Method

Samples are obtained in conjunction with Florida DEP at 8 sampling sites. Zooplankton are collected with 64 um mesh 1/4m circular nets equipped with flowmeters. Tows are short (< 5 minutes duration) with the boat slowly underway at 1-2 kts. At all stations a 5 gallon bucket is used to obtain a surface sample which is filtered through 20 um mesh and the concentrate retained. Whole water filtrates better estimate the food available to fish larvae since smaller forms like nauplii are quantitatively collected. Net samples are used for both enumeration of dominant taxa (copepods and other zooplankton) and for coarse-community analysis. In net samples to be used for grazing determination an aliquot of the cod-end sample is poured through a filter apparatus containing a 47mm piece of 150um mesh Nitex which is rapidly frozen in liquid nitrogen. Grazing rate is measured by the gut fluorescence method. The ingestion of phytoplankton by each copepod taxon will be determined from the product of ingestion rate per copepod and the abundance of that copepod. Grazing by other numerically abundant mesozooplankton is estimated by applying either literature values for grazing at similar temperatures or size specific rates estimated from the copepods to the abundances derived from our net tows. Community grazing rates determined at specific sites will be scaled up to larger areas based on more extensive measurements of zooplankton abundance and concomitant water properties and the degree to which taxonomic distribution and abundancecan be determined by hydrographic variation determined using multivariate statistics like correspondence analysis. Larval fish are sorted from 150um neuston tows to obtain individuals for gut contents analysis. Individuals are measured(notochord length) and their guts excised, measured (width) and identified. The guts of only morphologically intact individuals will be included in the analysis. Identifiable gut contents are be compared to the density of food organisms enumerated in net tows, sieve samples and whole water samples. The same procedures are being used with small-mouthed juvenile and adult fishes captured in Fla. DEP trawl and seine net samples. Using Acartia tonsa collected in Biscayne Bay, we amplified a partial region of the large subunit of ribosomal DNA using the PCR (polymerase chain reaction) method. We then sequenced this region on a LiCor automated sequencer and isolated a unique species- specific area of the subunit. A non-isotopic DNA probe was then prepared for that oligonucleotide sequence signature. This probe is used to identify unrecognizable larval fish gut content fragments with a competitive PCR detection technique. The approach is not only qualitative but quantifiable.