"Hot" news - seaweed burns in winter? (due to UV?)

Debbie MacKenzie debimack at auracom.com
Thu Apr 11 11:26:01 EDT 2002

Dear Coral list,

Thanks for the feedback. Ove suggested that the Ascophyllum may have been
damaged by unusually cold winter weather, and asked:

>.  What was the temperature
>relative to the long term average?

I had described it as "cold" but what I meant was only that it is still
uncomfortable to take photos without gloves on - which is not unusual.
Temperatures here have been within normal, a bit milder than average if
anything, during the last 6 weeks. We had a cold snap early in February
with temperature dropping below the long term average, but this does not
stand out as unusual since it seems to happen every winter at some point
during January-February. List members tend not to appreciate email
attachments so if you're interested, I've added a temperatue graph from
Environment Canada to the bottom of the references for my 'burnt seaweed'
article. It shows temperature fluctuations for the past year as compared to
a 30 year average. ( http://www.fisherycrisis.com/seaweed3.html )  Also,
Ascophyllum has a very high tolerance for cold, extending it's range well
into northern areas that are far colder than this one. Simple cold injury
looks extremely unlikely.

Several people suggested that the damage to the seaweed might have been
caused by an increase in UV radiation and that I'd dismissed that
possibility too quickly. Maybe so, probably UV damage deserves a closer
look, although the pattern of vulnerability and resistance certainly does
not correlate well simply to degrees of solar radiation exposure. But I
can't rule out the possibility that it's the combination of rising UV
radiation and lowered nutrient availability. (BTW, Environment Canada
estimates that UV radiation has increased by 7 - 10% over the last few
decades in this area.)

The biggest reason that I don't see this new 'natural mortality' in
Asclophyllum as likely to be primarily caused by increasing UV is that
increasing UV simply does not explain coincident and very similar changes
that are visible in other organisms in the immediate area. For example,
there has been a major change in populations of barnacles and mussels in
the area, with vertical range contraction very apparent in the barnacles
and concentration of both species now being limited to high water flow
areas (or heavily nutrient enriched areas such as polluted harbours). It is
hard to imagine these species, with their heavy shells, being particularly
vulnerable to UV or being the earliest casualties...and even if they were,
their pattern of redistribution only makes sense in relation to feeding
opportunities. I have described this in detail in
http://www.fisherycrisis.com/barnacles.html .

And comparing the 'burnt' damage in Ascophyllum to a very similar pattern
occuring in neighbouring perennial "fucus" seaweeds seems to strengthen the
'nutrient' connection. (Very interesting, two brown seaweeds, one capable
of translocation of nutrients to the growth tips (fucus), one not (Asco)...
with the result being that fucus appears to 'burn' in reverse - "heat" or
"light" or "whatever" damage occurring from the holdfast up. If you'd like
to see what I mean, look at http://www.fisherycrisis.com/seaweed2.htm ).

I see the whole ecosystem as changing, looking 'sick,' and a symptom like
the 'burnt Asco' needs to be assessed in the context of the total picture
of co-occurring signs/symptoms/changes. Regarding the area of the rocky
reef that I featured in the 'burnt Asco' article, the last few decades have
seen enormous change in the marine life living there. Once there were many
mussels growing on the reef (now there are none), and many species of small
fish lived in the water (little perch, flatfish, sculpins, eels, etc...now
these are never seen). Starfish and anemones have disappeared, as have
clams. A bed of eelgrass grew beside the reef, but not a blade has been
seen for at least 20 years. The salt marsh is gradually shrinking. There is
no reason to think that terrestrial source organic input to the cove has
changed, yet water clarity seems to have improved. There are a few snails
(much fewer than years ago) and a few very small crabs and virtually
nothing else visible that moves. Visible new organisms include a very heavy
brown filamentous epiphyte on the subtidal rockweeds and short-lived green
filamentous growths on the rocks and upper rockweeds.

Like a patient presenting to a doctor with 'dry itchy skin,' the 'burnt
Asco' is only one sign of what seems to be a systemic malady. Efforts to
diagnose the cause of 'itchy skin' must obviously go far beyond looking at
temperature and UV exposure patterns and examining skin scrapings under a
microscope (although these investigations are relevant). A complete
'history and physical' needs to be done. If the patient turns out to have
split fingernails, falling hair, losing teeth, extremely low body weight,
depression and anorexia...the 'dry itchy skin' fits perfectly into a
pattern of chronic malnutrition. If the patient, on the other hand, appears
to be in otherwise normal health, the 'dry itchy skin' might simply be the
result of transient exposure to environmental extremes of temperature or
solar radiation.

Debbie MacKenize

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