The fauna, associated with Laminaria and other large brown macroalgae
was studied by using SCUBA and dredging in two different types of unde
rwater habitats of the White Sea. In shallow water fjords and bays, wi
th a depth of no more than 30-40 m, detached kelp (mainly Laminaria sa
ccharina, L. digitata and Alaria esculenta) formed large accumulations
. One of these benthic accumulations, which has existed more than 20 y
ears, was studied. It covers about 2000 m(2), and is about 2 m thick.
The upper layer of the accumulation of fronds is characterized by high
turbulence and is well aerated. The lower layer is characterized by a
noxic conditions. Mats of sulphur bacteria were not observed, although
fronds in the middle layer were covered by layers of cyanobacteria. A
bout 50 species of macroinvertebrates were found, mainly species that
are normally associated with living kelp, such as the detritivorous sp
ecies Ophiura robusta and Gammarus oceanicus, and few species that are
specific inhabitants of organic-rich biotopes in the White Sea such a
s Capitella capitata, Ophryotrocha irinae and Nebalia bipes. It was re
markable that in the shallow water basins of the White Sea, the proces
s of decomposition of brown algae in the sublittoral takes place witho
ut sea urchins, and no other macrofaunal form plays an ecological role
in the mechanical breakdown of the plant substratum, even not in the
large accumulations of detached kelp. Along the open rocky shoreline,
communities associated with dead detached kelp were situated at a dept
h of 60-90 m, 40-50 m below the belt of living kelp. In this deep zone
, no macroinvertebrates typical of the kelp community in the photic zo
ne were found. During the passage from the shoreline to the deeper ben
thic community, where sea urchins were dominant, all plant debris beca
me fragmented. These deeper benthic communities appeared to be the zon
e for decomposition of the detached kelp.