Vertical Distribution and Longevity of Subtidal Seaweeds in Northern New England, U.S.A.

Seasonal collections of subtidal seaweeds were made at 12 adjacent open coastal sites in northern New England from 1965-69, in order to document the longevity and vertical distribution of the flora. A total of 110 taxa were recorded. Wide variations of species diversity were noted at nearby locations with similar hydrographic conditions, depending upon substrate availability, sand scouring and wave action. Most of the species (88%) showed a continuous vertical distribution from the upper to the mid or lower subtidal zone. The lower limits of vegetation were dominated by a variety of turf, crustose and foliose-fleshy red algae. A consistent vertical pattern was recorded, with decreasing ratios of annuals/perennials, ChJorophyceae/Rhodophyceae and number of species with increasing depths. The composition and distribution of the subtidal flora are discussed in relation to a variety of parameters, including light, temperature and substrate. In addition, several generalizations regarding the biology-ecology of the deep water North Atlantic flora are summarized. Introduction Little is known of the seasonal occurrence and development of the subtidal vegetation of the northwestern Atlantic. The extreme winter conditions of the area have discouraged many investigators, and as a result few yearround floristic studies of subtidal vegetation have been conducted employing direct observations by SCUBA (Lamb and Zimmerman 1964, Mathieson etal. in press, a, Sears and Wilce 1975). As a result, there is a paucity of information regarding the winter-early spring subtidal vegetation within the northwestern Atlantic, as well as the seasonal reproductive periodicity of the subtidal flora. The present study summarizes the results of a five year investigation of the subtidal flora in New Hampshiresouthern Maine. Particular emphasis has been placed upon an evaluation of the longevity and vertical distribution of the conspicuous macroscopic seaweeds. SCUBA equipment has been used to make direct observations and collections of the subtidal vegetation. * Scientific Contribution No. 989 from the New Hampshire Agricultural Experiment Station. Scientific Contribution No. 71 of the Jackson Estuarine Laboratory. Methods and Materials Seasonal collections and observations of subtidal seaweeds were made at 12 adjacent open coastal sites in southern Maine and New Hampshire (Fig. 1) from 1965-1969. Representative samples of all conspicuous seaweeds at each site were made by SCUBA diving to multiple depths from mean low water (M.L.W.) to the lower distributional limits of benthic plants (i.e. -15.0 to -34,0 meters). A complete set of herbarium voucher specimens was prepared seasonally for each site and deposited in the Algal Herbarium of the University of New Hampshire (NHA). Taylor (1957), Adey (1964, 1965, 1966a), Collins (1909), Conway (1964a, b), Hoek (1963), Powell (1957a, b, 1963) and WUce (1965) were the primary sources of identifications. The nomenclature of Parke and Dixon (1976), and South (1976) were employed. A comparison of the species diversity/site and the number (%) of taxa shared by the 12 sites are summarized. Tabulations of the subtidal distribution and longevity of each taxa are also given; the longevity information is primarily summarized from Mathieson et al. (in press, a). Table I gives a brief description of the twelve sites, based in part on Hehre and Mathieson (1970) and Mathieson etal. (in press, a). Stations 3-11 were located Botanica Marina / Vol. XXII / 1979 / Fasc. 8 0006-8055/79/0022-0511S02.00 © by Walter de Gruyter & Co. · Berlin · New York 512 Mathieson: Distribution and longevity of subtidal seaweeds Tab. I. Description of Study Sites Cape Neddick or Nubble Lighthouse, Maine (Fig. 1, station 1) is an exposed coastal site with substrate consisting of massive granitic rock outcrops and boulders grading into sand. Gerrish Island» Maine {Fig, 1, station 2) is a semi-exposed coastal site at the mouth of Portsmouth Harbor, with massive granitic outcrops and boulders for substrate. Fort Constitution, New Hampshire (Fig, 1, station 3) is a sheltered location within the entrance to Portsmouth Harbor. The substrate consists of small rock outcrops, pebbles, mud and sand. Jaffrey Point or Fort Stark, New Hampshire (Fig. 1, station 4) is a semi-exposed coastal site just south of the entrance to Portsmouth Harbor with substrate primarily consisting of massive granitic rocks. Odiorne's Point or Fort Dearborn, New Hampshire (Fig. 1, station 5) is a semi-exposed coastal site consisting of a mixture of cobbles and granitic rock outcrops. North Wallis Sands, New Hampshire (Fig. 1, station 6) is a semi-exposed coastal site with massive rock outcrops on a sandy beach. Concord Point, New Hampshire (Fig. 1, station 7) has substrate and exposure similar to station 5. Ragged Neck or Rye Harbor, New Hampshire (Fig. 1, station 8) is a semi-exposed coastal site with cobble substrate. Rye Ledge, New Hampshire (Fig, 1 > station 9) is an exposed coastal site consisting of massive rock outcrops, as well as large boulders and cobbles. Great Boar's Head, New Hampshire (Fig. 1, station 10) is an exposed coastal site with substrate consisting of cobble and scattered boulders on sandy surfaces, Hampton, New Hampshire (Fig. 1, station 11) is an exposed site offshore from the mouth of Hampton Harbor with substrate consisting of rock outcrops and boulders on a sandy beach. Appledore Island, Isles of Shoals, Maine (Fig. 1, station 12) is the most exposed coastal site studied. It is located on the eastern side of the island with substrate consisting of massive granitic outcroppings. and 11) were also studied, as well as six semi-exposed coastal (i.e. 2,4—8), and one sheltered locations within the entrance to Portsmouth Harbor (i.e. 3). A wide diversity of substrate was found at the 12 sites (Tab. I), ranging from large granitic outcrops to boulders, cobbles and sandy beaches with rock outcrops. A vertical gradient of substrate was evident at most of the nearshore sites, grading from rocky substrate in the upper subtidal zone to silt-sand at -11.0 to -18.0 meters. Results A total of 110 taxa of subtidal seaweeds were recorded at the 12 coastal sites, including 57 Rhodophyceae, 38 Phaeophyceae and 15 Qdorophyceae (Tab. II and Fig. 2). The highest species diversity of 83 taxa was recorded at Fort Stark (Fig. 2, Station 4) where monthly collections were made over a two year period (Mathieson et at in press, a). Seasonal collections were made at the other 11 sites, and their species diversity ranged from 24 to 60 taxa at North Wallis Sands and Hampton, respectively (Fig. 2, stations 6 and 11), The red algae contributed the greatest number of species at each site, while the brown and green algae consistently ranked second and third in species numbers. The floristic affinities of the 12 sites, expressed as the number and percentage of taxa shared by the different sites are shown in Table III. The high species diversity at Fort Stark (Station 4), Fort Dearborn (Station 5), Hampton (Station 11), and Nubble (Station 1) was associated with a correspondingly high number (%) of taxa shared by these different stations. Specific details of floristic affinities can be ascertained in Table II. Fourteen of the 110 taxa recorded were present at all sites (Tab, II): Agarum cribrosum, Ahnfeltia plicata, Cattophyllis cristata, Ceramium rubrum, Chondrus crispus, Corallina officinalis, Cystoclonium purpureum Atlantic Ocean ö 10 4255-I Fig. 1. Location of 12 study sites in New Hampshire and southern Maine, along the 29.0 km coastline of New Hampshire, while, 1, 2 and 12 were in southern Maine (Fig. 1). The The Appledore, Maine site at the Isles of Shoals (station 12) was the most exposed location, as demonstrated by its topography, fetch and biological communities (Lewis 1964). It was situated on the eastern side of the Island, approximately 14.5 km SSE of Portsmouth Harbor and station 3. Four other exposed coastal sites (i.e. 1, 9,10 Botanica Marina / Vol. XXII / 1979 / Fasc. 8 Mathieson: Dutributim «otf toflgwity of Mbtttti mweeds 513 •3 ía> ß S C/3 1+3 3 C/3 *O **\ II. V er tic al D ist rib ut io n an d Lo ng ev il