Expanding range of
"White Rocks" during summer, 2004:
This offers evidence of declining growth of perennial seaweeds
...might this be due to lowered fertility of seawater?
Debbie MacKenzie
Shallow
granite seabed increasingly lacks its normal seaweed cover at sheltered
locations along the Atlantic coast of Nova Scotia. The underwater granite
contours illustrated on this page were never visible decades ago, because these
rocks were always completely covered by perennial seaweeds, mainly by kelp, but also
by rockweeds and
some Irish moss. Coralline algae, which once formed a pink encrusting under-story below
the taller, dark seaweed canopy, has now bleached to white, enhancing the
visibility of the nearly-bare underwater rocks. This change is not the result of ice scour (note, for
instance, that intertidal rockweeds remain intact, and that these are usually greatly
affected when ice scour occurs.) Neither has this been caused by intense grazing
of seaweeds by sea urchins (at other times, and on other occasions, kelp beds have been
observed to have been eliminated by sea urchins. No sea urchins have been seen
in this vicinity for over twenty years. A few periwinkles, but no limpets, are
visible. Only a few green crabs are seen. Grazing by herbivores is therefore not
a plausible explanation for the recent seaweed loss.)
It seems unexpected that these stable, shallow sub-tidal rocks are no longer colonized by seaweeds, because this appears to be a type of classically ideal seaweed habitat: covered by seawater, sunny and not unduly rough. But, very few examples of young kelp and rockweed are seen today, although some older, deteriorating specimens remain. Sparse tufts of bleached Irish moss are seen, possibly growing from attachments that were established several years ago. Frequently described in the literature of marine ecology has been how newly-exposed stable underwater rocks like these are routinely colonized by a predictable succession of seaweeds. The expansion, instead, of bare rock at this location, seems to be one more reflection of a generalized "breaking of the rules" in marine life today. Why? (Click on thumbnails to see larger images. Photos taken at East Dover, N.S. Text continued below.)
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The seaweeds that are vanishing from this scene, a broad-bladed kelp, sub-tidal fucoids and Irish moss, all remain very common along the Nova Scotia shoreline. The factor that seems to be most strongly related to their recent disappearance from the "white rocks" is the degree of shelter from wave action. All of these relatively heavy types of seaweed normally colonize rocks exposed to quite a range of intensity of water movement, and this has a direct effect on the ability of plants to take fertilizer from the water. It is more difficult for seaweeds to obtain fertilizer in still water. The large seaweeds that once lived on these rocks were existing at the calm water periphery of their normal range. Their recent disappearance from this area can therefore be seen as a retreat from the least naturally rich part of their wider habitat. If the fertilizer content of the seawater were to decline, then exactly this type of subtle change in seaweed growth would be predicted.
If a subtle systemic decline in the coastal ocean seawater fertility explains the appearance of white rocks in this case, it is predictable that the same trend should be observed at other locations sharing the same physical features. And an informal survey by this author of various clean, sheltered inlets along the Atlantic coast of Nova Scotia indicates that the emerging pattern of "white rocks" illustrated here is consistent.
Unfortunately, no systematic scientific monitoring of
shoreline life has been done by Canadian oceanographers, that might have picked
up on ominous warnings like this one. A consistently high rate of photosynthesis
must occur in the ocean to provide the energy that sustains all fish and other
marine animals. While the amount of photosynthesis done by these humble seaweeds
may not be a strong factor directly affecting the growth of fish, the
photosynthesis done by small free-floating plant cells (phytoplankton) is
crucial. However, both types of sea plants grow in response to the same
fertilizers...and if seaweed is feeling a pinch today, then so is phytoplankton
(although phytoplankton, short-lived, tending to be eaten and to sink, is much
more difficult to assess directly). Large, anchored seaweeds represent unique
ocean fertility indicators, but conventional marine science has missed this.
Conventional
marine science in Canada, the Department of Fisheries and Oceans (DFO),
remains officially "baffled" by the failed rebuilding of the groundfish stocks
and by the starvation of cod. But those high profile
"economically important" fish stories are not unrelated to this story of a
subtle, overlooked loss of "unimportant" seaweeds.
"White rocks"...another baffling new sign of the times? Rather than the mowed-down "urchin barrens" formerly described by marine scientists, this recent appearance of bare rocky sea-bottom seems to be something new and unexpected, "calm, clean, sunlit water barrens?" If so, this is a far more worrisome development. But, will DFO Science mount an investigation and offer an explanation for this latest unexpected change in marine life? No, there seems to be no chance, and not only because these seaweeds have been mistakenly assumed to be stable but unimportant. The larger problem is that DFO does not really employ an openly curious "science" department to diagnose the ocean, but a group of individuals forbidden to communicate messages that might threaten the commercial fishing industry. All "government science" must be passed through DFO's policy filter, and politically undesirable information is suppressed. Finding unexpected evidence of declining ocean fertility would be bad enough (because fish production would inevitably decline too, and fisheries might be seen to need to be curtailed in advance), but discovering that the decline in fertility had most likely been caused by fishing, as I have argued at length on this website, would be absolutely unthinkable. So for now, DFO's answer to the changing seaweed question is that they have no money** to look into it.
"See no evil, hear no evil, speak no evil...?"
(** On the other hand, DFO does have the money to conduct some questionable research that has been demanded by their bosses in the fishing industry. For example, see the recently completed "Consideration of the use of the .22 caliber rimfire Winchester magnum cartridge for instant killing of young harp seals" - DFO CSAS research document 2004/072)
See also:
"Pseudo-eutrophication?" Beyond "white rocks," much
else is changing on the shoreline and trying to make sense of the entire picture
is more complex than it is usually assumed to be.
Seaweed photo galleries