Zinc phosphate granules in tissue surrounding the midgut of the barnacle Balanus balanoides

The chemical composition of inorganic granules found in parenchyma cells surrounding the midgut of adult Balanus balanoides (L.) was determined. X-ray microanalysis indicated the presence of magnesium, phosphorus, potassium, calcium, iron and zinc in the granules. A quantitative analysis of granule-rich pellets isolated from the midguts of adult barnacles showed that the granules were composed mainly of zinc phosphate, the remaining elements being minor constituents only.     

Particle interception,transport and rejection by the feather star Oligometra serripinna (Echinodermata: Crinoidea), studied by frame analysis of videotapes

Suspension feeding by a stalkless crinoid (Oligometra serripinna) was studied at Lizard Island, Australia, in 1985. The crinoids were placed in a laboratory flume with a slow, unidirectional current of seawater. Nutritive and non-nutritive particles (15 to 180 m) were introduced upstream from the crinoid, and feeding behavior was recorded at high magnifications on videotape for frame analysis. These direct observations showed that each intercepted particle (whether a dejellied clam egg, Sephadex bead or latex sphere) contacts a single, evidently adhesive tube foot and is rapidly transferred to the pinnular food groove by a bend of the tube foot. The tube foot bends in about 0.1 s and returns to its extended position in 1 to 2 s. Spheres less than 20 m in diameter cause only the intercepting tube foot to bend. In contrast, larger spheres cause the coordinated bending of the intercepting tube foot plus many of the neighboring tube feet: the stimulus spreads through the reacting group of tube feet at about 1 cm s^-1. After transfer to the pinnular food groove, the nutritive particles (dejellied clam eggs) travel at about 1 cm min^-1 to the arm axis and thence down the arm food groove at about 4 cm min^-1 to the mouth; in contrast, non-nutritive particles (Sephadex beads and latex spheres) are discarded from the pinnular food groove between 1 and 30 s after capture. Tube-foot bending is presumably triggered when arriving particles (whether nutritive or non-nutritive) are detected by sensory cells in the tubefoot epithelium: mechanoreception by itself appears sufficient to initiate bending, although chemoreception may modify the reaction. Then, soon after captured particles have been transferred to the pinnular food groove, the crinoid discards those judged unsuitable (probably by contact chemoreceptors in the food-groove epithelium). Clam eggs with intact jelly layers temporarily hang up on tube feet they contact and then float away in the curent: the jelly evidently interferes with mechanoreception and/or chemoreception by the tube-foot epithelium. Some previous studies of crinoid feeding have suggested that particles are trapped in extensive nets or strands of mucus: we found no evidence for this in O. serripinna, which captures particles predominantly be the direct interception method of the aerosol filtration model.     

Effects of current speed on filtration during suspension feeding in Oligometra serripinna (Echinodermata: Crinoidea)

Suspension feeding by the crinod Oligometra serripinna was studied at Lizard Island, Australia, in 1986. Video recordings were made of 90-m particles interacting with the filter of the crinoid in a laboratory flow chamber. A complete census of particles was possible because both the capture event and the filter area could be defined unequivocally. Also, because O. serripinna is a passive suspension feeder, a census of partcles could be made at different ambient current speeds without interference due to active pumping by the crinoid. Experiments were run at seven current speeds from 0.9 to 13.3 cm s^-1. Particles approaching the filter: (1) were captured, (2) passed through the filter without triggering a capture event, (3) passed through the filter after escaping from an unsuccessful capture event, or (4) were deflected around the filter. With increasing current speed, the proportion of deflections declined and the proportion of particles passing through rose: these results could be partially explained by the progressive widening of the spaces within the filter due to distortion of filter parts by the current. The proportion of captures (normalized to approaches) was comparatively low at 0.9 cm s^-1, rose to a relatively constant maximum from 1.7 to 6.4 cm s^-1, and then declined progressively at 9.5 and 13.3 cm s^-1. These proportions were translated into capture rates for whole crinoids by taking into consideration both the encounters with particles and the reduction of filter area by distortion of body parts at higher speeds. When plotted against current speed, capture rate peaked at 6.4 cm s^-1, which was close to the mean current speed that we measured on the reef in the microhabitat of O. serripinna.     

Extraction capacity and the optimal order of extraction

The least-cost-first extraction rule for deposits with different extraction costs previously has been shown to be invalid in general equilibrium. This paper demonstrates that this rule also does not hold in partial equilibrium when extraction capacity is limited. Necessary and sufficient conditions for several surprising extraction orders are presented. If extraction from a high-cost resource is constrained, it may be optimal to begin extraction from a high-cost deposit (or backstop) strictly before extracting from a lower-cost deposit. If extraction from a low-cost resource is limited, it may be optimal to exhaust a high-cost deposit strictly before the low-cost deposit is exhausted or to abandon extraction temporarily from a high-cost deposit and then to exhaust it later. The analysis demonstrates how extraction constraints affect the order of extraction and shows that certain cost reversals are caused by limited extraction capacity rather than by the general equilibrium definition of extraction costs.     

Set-up costs and the existence of competitive equilibrium when extraction capacity is limited

Although set-up costs are prevalent and substantial in natural resource extraction, it is known that a Walrasian competitive equilibrium cannot exist in simple extraction models with set-up costs. This paper demonstrates that this result is sensitive to the assumption of unlimited extraction capacity and derives sufficient conditions for existence. An equilibrium exists if extraction is limited such that each firm earns sufficient surplus to cover its set-up costs or if firms choose extraction capacity subject to non-increasing returns. The resulting competitive equilibrium price either grows at the rate of interest when total extraction is below industry capacity or is constant when industry capacity is fully utilized. In the equilibrium, identical deposits are opened simultaneously, and set-up costs for new deposits are incurred when the industry has excess capacity rather than when capacity is fully utilized.     

Towards a climate change adaptation strategy for coffee communities and ecosystems in the Sierra Madre de Chiapas, Mexico

The mountain chain of the Sierra Madre de Chiapas in southern Mexico is globally significant for its biodiversity and is one of the most important coffee production areas of Mexico. It provides water for several municipalities and its biosphere reserves are important tourist attractions. Much of the forest cover outside the core protected areas is in fact coffee grown under traditional forest shade. Unless this (agro)forest cover can be sustained, the biodiversity of the Sierra Madre and the environmental services it provides are at risk. We analyzed the threats to livelihoods and environment from climate change through crop suitability modeling based on downscaled climate scenarios for the period 2040 to 2069 (referred to as 2050s) and developed adaptation options through an expert workshop. Significant areas of forest and occasionally coffee are destroyed every year by wildfires, and this problem is bound to increase in a hotter and drier future climate. Widespread landslides and inundations, including on coffee farms, have recently been caused by hurricanes whose intensity is predicted to increase. A hotter climate with more irregular rainfall will be less favorable to the production of quality coffee and lower profitability may compel farmers to abandon shade coffee and expand other land uses of less biodiversity value, probably at the expense of forest. A comprehensive strategy to sustain the biodiversity, ecosystem services and livelihoods of the Sierra Madre in the face of climate change should include the promotion of biodiversity friendly coffee growing and processing practices including complex shade which can offer some hurricane protection and product diversification; payments for forest conservation and restoration from existing government programs complemented by private initiatives; diversification of income sources to mitigate risks associated with unstable environmental conditions and coffee markets; integrated fire management; development of markets that reward sustainable land use practices and forest conservation; crop insurance programs that are accessible to smallholders; and the strengthening of local capacity for adaptive resource management.     

Movements of tiger sharks (Galeocerdo cuvier) in coastal Hawaiian waters

The giant clam Tridacna crocea harbors in the mantle tissue symbiotic microalgae commonly called zooxanthellae. Isolated zooxanthellae release glycerol into the medium in the presence of mantle tissue homogenate (MH), but it is not clear whether the cells do so in situ. In order to determine the photosynthetic products released by zooxanthellae in the mantle of the giant clam we traced photosynthetic fixation products from ¹³C- and ¹⁴C-bicarbonate both in the clam and in isolated zooxanthellae (IZ) in the presence or absence of MH. After 15 min incubation in the absence of MH the IZ released less than 0.6% of the fixed labeled carbon, mainly as glucose. The major intracellular photosynthates were neutral lipids, which constituted 20 to 40% of the total extractable ¹⁴C. In the presence of MH, the IZ released up to 5.6% of the total fixed ¹⁴C, mostly as glycerol, and the major intracellular photosynthate was glucose. In an intact clam incubated in sea water containing ¹⁴C-bicarbonate, 46 to 80% of the fixed ¹⁴C was translocated from the zooxanthellae to the host tissues. Most of the ¹⁴C in the hemolymph, in the isolated zooxanthellae and in intact mantle tissue (containing zooxanthellae) was recovered as glucose. No ¹⁴C-glycerol was detected in the mantle after 1 to 30 min incubation, and, even after 60 min, far less ¹⁴C-glycerol was synthesized than by IZ in the presence of MH. The possibility that in clam tissue glycerol is converted to glucose was examined by tracing the labeled carbon from ¹⁴C-glycerol injected into the adductor muscle. After 5 min incubation, no labeled glucose was found in the hemolymph, but after 60 min, some 20% was found as glucose. Thin slices containing zooxanthellae, cut from the surface of the mantle, fixed inorganic carbon supplied as NaH¹⁴CO₃ in the medium and mainly released ¹⁴C-glucose. The addition of MH to the surrounding medium did not affect the release rate or form of release product. When the slices were cut into smaller pieces, however, the ratio of glycerol to glucose in the release product increased. These results indicate that in the presence of MH the metabolism of isolated zooxan- thellae was different from that of zooxanthellae in the mantle. In the presence of MH, isolated zooxanthellae release mostly glycerol, whereas in the mantle they release glucose. Received: 18 February 1998 / Accepted: 4 December 1998     

Size-dependent behavior of tuna in an array of fish aggregating devices (FADs)

Several lines of evidence indicate that aggregations of yellowfin tuna associated with floating objects are more frequently composed of small animals than larger ones. Also, the diet of small yellowfin tuna caught at anchored fish aggregating devices (FADs) around Oahu, Hawaii, was found to shift quite rapidly when these fish reached approximately 50 cm FL. In order to test for ontogenetic changes in aggregation behavior, we tagged and released two distinct size classes of yellowfin tuna in an array of anchored FADs around Oahu, Hawaii. Twenty-four yellowfin tuna 30–39 cm FL and 16 yellowfin tuna 63–83 cm FL were tagged with acoustic transmitters and released near anchored FADs equipped with automated acoustic receivers. Fish in the smaller size class stayed about 2.5 times longer at individual FADs than the larger fish (mean 4.05 days vs. 1.65 days) and displayed larger horizontal movements within the array. However, the durations of unassociated phases, residence times in the entire FAD array, percentage of time spent associated with FADs and numbers of movements between FADs did not show any difference between the two size groups. The observed size-dependent behavior is discussed in terms of physiological abilities, diet segregation and anti-predator behavior.