The shell-boring polychaete worm Polydora websteri, also known as blister worm, is a pest species that infests the shells of several commercially important shellfish species, including those of the oysters Crassostrea virginica and C. gigas. Historical records indicate that infestations of blister worm have impacted shellfish culture worldwide for over 100 yr. Although a lot of attention has been given to the burrowing habits of and damage created by blister worms, few studies have examined the levels of population genetic structure in this cosmopolitan species. We examined the patterns of sequence divergence at the mitochondrial cytochrome c oxidase subunit I (mtCOI) gene for individual P. websteri specimens sampled from oysters and scallops collected from shellfish farms along the US Atlantic and Gulf coasts, and Hawaii. The mtCOI sequences we obtained were aligned and compared with published sequences for P. websteri adults and larvae sampled at an oyster farm in Guangdong Province, China. We observed little genetic variation, overall, and no differentiation between populations of P. websteri, a pattern that suggests high levels of connectivity among locations. It is unlikely that natural dispersal alone can account for this lack of differentiation; rather, our results are consistent with the hypothesis that human-mediated introductions have led to genetic homogeneity across large geographic distances for this pest polychaete species.

Red tree corals (Primnoa pacifica) are abundant in the eastern Gulf of Alaska, from the glacial fjords of Southeast Alaska where they emerge to as shallow as 6 m, to the continental shelf edge and seamounts where they are more commonly found at depths greater than 150 -500 m. This keystone species forms large thickets, creating habitat for many associated species, including economically valuable fishes and crabs, and so are important benthic suspension feeders in this region. Though the reproductive periodicity of this species was reported in 2014 from a shallow fjord (Tracy Arm), this study examined reproductive ecologies from 8 sites -two within Glacier Bay National Park and Preserve, three on the continental shelf edge, one within Endicott Arm (Holkham Bay) and two time points from the Tracy Arm (Holkham Bay) study. Male reproductive traits were similar at all sites but there were distinct differences in oogenesis. Though per polyp fecundity mostly showed no significant difference between sites, there was a non-significant trend of increasing number of oocytes with depth. In addition, the average oocyte size from Tracy Arm (the shallowest site) was 105 µm, whereas from Shutter Ridge (one of the deepest sites) the average size was 309 µm. Moreover, the maximum oocyte size at Endicott Arm was 221 µm and at Tracy Arm was 802 µm (both shallow sites), whereas at Dixon Entrance (a deep site) it was 2120 µm, a difference not usually observed within a single species. We propose two theories to explain the observed differences, (a) this species shows great phenotypic plasticity in reproductive ecology, adjusting to different environmental variables based on energetic need and potentially demonstrating micro-evolution; or (b) the fjord sites are at a reproductive dead end, with the stress of shallow-water conditions effectively preventing gametogenesis reaching full potential and likely limiting successful reproductive events from occurring, at least on a regular basis.

The mud star Ctenodiscus crispatus has a broad distribution from Arctic waters into the northern Atlantic and Pacific oceans. Populations in the Atlantic are well studied and show oocyte sizes indicative of continuous gametogenesis with aseasonal spawning. In contrast, knowledge on the reproductive biology of Pacific populations is lacking. Thus, this study aims to examine the reproduction of C. crispatus in the northeastern Pacific. We sampled a population from the Pacific Ocean off Oregon and confirmed the species identity through 16S and cytochrome oxidase subunit I (COI) genetic barcoding. The majority of adults were 22-27 mm in size. Oocytes were obtained from dissected gonads soaked in a 1-methyladenine solution and fertilized with spawned sperm. Other individuals were preserved whole in 10% buffered formalin, and oocytes were measured from preserved gonads. Strip-spawned oocytes had a mean diameter of $485 μm, consistent with Atlantic populations. Sperm had a mean head diameter and flagellum length of 3.1 and 65.9 μm, respectively. The time between first and second cell divisions was $2 h, but larval cultures failed, and very few embryos developed to blastulae. Both strip-spawned and preserved oocytes had a bimodal sizefrequency distribution indicative of semicontinuous gametogenesis. Comparison among individuals showed evidence of asynchrony among the population. This asynchrony and bimodal oocyte distribution may be driven by regular pulses of food, as has been postulated for other populations of this species. The reproductive plasticity seen among populations of this species in different regions could explain how it successfully inhabits such a wide geographic range.