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BackgroundA second species in the siphonous green algal genus Avrainvillea was recently discovered off the island of O‘ahu in the Main Hawaiian Islands. Specimens were collected from Honolulu Harbor, including its entrance channel, and near Ke‘ehi Harbor. These locations are both in Mālama Bay on O‘ahu’s south shore in or adjacent to urbanized estuaries, respectively. In situ observations, morphological and molecular assessments were conducted to examine the alga’s habit and distribution, as well as to assess its putative species identification.New informationThe alga occurred in sand as single individuals or in clusters of several individuals at both sites, and near or within seagrass beds (Halophila decipiens) and algal meadows composed of the green alga Halimeda kanaloana and an unidentified Udotea species at the Ke‘ehi Harbor site. All analyses supported both populations as representative of the same taxa, reported until further investigation in the broad Pacific as Avrainvillea cf. erecta based on morphological and molecular analyses. This record of a second Avrainvillea species in Hawai'i is of particular concern considering that an alga recognized as A. amadelpha, first observed in 1981 from two locales on O‘ahu’s south shore, has become invasive in Hawai‘i’s intertidal to mesophotic environments.

SummaryLength-weight relationships (LWR) using 3876 individuals were determined for 39 species sampled in estuarine systems in the main Hawaiian Islands, including 33 species of fish from 21 families, five species of crustaceans (prey) from two families, and one mollusk species. For 17 species, LWRs were estimated for the first time. For another 14 species their LWRs were newly reported for Hawaiian waters, including seven introduced taxa that are well established in the islands' estuaries. The LWRs for all taxa include juvenile and subadult size ranges commonly encountered in Hawaiian estuaries.

The Indo-Pacific damselfish Abudefduf vaigiensis (Quoy & Gaimard, 1825) was first observed in the Hawaiian Islands in the early 1990s and is now clearly established as a breeding population in the Islands. Sightings of fish with color patterns intermediate between those of A. vaigiensis and the very similar endemic Hawaiian sergeant, Abudefduf abdominalis (Quoy & Gaimard, 1825), suggest that hybridization of the two has occurred naturally. This study provides direct evidence of crossbreeding from observations and video footage of two separate spawnings in nearshore waters of O'ahu and a third spawning in a public aquarium display tank. Reproductive behaviors were similar in intra-and interspecific spawning. However, one important difference was the absence of courtship by the male A. abdominalis toward the female A. vaigiensis in the interspecific spawnings. Instead, the female A. vaigiensis initiated spawning and the male A. abdominalis remained to fertilize, guard, fan, and clean the hybrid clutch along with a previous clutch until the embryos hatched. Embryos collected from one hybrid clutch showed normal embryonic development and subsequently hatched to produce viable swimming larvae. These observations represent a rare example of interspecific spawning in the damselfish family (Pomacentridae) and an exceptional opportunity to study hybridization and introgression in a wild population of coral reef fishes.