J. Frederick Grassle

DEEP-SEA SPECIES RICHNESS: REGIONAL AND LOCAL DIVERSITY ESTIMATES FROM QUANTITATIVE BOTTOM SAMPLES

The deep-sea communities of the continental slope and rise off the eastern coast of the United States have a remarkably high diversity-measured regionally or locally either as species richness or as the evenness of relative abundance among species. In a 1,500-2,500-m depth range off New Jersey and Delaware, 233 30 x 30-cm samples contained 798 species in 171 families and 14 phyla. Addition of stations from sites to the north and south approximately doubled the number of samples and doubled the number of species to 1,597. Species-area curves do not level off within stations or when stations are added together. Moreover, the proportion of species represented by single individuals is high at all scales of sampling, which indicates that much more sampling is needed to adequately represent the species richness either locally or regionally. Diversity changes very little through time at a single site or with distance along a 180-km transect at a depth of 2,100 m. Diversity is maintained by a combination of biogenic microhabitat heterogeneity in a system with few barriers to dispersal, disturbance created by feeding activities of larger animals, and food resources divided into patches of a few square meters to square centimeters initiated by specific temporally separated events.

Life histories and the role of disturbance

Abstract An alternative to the stability-time hypothesis explaining the high benthic faunal diversities in the deep sea ( Sanders , 1968; Slobodkin and Sanders , 1969) has been proposed by Dayton and Hessler (1972). According to Dayton and Hessler, nonselective predation reduces competition between species thereby allowing more species to coexist. Much controversy relating to the concept of diversity and what it implies can be resolved by realizing that an increase of within-habitat diversity is achieved by two entirely different and unrelated pathways. The resultant diversities are differentiated as follows: short-term, non-equilibrium , or transient diversity —induced by a low level or unpredictable physical or biological perturbation or stress resulting in biological ‘undersaturation’. Long-term or evolutionary diversity —increase in diversity is the product of past biological interactions in physical benign and predictable environments. Although predation may play a role in the evolution of deep-sea species, the life histories indicate that it does not seem a likely means for control of population size, regardless of whether predation is selective or non-selective. The known life history characteristics of deep-sea animals—small brood size, age-class structure not dominated by younger stages, probable slow growth rates—are features that neither would be expected nor have high survival value in predator-controlled communities or any environment where short-term or transient diversity is important. Non-selective cropping proposed by Dayton and Hessler as a mechanism for controlling population size of prey species would result in rapid extinction of species with relatively low reproductive rates. In addition to feeding behavior, niche diversification may be the product of biochemical specialization, biotic relationships and microhabitat specialization. Niche diversification may also result from adaptation to different parts of a temporal mosaic. The stability-time hypothesis does not state that disturbance plays no role in predictable environments. The relative predictability of the environment enables species to survive with lower reproductive rates, lower mortality rates, and smaller population size. Rates of competitive exclusion are lower and species are able to become more specialized on both biotic and physical components of the environment. Control of population size is seldom the result of changes in the physical environment or any disturbance, including predation, so that we may say that the community is biologically accommodated rather than physically regulated.

Macrofaunal colonization of disturbed deep-sea environments and the structure of deep-sea benthic communities

Trays of azoic sediment and organic additions were used to determine the responses of deep-sea species to disturbance at two sites and south of New England: Deep Ocean Station One (DOS 1) at 1800-m depth and Deep Ocen Station Two (DOS 2) at 3600-m depth. Species diversity was higher in the natural community at the deeper site. Rates of colonization were similar at the two sites, but slow relative to those in similar experiments conducted in shallow water. Trays of azoic sediment resting on the bottom for 5 years did not achieve the density of individuals or species found in the natural community. Species of polychaete worms in the families Spionidae, Capitellidae, and Sigalionidae were the most consistent colonists regardless of the kind of disturbance. Highest densities were achieved in patches of organic material. At the deeper DOS 2 site, densities of the sibling species of Capitella were 829 per m2 in the vicinity of wood blocks, and the dorvilleid polychaete, Ophryothrocha sp. A, occurred dat 1274 per m2 in natural, patchy accumulations of decomposing seaweed, Sargassum. The response to disturbance represented by the sediment trays was much more variable at DOS 2 than at DOS 1, with several taxa achieving high densities in only one tray. Pholoe anoculata, Ophelina cylindricaudata, and Hesionidae spp. were consistent colonists of the sediment trays at DOS 1. A few taxa such as Capitella spp., Myriotrochus spp. and Ophiura ljungmani increased greatly under screens. Predators excluded by the screens in these experiments may normally prevent juveniles of these species from becoming abundant. Occasional escape from predation may explain the rare instances of dense populations of these species. The responses of deep-sea populations to Sargassum, wood and azoic sediments indicate that a temporal mosaic of small-scale patches of organic enrichment and disturbance are very important in structuring deep-sea communities. The high diversity of species in the deep sea is maintained by: (1) patchiness of organic input against a background of low productivity; (2) sporadic, small-scale, discrete disturbance events occurring against a background of relative constancy; (3) the lack of barriers to dispersal among populations distributed over an enormous area.

The Ecology of Deep-Sea Hydrothermal Vent Communities

Publisher Summary Hydrothermal vents, first discovered in 1977 at 2500m depth on the Galapagos Rift, provide an example of such an alternative ecosystem supported by chemosynthetic primary production (Jannasch and Mottl, 1985). Hydrothermal fluid pouring from the cracks, crevices, and chimneys in the sea floor supports large numbers and kinds of bacteria capable of deriving energy from reduced compounds, such as hydrogen sulfide. This life-supporting fluid is the result of sea water circulating deep within porous basalts and reacting at high temperatures with the rock from magma chambers along ridge axes, where new sea floor is being formed. Large clusters of red-plumed tube-worms emerging from 2- to 3-m-long, thick, white tubes give another-worldly appearance to the rich community of animals sustained by the bacteria. These oases contrast sharply with the surrounding relatively barren rock surfaces on the mid-ocean ridge. Hydrothermal vent populations are of particular interest since these dense populations of large, fast-growing animals flourish in the dark at high pressures and low temperatures, the usual environment of the deep sea.

Sampling Properties of a Family of Diversity Measures

A Jamlily oJfspecies diversity mceasures proposed by Hurlbert (1971) is defined as the expected niumiiber oJ species in a random sample of m individuals Jrom a population. For m = 2 this miieasure is equivalent to Simpson s diversity index. For larger m, the mneasure is increasingly sensitive to rare species. In this paper we use unbiased estimation theory to obtain a minimum variance unbiased estimwator Jor this family of diversity measures. A n unbiased estimator oJ the samiipling varianice is also obtained. These results are then used to partition the variation in sam^ple diversity betweeni randomii samiipling error and local variation community diversity.

A similarity measure sensitive to the contribution of rare species and its use in investigation of variation in marine benthic communities

SummaryWe propose a new measure of similarity, the normalized expected species shared or NESS. The measure is based on the expected number of species shared between random samples of size, m, drawn from a population. The NESS measure is shown to be a generalization of Morisitas similarity and is demonstrated to be less biased than other commonly used measures. The contribution of dominant and rare species is explicit according to the sample size, m, chosen. For large m, NESS is sensitive to the less common species in the populations to be compared.The NESS measure has been used to cluster a 2-year sequence of subtidal benthic samples taken after a severe disturbance. The NESS measure is responsive to the less common species so that both a temporal progression in community recovery and seasonal variation are revealed.

Species diversity in deep-sea communities

Recent extensive quantitative sampling of the deep-sea bottom has revealed communities much richer in species than previously thought. In situ experiments and more precise sampling using free-vehicle instruments and submersibles have provided a more accurate assessment of spatial and temporal variation on the sea floor. These studies have demonstrated the importance of small patches (millimeters to meters) of biogenic disturbance and food input separated on spatial scales of meters to kilometers. In this respect, the processes maintaining deep-sea diversity are similar to those in other species-rich environments such as rain forests.

Benthic community structure on the U.S. South Atlantic slope off the Carolinas: Spatial heterogeneity in a current-dominated system

Faunal communities of the continental slope and rise seaward of North and South Carolina (U.S.A.) are strongly influenced by the Gulf Stream, the Western Boundary Undercurrent, and an increasingly steep declination of the slope toward Cape Hatteras. Sixteen stations in depths of 600–3500 m were sampled to characterized the sediment and benthic macrofauna. Box cores were taken along four transects: Cape Hatteras, Cape Lookout, Cape Fear and Charleston. On the Cape Hatteras transect infaunal densities at the 600-m station were as high as those typical of shallower waters, and the dominant organisms were species that are more characteristic of continental shelf depths. There is high, nearly continuous sedimentation of terrigenous fine sandy sediments that are funneled over the Cape Hatteras slope by southerly-flowing, long-shelf currents. We postulate that organic material is transported rapidly over the site and the high depositional rates are enhanced by scavenging activities of filter-feeding organisms. Large, deep-burrowing deposit feeders serve to carry organic material deep into the sediments. The shallow stations on the Charleston transect were dominated by sand waves generated by the Gulf Stream, while deeper stations were enriched by macroalgae transported downslope. Transects off Cape Lookout and Cape Fear were more typical of those found elsewhere in the western North Atlantic. Macrofaunal analysis yielded 1202 species, 520 of which were new to science. Annelids were the dominant taxa in terms of density and numbers of species. A partial zoogeographic barrier was identified between Cape Lookout and Cape Fear. Species diversity was high at most stations, with the highest at an 800-m site off Charleston where 436 species were taken from nine ☐ cores (0.81 m2). Diversity data from off the Carolinas support previously stated views that the deep sea is a resource of high species richness and biodiversity. Densities of macrofauna from all depths were generally higher than in previously published accounts. The faunal assemblage at each station was consistent over 2 years in that samples from one station were always more similar to one another than to any other station. Stations grouped into upper slope, middle slope, lower slope and continental rise assemblages; the upper slope stations were the most variable, both in density and community composition. Transect differences in types of sediment and macrofaunal communities along and across isobaths, indicated considerable regional heterogeneity.

The role of colonization in establishing patterns of community composition and diversity in shallow-water sedimentary communities

To determine whether pattern and diversity in benthic sedimentary communities are set primarily at colonization or by post-settlement biological interactions, we collected faunal cores and conducted reciprocal sediment transplant experiments at a sandy and a muddy site at 12 m depth, ∼3 km apart off New Jersey. Multivariate analyses of cores collected at these sites in September 1994 indicated differences in the taxa determining local pattern, with the bivalve Spisula solidissima and the polychaete Polygordius sp. being dominant at the sandy site, and oligochaetes, several polychaete species, and the bivalve Nucula annulata dominant at the muddy site. Individual cores from the sandy site were significantly less diverse than those at the muddy site. Short-term experiments (3-5 d) were deployed by divers at three different times (August-September, 1994). Replicate trays (100 cm 2 ) filled with azoic sand or mud were placed flush with the ambient seafloor at both sites. Multivariate comparisons indicated that sediment treatment in trays played a greater role in determining colonization patterns in the first experiment, site played a greater role in the second, and both variables contributed in the third. This pattern suggests that larval settlement and habitat choice played an important role in the first and third experiments, and that local transport of recently settled juveniles from the surrounding sediments was important in the second and third experiments. Sandy-site trays had significantly lower diversity than muddy-site trays, but there was no effect of sediment type in trays on diversity of colonizers. These experiments focused on small spatial scales and three short time periods, but they demonstrate that species patterns in some environments may be set by habitat selection by larvae and by juvenile colonization from the surrounding community. Post-colonization processes such as predation and competition likely play a major role for some species, but patterns of initial colonization corresponded well with those in the local community.

A portal for the ocean biogeographic information system

Since its inception in 1999 the Ocean Biogeographic Information System (OBIS) has developed into an international science program as well as a globally distributed network of biogeographic databases. An OBIS portal at Rutgers University provides the links and functional interoperability among member database systems. Protocols and standards have been established to support effective communication between the portal and these functional units. The portal provides distributed data searching, a taxonomy name service, a GIS with access to relevant environmental data, biological modeling, and education modules for mariners, students, environmental managers, and scientists. The portal will integrate Census of Marine Life field projects, national data archives, and other functional modules, and provides for network-wide analyses and modeling tools.