DRAFTING…
Depths and occurrence of T. testudinum (Tt) Syringodium filiforme (Sf), Porites furcata (Pf), Anrainvillea nigricans (An) and Avrainvillea rawsonii (Ar) on Transects M and 4S in 1969 and 1994.
Seagrasses at Bath occur partially in the lee Of algal- and coral-encrusted rocks rising to MLW level and abve lying at 150-300 m from shQre (Fig. 2). The bed has a complex topography and distribution Qf sediQments as a result Qf the irregular tQpography Qf the bedrock, the cQmplex wave regime, and prolific biQgenic productiQn Qf particles Qf clay tQ cQbble size. The seagrass bed is shallQW (mQstly less than I m) and conditiQns are generally turbulent except fQr a few hQurs at IQW water; during the winter mQnths, waves Qver the seagrass bed may reach Qne meter in height and IQngshQre currents speeds in excess Qf 60 cm/sec Patriquin (1975). FQur seagrass substrate types with well defined distributiQn were distinguishable in 1969. These included T. testudinum stabilized accumulatiQns Qf cQbble sized rhQdiles and CQral debris at the seaward fringe Qf the bed; T. testudinum and H. wrightii stabilized accumulatiQns Qf PJurcata debris rising to close to MLW nearshQre alternating with T. testudinum and S. filifQrme cQIQnized predQminantly sand substrates, and a mixed cobble-sand substrate stabilized by T. testudinum and S. fIliforme thrQugh the rest Qf the area (Fig. 2). TopQgraphic profiles and the distributiQn Qf “cQbble framewQrk” substrate in 1969 and 1994 are presented fQr the tWQ transects (nQs. 3 and 7) which CQuld be most accurately relocated in 1994 (Fig. 3).
In 1994, the cQbble framewQrk accumulations had largely disappeared from the seaward fringe, the depth increased and the continuQus seagrass cover Qf that area was broken up intQ patches (Fig. 3a: compare profiles for 1969 and 1994 at 120 to 170 m). In 1994, cQbble framework substrates, and Qverall, much more CQarse rubble were also observed shQreward of where the cobble framewQrk had been in 1969 (Fig. 2a). Large areas Qf this cQbble framewQrk Qr mixed rubble-sand substrates were QvergrQwn and stabilized by a carpet-like cover of the green algae Avrainvillea rawsQnii and A. nigricans (phQtQ), which had been seen Qn1y in a few mQre restricted areas in 1969. An erQsiQnal scarp in the regiQn of StatiQn 14**** revealed 10 tQ 30 cm Qfrubble including rhQdiles on tQP of cQbble-sand substrate.
On transect 7, there was an overall dQwnward slope seaward (Fig. 3b). In 1969, a bed QfcQbbles not exhibiting distinct relief, Qccurred at 2-3 meters depth Qver a distance Qf20 m in 1969. In 1994, an area Qf cQbble framewQrk with distinct relief occurred shQreward of this area, and there was an Qverall pattern Qf greater relief and occurrence of CQbble-sized materials towards shQre.
These patterns suggest that a majQr storm event disrupted the cobble accumulations and moved much Qf that material clQser tQ shore. An elderly local resident was asked whether he was aware of any majQr disruptions Qf this sort in recent years. He said that in the 1980s, wave actiQn during a hurricane had depQsited massive amounts of cQral debris Qn shore Qne day, and then took it back tQ sea the next; it was the most severe storm disturbance of the Bath area that he CQuld remember.