6 



excellent in quality. Like those growing on the reefs they are well adapted for separation and cultiva- 

 tion on the banks, though the tenacity with which they adhere to their rocky basis involves considerable 

 more care and labour in their detachment. 



What are known as "Mangrove" oysters represent an important item in the Queensland growth 

 conditions of Ostrea glomerata. These are the oysters with which originated the supposed travellers' 

 tales of earlier days concerning oysters growing upon trees. The most typical and commercially important 

 phase of mangrove oyster growth ia represented by those instances in which the oysters start to grow on 

 the exposed roots and respiratory shoots or so-called " cobblers'-pegs " of the white mangrove, Avicennia 

 officinalis, and by the process of accumulation may increase to such an extent as to constitute under the most 

 favourable circumstances massive banks scarcely less prolific than the typical reefs previously described. 

 The initial form of such a mangrove oyster bank, together with the perfected luxuriance to which it ia 

 capable of attaining, is Illustrated by Plate VI., Fig. 1, and Plate VII., Pig 2, representing reproductions 

 of selected photographic views taken respectively in Moreton and Keppel Bays. Where growing in the 

 prolific manner represented on Plate VII., they constitute, as in the case of the typical reefs previously 

 described, valuable material for segregation and artificial cultivation on the banks. 



A second and somewhat less prolific variety of mangrove oyster growth is that in which the species 

 is found attached to the luxuriantly ramifying aerial roots of the red or orange mangrove, Rhizophora 

 mucronata, as illustrated in Plate VI., Fig. 2. Oysters on this description of mangrove more commonly 

 occur in the northern area of distribution of the species, and in such localities as the mouth of the 

 Endeavour River, near Cooktown, and at Bowen, Port Denison, constitute the almost exclusive representa- 

 tive variety of the species. This mangrove oyster occurs also in some abundance in certain parts of 

 Wide Bay such as the vicinity of the South Head. In consequence of its adaptation of contour to the 

 shape of its supporting fulchra, this oyster is apt to develope a very irregular form of growth ; if, how- 

 ever, moved at an early stage of its existence and spread out under favourable conditions for culture on 

 the banks, it has been found by systematic oyster growers to well repay such attention. This being the 

 experience gained on the Wide Bay oyster grounds, it may be anticipated that successful results would 

 also accompany a like treatment of the variety in its natural habitat further North. This anticipation is 

 supported by the circumstances that oysters of larger and edible dimensions and quality are to be 

 gathered from among the fallen debris lying around the mangrove trees, and where living more or less 

 separated from one another, they have room to expand. Griving due weight to this fact I am of the 

 opinion that remunerative banks, productive of oysters in at least sufficient quantities for local consump- 

 tion, might be established, with stock derived from the mangroves, in these more Northern districts. In 

 the establishment of such experimental banks attention should be given to imitating as nearly as possible 

 Nature's own pattern, the banks being formed, not on the open sun-exposed flats but within that 

 umbrageous shelter of the mangrove trees where the species attains to its finest development in these 

 higher latitudes. The conditions indicated obtain on a sufficiently extensive scale for the practical 

 application of the above suggestions in both the estuary of the Endeavour Eiver and at the mouths of 

 the several creeks debouching into Port Denison, in the neighbourhood of Bowen. 



I have been recently informed by Mr. Teo, the manager of the Moreton Bay Oyster Company, 

 that the above described variety of mangrove oyster grows so luxuriantly in favourable localities in the 

 neighbourhood of Eodd Harbour that as many as twenty or thirty bags of oysters suitable for cultivation 

 on the banks have been gathered by their agents from a single tree. 



The collective growth forms of Ostrea fiJomerata, known as dredge and drift oysters, remain to be 

 noticed. The first-named title is applied generally to all oysters growing below the level of usual ebb 

 tide, that of drift oysters being more exclusively associated with those lying loose and separately at the 

 bottom of the water, and which are supposed to have been washed from off the banks or beds, and to 

 drift here and there at the mercy of the prevailing currents. The tendency of the dredge, or deep water 

 oyster, to develop a more elongate shape with a much smoother and less crenulated marginal border has 

 been referred to on a previous page. With the typical " drift" variety the tendency, through continued 

 erosion, to develop an abnormally massive shell is especially noteworthy, instances occasionally occurring in 

 which the lower or right valve weighs as much as half a pound avoirdupois. The concavity of such a shell is 

 rarely of sufficient size as to contain more than a single fluid ounce, while the corresponding shell 

 of a large cultivated "bank" oyster, having an internal capacity of two fluid ounces, yields an 

 average weight of scarcely three ounces. Dredge and drift, as compared with bank, oysters eon- 

 tribute to a less extent to the oyster trade of Queensland, the relative proportions so far as it 

 can be ascertained, while formerly considerably larger, being now about 20 per cent. In 

 this respect the Queensland oyster fisheries present a marked contrast to those of the neighbouring 

 colony of New South Wales, and in which the dredge and drift varieties have until within recent times 

 represented the most important commercial factor. Among the arguments that have been advanced in 

 favour of the specific distinctness of the deep-water oyster, or Ostrea sulitrigona, as it is designated by 

 those who advocate its distinction, is the one that this deep-water form wiU not live if transported to 

 the tidally-exposed banks, nor the bank variety if consigned to deep water. If the transition is made 

 unseasonably, unfavourable results are likely to ensue. Where, however, the change is judiciously effected, 

 no difficulty is experienced in cultivating dredge or drift oysters on the ordinary banks, or vice versa. In 

 various localities in Moreton Bay, and notably at the Breakwater in Nerang Creek, oysters grow in a 

 continuous sloping series from a depth in which they are covered by a fathom or more of water to the 

 tops of rocks that are dry with every ebb. Oysters taken from these exposed rocks are, moreover, 

 systematically and successfully laid down as "cultivation" on a neighbouring dredge section, where 

 they are covered by at least two fathoms of water. No more practical evidence, probably, could be 

 furnished in demonstration of the specific identity of the deepwater and tidally-exposed series. Parallel 

 illustrations of a species of oyster adapting itself to the varied conditions of either total or partial 

 submersion are afforded by the typical European oyster, Ostrea edulis, or its Australian variety, O. angasi, 

 as it occurs in the more southern colonies. In the former inst.ances it may bo dredged in the open sea 

 at a depth of as much as twenty fathoms, being then represented by the large rough form commercially 

 known as Channel oysters, or it may be gathered somewhat rarely in England, but more abundantly in the 

 warmer waters of the Channel Islands, or on the neighbouring coast of France, adhering to the rocks 

 tiiiev the mviwaer oi Ostrea glomerata. It is this same species, moreover, in its coarser natural form, 

 ordinarily taken with the dredge, that is cultivated on so extensive a scale on the tidally exposed foresliores 

 of France, or that is transformed, through a long and tedious course of manipulation, into the costly world- 

 renowned 



