Macrofaunal foraminifera from a former benthic impact experiment site (IOM contract area) in the abyssal eastern Clarion-Clipperton Zone

Stachowska-Kamińska, Zofia; Gooday, Andrew J. ORCID:; Radziejewska, Teresa; Arbizu, Pedro Martínez. 2022 Macrofaunal foraminifera from a former benthic impact experiment site (IOM contract area) in the abyssal eastern Clarion-Clipperton Zone. Deep Sea Research Part I: Oceanographic Research Papers, 188, 103848.

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We analysed macrofaunal (>250 μm) foraminifera in the 0–1 cm layer of three replicate multicorer samples collected in 2015 at each of three abyssal sites (‘impacted’, ‘resedimented’ and ‘control’) in the IOM contract area of the eastern Clarion-Clipperton Zone (CCZ), where a benthic impact experiment (BIE) had been conducted in 1995 in order to simulate disturbances resulting from the seabed mining of polymetallic nodules. Taxonomic composition was similar between sites, with monothalamids representing 79% of complete ‘live’ (Rose-Bengal-stained) tests and multichambered taxa constituting a slim majority (55% overall) of dead tests. Monothalamids comprised a mixture of formal taxa and informal morphological groupings. Komokiaceans in the family Baculellidae predominated and included the top-ranked species Edgertonia sp. 7. Other komokiaceans (Komokiidae) and tubular, spindle-shaped and spherical morphotypes were also common. Multichambered taxa were mainly agglutinated, uniserial hormosinids being well represented together with coiled species, notably Cribrostomoides subglobosus (2nd ranked species). Fragments were almost three times as abundant as complete tests and dominated by tubes (notably Rhizammina sp.), many of them ‘live’. Our results are consistent with earlier studies showing that monothalamids, many of them undescribed, are important elements of abyssal foraminiferal assemblages in the eastern CCZ. Mean specimen counts for ‘live’ and dead tests (50.7–75.7 and 54.3–72.7 individuals/sample, respectively) were not significantly different between sites. Assemblages were very diverse with 43–85 morphospecies per sample and 220 in total (201–1081 specimens per sample, 4361 total), more than three-quarters of them monothalamids. Species richness and diversity were lower at the control site than at the impacted and resedimented sites, and eveness and Rank 1 dominance lowest at the resedimented site, but differences were not significant for any of these metrics. The absence of significant differences in faunal density, diversity, and taxonomic composition at impacted, resedimented and control sites 20 years after the experimental disturbance may reflect a number of factors, including insufficient sample replication.

Item Type: Publication - Article
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ISSN: 09670637
Date made live: 12 Sep 2022 13:54 +0 (UTC)

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