Marine Biology (1996) 126: 725-733
Settlement of the tube worm Hydroides
dianthus (Polychaeta: Serpulidae):
cues for gregarious settlement
R.J. Toonen1 & J.R. Pawlik
Department of Biological
Sciences, Center for Marine Science Research,
1 Present address: Center for Population Biology,
Abstract: The larvae of many benthic marine invertebrates settle to form conspecific aggregations and are thought to rely on
chemical cues associated with adults as indicators of habitat suitability,
although the identification of inductive compounds has proven difficult.
Still-water laboratory assays carried out during the summers of 1992 and 1993
with larvae of the serpulid polychaete,
Hydroides dianthus (Verrill,
1873), demonstrate that unidentified water-borne compound(s) were responsible
for gregarious settlement of competent larvae. Unlike inductive compounds
associated with other tube-dwelling polychaetes, the
settlement cue was soluble in water and was not associated with the tube, but
rather with the body of live adults. In assay chambers divided by a 52-Jlm
mesh barrier, a greater percentage of larvae settled on biofilmed
substrata when adult worms were present on the other side of the barrier than
when adults were absent. Settlement in response to conspecific
adults, live worms removed from their tubes, and amputated tentacular
crowns of live worms was significantly greater than settlement in response to
dead worms, empty tubes, or biofilmed slides. The
settlement inducer appears to emanate from the openings of occupied tubes;
settlement was greatest along the anterior two-fifths of the tube of living con
specific adults. A single adult was equally capable of eliciting a gregarious
response as were five or 25 con specifics, and newly settled juveniles began to
elicit gregarious settlement after approximately 96 h. Extraction of
aggregations of adult worms with organic solvents removed the inductive
capacity of the tissue, and activity was found in both nonpolar
and polar fractions of an extraction series.
KEY WORDS: Colonization, Gregarious settlement, Habitat
choice, Hydroides dianthus, Polychaete