Habitat Classification

Strategy

A habitat classification strategy was developed for integrating the imagery and grab data in order to identify the principal benthic habitats in NY/NJ Harbor. This strategy focused on distinguishing habitats dominated by 1) economically important bivalves, 2) species that build substantial biogenic structures or control important physical processes, and 3) sediment characteristics that likely correlate with the diversity and biomass of benthic infauna. For NY/NJ Harbor, this meant focusing on northern quahogs (Mercenaria mercenaria), surf clams (Spisula solidissima), softshell clams (Mya arenaria), blue mussels (Mytilus edulis), American oysters (Crassostrea virginica), amphipods (Ampelisca abdita) and polychaetes that build extensive tube mats, and polluted sediments. While this classification strategy was appropriate in the context of dredge material management, a different approach to habitat classification than developed here may be needed to address different management concerns.

This study is the first to integrate extensive amounts of SPI, plan-view imagery, benthic, and sediment data to develop habitat maps, so a precise integration process needed to be developed. In order to minimize the probability of classifying habitats based on "false-negative" results (concluding a particular habitat is absent when in fact it is present), the results of the imagery and grab analyses were combined in an additive manner. For example, if SPI showed a clam bed was present but the benthic grab yielded no clams, the station was still considered a clam bed.

Habitat Classes

Shell beds were considered valuable habitat with functions difficult to replace without concerted mitigation efforts, so this habitat class was given the highest priority; i.e., stations with shell beds present were classified as shell bed habitat even when the station had characteristics of other habitat classes. Shell bed classes included clam beds (quahogs or hard clams, soft clams, and surf clams), mussel beds, and oyster beds.

Similar to shell beds, Ampelisca (amphipod) mats were given priority over the sandy bottom and silty bottom classes, and they were observed over three major sediment types: sands, sandy silts, and silts. High densities of tubes characterize Ampelisca mats, and, similar to seagrass beds, they may occur as a patch quilt of open areas and areas with different tube densities. Given the ecological importance of this habitat class in terms of secondary production, all stations with a) Ampelisca present in the imagery or b) 200 or more Ampelisca in the benthic grab were classified as Ampelisca mat habitat.

Sandy bottom habitat was defined as the sandy areas that did not have shellfish beds or Ampelisca mats. The characteristics of sandy habitat most amenable to imagery analyses had a physical, rather than biological, origin. The first division grouped the subclasses into two mutually exclusive families, sandy bottoms with bedforms (ripples) and sandy bottoms without bedforms. Within each of these families, five subclasses were recognized: epifauna present (usually hydroids, algae, or tube-dwelling polychaetes), surface gravel, surface shell hash, infauna present, and no modifier. The first three subclasses represented habitats with structural features that might provide refuge from disturbance, indicate disturbance intensity, and/or simply increase habitat diversity. The latter two subclasses represented habitats lacking a structural component. This hierarchical scheme placed greater emphasis on the SPI data compared to the benthic grab data, so the grab data played a smaller role in the classification of sandy habitats than any other habitat class.

The silty bottom subclasses first keyed on identifying sediments with high pollutant or organic loads (the gas void subclass), then on evidence of high sedimentation (soft sediments) or presence of algae or fauna.

Oligozoic habitats classified stations having 1) no obvious epifauna, infauna or trails of infauna (azoic subclass) and 2) those with Beggiatoa spp. mats at the sediment surface (bacteria subclass). These stations were relatively few in number, and they were usually associated with silty sediments.

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