MARINE ALGAL VEGETATION 157 



B. The Sea-grass Vegetation. 



The Zostera-association. 



This association differs so much from the other marine com- 

 munities in Iceland — the marine algal communities — that it 

 must be regarded as not being in any way connected with them. 

 The present community occurs especially on a substratum of muddy 

 clay, which the algae avoid. The ''roots" of the algae — the haptera — 

 are organs of attachment only, their sole function being, in most 

 cases, to attach the plant to the substratum — the stony substra- 

 tum — , while Zostera has true roots which obtain nourishment from 

 the substratum. For this reason Zostera requires a good nutrient 

 substratum which is generally soft. It is rare, indeed it must be 

 reckoned exceptional, for Zostera to be found growing on a hard 

 clay-substratum. I understand such cases to indicate that formerly 

 the substratum had been softer and then became more compact 

 owing to the deposition of clay and sand, and that the Zostera is 

 consequently about to disappear from such a spot. In places where 

 there is no danger of either sand or clay being deposited from 

 brooks or rivers the substratum will, nevertheless, scarcely remain 

 unchanged, as the mud and ooze which are thrown down every- 

 where in the ocean, when once they have been brought to a place, 

 readily accumulate and remain, in the shelter of the dense vegetation. 



The Zosfera-vegetation occurs widely distributed, especially in 

 SW. Iceland where, in many places, both inside the smaller arms 

 of the fjords and in the large fjords such as Brei5ifjor5ur, a sub- 

 stratum of muddy clay occurs between the coast and the skerries 

 which lie nearest. At Brei5ifjor5ur, during low-tide, the pale-green 

 Zosfera-belt may be observed stretching for miles along the coast. 

 At Faxafloi also the Zosfera-vegetation has an extensive distribution. 

 Zostera is found, most certainly, on other parts of the coast of Ice- 

 land, but nowhere have I seen such extensive "meadows" of it as 

 in SW. Iceland. 



The vegetation is generally pure and there is hardly an asso- 

 ciation of species in the sea off these coasts which is less mixed 

 than the Zostera-association. In other places Zostera is a fa- 

 vourite substratum for epiphytes, but however much I searched I 

 did not find anything worth mentioning on the Zostera plants here; 

 in this respect the Zosfera-meadow of Iceland agrees with that of 

 the Faeroes. At times, species belonging to the semi-littoral commu- 



