Effects of hypoxia on Mnemiopsis leidyi, ichthyoplankton and copepods: clearance rates and vertical habitat overlap

Mesoscale fronts occur frequently in many coastal areas and often are sites of elevated productivity; however, knowledge of the fine-scale distribution of zooplankton at these fronts is lacking, particularly within the mid-trophic levels. Furthermore, small (<13 cm) gelatinous zooplankton are ubiquitous, but are under-studied, and their abundances underestimated due to inadequate sampling technology. Using the In Situ Ichthyoplankton Imaging System (ISIIS), we describe the fine-scale distribution of small gelatinous zooplankton at a sharp salinitydriven front in the Southern California Bight. Between 15 and 17 October 2010, over 129 000 hydromedusae, ctenophores, and siphonophores within 44 taxa, and nearly 650 000 pelagic tunicates were imaged in 5450 m 3 of water. Organisms were separated into 4 major assemblages which were largely associated with depth-related factors. Species distribution modeling using boosted regression trees revealed that hydromedusae and tunicates were primarily associated with temperature and depth, siphonophores with dissolved oxygen (DO) and chlorophyll a fluorescence, and ctenophores with DO. The front was the least influential out of all environmental variables modeled. Additionally, except for 6 taxa, all other taxa were not aggregated at the front. Results provide new insights into the biophysical drivers of gelatinous zooplankton distributions and the varying influence of mesoscale fronts in structuring zooplankton communities.

Section: Physical Processes Structuring Populations and Frontal Dynamicssupporting

confidence: 71%

Environmental drivers of the fine-scale distribution of a gelatinous zooplankton community across a mesoscale front

Luo¹,

Grassian²,

Tang³

et al. 2014

“…On the same date and during one night sample on 13 July, bottom oxygen was < 2 mg l −1 in lower St. Leonard Creek, and again Chrysaora were more abundant near the surface than in the bottom layer. These results, along with results in Keister et al (2000) and Kolesar et al (2010) indicate that bottom layer oxygen depletion may reduce retention of Chrysaora by reducing their use of bottom waters. Similarly, when medusae are abundant, predation or predation threat by Chrysaora in the bottom layer could negatively affect retention of Mnemiopsis.…”

Section: Discussionmentioning

confidence: 52%

“…Previous work on gelatinous zooplankton, including the 2 species that were the focus of the current study, has shown variation in densities on scales of meters to 100s of kilometers related to temperature, salinity, hydrographic conditions, dissolved oxygen, and depth (Keister et al 2000, Costello & Mianzan 2003, Purcell & Decker 2005, Costello et al 2006, Decker et al 2007, Condon & Steinberg 2008, Kolesar et al 2010, Sexton et al 2010). Although we were unable to identify the specific mechanisms responsible for these patterns, spatial variation in Chrysaora density in the Patuxent River system showed the same pattern of higher densities in creeks than in the mainstem river in studies spanning nearly 40 yr (Cargo & Schultz 1966, this study), and similar patterns have been found in both the eastern (Purcell 1992) and western shores of the Chesapeake Bay system.…”

Section: Discussionmentioning

confidence: 81%

Predator-mediated landscape structure: seasonal patterns of spatial expansion and prey control by Chrysaora quinquecirrha and Mnemiopsis leidyi

Breitburg

Burrell²

2014

The scyphomedusa Chrysaora quinquecirrha and lobate ctenophore Mnemiopsis leidyi are dominant consumers in the planktivorous food web in Chesapeake Bay, USA, and are important predators throughout much of their ranges. Our studies in the Patuxent River (a subestuary of Chesapeake Bay) and its tributary creeks suggest successive waves of population spread and trophic influence of these 2 gelatinous species in opposing directions across the aquatic landscape. In years when both species were abundant, Mnemiopsis appeared first in the main channel of the Patuxent River and initially was most abundant in the bottom layer of the water column. Mnemiopsis densities then rapidly increased in shallow tributaries and coves, with distributions likely caused by a combination of transport and temporally and spatially varying patterns of growth and reproduction. In contrast, densities of Chrysaora ephyrae were initially highest in small coves and tributary creeks, with densities of Chrysaora medusae spreading outward from these small systems to the main river as summer progressed. We found no conclusive evidence for tidally-cued vertical migrations of either species or directional swimming by Chrysaora that would create these differing spatio-temporal patterns. As Chrysaora increased and spread, it likely reduced or eliminated Mnemiopsis by direct predation, and possibly through the effect that partial predation could have on Mnemiopsis reproduction. Because of differences in diets and feeding rates, these shifting temporal and spatial patterns of medusa and ctenophore dominance potentially influence spatial distributions and temporal patterns of survival of ichthyoplankton, oyster larvae, and copepods.

“…Densities of C. quinquecirrha and M. leidyi were greater above than below the pycnocline in the mainstem bay, where waters below ~11 m were anoxic (Purcell et al 1994a). Sampling in the Patuxent River indicated that C. quinquecirrha did not use bottom waters when DO was < 2.0 mg O 2 l −1 , but that M. leidyi could use bottom waters even at 1.0 mg O 2 l −1 (Keister et al 2000, Breitburg et al 2003, Kolesar et al 2010.When DO levels are not lethally low (reviewed by Marcus 2001, Breitburg 2002, 2009, Miller et al 2002, they can affect the predatory and escape behaviors of various animals differently and alter trophic interactions in complex ways (Breitburg et al 1997(Breitburg et al , 1999). Short-term (< 24 h) laboratory and mesocosm experiments (Breitburg et al 1994, 1997, Decker et al 2004, Kolesar et al 2010) on fish eggs, fish larvae, and copepods suggest that Mnemiopsis leidyi feeds better at low DO than Chrysaora quinquecirrha medusae and that ctenophores may be able take advantage of planktonic prey in hypoxic waters that medusae avoid (Breitburg et al 1999).…”

mentioning

confidence: 99%

Fine-scale vertical distributions of Mnemiopsis leidyi ctenophores: predation on copepods relative to stratification and hypoxia

Purcell¹,

Decker²,

Breitburg³

et al. 2014

Self Cite

Plankton concentrations near discontinuities in the water column (clines) are believed to be important for intensifying trophic interactions; however, evidence for increased feeding by predators at clines in situ is scarce. Here we demonstrate enhanced feeding near pycnoclines by a voracious planktivore, the ctenophore Mnemiopsis leidyi. To determine their feeding relative to stratification, we quantified temperature, salinity, dissolved oxygen concentration (DO), densities of ctenophores and copepods at 1 to 2 m depth intervals, and gut contents of ctenophores collected by depth layer at stations in a tributary and in the mainstem Chesapeake Bay during summer from 1999 to 2001. We tested the null hypotheses that patterns in the tributary and the bay were similar and that ctenophore vertical distributions and feeding were independent of the vertical distributions of the physical variables, stratification, and copepods. We rejected all null hypotheses. Ctenophores and copepods had peak densities below the pycnocline in the weakly stratified tributary, where DO was above 2 mg l −1 throughout the water column; by contrast, they were more concentrated above the strong pycnocline and near-anoxic waters at ~11 m in the bay. Predation on copepods by ctenophores was highest where both populations were concentrated. Our results illustrate the importance of stratification to planktonic trophic interactions for M. leidyi, which thrives in anthropogenically degraded waters and now is established throughout European seas, where it can negatively affect planktonic food webs and fisheries.KEY WORDS: Jellyfish · Aggregation · Cline · Acartia · Zooplankton · Low dissolved oxygen · Feeding · Clearance · Chesapeake Bay (USA) Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 500: [103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120] 2014 tion of organisms and enhanced feeding at clines abounds in the laboratory (e.g. Woodson & McManus 2007); however, evidence of increased feeding in situ is rare (see Möller et al. 2012).Ctenophores, medusae, and copepods are known to accumulate at density discontinuities in the water column (Arai 1992, Graham et al. 2001, Malej et al. 2007, Jacobsen & Norrbin 2009, Frost et al. 2010. Arai (1992) concluded that Sarsia tubulosa hydromedusae behaviorally aggregate at salinity discontinuities. Similarly, hydromedusae of Nemopsis bachei remain in discontinuities created by salinity gradients with and without thin layers of algae and copepods (Frost et al. 2010). Most Aurelia spp. medusae occur at clines (Rakow & Graham 2006, Malej et al. 2007. Acartia tonsa copepods also aggregate in layers ). Thus, gelatinous predators and their prey actively aggregate at density discontinuities. Although medusae and their feeding increase at clines (Frost et al. 2010), we know of no previous studies on ctenophore feeding in situ in relation to stratification.The mesohaline Chesapeake Bay (USA) and its tributaries can have ...