Seasonality and depth distribution of a mesopelagic foraminifer, Hastigerinella digitata, in Monterey Bay, California

Abstract

We investigated the habitat depth and population dynamics of mesopelagic foraminifera in Monterey Bay, California, using 12 yr of video surveys and specimens from live collections. The water column over Monterey Canyon continuously supports two distinct species of mesopelagic foraminifera, Hastigerinella digitata and a previously unknown species referred to as Hastigerina sp., with H. digitata dominating the planktonic foraminiferal assemblage at mesopelagic depths. H. digitata populations live within a narrow depth horizon that lies above the core of the regional oxygen minimum zone at a depth of 280-358 m and O 2 concentrations of 1-1.3 mL L 21 . Our observations provide a modern calibration for understanding fossil digitate planktonic foraminifera. We observed numerous copepods in various stages of ingestion on the spines of H. digitata and a conspicuous lack of detritus attached to the spine network, providing support for the hypothesis that H. digitata is an obligate carnivore. H. digitata populations did not show the strong two-phase seasonality that characterizes the population dynamics of many mesopelagic species that live above the Monterey Canyon, although H. digitata was generally more abundant in cooler waters on seasonal and interannual timescales.The ecology of midwater organisms-inhabitants of the waters lying below the well-lit surface waters and above the deep seafloor-is poorly known despite the areal extent of their habitat and their long evolutionary history (Robison 2004(Robison , 2009). The lack of information pertaining to the largest ecosystem on Earth (by volume) arises in part from the difficulty of accessing the midwater habitat and limitations of studying communities with trawl nets and acoustics. Trawl nets destroy the delicate organisms that make up a major component of midwater communities and preclude observations of organism interactions in situ. Acoustics generally cannot provide count data or distinguish between individuals and/or species (NRC 2003; Robison 2004). The advent of remotely operated vehicle (ROV) technology provided a needed complement to trawl and acoustic sampling by allowing the direct observation of organismal behavior in nature (Haddock 2007) and by enabling the collection of time series of the relative abundance and depth distribution of taxa (Robison et al. 1998; Robison 2004;Osborn et al. 2007).Here, we investigate the ecology and distribution of mesopelagic planktonic foraminifera in Monterey Bay, California, using 12 yr of effort-standardized, ROV video transect observations and specimens captured in situ with a ROV. We focus on planktonic foraminifera, just one of the many mesopelagic groups quantified within the ROV time series, as they showcase the potential of ROV video transects to provide reliable, in situ observations of even small organisms that were poorly sampled and understood with traditional plankton net sampling. As such, this study provides baseline data on the population dynamics and distribution of mesopelagic foraminifera an...

Origin of the Eocene planktonic foraminifer Hantkenina by gradual evolution

“…These species are carnivorous, preying on deep‐dwelling copepods that also peak in abundance at this depth, as does mesopelagic biomass in general (Hull et al . ). Hull et al .…”

“…Hull et al . () recently described the first detailed observations of living deep‐dwelling planktonic foraminifera based on observations and collections made by a remotely operated vehicle (ROV) in Monterey Bay, California. They found Hastigerinella digitata and another related species living at depths of 150–500 m, with a clear peak in abundance at c .…”

“…Hull et al . (, p. 573) described Hastigerinella as ‘planktivorous sit‐and‐wait predators’ that prey mainly on copepods year round with a peak population density of about one individual per 5 m 3 of water. Not all deep‐dwelling planktonic foraminifera are this specialized, however; others feed on sinking phytodetritus or are omnivorous (Hemleben et al .…”

“…If H. singanoae was carnivorous like modern Hastigerinella , in which rhizopodia stream from the tips of true spines (Hull et al . , p. 563), these networks would have been useful for catching and securing large prey such as copepods. Alternatively, if they were herbivorous, they could have been used for scavenging small food particles, such as sinking phytodetritus, from the surrounding water, which could then have been passed into the shell through the primary or even terminal aperture, if one was present.…”

Tintinnina (Ciliophora) and Foraminifera in plankton of hypersaline Lagoon Bardawil (Egypt): spatial and temporal variability

“…Hastigerinella digitata (Rhumbler, 1911) was probably incorrectly identified in the lagoon (Fouda et al, 1985) because it is a rare deep-dwelling form usually occurring at depths greater than 100 m (Hull et al, 2011;Weiner et al, 2012). The authors think that it was Hastigerina pelagica (d'Orbigny, 1839), a common predatory species in the sea (Pujol and Grazzini, 1995;Mallo et al, 2017).…”