Accomplishment
To date samples have been collected over one annual cycle at a bimonthly interval commencing in September 1994. All ninety-six samples have been enumerated but only the first three fully analyzed. In addition one Night-Day comparison series of twelve 150um net tows was made at Twin Key basin in the South Central region and has been analyzed. Forty eight macro zooplankton samples from September and November have been enumerated and analyzed as have twelve January Night-Day intercomparison samples and sixteen microzooplankton bucket samples. Initial results are discussed below: The most abundant net caught copepods were Acartia tonsa, Oithona nana and Paracalanus crassirostris. In September when salinity ranged from 33-43ppt Acartia abundances ranged from 16 to 8216/m3, Oithona from 307 to 40460/m3, Paracalanus from 10 to 785/m3. In November when salinity ranged from 22-32 ppt. Acartia abundances ranged from 79 to 5948/m3, Oithona from 427 to 29952/m3, Paracalanus from 204 to 15384/m3. Only Paracalanus was significantly more abundant in November. In the one January station already analyzed salinities were slightly lower than in November and Acartia abundances were considerably higher (fourfold or more in comparable 150um net tows). In September, bucket sampled copepod nauplii ranged from 21 to 284 liter-1 while in November from 36 to 235 liter-1. The average length of a copepod nauplius was 116 um and the average width was 55 um. Such small nauplii are expected since the dominant copepods are comparatively small but from morphological examination alone it is difficult to determine the species of the nauplii enumerated.Other copepods that were common but much less abundant included Tortanus setulosis, Euterpina acutifrons, Longipedia helgolandicus and Calanopia americana. The most abundant meroplankton in net samples were gastropod larvae and pelecypod larvae. While more highly variable than the copepods these were on occasion the most abundant organisms in the 64um net tows. In September they ranged from 553 to 69,732/m3 and in November from 42 to 187,436/m3. Other meroplankton included zoea,decapod larvae,echinopluteus and heteropod larvae. Comparison of 150um mesh tows taken during the day and at night indicated that large Acartia(0.5-1.0mm body length) and Calanopia americana were significantly more abundant. In fact Calanopia was rarely sampled during the day. The abundances of Oithona, Paracalanus, Longipedia and Euterpina and chaetognaths were insignificantly different night and day. In other shallow estuarine systems older Acartia are reported to have a semi-demersal behavior, staying close to or on the bottom during the day and rising up into the water column at night. Because Acartia is the largest of the dominant species and is well known to have a high tolerance for varying salinity, additional night-day comparisons are planned.