Four new hydrothermal vent fields were discovered on the slow spreading Central Indian Ridge (8–12°S; Segments 1–3), all located off‐axis on abyssal hill structures or Ocean Core Complexes (OCCs). Each site was characterized using seafloor observation (towed camera system), plume chemistry (Fe, Mn, and CH4; Conductivity, Temperature, and Depth sensor [CTD]/Miniature Autonomous Plume Recorder [MAPR]), and rock sampling (TVgrab/dredges). Different styles of venting on each segment reflect different geological settings, rock types, likely heat sources, and fluid pathways. The segment 1 field was located on the western flank of the axial valley at the base of OCC‐1‐1. High‐temperature venting was inferred from plume characteristics and extensive seafloor sulfide mineralization, but only diffuse venting was observed. This site appears to be a magmatic‐influenced basaltic‐hosted system despite its off‐axis location. Two low‐temperature diffusely venting sites were located on abyssal hills 6 and 9 km off‐axis on Segment 2. Plume particle, metal, and CH4 concentrations were all very low, suggesting dilution of hydrothermal fluids by intrusion of seawater into the highly permeable flank area fault zone. The “Onnuri Vent Field” (OVF), located at the summit of OCC‐3‐2, vented clear, low‐temperature fluids supporting abundant vent organisms (21 macrofaunal taxa). The plume particle signal was low to absent, but strong ORP anomalies correlated with high CH4 and low metal concentrations. Sulfide mineralization was present, which suggests both serpentinization and magmatic/lithospheric influence on fluid composition. The detachment fault is the likely pathway for hydrothermal fluid circulation at this off‐axis location. These new vent field discoveries, especially the OVF, contribute valuable information toward understanding Indian Ocean hydrothermal systems and their ecology/biogeography.

Macrofauna are an abundant and diverse component of abyssal benthic communities and are likely to be heavily impacted by polymetallic nodule mining in the Clarion-Clipperton Zone (CCZ). In 2012, the International Seabed Authority (ISA) used available benthic biodiversity data and environmental proxies to establish nine no-mining areas, called Areas of Particular Environmental Interest (APEIs) in the CCZ. The APEIs were intended as a representative system of protected areas to safeguard biodiversity and ecosystem function across the region from mining impacts. Since 2012, a number of research programs have collected additional ecological baseline data from the CCZ. We assemble and analyze macrofaunal biodiversity data sets from eight studies, focusing on three dominant taxa (Polychaeta, Tanaidacea, and Isopoda), and encompassing 477 box-core samples to address the following questions: (1) How do macrofaunal abundance, biodiversity, and community structure vary across the CCZ, and what are the potential ecological drivers? (2) How representative are APEIs of the nearest contractor areas? (3) How broadly do macrofaunal species range across the CCZ region? and (4) What scientific gaps hinder our understanding of macrofaunal biodiversity and biogeography in the CCZ? Our analyses led us to hypothesize that sampling efficiencies vary across macrofaunal data sets from the CCZ, making quantitative comparisons between studies challenging. Nonetheless, we found that macrofaunal abundance and diversity varied substantially across the CCZ, likely due in part to variations in particulate organic carbon (POC) flux and nodule abundance. Most macrofaunal species were collected only as singletons or doubletons, with additional species still accumulating rapidly at all sites, and with most collected species appearing to be new to science. Thus, macrofaunal diversity remains poorly sampled and described across the CCZ, especially within APEIs, where a total of nine box cores have been taken across three APEIs. Some common macrofaunal species ranged over 600–3000 km, while other locally abundant species were collected across ≤ 200 km. The vast majority of macrofaunal species are rare, have been collected only at single sites, and may have restricted ranges. Major impediments to understanding baseline conditions of macrofaunal biodiversity across the CCZ include: (1) limited taxonomic description and/or barcoding of the diverse macrofauna, (2) inadequate sampling in most of the CCZ, especially within APEIs, and (3) lack of consistent sampling protocols and efficiencies.

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The influence of seasonal and ontogenetic changes on the dietary composition of 3 amphipod species (Synchelidium lenorostralum, S. trioostegitum and Gitanopsis japonica) were studied in the surf zone of a sandy shore habitat in Dolsando, southern Korea. The 2 species of Synchelidium were found to be carnivorous feeders, consuming mainly benthic harpacticoid copepods, whereas G. japonica had a diet consisting of both copepods and detritus. The dietary composition of S. lenorostralum and S. trioostegitum overlapped for all ontogenetic stages. Little overlap was found in the dietary composition of G. japonica compared with the 2 Synchelidium species, a characteristic that might favor the co-existence of the 3 species. S. lenorostralum displayed significant differences in dietary composition between sexes, among developmental stages, and over the seasonal cycle. For S. trioostegitum, dietary composition varied over the seasonal cycle. Juveniles of Synchelidium fed mainly on copepod nauplii and nematodes as well as on benthic harpacticoid copepods. Our results suggest that the biological interactions between benthic amphipods and meiofauna, such as benthic harpacticoid copepods and nematodes, may be important in the trophic chain of sandy shore surf zone habitats.KEY WORDS: Synchelidium lenorostralum · S. trioostegitum · Gitanopsis japonica · Amphipoda · Feeding · Sandy surf zone Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 258: [189][190][191][192][193][194][195][196][197][198][199] 2003 sandy shore habitats, often dominating benthic macrofaunal communities in terms of both numbers and biomass (Fenchel et al. 1975, Wijnsma et al. 1999, Dittmann 2000. Moreover, amphipods are considered to be one of the most important secondary producers (Carrasco & Arcos 1984) and a major food source for a variety of marine predators (Kline & Wood 1996, Schlacher & Wooldridge 1996, Beare & Moore 1997, MacNeil et al. 1999, Takahashi et al. 1999. Amphipods play an important role in surf zone food webs, acting as a trophic link from primary producers to higher-order consumers. Clearly, quantitative assessments of trophic relationships between amphipods and their prey/predators are important for our understanding of energy flow in sandy shore surf zone environments (Gerdol & Hughes 1994).Various aspects of amphipod feeding activity have been studied, including diet (Fenchel et al. 1975, Biernbaum 1979, Nielsen & Kofoed 1982, Icely & Nott 1985, Stuart et al. 1985, diel feeding patterns (SainteMarie 1986, Gerdol & Hughes 1994, Ingolfsson & Agnarsson 1999) and the influence of food quality on growth and reproduction (Gee 1988, Johnson & Wiederholm 1989, Delong et al. 1993, Pöckl 1995, Poltermann 2000. These studies have provided basic information on the feeding ecology of freshwater and marine amphipods inhabiting sublittoral and intertidal habitats. However, there is no information available on the feeding characteristics of amphipods in sandy shore surf zone habitats.In the s...

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