Biology subjects

Fender, C. K.

Publications and source records attributed to Fender, C. K..

4 recordsLinked to original sources

bioRxiv2026

Comparative food-web analysis of bluefin tuna spawning habitats in the eastern Indian Ocean and Gulf of Mexico

Using linear inverse ecosystem modeling as a data assimilation tool, we compare spawning grounds of Atlantic and Southern Bluefin Tuna (ABT and SBT, respectively) based on results from field campaigns in the Gulf of Mexico (GoM) and eastern Indian Ocean off northwest Australia (Argo Basin). Both regions are warm, stratified, low-nutrient waters dominated by cyanobacteria (Prochlorococcus). Despite these similarities, the Argo Basin is more productive, with [~]1.5X higher net primary production and nearly 2X higher production of top trophic levels in the model (tuna larvae, planktivorous fish, and predatory gelatinous zooplankton). Higher primary production in the Argo Basin is mainly driven by higher N2 fixation and storm mixing of new nutrients in the upper and lower euphotic zone, respectively. Increased ecosystem efficiency (secondary production of top trophic levels / primary production) results from differences in plankton food web organization. In the GoM, protistan zooplankton are the direct consumers of nearly all phytoplankton production. In contrast, higher rates of herbivory by crustaceans feeding on nanophytoplankton combines with a higher impact of appendicularians on cyanobacteria to convert plankton production into larval tuna prey more efficiently in the Argo Basin. Despite similarities in the proportions of phytoplankton production mediated by cyanobacteria and other picoplankton in both systems, food web pathways to larval tuna and other planktivorous fish are substantially shorter in the Argo Basin. Our results highlight the impact of distinct zooplankton ecological niches on ecosystem efficiency and suggest a need for better inclusion of plankton food-web structure in models simulating climate impacts on fisheries production. HIGHLIGHTSO_LIDeveloped food web models of tuna spawning habitat (Indian Ocean & Gulf of Mexico) C_LIO_LISpawning habitats in the Argo Basin and Gulf of Mexico (GoM) are both oligotrophic C_LIO_LIArgo Basin had higher net primary production in part as a result of nitrogen fixation C_LIO_LIArgo Basin had higher rates of direct herbivory by metazoan zooplankton C_LIO_LIThis resulted in greater ecosystem efficiency in the Argo Basin. C_LI

ecology↗

bioRxiv2025

Microbial food web dynamics in tropical waters of the bluefin tuna spawning region off northwestern Australia

Whereas recruitment success for many fisheries depends on coincident timing of larvae with abundance peaks of their prey, less can be more in the tropical/subtropical spawning areas of bluefin tunas if lower but steady food resources are offset by reduced larval vulnerability to pelagic predators. To understand larval habitat characteristics for Southern Bluefin Tuna (SBT), we quantified microbial community carbon flows based on growth and grazing rates from depth profiles of dilution incubations and carbon biomass assessments from microscopy and flow cytometry (FCM) during their peak spawning off NW Australia (Indian Ocean) in February 2022. Two Chla-based estimates of phytoplankton production gave differing offsets due to cycling or mixotrophy, exceeding 14C net community production on average (677 {+/-} 98 versus 447 {+/-} 43 mg C m-2 d-1). Productivity was higher than in the Gulf of Mexico spawning area for Atlantic Bluefin Tuna but less than similar studies of oceanic upwelling regions. Microzooplankton grazing averaged 482 {+/-} 63 mg C m- 2 d-1 (71 {+/-} 13% of production). Two measurement variables for Prochlorococcus gave average production and grazing rates of 282 {+/-} 36 and 248 {+/-} 32 mg C m-2 d-1 (86 {+/-} 6% grazed). Prochlorococcus comprised almost half of production and grazing fluxes in the upper (0-25 m) euphotic zone where SBT larvae reside. Prochlorococcus declined and eukaryotic phytoplankton and heterotrophic bacteria increased in relative importance in the lower euphotic zone. These results describe relatively classic open-ocean oligotrophic conditions as the food web base for nutritional flows to SBT larvae.

ecology↗

bioRxiv2025

Sinking particle export within and beneath the euphotic zone in the eastern Indian Ocean

The eastern Indian Ocean is substantially under sampled with respect to the biological carbon pump - the suite of processes that transport the carbon fixed by phytoplankton into the deeper ocean. Using sediment traps and other ecosystem measurements, we quantified sinking organic matter flux and investigated the characteristics of sinking particles in waters overlying the Argo Abyssal Plain directly downstream of the Indonesian Throughflow off northwest Australia. Carbon export from the euphotic zone averaged 7.0 mmol C m-2 d-1, which equated to an average export efficiency (export / net primary production) of 0.17. Sinking particle flux within the euphotic zone (beneath the mixed layer, but above the deep chlorophyll maximum) averaged slightly higher than flux at the base of the euphotic zone, suggesting that the deep euphotic zone was a depth stratum of net particle remineralization. Carbon flux attenuation continued into the twilight zone with a transfer efficiency (export at euphotic depth + 100m / export at euphotic depth) of 0.62 and an average Martins b-value of 1.1. Within the euphotic zone, fresh phytoplankton (chlorophyll associated with sinking particles, possibly contained within appendicularian houses) were an important component of sinking particles, but beneath the euphotic zone the fecal pellets of herbivorous zooplankton (phaeopigments) were more important. Changes in carbon and nitrogen isotopic composition with depth further reflected remineralization processes occurring as particles sank. We show similarities with biological carbon pump functioning in a similar semi-enclosed oligotrophic marginal sea, the Gulf of Mexico, including net remineralization across the deep chlorophyll maximum. Submitted to: Deep-sea Research II HighlightsDespite low productivity, export efficiency was 17% of primary production Flux attenuation beneath the euphotic zone (EZ) was low for a tropical region Sinking particle flux from the upper to lower EZ exceeded export from lower EZ The deep EZ was a stratum of net particle remineralization (and net heterotrophy)

ecology↗

bioRxiv2022

Prey Size Spectra and Predator:Prey ratios of 7 Species of New Zealand Salps

Salp grazing is important in shaping planktonic food-web structure. However, little is known about the size ranges of their prey in the field or how grazing impacts size structure. This study investigated the feeding habits of 7 different species of salps, representing a variety of sizes and life stages across subtropical and subantarctic waters east of New Zealand. Scanning electron microscopy was used to examine the gut contents of 58 salps, which were then compared to water column plankton communities characterized via epifluorescence microscopy, FlowCam, and flow cytometry. While most of the gut contents resembled ambient waters, substantial differences were found amongst some co-occurring species, such as increased retention of submicron bacteria amongst smaller salps like Thalia democratica. We found that even for those salps capable of feeding on bacteria efficiently, nanoplankton and small microplankton still made up the majority of gut biomass. Larger microplankton were rarer in the guts than in the water column, potentially suggesting an upper size-threshold in addition to the lower size-threshold that has been the focus of most previous work. Salp carbon-weighted predator to prey size ratios were variable, with the majority falling between 1,000:1 and 10,000:1 depending largely on the size of the salp. Taken together our results indicate that despite being able to feed on submicron particles, picoplankton make up at most 26.4% (mean = 6.4%) of salp gut carbon and are relatively unimportant to the energetics of most salps in this region compared to nanoplankton such as small dinoflagellates and diatoms.

ecology↗