Abstract
Marine soft-sediments sustain functionally important benthic assemblages that are critical for remineralization of organic matter and supply of nutrients to the water column. While these assemblages are well studied along continental margins, investigations from insular margin that surround oceanic islands are very limited. This paper examines the distribution and standing stock of macrozoobenthos at 50, 100, and 200 m depth contours surrounding the Andaman and Nicobar archipelago in the tropical Indian Ocean. The standing stock of macrozoobenthos decreased from the mesophotic reef areas (50 m depth) to the deeper strata (200 m), particularly in the case of the dominant groups, the polychaetes and crustaceans. Smaller-sized, interstitial polychaetes and crustaceans were abundant in the coarser sandy sediments at the shallower sites. The polychaetes were represented by 606 species (279 genera) in the study, of which >50% were rare species. Based on polychaete species composition, three regions were delineated in the study area - the Nicobar margin, the western margin of the Andaman (Bay of Bengal sector), and the eastern margin of the Andaman (Andaman Sea sector). The long, uninterrupted Andaman Island chain formed a geographic barrier separating the eastern and western margins, resulting in the regional distinctions in sediment nature and hydrographic characteristics, which in turn influenced species distribution. Corresponding differences were absent in the case of the Nicobar Islands, which are widely separated by transecting channels, permitting exchange of water between the Bay of Bengal and the Andaman Sea. Within the three regions, polychaete communities changed significantly in taxonomic and functional composition with increasing depth. The well oxygenated, coarse sandy sediments around mesophotic reefs (50 m) harboured predator-dominated assemblages. The 200 m sites, which were characterised by oxygen minimum conditions (<0.5 ml.l-1), particularly around the Andaman Island mass, were dominated by deposit feeders. This study provides the first comprehensive dataset on distribution and standing stock of macrozoobenthos, and community structure of polychaetes along the Andaman and Nicobar insular margin. It also revealed the highest number of polychaete species ever recorded in the northern Indian Ocean, indicating that the Andaman and Nicobar margin is a significant marine biodiversity hotspot.
Highlights
Insular margins surrounding tropical oceanic islands are pristine, species-rich environments, with high rates of endemism (Allen, 2008; Anderson et al, 2013)
Based on two systematic surveys covering 80 sites (23 transects) between 50 and 200 m depths around the entire island chain (6–14◦ N), sampled during north east monsoon (NEM), the present paper provides the first comprehensive picture on the benthic environment, macrozoobenthic standing stock and polychaete community structure around Andaman and Nicobar archipelago
This indicates that the waters around Andaman and Nicobar Islands are an important biodiversity hotspot
Summary
Insular margins surrounding tropical oceanic islands are pristine, species-rich environments, with high rates of endemism (Allen, 2008; Anderson et al, 2013). The nature of sediments in turn influence the structure of benthic communities, even at substantial distances from the reefs (Riddle, 1988; Demopoulos et al, 2014; Sibaja-Cordero et al, 2016) In oligotrophic systems, such as around oceanic islands associated with coral reefs, the bioturbation and remineralization of sedimentary organic matter by benthic fauna is of critical importance to supply nutrients back to the water column, thereby sustaining biological production (Snelgrove, 1998; Griffiths et al, 2017). The ubiquity of polychaetes in soft sediments is due to their functional diversity (Snelgrove, 1999), as they can utilize organic matter as food either directly (i.e., deposit feeders and suspension feeders) or indirectly (e.g., predation and scavenging) (Fauchald and Jumars, 1979; Jumars et al, 2015) They exhibit a wide range of reproductive strategies from brooding to broadcast spawning, enabling species dispersal to suitable habitats even at great distances (Carson and Hentschel, 2006). They are used as surrogates for estimation of diversity, dynamics and functioning of benthic communities (Olsgard et al, 2003)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
