Mesoscale fronts occur frequently in many coastal areas and often are sites of elevated productivity; however, knowledge of the fine-scale distribution of zooplankton at these fronts is lacking, particularly within the mid-trophic levels. Furthermore, small (<13 cm) gelatinous zooplankton are ubiquitous, but are under-studied, and their abundances underestimated due to inadequate sampling technology. Using the In Situ Ichthyoplankton Imaging System (ISIIS), we describe the fine-scale distribution of small gelatinous zooplankton at a sharp salinitydriven front in the Southern California Bight. Between 15 and 17 October 2010, over 129 000 hydromedusae, ctenophores, and siphonophores within 44 taxa, and nearly 650 000 pelagic tunicates were imaged in 5450 m 3 of water. Organisms were separated into 4 major assemblages which were largely associated with depth-related factors. Species distribution modeling using boosted regression trees revealed that hydromedusae and tunicates were primarily associated with temperature and depth, siphonophores with dissolved oxygen (DO) and chlorophyll a fluorescence, and ctenophores with DO. The front was the least influential out of all environmental variables modeled. Additionally, except for 6 taxa, all other taxa were not aggregated at the front. Results provide new insights into the biophysical drivers of gelatinous zooplankton distributions and the varying influence of mesoscale fronts in structuring zooplankton communities.

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Siderastrea glynni Budd & Guzmán, 1994 was erroneously erected from live colonies of S. siderea (Ellis & Solander, 1768) unintentionally transferred from the Caribbean to the Pacific side of the Isthmus of Panamá.These corals had been used in experiments conducted in the early 1980s by KH Kleemann at Urabá Island, Taboga Islands, Gulf of Panamá, at the same site of the subsequent S. glynni discovery. Here, we offer evidence that live fragments deposited at Urabá Island in 1982 are the same found by Guzmán in 1992, and were inadvertently introduced from colonies of Caribbean S. siderea that were presumed to be dead. This morphological study builds on and supports recent genetic analyses of the S. glynni holobiont. In light of these findings, S. glynni should be regarded as a subjective junior synonym of S. siderea.

Collecting detailed surveys of the environmental and biological distributions in the epipelagic and mesopelagic ocean is important for understanding the basic processes that govern these expansive habitats and influence the earth system at large. Common ocean sampling platforms (e.g., net systems, moored, and shipboard sensors), are often unable to resolve marine biota at scales comparable to the variability associated with their own behavior or that of their physical environment. Newer approaches using mobile robotic systems carrying multiple environmental sensors have enabled detailed interrogation of the fine and sub-mesoscale distribution of animals and have provided more context for the water column structure. We integrated a dual-frequency broadband split-beam echosounder (Simrad EK80 with 70 and 200 kHz transducers) into the Wire Flyer profiling vehicle to achieve concurrent hydrographic and acoustic sections in the midwater environment (0-1000 m) at novel scales. The Wire Flyer provides high-resolution repeat profiling (0-2.5 m s À1 up and down velocity) within specified water column depth bands typically spanning 300-400 m. This system can provide acoustic backscatter data at depths unavailable to shipboard surveys due to attenuation limits and can be operated in tandem with conventional shipboard echosounders to provide overlapping acoustic coverage with concurrent hydrographic sections. The side-looking transducer orientation, as opposed to the traditional vertically oriented arrangement on ships, samples orthogonal to the vehicle's profiling survey path and provides a direct measurement of animal distributions in the horizontal. The processed data have demonstrated the system's capacity to track migrating layers and resolve coherent biological patches and single targets in the horizontal, rising seafloor gas plumes, and scattering layer distributions tightly coupled to measured sub-mesoscale features such as strong vertical oxygen gradients.