Longitud de Racimo

classification and further assessed the maturity of the water body in terms of

the degree of infilling. The status of the entrance was also recorded, whether

open to the sea, intermittently open or closed, or primarily closed, and if it had

been mechanically opened or training walls constructed .

. ,

2.3.3 Studies Tasmanian coastal habitats

Tasmania has a wide variety of marine coastal habitats . . A number of studies have attempted a classification of the Tasmanian coastline suitable for their particular goals. Two such works (Mollison 1963; Last 1983) have focussed on inshore and estuarine fish habitats, and these are relevant to seagrass habitats

in the State.

A classification of river estuaries and coastal lagoons in Tasmania was proposed by Mollison (1963). He divided these areas into three groups:

(a) those permanently open to the sea (bay estuarine waters, coast estuarine waters, and tidal arms);

(b)

those dammed by sand, breaking open to the sea irregularly (bar dammed rivers, bar dammed lagoons, beach dammed rivers); and,

(c) waters not connected to the sea (eutrophic dune lakes and inland saltpans). The first two of these groups cover the majority of seagrass communities in the State. However, Mollison confined the study to areas upstream of a true marine environment in terms of salinity, and did not survey bays or offshore areas. He recorded seagrasses in a number of locations.

Last (1983) made a more detailed categorisation of the Tasmanian coastline, focussing on sedimentary environments. He recognised three basic geomorphological types, which were further sub-divided into 55 minor habitats. These were based on the criteria of exposure, substrate characteristics, topographic position, geomorphology, bathymetry and hydrology. The three major categories described are:

(a) closed or semi-closed drainage systems (including coastal lakes, bar­ dammed lagoons and rivers, and beach-dammed rivers);

(b)

open drainage systems (including open lagoons, bay estuaries, and tidal rivers and creeks); and,

(c) beach systems (including sheltered, semi-exposed and exposed beaches). This work (Last 1983) was directly concerned with soft-bottomed habitats in Tasmania. Seagrasses are also confined to these habitats, and the same major categories have been broadly adopted here. Last's study was further limited to the 'shore zone', for which the lower limits were taken as

50 m offshore from

mean low water spring (L.M.W.S.) or the 6 m depth level below L.M.W.S. (Last 1983). Although many seagrasses in Tasmania are found within that zone, there are extensive communities that are either further offshore, and/or at a greater depth. Those limits of distance and depth have not therefore been adopted, and modifications to the range of habitat types have been made to Chapter _{2. The Tasmanian coast and seagrass habitat classification}

include these communities.

2.3.4 A coastline classification in this

It was decided to use a relatively simple 11 point classification of coastal areas based on exposure and geomorphology, illustrated in Figure 2.3. The minor classifications presented by Last (1983) have not been adopted since parameters such as the bathymetry and substratum are included in the samp�e site data, and the topographic position of the seagrass communities is indicated on maps (see Chapter 5). Only the hydrographic information of salinity and light attenuation has been excluded from both the sampling and habitat classification,

although regional trends are described

in

section 2.2.

The maturity of coastal

formations has not been assessed as in West et al. (1985), and, since mechanical opening of otherwise clos�d systems is uncommon in Tasmania, and training walls are rare, these are included in comments on individual sample areas (see Chapter 5 & 6).

The 11 major habitats and their numerical codes are:

Closed or Semi-closed svstems

(1) coastal lakes

(2) bar or beach dammed lagoons (3) bar or beach dammed rivers

( 4) open lagoons

(S) estuaries

(6)

tidal rivers, creeks and tributaries

(7)

tidal arms

(8)

sheltered beaches

(9) semi-exposed beaches (1

0)

exposed beaches

Other areas

(11) straits and channels.

Major types of coastal landform and codes adopte:I in this study {after Last 1983).

�

dhection of swell

1 coastal lakes

2 bar or beach dammed lagoons

3 bar or beach dammed rivers

4 open lagoons 5 estuaries

6 tidal rivers, creeks and tributaries

7 tidal arms

8 sheltered beaches & bays 9 semi-exposed beaches & bays

10 exposed beaches & bays

11 straits & channels

2.3.5 of habitat

The following descriptions of the habitat categories adopted in this study are derived from Mollison (1963) and Last (1983). Comments on the occurrence of seagrasses have been added by the author:

Closed or semi-closed drainage systems

Although occasionally open to _{the sea by channels or overflows, these estuarine} and freshwater basins are usually closed by sedimentary barriers. They range from being permanently closed to permanently open, varying over time, and include:

(1) lakes - these are not connected to other drainage systems and include basins, such as saltpans, and dune lakes. No coastal lakes have been sampled in this study, though it is possible that some contain isolated communities of Zostera muelleri.

(2) bar or beach dammed - these estuarine systems are brackish,

with salinity increasing over the time since their last closure. This may be a number of years in some cases. They are often deep, and can be highly productive ecosystems. Communities of

Ruppia

spp. and

Zostera

muelleri

often occur in shallow areas of these lagoons. Examples include Big Lagoon and Dianas Basin on the east coast.

(3) bar or beach dammed rivers - these may drain through seepage channels over the bar or beach, and be penetrated by sea water over the same barrier during storms. Their salinity is generally low.

Zostera muelleri

and species of

Ruppia

may occur in the shallows. Only Scamander River has been sampled in this study. The Nelson and Thornton Rivers on the west and south coasts are other examples.

Open drainage systems

These permanently open estuarine systems vary in width, depth and flow characteristics considerably, and are mostly brackish.

(4) _{these are often very large tidal lagoons with extensive} shallows and channels less than 4 m deep. Examples are Pittwater in the south, Great Swanport and Mussel Roe Bay on the east coast, and North East River on Flinders Island

Zostera muelleri

_{commonly forms beds in}

shallow areas and intertidal flats, and

_{Heterozostera tasmanica}

_{may be} found in the channels, particularly close to the entrance where a wedge of seawater penetrates.

(5) estuaries - most of the major estuarine systems in Tasmania fall within

Chapter 2. _{The Tasmanian coast .and seagrass habitat classification}

' '.

this category, including the Tamar and Mersey Rivers and Port Sorell on

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