410
N. BALAKRISHNAN NAIEt AND M, SmASWA'l'HY
that there is the possibility of spawning without settlement. In certaiB
instances detailed studies on the season of settlement of timber boring
organisms have shown effective ecological adjustments, the different
species occurring in an area showing inter-relationships so that interspecific competition is reduced to a minimum through characteristio
zonation in settlement (Nair, 1959). Alternation of breeding periods
prevents simultaneous settlement, the different species occurring in the
area settling over the limited amount of available timber at different
times of the year leading to a succession in settlement (Nair, 1965). The
breeding activities of closely allied species show differences and even
those of the same may vary according to the hydrographic conditions
prevailing in the area (Nagabhushanam, 1962 ; Nair, 1965). The density of distribution of shipworms has fluctuated over long periods and
within the same period their attacks have differed considerably in
various locations along the same stretch of coast line (Becker, 1958).
This aspect of the activity of shipworms has been the subject of
study in three localities along the coasts of India. At Cochin harbour,
south-west coast, Nab (1965) observed that Teredo furcifera settles
chiefly during the hot, highly saline pre-monsoon period, February to
June, with sparse settlement during the early part of the monsoon and
later part of the post-monsoon periods. The settlement of the estuarine
species Nazcsitora hedleyi is confined to the low saline periods of the
monsoon and post-monsoon periods (August-February) with apparently no settlement during the pre-monsoon. Thus, the settlement
of these two species alternates in Cochin harbour. Nagabhushanam
(1962) noted in Visakhapatnam (east coast of India) the occurrence of
Teredofurcillatus ( T . furcifera) on test panels throughout the year with
a maximum attack during the summer months between March and
June with a peak in May during 1966. The difference noticeable in the
nature of settlement along the south-west coast and the east coast of
India may be explained on the basis of the prevailing hydrographic
conditions. Beeson (1936) observed that the settlement of the free
swimming larvae of Bartesia striata, a boring pholad, on test panels at
the mouth of the Beypore river, south-west coast of India, is from
November to June. The period of settlement of Bankia campanellata
common at Visakhapatnam is from August till February and the species
is absent from test panels during the period March to July, the maximum intensity of attack was noticed in November, December and
January. Nagabhushanam (1962), pointed out a direct relationship between the relative abundance of shipworm settlement and temperature
and salinity. The comparatively smaller attack rate by Teredo during
the winter months (November-January) was attributed to a biological
N. BALAKRISHNAN NAIEt AND M, SmASWA'l'HY
that there is the possibility of spawning without settlement. In certaiB
instances detailed studies on the season of settlement of timber boring
organisms have shown effective ecological adjustments, the different
species occurring in an area showing inter-relationships so that interspecific competition is reduced to a minimum through characteristio
zonation in settlement (Nair, 1959). Alternation of breeding periods
prevents simultaneous settlement, the different species occurring in the
area settling over the limited amount of available timber at different
times of the year leading to a succession in settlement (Nair, 1965). The
breeding activities of closely allied species show differences and even
those of the same may vary according to the hydrographic conditions
prevailing in the area (Nagabhushanam, 1962 ; Nair, 1965). The density of distribution of shipworms has fluctuated over long periods and
within the same period their attacks have differed considerably in
various locations along the same stretch of coast line (Becker, 1958).
This aspect of the activity of shipworms has been the subject of
study in three localities along the coasts of India. At Cochin harbour,
south-west coast, Nab (1965) observed that Teredo furcifera settles
chiefly during the hot, highly saline pre-monsoon period, February to
June, with sparse settlement during the early part of the monsoon and
later part of the post-monsoon periods. The settlement of the estuarine
species Nazcsitora hedleyi is confined to the low saline periods of the
monsoon and post-monsoon periods (August-February) with apparently no settlement during the pre-monsoon. Thus, the settlement
of these two species alternates in Cochin harbour. Nagabhushanam
(1962) noted in Visakhapatnam (east coast of India) the occurrence of
Teredofurcillatus ( T . furcifera) on test panels throughout the year with
a maximum attack during the summer months between March and
June with a peak in May during 1966. The difference noticeable in the
nature of settlement along the south-west coast and the east coast of
India may be explained on the basis of the prevailing hydrographic
conditions. Beeson (1936) observed that the settlement of the free
swimming larvae of Bartesia striata, a boring pholad, on test panels at
the mouth of the Beypore river, south-west coast of India, is from
November to June. The period of settlement of Bankia campanellata
common at Visakhapatnam is from August till February and the species
is absent from test panels during the period March to July, the maximum intensity of attack was noticed in November, December and
January. Nagabhushanam (1962), pointed out a direct relationship between the relative abundance of shipworm settlement and temperature
and salinity. The comparatively smaller attack rate by Teredo during
the winter months (November-January) was attributed to a biological