The benthos of the Hudsonis dominatedby species capable of living in soft bottoms. In freshwater areas the benthos consists mainly of diminutive animal species such as larvae of chironomid flies, oligochaete worms who depend upon organic detritus and sediment microbes for food (Chapter 19). Predatory fly larvae and amphipods are also common. In the saline reaches of the estuary, these species are supplanted by abundant polychaete annelids, amphipods, and patchy occurrences of mollusks such as clams. Again, a dependence on particulate organic matter and sediment microbes is widespread (Chapter 18). These animal species form rich populations that burrow in the sediment and accelerate the breakdown of organic matter and recycling of this material back to the water column. A few invertebrate species are specialized and are confined to the low salinity (oligohaline and mesohaline) parts of the Hudson and are neither commonin open marine nor purely freshwater habitats.
Both the freshwater and saline parts of the Hudson Estuary were once far more dominated by native suspension-feeding bivalves. In the limnetic region, freshwater mussels (members of the bivalve family Unionidae) were common in both the tributaries and in the main course of the Hudson, but they have been decreasing for decades, probably owing to habitat alteration. The invasion of the zebra mussel has probably further accelerated the decline of this group. In the saline part of the estuary, oyster beds were once ubiquitous, and the Fresh Kills area of Staten Island was one of the most productive oyster grounds in the United States in the early part of the nineteenth century. Pollution and exploitation have taken their toll, however, and oysters remain uncommon in New York Harbor. Clams are still exploited in Raritan Bay but they have recently suffered from disease.
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