Enhancement of Important Bottom Sediments for American Lobster and Other Marine Species in Massachusetts Bay

Bob Glenn, Kelly Whitmore

A multibeam image of the reef structures and the cobble fill covering the HubLine.

Project Updates Oct 12, 2006 Dec 22, 2005 Jul 7, 2005 Photo Gallery

MarineFisheries has enhanced key bottom sediments by building a rocky reef in Massachusetts Bay in order to provide partial mitigation for the assumed biological impacts of the HubLine construction. A substantial amount of the impacted sediment along the pipeline footprint is comprised of hard bottom habitat, a habitat type that is not easily restored to its original state upon completion of construction.

Lumpfish inhabit rock reefs.

This type of habitat is critical to several life stages of commercially important species such as American lobster, winter flounder, sea scallops, sea urchins, Atlantic cod, and numerous other species of fish and invertebrates. Sessile invertebrates, important to the productivity and diversity of an area, are also dependent on complex hard bottom. MarineFisheries is obligated to provide appropriate mitigation for any perceived impacts to these aquatic resources that may be related to HubLine construction activities. As mitigation for the assumed impacts from hard bottom habitat loss, this project provides variable-sized rocks in order to target different life history stages of invertebrate and finfish species.

The habitat enhancement project consists of four phases: (1) experimental design, (2) site selection and permitting, (3) installation, and (4) monitoring. Reef composition and orientation, cobble/boulder arrangement within the footprint, and site location will allow MarineFisheries biologists to address scientific questions involving environmental variability and behavioral ecology. The "impact" control areas within the reef footprint will establish a comparison for effects due to the reef presence. Furthermore, a near-by, natural reef was identified during the site selection process for evaluating the progress of the installed reef. Our habitat enhancement area will also be compared with data from a nearby HubLine fill area (an area where cobble rocks were placed on top of the pipeline).

MarineFisheries plans on placing an array of six 4300 ft 2 (33ft x 131ft) rectangular reefs and three impact area control sites within a total footprint area of 1.7 acres. The actual reef area (0.59 acres) is twice the size of successful cobble/boulder reefs deployed in Boston Harbor, MA and in Narragansett Bay, RI. Variable rock sizes (e.g., 2-4 inch cobble, 4.5-10 inch cobble, 11-17 inch boulder, and 19-30 inch boulder) will comprise each of the six reef structures in order to best accommodate multiple life stages of lobsters, finfish, and other benthic invertebrates. These rocks will be separated and arranged by size in a graduated fashion within each plot so that each rock size group will contribute equally to the total area.

Collecting substrate data from a potential reef site.

MarineFisheries placed an array of six 4300 ft 2 (33 ft x 131 ft) rectangular reefs and three impact area control sites within a total footprint area of 1.7 acres. The actual reef area (0.59 acres) is twice the size of successful cobble/boulder reefs deployed in Boston Harbor, MA and in Narragansett Bay, RI. Variable rock sizes (e.g., 2-4 inch cobble, 4.5-10 inch cobble, 11-17 inch boulder, 19-30 inch boulder, a mix of cobble sizes, and a mix of boulder sizes) comprise each of the six reef structures in order to best accommodate multiple life stages of lobsters, finfish, and other benthic invertebrates. The rocks are arranged by size in a graduated fashion within each plot so that each rock size group contributes equally to the total area.

To best identify the sites most appropriate for reef placement, the site selection phase examined a number of important criteria along the corridor of habitat presumably impacted by the HubLine construction. These criteria included: proximity to the HubLine, adequate depth, sediment type, bottom slope, current speed and direction, post larval lobster settlement, user conflicts, accessibility, water quality, and established fauna, flora, and habitat. We used GIS (Geographic Information System mapping software) to identify four prime areas for the installation of the habitat enhancement area. Within these areas, we selected 24 sites in close proximity to naturally occurring rocky reefs. These initial sites were located in the district waters of Beverly, Marblehead, Hull, and Boston.

A DMF biologist measuring lobsters.

Suction sampling a natural reef.	An early benthic phase lobster.

After selecting these three sites, we determined if they received a natural larval supply. We accomplished this using two methods: (1) suction sampling the potential reefs and nearby natural reefs and (2) deploying settlement collectors. Suction sampling is a method commonly used by biologists to assess larval settlement on hard bottom habitat. Samples were air-lifted into a nylon mesh bag attached to the upper end of a suction tube and postlarvae were counted when divers surfaced. The settlement collectors were used to create prime habitat at the potential reef sites which were naturally devoid of cobbles and boulders. These collectors allowed us to determine if larvae would settle at the potential reef sites when provided with their preferred habitat.

Lobstermen deploying a settlement collector from their vessel.	Settlement collectors were inspected for all biota upon retrieval.

Using these data, we were able to conduct analyses on species diversity and compare the three final sites with natural rocky reefs. Site 29 clearly met the majority of our site selection criteria when compared to our two other sites (23 and 6). Site 29 is the closest to the HubLine, received little wave action, had low species diversity and abundance, had a natural larval supply, and would be more cost effective than the other sites. Therefore, MarineFisheries selected Site 29, located near Lovell Island in Boston Harbor, as the site for our habitat enhancement project.

Rocks in one section of the dump scow about to be deployed.	Dump scow and crane used to deploy rocks during reef construction.

Upon completion of the site selection process, MarineFisheries solicited bids from independent contractors for reef construction and completed the permitting process. Construction required the precise placement of rocks by size within each footprint. This placement was accomplished by use of a dump scow with six pockets to accommodate each of the rock sizes. One reef was dropped each day during the construction period in March and April of 2006, until all six reefs were deployed. Adherence to reef specifications was confirmed via post-installation side scan sonar and multi-beam (bottom) surveys, and visual dive surveys.

Scientists tagging cunner captured at the artificial reef.	Tagged fish are returned to the reef for recapture analysis.

To evaluate the success of this project, MarineFisheries initiated a structured monitoring program directly following reef construction. The monitoring program is designed to characterize and track larval settlement and the development of benthic invertebrate and finfish populations. The program includes seasonal visual dive surveys along permanent transects, semi-annual small fish trapping, annual larval suction sampling, and a ventless trap survey. Control sites on impacted and non-impacted substrates are also being monitored for comparison.

Diver surveying substrate on an artificial reef.	Diver inspecting newly installed reef.

Transects have been established on six artificial reefs, three sandy control sites near the artificial reefs, three HubLine cobble fill points, and three natural rocky reefs. The permanent transect sampling will allow us to repeatedly sample the same transects over time to quantify changes in species abundance and diversity.

MarineFisheries encourages public use of the artificial reef for fishing and diving. The reef is located at and around position N 42º 20.63’ W 070º 54.41’. Use of a sounder may aid in identifying the location of individual reef components. The reef’s profile ranges from 1 to 6 ft above the surrounding bottom.