A Census of Zooplankton of the Global Ocean
Ann Bucklin1, Shuhei Nishida2, Sigrid Schnack‐Schiel3, Peter H. Wiebe4, Dhugal Lindsay5, Ryuji J. Machida2, Nancy J. Copley4
1Department of Marine Sciences, University of Connecticut, Groton, Connecticut, USA
2Ocean Research Institute, University of Tokyo, Tokyo, Japan
3Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
4Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
5Japan Agency for Marine‐Earth Science and Technology, Yokosuka City, Japan
The animals that drift with ocean currents throughout their lives (that is, the holozooplankton) include approximately 7,000 described species in 15 phyla. The holozooplankton assemblage is the focus of the Census of Marine Zooplankton (CMarZ; www.CMarZ.org), which has produced comprehensive new information on species diversity, distribution, abundance, biomass, and genetic diversity. Our realm among Census of Marine Life projects is the open ocean; we have sampled biodiversity hot spots throughout the world's oceans: little-known seas of Southeast Asia, deep-sea zones below 5,000 m, and polar seas. We have used traditional plankton nets and newer sensing systems deployed from ships and submersibles. Our analysis has included traditional microscopic and morphological examination, as well as molecular genetic analysis of zooplankton populations and species. CMarZ has contributed to Census legacies in data and information for the Ocean Biogeographic Information System (see Chapter 17) and proven technologies of DNA barcoding. Our photograph galleries of living plankton have captured public interest, and our training workshops have enhanced taxonomic expertise in many countries. The knowledge gained will provide a new baseline for detection of impacts of climate change, and will contribute to our fundamental understanding of biogeochemical transports, fluxes and sinks, productivity of living marine resources, and marine ecosystem health.
13.2. Historical Perspective
Despite more than a century of sampling the oceans, comprehensive understanding of zooplankton biodiversity has eluded oceanographers because of the fragility, rarity, small size, and/or systematic complexity of many taxa. For many zooplankton groups, there are long-standing and unresolved questions of species identification, systematic relationships, genetic diversity and structure, and biogeography.
There has never been a taxonomically comprehensive, global-scale summary of the current status of our knowledge of biodiversity of marine zooplankton. Although studies of the taxonomy, distribution, and abundance of zooplankton date back as far as the middle of the nineteenth century, worldwide distribution patterns have not been mapped for all described species. The cosmopolitan or circumglobal distributions characteristic of holozooplankton species of many groups have created special difficulties for accurate biodiversity assessment. The snapshots from different parts of the world ocean have rarely been merged together, in part because the complicated and time-consuming task of compiling the information from numerous individual publications is undervalued (but see Irigoien et al. 2004).
For most zooplankton groups, significant numbers of species remain to be discovered. This is especially true for fragile (for example gelatinous) forms that are difficult to sample properly and for forms living in unique and isolated habitats, such as the water surrounding hydrothermal vents and seeps (Ramirez-Llodra et al. 2007; Chapter ). All regions of the deep sea are certain to continue to yield many new species in multiple taxonomic groups. The practical difficulties of exploring these regions are gradually being overcome, and they are likely to continue to yield new species discoveries for many years.
Our perception of zooplankton biodiversity has almost certainly been affected by their small size, resulting in a marked under-description of species and morphological types. Until recently, some pelagic taxa (for example foraminifers, copepods, euphausiids, and chaetognaths) have been thought to be well known taxonomically, but the advent of molecular genetics has altered this perspective. Morphologically cryptic, but genetically distinctive, species of zooplankton are being found with increasing frequency (see, for example, Bucklin et al. 1996, 2003; de Vargas et al. 1999; Dawson & Jacobs 2001; Goetze 2003) and will probably prove to be the norm across a broad range of taxa. Many putative cosmopolitan species may comprise morphologically similar, genetically distinct sibling species, with discrete biogeographical distributions. This issue is especially relevant for widely distributed species and/or for species with disjoint distributional ranges, including those occupying coastal environments (Conway et al. 2003). It is likely that many morphologically defined zooplankton species will be found to consist of complexes of genetically distinct populations, but how many cryptic species are present is currently unknown, even for well-known zooplankton groups.
Marine zooplankton are important indicators of environmental change associated with global warming and acidification of the oceans. A global-scale baseline assessment of marine zooplankton biodiversity, including long-term monitoring and retrospective analysis, is critically needed to provide a contemporary benchmark against which future changes can be measured. Knowledge of previous and existing patterns of zooplankton distribution and diversity is useful for management of marine ecosystems and assessment of their status and health (Link et al. 2002). Marine zooplankton are also significant mediators of fluxes of carbon, nitrogen, and other critical elements in ocean biogeochemical cycles (Buitenhuis et al. 2006). Species composition of zooplankton assemblages may have strong impacts on rates of recycling and vertical export (see, for example, Gorsky & Fenaux 1998); long-term changes in fluxes into the deep sea (Smith et al. 2001) may be related to zooplankton species composition in overlying waters (Roemmich & McGowan 1995; Lavaniegos & Ohman 2003).
Compared with the dimensions of the known – in terms of numbers of species and regions of the world's oceans – the unknown is thought to be many times larger. Introducing his monograph on the biogeography of the Pacific Ocean, McGowan (1971) posed several questions that help frame the unknown territory of zooplankton biodiversity. “What species are present? What are the main patterns of species distribution and abundance? What maintains the shape of these patterns? How and why did the patterns develop?” Nearly 40 years later, the answers to these questions remain poorly known for many ocean regions and most zooplankton groups.
13.3. Approaches to the Study of Marine Zooplankton
13.3.1. Zooplankton Sampling
Zooplankton samples for CMarZ have been collected by nets, buckets, water bottles, sediment traps, light traps, remotely operated vehicles (ROVs), submersibles, and divers. Sampling strategies have trade-offs for each type of sampling gear: some may obtain numerous specimens, but under-sample fragile taxa, whereas others may be suited for collecting fragile organisms for taxonomic analysis, but may be unable to sample at spatial resolutions and scales appropriate for accurate characterization of patterns of distribution and abundance.
During CMarZ dedicated cruises in the Atlantic Ocean, zooplankton and micronekton were quantitatively sampled throughout the water column using MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System; Wiebe et al. 1985; Wiebe & Benfield 2003). In addition to collecting depth-stratified plankton samples, the MOCNESS transmits environmental data (depth, temperature, salinity, horizontal speed, and volume filtered) to the ship throughout the tow; the data are recorded for subsequent analysis. A uniquely equipped 10-meter MOCNESS allowed CMarZ to sample to 5,000 m in the Atlantic Ocean and rapidly filter large volumes (tens of thousands of cubic meters) to capture rare deep-sea zooplankton (Wiebe et al. 2010). The collections included first-ever observation of living specimens of rare deep-sea species (see, for example, Johnson et al. 2009; Bradford-Grieve 1999), and offered remarkable opportunities for photographing living specimens (Fig. 13.1) and barcoding novel species.
|Figure 13.1 Photograph gallery of living marine zooplankton. Row 1 (left to right): Valdiviella sp. and Sapphirina metalina (Copepoda); Cyphlocaris sp. (Amphipoda); row 2: Clio cuspidate (Pteropoda); Pyrosoma sp. (Thaliacea); Histioteuthis sp. (Cephalopoda); row 3: Oxygyrus keraudreni (Heteropoda); Conchoecissa plinthina (Ostracoda), Aglantha sp. (Hydrozoa); row 4: unidentified Chaetognatha with a copepod; Athorybia rosacea (Siphonophora); Lucicutia sp. (Copepoda). Photograph credits R.R. Hopcroft and C. Clarke (University of Alaska – Fairbanks) and L.P. Madin (Woods Hole Oceanographic Institution).
CMarZ has used modern in situ survey technologies, including crewed submersibles, ROVs, towed camera arrays, and visual/video plankton recorders (VPR; Davis et al. 1992) to observe and collect zooplankton, especially fragile gelatinous forms, in many areas of the ocean. These sampling approaches have led to new species discoveries (Haddock et al. 2005; Lindsay & Miyake 2007), and rapid advances in our understanding of deep sea biology and ecology (Pagès et al. 2006; Ates et al. 2007; Fujioka & Lindsay 2007; Kitamura et al. 2008a, 2008b; Lindsay et al. 2008). In 2006, Dhugal Lindsay (Japan Agency for Marine-Earth Science and Technology) led a pilot study to census gelatinous and hard-bodied zooplankton in Sagami Bay (Japan) using diverse sampling technologies, including an autonomous video plankton recorder (AVPR) with a high-definition video camera for color imagery. The study yielded images and samples of zooplankton and marine snow that are being analyzed to model and predict effects of climate change on carbon cycling and sequestration.
Blue-water SCUBA diving for observing and collecting fragile zooplankton was developed during the past 30 years (Hamner 1975), and has been used to advantage by CMarZ. A group of divers work from an inflatable boat launched from a research vessel; they are connected to a central line by a 10-meter tether line and overseen by a safety-diver. This technique has proven ideal to locate, observe, photograph, and collect live and undamaged specimens of free-swimming gelatinous animals.
A variety of remote plankton-sensing platforms (that is, those deployed from ships that return data – but not necessarily samples) has been developed for the study of zooplankton diversity, distribution, and abundance. CMarZ has used several among the many instruments developed for this purpose, including the video plankton recorder (VPR; Davis et al. 1992); underwater video profiler (UVP; Gorsky et al. 1992, 2000); optical plankton counter (OPC; Herman 1988); and continuous plankton recorder (CPR; Hardy 1926; Glover 1962). In general, these systems provide higher spatial resolution than nets and more accurate depiction of the animal in its environment (Mori & Lindsay 2008). For those species that can be remotely identified, these instruments are valuable tools in describing the geographical and temporal changes in zooplankton populations in relation to behavior and the environment.
To census the world's oceans, CMarZ has used ships of opportunity to sample zooplankton in open-ocean waters and areas not regularly frequented by large research vessels. Ships of opportunity have deployed ROVs and crewed submersibles, which usually require large ocean-going vessels for their deployment, in studies in Monterey Bay, California (Matsumoto et al. 2003; Raskoff & Matsumoto 2004) and off the coast of Japan (Lindsay et al. 2004, 2008; Kitamura et al. 2005; Lindsay & Hunt 2005; Lindsay & Miyake 2009). In particular, the Plankton Investigatory Collaborative Autonomous Survey System Operon (PICASSO) ROV system was designed for deployment from ships of opportunity to study gelatinous plankton as deep as 1,000 m (Yoshida et al. 2007a, 2007b; Yoshida & Lindsay 2007).
13.3.2. Sample Preservation
Zooplankton samples for CMarZ have been processed as bulk unsorted samples, especially during cruises of opportunity, and as individual expertly identified specimens, usually during dedicated CMarZ surveys. No single sampling-handling approach can preserve the appearance and morphological, molecular, and biochemical properties of zooplankton specimens. CMarZ developed and has used a sample-splitting protocol that entails immediate bulk processing of a portion of the sample (partly in formalin for morphological analysis and partly in alcohol for molecular analysis), with another portion retained alive for photography, observation, and identification of living specimens, some of which may not be suitable for eventual preservation. Splitting is not recommended for samples with few individuals or rare species, but may in other cases optimize sample use among scientists. Samples for molecular analysis were preserved in 95% non-denatured ethanol or buffer solution (for example RNAlater) and then stored at low temperatures (–20 °C) to slow degradation. Identified specimens were flash-frozen in individual vials in liquid nitrogen. Overall, best results were obtained when DNA extractions were done very soon after collection.
13.3.3. Sample Analysis
An essential element of CMarZ has been traditional morphological examination of samples by taxonomic experts, who are essential to validate species identifications for uncertain and possible new species, examine and confirm putative new or cryptic species, and describe new species. Such skills are the domain of a very few specialists worldwide and are a diminishing resource. The lack of manpower – both expert and technical – has been a bottleneck for CMarZ in our progress toward our goal of a global, taxonomically comprehensive biodiversity census.
Consequently, CMarZ has championed integrated morphological and molecular genetic approaches to analysis of zooplankton species’ diversity. A revolution in the analysis of global patterns of species diversity has been driven by the widespread use of DNA barcodes (that is, short DNA sequence used for species recognition and discrimination; Hebert et al. 2003). The usual barcode gene region for metazoan animals is a 708 base-pair region of mitochondrial cytochrome oxidase I, mtCOI (Schindel & Miller 2005). CMarZ barcoding efforts have included analysis of both targeted taxonomic groups and particular ocean regions or domains. Five CMarZ barcoding centers (at the University of Connecticut, USA; Ocean Research Institute, Japan; Institute of Oceanology, China; Alfred Wegener Institute, Germany; and National Institute of Oceanography, India) have worked together toward a shared goal of determining DNA barcodes for the approximately 7,000 described species of zooplankton. CMarZ has also uniquely demonstrated the use of off-the-shelf automated DNA sequencers in ship-board molecular laboratories, allowing a continuous at-sea analytical “assembly line” from collection, identification, and DNA barcoding.
Environmental DNA surveys (that is, determination of sequences for 16S or 16S-like rRNA coding regions from mixed environmental samples) have transformed our understanding of microbial diversity in the oceans (Pace 1997; Sogin et al. 2006). CMarZ has applied this revolutionary approach to the analysis of zooplankton species diversity based upon COI barcodes, using an approach dubbed environmental barcoding (that is, DNA sequencing of the COI barcode region from unsorted bulk samples). This approach has the marked advantage of not requiring morphologically based species identification. For zooplankton, environmental barcoding entails comparison of the resultant DNA sequences with “gold standard” DNA barcode data to identify species and characterize species diversity (Machida et al. 2009).
13.3.4. Data and Information Management
CMarZ uses a centralized distributed data and information management system, an outgrowth of the US GLOBEC Data and Information Management System (Groman & Wiebe 1998; Groman et al. 2008), which integrates among three primary data centers: Woods Hole Oceanographic Institution (Woods Hole, USA), Ocean Research Institute (Tokyo, Japan), and Alfred Wegener Institute (Bremerhaven, Germany). The ready and open exchange of information helps ensure that CMarZ project participants can coordinate and avoid duplication of effort, and thus speed progress toward the goal of a comprehensive and complete DNA barcode database for zooplankton.
13.4. Results from CMarZ
13.4.1. Toward a Global View of Pelagic Biodiversity
Compared with the approximately 1 million described terrestrial insects and more than 1 million benthic marine organisms, the diversity of marine zooplankton, with about 7,000 species, is by no means rich. A unique attribute of this assemblage is the relative magnitude of local diversity to global diversity (Angel et al. 1997). As an example, the Copepoda – the most species-rich group of marine zooplankton – are very common and species are frequently very abundant. One net sample from oceanic waters may contain hundreds of copepod species or about 10% of the global total of approximately 2,200 species. This ratio is nearly unique among animal groups and habitats. Low global diversity has been attributed to the homogenous and unstructured pelagic environment compared with terrestrial, intertidal, or benthic habitats. High local diversity has been attributed to the coexistence of many species, through vertical or other modes of niche partitioning, but the exact mechanism for their co-existence is still poorly understood (Lindsay & Hunt 2005; Kuriyama & Nishida 2006). Recently, the contribution of biological associations toward the enhancement of species diversity has been attracting much attention (Pagès et al. 2007; Lindsay & Takeuchi 2008; Ohtsuka et al. 2009).
Since 2004, CMarZ has completed more than 90 cruises, and samples for CMarZ have been collected at more than 12,000 stations; an additional 6,500 archived samples have been available for analysis. CMarZ has sampled from every ocean basin (Fig. 13.2). For selected groups of zooplankton, CMarZ has made excellent progress toward a new global view of biodiversity. Although zooplankton are not as prevalent as microbes, for which an “everything is everywhere” debate continues (see, for example, Patterson 2009), species with circumglobal distributions are found in every phylum of the zooplankton assemblage from Protista to Chordata. Such broadly distributed species have been a focus of particular attention for CMarZ. The global biogeography of planktonic Foraminifera has been mapped by Colomban de Vargas (CNRS, France), based upon integrated morphological and molecular systematic analysis (de Vargas et al. 2002; Morarda et al. 2009). Demetrio Boltovskoy (University of Buenos Aires, Argentina) has produced an atlas of Radiolaria (Polycystina) distributions based upon 6,719 samples that reveals relations between radiolarian distributions and worldwide water mass and circulation patterns (Boltovskoy et al. 2003, 2005). CMarZ contributed to production of a monograph on the known genera of Hydrozoa in the world ocean (Bouillon et al. 2006). Analysis of global patterns of copepod diversity and abundance is being performed by Sigrid Schnack-Schiel (Alfred Wegener Institute, Germany), who is comparing regional patterns in tropical, temperate, and polar seas; in all regions, more than 50% of all species occur in low abundances (not more than 10 individuals per 100 cubic meters); in Antarctic waters, more than 80% of species are rare (Fig. 13.3).
|Figure 13.3 Comparisons for tropical, temperate, and polar regions of patterns of Copepoda species diversity and abundance for two ocean depth strata: (A) surface to 300 m and (B) surface to 1,000 m. Regions shown top and bottom are as follows: Trans, Polarstern Transect 2002 (temperate Atlantic); MS, Meteor Seamount 1998 (subtropical North Atlantic); GA/RS, Gulf of Aqaba, Red Sea 1999 (tropical); Ant, Weddell Sea and Bellingshausen Sea, Antarctica (polar); Mag, Magellan Strait (sub-polar South Atlantic).
CMarZ has also contributed to new understanding of ocean-basin scale patterns of species diversity through monographic treatments of selected zooplankton groups. Notable among these are analyses of planktonic Ostracoda of the Atlantic Ocean (Angel et al. 2007; Angel 2008; Angel & Blachowiak-Samolyk 2009; Angel 2010). Also, Vijayalakshmi Nair (National Institute of Oceanography, India) has advanced understanding of species diversity of the Chaetognatha, a taxonomically challenging group, in the Indian Ocean (Nair et al. 2008) and, working with Annelies Pierrot-Bults (University of Amsterdam, The Netherlands), in the Atlantic Ocean. Gelatinous zooplankton diversity patterns have been found to differ between the Pacific Ocean and Japan Sea sides of Japan (Lindsay & Hunt 2005), including unique investigations of ctenophores and other fragile gelatinous zooplankton using submersibles below 2,000 m (Lindsay 2006; Lindsay & Miyake 2007). An in-depth study on the gelatinous fauna of the Gulf of Maine was published by Pagès et al. (2006). Also, checklists and field guides have been produced to aid in species identification of gelatinous plankton for Japanese waters (Lindsay 2006; Kitamura et al. 2008a, 2008b; Lindsay & Miyake 2009); for waters off California (Mills et al. 2007; Mills & Haddock 2007); and for the Mediterranean (Bouillon et al. 2004).
13.4.2. Biodiversity Hot Spots
Sampling within regions and/or for taxa that have historically been ignored or understudied has been a key objective of CMarZ. Our efforts have been focused on biodiversity hot spots (that is, geographic or taxonomic domains for which there is greatest scope for improved knowledge of species richness), which may be specific areas of the ocean, taxonomic groups, or ecological guilds. Marine ecologists and oceanographers must identify and prioritize such regions, similar to terrestrial ecologists, who have identified 18 biodiversity hot spots based primarily on degree of endemism and impacts of human activities (Wilson 1999).
Among the numerous acknowledged biodiversity hot spots for marine zooplankton, CMarZ has focused on diversity in the deep sea, polar seas, and coastal regions and marginal seas of Southeast Asia. Our taxonomic targets have included gelatinous groups and other taxonomically challenging and under-appreciated groups throughout the zooplankton assemblage. The CMarZ focus on geographic and taxonomic areas with high potential for species discovery has resulted in discoveries of 89 new species, of which 52 have been formally described (Table 13.1).
18.104.22.168. Southeast Asian Coastal Waters and Marginal Seas
Comprehensive research has been conducted in the embayed waters, coastal areas, and marginal seas of Southeast Asia. This is a major biodiversity hot spot in the world and has a very complicated geography and geological history. New species discoveries here have been dominated by copepods (including Pseudodiaptomus, Tortanus (Atortus), and species of the families Pontellidae and Pseudocyclopidae) and mysids collected using sledge nets from coastal near-bottom habitats and by night-time or SCUBA sampling in coral reefs, indicating that the high diversity of these habitats has been overlooked by conventional daytime net sampling (see, for example, Nishida & Cho 2005; Murano & Fukuoka 2008). The Sulu Sea, a semi-enclosed marginal sea in the tropical Western Pacific Ocean, has been a particular focus for CMarZ studies (Nishikawa et al. 2007) and has yielded several discoveries of new species and genera, including copepods (Ohtsuka et al. 2005).
Species discoveries by CMarZ within the Copepoda have added another 8% to the total number of copepod species in Southeast Asia (another 2% to the global total), and new species discoveries of Mysidacea in Southeast Asia have added 15% to the global total for that group. Understanding the significance of these numbers must also take into account the ecological importance of the species and their role in the ecosystem. Regardless, CMarZ has made exceptional progress in improving our knowledge of zooplankton biodiversity in Southeast Asia by building effective teams of expert taxonomists who collaborate with CMarZ scientists.
22.214.171.124. The Deep Sea
By volume, 88% of the ocean environment is deeper than 1 km and 76% is between a depth of 3 and 6 km (Table 13.2; Menard & Smith 1966; Hering 2002). The deep sea is thus the largest habitat on earth – and also the one least known. Previous studies have yielded several general characteristics of pattern of zooplankton diversity, distribution, and abundance in the deep sea. A primary finding is that numbers of species and their abundances tend to decrease with depth (Longhurst 1995). The decrease in number of species is not linear; there is a peak in mid-water layers and a decrease with greater depth (Fig. 13.4). However, better sampling in the deep sea and discovery of new species at depth may alter this trend. Latitude affects this general trend, with higher numbers of species at all depths in lower latitudes than at higher latitudes (Angel 2003). Other general trends are that deeper-dwelling species are less likely to be endemic (that is, native and restricted to a particular region) and more likely to be geographically widespread. Usual feeding mode varies through the depth strata, with filter-feeding herbivorous species occurring in the upper water layers, and detritivores and carnivores most abundant below the light-filled surface waters.
|Figure 13.4 Vertical profiles of abundance (A) and numbers (B) of calanoid Copepoda species in different geographical regions during summer (excluding the benthopelagic zone). Abbreviations are as follows: Meteor Seamount (MS), Eastern Weddell Sea (EWS), Lomonosov Ridge (LR), Canada Basin (CB). Arctic data from Kosobokova ( 1989) and Kosobokova & Hirche ( 2000); Antarctic data from S. Schnack-Schiel (unpublished data).
Exploration and discovery in the deep sea have been slowed by the inherent difficulties of sampling at great depths. Deeper than 1,500 m in most ocean areas, the very low abundances of most species requires that huge volumes of water be filtered, with sampling over many hours using huge sampling systems deployed from large ships, to collect significant numbers of individuals. Despite these challenges, many new deep-sea species have been discovered in the past decade, strongly indicating that deep-sea biodiversity has so far been markedly underestimated.
CMarZ’ unique approach to sampling deep-sea zooplankton using a 10-meter MOCNESS with fine mesh nets has yielded many discoveries and first-time observations of living specimens. During two CMarZ cruises using this gear to explore the deep tropical/subtropical Atlantic Ocean regions (that is, the Sargasso Sea on the R/V RH Brown in 2006, and the eastern Atlantic on the FS Polarstern in 2007), zooplankton were collected from the entire water column with a focus on describing species composition and richness and discovering new species in the poorly known meso- and bathypelagic zones. The Sargasso Sea cruise yielded a treasure-trove of specimens, including Ctenophora (22 species), Cnidaria (110 species), Ostracoda (58 of 140 known Atlantic species), Copepoda (134 species), euthecosome pteropod Mollusca (20 of approximately 33 species), heteropod Mollusca (17 of 29 species), Cephalopoda (13 species), and Appendicularia (13 of approximately 70 species). In addition, 3,965 fish specimens were collected, including 127 species of 84 genera from 42 families. Below 1,000 m depth, the MOCNESS-10 collected several little-known species, including the siphonophores Nectadamas richardi (Pugh 1992) and Lensia quadriculata (Pagès et al. 2006).
During the eastern Atlantic cruise, more than 1,000,000 cubic meters of seawater was filtered and approximately 60,000 specimens were identified. In some cases, collections represented a significant fraction of the species known from the South Atlantic; 104 copepod species were identified of an estimated total of 500 species known (Bradford-Grieve et al. 1999). A sample from the bathypelagic captured a putative new copepod species, the third to be described from the family Hyperbionychidae (Bradford-Grieve 2010). From the two CMarZ deep-sea Atlantic cruises, at least 15 novel ostracod species were discovered and are in process of description (Martin Angel, unpublished data).
In recent years, CMarZ’ use of in situ sampling and observation from submersibles and ROVs has dramatically improved our understanding of deep-sea biodiversity, biology, and ecology. Laurence P. Madin (Woods Hole Oceanographic Institution, USA) led a CMarZ exploration to the Celebes Sea, a tropical sea and biodiversity hot spot in the Indonesia/New Guinea/Philippine triangle between the Pacific and Indian Oceans. Sampling was performed by blue-water diving and net systems; deep-sea observations to 3,000 m used a Global Explorer ROV with high-definition television and benthic-baited video “Ropecams”. The team discovered that the overall biomass of the water column was high, with exceptional abundance of the nitrogen fixing, blue-green bacteria Trichodesmium. Sperm whales and spinner dolphins were observed at the surface, squid were seen from the ROV, and myctophid fishes were collected in the trawl. Ten of 23 known worldwide species of Salpidae, a group of gelatinous zooplankton, were collected by blue-water divers. Two species thought to be new to science were observed: a black, benthopelagic lobate ctenophore and a large pelagic polychaete worm with ten long cephalic tentacles.
Further CMarZ deep-sea exploration using ROVs and submersibles uncovered a cascade of biological associations of the deep-sea hydromedusan, Pandea rubra, which is dependent upon a pteropod mollusk for the polyp stage of its life cycle (Lindsay et al. 2008). Ocean acidification is thought to be detrimental to calcareous shell-bearing Mollusca, and the newly discovered linkage between these species may represent a threat to the medusa. Pandea rubra was found to host many other species during its deep-sea medusa stage, including Pycnogonida (sea spiders) (Pagès et al. 2007), hyperiid Amphipoda, and larval stages of other hydromedusae (Lindsay et al. 2008). Invaluable archived video from the 11,000 m ROV Kaiko revealed what appeared to be a new order of Ctenophora in the Ryukyu Trench (Japan); a comb jelly was observed floating above and attached by “strings” to the sea floor at a depth of 7,217 m (Lindsay & Miyake 2007).
126.96.36.199. Polar Seas
As a general rule across pelagic groups, species diversity is lower at high latitudes than at low latitudes (see Chapters 10 and 11). Although the explanation for this remains unclear, low temperature and dramatic seasonal shifts in light levels and sea ice cover – and thus primary production – surely represent significant challenges to survival. Although the most characteristic feature of polar seas is sea ice, early studies of polar zooplankton were largely restricted to ice-free areas and summer months. This has severely limited our understanding of polar ecosystems, because the sea ice environment is a unique environment harboring a diverse fauna (Bluhm et al. 2010) and plays a vital role in ecosystem dynamics of both polar oceans (see, for example, Schnack-Schiel 2001; Arndt & Swadling 2006; Kiko et al. 2008; Schnack-Schiel et al. 2008).
In the Antarctic, where sea ice is predominantly seasonal, the Southern Ocean krill (Euphausia superba) is the keystone species and inhabits the seasonal pack-ice zone of Antarctic Coastal Current (Atkinson et al. 2004; Siegel 2005). Copepoda are dominant in many Antarctic regions in terms of both biomass and abundance, with few large species (for example Calanus propinquus, Calanoides acutus) making up more than 40% of total copepod biomass, and frequently neglected smaller species (for example Oithona, Oncaea, Microcalanus, Ctenocalanus, and others) accounting for more than 80% of total copepod abundance (Kosobokova & Hirche 2000; Hopcroft & Robison 2005; Schnack-Schiel et al. 2008). Park & Ferrari ( 2008) reported a total of 205 calanoid copepod species from the Southern Ocean: 184 species (of which 50 are endemic) were restricted to deep waters, 13 species (8 endemic) were epipelagic, and 8 species (all endemic) were neritic.
The Arctic Ocean is unique owing to its permanent and seasonal ice cover, and restricted exchange of deep-water biota with the Pacific and Atlantic Oceans (see, for example, Carmack & Wassmann 2006). Extreme environmental conditions and limited exchange with the adjacent ocean regions have resulted in a zooplankton assemblage comprising species endemic to the Arctic Ocean and uniquely adapted to cold temperatures (Smith & Schnack-Schiel 1990; Kosobokova & Hirche 2000; Deibel & Daly 2007). Approximately 300 species of holozooplankton have been recorded for the Arctic (Sirenko 2001). The greatest diversity occurs within the Copepoda (approximately 150 species), which dominate the zooplankton community in both abundance and biomass (Kosobokova & Hopcroft 2009). Four large calanoid species (Calanus glacialis, C. hyperboreus, C. finmarchicus, and Metridia longa) are by far the most dominant species, contributing 60–70% of total zooplankton biomass (see, for example, Kosobokova et al. 1998; Kosobokova & Hirche 2000). Cnidaria are represented by approximately 50 species, mostly hydromedusae; mysids contribute approximately 30 species, most of which are epibenthic. Other groups are each represented by fewer than a dozen described species.
188.8.131.52. Gelatinous Zooplankton
Special attention has been paid to the biodiversity of gelatinous plankton as a hot spot for species discovery. Discoveries of novel Cnidaria and Ctenophora species have resulted (Kitamura et al. 2005; Fuentes & Pagès 2006; Pagès et al. 2006; Hosia & Pagès 2007), some requiring the establishment of new higher taxonomic groups (Lindsay & Miyake 2007). This work has also allowed comparisons among regional faunas in light of geological history and environmental conditions, and revealed novel relationships among gelatinous plankton and other organisms (Ates et al. 2007; Pagès et al. 2007; Lindsay & Takeuchi 2008; Ohtsuka et al. 2009).
13.4.3. DNA Barcoding
CMarZ has championed integrated morphological and molecular genetic approaches to analysis of zooplankton species’ diversity (see, for example, Lindeque et al. 2006; Ueda & Bucklin 2006; Bucklin et al. 2007; Bucklin & Frost 2009; Goetze & Ohman 2010; Jennings et al. 2010a). Importantly, CMarZ has placed a high priority on “gold-standard” barcoding (that is, determination of a 500+ base-pair DNA sequence for mtCOI for an identified vouchered specimen, with specified metadata for protocols and collections) for described species of zooplankton. The growing CMarZ barcode database – now approaching 2,000 species or about 30% of the approximately 7,000 described species – will serve as a “Rosetta Stone” for species identification of marine zooplankton, linking species names, morphology, and DNA sequence variation. DNA barcodes will thus facilitate rapid characterization of patterns of species diversity and distribution in the pelagic realm.
Taxon-specific barcoding efforts by CMarZ researchers have included analysis of every phylum and taxonomic group within the zooplankton assemblage, including Protista (Morarda et al. 2009); Cnidaria (Ortman 2008; Ortman et al. 2010), calanoid Copepoda (Machida et al. 2006), Euphausiacea (Bucklin et al. 2007), Ostracoda (Angel et al. 2008), pteropod Mollusca (Jennings et al. 2010a), Chaetognatha (Jennings et al. 2010b), among other groups. These studies have demonstrated the usefulness of DNA barcodes for identification of known species, discovery of new species, and recognition of cryptic species within widespread or poorly known taxa. Alternatively, CMarZ barcoding campaigns have had a regional focus, with barcoding of all identified specimens collected from a particular ocean region or during a survey cruise. CMarZ has regionally focused barcoding efforts either completed or ongoing in the Arctic Ocean (Bucklin et al. 2010a), Sargasso Sea (Bucklin et al. 2010b), Eastern Atlantic and the Bay of Biscay, and South China Sea.
DNA barcodes have been used to characterize large-scale patterns of population genetic diversity and structure (that is, the amount and distribution of genetic variance within and among natural populations of organisms). Global-scale sampling and molecular analysis of zooplankton has revealed geographically distinct and genetically differentiated populations of Copepoda (Blanco-Bercial et al. 2009; Machida & Nishida 2010); Euphausiacea (Bucklin et al. 2007); and Chaetognatha (Peijnenburg et al. 2004; Miyamoto et al. 2010). Although geographic populations of zooplankton are not reproductively isolated, they are important units of evolution; studies of population genetic diversity and structure, using the barcoding gene region of choice, have been a critical aspect of the CMarZ global biodiversity assessment.
CMarZ has uniquely demonstrated the feasibility and value of performing DNA barcoding at sea during oceanographic research cruises. During two CMarZ biodiversity surveys to the Sargasso Sea and the Eastern Atlantic, DNA extraction, polymerase chain reaction (PCR), and DNA sequencing were performed in shipboard barcoding laboratories. Hundreds of species were barcoded, based on specimens identified by the taxonomic experts also participating in the cruise. During the Sargasso Sea cruise, 329 DNA barcodes were determined for 191 holozooplankton species, including hydrozoans, crustaceans, chaetognaths, and mollusks; barcodes were determined for an additional 35 fish species (Bucklin et al. 2010b).
CMarZ has pioneered the use of environmental barcoding for zooplankton communities: Machida et al. (2009) sequenced the COI barcode from an unsorted bulk sample collected in the western equatorial Pacific Ocean, detected 189 species of zooplankton based on COI sequences, and demonstrated the usefulness of this powerful approach to estimating species diversity of metazoan animals (Fig. 13.5).
As the DNA barcode database has grown to include described species collected from diverse ocean regions, CMarZ has explored new approaches for computationally efficient analysis and useful presentation of DNA sequence data and results. A novel approach is vector analysis (Sirovich et al. 2009), scalable analysis for very large datasets that produces heuristic displays of barcode similarity called heat maps or – because of their resemblance to modern art – “Klee diagrams” (Fig. 13.6).
|Figure 13.6 Results of vector analysis shown as a heat map or “Klee diagram” for 329 DNA barcodes for 191 zooplankton species collected from the Sargasso Sea, Northwest Atlantic Ocean, during a CMarZ cruise on the R/V RH Brown in April 2006. The vector analysis method is from Sirovich et al. ( 2009). Analysis includes species of diverse zooplankton groups, including Cnidaria (Hydrozoa, 54 species); Crustacea (Amphipoda, 8; Copepoda, 38; Euphausiacea, 10; Ostracoda, 33; other Crustacea, 11); Chaetognatha (5); and Mollusca (Cephalopoda, 12; Gastropoda, 21), as well as fish (Osteichthyes, 35).
13.4.4. Patterns of Historical Change
Time-series observations and monitoring programs that span many years are needed to document long-term changes in zooplankton diversity, distribution, abundance, and biomass in ocean ecosystems (Perry et al. 2004). CMarZ has sought to embed our field activities in the context of such valuable programs in order to provide benchmark biodiversity information for the analysis of temporal changes associated with global climate change.
184.108.40.206. Northeast Atlantic Ocean, UK
Since 1946, the Continuous Plankton Recorder (CPR) Survey Program (Sir Alister Hardy Foundation for Ocean Science, UK) has sought to characterize and understand changes in the species composition of North Atlantic zooplankton. Approximately 2.5 million non-zero records have indicated that zooplankton biomass has declined below the long-term average. In the North Sea, present biomass levels are one-half those in 1960 and warm-water species (for example the copepod Calanus helgolandicus) are displacing cold-water species (for example C. finmarchicus). This change affects the survival of fish larvae that depend on C. finmarchicus and has far-reaching consequences for the ecosystem (Beaugrand et al. 2002; Edwards et al. 2007). Another finding from analysis of CPR data is evidence of seasonal shifts in spawning and other life-history processes related to climate warming, creating mismatch between fish larvae and their food (Edwards & Richardson 2004; Edwards et al. 2008) and resulting in low fish recruitment. CPR surveys are beginning to document trans-Arctic migrations, with unknown consequences for pelagic communities (Edwards et al. 2008). CPR data have revealed what are called “regime shifts” (that is, markedly increased diversity and decreased productivity of zooplankton) in the North Sea (Edwards et al. 2007), as well as the Northwest Atlantic, Northeast Pacific, and Northwest Pacific Oceans (Kane & Green 1990; Pershing et al. 2005; Kane 2007; Mackas et al. 2007; Tian et al. 2008).
220.127.116.11. Northwest Atlantic Ocean, USA
A 40-year survey by the US National Marine Fisheries Service (NMFS) has used the CPR (Jossi & Goulet 1993) to correlate effects on zooplankton populations with decadal-scale forcing by the North Atlantic Oscillation (Greene & Pershing 2000; Conversi et al. 2001; Piontkovski et al. 2006; Turner et al. 2006). Analysis of data and samples collected during 1977–2004 by NMFS’ Marine Resources Monitoring, Assessment and Prediction (MARMAP) program (Jossi & Kane 2000; Kane 2007), demonstrated that total zooplankton counts over Georges Bank were at or above long-term average levels between 1989 and 2004 (Kane & Green 1990; Kane 2007). This regime shift was also observed in CPR records from the Gulf of Maine, which showed an increase in smaller-sized species (Pershing et al. 2005; Greene & Pershing 2007). The US GLOBEC Northwest Atlantic Program/Georges Bank Study examined zooplankton dynamics during 1994–1999, and provided one of the most comprehensive species datasets available for an historical fishing ground (Wiebe et al. 2002). Since 2004, NMFS has provided samples to CMarZ from quarterly ecosystem monitoring surveys over the Northwest Atlantic continental shelf; these samples are being used to barcode 200 of the most abundant zooplankton species, with a goal of allowing rapid DNA-based biodiversity assessments for fisheries management in this area.
18.104.22.168. Benguela Current, South Africa
Zooplankton diversity and biomass have been recorded for the Benguela Current, west of South Africa, since 1951. In contrast to most Eastern Boundary Currents, numerical abundances have increased 100-fold over recent decades. Species composition has shifted, with smaller-bodied Copepoda and Cladocera now dominating in the region, perhaps because of the combined effects of changes in climate, circulation patterns, and predator dynamics (Verheye & Richardson 1998; Verheye 2000).
22.214.171.124. California Current, USA
The California Cooperative Oceanic Fisheries Investigations (CalCoFI) is a 60-year time-series of quarterly surveys off southern and central California. No long-term trend was detectable in total zooplankton carbon biomass, although zooplankton displacement volume has declined in both regions, likely due to declines in salp abundances (which are mostly water and contribute little to carbon biomass; Lavaniegos & Ohman 2007). Zooplankton biomass varied among areas along the coast (Fernandez-Alamo & Färber-Lorda 2006). The time-series showed a marked shift from a “warm” regime with low zooplankton biomass and high sardine populations to a “cool” regime with high zooplankton biomass and high anchovy populations.
126.96.36.199. Western Pacific, Japan
The Odate collection at the Tohoku National Fisheries Research Institute (Japan) contains 20,000 formalin-preserved zooplankton samples collected throughout the western North Pacific from 1950 to 1990. Analysis of this extensive collection revealed decadal oscillations in copepod diversity and abundance. Compared with all other decades, the late 1980s showed a climatic regime shift: the copepod Metridia pacifica was dominant, whereas the abundance of Neocalanus plumchrus was low (Sugisaki 2006; Tian et al. 2008).
188.8.131.52. Indian Ocean, India
The International Indian Ocean Expedition (IIOE), carried out during 1962–1965, was the most intensive sampling program to characterize zooplankton species diversity and abundance in the region. Digitization and analysis of the IIOE data by CMarZ scientists have characterized seasonal variability associated with monsoon conditions and revealed long-term trends in species abundances and biogeographical distributions (Nair et al. 2008; Nair & Gireesh 2010). The data and results from IIOE represent an invaluable resource for detecting seasonal, interannual, and long-term shifts in the zooplankton assemblage (Baars 1999).
184.108.40.206. Marginal Seas
In the Caspian Sea, the invasive comb jelly Mnemiopsis leidyi has severely impacted the entire ecosystem since its introduction in the late 1990s (Kideys et al. 2005, 2008). In the Black Sea, 130 years of plankton records (1870–2000) documented a long-term increase in the diversity of tintinnid Ciliata until 1960, followed by a decline into the 1990s. Ctenophore blooms in the 1990s may have impacted the anchovy fishery by causing replacements of copepod species (Gavrilova & Dolan 2007) and generating a trophic cascade with disastrous consequences for the ecosystem (Kideys et al. 2005).
220.127.116.11. Arctic Ocean
Changes in zooplankton species diversity, distribution, and abundance can be expected to occur in the Arctic Ocean, as climate change alters water temperature and thus timing and magnitude of productivity cycles (Grebmeier et al. 2006; Bluhm & Gradinger 2008). The introduction of exotic species through increased commercial traffic and the establishment of expatriate species from adjoining regions with warming are likely for the Arctic Ocean in the near future (Acia 2004). Comparisons of zooplankton abundances in recent years with the early 1950s suggest that some taxa were more abundant in the Chukchi and Beaufort shelf and slope regions and the Canada Basin in 2002 than about 50 years ago (Grebmeier et al. 2006).
13.5. Significance and Impacts
13.5.1. Taxonomic Training
CMarZ has enhanced research capacity in marine biodiversity and zooplankton ecology through the training of graduate students by CMarZ scientists and through international exchanges of students, staff, and researchers among CMarZ laboratories. CMarZ has placed a high priority on training new zooplankton taxonomists, with a total of 252 participants for 27 Taxonomic Training Workshops during 2004–2009. Many students have joined the CMarZ Network, which now includes more than 150 members, to seek information and access to expertise to facilitate their research. CMarZ has sought to enhance capacity for taxonomic analysis of zooplankton through both traditional morphological and molecular systematic analysis.
13.5.2. Applications of CMarZ Results
CMarZ’ efforts toward a global assessment of marine zooplankton biodiversity, focusing on geographic and taxonomic hot spots, will provide a benchmark baseline biodiversity assessment for measurement of future changes resulting from climate change or other anthropogenic or natural variation. Zooplankton diversity can also be used as a measure of the health of marine ecosystems, and knowledge of prior and existing patterns of zooplankton distribution and diversity is needed for the management of coastal marine ecosystems (Link et al. 2002). Zooplankton are pivotal players in the dynamics of marine ecosystems, and new knowledge is needed of their roles in biogeochemical cycles (Buitenhuis et al. 2006).
CMarZ’ barcode database, protocols for barcoding diverse marine phyla, and techniques for environmental sequencing of zooplankton will be useful in accelerating analysis of zooplankton diversity and distribution for a variety of applications in ocean research, management, and conservation. DNA barcodes will be used to produce DNA microarray “chips” for automated and/or remote identification and quantification of zooplankton. In the not-too-distant future, ocean-observing stations may include moored instruments with DNA-based detection systems for in situ species identification. These same approaches may allow rapid and accurate species identification for ecosystem monitoring and fisheries management, detection of invasive species in ballast water, and other possibilities central to ocean observing, management, and regulation.
13.6. Challenges and Opportunities for the Future
The question of how many species are present still remains, and future studies will continue to challenge our understanding of diversity. Large-scale studies of zooplankton are needed to evaluate patterns of biodiversity at scales appropriate to dispersal ability in ocean currents. Shifts in geographic ranges may underlie apparent temporal changes observed during spatially limited studies. In the case of species introductions, clear definition of potential source populations and likely colonization pathways require an understanding of global-scale distributions. For some cosmopolitan species, there may be little genuine endemism, whereas others may consist of complexes of genetically distinct entities, representing geographically isolated populations or cryptic species.
There remain large gaps in the sampling coverage done by CMarZ, especially in the deep sea and under-sampled ocean regions. Despite the increase of deep-sea studies, these investigations still represent rare snapshots of this huge habitat and vast areas of the deep sea remain unexplored. Despite new capabilities of ice-breaking research vessels, our understanding of polar ecosystems during the dark season remains fragmentary. Despite our efforts, CMarZ has only performed limited sampling in the Central Pacific Ocean, obtaining some samples from ships of opportunity (for example sailing ships associated with the Sea Education Association, Woods Hole, USA). Comprehensive sampling in the Indian and tropical Pacific Oceans has not yet extended below a few hundred meters. The richly diverse benthopelagic communities have received almost no attention because of sampling difficulties.
The urgency and/or vulnerability of regions or taxa to anthropogenic or natural threats must be weighed in determining future research priorities. These include regions where rates and impacts of climate change are most likely to be amplified, and poorly studied areas threatened by anthropogenic inputs (such as near population centers in emerging nations). The availability of baseline data is a critical issue, because evaluation of biodiversity patterns and hot spots requires improved knowledge of existing data and trends. Sites where time-series collections or long-term monitoring studies have been done are of high priority for continued assessment.
An essential feature for continued progress toward a global zooplankton census will be an international partnership, ideally coordinated through a network of regional centers that can identify opportunities for cooperative field work, arrange sampling from ships of opportunity, and lead efforts to secure funding for dedicated cruises. Interdisciplinary collaborations – among oceanographers, ecologists, taxonomists, geneticists, geochemists, and others – will continue to be needed to answer increasingly complex questions and address increasingly critical issues about the future and health of the global ocean. Knowledge of the species diversity, distribution, and abundance of the zooplankton assemblage will continue to be a critical element for monitoring, understanding, and predicting the complex global system.
The effort, enthusiasm, and expertise of the CMarZ Steering Group members are the basis of the results reported here. We acknowledge the many contributions by the CMarZ Steering Group members who are not listed as authors herein. They are the following: Martin Angel (National Oceanography Centre, UK); Demetrio Boltovskoy (Universidad de Buenos Aires, Argentina); Janet M. Bradford-Grieve (NIWA, New Zealand); Rubén Escribano (Universidad de Concepción, Chile); Erica Goetze (University of Hawaii, USA); Steven Haddock (Monterey Bay Aquarium Research Institute, USA); Steve Hay (Fisheries Research Services Marine Laboratory, UK); Russell R. Hopcroft (University of Alaska – Fairbanks, USA); Ahmet Kideys (Institute of Marine Sciences, Turkey); Laurence P. Madin (Woods Hole Oceanographic Institution, USA); Webjørn Melle (Institute of Marine Research, Norway); Vijayalakshmi R. Nair (National Institute of Oceanography, India); Mark Ohman (Scripps Institution of Oceanography, USA); Francesc Pagés (deceased) (Institute of Marine Sciences, Barcelona, Spain); Annelies C. Pierrot-Bults (University of Amsterdam, The Netherlands); Philip C. Reid (Sir Alister Hardy Foundation for Ocean Science, UK); Song Sun (Institute of Oceanology, Chinese Academy of Sciences, China); Erik V. Thuesen (The Evergreen State College, USA); Colomban de Vargas (Roscoff Marine Station, France); Hans M. Verheye (Marine & Coastal Management, South Africa). We acknowledge the support of the Alfred P. Sloan Foundation. This study is a contribution from the Census of Marine Zooplankton (CMarZ; www.CMarZ.org), an ocean realm field project of the Census of Marine Life.
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