Premium
The Distribution of a Bryozoan on Seagrass Blades: Settlement, Growth, and Mortality
Author(s) -
Keough Michael J.
Publication year - 1986
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1939807
Subject(s) - seagrass , ecology , settlement (finance) , distribution (mathematics) , geography , fishery , biology , habitat , mathematics , business , payment , mathematical analysis , finance
The extent to which the distribution of adults is influenced by larval settlement and post—settlement growth and survival was determined for the arborescent bryozoan Bugula neritina in the Gulf of Mexico. Most colonies live attached to blades of the seagrass Thalassia testudinum. Reproductive adults tended to occur on the distal (oldest) portions of blades. Settlement occurred mostly on the distal sections, but the distribution of newly settled juveniles was not as skewed toward the tips as that of large colonies. Settlement accounted for <20% of the observed deviation from a uniform distribution of colonies along seagrass blades. On both artificial and natural seagrass blades, the distribution of colonies changed only gradually with colony size, suggesting that seagrass growth contributed little to the observed distribution. Juvenile survival was estimated by outplanting newly settled individuals to the field in three separate experiments. In the 1st wk after settlement, °70% died, regardless of their position on the seagrass blade. Later, the mortality rate was lower among juveniles at the distal tips of seagrass blades than for those on the basal sections. Of >700 juveniles outplanted on the basal third of seagrass blades, none survived to reproduce. Survivorship of colonies at the distal ends of seagrass blades was also low; only °5% of colonies survived for >5 wk, with mortality of colonies on the distal third of blades °30%/wk. Mortality of juveniles was clumped, and those together on the same blade all tended to suffer the same fate. The relation between mortality during the 1st wk after settlement and juvenile density was variable; there was a positive correlation in January, but no correlation in February or March. For weeks 2 and 3 after settlement, there was also no relationship. Growth rates also varied markedly with position and time of year; from January until March, all colonies grew very slowly. Higher temperatures beginning in March led to colonies growing faster at the tops of seagrass blades than on the basal sections. The difference in growth rate would result in colonies on the distal third becoming reproductive 1—2 wk earlier than those on the bottom.