Don Maurer

Vertical migration and mortality of benthos in dredged material: Part II—crustacea

Benthic invertebrates have many characteristics which make them prime candidates for burial studies in dredged material. A major concern in dredging and disposal projects is the effect of burial on the survival of benthic invertebrates. The purpose of the research reported in this paper was to determine the ability of estuarine benthos—in particular three species of molluscs (Mercenaria mercenaria, Nucula proxima and Ilyanassa obsoleta)—to migrate vertically in natural and exotic sediments and to determine the survival of benthos when exposed to particular amounts of simulated dredged material. n nMortalities generally increased with increased sediment depth, with increased burial time and with overlying sediments whose particle size distribution differed from that of the species native sediment. Temperature affected mortalities and vertical migration. It was concluded that vertical migration is a viable process which can significantly affect rehabilitation of a dredged disposal area. Under certain conditions, vertical migration should be considered, together with larval settling and immigration from outside impacted areas, as a mechanism of recruiting a dredgedump site.

Benthic invertebrate assemblages of Delaware Bay

During two consecutive summers, the first quantitative bay-wide survey (207 stations) of benthic invertebrates was conducted in Delaware Bay (USA). In 1972, 109 species were collected at 105 stations; and in 1973, 125 species were collected at 102 stations. A total of 169 different species were collected for both summers. The number of species and number of individuals increased with increasing salinity and increasing median grain size. These relationships were compared and were found similar to those in estuaries and bays throughout the world. Average density was 722 individuals m2, which is low compared to other estuaries. The relationship of low secondary production to pollution, macroscopic algae, sediment transport, predation, and hydrography is discussed. Deposit feeders comparised the major feeding type. Local species composition was similar to that in Chesapeake Bay, and dominant species occurred in estuaries throughout the Mid-Atlantic Bight. The benthic invertebrates of Delaware Bay were related to the cosmopolitan mode of estuarine faunas. Faunal assemblages were identified by cluster analysis. The assemblages were associated with sediment type and salinity. It was concluded that Delaware Bay comprises a mosaic of animal assemblages, some of which have relatively sharp boundaries similar to classical level bottom type communities, whereas the boundaries of others are almost impossible to detect, and these represent species distributed along an environmental continum.

Polychaete feeding guilds from Georges Bank, USA

Based on 408 quantitative samples distributed over two seasons (winter and spring) and 42 stations, from Georges Bank, New England, USA, the feeding guild classification presented by Fauchald and Jumars was examined. Hypotheses involving the association of particular feeding guilds with environmental variables were posed and tested. In this study, herbivore, motile, jawed (HMJ); filtering and surface deposit feeding, sessile or discretely motile, and tentaculate (F-SD-SDT); burrowing, sessile, non-jawed (BSX); surface deposit feeding, motile, non-jawed (SMX); carnivore, motile, jawed (CMJ), and filter feeding, discretely motile, non-jawed (FDT) were the major feeding guilds of polychaetes. There were more significant associations between feeding guilds and depth, dissolved oxygen, and mean phi and gravel than any other environmental variables. Some significant relationships between feeding guilds and depth, fine-grained sediment, nutrition in sediment (carbon, nitrogen, bacterial biomass, and microbial biomass) emerged. Burrowing, motile, non-jawed (BMX), surface deposit feeding, discretely motile, tentaculate (SDT) and FDT increased with depth. BMX, BSX, and FDT increased with carbon, microbial biomass, and nitrogen, respectively. Some preliminary polychaete feeding surfaces were posed. Nantucket Shoals and Georges Bank were characterized by HMJ and F-SD-SDT; Northern Slope by FDT; Southern Slope by FDT and HMJ; Southwestern Slope by HMJ, SMX, BMX; and the Gulf of Maine by F-SD-SDT, SDT and surface deposit feeding, sessile, tentaculate (SST).

Vertical migration and mortality of benthos in dredged material: Part III—polychaeta☆

Abstract The survival of benthic invertebrates from dredging and disposal activities is a major environmental concern in such projects. The purpose of the research described in this paper was to determine the ability of benthos (polychaetes, Scoloplos fragilis and Nereis succinea ) to migrate vertically in natural and exotic sediments and to determine the survival of benthos when exposed to particular amounts of simulated dredged material. Mortalities generally increased with increased sediment depth, exotic sediment and burial time. Temperature also affected vertical migration and mortalities. These experiments, together with other experiments conducted by us and other workers, indicate that polychaetes in particular, and benthos in general, can survive dredging and disposal projects. Under certain conditions several major taxa (polychaetes, molluscs, crustaceans) can be expected to successfully recolonise disposal sites by vertical migration.

Seasonal changes in feeding types of estuarine benthic invertebrates from delaware bay

Abstract One hundred and fifty quantitative benthic invertebrate samples were collected during five consecutive seasonal cruises (May 1974 to May 1975) in a small area of southwestern Delaware Bay. The samples were divided into four site groups: 1. 1) clean, fine sand 2. 2) coarse sand 3. 3) serpulid tubes; and 4. 4) muddy sand. Each group was characterized by percentage composition of feeding type, dominance, density, and an evenness measure or scaled standard deviation (SDN). Based on earlier work in a small, relatively homogeneous area, SDN had been used to relate diversity to resource sharing in a benthic community; and so this measure was applied to a larger, more heterogeneous area. Present classifications of feeding types are inadequate for an assessment of resource sharing in mixed habitats. Significant problems in analysis emerge because of insufficient data on individual feeding habits. Similar problems were noted in research from European coastal waters. The seasonal effect of meroplankton on the structure and function of benthic assemblages was inferred from plankton samples. These samples suggested explanations for heavy recruitment of a few dominant species. Finally, the biota of the four groups was compared with other assemblages in the mid-Atlantic Bight which show some strong similarities.

A COMPARATIVE STUDY OF THE HARD CLAM GONAD DEVELOPMENTAL CYCLE

1. This study has shown that hard clam reproductive cycles in Delaware Bay are in phase and that spawning activity during 1971-1973 was of sufficient intensity to provide ample larval stocks.2. The gonad developmental patterns for clams in Delaware are intermediate between those for Long Island and North Carolina. The data provide supporting evidence that different physiological races exist in the three areas compared. A further test on the validity of physiological races could be determined by studying the developmental patterns of Long Island and North Carolina clams held experimentally in Delaware Bay.3. Environmental factors attribute to subtle differences in reproductive physiology as evidenced by the different mechanisms of regeneration and development between Delaware Bay and Henlopen hard clam females.The authors wish to thank Dr. Melbourne R. Carriker, Dr. R. W. Menzel, Dr. L. Watling, Mr. Hugh Porter for critical review of the manuscript, and Dr. Jonathan Taylor and Ms. Ann Taylor who provided p...

Benthic faunal assemblages off the Delmarva Peninsula

Abstract Based on 90 quantitative samples collected May and November 1973 the species composition, distribution and abundance of benthic invertebrates on the inner continental shelf off the Delmarva Peninsula (38 ° 23′N and 47 ° 15′W) were determined. A total of 149 species were identified. Thirty-five were found only in May and 65 only in November. In May the fauna consisted primarily of nearly equal numbers of polychaete and crustacean species with an increase in the number of polychaete species and a decrease in crustacean species in November. In May the polychaetes Goniadella gracilis and Lumbrineris acuta were co-dominants (Biological Index Value) while in November the archiannelid Polygordius sp. was strongly dominant. There was essentially no change in the number of deposit-feeding individuals from May to November. Even though the trophic structure remained unchanged, the species changed and the total number of individuals increased by 50% from May to November. The Delmarva assemblage was briefly compared to benthic assemblages closer to the Delaware Bay estuary. Comparison revealed the importance of estuaries and ridge and swale microtopography in influencing the distribution of the shelf fauna. It was concluded that the Delmarva assemblage belonged to a clean sand fauna which occurs throughout the inner continental shelf of the Middle Atlantic Bight. A number of species representing polychaetes, crustaceans, mollusks and echinoderms were proposed as characteristic sand fauna species.

Distribution of the Fiddler Crabs,Uca pugnax andUca minax, in Relation to Salinity in Delaware Rivers

The distribution and abundance of the fiddler crabs,Uca pugnax andU. minax were determined in relation to salinity in three tidal tributaries of Delaware Bay, U.S.A. OnlyUca pugnax was present in high salinity (21–29 o/oo) whileU. minax was present in lower salinities and even in fresh water. Their distributions overlapped along the salinity gradient and both species were equally abundant in salinities of 8–12 o/oo. There was a statistically significant positive association between abundance and salinity forUca pugnax and a negative association forU. minax.

Seasonal fluctuations in coastal benthic invertebrate assemblages

Abstract Two hundred and eighty-eight quantitative benthic invertebrate samples were collected during four quarterly sampling cruises at two areas off the Delaware coast. Species composition, species dominance (abundance and frequency of occurrence), density, and species evenness were compared. Based on cluster analysis three species-site groups emerged: (1) a high energy shoal assemblage characterized by a year-round suite of haustoriids and a few bivalves, (2) a mixed hard bottom-sand assemblage that featured marked seasonal dominance of Mytilus edulis with a variety of seasonal epifaunal and infaunal species, (3) a medium sand assemblage with a variety of seasonal infaunal species. Similar assemblages have been recognized off New Jersey and New York. Seasonal fluctuations in undisturbed coastal invertebrate assemblages can be so marked that many environmental impact studies are inadequate to assess the effects of human activities.

Evaluation of sludge dumping off Delaware Bay

Abstract Sewage sludge from Philadelphia and Camden has been dumped off the mouth of Delaware Bay since 1961. Local residents have claimed that sludge is washed ashore, is a health hazard and has impoverished the fauna of the seabed in the area. In the survey reported here, an assessment has been made of the composition and abundance of the benthic marine fauna of the dumping grounds. The results suggest that dominant species of the area are changing as particulate organic matter accumulates.