The life cycle of the cestode Rhinebothrium urobatidium, whose final host is the round stingray, Urobatis halleri, includes a copepod as the first intermediate host and small benthic fishes as second intermediate hosts. Hexacanth embryos within nonoperculate, untanned eggs collected from round stingray developed in the tidepool copepod Tigriopus californicus into caudate procercoids with an apical organ/sucker and cercomer, and rarely, bothridia. The procercoids, which developed in the body cavity within a membrane, adhered to the copepod intestine, were infective to arrow gobies, Clevelandia ios, within 15 d of exposure at 21°C. When infected copepods were fed to arrow gobies, procercoids developed into nonlacunate plerocercoids each bearing individually retractable bothridia and an apical sucker. Within 10 d of exposure to the second intermediate host, the larvae had migrated up the bile/cystic duct into the gall bladder, where they developed bothridia similar to those of adult worms. Between 30 to 51 d post-infection in the goby, plerocercoids approached the size of larvae found in natural infections, and the scolex became morphologically similar to that of adult worms from round stingrays. Only presumptive filiform microtriches (filitriches) were present on procercoids while both filitrichs and spiniform microtriches (spinitrichs) were present on plerocercoids. Identification of plerocercoids from experimental infections as those of R. urobatidium was confirmed through morphology of the scolex and using cytochrome c oxidase I sequences. The experimental transmission of R. urobatidium to first and second intermediate hosts provides improved understanding of the transmission and ontogeny of shark tapeworms. The biological characteristics of U. halleri, with its diverse parasite fauna, provide significant opportunities to examine the biology of an array of elasmobranch tapeworm taxa.

Seagrasses are an important refuge for fishes and provide ecosystem services worldwide. Along the Pacific Coast, however, quantitative assessments of the ecological role of seagrass habitats with limited anthropogenic impacts are lacking despite their value to resource management. To address these issues, the ecological function of the eelgrass Zostera marina Linnaeus in a protected area off Santa Catalina Island, California, USA was quantified using estimates of secondary production in the kelp bass Paralabrax clathratus (Girard, 1854). Monthly assessments of Zostera structural complexity, as well as the size and abundance of juvenile kelp bass were used to establish a baseline of fish biomass and recruitment associated with Zostera habitat. The greatest number of kelp bass was recorded in the summer and fall months and the fewest during the winter and spring. Secondary production in kelp bass (0.1 to 0.59 g m^–2 mo^–1) followed monthly changes in Zostera habitat structure throughout the 24-month study period. Seasonal changes in the structural complexity of coastal Zostera beds may influence the flow of energy to adjacent reef environments through the transfer of fish biomass. These findings help define the potential role of Zostera habitat within the larger context of nearshore coastal ecosystems in the Southern California Bight.

Record drought from 2012 to 2016 followed by rainfall in the winter of 2017 provided an opportunity to examine how changing climate conditions may affect migration opportunities for the endangered southern steelhead trout (Oncorhynchus mykiss). This study examined how intermittently open estuary-ocean interfaces in the Santa Monica Bay that have historically supported steelhead evolved temporally and volumetrically. All seven lagoons in the study area breached by January 2017 after five years of drought and nearly exclusively closed conditions. Duration of breach was affected by the size of the lagoon, with smaller lagoons remaining breached longer than larger lagoons. Conversely, volume capacity persisted longer in larger lagoons. Lagoon condition was quantified by presence/absence of breach and passibility, coupled with daily rainfall. This study provides important lagoon planning, restoration and management information needed to support recovery of southern steelhead trout populations in the face of climate change.