The ecology and reproductive biology of two intertidal barnacles, capitulum mitella and ibla cumingi (cirripedia: pedunculata), in Hong Kong
THE ECOLOGY AND REPRODUCTIVE BIOLOGY OF TWO INTERTIDAL BARNACLES, Capitulum mitella AND [bla cumingi (CIRRIPEDIA:
PEDUNCULATA), IN HONG KONG
Submitted by LEUNG To Yan
for the degree of Doctor of Philosophy at The University of Hong Kong
in September 2002
Capitulum mitella and Ibla cumingi are common intertidal stalked barnacles on rocky shores in the Indo-West Pacific, including Hong Kong. Population dynamics and reproduction were investigated on two exposed shores at Cape d' Aguilar for C. mitella and two enclosed ones within Tolo Harbour for 1. cumingi. Temporal variations in population structure were illustrated using length-frequency histograms. Growth parameters were estimated using the von Bertalanffy growth function (VBGF) model. It has been shown that Lex) = 32.9 and 39.5 mm RC and K = 0.68 and 0.46 for C. mitella on the east- and south-facing shores at Cape d' Aguilar and Lao = 9.0 and 7.5 mm CW and K = 0.96 and 0.84 for 1. cumingi at Ma Shi Chau and Starfish Bay in Tolo Harbour, respectively. Near-continuous recruitment but with several (- 3) more intense episodes were recorded for both species. These episodes occurred twice in winter and once in summer for C. mitella and once in winter, spring and summer for I cumingi. Total mortality rates (Z) were estimated at 2.40?year-1 and 2.01 . year-1 for C. mitella at the two sites in Cape d' Aguilar and 4.73' year"l and 2.56?year"l for I cumingi at those in Tolo Harbour.
Reproduction in the two species was studied using GSI, histology and brooding frequency. Capitulum mitella is hermaphroditic whereas [bla cumingi is dioecious, i.e., females carry a dwarf male(s) within their mantle cavities. C. mitella was
reproductively mature from March to September whereas no obvious reproductive seasonality was recorded for I. cumingi. The latter possessed mature gonads yearround with peak brooding occurring from April to October. Size at maturity was ~ 14 mm RC for C. mitella and ~ 3 mm CW for I. cumingi. Estimated annual brood numbers were higher in I. cumingi than C. mitella. Brood size and estimated fecundity were, however, higher in C. mitella than I. cumingi. It was shown experimentally that higher seawater temperatures initiate reproduction and enhance brooding activity by I cUfningi, but not C. mitella. Food ration had no apparent effect on the reproduction of either species.
The genetic structure of [bla cumingi samples from the two enclosed shores within Tolo Harbour and three other shores at Cape d' Aguilar, Lung Ha Wan and Butterfly Beach were investigated using RAPD (Random amplified polymorphic DNA) markers. Significant genetic differences were identified between sites within and outside Tolo Harbour. Such differences may relate to the limited dispersal ability of I cumingi in terms of its actaeplanic and lecithotrophic mode of larval development which, in addition to low fecundity, may result in high larval mortality. In an enclosed environment such as Tolo Harbour, moreover, the dispersal ability of I. cumingi is probably further reduced.
Capitulum mitella and Ibla cumingi showed differences in cirral activity in relation to different conditions of water flow and food effects. Cirral extension by C. mitella was more influenced by flow and the presence of food than in I cumingi. Increases in pumping frequency were recorded under still water conditions but pumping activity was rare with uni-directional flow.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:cirripedia china hong kong environmental aspects pedunculata barnacles
Date of Publication:01/01/2003