REEF ZOOPLANKTON COLLECTED ALONG A DEPTH GRADIENT 

 AT DISCOVERY BAY, JAMAICA 



Sharon L. Ohlhorst 

 Fisheries and Wildlife Department 

 Utah State University 

 Logan, Utah 84322 



ABSTRACT 



Reef zooplankton from three sites in the vicinity of Discovery Bay, Jamaica, 

 were sampled on 29 nights during 1976-77 to determine their abundance and 

 species composition. Depth was inversely correlated with zooplankton volume; 

 10.2 ml of zooplankton/m^/night were collected at 6 m, 5.3 ml at 15 m, and 3.2 

 ml at 24 m. No seasonality in volume of zooplankton was observed. Variability 

 in volume both within and between nights at any one site was high, but never 

 were enough zooplankton collected to meet more than an estimated 12% of the 

 metabolic requirements of the sessile reef dwellers. 



Volume of zooplankton was positively correlated with the number of 

 individuals in the sample. The unpredictability of zooplankton abundance is at 

 least partially explained by the swarming behavior of the dominant (usually > 

 95% of individuals) copepod, the hoi oplanktonic Oithona colcarva Bowman. 

 Because of this variability, it is unlikely that local zooplankton abundance 

 and distribution has any causal effect upon reef species diversity. In addition 

 to many groups of holoplanktonic copepods, ostracods, isopods, and decapods 

 were among the most numerous taxa represented. The 6 m site differed from the 

 sites at 15 m and 24 m in the relative abundance of noncopepod groups. 



INTRODUCTION 



Zooplankton are an important component of food webs in coral reef 

 communities. They provide nutrients to corals (Goreau, et al . , 1971; Johannes, 

 et al . , 1970; Porter, 1974) and to other benthic suspension feeders such as 

 zoanthids (Sebens, 1977), crinoids (Liddell, 1980; 1982) and ophiuroids (Macurda, 

 1976), and they form a major part of the diet of many reef fish (Hobson, 1974; 

 Gerber and Marshall, 1974; Hobson and Chess, 1978). Emery (1968) first reported 

 that many zooplankton reside within coral reefs and, more recently, researchers 

 using light (Sale, et al. , 1976) and emergence traps (e.g., Alldredge and King, 

 1977, 1980; Hobson ancTcKess, 1979; McWilliam, et al, , 1981; Porter and Porter, 

 1977; Porter, et al^, 1977; Walter, et a_L_, 198"2j have characterized certain 

 aspects of the resident zooplankton of shallow reefs and lagoons in the Pacific. 

 Few studies have examined reef-associated zooplankton in the Caribbean; Robichaux, 

 et al . (1981) and Youngbluth (1982) placed traps over sand and/or seagrass 

 beds, while Ohlhorst (1982) reported on di el patterns over reef substrata at 

 one depth. Only one study (McWilliam, et al . , 1981) has addressed the question 

 of seasonality in zooplankton (from the Pacific), and none have sampled along a 

 depth gradient on a reef. Further information on the abundance and behavioral 

 patterns of these zooplankton, especially in the Caribbean, is necessary to the 



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