Discussion 



Ecology 



Collection of molluscs by humans must depend 

 on what forms are available along any particular 

 beach or coast and, particularly in the significant col- 

 lection for food, in what quantity they are present. 

 Some species are found virtually everywhere; others 

 demand rather specific environmental conditions 

 and are therefore of more restricted distribution. In 

 archaeological shell, these distributions can often 

 define original proveniences, and must be carefully 

 taken into consideration when attempting to reach 

 any conclusions regarding early trade relationships. 



The coast of the Yucatan Peninsula falls into 

 several quite distinct ecological provinces (fig. 2). 



Zone I, Caribbean Province, comprising the main- 

 land coast and nearby offshore islands of Quintana 

 Roo, Mexico, and British Honduras. Both coast and 

 islands are largely a coral-reef formation, character- 

 ized by alternating sandy and rocky shores dropping 

 ofl sharply to very deep waters. Water, even near 

 the shore and inside the islands, is ordinarily clear 

 and clean all year. With offshore winds, which pre- 

 vail most of the year, waves are frequently very 

 large, and their effects on the shallow-water fauna 

 very violent. 



Zone U, Offshore Atolls, Alacran Reef to Cayo 

 Areas. Along the edge of the Campeche Bank, where 

 it drops off into deep water, there is a series of coral 

 reefs, usually in the form of atolls, which seem to 

 form a separate ecological province. The fauna in- 

 cludes not only most of the species present on the 

 Caribbean coast and absent on the Campeche Bank, 

 but also others characteristic of the sandy shelf whose 

 outer edge they inhabit. Although numerous, the 

 principal atolls are the so-called Alacran and Tri- 

 angulos Reefs, Isla Arena, and Cayo Areas, only the 

 first and last of which have been collected by us. 

 (For more detailed description of the geology and 

 ecology of these fringe atolls, see Kornicker and 

 others, 1959; Rice and Kornicker, 1962, 1965.) 



Zone III, North Coastal Province, from Isla Hol- 

 box, Q.R., to Punta Palmar, Yucatan. This is the 

 final extension of the Campeche Bank, which slopes 

 very gradually from the shore to a depth of 25 

 fathoms at about 100 miles, then drops sharply into 

 deeper water. Virtually the entire north coast is 

 bordered by a brackish-water swamp of mud and 

 mangroves {la cienaga) extensively mined for salt, 

 both before and after the Spanish conquest. Except 

 for a broken area between Dzilam Bravo and the 

 mouth of Rio Lagartos at San Felipe, a low narrow 



sandbar separates the swamp from the Gulf of Mex- 

 ico, usually extending out as a sandy floor to the 

 edge of the Campeche Bank. All coastal settlements 

 are situated on this sandbar. Water along the shore, 

 in strong contrast to Zone I, is usually murky, either 

 from cienaga mud, or the fine calcareous sand. Ac- 

 cumulations of seaweed are common on the beach. 

 Because of the shallow gradient, wave disturbance is 

 much less severe than on the Caribbean coast. 



Zone IV, West Coast Province, from Punta 

 Palmar to Isla Carmen and the Laguna de Ter- 

 minos, Campeche. This coast again is bordered by 

 the Campeche Bank, and the consequent shallow 

 gradient found on the north coast. It is a lee shore, 

 protected by the peninsula from the prevailing 

 northeast trade winds and lacking the strong east- 

 west current traversing the north coast. Perhaps 

 because of its protected position, sandy beaches are 

 much less common, and large sections of the coast 

 are formed of mangrove swamp. 



It will be seen that the north and west coasts are 

 much less sharply differentiated from each other 

 than they are from the Caribbean Province and the 

 atolls. A number of the faunal changes (e.g., Strom- 

 bus costatus to pugilis or Busycon contrarium to 

 perversum) begin well to the east of Punta Palmar. 

 Much distinctive material from the west coast may 

 well be extensions of the western gulf fauna onto 

 the peninsula (e.g., Nerita julgurans, Mulinia late- 

 ralis, Lunarca ovalis). It might well be wiser (al- 

 though I have not done so because of our interest 

 in precise provenience) to suggest only the deep, 

 clear-water reef environment as one ecological prov- 

 ince (calling Zones I and II above I and la) and 

 the deeply contrasting shallow, turgid waters of the 

 Campeche Bank as a second (calling Zones III and 

 IV above II and Ila). The faunal changes involved 

 are, of course, more marked in the much larger 

 collection of present-day Mollusca than they are 

 in the few selected species found in archaeological 

 deposits. 



Table I specifies archaeological provenience and 

 known present-day distribution of the species listed 

 in the checklist, to facilitate discussion in the next 

 section. It should be re-emphasized at this point that 

 the modern distributions are solely those of our own 

 collecting in the area and at times may often be 

 incomplete. 



35 



