CalCOFI Reports, Vol. 27, 1986 - California Cooperative Oceanic ...

BRINTON ET AL.: GULF OF CALIFORNIA PLANKTONIC BIOTASCalCOFI Rep., Vol. XXVII, 1986Gonyaulax polygramma in 1959 are recorded from thislocality. Such blooms to the west and north of IslaAngel de la Guarda may occur in the mixing of midgulfand northern gulf waters as the tidal wave ascendingthe gulf is deflected by Isla Tiburon into the deep,narrow Canal de Ballenas (Roden and Groves 1959).The northern gulf (Zone 4) is characterized by a lowphytoplankton diversity, with local intense blooms ofGonyaulax polyedra and G. catenella. Further informationabout the northern gulf biota is given byBrenner ( 1962) and Phleger ( 1964).Round (1967) concludes that the components of gulfphytoplankton are of tropical origin and that there islittle likelihood of endemic species occurring there; itis necessary to look south of 60"s in the South Pacificbefore the flora changes significantly.All gulf phytoplankton species reported in the literaturehave been collated with respect to distributionalrecords (table available from authors). Some patternsmay be discerned: many species penetrate the gulf nofarther than zone 1 (e.g., Asterolampra marylandica,Biddulphia mobiliensis, Chaetoceros laevis, andRhizosolenia castracanei); others are found throughoutthe gulf (e.g., Chaetoceros debilis and Cyclotellastriata); some species have been found as far north aszone 3, yet not in zone 2 (e.g., Actinocyclus ehrenbergi,Coscinosira polychorda, Epithemia gibba); thegroups Biddulphioidea and Solenioideae are generallyabsent from zone 3, but the Discoideae and Actinodiscaeare locally dominant there; zone 4 is characterizedby low diversity of species, with occasionalimmense blooms. It may be noted that most collectionswere obtained during March of different years.Licea-Duran ( 1974) examined systematics anddistribution of diatoms in Laguna de Agiabampo inSonora, and Gilmartin and Revelante (1978) sampledthe phytoplankton of the lagoons and open waters ofthe gulf, southward from Isla Tiburbn, in fall 1972.Gilmartin and Revelante's results from the open watersagree generally with Gilbert and Allen (1943) andRound (1967), but their southernmost floristic breakwas drawn at 26"N, north of that reported by Gilbertand Allen or Round (possibly because station positionsdiffered between the studies). This apparent differencewas attributed to decreased upwelling and high temperatures,which allowed a northward extension oftropical southern species such as Trichodesmiumhildebrantii, Climacodium biconcavum, Hemiaulushauckii, and Chaetoceros laevis (see also Gilmartinand Revelante 1978).In the lagoons the composition and abundance ofestaurine phytoplankton differed most from the adjacentopen waters when flushing rates of the lagoonwere low, and least when flushing rates were high.Some species were more abundant in the lagoons; forexample, Thalassionema nitzschiodes in the north wasreplaced by Skeletonema costatum in southern hyposalinelagoons with low flushing rates. The lagoonflora was generally dominated by diatoms, except intwo locations: Bahia Guaymas (zone 3) was dominatedby the dinoflagellates Gonyaulax digitale and Protoceratiumreticulatum, and Estero de Quevedo (zone 1)was dominated by Gonyaulax minuta.Where dinoflagellates are numerous, phytoplanktonmaxima may change depth>as the motile cells migrateduring the 24-hour period. Kiefer and Lasker (1975)described a bloom in Coyote Bay of Bahia Conceptiondominated by the dinoflagellate Gymnodiniumsplendens (1.O X lo5 cells per liter). The profiles of theconcentration of chlorophyll a based on fluorescenceprofiles showed an upper layer at 6-m depth near noon,at 8 m at dusk, and at 15 m near midnight. Upwardmovement began at 0200, reaching 10 m by daylight.Diatoms contributing to these chlorophyll profilesincluded Leptocylindricus danicus, Skeletonemacostatum, Cerataulina bergonii, and Thalassiothrixfrauenfeldii.Silicoflagellates were found by Murray andSchrader (1983) to be generally less than 2% of the siliciousphytoplankton of the gulf, but up to 5% inblooms. Combining material from surface waters andsurface sediments, Murray and Schrader found that thedistributions of eight species were related to Round'sthree biogeographic zones. Octatis pulchra wasassociated with high primary productivity in the centralgulf, north of 26"N, especially in the Guaymas andCarmen basins, but was also abundant at the mouth.Dictyocha messanensis-cosmopolitan in the NorthPacific-tended to dominate where silicoflagellateswere rare, as at the gulf's mouth. D. calida and twoother unnamed tropical Dictyocha species were mostabundant at the mouth, decreasing northward. Dictyochaepiodon and Distephanus epiodon are CaliforniaCurrent species that sometimes enter the gulf.Phytoplankton and Seston Biomass and ChlorophyllZeitzschel (1970) examined the roles of the fourmajor phytoplankton taxa in the carbon budget of gulfwaters. Dominance by diatoms was evident: they contained50% of the carbon of living cells, but were only10% of the number of cells (Figure 3). Naked flagellates,on the other hand, contained only 10% of allcarbon, but constituted 70% of numbers. Dinoflagellatescontributed 30% of the carbon and 15% ofnumbers, whereas the much smaller coccolithophorescontributed about 10% of carbon and 5% of numbers.Given as average proportions of total weight ofseston (living, dead, and inorganic material combined)232