Baseline seabed habitat and biotope mapping for a proposed marine reserve

Abstract

Seabed mapping can quantify the extent of benthic habitats that comprise marine ecosystems, and assess the impact of fisheries on an ecosystem. In this study, the distribution of seabed habitats in a proposed no-take Marine Reserve along the northeast coast of Great Barrier Island, New Zealand, was mapped using underwater video combined with bathymetry and substratum data. As a result of the boundary extending to the 12 nautical mile Territorial Limit, it would have been the largest coastal Marine Reserve in the country. Recreational and commercial fisheries occur in the region and would be expected to affect species' abundance. The seabed of the study area and adjacent coastal waters has been trawled up to five times per year. Benthic communities were grouped by multivariate cluster analysis into four biotope classes; namely (1) shallow water macroalgae Ecklonia sp. and Ulva sp. on rocky substrata (Eck.Ulv); and deeper (2) diverse epifauna of sponges and bryozoans on rocky substrata (Por.Bry), (3) brittle star Amphiura sp. and sea anemone Edwardsia sp. on muddy sand (Amph.Edw), and (4) hydroids on mud (Hyd). In biotopes Por.Bry, Amph.Edw and Hyd, there where boulders and rocks were present, and diverse sponge, bryozoan and coral communities. Fifty species were recorded in the deep water survey including significant numbers of the shallow-water hexactinellid glass sponges Symplectella rowi Dendy, 1924 and Rossella ijimai Dendy, 1924, the giant pipe demosponge Isodictya cavicornuta Dendy, 1924, black corals, and locally endemic gorgonians. The habitats identified in the waters to the northeast of Great Barrier Island are likely to be representative of similar depth ranges in northeast New Zealand. This study provides a baseline of the benthic habitats so that should the area become a Marine Reserve, any habitat change might be related to protection from fishing activities and impacts, such as recovery of epifauna following cessation of trawling. The habitat map may also be used to stratify future sampling that would aim to collect and identify epifauna and infauna for identification, and thus better describe the biodiversity of the area.

Keywords: Benthos; Biodiversity; Corals; Fish; Marine Protected Areas (MPA); Sponges.

Figure 1. The study area to the northeast of Great Barrier Island in New Zealand, southwest Pacific.

The proposed Marine Reserve boundary is shown (solid line). Depth is shown from shallow (red) to deep (blue) with 30, 60, 90 and 120 m depth contours. Dots indicate locations of 119 sampling stations using ROV, BUV, and DDV underwater video.

Figure 2

The drop-down video (DDV) system used at most 85 sampling stations in cruise 3 between April 2006 and September 2009.

Figure 3. Cluster analysis.

Dendrogram of results of cluster analysis of samples based on taxa present. The substrata (symbols) and depth (numbers against samples) of each sample are indicated. The four clusters are from the top of the figure, deep-water samples dominated by (A) brittle star Amphiura sp. and sea anemone Edwardsia sp. (Amph.Edw), (B) diverse epifauna of sponges and bryozoans (Por.Bry), (C) hydroids (Hyd), (D) algae (Eck.Ulv).

Figure 4. Cluster analysis.

Clustering of samples shows four species assemblages: (A) the sea anemone Edwardsia sp. and brittle star Amphiura sp. (Amph.Edw); (B) the diverse epifauna on hard substrata in deeper waters (Por.Bry); (C) hydroids (Hyd); and (D) the kelp Ecklonia sp. and green algae Ulva sp. group (Eck.Ulv).

Figure 5. Cluster analysis.

An alternative presentation of the samples in Fig. 3 using non-metric multi-dimensional scaling (MDS). Vectors show selected (to avoid cluttering plot) taxa indicating the species assemblages. Symbols indicate substrata as in Fig. 3. The four biotopes are indicated by dotted circles: (A) brittle star Amphiura sp. and sea anemone Edwardsia sp. (Amph.Edw), (B) diverse epifauna of sponges and bryozoans (Por.Bry), (C) hydroids (Hyd), (D) algae (Eck.Ulv).

Figure 6. Biotopes matrix.

Map and matrix of the biotopes in the study area off Great Barrier Island, latitude 36.03° and 36.45° south and longitude 175.58° and 176.28° east (land is dark green). Depth contours are in metres. White areas on the map were muddy with no visible epifauna.

Figure 7. Biotopes.

Images of the biotopes found. (A) Shallow (<20 m) rocks covered with encrusting coralline algae, kelp, sponges, corals and bryozoans in biotope Eck.Ulv. (B) Deep (>80 m) mud with sponges and bryozoans growing on any hard substrata in Por.Bry. (C) Brittle star Amphiura sp. and sea anemone Edwardsia sp. on muddy sand in Amph.Edw (D) Deep (>90 m) mud with hydroids and no identifiable epifauna in Hyd.

Figure 8. Glass sponges and demosponges identified from images from deep-reef sites off Great Barrier Island.

(A) Petrosia hebes Lendenfeld, 1888; (B) Hymeniacidon sphaerodigitata Bergquist, 1970; (C) glass sponge Rossella ijimai Dendy, 1924; (D) Aciculites pulchra Dendy, 1924; (E) glass sponge Symplectella rowi Dendy, 1924; (F) Stelletta maori Dendy, 1924; (G) Calyx imperialis (Dendy, 1924); (H) Stelletta crater Dendy, 1924 (left), Spongia (Heterofibria) gorgonocephalus Cook & Bergquist, 2001 (right); (I) Symplectella rowi Dendy, 1924; (J) Iophon laevistylus Dendy, 1924 (left) and Pleroma menoui Lévi & Lévi, 1983 (right); (K) Haliclona (Gellius) petrocalyx (Dendy, 1924); (L) Geodia rex Dendy, 1924; (M, N) Isodictya cavicornuta Dendy, 1924.