headlands (which moves their positions to the right in the diagram). These barrens without urchins vindicated our hypothesis that the barrens are indeed caused by storms.
Because these discoveries were made in 1993 and have since not been proved wrong by mainstream science, we will introduce the word storm barrens for the general case. Urchin barrens are a special case when urchins are their main grazers.


 
Rules for storm barrens
Because storm barrens are caused by physical factors, and then modified by biological factors (their grazers), they follow strict rules. These rules help to understand the underwater environment. 
These rules are strict and exceptions should not be found.



 
Other barren areas
Barren areas are areas without the large habitat-forming seaweeds (macroalgae) like kelps. But seaweeds need moisture and light, so when either is absent, a barren area results. So it pays to distinguish these from storm barrens.
  • the intertidal rocky shore extends above low tide where seaweeds cannot live. Not surprisingly, they are barren.
  • inside caves and archways there is not enough light for seaweeds, so they remain barren.
  • on degraded shores the water may be too murky to allow plant life below the storm barrens.
  • the water may become too unhealthy for plants to live or for spores to settle, even though the amount of light remains adequate.
  • strong grazers may create barren patches here and there
loss of light affecting habitat zonesThis diagram shows how loss of light due to murky water creates a barren area where normally none would be expected. On left a healthy situation with shallow stringy seaweeds (fucalia), an urchin-grazed storm barren, a kelp forest (laminaria) and a deep reef habitat with sponges. When the water is clear and healthy, there is standing room only in an environment which is rich in variety.
But degrading water quality pulls the lower light boundary up, while also diminishing density and diversity. Eventually the whole shore becomes barren, devoid of the species one would have expected there. In the end also crustose coralline algae (pink paint) disappear.

 
dying sponges
f033810: due to murky water, the kelp boundary has moved up and these grey sponges are infested and dying. The whole barren area extends from 6m down. Martins Bay. Note how the pink paint has become patchy. Note also that one cannot take overview photos due to severely limited visibility.
dying kelp Arid Island
f036804: the kelp forest is dying even though there is enough light. There are no young plants (recruits) and there are no sea urchins. This becomes a barren zone caused by degradation of water quality. Arid Island.
entrance to Rikoriko cave
f043124: a diver swims into Rikoriko cave at the Poor Knights, where the barrens are densely populated but where seaweeds cannot grow. Notice the large purple urchins. These barrens are caused by lack of light.
f020032: life inside an archway can be very rich because the current brings food. But plants can't grow here. Notice the purple urchin in the foreground. Apparently it can live from animal life. Poor Knights.
barren zone inside an archway
purple urchin barren
f030621: purple urchins have carved out a barren patch in a sheltered place. This is not a storm barren. Poor Knights.
purple urchin baren centrostephanus
f029902: purple urchins (Centrostephanus rodgersi) and their local barren. Notice the many sockets in the rocks, carved by generations of urchins. Poor Knights.
vertical wall with deadmans finger alcyonium
f036012: strong grazers like sea urchins and large snails can easily fall off steep rock faces, reason why they are easily bared. This is a boundary case of a storm barren. Deadmans fingers Alcyonium sp. Mimiwhangata.
urchins crowding a boulder
f033926: a storm cleared a high patch on a boulder and urchins occupy its sheltered side, which has been cleared completely compared to the exposed side. Note that urchins do not need to graze because they can catch broken seaweeds. Mayor Island.
urchins crowding on a rock
f007213: a storm cleared a high boulder and sea urchins are grazing it further. Notice how they are penned into their patch by the steep sides of the boulder. By staying closely together, they resist attacks from predating starfish, whelks and fish.



 
Ecology of the storm barrens
The ecology of storm barrens is actually quite simple: what is not removed by storms, stays and thrives. But this can have interesting twists, illustrated here with photographs. Once an area is cleared from tall seaweeds, it lets the light in. Immediately kelp 'seedlings' pop up but because these are rare in the whole area dominated by a dense tough canopy, they are also immediately eaten by mobile browsers like fish. It will take up to 4 years for kelp to effectively re-establish itself. This gives slow grazers like sea urchins enough time to take over as they mature in about two years. As the sea urchins grow, they more or less run out of food, so removing a few helps the vitality of all. In any case, their grazing power is far more than needed to keep the rock barren. Note that urchins can catch broken seaweeds that float by, and many live entirely from this food source, without ever moving (cryptic or hidden urchins).
However, with their five teeth, they cannot reach into cracks and crevices and they cannot graze the pink paint that gives the rock a whitish cover. soon an army of more suitable grazers arrives, and they specialise on the patches that the urchins can't reach.

The main grazers of the storm barrens in NZ are:

urchins, barren, cooks turban, snails
f001319: urchins do the ground work by night while they shelter inside their sockets by day. Large Cook's turban shells do some rough grazing whereas the finer work is done by smaller catseyes, top shells and limpets. Goat Island.
large urchin barren Goat Island
f001932: a cluster of sea urchins at the sheltered side of a protruding rock. The habitat is barren as far as the eye can see. Goat Island marine reserve Waterfall Reef June 1995. Note that the kelp has not yet invaded this habitat, contrary to what scientists claim! 
overlapping fronds encrusting calcareous algae
f035721: detail of overlapping fronds of pink paint. The whitish spots are dead because some organism once grew there (sponges, kelp). Dark red patches are a different species.
cooks turban cookia sulcata
f036235: the Cook's turban snail (Cookia sulcata) is a powerful grazer but sea urchins need to do the clearing first. A variable triplefin sits on its shell. The shell's rate of growth (and health) is revealed by a band of bare shell.
urchin ready to chop kelp tree
f006828: a lonely sea urchin about to clear-fell the last kelp tree on its patch. Once the plant is bleeding, other urchins are attracted. Mayor Island.
finely trimmed patch of sea lettuce
f033937: a marblefish has also made use of a barren patch by meticulously trimming a stand of sea lettuce, thereby encouraging it to grow very densely. No other grazers allowed here! Mayor Island.
sea lettuce out of reach of urchins
f007210: a lot of food in the form of sea lettuce is found above the urchin zone but it is too risky to go there. This shows the subtle difference between urchin barren (below) and storm barren (above). Mayor Island.

 
f045604: the urchin barrens support a highly productive and diverse community. In the photo the green sea urchin (Evechinus chloroticus), top shells (Trochus viridis), a stellar limpet above (Cellana stellifera), an unidentified limpet perhaps (Cellana radians), and a host of tiny snails. Notice the various forms of crustose calcareous algae (Lithothamnion spp.). Mimiwhangata.
f049611: detail of some little actors on the urchin barrens. Notice the rough terrain created by some crustose calcareous algae possibly Corallina officinalis. Cavalli Islands.



 
Examples
Enjoy the examples of storm barrens and how varied they can be, and also how beautiful.
f022424: for demoiselles to lay their nests of eggs, they need barren rock as shown here. The blue males guard the eggs while the green females feed in the currents. Demoiselles keep the rock face free from small snails and they even prod sea urchins along. Poor Knights.
f048302: demoiselles have cleared their rocks from grazers, but are thereby allowing the sea lettuce to invade. Poor Knights.
f017317: as the kelp boundary moved up due to increasing murkiness of the water, it left behind a barren area where sponges fight deposition by mud. Martins Bay.
f017316: sponges in a degrading environment enjoying the cleaning services of sea cucumbers (Stichopus mollis). Martins Bay.
f036001: a colourful storm barren with isolated shrubs of tangleweed (Carpophyllum flexuosum). The tangle weed has been trimmed by storms and it is too tough for sea urchins to eat. Notice the many white sea anemones. Mimiwhangata.
f045827: urchins in a diverse storm barren with red carpet sponges, large grey sponges, white anemones, tangle weed and pink coralline algae. Apparently the carpets can repair themselves rapidly. Notice how all urchins sit on pink paint patches. Mimiwhangata.
f051809: a storm barren covered in encrusting sponges (Crella incrustans) that survive the gnawing from sea urchins as the only grazers. Cuvier Island.

f020605: short red seaweeds (Champia spp) and a flat tough green seaweed (Gigartina sp) surviving in a storm barren where urchins can't. Poor Knights.
f051822: turfing calcareous algae dominating in a very exposed storm barren. Cuvier Island.
f020915: detail of turfing calcareous algae in a storm barren. Hahei.
f036520: detail of turfing calcareous algae in a storm barren. Cape Brett.
f034100: detail of one of the toughest calcareous algae in a storm barren. Mayor Island.
f036523: detail of a most varied storm barren coralline garden - standing room only. These plants made from bits of stone hinged together, are able to survive in the most exposed conditions. Cape Brett.
f049016: a storm baren covered in jewel anemones and encrusting sponges. No unoccupied space left. Truelove Reef Cavalli Islands.
f028104: a sheer storm barren cannot be populated by urchins for once they fall down, they cannot make it back up again. Cape Brett Pearcy Island.
f051912: a very rich storm barren at a very exposed pinnacle. In the distance nothing but storm barrens. Never Fail Rock, Mercury Islands.
f051900: detail of the storm barrens around Never Fail Rock. Huge diversity. Standing room only. No urchins.
f031419: storm barrens on a basalt bommy at Raoul Island, Kermadecs. Two kinds of urchin and a large snail in the foreground. Note that there are no large seaweeds (kelps) at the Kermadecs, possibly because the storm barrens extend over the whole photic (light-) zone.
f031804: storm barrens populated by large urchins (Centrostephanus rodgersi) a far as the eye can see. McDonald's Rock, Kermadecs.
f047302: Because Niue island does not have a continental shelf, hurricanes can arrive with exceptional strength, creating storm barrens from the surface down  to 80m deep, where no branching corals can survive. See Niue ecology
f047110: At night millions of sea urchins appear from their dens and tunnels in the soft rock, to graze the film of algae. Notice their scrape marks. Molluscs like seashells also join in.

You may now be interested in the extensive rebuttal of the urchin barrens myth, the ecology of the Kermadec Islands and that of Niue. Perhaps also in why marine reserves in NZ are disappointing.



 
References

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