Research study 1

Field and laboratory studies of an infaunal polychaete assemblage at Mission Bay, California reveal that many of the species in the assemblage share several life-history attributes that contribute to a limited ability for dispersal. Dispersal is tested experimentally by the author using settlement trays and rates of colonisation of “defaunated” sediment patches.  One finding noted by the author, which perhaps is to be expected, is that dispersal ability is distinct from actual colonisation ability.  Thus, for several species, common features such as small adult size, within-tube brood protection, small brood size, reduced planktonic laval phases, and limited postlarval movement of adults, permit only small-scale dispersal abilities, but nonetheless enable relatively rapid colonisation of suitable space, often leading to high infaunal densities (>200,000 individuals ^. m^-2).  The author comments that the attributes of annual life cycle and flexible, small-scale motility of species in the assemblage enable long-term persistence despite frequent physical disturbance of the habitat.  The study provides much information on recruitment times, before-and-after abundances in the "defaunation" experiments, and colonisation of settling trays, too detailed to include here.  Levin 1984 Ecology 65: 1185.

NOTE  the most common species are the spionids Rhynchospio (arenincola) glutaea, Streblospio benedicti, Pseudopolydora paucibranchiata, and Polydora (ligni) cornuta; a sabellid Fabricia limnicola; a sillid Exogone lourei; and a capitellid Capitella spp.  These 7 species comprise up to 90% of the infauna throughout most of the year.  As most of the assemblage is made up of deposit-feeding, tube-dwelling spionids, this Research Study is included in the lugworm section of the ODYSSEY

Research study 2

Polydora cornuta is a small tube-dwelling spionid, introduced from the east coast of North America and now quite common on mud/sand beaches along the west coast.  A group of researchers at the Bamfield Marine Sciences Centre, British Columbia investigate the effects of delayed settlement on its survival, growth, and reproduction.  Competent larvae are collected from the plankton and half are forced to delay settlement for 6d by withholding suitable substratum.  The other half are tested for immediate settlement capability by providing mud from the adult habitat.  Results indicate no direct effect of delayed settlement, as 75-81% settle successfully in both the experimental and control groups, and the resulting juveniles are of similar size.  There are long-term negative effects of the delay, however, manifested in significant post-settlement decreases in somatic and reproductive growth.  The authors surmise that these costs more than compensate for any advantages in increased dispersal gained from extension of the larval period through delayed metamorphosis.  Qian et al. 1990 Invert Reprod Dev 18: 147. Photograph courtesy Irving & Martindale, Biological Bulletin, Woods Hole, Massachusetts.

NOTE  the authors use an older specific name ligni in the paper

Research study 3

Further studies on polychaete larvae at the Bamfield Marine Sciences Centre, British Columbia examine whether larvae of the capitellid Capitella capitata and the spionid Polydora cornuta are able to utilise suspended detritus as food.  Normal food for the larvae of both species would be phytoplankton. Results show that growth rates of C. capitata larvae feeding on detritus are similar to those of larvae feeding on phytoplankton at naturally occurring concentrations (see lower histogram, first 4 bars). However, the worms do not survive as well on suspended detritus as they do on natural phytoplankton (see upper histogram).

Although larvae of P. cornuta are able to feed on detritus their rates of growth are significantly less than on phytoplankton (data not shown here).  The authors discuss the role of detritus as a possible supplementary food source for polychaete larvae in culture.  Qian & Chia 1990 J Exp Mar Biol Ecol 143: 63.

NOTE  in addition to the 2 species mentioned here, the researchers also test larvae of the sabellarid Sabellaria cementarium.  Results for this species are similar to those of P. cornuta

Other work by the same researchers at the Bamfield Marine Sciences Centre, British Columbia examines the effects of food limitation on larval growth and settlement in the 2 burrow-inhabiting polychaetes, the spionid Polydora cornuta and a capitellid Capitella sp. Both are common infaunal species in the Barkely Sound area, and both can be easily cultured in the lab on a diet of finely ground green alga Ulva and freshly collected phytoplankton.  Under these dietary conditions and at an incubation temperature of 10^oC, settlement occurs about 18d after hatching (see schematic on Right).  When starved for periods of up to 3wk, however, the larvae begin to die within 2wk and those that do survive take almost twice as long to settle than the control larvae.  If fed after 2wk starvation, the larvae can rebound, and continue to develop and settle.  A point-of-no-return is reached sometime between 2-3wk.  Qian & Chia 1993 J Exp Mar Biol Ecol 166: 93.

NOTE  only data for Capitella sp. are provided here; results are similar for the 2 species

As noted in Research Study 2 above, the spionid Polydora cornuta is thought to have been introduced to the west coast from east-coast populations.  The species actually is distributed globally, with representatives in almost all the world’s oceans, excluding polar regions.  What is the liklihood that these widely dispersed populations are still interconnected by migration and gene flow?  This is examined by a research consortium based at University of Tampa, Florida using specimens from 4 widely scattered locations: Florida, Maine, New Zealand and, of particular interest to the ODYSSEY, California.  The researchers culture each set of worms in the laboratory and assess reproductive compatibility, genetic similarity, and other morphological and reproductive traits.  Results show that % fertilisation is low for all combinations save for California females crossed with Florida males (42%).  No cross produces viable larvae, however, and other reproductive-trait differences exist.  Gene sequences show large differences between Florida and California worms and Florida and Maine worms, and comparatively less difference betwee Maine and California worms (see figure).  California and New Zealand worms are genetically almost identical.  The authors conclude that there are at least 3 reproductively and genetically distinct species of P. cornuta in North America.  Rice et al. 2008 Invert Biol 127: 45.

NOTE  comparison of mitochondrial cytochrome-oxidase subunit-I DNA sequences

NOTE  the authors provide a good description of reproduction in P. cornuta, summarised here.  Sexes are separate and males produce spermatophores or sperm packets that they leave around the culture vessel.  Females locate and pick up these packets with their palps (see photograph) and pull them to the mouths of their tubes.  The packets break open and the sperm cloud is sucked into the tube along with the respiratory current.  One spermatophore provides enough sperm for 7wk or 8 spawning events, or around 2800 eggs in total.  Eggs are deposited within capsules (number per capsule not specified) inside the female’s tube, where they hatch to 3-setiger 3-(segment) nectochaetes within 5d.  Interestingly, the female releases the larvae by breaking the capsules one by one with her mouth.  A bit of wiggling then expels the larvae from the tube.  Metamorphosis occurs 6-9d after their release from the female’s tube (at 22-25^oC) at a size of about 16 setigers. Adult worms have about 26 setigers.  The authors provide a wealth of information on various aspects of reproduction in P. cornuta not repeated here