An official website of the United States government
Abstract Diel vertical migration (DVM) is a widespread phenomenon in aquatic environments. The primary hypothesis explaining DVM is the predation‐avoidance hypothesis, which suggests that zooplankton migrate to deeper waters to avoid detection during daylight. Copepods are the predominant mesozooplankton undergoing these migrations; however, they display massive morphological variation. Visual risk also depends on a copepod's morphology. In this study, we investigate hypotheses related to morphology and DVM: (H1) as size increases visual risk, increases in body size will increase DVM magnitude and (H2) if copepod transparency can reduce visual risk, increases in transparency will reduce DVM magnitude. In situ copepod images were collected across several cruises in the Sargasso Sea using an Underwater Vision Profiler 5. Copepod morphology was characterized from these images and a dimension reduction approach. Although in situ imaging offers challenges for quantifying mesozooplankton behavior, we introduce a robust method for quantifying DVM. The results show a clear relationship in which larger copepods have a larger DVM signal. Darker copepods also have a larger DVM signal, however, only among the largest group of copepods and not smaller ones. These findings highlight the complexity of copepod morphology and DVM behavior.
more »
« less
Body size‐ and season‐dependent diel vertical migration of mesozooplankton resolved acoustically in the San Diego Trough
Abstract Diel vertical migration (DVM) is a common behavior among marine organisms to balance the trade‐off between surface feeding opportunities and predation‐related mortality risk. Body size is a master trait that impacts predation risk to both visual and nonvisual predators. Acoustic measurements from the autonomousZoogliderrevealed size‐dependent DVM behaviors in the San Diego Trough. Dual frequency (200 and 1000 kHz) backscatter, in conjunction with physical properties of the ambient water and optical imaging of zooplankton, were recorded during 12Zooglidermissions over 2 yr. Acoustic size‐categories were identified based on the theoretical scattering properties of dominant taxonomic groups identified optically by the Zoocam. Acoustic modeling suggests that the measured acoustic backscatter in this region is largely dominated by copepods, with appreciable contributions from other taxa. We found that larger organisms migrated deeper (245–227 m) and faster (> 20 m h−1) compared to smaller organisms (156 m, > 15 m h−1). Larger organisms entered the upper layer of the water column later in the evening (0.2–1.5 h later) and descended into deeper water earlier in the morning (0.4–3.7 h earlier) than smaller‐bodied organisms, consistent with body size‐dependent visual predation risk. The variability in daytime depths occupied by small, intermediate, and large‐bodied backscatterers was related to the depth of the euphotic zone, again consistent with light‐dependent risk of predation.
more »
« less
- Award ID(s):
- 1637632
- PAR ID:
- 10367695
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 67
- Issue:
- 2
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 300-313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Some planktonic patches have markedly higher concentrations of organisms compared to ambient conditions and are <5 m in thickness (i.e. thin layers). Conventional net sampling techniques are unable to resolve this vertical microstructure, while optical imaging systems can measure it for limited durations. Zooglider, an autonomous zooplankton-sensing glider, uses a low-power optical imaging system (Zoocam) to resolve mesozooplankton at a vertical scale of 5 cm while making concurrent physical and acoustic measurements (Zonar). In March 2017, Zooglider was compared with traditional nets (MOCNESS) and ship-based acoustics (Simrad EK80). Zoocam recorded significantly higher vertically integrated abundances of smaller copepods and appendicularians, and larger gelatinous predators and mineralized protists, but similar abundances of chaetognaths, euphausiids, and nauplii. Differences in concentrations and size-frequency distributions are attributable to net extrusion and preservation artifacts, suggesting advantages of in situ imaging of organisms by Zooglider. Zoocam detected much higher local concentrations of copepods and appendicularians (53 000 and 29 000 animals m−3, respectively) than were resolvable by nets. The EK80 and Zonar at 200 kHz agreed in relative magnitude and distribution of acoustic backscatter. The profiling capability of Zooglider allows for deeper high-frequency acoustic sampling than conventional ship-based acoustics.more » « less
-
Abstract Bergmann's rule predicts that organisms at higher latitudes are larger than ones at lower latitudes. Here, we examine the body size pattern of the Atlantic marsh fiddler crab,Minucapugnax (formerly Uca pugnax), from salt marshes on the east coast of the United States across 12 degrees of latitude. We found thatM. pugnaxfollowed Bergmann's rule and that, on average, crab carapace width increased by 0.5 mm per degree of latitude.Minuca pugnaxbody size also followed the temperature–size rule with body size inversely related to mean water temperature. Because an organism's size influences its impact on an ecosystem, andM. pugnaxis an ecosystem engineer that affects marsh functioning, the larger crabs at higher latitudes may have greater per‐capita impacts on salt marshes than the smaller crabs at lower latitudes.more » « less
-
Abstract Larger body size has long been assumed to correlate with greater risk of extinction, helping to shape body-size distributions across the tree of life, but a lack of comprehensive size data for fossil taxa has left this hypothesis untested for most higher taxa across the vast majority of evolutionary time. Here we assess the relationship between body size and extinction using a data set comprising the body sizes, stratigraphic ranges, and occurrence patterns of 9408 genera of fossil marine animals spanning eight Linnaean classes across the past 485 Myr. We find that preferential extinction of smaller-bodied genera within classes is substantially more common than expected due to chance and that there is little evidence for preferential extinction of larger-bodied genera. Using a capture–mark–recapture analysis, we find that this size bias of extinction persists even after accounting for a pervasive bias against the sampling of smaller-bodied genera within classes. The size bias in extinction also persists after including geographic range as an additional predictor of extinction, indicating that correlation between body size and geographic range does not provide a simple explanation for the association between size and extinction. Regardless of the underlying causes, the preferential extinction of smaller-bodied genera across many higher taxa and most of geologic time indicates that the selective loss of large-bodied animals is the exception, rather than the rule, in the evolution of marine animals.more » « less
-
Tanentzap, Andrew J (Ed.)A principal goal in ecology is to identify the determinants of species abundances in nature. Body size has emerged as a fundamental and repeatable predictor of abundance, with smaller organisms occurring in greater numbers than larger ones. A biogeographic component, known as Bergmann’s rule, describes the preponderance, across taxonomic groups, of larger-bodied organisms in colder areas. Although undeniably important, the extent to which body size is the key trait underlying these patterns is unclear. We explored these questions in diatoms, unicellular algae of global importance for their roles in carbon fixation and energy flow through marine food webs. Using a phylogenomic dataset from a single lineage with worldwide distribution, we found that body size (cell volume) was strongly correlated with genome size, which varied by 50-fold across species and was driven by differences in the amount of repetitive DNA. However, directional models identified temperature and genome size, not cell size, as having the greatest influence on maximum population growth rate. A global metabarcoding dataset further identified genome size as a strong predictor of species abundance in the ocean, but only in colder regions at high and low latitudes where diatoms with large genomes dominated, a pattern consistent with Bergmann’s rule. Although species abundances are shaped by myriad interacting abiotic and biotic factors, genome size alone was a remarkably strong predictor of abundance. Taken together, these results highlight the cascading cellular and ecological consequences of macroevolutionary changes in an emergent trait, genome size, one of the most fundamental and irreducible properties of an organism.more » « less
