Howard L. Sanders

MARINE BENTHIC DIVERSITY: A COMPARATIVE STUDY*

In this paper a methodology is presented for measuring diversity based on rarefaction of actual samples. By the use of this technique, a within-habitat analysis was made of the bivalve and polychaete components of soft-bottom marine faunas which differed in latitude, depth, temperature, and salinity. The resulting diversity values were highly correlated with the physical stability and past history of these environments. A stability-time hypothesis was invoked to fit these findings, and, with this hypothesis, predictions were made about the diversities present in certain other environments as yet unstudied. The two types of diversity, based on numerical percentage composition and on number of species, were compared and shown to be poorly correlated with each other. Our data indicated that species number is the more valid diversity measurement. The rarefaction methodology was compared with a number of diversity indexes using identical data. Many of these indexes were markedly influenced by sample size. Good agreement was found between the rarefaction methodology and the Shannon-Wiener information function.

Faunal diversity in the deep-sea

Abstract Analysis of deep-sea benthic samples gathered with a new collecting device reveals a greater diversity (defined ab absolute number of species) of fauna in single environments than has ever been measured before. This high diversity is not an artifact of sampling procedure and demonstrates tat the deep-sea benthos is not faunally depauperate, as is commonly believed. The previous idea of low diversity stems from lack of appreciation of the fact that apparent diversity is dependent on sample size, especially in small samples. Diversity in the deep-sea is much greater han in equivalent shallow marine environments from temperate latitudes and is of the some magnitude as in the shallow marine tropics. High diversity in the deep-sea is best explained as resulting from the great stability of the physical environment.

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.

An introduction to the study of deep-sea benthic faunal assemblages along the Gay Head-Bermuda transect*

Abstract This paper is the introduction to a long-term, detailed study of open ocean, benthic assemblages. Attention will be paid to taxonomy, community structure, physiology, recruitment, patchiness, modes of feeding, zoogeography, and many other related topics. The major area of study is a transect between Massachusetts, U.S.A., and Bermuda, in the North Atlantic Ocean. Quantitative samples were taken with an anchor dredge and were washed through a 0·42-millimeter-aperture screen. The sediments along the transect range from fine sands of terrigenous origin on the upper continental slope, to silty clays and clays composed primarily of pelagically derived calcium carbonate in the Sargasso Sea. With increasing depth. temperature at the stations not only decreases, but shows more restricted fluctuation. Analysis of results shows much greater faunal densities than those reported from previous studies; this probably results from our using a smaller screen aperture. Each region of the transect supports a characteristic number of animals per square meter in a general trend of decreasing density with increasing depth and distance from the continent: outer continental shelf, 6,000–13,000; upper continental slope, 6,000–23,000; lower continental slope, 1,500–3,000; abyssal rise, 500–1,200; abyss under the Gulf Stream, 150–270; abyss in the Sargasso Sea, 31–130; lower Bermuda Slope, 140–300; upper Bermuda Slope, 500–850. From all but three stations, Polychaeta, Crustacea, Pelecypoda and Sipunculoidea combined comprised 85–100% of the fauna, with the former group being particularly important. Pogonophorans, ophiuroids, anemones, solenogastres, gastrods, and scaphopods were also important, but less abundant. The dominance of polychaetes tended to decrease with distance from the continent, while the crustaceans correspondingly increased in importance. Attempts to relate the density of animals to the amount of organics in the sediment provided no clear correlation. It is suggested that this results from the fact that the analytical techniques do not differentiate between labile and more refractory organic compounds.

Pattern and zonation: a study of the bathyal megafauna using the research submersible Alvin

Abstract The pattern of distribution of benthic megafauna (defined as the animals readily visible in photographs) on the Gay Head-Bermuda transect differs considerably at the three sclaes measured: within photographs, between photographs and between depths. Detailed natural history observations are given for a series of dives at 1300 and 1800 m. The composition of the megafauna varies markedly between the five depths studied (500, 1000, 1300, 1500 and 1800 m). This corresponds with the high rate of depth-correlated species replacement described elsewhere for the macrofauna. Relative to the macrofauna, the megafauna provides virtually no information on density and diversity in the deep sea. Within a single depth the dominant pattern of species distribution is random, both between and within individual photographs. A regular or even pattern occurs in the brittle star, Ophiomusium lymani , owing to spacing of individuals at high densities. The most pronounced aggregation occurs in the sea urchin, Phormosoma placenta . This deposit-feeding species continually moves as it depletes its food resources in one spot. Unlike Phormosoma , the other sea urchin, Echinus affinis sometimes responds to concentrations of food although only relatively weak aggregations appear in the photographs analyzed. Thus, the food of this species is not usually concentrated. The patchiness of Ophiomusium at low densities is attributed to avoidance of disturbed areas that appear as large burrow-like depressions.

Distribution of Cumacea in the deep Atlantic

Abstract The cumacean crustaceans are an important faunal component of the deep-sea benthos. Using improved sampling methods, 202 species have been collected from bathyal and abyssal depths from four regions of the Atlantic and 117 of these species are probably new. Considerable regional endemism has been found. The Cumacea have narrow and discrete depth ranges and are sharply zoned by depth. Diversity values are highest in the tropical deep-sea samples and lowest in the upper slope samples taken south of New England.

MICTACEA, A NEW ORDER OF CRUSTACEA PERACARIDA

ABSTRACT A new order, Mictacea, is proposed within the superorder Peracarida for Hirsutia bathyalis Sanders, Hessler, and Garner and Mictocaris halope Bowman and Iliffe. The new order is characterized by a unique combination of characters, most of which are not unique to the Mictacea, but are found in at least one other peracaridan order.

Adaptations to abyssal life as shown by the bivalve Abra profundorum (Smith)

Abstract Abra profundorum is widely distributed in the northern Atlantic in abyssal depths. A comparison is made between the gross morphology of A. profundorum and that of other north Atlantic species in this genus. This shows that when these species are arranged according to their depth distribution (H.W.M. to Abyssal Plain), there is a correlation between depth and the size of the gills and palps as well as the length and volume of the hind gut. In those species occurring in deep water the gill becomes much reduced in size and, apart from its respiratory function, acts essentially as a conveyer belt transporting the incoming sediment from the incurrent siphon to the pals. The palps of deep water species are enlarged and possibly this is a compensation for the loss of ciliated surface of the gills, in order to maintain the power to suck in vast quantities of bottom sediment. The hind gut becomes progressively elongated and the consequent storage of faecal material can probably be explained in terms of the increased bulk of material ingested and the necessity of ensuring that all nutritive material is extracted from deep water sediments which are poor in available organic nutritive materials.

Two New Species of Sandersiella (Cephalocarida), Including One From the Deep Sea 1)

Two new species of Cephalocarida, Sandersiella calmani from shallow Peruvian waters, and S. bathyalis from deep water off Southwest Africa, allow realistic determination of the generic characteristics of this previously monotypic genus. This re-evaluation of Sandersiella necessitates rediagnosis of the other two genera, Hutchinsoniella and Lightiella. Full enumeration of known localities shows the cephalocarids to have a disjunct, cosmopolitan distribution with broad environmental range. Nevertheless, the morphological range of this subclass is quite limited. This pattern is like that of other primitive arthropods, including the Mystacocarida, Leptostraca, and Xiphosura.

The West Falmouth oil spill : persistence of the pollution eight months after the accident

Submitted to the Office of Naval Research under Contract ONR N00014-66-C0241; NR 083-0043 and partially supported by the Federal Water Quality Act Grant 18050-EBN3 and with the National Science Foundation Grant GA-1625.