fulltext - DiVA

A Vista on the Marine VegetationBy MATS W LE RNPerpetual motion and permanent rest in submarineenvironmentsIt is easy to observe the algal growth on a rockyshore, particularly at ebb tide or, in the tidelessseas, at low waters. To some degree we are alsoable to extend our inspection downwards throughthe superficial layers of water, a penetration attemptedat when we wade in the modest surf on acalm summer's day or lean over the gunwhalewhile hugging the shore at the edge of islands orskerries. Except in the calmest coves, what we seeare clean plants without a coating of sediments.The "fucoid" algae appear, we may say, regular,and the "confervoid" tufts are short and dense.An impression of almost universal, deep-reachingcleanness will be perceived especially by thosealgologists who explore the cliffs on the exposededge of archipelagos or promontories. Beaten by thewaves or cradled by the swell, this is the vegetationthat forms the basis of our general idea of marinegrowth.The diver meets more shifting views. The vegetationhas quite a different aspect when one is standingamidst it, than the way it looks when watchedfrom above with downward fading sharpness. Themost striking feature of submarine observation, atleast inshore, is however the experience of thecomplete quietude in the landscape on the lowerside of the reach of the waves. When walking in anarea of extreme calmness, the diver stirs up a cloudof finely divided mud which obscures his sight untilit is carried away by some sluggish current. Thewater itself, if undisturbed, is generally clearerhere than in the surf region above where the wavescradle the algae to and fro, and lots of particleswhirl around.To GrsLEN (1929) who was perhaps the first biologistto have a direct physical contact with submarinesedimentation, this confrontation was impressive,and he was astonished to observe its profoundand far-reaching effects in all its stages (p. 99):"One of the things which is most surprising whenwe make a comparison between bottoms from theinner and outer parts of the fjord is the increasinglypronounced layer of dirt covering the plants and stonestowards the interior. While outside the fjord one walkson hard bottoms without having the view spoilt bythe whirling up of any detritus or sedimentary particles,in the inner parts one cannot take a step onthe seabottom without a thick cloud of dust, one istempted to say, whirling up."He also described observations on the opacity of athin stratum of fresher water, not rare to occur in theinterior Gullmar Fjord, quoting a diver's statementthat it was dreadfully dark working in the algous belt"but lightened farther down".The possible nutritional effect of the "dust" on thealgae was also commented on by GrSLEN (p. 100):"The rich sedimentary deposit on the algae and theabsence of strong motions of the waves, make it possiblefor certain epiphytes to flourish here which never,or very rarely, appear beyond or in the outer parts ofthe fjord. To what extent they are nitrophile or notI cannot decide, but it seems probable that such isthe case.''The coarser algae, when growing dust-covered inthe calm, acquire distorted, bizarre shapes andthus appear as a "warped" formation. The fucoidspecies, when identical with those of the "cradled"facies (e.g. Halidrys siliquosa, Chondrus crispus,Phyllophora membranifolia, Furcellaria fastigiata),grow large and look different, and are surroundedby tuft algae in big but thin clouds. Within somefjord-like inlets in Bohuslan, e.g. the Gullmar Fjord,a typical ·warped formation may begin only a fewActa Phytogeogr. Suec. 50