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What constitutes a harmful alteration, disruption or destruction of habitat (HADD) for eelgrass?

Regional Advisory Process – Gulf

March 17-18, 2011
Moncton, NB

Chairperson: Gérald Chaput


Eelgrass (Zostera marina L.) is a common highly productive perennial aquatic plant that can form extensive intertidal and subtidal beds in estuaries and coastal areas. Its function as a habitat structure includes providing cover from predation, reducing local current regimes, and increasing secondary productivity by adding to local habitat complexity and surface area (DFO 2009). Eelgrass in eastern Canada has characteristics which meet the criteria of an Ecologically Significant Species because if the species were to be perturbed severely, the ecological consequences would be substantially greater than an equal perturbation of most other species associated with this community (DFO. 2009). Eelgrass, in terms of an aggregation (also referred to as a bed), is also considered fish habitat and is therefore protected from harmful alteration, disruption and destruction (HADD) unless authorized under Section 35 or Section 44 of the Fisheries Act. A harmful alteration is more severe than a disruption and destruction is the most severe impact.

Environmental requirements for eelgrass and its sensitivity as fish habitat have been previously described (Vandermeulen 2005, 2009; Vandermeulen et al. 2006). Environmental effects of greatest concern to eelgrass and its function as fish habitat are associated with the following: sedimentation, turbidity / shading, nutrients, flow patterns, and physical removal.

Transport Canada (2007) developed a Replacement Class Screening Report (RCSR) for “water column oyster aquaculture in New Brunswick” that described mitigation measures that if applied would eliminate any significant residual effects of the activities on the functioning of eelgrass as fish habitat. The three residual environmental effects which required mitigation included physical removal of the plant, damage to the plant by infrastructure and operations, and shading of the plant by the infrastructure. An update to the RCSR is expected in 2012.

DFO Habitat Management evaluates proposed activities regarding their effects on fish habitat using a risk assessment matrix. One axis of the matrix corresponds to the scale of the effect (from no effect to high) on the feature of interest (in this case, eelgrass). The second axis defines the sensitivity of the habitat to the effect (on a scale of low sensitivity to highly sensitive). Details on evaluating the scale of the effects and the sensitivity of the habitat are described in DFO (2006).

To assist in the risk assessment of effects of projects on fish and fish habitat, DFO Habitat Management has asked for advice on what would constitute a HADD for eelgrass, i.e. at what point the function of eelgrass as fish habitat is compromised. Specifically, advice is being requested on the following questions:

  1. how to scale (from no effect to high) the environmental effects of sedimentation, turbidity or light penetration, nutrients, flow regime, and physical removal on eelgrass, and
  2. how sensitive is the fish habitat function provided by eelgrass to the environmental effects.


The objectives of the science peer review meeting are to develop advice related to the scaling of environmental effects of five stressors on eelgrass. The five stressors of interest are:

In this review, when referring to eelgrass, it is the aggregation of individual plants into what is commonly called an eelgrass bed, rather than the individual plant, that is being considered.

For each of the five stressors, advice is required for the following:

  1. Does the functional role of eelgrass as fish habitat depend upon the size of the contiguous bed, or the density of the bed, or the patchiness of the bed?
  2. How does eelgrass respond to each stressor (for ex. by reduction in size of the contiguous bed area, by thinning, or by development of patchiness) and how does the response depend upon the intensity, duration, area scale and frequency of the stressor?
  3. Given the response of eelgrass to different levels of the stressor (as above), how do you scale (no effect to high effect) the negative effect of the stressor to the functional role of eelgrass as fish habitat?

Products of the meeting

A Science Advisory Report and supporting research documents are expected outputs of the meeting. As well, a proceedings report that summarizes the review of the working papers during the meeting will be produced.

The Science Advisory Report is expected to be produced within eight weeks of the meeting. The supporting research documents and proceedings document are expected within four months of the date of the meeting.

When finalized, the products from the meeting will be posted on the DFO Canadian Science Advisory Secretariat website.


To assist in the review and the drafting of the advice, participation is expected from:


DFO. 2006. Practitioners Guide to the Risk Management Framework for DFO Habitat Management Staff. (2010-08-12)

DFO. 2009. Does eelgrass (Zostera marina) meet the criteria as an ecologically significant species? DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2009/018.

Canada. Transport Canada. 2007. Replacement Class Screening for Water Column Aquaculture in New Brunswick. Report of the Environmental Assessment Agency. Moncton, N.B. 124p. available online :

Vandermeulen, H. 2005. Assessing marine habitat sensitivity: A case study with eelgrass (Zostera marina L.) and kelps (Laminaria, Macrocystis). DFO Can. Sci. Advis. Sec. Res. Doc. 2005/032.

Vandermeulen, H., G. Jamieson, and M. Ouellette. 2006. Shellfish aquaculture and marine habitat sensitivity case studies. DFO Can. Sci. Advis. Sec. Res. Doc. 2006/036.

Vandermeulen, H. 2009. An Introduction to Eelgrass (Zostera marina L.): The Persistent Ecosystem Engineer. DFO Can. Sci. Advis. Sec. Res. Doc. 2009/085: vi + 11 p.


Participation to CSAS peer review meetings is by invitation only.

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