48
Chapter 3: Fronts and Pycnoclines: Ecological Discontinuities
D1
SCM
NO3
D2
200 m
1% light
Pt
COPEPOD
HERBIVORES
Clausocalanus
Calocalanus
Mecynocera
Paracalanus
Temoropia
Acartia
Acrocalanus
Pseudocalanus
Oithona
Nanocalanus
Undinula, etc.
COPEPOD
OMNIVORES
Spinocalanus
Scolecithrix
Aetideus
Gaetanus
Metridia
Gaidius
COPEPOD
PREDATORS
Copilia
Euchaeta
Sapphirina
Corycaeus
Pontella
Euaetidius
Mormonilla
CHORDATE
HERBIVORES
Oikopleura
Salpa
Doliolum
COPEPOD
OMNIVORES
Scolecithricella
Scolecihrix
Aetidius
Gaetanus
Metridia
Rhincalanus
Gaidius
COPEPOD
PREDATORS
Haloptilus
Heterorhabdus
Augaptilus
Arietellus
Pontella
Euchaeta
OSTRACOD
OMNIVORES
Conchoecia
wind stress at sea surface
MIXED LAYER
MIXED LAYER
Fig. 3.5 Some ecological relationships in a “typical tropical situation” in the eastern tropical Pacific at
BIOSTAT in day and night LHPR profiles of groups of plankton that have similar feeding strategies. Shown
are the depth of maximum numbers, the depth range of 50% of the population, and the depth range that
excludes only extreme outliers. The top and bottom of the thermocline is D1 and D2, respectively; the DCM
lies within the depth zone of relatively high chlorophyll while P is the depth of maximum production, NO 3
is the depth at which nitrate become undetectable, and 1% is the depth of this level of illumination.
the DCM. However, this is the most narrowly specialized group in its selection of
preferred depths.
Larger herbivores (2.5–6.5 mm) and most omnivores (1.5–4.6 mm): These occupied a
wider layer depth than the small herbivores. Most exploit the lower shoulder of the
DCM down to and even below the bottom of the thermocline, with some extending as deep as 250 m. These are species of Eucalanus, Rhincalanus, Scaphocalanus,
Lucicutia, Gaetanus, and Neocalanus.
Interzonal migrant omnivores: Mostly Pleuromamma, these occurred at night both in the
mixed layer and at the DCM; diel migrant Euphausia, small fish, and siphonophores
were similarly distributed. By day, all diel migrants occurred well below the pycnocline.
Predatory species: Preferred depths included both the mixed layer and depths down
to 250 m, although there was much individual specialization. For example, the two
smallest (2.5–3.3 mm) species of Euchaeta preferentially occurred with the small
herbivorous copepods on the upper shoulder of the DCM.
Obviously, this analysis supports the hypothesis of a specialized fauna of the ecotone
associated with the pycnocline and emphasizes how herbivorous copepod taxa cluster
in the upper part of the feature. Other taxa were similarly ordered down these profiles.
Ostracods, which are all detrital feeders, occurred preferentially just below the pycnocline.
Noncrustacean herbivores (e.g., Oikopleura) tended to aggregate like herbivorous copepods on the upper shoulder of the DCM, though doliolids exploited a wider depth range;
predatory chaetognaths, like predatory copepods, had overlapping depth ranges covering the whole mixed layer. This vertical distribution of feeding groups is recognizable
Chapter 3: Fronts and Pycnoclines: Ecological Discontinuities
D1
SCM
NO3
D2
200 m
1% light
Pt
COPEPOD
HERBIVORES
Clausocalanus
Calocalanus
Mecynocera
Paracalanus
Temoropia
Acartia
Acrocalanus
Pseudocalanus
Oithona
Nanocalanus
Undinula, etc.
COPEPOD
OMNIVORES
Spinocalanus
Scolecithrix
Aetideus
Gaetanus
Metridia
Gaidius
COPEPOD
PREDATORS
Copilia
Euchaeta
Sapphirina
Corycaeus
Pontella
Euaetidius
Mormonilla
CHORDATE
HERBIVORES
Oikopleura
Salpa
Doliolum
COPEPOD
OMNIVORES
Scolecithricella
Scolecihrix
Aetidius
Gaetanus
Metridia
Rhincalanus
Gaidius
COPEPOD
PREDATORS
Haloptilus
Heterorhabdus
Augaptilus
Arietellus
Pontella
Euchaeta
OSTRACOD
OMNIVORES
Conchoecia
wind stress at sea surface
MIXED LAYER
MIXED LAYER
Fig. 3.5 Some ecological relationships in a “typical tropical situation” in the eastern tropical Pacific at
BIOSTAT in day and night LHPR profiles of groups of plankton that have similar feeding strategies. Shown
are the depth of maximum numbers, the depth range of 50% of the population, and the depth range that
excludes only extreme outliers. The top and bottom of the thermocline is D1 and D2, respectively; the DCM
lies within the depth zone of relatively high chlorophyll while P is the depth of maximum production, NO 3
is the depth at which nitrate become undetectable, and 1% is the depth of this level of illumination.
the DCM. However, this is the most narrowly specialized group in its selection of
preferred depths.
Larger herbivores (2.5–6.5 mm) and most omnivores (1.5–4.6 mm): These occupied a
wider layer depth than the small herbivores. Most exploit the lower shoulder of the
DCM down to and even below the bottom of the thermocline, with some extending as deep as 250 m. These are species of Eucalanus, Rhincalanus, Scaphocalanus,
Lucicutia, Gaetanus, and Neocalanus.
Interzonal migrant omnivores: Mostly Pleuromamma, these occurred at night both in the
mixed layer and at the DCM; diel migrant Euphausia, small fish, and siphonophores
were similarly distributed. By day, all diel migrants occurred well below the pycnocline.
Predatory species: Preferred depths included both the mixed layer and depths down
to 250 m, although there was much individual specialization. For example, the two
smallest (2.5–3.3 mm) species of Euchaeta preferentially occurred with the small
herbivorous copepods on the upper shoulder of the DCM.
Obviously, this analysis supports the hypothesis of a specialized fauna of the ecotone
associated with the pycnocline and emphasizes how herbivorous copepod taxa cluster
in the upper part of the feature. Other taxa were similarly ordered down these profiles.
Ostracods, which are all detrital feeders, occurred preferentially just below the pycnocline.
Noncrustacean herbivores (e.g., Oikopleura) tended to aggregate like herbivorous copepods on the upper shoulder of the DCM, though doliolids exploited a wider depth range;
predatory chaetognaths, like predatory copepods, had overlapping depth ranges covering the whole mixed layer. This vertical distribution of feeding groups is recognizable