Nutrition
 
 

cartoon of octopus with bell and sign
Actually, all possibilities have merit, and there are likely to be others not listed here.

 

 

 

 

Respiration rates are not taken into account. Yes. Apparently, most algae can live even in the dim light of 30-40m depth if their respiration rates are low enough. Red algae have comparatively low respiration rates and therefore are theoretically capable of living deeper than the other types. Brown algae, in contrast, have comparatively high repiration rates and thus tend to be found, other things being equal, in conditions of brighter light.

Physical features of the seaweeds are not considered. Yes. If an alga is fragile or intolerant of drying, then it would be unlikely to inhabit shallow intertidal areas. In face of waves or currents, is it bendable or rigid? Can it withstand being buried in sand or mud? These and other similar questions would need to be addressed.

Certain biological factors are not included. Yes. One issue in this regard is the extent of hervivore grazing. Even if other conditions were suitable in a given area, grazing by herbivores might restrict a species' presence. Adaptations to protect against being eaten, such as heavy calcification or leathery texture, might interfere with light penetration regardless of what wavelengths were available for photosynthesis. Also, even if a spcies could survive in the dim light at deeper depths, its growth and reproduction would likely be severely affected.

Effects of ultraviolet light are not dealt with. Yes. This relates also to the physical attributes of a seaweed. Lack of physical or chemical protection from the bleaching effects of UV light could prevent a seaweed from inhabiting intertidal or shallow subtidal regions.

photograph of green alga Ulva sp.Other habitat preferences of a seaweed are ignored. Yes. Thre may be conditions favouring survival that are unrelated to light. For example, the green algae Ulva and Enteromorpha favour areas of freshwater input, species of coralline algae thrive in high-energy wave-impact areas, and so on.

NOTE plants, like other living things, need to respire to survive. In so doing they oxidise glucose created by photosynthesis. The depth at which the amount of oxidisable matter produced by photosynthesis equals the amount used in respiration is known as the plant's compensation depth. A plant cannot survive deeper than its compensation depth


Abundant growth of sea lettuce
Ulva fasciata is often indicative
of freshwater seepage 0.5X

 
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