Epibenthic Invertebrates Research Articles

Macrobenthic Communities of the Eastern Mediterranean Continental Shelf

Abstract. The results of a year long study in which soft-bottom epibenthic invertebrates were collected by grab, dredge and beam-trawl, along the southern Mediterranean coast of Israel, are described in this paper. The classificatory analysis used for both normal and inverse analyses used two measures of dissimilarity - Canberra metric and Bray-Curtis, and both group-average and nearest-neighbour clustering. The results were displayed as dendrograms. Four site groups and five species groups characterised a total of 58 site samples and 245 species. The prominent species in each of the five species groups are mentioned. The applicability of “community concepts” and the effects of sediment properties on community structure are discussed.

Competitive ability influences habitat choice in marine invertebrates

Patterns of distribution and abundance of sessile marine epi-benthic invertebrates are controlled by three factors: (1) the presence and abundance of larvae which are competent to settle, (2) the choice of settling sites by recruiting larvae, and (3) the biotic and physical events occurring during and after settlement. Although there is much information on the distribution of larvae and seasons of recruitment 1–3, substratum selection 4–6 and post-settlement events 7–15, very little is known of the ecological and evolutionary relationships between these factors5,16–18. Natural selection acts on entire life cycles, thus information about these relationships is essential for understanding patterns of recruitment and survival. For example, sessile organisms can modify the course of post-recruitment events by selective settlement and directional growth19. Here, I present evidence that the larvae of several taxa of marine invertebrates avoid substrata where there is a high probability of death caused by a superior spatial competitor.

Sea Otter Predation and Community Organization in the Western Aleutian Islands, Alaska

Predation by the sea otter (Enhydra lutris) limits epibenthic invertebrates, especially sea urchins (Strongylocentrotus polyacanthus), in turn allowing a luxuriant development of the macroalgal canopy. Where sea otters are abundant, sea urchins are small and scarce in shallow water, and the association of fleshy macroalgae apparently is regulated by competition. Sea urchins are larger and more abundant in deeper water, where they are less accessible to sea otters. Macroalgae are most abundant, and competition in the plant association is severest, near the sublittoral fringe where sea otters can remove sea urchins most efficiently. In deep water, competition among maccroalgae is reduced because the light intensity is lower and grazing by sea urchins increases. On islands where sea otters are absent, sea urchins are abundant, large, and are probably limited by intraspecific competition; and they have eliminated fleshly macroalgae. Available data suggest that the association of Laminaria spp. and Agarum cribrosum contributes most to primary production in nearshore areas of the western Aleutian Islands. Where sea otters are absent and sea urchins have eliminated this plant association, some higher trophic forms also are absent or less abundant than where sea otters are common and the plant association is well developed. Earlier studies of sea otter food suggested that low—density populations of sea otters consume primarily sea urchins and mollusks in the western Aleutian Islands. Later studies of high—density populations showed a wider variety of foods consumed, with fish an important component of the diet. These studies support our observations on the differences in availability of these foods between islands with and without sea otters.

Epibenthic Feeding by Rainbow Trout (Salmo gairdneri) in the McCloud River, California

SUMMARY (1) The stomach contents of rainbow trout from the McCloud River, California, were compared with the composition of the epibenthic invertebrate fauna and the composition of the invertebrate drift. The epibenthic fauna was dominated by Ephemeroptera and Plecoptera nymphs and immature Trichoptera and Diptera while the drift was dominated by Baetidae nymphs (Ephemeroptera), larval Simuliidae and Chironomidae (Diptera), and flying adult insects of both terrestrial and aquatic origin. Although the different groups of drifting invertebrates had different patterns and rates of drift, the overall peak in numbers of drifting organisms occurred at night. (2) Rainbow trout fry and juveniles relied predominantly upon drifting benthic invertebrates. During the day these fish consumed very little food. The most abundant organisms in the adult trout stomachs were larvae of Trichoptera (especially Dicosmoecus), Plecoptera, Ephemeroptera, Diptera, and terrestrial insects. Nearly half the stomach contents were undigestible algae, debris and exuviae. Feeding appeared to be continuous throughout the day, with no striking peaks in stomach fullness. The stomach contents showed no apparent relationship with the patterns and rates of drifting. (3) The epibenthic feeding behavior of the adult trout is probably due to the turbidity of the river, which makes drift feeding difficult when light levels are low. Epibenthic feeding, coupled with the high level of intraspecific competition probably present in an unexploited trout population, is probably responsible for the slow growth rates of the McCloud River trout.

Comparative species richness, composition, and abundance of invertebrates in Caribbean seagrass (Thalassia testudinum) meadows (Panamá)

The results of a year-long study in which epibenthic invertebrates were collected monthly from seagrass (Thalassia testudinum) meadows along the Caribbean coast of Panama and the Panama Canal Zone are described in this paper. Differences in species composition and abundance among sites were primarily due to the proximity of surrounding habitats, especially coral reefs, which contain a number of species that utilize the seagrass meadows. In contrast to many previous characterizations of tropical marine habitats, important seasonal fluctuations in both species number and abundance took place at each of the sites. Data on breeding activity among several species of decapod crustaceans indicate year-round reproduction, although considerable seasonal differences occur in the percentage of ovigerous females. These interspecific differences in observed reproductive output may be explained by differences in life-cycle length, a factor not often considered in discussions of seasonal breeding patterns in tropical marine invertebrates. Overall species composition was qualitatively similar to that reported in comparable studies of tropical and subtropical seagrass meadows elsewhere, although caridean shrimp and xanthid orab species were reduced in number and total abundance were much lower than in previous studies.

Community structure and the effects of pollution in sea-grass meadows and adjacent habitats

Differences in the structure of epibenthic invertebrate species assemblages were investigated in two estuarine areas in Apalachee Bay, Florida (USA), and related to the presence or absence of pulp-mill effluents. Invertebrate species associated with sea-grass beds, mud flats, and oyster reefs were included in the analyses. Surprisingly, several commonly used indicators of pollution stress were ineffective in differentiating the study areas, even though there were large differences in abundance and dominance relationships between them, and these differences were clearly related to the presence of the pulp-mill effluents. Recommendations for data analyses in similar types of studies are made, based on the results of this investigation and others in the same study areas.

Deep-Sea Faunal Zonation of Benthos along Beaufort-Bermuda Transect in the North-western Atlantic

SynopsisIn this paper the subject of faunal zonation in the ocean floor from the intertidal, and over the continental shelf, slope and rise and to the abyssal plain is examined on the basis of faunal change at the generic and species level. The region investigated over a period of five years aboard R/V Eastward is a Beaufort-Bermuda transect, approximately 75 kilometres wide and 500 kilometres long and bounded between 32° and 36°N latitude and 64° and 79°W longitude. A new method, involving numerical indices reflecting changes in the composition of taxa, endemism and diversity between adjacent depth levels, was developed for defining faunal boundaries. Isotherms and isobaths utilised by earlier authors for characterising deep-sea boundary on a global scale do not coincide with natural faunal boundaries. This study analyses the vertical distribution of 128 species of isopod crustaceans and 28 species of large epibenthic invertebrates. The zonation patterns seem to correspond with correlations in environmental conditions such as currents, topography and sediments.We suggest four major vertical faunal provinces, characterised at the generic level, namely (1) the Intertidal Faunal Province; (2) the Shelf Faunal Province; (3) the Archibenthal Zone of Transition; and (4) the Abyssal Faunal Province and internal zones within these characterised at the species level. The main aspects of interest include the presence of a narrow ‘meso abyssal zone’ with a species maximum, the demonstration of the true transitional nature of the Archibenthal Zone in biotic and abiotic factors and the characteristic low-biomass Red Clay environment showing definite faunal isolation from the continental margin.

Zonation of large benthic invertebrates in the deep-sea off the Carolinas

Populations of large epibenthic invertebrates in the deep-sea off North Carolina have restricted distributions which are narrow ribbons parallle to depth contours. On the upper continental slope (200–800m) these ribbons or bands correlated with marked changes in sediment size distribution parameters and temperature variation which in turn were related to the movements and proximity of the Gulf Stream current. At depths greater than approximately 1000 m temperature variation with time ceased and the small differences in sediment size were not correlative with the continued zonation of populations with depth down the slope. Some of the most common species formed broad bands which were confined to large physiographic features and areas where the Western Boundary Undercurrent impinged on the bottom. Within these bands on the continental slope and its base, on the other hand, narrower ribbons appeared to be related to a zonation of detrita food supplies, with suspension feeders recuiring in isolated regions. This binding, however, may have resulted from interactions between species, with the narrow ribbons being a function of which animals can or cannot successfully survive in the midst of the dominant ophiuroid ( Ophimusium lymani) population.

Caloric Content of the Standing Crop of Benthic and Epibenthic Invertebrates of St. Margaret's Bay, Nova Scotia

The benthos of St. Margaret's Bay at depths of 28–62 m was sampled quantitatively during the summer and the caloric contents of the common invertebrates determined. The shrimps, amphipods, and the polychaete Lumbrinereis with caloric contents between 1000 and 1300 cal/g wet weight had the highest caloric content of those tested. The mean caloric content of the standing crop was 76 kcal/m2 with the highest values occurring where the sand and silt–clay fractions of the sediment were nearly equal and the lowest where either sand or silt–clay predominated. Annelids and echinoderms together accounted for more than three-quarters of the caloric content of the standing crop.

The bathymetric and seasonal distribution, and reproduction of adult tanner crabs, Chionoecetes tanneri rathbun [brachyura: majidae], off the northern Oregon coast

On a trackline running southwest from the Columbia River mouth at depths from 50 to 1050 fm (91–1920 m), adult Tanner crabs were distributed at depths from 250 to 850 fm (457–1554 m) with greatest abundance occurring from 275 to 400 fm (503–732 m). Over this depth range, Tanner crabs made up a substantial part of the standing crop of epibenthic invertebrates during all seasons. Female crabs were generally distributed in greatest numbers over one depth interval [350–375 fm (640–686 m)] throughout the year whereas the relative abundance of males changed with depth seasonally. During the spring and summer, the males were segregated from the females, being most abundant at depths between 275 and 300 fm (503–549 m). Following this period, the male population shifted into deeper water, and mingled with the female population during the winter. The percentage of oviferous female crabs was high throughout the year. Egg development followed a yearly cycle with release of maturated eggs and the ovulation of new eggs occurring during the winter. Indications are that mating occurred during the period of population intermixing. The average carapace width of male and femal crabs was 148·9 and 102·5 mm, respectively, with the average size of both sexes being greater over the shallow end of their respective depth ranges.