Hydrography and the distribution of phytoplankton in Killary Harbour: a fjord in western Ireland

Abstract

Killary Harbour is a fjord or sea loch on the west coast of Ireland. With the growth of aquaculture the harbour has become the site of both raft mussel cultivation and more recently, salmon farming. The successful management of these resources requires a detailed knowledge of the harbour's hydrography and ecology. In 1980/1 an extensive survey of the harbour was made. Papers dealing with primary productivity (McMahon & Patching, 1984) zooplankton (Ryan et al. 1986) and the biology of mussels (Rodhouse et al. 1984 a, b, 1985) have already been published. In this paper, we describe the phytoplankton of the harbour and factors which influence distribution and growth.

A strategic simulation model of a fjord ecosystem

“…The concentrations of phytoplankton and DIN in the incoming seawater are also assumed to have two peaks per year, as continental shelf waters off the west coast typically have a spring bloom followed by a smaller autumn bloom (Colebrook 1984;Roden 1984). Guided by these data we have assumed the fall bloom is half the magnitude of the spring bloom.…”

“…To test its success in this enterprise we require a reasonably spaced time series of data on the spatially averaged abundance of the three trophic levels we model, as well as free N inside the system and acceptable estimates of the external physical and biological influences on the system. Such data are not yet available for Loch Linnhe, but we have been able to assemble an acceptably complete data set for a fjordic inlet on the west coast of Ireland in 198 1 (McMahon and Patching 1984; Ryan et al 1986;Roden et al 1987;Rodhouse and Roden 1987). Killary Harbor is a shallow fjord with a maximum depth of 45 m, a mean depth of 14.5 m, and a total volume of -1.1 x 1 O8 m3 ).…”

“…Killary Harbor is a shallow fjord with a maximum depth of 45 m, a mean depth of 14.5 m, and a total volume of -1.1 x 1 O8 m3 ). According to Booth (1975), the outflowing surface layer varies in depth between 5 and 10 m; Roden et al (1987) report brackish layer depths of l-3 m from three samples in spring and summer in the inner loch, but suggest that this structure is broken down quite quickly. We therefore assume a surfacelayer depth of 7.5 m. Given the shallow overall depth of this loch, no lower pycnocline is formed and the intermediate layer extends down to the sediment-water boundary.…”

“…Although there are no direct measurements of DIN or phytoplankton concentrations at the mouth of Killary Harbor, Roden (1984) gave some rather sparse data from these quantities for the coastal waters off Connemara, a few kilometers to the south, during 1980-198 1. From these data we can make rough but serviceable estimates of the appropriate driving functions.…”

“…We estimated the phytoplankton concentrations within the system from the mean of several subsamples of chlorophyll concentration given by Roden et al ( 1987), using a C : Chl ratio of 20 : 1. Although they specify data from brackish and nonbrackish water, the incom- (Tables 6-9) and site-specific physical parameters (see text) with a data set for Killary Harbor from 198 1 (sources given in text, the first zooplankton and carnivore data points are from 1982 and the last three phytoplankton data points are from 1980).…”